SalvageS10 Build Thread
 

I guess it's time to start a thread.

The SalvageS10 is a 1991 chevy S10. It'll be a proof of concept - proof to my wife that I can finish the thing, proof to myself that the concepts are sound and I really can do direct drive with no transmission. When the proof is done, perhaps I can put some money into a more reliable donor vehicle that I can use as a daily driver. If the SalvageS10 makes it into service as a daily driver, it will likely need to be a hybrid to get the necessary range.

My commute is 30 miles each way, highway driving with 5 corners, each 90 degrees with a yield or stop sign. The posted speed is 100 kph or 62.5 mph but I need to be able to drive at least 70 mph to keep from being run over.

I may be able to convince my boss to store the lead-acid batteries for a high-power charger at work ... we'll see.

The SalvageS10 will be guided by a couple of concepts:
- make it safe
- make it cheap

The next few posts will deal with some of the high-level ideas. I also have some research stuff that I'd like to do with this project. I want to know more about electric motors and how they work. This is how I intend to find out.

I know that Jack Rickard will be disappointed with this build - it will be powered by lead acid. As pricing comes down, and my expertise goes up, that may change.

Are you thinking of a series hybrid? Like a high powered charger and generator to charge the batteries onboard?

Salvage S10 high level design
 

My desire is to remove as much mechanical stuff as I can:
- ICE engine
- automatic transmission
- radiator
- gas tank
- exhaust system

The main parts of the conversion are targeted to be:
- direct drive from 1770 rpm 40 hp 3 phase 575 Volt electric motor to the 3.43 rear end
- Industrial VFD mounted in the front portion of the cargo box, with heat sinks bolted to the box frame, 302 amps at 575 VAC continuous
- Industrial computer mounted in the back seat of the extended cab to control the VFD, interface to the truck sensors, and control the charging

It would be a series hybrid, if I can't carry enough batteries to make 30 miles reliably. I have a vertical Kohler 13 HP as well as an 8 HP horizontal Briggs & Stratton that could be cleaned up and put into service. It would need to be a belt drive arrangement to an induction motor (in the 5 - 10 hp range) and using another VFD to create the appropriate output voltage.

That's something I've checked out, it works.

Batteries and Power in general
 

I am undecided on how to tackle THE central question of EVs - the batteries.

I have a line on some larger lead-acid batteries (no, I don't have details yet. I don't have them yet) that are regularly 'traded in' for a core charge when they can no longer last half a shift - 4 hours.

The GVRW limit for the truck is 5200 lbs. 1411 lbs listed as the payload.

If I add me - 250 - and make some assumptions about the weights of the stuff that is removed - I have about 1300 lbs for power. That includes the batteries and any power electronics on them as well as the cabling.

1300 lbs, at 150 - 200 lb per battery. Let's say around 96 VDC. I may be able to modify the VFD to run on a lower voltage. The motor would need to be properly matched to work well. 208VAC is about as low as our industrial motors go, and 30 - 40 HP at 208V three phase is not common.

So I'm looking at using a DC-DC converter on each of these large batteries, boosting the 12V up to around 150 VDC. I can use these converters, and chain the converters together in series to boost the voltage but it is inefficient. Around 85% - which makes for a lot of heat to get rid of and a lot of valuable battery power.

Still to be determined

Wow this is going to be good! Totally outside of the box. I can't wait to see it come together!

Looks interesting, like Forkenswift goes pick-up.

You will need higher voltages for the motor and VFD. The motor will run much better on 240 or 480.
This also will reduce you component sizes due to lower amps. Problem is the DC bus voltage on a 480 VFD is around 670VDC !! Most wire is only rated for 600V, but going to 1000V MTW is cheaper than going to larger diameter cables. JUST BE CAREFULL !! High voltage DC doesn't play and will kill you quickly.
Going with 240VAC will drop your bus to 338vdc, much more manageable but at twice the amps to deal with.
Either way, 96VDC isn't going to cut it. 60 some VAC motors don't really exist. A 120V motor will run on it, but will have very low torque.

I look forward to this build.

Agreed. I'll be using as high a voltage as I can reasonably get. 600 VDC is as low as I'd like to go. The VFD shuts itself down on overvoltage at 965 VDC.

The wiring I'll be using is industrial, rated for 1000 VAC. And if I know me, it will be a size or two (perhaps 3) larger than it needs to be. Whatever size I can fit into the lugs and the terminals.

If I'm using DC/DC converters, the high voltage will be somewhat isolated. The DC/DC converter isolates from the input battery voltage to the higher output voltage. The terminals of the DC/DC converters over to the VFD should be the only high voltage 'bus'. Liberal use of fuses (which are not cheap, unfortunately) should limit the damage if a wrench falls where it should not. The DC/DC converters have a rated output current, which is 10 or 100 times lower than the current available at the terminals of a battery string - so I should not vaporize the wrench, or weld it to the terminals.

