DIY Volt Hybrid - Open ReVolt style

[bennelson]

It doesn't have slip rings.
Slip rings are used when you need to run current to/from something that rotates.

In this case, the permanent magnets rotate, they don't need current.
The electro magnets stay still, so they just have regular cables going to them.

It's easier to show than describe. I'll make sure to take a photo next time I have the thing open.

[UFO]

I misunderstood you, I thought it was your rotor with the electromagnets. Brushless motors can be either DC or AC, but the current waveform from your windings will always be AC. I think you are better off efficiency-wise to keep the AC if your charger input will tolerate it.

[bennelson]

Sorry, no updates on this for a while.

Too many other things going on lately. (Birth of my first-born child was a big one! )

Anyways, I figure I am only going to actually do this is if:

A) I set a deadline for it to happen by.

B) I get a little help from my friends. That means you guys!


The car is currently running a 72V system.

My plan was to run an analog 72-volt battery charger from the AC output on the generator to the batteries. This would run 20 amps continuously to the batteries (max charge rate on that charger). While not enough power to drive the car directly, that would be enough energy to EXTEND the RANGE of the car by always adding to the batteries (or slowing the discharge, if you want to look at it that way.)

So, my main challenges right now are:

Need solenoid and regulator for LP generator
Need appropriate regulator for LP tank - not sure exactly what I need
Need fuel tank (as small as I can get!) I would love to use standard 20lb gas grill bottles if possible.
I do have a propane tank (from a forklift?) it's about 4 feet tall - not sure how well that would fit on a Metro...

My charger has been acting weird. I pulled it off and have been doing individual charging lately. Could anyone gifted with electronic knowledge give me a hand with it? It's a K&W BC-20. I have no idea where to start on trouble-shooting it! (Also wondering what would be need to possibly even upgrade its rated output amperage?)

If that charger wouldn't work, what would it take to design a device that would simply create a 20-30 amp, 98V (14.1 x 6 batts) output from that generator?

Then, I need to make a "rack" that would mount on the back of the car - similar to those truck ones that slide in the hitch receiver. That would hold the generator (about the size of a push lawn mower engine) and fuel tank. I would like to cover both with some sort of semi-attractive cover, perhaps with vinyl lettering to advertise the project? Link to my blog and the Makerspace page?

Anyhow, I would really like to do this, but still need to learn more about LP generators, battery chargers, etc. All help and suggestions greatly appreciated!

-Ben

[todayican]

Ben, im guessing that if you change the gen head for a little etek with that kind of amp draw, you could just feed it into the pack and extend your range.

Im no expert beleive me, but for the kind help from people on sites like these im building something similar. The key might be in losing the charger, feeding in dc current and focusing on not feeding it too low a voltage (The reason I say that is when the dc gen is putting out 96v its a whole other price class of gen ;-)

Just my .02c

[bennelson]

Here's some more info.

(I'm trying to post more or less the same information on this forum and a couple of e-mailing lists. If you see odd references, that's why...)


The Generator is a Generac NP-40G.

It is a "Computer Controlled Variable Speed RV Generator".
It uses a permanent magnet rotor, which is on the OUTSIDE of, and rotates around the stator. Circuitry in the generator controls the engine speed to maintain a constant voltage out. (The circuit board controls a stepper motor, which adjusts the throttle.)

There were both gasoline and LP versions of this generator built. This is the LP version. ( I think the only difference may be the carburator. I would prefer it as LP anyways.)

The generator has electric start, and and recharges the 12V starter battery. There is also a Remote Start Panel available as an accessory. That lets you start the generator from the cab of the RV and monitor if it is running or not. I have the service manual for this generator, which includes a wiring diagram of the remote start. I would think it would be fairly easy to build a remote start for this unit.

The specs on the generator are:
rated for 3750 watts
115v
1-phase
31.3 max load amps
60hz
220 cc single cylinder, vertical shaft engine
LP gas fueled
Air cooled
Electric start
RPM range of 2200-2600 at 0 amps and going up to 3250-3910 rpm at 30 amps.



According to the manual, the generator comes with:
Fuel Lockoff Solenoid (missing)
LP Gas Regulator (missing, should be pretty standard though)
LP Carburetor (at least that's still there!)

The manual goes on to state that the installer must provide:
Vapor withdrawl type fuel tank
Primary regulator that will deliver 11 psi

I did not see any reference to a flow rate of any regulators. When I did get engine running, it was with a propane grill regulator on the engine and somebody manually opening and closing a valve on a propane tank trying to get the right flow. I believe that some regulators use the vacuum of the engine to pull on a spring to vary the flow? Any insight on that from anyone?

To run power to the electric car, I would much rather modify some sort of device EXTERNAL to the generator itself. Seems like it's a nice little generator someday. I may want to be able to keep it around for other purposes.

I am using lead-acid (AGM) batteries with the car. My idea of using the analog battery charger connected to the batteries and AC out of the generator is that it keeps it very simple. The charger itself would limit the amperage between the generator and the batteries. (The charger is designed to only "pull" so much power from the wall, or in this case, the generator.)

I would also be interested in some sort of "black box" that would go between the AC out of the generator and the batteries. It would have to be simple enough for ME to build, or at least build with the help of some local electronics friends. It would also have to limit the maximum draw on the generator.
I think that ideally, I would want to run the generator more or less full-tilt. I know that gasoline engines are most efficient when running wide open. However, that means your car is driving really fast, and even if the speed limit doesn't slow you down, are resistance eventually will. In a serial-hybrid the speed of the engine and the speed of the car are unrelated. Seems like there is no reason NOT to try to run the generator engine as efficient as possible.

