Bafang BBSxx - fault finding and fixes

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Justas   1 mW

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Re: Bafang BBSxx - fault finding and fixes

Post by Justas » Oct 08 2018 1:34pm

Done some measuring and got some weird results. High side driving seems okay, but all three low side gate signals looks weird. Will try to replace the driver.

Can somebody explain how this 9 fet configuration works? Seems like low side switch have 2 fets in parallel.

P. S signals measured relative to battery negative.
Attachments
20181008_184501-1024x768.jpg
High side gate signal
20181008_183007-1024x768.jpg
Low side gate signal

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fechter   100 GW

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Re: Bafang BBSxx - fault finding and fixes

Post by fechter » Oct 08 2018 2:12pm

The low side drive does not look healthy.
Justas wrote:
Oct 08 2018 1:34pm
Can somebody explain how this 9 fet configuration works? Seems like low side switch have 2 fets in parallel.
Yes, two in parallel on the low side but only one on the high side. In designs that are not using synchronous rectification, the low side FETs have to throw off more heat when they are acting like freewheel diodes.

The BBSHD controller apparently uses synchronous rectification. I have never tested the BBS02, but your waveform indicates synchronous rectification. Otherwise, the low side would only be switching for commutation and not at the PWM frequency.

So go figure why they used 9. Better than 6 but didn't have room for 12?
"One test is worth a thousand opinions"

banzai   100 µW

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Re: Bafang BBSxx - fault finding and fixes

Post by banzai » Oct 09 2018 4:46pm

Searched full thread but could not find a good pic of the back side of a bbs02b controller. I have a 36V500W with some burned parts, resistor suppose, if someone can check with a miltimeter to give me the data of the burned two and maybe the two nearby...
The place where resistor are attached to board are partially damaged, so if someone can also draw a line on how to connect them to the next contact, it would be perfect.

Strangely enough this controller, coming from a 36v500w bbs02b motor, had a 48V500W label under the rubber. But this is another story...
https://drive.google.com/file/d/1XWa2Pu ... p=drivesdk

Justas   1 mW

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Re: Bafang BBSxx - fault finding and fixes

Post by Justas » Oct 09 2018 11:52pm

banzai wrote:
Oct 09 2018 4:46pm
Searched full thread but could not find a good pic of the back side of a bbs02b controller. I have a 36V500W with some burned parts, resistor suppose, if someone can check with a miltimeter to give me the data of the burned two and maybe the two nearby...
The place where resistor are attached to board are partially damaged, so if someone can also draw a line on how to connect them to the next contact, it would be perfect.

Strangely enough this controller, coming from a 36v500w bbs02b motor, had a 48V500W label under the rubber. But this is another story...
https://drive.google.com/file/d/1XWa2Pu ... p=drivesdk
These are ferrite beads for suppressing noise in signal lines. You could try to short them if don't have any at hand. This is my controller photo:
https://photos.app.goo.gl/5hpm49AGH5Tb2sRH6

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fechter   100 GW

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Re: Bafang BBSxx - fault finding and fixes

Post by fechter » Oct 10 2018 10:16am

The way those are burnt is not a good sign. Something likely shorted to blow those out. If you are lucky, it didn't take out more parts.

I have a BBS02 board around somewhere but at another location. I'll see if I can find it and trace out what those go to.
"One test is worth a thousand opinions"

banzai   100 µW

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Re: Bafang BBSxx - fault finding and fixes

Post by banzai » Oct 11 2018 3:34am

Thanks Justas and fechter, now board at home and I'm out, yes agree with you, I found the main cable just near connector compressed, need to verify if some of the cables are shorted. I tested the Fets from the three cables (YGB) and they seem disconnected, but if I test to the fet legs, and have similar results so they should be OK.

KD5ZXG   1 W

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Re: Bafang BBSxx - fault finding and fixes

Post by KD5ZXG » Oct 11 2018 5:18pm

The way I test N-CH FETs:
0) Disconnect any other source of power.
1) Disconnect any load that mimics a short (motor windings)
2) Using two volt/ohmeters to measure each other. Set one Ohms the other Volts.
3) Each need to output more than 4V on ohms test to have any chance of working.
4) Abuse one ohmmeter across +drain to -source to power and measure the channel.
5) Abuse another ohmmeter to bias +gate to -source.
6) Observe the channel begins to conduct, or at least it should.
7) Reverse bias -gate to +source, but leave +drain to -source ohmmeter as-is.
8) Observe the channel begins to insulate, or at least it should.

Forward biased gate to source probably shouldn't conduct, but depends on circuit.
If less than 500 ohms and not driven by a pulse transformer, I'd be suspicious...
An ohmmeter won't be able to bias that sort of circuit.

banzai   100 µW

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Re: Bafang BBSxx - fault finding and fixes

Post by banzai » Oct 19 2018 3:29pm

Traced the spot, goes to Brown cable, P+ from display cable. Anyone can give a clue on ferrite beads values? Managed to found four of them near mouse/keyboard ps2 connectors from an old mainboard, could be ok? Stupid question maybe...

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fechter   100 GW

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Re: Bafang BBSxx - fault finding and fixes

Post by fechter » Oct 21 2018 2:05pm

I don't think it's critical. Pretty much anything that fits should work.
The brown wire feeds full pack voltage to the display, so if the wires shorted, there would be enough to blow it.
"One test is worth a thousand opinions"

Fastwanabe   10 mW

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Re: Bafang BBSxx - fault finding and fixes

Post by Fastwanabe » Nov 01 2018 12:48am

Im making a poor man BBSHD, I plan on bolting a bbshd core to my BBS02B case and see if that woks. Im just wondering if the rotor shaft of the BBSHD is longer or shorter than the BBS02B, I know the rotor itself is longer but dont know if the coiled shaft is. I know the bearings are the same. Cant do this for another month so we'll see.

tomjasz   1.21 GW

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Re: Bafang BBSxx - fault finding and fixes

Post by tomjasz » Nov 01 2018 12:32pm

Nope. Two very different builds.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

Fastwanabe   10 mW

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Re: Bafang BBSxx - fault finding and fixes

Post by Fastwanabe » Nov 13 2018 4:14pm

tomjasz wrote:
Nov 01 2018 12:32pm
Nope. Two very different builds.
yes it is possible I did it.
Attachments
IMG_17112018_183959_(1080_x_1080_pixel).jpg
IMG_17112018_183943_(1080_x_1080_pixel).jpg

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