I have no reasonable way to limit the high voltage current that I am exposed to during a shock to under 4 mA (if memory serves) - the 'safe' limit for the human body according to my Arc Flash documentation (NFPA 70E for the USA, CSA Z462 for Canada). If anyone has suggestions, please let me know.

Me Too! Creating a build log is a way to give myself some incentive to get off the couch and do something.

We'll see if that's successful.

How about having a gas engine that is on a direct drive to the drive shaft that is going to the rear axle? use a centrifugal clutch so that it spins free when the engine is not running and have it geared so the engine is running at it's max RPM when you are going 65mph or whatever you want your top speed to be, that way you extend your range while driving on the highway, you also keep it really simple and you don't have the losses from going mechanical to a generator to a speed controller to a motor to the wheels.

Hybrid ideas
 

Thanks for the input. I think that setup would be a lot more efficient.

There are a couple of implementation issues.

My present plan for the electric motor is a taper lock that increases the 2.125 inch motor shaft to the 3 inch inner diameter of the drive shaft. The motor is suspended by the normal foot mounts from a pivot on the truck bed frame and the drive end bearing of the motor supports the stub of the drive shaft to the u-joint, before going to the rear end.

This is as simple a connection as I can come up with so far. I'm not mechanically inclined.

My available gas engines all have much smaller shaft diameters and would be challenging to mount between the electric motor and the rear end. Since the engines are much lower horsepower, they may not take the flow-through power.

If the centrifugal clutch was on a belt-driven pulley that was mounted on part of the existing drive shaft, I think more bearings would be required? I make the assumption of belt drive. Would that be a belt or a chain drive? I looked briefly into a chain drive and was told, by someone much more knowledgeable about power transfer than I am, that a chain is not suitable for the speeds involved. He suggested a high speed synthetic belt that did good power transfer, isolated vibration pretty well, and was quite tolerant of getting wet. The problem was the price. The belt itself was over $500, 900 with the shieves (pulleys?).

I know I've got a LOT of losses planned with ICE -> induction motor -> VFD -> DC bus. I just happen to solve most of my issues electrically and minimize mechanical stuff that I need to get help with. We go with what we know.

You shouldn't have an issue with a chain drive, motorcycle chains are moving much faster and the clutches that I've seen have a sprocket right on the clutch so that side is already designed to go as fast as the engine is turning and you shouldn't have to worry about the chain being to small because the largest load that it will see is that of the small gasoline engine that is being used to maintain vehicle speed, so at that point I would figure out the gear ratio of your rear end of your truck and figure out what size gear ratio you would need to make the gasoline engine run at near top speed, maybe gear it for 70mph? 10% slower would be 63mph and if your engine is designed to run at 3,600rpm then 3,200RPM isn't a bad speed for cruising, that way you don't destroy your engine if you go to pass someone.
I would weld your sprocket that goes on the trucks drive shaft right on to the drive shaft if you could, or if you can find a hub for a range of sprocket sizes weld that on so you can change sprockets if you have to.

I guess I'll cross that bridge when I come to it. There are many steps between now and when I need to decide on a hybrid drive type.

First, there is much motor, controller, and DC/DC converter experimentation.

Then I figure out how many batteries I can install, making allowances for the battery frames.

Then I can determine where the batteries will fit, make the battery boxes, get them installed and working.

After I can finally put a license on it, then I'll find out the range.

At that point I find out whether I need to go hybrid.

Dec 2 - the VFD
 

They are 'cleaning up' at work today and the 300 HP VFD that I was wanting a gate pass for was close to being thrown in the scrap heap. I caught them before the fork truck picked it up.

I will be bringing our utility trailer to work to pick up the VFD, line and load reactors. If I want to work on removing the VFD from the cabinet (6 feet tall, 3 feet wide, 18 inches deep) then my car will be outside and these parts in the garage. A bit of incentive to get some work done on SalvageS10!

The VFD is larger than I remember. It needs to be re-arranged to fit into the bed of the S10, but Im confident that I can make it fit.

The VFD has not been run for 2 years. It was in running condition when it was turned off and decommissioned. I'll need to apply some elbow grease to clean it up, and I'll likely disconnect the capacitors before powering it up for a test.

Dec 3 - getting the VFD home
 

I got the 300 HP VFD loaded into my utility trailer. A lot more people at work know about the electric truck now. I have more incentive to get the thing done!

The VFD, with the enclosure and heat sinks, is about 600 lbs as measured by the scale on the fork truck that lifted it. Some of the sheet metal was bent up as we loaded it, but the electronics were kept safe.

I also collected a 5 hp, a 10 hp and a 20 hp VFD that were stacked and ready for the dumpster.

