Cheap VESC (VESC 4.12 redesign)

General Discussion about electric vehicles.
shaman   100 mW

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Re: Cheap VESC (VESC 4.12 redesign)

Post by shaman » Jan 11 2019 8:59pm

wil wrote: ↑
Jan 11 2019 8:14pm
Looking at your photo it looks like already had the via thing suggested above?

What is your approximate BOM cost for this iteration?

You can always just drill out the holes to fit thicker wires, it's not like the tiny extra amount of contact gained by the PCB depth being coated really adds much in the overall scheme of things.
Right now the BOM cost is $30ish USD. That's the boards and components and utilizing the "free sample" technique I mentioned before. I haven't factored in cost of wires, connectors, and other hardware yet. Yes the via thing was already there in the design for thermal management reasons. I didn't have the soldering technique in mind mentioned by BotoXbz. Agreed that one can just drill the holes out for this version but I will be making another revision with all the minor tweaks and lessons learned from this one. I want 12awg wire to fit comfortably and maybe even 10 awg.

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pavlik1   10 W

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Re: Cheap VESC (VESC 4.12 redesign)

Post by pavlik1 » Jan 12 2019 3:13am

Hello

I am interested to have one populated board for testing. I will pay the BOM and shipping.
I have various e-bikes and electric car.

Please let me know if you are interested.

Cheers
1st old radiator fan motors, 20km/h - stolen after 2 days - no pictures
2nd 250W-24V eZiplike motor with gear. running on 36V, 8Ah, peak 1000W, 40km/h. Just disassembled (running again)
3th GM 48V 1000W, running with 16S 20Ah WinForce Lipo. different controllers, speed over 72km/h - LiPo FIRE
4th Recumbent HS3540 2X16s 48V 20Ah
5th full suspension Haibike Attack FX, running with e-novation M15 16S 10Ah LiFePo4 or 13S LiIon
6th Hardtail alu 26'' with e-novation M15 10S, VESC and throttle

shaman   100 mW

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Location: Fort Worth, TX, USA

Re: Cheap VESC (VESC 4.12 redesign)

Post by shaman » Jan 13 2019 2:14pm

pavlik1 wrote: ↑
Jan 12 2019 3:13am
Hello

I am interested to have one populated board for testing. I will pay the BOM and shipping.
I have various e-bikes and electric car.

Please let me know if you are interested.

Cheers
PM sent and was responded to.

shaman   100 mW

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Joined: Dec 10 2018 7:03pm
Location: Fort Worth, TX, USA

Re: Cheap VESC (VESC 4.12 redesign)

Post by shaman » Jan 13 2019 2:24pm

Additional thoughts for this and future controllers:

I want these to able to fit in 1590B or other common aluminum enclosures. These are widely available for decent prices. The current design would only fit in a 1590B2 due to the height of the 1000uF capacitors. I could swap them out for the shorter 680uF caps and it would most likely fit in a standard 1590B. I could also alter the design slightly so that the caps can just lay down over the board, but that bothers me for some reason and idk why. There are also IP65 versions of these enclosures called the 1590WB. They simply have a gasket on the lid and o-rings on the screws. This will help keep dust and moisture out of the controller. Additionally, the enclosure might be able to retain mineral oil inside. I have been playing with the idea of utilizing mineral oil for improved heat dissipation of the whole controller board. As long as I use proper cable glands I think this is possible. Doing this could increase the current limits of this and future designs by a fair amount. Let me know what you think about this!

wil   100 mW

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Re: Cheap VESC (VESC 4.12 redesign)

Post by wil » Jan 13 2019 8:30pm

Gland or not the oil will wick down the wires and out of the enclosure like that.

Also I noticed you have thickened up the traces from the driver circuit to the FET gates, but only on G1, G4, G2. Any specific reason?

