2 VESC`s and two antispark switches

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Rallye82
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Joined: 28 Jun 2016, 09:48
Location: ÅLESUND, Norway
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2 VESC`s and two antispark switches

Postby Rallye82 » 07 Dec 2016, 13:08

Hi

Just want to share my experience with the setup in the topic.
i`ve got a dual motor eBike with two VESC`S (and a couple og electric longboards and my kids electric peg perego, all with two VESC`s)
The challange started when i wanted to install two antispark switches on my bike.
i am running the VESC`s on my bike pretty hard, with 50A from the battery, and 95A through the motor.

The experiment started when i wanted to swich the front VESC on/off independently from the rear.
The VESC for the rear motor has all the signals connected to it, and it is shared eith the other one trough CAN. (connected only CAN h and CAN l)

This setup will frie the CAN-controllers instansly, causing the 3.3V to be shorted to ground, and after a while making the 3.3v regulator very hot.

I have tried many different setups, but all with antispark switches and no mather what i do, it will kill the CAN-controller.

After som thinking, i have gone away from the dual antispark setup, and now i use a XT90 antispark connector,powering both VESC`s, and it works fine.(i realy do not have any needs for driving the bike with only one motor, the VESC will get very hot quick, and start to reduce the current to protect it self)

Do anybody else have similar problems? and/or found a solution?

Best regards
Øystein
Regards
Øystein N

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
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Re: 2 VESC`s and two antispark switches

Postby rew » 08 Dec 2016, 09:13

As far as I know, the electronic antispark uses an N-fet. So when you switch off ONE VESC, the WHOLE unit will be connected to the battery voltage. NO voltage differences inside the unit -> No currents -> things are OFF.

However, if you connect two VESCs and click one OFF, then the other one will be fed the battery voltage through the connecting datalines. 5V tolerant, ok, but not 50V tolerant.
Last edited by rew on 09 Dec 2016, 09:07, edited 1 time in total.

Rallye82
Posts: 21
Joined: 28 Jun 2016, 09:48
Location: ÅLESUND, Norway
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Re: 2 VESC`s and two antispark switches

Postby Rallye82 » 08 Dec 2016, 10:46

Hi

That sounds like a resonable explaination.
The way to go is to disconnect the positive lead from the battery... that means using i p-channel mosfet, and a total redesign of the antispark switch.?

For now i think i will stick with the tx90 connector
Regards
Øystein N

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
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Re: 2 VESC`s and two antispark switches

Postby rew » 09 Dec 2016, 09:13

Yeah, but the battery current max is around 50A, and we've selected a 300A Max FET.... And paralleled two of those.

Those are state-of-the-art N-fets. The best you can get for reasonable money. If you try to find that as a P-fet, I think you're out of luck.

What you could do is "generate 12V", generate VMOT + 12V from there, and use that to drive an N-fet as a normal antispark has now. This complicates stuff A LOT.

Rallye82
Posts: 21
Joined: 28 Jun 2016, 09:48
Location: ÅLESUND, Norway
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Re: 2 VESC`s and two antispark switches

Postby Rallye82 » 12 Dec 2016, 13:01

Hi again

Are there any test, or proven applications where the antispark switch has been used in a high current circuit?
100-150A normal current draw? and some short time peaks even higher?

do you think 2 VESC`s on one antispark swich is no problem?

The Mosfet`s can handle 300A with enough cooling.
but i thing if you try to pull 600A trough this little board, it will burn in a short time.
but i might be wrong:)
Regards
Øystein N

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
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Re: 2 VESC`s and two antispark switches

Postby rew » 12 Dec 2016, 22:19

The 300A rating is the engineers being pushed by the marketing guys to provide an even higher number than the competition. It is achieved under ideal conditions. For some FETs the footnote says: "at Tc = 25 degrees". This means you need to have a 1.2 K/W cooling element with the cooling air at -83 C, or something like that....

Without cooling fans or even heatsinks, the DPAK7 package can dissipate about 2W, you're at 3W per FET at 50Amps. This goes up quadratically with amps. So 75A per fet means 7W per FET, or 15W for the two fets. You'll need a reasonable heatsink for that.....

(I'm using 1.2mOhm as the "typical" value, from memory. You should formally use the "worst case" number, 1.4 mOhm....)

Rallye82
Posts: 21
Joined: 28 Jun 2016, 09:48
Location: ÅLESUND, Norway
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Re: 2 VESC`s and two antispark switches

Postby Rallye82 » 14 Dec 2016, 14:34

Hi again

Yes this is the reason i used two (Anti-spark switches) for my application.
just to be sure there is no problem.

and maybe 100A i periodes is ok, i realy do`nt know.
i usually reach max spped in 4-5 seconds, and then my current draw reduces alot, just maintaining the speed.

the real problem occur at long steep hills.
Regards
Øystein N

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
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Re: 2 VESC`s and two antispark switches

Postby rew » 15 Dec 2016, 23:22

My current setup gets close to max-power near max-speed. This is of course partly due to my battery being a bit low-quality and therefore I have to reduce the max-power....


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