Dec 5 - start work on the VFD
 

Move small VFDs into the garage for storage.

Check the various mounting bolts on the 300 HP- 1/2 inch, 3/8 and 5/16. Nothing like consistency.

I'll need to remove the lexan cover that keeps errant fingers out of the high voltage electronics before all of bolts are accessible. I might have to remove a couple of jumper cables within the cabinet as well. The capacitors are mounted in the base, partially buried in the cooling cabinet. There is also a 'DC Bus Reactor'. This is going to be interesting.

The VFD is still outside and there is not much daylight after I get home from work.

I should get some pictures posted.

Dec 12 - problems working on
 

All the bolts removed. A couple of cables removed from 'DC Bus Reactor' to buss bars. With all bolts removed from the frame I still cannot remove the drive from the cabinet. In fact, I can't move the drive at all. I'm starting to think that the VFD will need to come into the garage with the trailer, and that I will still have difficulty disassembling the unit.

Perhaps if all else fails I can use the large VFD as a rack, with all of the required spacing already set for 600V, the insulators (once they are cleaned up) and the bracing. Add new IGBTs, a newer set of (perhaps smaller) capacitors and a new control board to drive the IGBTs. The mechanical stuff is done, which is normally my big problem …

Dec 13 - the utility Trailer and VFD are inside
 

I got the utility trailer with the VFD in the garage (a small success).

I hope to post some pictures when I get them downloaded from the camera

Pictures of truck, before beginning of conversion
 

Nothing special, but here is SalvageS10

1991 Chev S10 4x4 extended cab, about 300,000 km

These pictures are from early August

Dec 15 - working on VFD
 

Almost everything on this Allen Bradley VFD is very corroded. If I am going to re-use this equipment it will need to be completely disassembled, cleaned, and assembled one section at a time. Verification of each section as it goes back together would be a good idea.

The cabinet that surrounds the electronics appears to be the frame that all of the components and component assemblies are attached to. The assemblies are mounted in layers. I have labeled about 40 connectors and individual wires that carry signals from one assembly to another. Pictures have been taken and audio notes recorded of what is coming apart, and how it needs to go back together. The original intent was to removed the electronics from the cabinet and use what appeared to be the frame - similar to angle iron - to mount the electronics in the box of the truck. It appears that this plan must be change.

I have been very optimistic on the chances of getting this thing back together again and operational. That optimism is faltering.

Dec 17 - VFD disassembly nearing completion
 

I spent another few hours trying to get this thing apart. For the most part, I've been successful.

I believe that the larger components can be re-used. These include:
- the 500 VDC electrolytic capacitors (two banks in series for 1000 VDC)
- the output terminals to connect to the motor
- the LEM current sensors which monitor the current out to the motor
- the DC bus fuse
- the capacitor mounting hardware
- the truly massive aluminum heat sinks
- the cooling fan

The transistors are not modern IGBTs. I have some research to do on them but they appear to be one or two generations older. I suspect that they are not as efficient as modern IGBTs (as evidenced by the size of the heat sinks). The driver electronics are separate boards. There are many signals between boards and a great deal of this design likely dealt with what I expect is a lot of signal noise.

Even if these transistors turned out to be efficient, there are too many interconnects for me to be confident in the outcome. It is unlikely that I will be able to assemble this properly after the cleaning is complete.

VFD weight
 

The VFD sections:

Cabinet 95
Output Section A 30
Output Section B 30
Output Section C 30
Diode Section 40
Bus Bar 20
Capacitors 50
Capacitor bus 35
Terminal block 25
Fan 10
Power Supply 10
Lugs, fuses 15
Control Board 1 15
Control Board 2 20
Control Board 3 15
Cover, keypad 5
Total 445 lbs

After removing all of the parts from the frame, I removed the frame easily - it came off as I expected it to with all of the parts bolted to it. The problem was that I was not expecting the contents to weigh 445 lbs.

While putting the parts back into the frame, for convenient storage until I can get them cleaned, the cabinet was standing on end. I went to lay it down flat, forgetting about the weight. It came down a little harder than it should have. I had decided not to trust the output transistors anyway. Dropping the cabinet on the garage floor just sealed the deal.

It was still careless and stupid.

Pictures of VFD before disassembly
 

Here are a few pictures of the VFD and cabinet before labeling and disassembly

Stuff done during the summer - How much force is needed to move an S10?
 

Measure how much force (in pounds) is needed to move SalvageS10. Use the existing engine and transmission. The truck normally starts (gently) when put into gear and the engine run at idle. Reproduce this and measure the force exerted.

How to measure the force that the truck puts on the ground (and uses to move the truck forward)?

An ordinary bathroom scale should be able to measure this. A truck that is stuck in winter can be pushed out by one person. The force required to move the truck should be less than one person leaning on the truck, maybe 100 - 200 lbs.