When you were designing did you consider having the high and low side FETs on opposite edges of the board? You could shift all logic down one end, + have smaller extra caps closer to the actual FETs themselves. I think you could also fit a 12 FET design into a maybe 30% longer board this way. In addition having the Caps closer to the FETs can eliminate ringing caused by the supply line inductance when they switch.

shaman   100 mW

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Location: Fort Worth, TX, USA

Re: Cheap VESC (VESC 4.12 redesign)

Post by shaman » Jan 13 2019 9:13pm

wil wrote: ↑
Jan 13 2019 8:30pm
Gland or not the oil will wick down the wires and out of the enclosure like that.

Also I noticed you have thickened up the traces from the driver circuit to the FET gates, but only on G1, G4, G2. Any specific reason?

When you were designing did you consider having the high and low side FETs on opposite edges of the board? You could shift all logic down one end, + have smaller extra caps closer to the actual FETs themselves. I think you could also fit a 12 FET design into a maybe 30% longer board this way. In addition having the Caps closer to the FETs can eliminate ringing caused by the supply line inductance when they switch.
Bummer to hear about the oil wicking down the wires. Had my hopes up...but maybe I'll find a way still.

I was going through thickening the gate drive traces, then stopped for some reason, then entirely forgot to finish the rest before having boards made. In other words, I messed up on that. That will be fixed in a future revision of this design. Hopefully it still functions decent enough.

The general FET layout was based off of existing designs that I knew worked. I didn't want to try anything too crazy since I don't have any experience with designing these kind of electronics. I do intend on having caps closer to the FETs in the high voltage design like the VESC 6. Wouldn't spreading the low side FETs from the high side FETs out from each other across the board be non-ideal for current flow?

shaman   100 mW

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Re: Cheap VESC (VESC 4.12 redesign)

Post by shaman » Jan 15 2019 8:38am

Found some good documentation on controlling ringing on MOSFET switch nodes. I have updated the PCB and schematic to have a 1206 100V ceramic cap by each set of 2 MOSFETs. These will be my snubbers to help reduce ringing during switching. I will measure any ringing during testing to make sure it's not excessive. My HV(high voltage) design will be more optimized to reduce loop inductance and minimize ringing at the root of the problem.


https://e2echina.ti.com/cfs-file/__key/ ... osfets.pdf

melonfrog5   1 mW

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Re: Cheap VESC (VESC 4.12 redesign)

Post by melonfrog5 » Jan 15 2019 4:29pm

:bigthumb:

So what DRV chip did you decide to use? The DRV8353?

Let me know if you need more testers, I'm happy to. Or you can join the https://www.electric-skateboard.builders and post your project here. We are always looking for new stuff like this 😁

shaman   100 mW

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Re: Cheap VESC (VESC 4.12 redesign)

Post by shaman » Jan 15 2019 6:48pm

melonfrog5 wrote: ↑
Jan 15 2019 4:29pm
:bigthumb:

So what DRV chip did you decide to use? The DRV8353?

Let me know if you need more testers, I'm happy to. Or you can join the https://www.electric-skateboard.builders and post your project here. We are always looking for new stuff like this 😁
The DRV8353 is what I'm using for the HV version as of right now. The HV version is still just a half done schematic/PCB in KiCAD right now so it's not set in stone. I've seen the eSk8 forum but I wasn't sure this belonged there. Is it eSk8 stuff only? If so, do you think my version of the VESC isn't too bulky for e-skate purposes? If you think me posting over there would be accepted then I'll do it. I'll PM you about testing.

wil   100 mW

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Re: Cheap VESC (VESC 4.12 redesign)

Post by wil » Jan 15 2019 8:57pm

shaman wrote: ↑
Jan 13 2019 9:13pm
Wouldn't spreading the low side FETs from the high side FETs out from each other across the board be non-ideal for current flow?
Shouldn't really matter, you already have huge inductance from the motor and the long phase wires, an extra couple of mm of trace won't make a difference IMO. Your currents are limited by the thickness of the FETs legs here anyway (well and the FETs)

shaman   100 mW

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Re: Cheap VESC (VESC 4.12 redesign)

