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Old 12-01-2014, 03:55 PM   #1351 (permalink)
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I really like the prototype possibilities with the heat gun, in fact I'm ordering one today. Any suggestions with those e-bay ones?

It looks pretty easy to populate a board section by section, testing your circuit along the way. Until I saw this video I though my only options were either the manual soldering (which I've been putting off . . . ) or to go full "semi production" with the toaster oven.

This is an awesome middle ground.

Paul - if you want to do even small batch stuff, I would suggest a stencil. I got a stainless stencil when I made my 1st rev BMS, and it really made the solder past job a lot easier. I just populated the board by hand after that. Regarding 64 pin chips and the like, they really do pull into place with surface tension, like the video.

- E*clipse


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It worked really well for me.

Not a single component failure that i can remember in over 50 cell top BMS modules and 3 master modules.

Also now i have a handy heat gun on my workbench for things like heatshrink and plastic bending.
I even used it to test the temperature sensor on each of the cell top modules.
I noticed in the video he "tidied" up the solder paste. I found that was unnecessary unless you had really piled on the paste. Even if the paste hangs off the pad a little, surface tension will bring it right back onto the pad when the paste melts.
After doing a few modules you get the hang of the paste syringe and excess like he had doesn't happen.

I was initially worried that i would over heat the components. But you quickly get to know how rapidly the heat gun melts the paste and you move on as soon as the paste melts fully.
Watching a few videos of toaster ovens and their temperature curves, they heat the components up a lot slower and cool them down a lot slower.
So the heat gun approach may cause more thermal stress as the outside of the component will heat up much more rapidly than the inside of the component.
But that may be a good thing as it is the solder paste we want to heat up not the component innards.

All i can say is it works perfectly for me.

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Old 12-01-2014, 04:10 PM   #1352 (permalink)
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regarding torque biasing for an electronic differential, I tried something that actually worked quite well:

I built a little circuit with two potentiometer inputs, each 0-5V

One potentiometer is the "steering" or "bias" adjustment. It immediately goes into a simple inverting op-amp circuit with 1:1 gain.

The second potentiometer is the "throttle"

The output from the steering potentiometer goes into another op-amp circuit arranged as a differential amplifier with 1:1 gain. The second input for the differential amplifier is the throttle.

A second differential amp takes the inverted steering output and the throttle .

Basically, the outputs track up and down together when adjusting the throttle, or opposite from each other when using the steering.

While this is a very simple proof of concept, it shows that two different motor controls could get the outputs from the op-amp circuits described above to accomplish adjustable torque control:
1) right-left torque biasing using steering position as input
2) fore - aft torque biasing using a user adjustable knob (like WRC rally cars)

I'm working out some safety/bypass circuits, but this looks really promising.
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Old 12-01-2014, 06:48 PM   #1353 (permalink)
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Quote:
Originally Posted by e*clipse View Post
I really like the prototype possibilities with the heat gun, in fact I'm ordering one today. Any suggestions with those e-bay ones?
I picked up a cheap eBay one. The only issue i have with it is that it didn't come with a power switch. I can switch the heat gun or soldering iron on or off but with the heat gun and soldering iron both off the unit is in a standby mode. I would have prefffered it have a nice mechanical power off switch. It is on my to-do list to add a switch. Other than that it is great.
Mine has a small fan in the heat gun wand rather than a fan in the main unit and an air hose. Not sure which is better as i have only ever used this one. But it is nice and quiet.

Quote:
Originally Posted by e*clipse View Post
Paul - if you want to do even small batch stuff, I would suggest a stencil. I got a stainless stencil when I made my 1st rev BMS, and it really made the solder past job a lot easier. I just populated the board by hand after that. Regarding 64 pin chips and the like, they really do pull into place with surface tension, like the video.
- E*clipse
Paul, i would second the idea of getting a stencil. Especially for a board with the number of components you are working with. Putting the paste on using the syringe isn't difficult but it does add to the time taken and the amount of time you are doing precision work which can be fatiguing.
If you do use a stencil then you would probably be populating the entire board. It would be difficult to just stencil a subset of the components unless the stencil had been designed to omit certain components.