What is required to rectify the AC to DC? What voltage DC do you get from 115V AC? Lets say we get that voltage, and then just knock it down to what the battery pack wants with some sort of resistor (Tom's light bulb). How we I control amp draw to keep from overloading the generator and popping the fuse? What would be an appropriate way to limit current?

Also, I was wondering what type of LP tank would be compatible with this generator. It's an RV generator, and whenever I see an RV with propane tanks on it, they look just like the type that's on my gas grill. The manual does say to use "A VAPOR WITHDRAWL type fuel tank" and further down states "Do not attempt to use any liquid withdrawl type tank with the RV generator."

-Ben

[TomEV]

Originally Posted by bennelson

What is required to rectify the AC to DC? What voltage DC do you get from 115V AC?

On 96 volt cars, some people use a 'bad boy' charger - essentially 120 volts rectified to DC with a bridge rectifier set. The finished charging voltage of a 96v lead acid pack is just over 120 volts.

Depending on who you talk to, this type of charging works great, or is too dangerous to consider. That being said, it is probably the cheapest kind of charging around.

Here is a link to a 'safer' bad boy -

Bonn Charger

In most cases, the resistance of the extension cord provides enough 'current limiting', but the farther the pack is depleted, the more amps it will try to draw. Cords get warm enough to melt snow (from pictures I've seen - no snow here!). Sometimes cheaper quality extension cords will melt as well.

For a 72 volt system, the finished voltage is just over 90 volts, so this kind of charger won't work.

[bennelson]

Here's a reply from one of my e-mail friends:



Ben
If you want to drive cross country at 65mph with no worries then Tom B's 15KW generator sizing will give you the "serial hybrid for $4500" smirk. If you can't afford a big power plant then you cannot go as fast for as long. A nice tool to give theoretical power required at the speeds you plan to travel is here:
Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

So for rough figuring at 35 mph your metro requires about 2700 watts of motor output (the spreadsheet includes drivetrain losses from motor to the road).
Unfortunately in a serial hybrid all of the inefficiencies in the energy chain "de-rate" this answer. As Tom G stated if you can eliminate the battery charger that is one less loss( or at least a smaller loss) to deal with. If your generator output is for 120 volt service normally you could size your battery pack for say 108 volts and directly rectify to the battery pack. Others with electronics experience may have other solutions as I was born 50 year too late. My guess is your 3700 watt will allow you to drive at around 35 mph in an urban cycle. Stop lights and slower operation will allow your generator to catch up with other inefficiencies such as hills etc. The key is to not drive faster than what your generator can output over time. (The batteries would only be supplying energy for acceleration for example). Carefully monitoring the amperage and voltage output and temperature of the generator while your driving is required unless you employ a solution that such as Tom B's generator spspigotTBSGS).

As far as setting the generator to run at full speed, I would let it operate as designed. Chances are it will be running at full speed most of the time anyway . If he pack is charged and your at a stoplight there is no advantage to running the generator at full speed.


That's pretty much exactly what I am looking for. Range extention for driving more or less city speeds. Some sort of basic homebuilt charger that would do a set voltage out from the generator and control amperage sounds like the right thing.

[bennelson]

More on the "Range-extender" Hybrid project.

I just tested the generator again. The electric start on it works great. It has a clean air filter rigged up and ready to go. I have not changed the oil, but there is the right amount of oil in there and an oil filter in place. It's a 220CC single-cylinder engine.

The generator also has a remote start feature, which I think would be really cool to connect to the "crank" position on the car's ignition.

The magical missing part is a Generac part number 075211. That's the demand-type LP regulator that goes directly on the generator. The owners manual says that it provides gas at 11 inches of water column. It has a 3/4" input and 3/8 output. Supposedly, it is identical to Garrettson model KN 039-122. I talked to a couple of Propane people on the phone today, and none of them had even heard of the BRAND of Garrettson - maybe it's particular to the generator industry or something odd like that. (The Generac part is about $160 and I would have to order it through a dealership.)

This generator also calls for a primary regulator on the fuel tank. That regulator needs to run at 11 inches of water column, but have a flow rate of at least 67 cubic feet per hour. (Any info online I can find always lists flow in terms of BTU output. How do I compare these!?!?)

I am also wondering if there are any issues with using a standard 20 gas grill LP tank. That's the size that I would like to use. (Cheap, convenient, tank swaps at gas station or Wal-Mart...) Is the overfill protection device or whatever else is on one of those tanks going to be a problem?

I do also have a very large LP tank (3 or 4 feet tall, can be vertical or horizontal mounted) that I can use for experimenting, but I would like to use something smaller for the finished version.

So, does anyone know if there is a less expensive secondary, demand-type regulator I can use? Does anyone have a spare primary regulator I could make use of?

All other suggestions and advice welcome.

-Ben Nelson

[Daox]

Found the generac regulator on ebay...

GENERAC GENERATOR REGULATOR, GAS FUEL PN 075211 - eBay (item 350360236503 end time Dec-24-10 18:36:44 PST)

And the Garretson here for less:

GARRETSON IMPCO MDL KN LOW PRESSURE REGULATOR # 039-122 - eBay (item 180352131235 end time Dec-21-10 01:51:11 PST)


But, there is this other one that seems to include a solenoid?

GARRETSON IMPCO MDL KN LOW PRESSURE REGULATOR # 039-122 - eBay (item 180373885447 end time Dec-18-10 02:57:47 PST)

I just plugged the part numbers into an ebay search.

[bennelson]

Hmm.

Looks like that one does include the solenoid. Generac wants a rediculous amount of money for their solenoid....