The scale measures weight pushing down from above, perpendicular to the scale, when the scale is level. To make one scale measure the whole force, I need to stop one wheel from turning. Drill the 2 x 6 for the bolt pattern on one wheel, fit the 2 x 6 onto the studs and jam it against the ground so that it won't turn. The other wheel should exert the force for both wheels, since the force would be equally split between the two wheels if both were free to spin.

1 - jack up the truck, put it on blocks
2 - remove wheels
3 - jam the passenger's side with a 2 x 6
4 - drill out another 2 x 6 for the driver's side wheel
5 - mount the 2 x 6 horizontally
6 - mount a vertical 2x4 to the 2 x 6
7 - shim a bathroom scale to level so it reads properly
8 - zero the bathroom scale
9 - set up a video camera to show the reading on the scale
10 - start the truck and put it into gear

Stuff done during the summer - How much force is needed to move an S10?
 

The sketch shows the rear hub, the horizontal 2 x 6, the vertical 2 x 4, the scale, and the video camera.

The measurement on the scale reads about 180 lbs. This is at 15 inches from the center of the wheel hub, the radius of the rear wheel. So this is the force exerted on the ground to move the truck forward at idle speed.

Press the accelerator gently, check the force on the scale

I saw the weight go momentarily up to 240 (maximum for the scale)
- then the back of the truck lifted off the ground
- then the 2 x 6 on the passenger's side broke and the passenger's side rear wheel started to accelerate

Check the available internet information. From EV Calculator with a 1994 chev s10 extended cab, an ADC FB-4001A motor, Concord 12105 batteries, a Curtis 1231C controller, 96V battery pack, 205/75r14 tires, 0 incline, 0 headwind, default rolling resistance and brake/steer resistance, the torque required to run the truck at 10 mph (the lowest calculated speed) is 41 foot-lbs at the motor. Put through a 3.43 rear end, 41 * 3.43 is 141 foot-lbs. With a 15 inch radius, that gives 141 foot-lbs * 12 inches/1 foot / 15 inches = 112 lbs of force. This is relatively close to the 180 lbs of force measured by my crudely constructed system.

The left sketch is an overhead view looking down on the rear end. The right is a side view from the driver's side of the truck

Stuff done during the summer - How much force is needed to move an S10?
 

I need to find out some clearances and verify a couple of measurements. Maybe it's time to remove the back of the truck.

Remove the cargo box from the truck
remove the skid plate below the gas tank
remove the gas tank
install a target for the tachometer on the drive shaft
verify the gear ratio on the rear end. Jam the passenger side wheel. Turn the drive shaft one turn with a pipe wrench. Count the revolutions on the driver's side rear tire.

3.5 revolutions of the drive shaft to 2 turns of the rear tire. If the passenger's side tire was not jammed, each tire would have turned once. The internet lists 3.43 to 1 as a typical gear ratio for the rear end. That's likely what I have. The other option appears to be 3.73 to 1.

I tried a few different ways to jam the accelerator and measure the rpm on the drive shaft with the tach. No success.

Correction
 

I should be paying more attention

The input stage of the VFD is normally 6 diodes and takes the 3 phase input and generates a pretty stable DC output with a smaller AC wave 'on top' of it.

This VFD, for some reason, uses something else. There are three sets of input semiconductors, but they don't look like the output transistors. They definitely have control signals going to them.

It might be 3 SCRs. I used those once to make a 3 phase rectifier.

Wagan 5000W continuous, 10 000W peak Auto AC Inverter
 

This is one of the surplus DC/AC inverters that I have.

The idea is to use the isolated DC/DC section, where 12V is boosted to around 150 VDC, before it is converted to modified sine wave.

I got this surplus. The manufacture date is 2004, so it's not exactly leading-edge technology.

I did manage to get the screws out. The heat sink splits into an upper half and a lower half. There is a 'power board' on each half and an 'electronics' board that sits between, on a lip between the halves of the heat sink.

There are several signal cables going from the electronics board to various locations. The power to the electronics appears to be unfiltered input voltage (10 - 15 VDC) which goes through a small regulator. The electronics board has a dark flash-burn on the bottom and a couple of resistors that have corroded badly.

The majority of the control signals appear to be switching signals to 32 power transistors that switch the 12VDC through 16 step-up transformers. There is a pair of 35V capacitors and a pair of transistors for each step-up transformer. I was expecting diodes to rectify the AC pulses from the transformers, but I don't see any. There are 8 larger 200V capacitors which appear to be for the output stage, along with 4 inductors. There are a couple of smaller capacitors between the large capacitors. One of these has corroded off.

Each step-up transformer has a 40A automotive fuse. All of these appear to be fine.