When i ran short of components at one stage of building my BMS modules i just continued on putting on the micros and a few other components. This allowed me to do the in circuit programming of the micro. This let me continue production while i awaited the extra components.
Maybe you could do the same. Offer the boards with the micro and a handful of other components fitted. Enough so that you could program the micro?
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Old 12-03-2014, 09:37 AM   #1354 (permalink)
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Rod Hower somewhat unexpectedly sent me a beautiful 2.5HP PMSM motor. Would one of the 2 beta testers be willing to wait a little longer while I get an encoder on it, and test the controllers on that? It's rated for 45amp (so a higher current test!!), and I haven't had the opportunity to get FOC working with brushless DC.
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Old 12-03-2014, 04:27 PM   #1355 (permalink)
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Yes, you can drive a motor (and a vehicle, for that matter) with V/Hz but it is not very efficient. The motor heats up. The FOC shifts the phase Voltage and Current (so I'm told) so that you are minimizing the core losses. With V/Hz you are doing a linear estimate on a non-linear load, and the extra current you pump into the motor is dumped as heat. We use V/Hz on pumps and fans. The load varies proportional to the cube of the speed. So 1/2 speed is about 1/8 load. Running in V/Hz is simple and allows us to replace motors without 'tuning' the controller to the new motor. But it wastes a bit of power.

I have no experience with an encoder on a V/Hz driven load. As I understand it, the controller does not have the option of changing the output voltage separate from the frequency when in V/Hz?
V/Hz is just a dumb term that is incorrectly used by manufactures to define a controller with no intelligence of its own. The technical name is scalar control and just derives that for a decrease in frequency one has to reduce the voltage as well to keep the same magnetic flux, which is also true for Field Oriented Control.

Scallar control can be modified to use in a vehicle. Closed loop control, space vector modulation and adaptive output voltage are used to achieve great efficiency.

One doesn't necessarily need Field Oriented Control to achieve good performance, although it makes development easier between different motor types.

Now if by V/Hz you want to say 'open loop scalar control', yes that's pretty much un-driveable on a road vehicle unless the driver has some practice. Its not something nice though.
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Old 12-03-2014, 04:38 PM   #1356 (permalink)
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Unless one's planning to make a lot of boards (Paul for example) I don't see much need on hot air working tools. Regular solder and soldering iron do the job quite nicely. If needed there are some cheap propane soldering irons as well that do a decent job (I use one for the thermal shrinking tubbing).

I regularly work on 64 and 100 TQFP chips and I trust hand soldering much more than any solder paste as I know my joints are perfect and short free. If needed I can post a video of how to do it.

Of course one needs a bit of practice, but the TQFP is an extreme case, most SMT parts on the inverter are soics?

Last edited by cts_casemod; 12-03-2014 at 05:20 PM..
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Old 12-03-2014, 06:48 PM   #1357 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
Rod Hower somewhat unexpectedly sent me a beautiful 2.5HP PMSM motor. Would one of the 2 beta testers be willing to wait a little longer while I get an encoder on it, and test the controllers on that? It's rated for 45amp (so a higher current test!!), and I haven't had the opportunity to get FOC working with brushless DC.
Paul,
I can wait.
The more testing you do the less likely i am to blow it up.

I am still plodding along with the build. Not getting much time on it due to work commitments but i have a couple of weeks off over Christmas so i am hopeful of making significant progress then.
The controller will be pretty much the final part added, so any delay just means it spends less time on a shelf in my garage watching me fumble around trying to make a nice home for it in the EV.
I was hoping my batteries would arrive tomorrow but they are currently sitting 1792km (1113 miles) away.
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Old 12-03-2014, 06:55 PM   #1358 (permalink)
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Quote:
Originally Posted by cts_casemod View Post
Unless one's planning to make a lot of boards (Paul for example) I don't see much need on hot air working tools. Regular solder and soldering iron do the job quite nicely. If needed there are some cheap propane soldering irons as well that do a decent job (I use one for the thermal shrinking tubbing).

