Assembled my VESC and need help with motor detection

Report your hardware problems here. Include as many details as possible with pictures to get the best possible help and feedback.
joaolino
Posts: 10
Joined: 31 Jul 2017, 21:03
Location: Lisboa

Re: Assembled my VESC and need help with motor detection

Postby joaolino » 18 Aug 2017, 20:22

Hi artteth, thanks for your help.

I went trough the schematics, BOM, the forum and the datasheets to better understand what the hell was going on.

on 12s you can kill vesc

It turns out that the VESC's BOM is not really aimed to accommodate 12s. Neither for testing nor use.

so all tests on 6s max

A assume you mean setup.

you need to check all solder check fets and in the end try to resolder drv

Did that twice, on 2 different days. I found a bridge in the USB pins, prior to actually upload the firmware, and fixed it.

What I actually did wrong was to not adjust the firmware for 0.5 mhom shunts. That could have fried the DRV8302. Adjusting the firmware or replacing the shunts with 1 mhom ones resulted in the same behaviour.

( every time i buy vesc i buy 2 pcs vescs and 10 pcs drv chips )

I think I'll go a bit further than that. I'll revise the BOM so it follows datasheet's recommendations for 12s.

My main concerns are now with:
1) the 50V ratings of many caps that should be higher rated: C39,C1,C8,C9,C40,C43,C44,C49,C37,C51,C2,C3,C27,C32...the list goes on.
2) The absence of a TVS on Vsupply

And beyond that I still have a lot of questions, like:
Why is C39 10u 50v and not 4.6uF + 0.1uF 100V?
Why are C28, 29, 30 220nF and not 100nF?

I'm going to have a lot of fun with the VESC. :)

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Assembled my VESC and need help with motor detection

Postby rew » 20 Aug 2017, 09:54

Working from memory here...

It doesn't hurt to have the boost capacitors a bit bigger than the minimum. You need a bigger boost capacitor if your mosfet is large and has a big gate capacitance. According to TI the 7530 mosfets are actually just beyond the limit of what the DRV can drive. So having a bit bigger capacitors is not unreasonable. That said, having bigger capacitors there is not really a problem. Or rather, unless you go overboard, it is never a problem.

So... when the phase wire is low, there is a diode charging the boost cap to about 12V. Then when the gate needs to be driven high, there is some charge-sharing between the gate capacitance and the boost capacitor. The voltage on the boost capacitor drops a little while the gate is turned on. Now, in this case we can calculate the end voltage of the boost capacitor. We start out with THE capacitor formula: i = C dV/dt . We rewrite that to dv = i . dt / C and plug in Q= i dt: dV = Q/C . The datasheet for the IRFP7530 mentions about 230 nC for the total gate charge (I haven't looked it up today). So for a 100nF capacitor we get: dV = 230nC/100nF = 2.3V. Now the capacitor is charged from 12V through a diode, so it should be charged to about 11.3V when we begin, giving us 9.0V at the end.

Worst case, the whole system is running at only 9V, the LDO trying to make 12V might be putting out only 7V, a diode drop and a charge sharing later your gate is at 4V. That's in the perfect range for blowing up mosfets.

Increasing the capacitor to 220uF improves the margins by 1.3V, sounds like a plan. :-)

joaolino
Posts: 10
Joined: 31 Jul 2017, 21:03
Location: Lisboa

Re: Assembled my VESC and need help with motor detection

Postby joaolino » 23 Aug 2017, 20:00

....I knew that!!! (no I did not :P)
Thank you so much for your answer.

OK so, this is what I came up with for my 12s system:
Component___________________Description___________Mouser Part
C1,C8,C9,C39,C40,C43,C44,C49__10uF 50V 10%_________963-UMK316BBJ106KL-T
C37,C51______________________22uF, 100V___________810-CKG57NX7S2A226JJ
C2,C3,C27,C32________________100nF, 100V 10%_______81-GRM188R72A104KA35
C28,C29,C30__________________220nF,25V____________963-TMK107B7224KA-T
C4-C7________________________4.7nF, 100V__________810-CGA3EAC0G2A472JC
C34, C36______________________2.2nF, 100V 5%_______810-CGA3E2C0G2A222JA
C15,C38______________________15pF, 100V___________81-GRM1885C2A150JA01
C19__________________________120pF, 100V__________81-GCM1885C2A121FA6D
C21__________________________6.8nF, 100V 5%_______810-CGA3E1C0G2A682J8
C22__________________________22nF, 100V 10%_______810-CGA3E2X7R2A223K
C24,C10,C11,C12,C13,C14,C16,C17,C18,C20,C23,C26,C31,C35,C41,C52,C401_________2.2uF, 25V 10%_________81-GRM188Z71E225KE3D


For C1, etc... there is no option for 100v in that component size, so I just got a better rated one.
And the cap board will be replaced with something that can handle 6 of these: 667-EEU-FR1J681L (mouser part no.)

If any one would care to comment on these changes that would be much appreciated.

Beyond from this, I'm thinking of adding one of these TVS to the battery input: 30KPA43A or 576-30KPA45A (mouser part no.)
The 576-30KPA45A has Vbr min at 50,3V. A 12s bat. goes up to 50,4V. While riding it will go down but charged and on I'm looking at 0,252W of power consumption. But the clamping voltage is 77,4V!! 60V would be lovely. I plotted the current from max. breakdown voltage to clamping voltage (linearly, which is wrong?) and got ~82,85A for 60V.

2 Questions:
Is this right?
If yes, guys with oscilloscopes, is it enough for the VESC 4.12 breaking on 12s?

This is the limit of my guesswork. Please help!

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Assembled my VESC and need help with motor detection

Postby rew » 24 Aug 2017, 07:35

Yes, your "linear' assumption is very wrong.

The "min" means that under worst-case conditions the device may start consuming (significant) current at that voltage. If you use the device, say 1 in 1000 controllers that you sell will drain the battery down to 50.3V through the TVS when fully charged. That sounds acceptable to me.

But the curve is far from linear. At some point there is a quick rise in the current. Below that it is almost zero, above that it quicly goes up. That max clamping voltage occurs again under worst-case conditions: 391A with "bad luck" in the draw of the production at the worst possible temperature etc etc. But the max breakdown voltage is 55.3V. So at that point it starts consuming significant (> 5mA!) current. The current quickly rises, but MIGHT not reach 391A before the voltage becomes 77V. I would say that this is likely to help.

You can often mount a smaller capacitor on larger pads if you can find one that satisfies the requirements. Or you can take a larger capacitor. Or as you decided: one rated for a higher voltage. Whatever you like.

My vesc works just fine on 12S. But it doesn't use an DRV. And I use a >60V diode. Make sure the diodes are rated for > 60V.

joaolino
Posts: 10
Joined: 31 Jul 2017, 21:03
Location: Lisboa

Re: Assembled my VESC and need help with motor detection

Postby joaolino » 26 Aug 2017, 09:04

Thanks rew.

My vesc works just fine on 12S. But it doesn't use an DRV. And I use a >60V diode. Make sure the diodes are rated for > 60V.


Back to Google search! :P


Return to “Hardware Problems”

Who is online

Users browsing this forum: No registered users and 1 guest