I pulled all of the fuses and put regulated 12.8VDC at 0.9A max into the power feed. The power draw is about 0.3 amps.

Turn off the power and put a pair of fuses back in - far right top. Apply power - the same 0.3 amps draw. No output power. No power indication on the display. No noise.

Check a few terminals within the circuit. There does not appear to be signal switching on the electronics board. I don't expect that any of the switching transistors are stepping the 12V up to 150 VDC, or 75 VDC, or whatever the design is.

Turn off the power and put a different pair of fuses back in a different location - far left, bottom board. Apply power - same 0.3 amps draw. Check power on the electronics board. 12V in. 5V regulator is working. No signal switching. Check the intermediate outputs on the bottom power board. Nothing.

Re-assemble, put the cables back together approximately as it was when I started. This is a source of parts for further experiments. If I can figure out how the display works, that might be useful. Put the 40A fuses back in - again, convenient storage. Label as 'parts' and as 'badly corroded'

I have other units to test. I guess it's time to move on to the next one. Not a lot of useful information from this one.

The Chevy S10 EV pickups that were made a little over a decade ago had AC motors and fairly compact controllers. Although it might not be as much fun, finding one of those would save you a lot of time. Also, because the motor was designed as a traction motor, it is relatively light. Ditto for the controller, which might have been 30 lb or so.

The EVDL Forum could offer help -- there are loads of S10s and Ford Ranger pickup conversions out there.

EVDL Archive / Forum Interface - Electric Vehicle Discussion List

I noticed that you wanted to know the force required to mover the truck.

You can assume that the truck will weigh about 5000 lbs.

30% grade is a reasonable minimum hill climbing capability. So, you will want a tractive force of 1500 lbs. Tires for an S10 can range from 25.5 to 28 inches in diameter. We'll pick 24 for simplicity, because then the radius is one foot. That means that a little more than 1500 lb ft torque is required, (more yet for larger tire sizes). With a 3.43:1 rear end, you'd need 437 lb ft of torque at the input to the rear end.

You need to decide what sort of top speed you want, to see if the gearing for 30% grade climbing will also give you adequate top speed (based upon the motor's max rpm). If not, then you'd need more than one speed in the transmission.

I want to use parts that I can source, and understand how to fix what I end up with, so I guess I'll be going with the 'more fun' way.

This forum and the evalbum are what pointed me to the S10 to begin with. I will be experimenting without a transmission ... and will likely verify that a standard transmission is the way to go. I don't have one, as the truck has an automatic right now.

I'm aiming a bit lower than that. None of the roads this commuter (if I get a range long enough to drive to work) will see will be steeper than 3%.

A 40 HP electric motor rated at 1770 rpm is about 120 foot-lbs of torque. From the specs on the motor, it peaks at 220% rated torque or 264 foot-lbs, but that assumes that it is starting from 0 rpm and the motor is started 'across the line' with a starter and a utility pumping up to 10 times rated current through it. I think I can reach 264 foot-lbs with a VFD and about 3 times rated current, or under 120 amps.

With the 3.43 ratio and 205/65 r14s (I measure them just under 30 inches in diameter so I use 15 inch radius) that will give me about 725 pounds of force to the road.

There's a lot of assumptions wrapped up in there. I'll see what I have when I get there. And I'll have some fun measuring everything along the way.

The off-the-shelf three phase 575V T frame motor is rated for 1770 rpm / 3.43 rear end * 30 inch diameter * pi converted to mph is about 45 mph. The motor is constructed the same as a 3600 rpm motor, so overspeeding it will reduce the life of the bearings, but that's about it.

Below 1770 rpm, theory tells me that the output torque is constant at about 120 foot-lbs at rated current (hopefully up to 264 with more current and a VFD). Above 1770 rpm the torque will be reduced - the theory that I've seen predicts approximately linear reduction in torque as speed rises. I'll run out of horsepower, even with extra forced-air cooling, hopefully above 70 mph but I'm sure that I'll run out of battery before that.

We'll see how close the theory matches reality.

Durafied 1350W continuous, 2700W peak Inverter S1350DI
 

I decided to try one of the inverters that I use, that works OK so I can get an idea of the signals. I can always go back and investigate the surplus stuff. The manufacture date is 2010.

The reason that I'm taking apart DC/AC inverters is to see if I can use the DC/DC converter part ( the first part) to boost the 12V up to 150 VDC, then chain them together in series to build up 300 VDC (for a 208VAC three phase test inverter) and eventually 900 VDC (for a 575VAC three phase inverter). Along the way, I'd like to do some testing on the inverters to determine the efficiency (estimated around 85%), what cooling is required (is a fan and a heat-sink enough?) and what sorts of things can be done to deal with a DC/DC converter failure while operating the electric vehicle. I have some crazy ideas I'd like to test out.