I regularly work on 64 and 100 TQFP chips and I trust hand soldering much more than any solder paste as I know my joints are perfect and short free. If needed I can post a video of how to do it.

Of course one needs a bit of practice, but the TQFP is an extreme case, most SMT parts on the inverter are soics?
The current board has no tqfp parts. There are 6 SOIC16 parts that are pretty easy to solder. I made sure to have the pad stick out past the legs so it's easier to do by hand. There are also a few 1210 caps and resistors. Everything else
is old fashioned through-hole. I wouldn't mind seeing a tqfp video! I could do a tqfp 44pin without much issue with my current tools, but a tqfp 64pin that's still 10mmx10mm (or was it 14mmx14mm??) is pushing it with the soldering tip I have.
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Old 12-03-2014, 07:19 PM   #1359 (permalink)
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Quote:
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The current board has no tqfp parts. There are 6 SOIC16 parts that are pretty easy to solder. I made sure to have the pad stick out past the legs so it's easier to do by hand. There are also a few 1210 caps and resistors. Everything else
is old fashioned through-hole. I wouldn't mind seeing a tqfp video! I could do a tqfp 44pin without much issue with my current tools, but a tqfp 64pin that's still 10mmx10mm (or was it 14mmx14mm??) is pushing it with the soldering tip I have.
That's the point. People get scared when someone mentions SMT but there's really no reason. those IGBT drivers are huge

Tip size is not important. My tip is 2mm wide. I don't like the thin ones as temperature regulation is quite poor. See If i can make a video next time I solder one. Friends ask all the time when they blow their Arduino mega/ Nucleo, etc.

Here's one I've been asked to get high resolution pictures from. Best my camera could do anyway.




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Old 12-03-2014, 08:05 PM   #1360 (permalink)
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Unless one's planning to make a lot of boards (Paul for example) I don't see much need on hot air working tools. Regular solder and soldering iron do the job quite nicely...
I used to do the same.

When i used to use the soldering iron for SMD i would sometimes get the components preferring to stick to the tip of the soldering iron rather than the PCB pad.
Also it was difficult to remove components. Many times i found myself heating one end of a resistor then quickly trying to heat the other end before the first end cooled enough to solidify again.

Then, when i contemplated doing all my BMS cell top boards (lots of boards and lots of SMD components) i thought i would treat my self to the hot air station. Always looking for justification to buy more tools.
I should have done it years ago. The hot air makes it so easy, neat and clean.

On one of the first few boards i did i manage to solder the pic micro in reversed. Doh.
With just a soldering iron this would have been a pain to fix without risking heat damage to the micro and probably making a mess of the board. With the hot air wand it only took a few seconds to heat it, lift it, rotate it and re-place it. Couldn't even tell it had been reworked afterwards. From then on i was a huge fan of hot air soldering.

The solder paste is brilliant as well. Each pad gets just the right amount of solder.
The couple of times i did get a solder bridge between micro pins. All i did was reheat the area for a couple of seconds and boom solder bridge gone. The flux in the solder paste really works well. The solder runs to the pad and component leg as if it was magnetised.
Mesmerising to watch.

Also the solder paste holds the component perfectly. I can pick and place the entire board before soldering without fear that i will bump the PCB and have the components move around. It also means i don't have to keep swapping between soldering and pick and placing.
I firstly place all the components one after another on all the boards,then when i finish that i move on to the heat gun. So the first step is just using the tweezers and the second step is just using the heat gun.
I was picking and placing between 10 and 20 boards at a time. This made the process much quicker and also reduced error as i would place the same component on each of the boards in turn then select the next component and place it on each of the boards in turn.

When i do have to solder a through hole component the solder station has a nice temperature controlled soldering iron as well.

It was $70 well spent.

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