Post by shaman » Jan 15 2019 9:27pm

wil wrote: ↑
Jan 15 2019 8:57pm
shaman wrote: ↑
Jan 13 2019 9:13pm
Wouldn't spreading the low side FETs from the high side FETs out from each other across the board be non-ideal for current flow?
Shouldn't really matter, you already have huge inductance from the motor and the long phase wires, an extra couple of mm of trace won't make a difference IMO. Your currents are limited by the thickness of the FETs legs here anyway (well and the FETs)
Maybe you're right though I feel like having FETs on opposite sides of the board would make it hard to utilize the enclosure as a heatsink. The enclosure interior width would have to be just right so that one could thermally couple the FET tabs to the walls. Also it would seem like I would have to separate the high current supply and ground traces a fair bit to reach the opposing FETs. This would work against my goal of trying to minimize ground loops and parasitic inductance. However, I may be completely overthinking this or misunderstanding what you're suggesting entirely.

wil   100 mW

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Re: Cheap VESC (VESC 4.12 redesign)

Post by wil » Jan 16 2019 12:54am

shaman wrote: ↑
Jan 15 2019 9:27pm
wil wrote: ↑
Jan 15 2019 8:57pm
shaman wrote: ↑
Jan 13 2019 9:13pm
Wouldn't spreading the low side FETs from the high side FETs out from each other across the board be non-ideal for current flow?
Shouldn't really matter, you already have huge inductance from the motor and the long phase wires, an extra couple of mm of trace won't make a difference IMO. Your currents are limited by the thickness of the FETs legs here anyway (well and the FETs)
Maybe you're right though I feel like having FETs on opposite sides of the board would make it hard to utilize the enclosure as a heatsink. The enclosure interior width would have to be just right so that one could thermally couple the FET tabs to the walls. Also it would seem like I would have to separate the high current supply and ground traces a fair bit to reach the opposing FETs. This would work against my goal of trying to minimize ground loops and parasitic inductance. However, I may be completely overthinking this or misunderstanding what you're suggesting entirely.
Not at all, all of the things you mention are valid and should definitely be taken into consideration.

Heatsink wise as you are using a metal spacer I think the give you will get just from the FET legs will be enough to account for sizing.

Image

Excuse it being hand drawn (and my handwriting, it's 2019, who writes by hand...) but this is essentially how I was picturing it for a 6 FET design. You will probably also want to run a GND up to the high side FETs for capacitors, VCC to low side, eg
Image
If these are SMD caps you can have them literally touching the leg of the MOSFET on the bottom, then have a larger cap on either side to help hold these secondary rails at their respective voltages. I think the BESC does something similar with caps increasing in size as they get further from the FETs.

Benefits are essentially half the power carrying bus length for power and ground, and obviously the packaging being the major one.

nieles   10 kW

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Re: Cheap VESC (VESC 4.12 redesign)

Post by nieles » Jan 16 2019 7:24am

wil wrote: ↑
Jan 15 2019 8:57pm
shaman wrote: ↑
Jan 13 2019 9:13pm
Wouldn't spreading the low side FETs from the high side FETs out from each other across the board be non-ideal for current flow?
Shouldn't really matter, you already have huge inductance from the motor and the long phase wires, an extra couple of mm of trace won't make a difference IMO. Your currents are limited by the thickness of the FETs legs here anyway (well and the FETs)
it definitely WILL matter. any inductance between the bulk capacity and mosfet will cause voltage spikes and kill mosfets like crazy if you switch fast. and you want to switch as fast as you can to lower your switching losses. i have seen voltage spikes on a bad layout as high as 100v with a 30v supply.

a voltage spike is induced with the following formula: Uspike = Di/Dt *Lstray

have a look at this: https://www.tf.uni-kiel.de/etit/LEA-dow ... hlfeld.pdf
some more info: http://www.irf.com/product-info/igbt/pc ... elines.pdf

this is actually why cheap controllers can get away with awful layout, as they switch super slow.

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