Back to the topic at hand

The ends come off after the screws are removed, then the bottom plate slides out the end to reveal a board mounted on standoffs from the 'top' of the heat sink.

The setup is remarkably similar to the Wagan, on a smaller scale. Perhaps this is an optimal design. I'd guess that some of the same people were involved in the design.

There are only four 40A fuses instead of 16. They are not associated with each of the 6 transformers, but are all in parallel. There are diodes visible beneath each of the transformers. There are two power transistors for each transformer. The output section has 4 power transistors, with only three larger capacitors in that area.

The electronics to switch the transistors appear to be distributed around the board, in areas that are not required for the power section. The control signals would be much more difficult to separate, since they are part of the multi-layer PC Board instead of routed through ribbon cables.

The power transistors are electrically isolated from the heat sink with a barrier that must be pretty good at thermal transfer. The transistors do not use the tabs, but rather have a mechanical clamp to hold them firmly against the barrier.

There are number of places on the board that are marked as resistors that have 16 gauge copper jumpers soldered in place.

Silly things which appear to be mistakes:
- the cooling fan has a cable pinched between the fan case and the bottom of the enclosure. The fan needs to be rotated 90 degrees and the cable would not be pinched.
- there is a pinch in the insulation of the output for outlet 1. There is clearance, but it was pinched anyway due to no cable management.

Connect the power supply to the DC to AC inverter. Turn on the inverter. The inverter powers up, then turns off? Check the voltage output from the power supply. 17.7V. Check the alligator clips, voltage at the inverter input terminals - all good. 17.7V was within the 10 - 18VDC for the other dc to ac inverter. The voltage range on this one is not printed on the outside of the case. Try lowering the voltage to 16. The inverter powers up, then off, then powers up, then off. There is an audible alarm that I think means the inverter input voltage is low. Check the voltage - it is dropping to 10V, the inverter powers down, then back up when the voltage rises above 13V, and the cycle continues.

The inverter appears to require more current than the power supply can put out. 1.1A is not enough.

Change power supplies. This one will do 5A at 20V max. The DC current in is around 2.5A at 16V to power up the inverter. I may have to revisit the other inverter. It is larger and likely needed more current to 'turn on'. Perhaps later.

Measure the output voltage - 0VDC, 0 VAC. What? It turned on. There should be voltage present. Verify good voltage in. The power LED is lit. The run LED is lit.

Try plugging in the WattsUpPro (a power, current and voltage measuring device for 120 VAC pluggable tools). It draws very little power, but it is a load and it will read voltage input. No display. How did I break this?

Turn off the power switch to the inverter. Turn it on again. Why? It was something that occurred to me, just because. The inverter powers up, the LEDs are both lit, and the WattsUpPro display lights up. 122.2VAC is what it shows. What gives? Dig out the manual - the inverter goes into a sleep mode if there is no load for 2 minutes. I guess I wasn't very fast getting the meter connected to check out the voltage.

Now that I know it needs a load, leave the WattsUpPro plugged in. The voltage at the output stage (the DC that is switched to generate the modified sine wave) is not easily measured with probes as large as the ones on a meter. I did get it done, eventually. The voltage is 135 VDC, which is lower than the 150 VDC I got from a smaller inverter that I had taken apart previously. I should check with a larger load on the inverter - perhaps it changes with load? Try a light - 1A at 120VAC is over 10A at 12VDC - overload and shut down. Same with the electric drill. I found a load small enough to plug and and not draw down the power supply. It's a 12V trickle charger, 12V at 1A output. The DC current rose from 2.5A to 2.6 or 2.7A. The DC Bus voltage drops to 134.5VDC. Unplug both the WattsUpPro and the charger. The voltage rises to 138 VDC. It's not regulated well, but I'm still at very low output power. I'll verify with a larger load when I get a battery connected. It's somewhere between 130 and 150 VDC.

The 'DC bus' is a bit hidden on this inverter. The transformers that step up the voltage go through a diode, and the output goes through the board. It may be to the other side or even to an internal layer, since this is a multi-layer board. It is not accessible from the top. To get access to the bottom of the board, I'd have to remove the clamps that tie the power transistors to the heat sink - all 16 of them. I'd rather not go there. The 'DC Bus' does come to the top of the board where it connects to the output transistors. That's the only location that I can see. It would not be easy to solder to that pad.

If I were to use this inverter as a DC/DC converter, the 'on/off' switch could easily be replaced by a relay. That would 'turn off' the load on the batteries. I should check what the current is when the switch is off. It drops to 0, then wanders a bit, from -0.1 to 0.1A - but I'm using a clamp-on meter since my regular meter does not measure currents above 100 mA. I expect that the inverter has no load when turned off, since the manual describes permanent mounting in a vehicle. If there was current draw when the switch was off, the vehicle battery would drain. That would not be a popular feature.

I'm not sure how I'd fake a 'load' for the 120 VAC outlet if I were to use this unit as a DC/DC converter.

Another thing that I have to verify when I get a battery connected. I guess that'll be it for tonight.

I can understand that completely.

Sounds like a great project. I'll try to follow along as it develops.
Ken

Some VFD-driven electric torque measurements - info from Oct 2011
 

This was a test to determine if the 5 HP 460VAC 1745 rpm motor that I am using for testing will really generate 220% starting torque if it is driven with about 300% rated full load current. It was being driven by a 5 HP 240 VAC three phase VFD.

The notes that I took, the readings that I recorded, and the theory do not match. I see that I need to repeat this test. But here is the information that I have.

The experiment is done with starting torque, since I can measure that with a fairly simple setup. The motor is rated for 1745 rpm, or 55 rpm of slip. That's not quite 1 Hz (60 rpm) of slip. The graph of the torque on a Design B motor appears to show maximum torque around 2 times the slip frequency. My testing should have varied the VFD frequency from 0.9 Hz (approximately slip frequency) to 2.7 Hz (approx 3X slip) to determine where maximum torque is. Somewhere along the line I got mixed up and did not get that testing done ...

-------------------- Begin ----------------------------------------------
The following is a bit of a history lesson for three phase motors. Please tune out until the end of this section if you don't like reading this sort of thing. Why the history lesson? I'm trying to explain what I'm trying to test. I want to determine if I can get 220% of the rated torque from my test electric motor - a 1745 rpm, 5 HP, three phase 460V design B motor. And if I can, how much current it takes for me to achieve that torque. My estimate is 300% of the full load current.

There are 4 NEMA 'standard designs' for three phase squirrel cage induction electric motors, creatively labelled A, B, C and D. A few extra have been added for specialty applications and use the letters up to M

Industrial and commercial motors that are available surplus are mostly Design B. There are minimum standards for how much torque a Design B motor has, but not all manufacturers stick with the minimums. For the Design A,B,C,D if the equipment designer used the 'minimum' values, another vendor's motor will work in the application.

The sizes that could be used in a vehicle are normally 'T' frame motors. The 'T' frame motors have standardized dimensions (mounting holes, shaft sizes, distance from the mounting feet to the shaft, etc) that allow you to replace a T frame from one vendor with a T frame from another vendor and everything fits.

The specifications for a Design B motor state that it will generate at least 220% of it's rated torque at a certain frequency. That frequency is related to the speed that the motor is turning, and the motor's rated slip.

-------------------- End ------------------------------------------------

The motor is mounted on a 2 x 8, which is bolted to a few 2 x 4s. This motor does not drive a belt, but a strap instead (it is rated for much more tension than any of the belts that I have). The strap is wrapped around the drive pulley a few times and secured to the pulley. It then runs to a wooden pulley with a couple of different diameters, and runs around half the pulley circumference where it is fitted into a slot so that it does not slip. The pulley is mounted to a rotating shaft with a bearing on each end. The wooden pulley has a 2x2 bolted to it that pushes down on a 2 x 6, which spreads that force across a bathroom scale, which is levelled. That scale is how the torque of the motor is measured, with a multiplier for the wooden pulley and the motor pulley. It gives me decent accuracy and a range of measurements. The motor is rated at 15 foot-lbs, so I need to use the pulleys to amplify this weight value to something that can be easily measured on the scale. I hope to measure 220%, which is 33 foot-lbs. My scale can measure 240 lbs, so the multiplier should be just over 7, but it ended up being just under 4.

The motor and pulley bearings are bolted to the 2 x 4s. This whole mess is suspended between a work bench and a metal rack. The scale is on the floor below.

When the motor is turned on, the rack is being pushed down or compressed, the work bench is being lifted. The work bench had to be over 200 pounds to make this work.

There is a sketch below that tries to show what is going on. I'm not that good at explaining - the people that I explained this test to have not understood what I'm doing. When I reviewed what I did and compared that to my explanation, I must confess that I have trouble figuring out what I did as well. It appears that I will be doing this test again, perhaps in the spring.


Here is the sketch, for what it's worth.

Some VFD-driven electric torque measurements - info from Oct 2011
 

Second part of the posting

There are a few more details, plus some assorted ramblings below.

I decided to split the spreadsheet into three tabs, for the three trials I did. The trials were different in what was measured and how it was measured. I thought that I was improving as I went along. Now I'm not so sure.

Settings:
The VFD is rated for 240 VAC three phase, 15A and will do 22A for about 30 seconds. It is set for linear V/Hz output.

Change - VFD boost settings. This is a percentage of the rated voltage, and the VFD allows the setting to vary from 0 - 40%. Changed from 0% up to 37%

Measure - motor temperature, motor current, scale reading

The VFD will display the output current, output voltage, or output frequency. This particular surplus unit appears to have an issue with the output current, since it displays the same value no matter what current it is actually sending out. The output frequency is always the same - 0.9 Hz. The output voltage displayed on the VFD never matched what I was measuring with the AC meter.

I have a clamp-on meter on one phase of the AC to the motor, another meter showing output voltage phase - phase, a hand-held infra-red meter for motor temperature (at the same spot each time - the meter is duct taped to the motor), a meter on the DC bus voltage of the VFD to make sure that I am not running out of power from my battery bank. I ran out of meters so I don't have the DC current from the battery bank, which would have been nice to show the power in versus power out for the VFD.

The results are not what I expected. That seems to be a recurring theme in the tests that I set up. The battery bank ran out of current the first time I ran the tests. So I fed 240 VAC into two of the terminals on the VFD, to supplement the battery power. I then spent the rest of the day ensuring that I did not over-charge the battery bank, or charge it too quickly. You will notice the DC voltage changes around 30 - 35% boost

I measured as high as 212% of the rated motor current, which gave me a reading of 100 pounds of force on the scale. Working that back through the pulleys, the motor put out 27.27 foot-lbs of torque. The 5 HP motor is rated at 15.04 foot-lbs, so the peak I measured was 181% torque. I was not able to put 300% current into the motor (my estimate) so I think it was reasonable to get less than the 220% torque listed in the motor specs.

These results are not what I remember them being. Some of the things that I thought were obvious about the setup - so I didn't write down the details - turn out to be important and not easy to interpret from what I did write down.

I don't know why I stopped testing when I got to the end of the 0.9 Hz set. I should have redone the whole test at 1.8 Hz and 2.7 Hz. If those showed any interesting trends, I should have added more test runs between them. I didn't even get up to 300% current. The last set of tests that I ran I didn't write down the motor current (!!!) That seems like a pretty important thing to miss.

I will be writing up what I want to see for the test before doing them, predicting the results, then performing the test and collecting the data. Working from memory while you are out in the garage does not seem to work very well.

You may very well wonder why I am using a test motor and a test VFD instead of using the equipment that I want to use in the truck. I didn't have a VFD with enough power to drive the 40 HP motor at 300% current when I did the tests, and I still don't have the VFD operational. It's just a whole lot safer to work on smaller (scale) models for testing than it is to perform full scale tests. I want to get some practise testing, predicting, logging. With 40 HP, 220% torque will be 120 * 2.2 = 264 foot-lbs of torque. That's a lot of torque to measure. My present setup will not handle it.

First three tabs are for trials 1,2, and 3. They are a bit of a mess.

VFD Settings is a listing of the parameters for the test VFD, an Allen Bradley 1333.

Motor Data lists the information from the nameplate for each of the motors that I have.

The test motor is:
reliance electric sabre 5 hp
184t frame
hp 5
460 VAC 3 phase design b type p
rpm 1745 amps 6.6
60 hz, ambient 40c s.f. 1.15
cont duty insul class f
enclosure prot code j
pf 83, nom eff 87.5
weight 69 lbs

This is great stuff! I like your experimental approach.

More DC to AC Inverter investigation
 

I have two of the "Durafied 1350W continuous, 2700W peak Inverter S1350DI" inverters. I have not dug out any more of the surplus units.

I connected each of these inverters to a 12V battery (a small one) to check out the isolation between the DC output sections.

As seen in my crude but readable sketch (I'm trying out google docs), I checked out the voltage of each inverter separately. The voltage starts out wandering a bit, but settles down to a small range of 140 - 142.2 VDC. Both inverters have this voltage (internally). I was not able to reproduce the 135 VDC that I had measured earlier. Nor was I able to have the inverter 'go to sleep' and disable it's output.

Prior to connecting these inverters in series, I checked the voltage between the + and - terminals on the battery with the + and - terminals on the 'output'. The voltmeter showed a consistent readings. If points in a circuit are isolated, you can see many voltage differences but they are somewhat random and not repeatable. - battery and - output were solid at 0.0VDC. I'll reference everything from - battery. + battery is 12.6VDC as expected. + output is 140 - 142VDC. The output is NOT ISOLATED from the battery at ALL.

In my excitement, I had assumed that boost transformers meant that the input and output were isolated from each other. This was a rather dangerous assumption. It is good that I checked it out as early as I have.

My confidence is a bit shaken - and my resolve to check absolutely EVERYTHING is much stronger.

On the agenda for tomorrow - power the inverters from separate 12V batteries, verify that the inverters can be connected in series to get about 280 VDC, and connect this voltage up to a test VFD to ensure that it powers up as it should.

This is really awesome!!! Totally out of my realm of expertise, so I'm learning a lot. Thank you!!!