New BMS for bq76PL455A based batteries

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Pete9008
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Re: New BMS for bq76PL455A based batteries

Post by Pete9008 »

catphish wrote: Thu Jul 07, 2022 9:56 am
catphish wrote: Thu Jul 07, 2022 9:40 am Edit: Might design a board with just the transformer. This would be small enough to heatshrink inline with the cable for testing.
Turns out SOIC16 breakout boards can be bought off the shelf, so will just use one of those and solder the wires, at least for testing.
That's a fix not a bodge! A bodge would be wires soldered to the pins (possibly with hot melt glue or epoxy to reinforce it).

Don't get me wrong here, it's great to see things being done properly!
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Good news! I was able to briefly test the transformer in the car today. It was running from laptop USB but with a good connection to chassis GND so hopefully a valid test.

I was able to charge at 10A without issue!

I'm slightly disappointed now that I didn't try this sooner. I will build some cables with inline transformers for a permanent installation.
Pete9008
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Re: New BMS for bq76PL455A based batteries

Post by Pete9008 »

Great news :D

Curious what the waveforms look like now. The low DC impedance of the transformer will mean that the idle state is very different so your likely to see lower signal levels. Not that that's a problem if the signal to noise is sooo much better.

Hindsight's a wonderful thing isn't it!
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Pete9008 wrote: Sat Jul 09, 2022 11:02 am The low DC impedance of the transformer will mean that the idle state is very different so your likely to see lower signal levels.
Not the case, because I still have the AC coupling capacitors. You have just pointed out exactly why I *shouldn't* remove them though!

I should be able to make up the cables with inline transformers today, and will try to capture waveforms for comparison.
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Transformer and breakout board.
PXL_20220709_112619843.jpg
Pete9008
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Re: New BMS for bq76PL455A based batteries

Post by Pete9008 »

catphish wrote: Sat Jul 09, 2022 11:17 am Not the case, because I still have the AC coupling capacitors. You have just pointed out exactly why I *shouldn't* remove them though!
Good point!
catphish wrote: Sat Jul 09, 2022 11:27 am Transformer and breakout board.
PXL_20220709_112619843.jpg
Looks ideal. Are you going to add something to support the cables (the interface between the soldered and stranded part of the cable is very susceptible to vibration)?
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Waveforms as promised. Here's a capture of a multi-byte transmission followed by a single byte reception as seen at the differential receiver. The second capture is a close up of a received byte. The transforrmer is definitely making the pull resistors a lot more impactful, almost to the point where at the end of the byte the differential voltage is pretty small.
PXL_20220709_121428752.jpg
PXL_20220709_121646050.jpg
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Pete9008 wrote: Sat Jul 09, 2022 12:22 pm Looks ideal. Are you going to add something to support the cables (the interface between the soldered and stranded part of the cable is very susceptible to vibration)?
Hot glue and heatshrink :)
Pete9008
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Re: New BMS for bq76PL455A based batteries

Post by Pete9008 »

catphish wrote: Sat Jul 09, 2022 12:24 pm Waveforms as promised. Here's a capture of a multi-byte transmission followed by a single byte reception as seen at the differential receiver. The second capture is a close up of a received byte. The transforrmer is definitely making the pull resistors a lot more impactful, almost to the point where at the end of the byte the differential voltage is pretty small.
PXL_20220709_121428752.jpg
PXL_20220709_121646050.jpg
Curious what it's like at the far end, with the smaller capacitors it could be worse.
catphish wrote: Sat Jul 09, 2022 12:25 pm Hot glue and heatshrink :)
That should work. If you don't already use it I'd recommend the adhesive lined stuff for use on cars. Keeps the moisture out and also does a better job of strain relief. The 4:1 shrink ratio stuff also makes life a lot easier.
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Pete9008 wrote: Sat Jul 09, 2022 12:35 pm Curious what it's like at the far end, with the smaller capacitors it could be worse.
It actually seems that a lot of this was my scope. Switched to 10x scope probe and the waveform looks somewhat different (notice 2V rather than 1V scale), and with twice as much differential voltage. 2V isn't nearly the desirable 10V but good enough for communication to work reliably it seems.
PXL_20220709_124009272.jpg
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Pete9008 wrote: Sat Jul 09, 2022 12:35 pm That should work. If you don't already use it I'd recommend the adhesive lined stuff for use on cars. Keeps the moisture out and also does a better job of strain relief. The 4:1 shrink ratio stuff also makes life a lot easier.
Yep I've been using this stuff, really makes a difference. The differential signal on the other (battery) side of the transformer looks excellent.
PXL_20220709_124637495.jpg
Pete9008
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Re: New BMS for bq76PL455A based batteries

Post by Pete9008 »

Well spotted. Much better!

Can't see a good reason why it would be better on the battery side though??

I try to never use 1x on a scope probe. Generally the only time I ever switch mine to 1x is if I'm using them backwards to feed a signal in from a sig gen (not recommended practise but often convenient!). Too much capacitance, you get the scope input capacitance, plus the lead capacitance, plus the probe capacitance, it can be as much as 100pF on a cheap probe - it can do a lot of damage on a high frequency high impedance signal!

Edit - just worked it out ~800R impedance on a 2MHz signal!
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Pete9008 wrote: Sat Jul 09, 2022 1:00 pm Well spotted. Much better!

Can't see a good reason why it would be better on the battery side though??

I try to never use 1x on a scope probe. Generally the only time I ever switch mine to 1x is if I'm using them backwards to feed a signal in from a sig gen (not recommended practise but often convenient!). Too much capacitance, you get the scope input capacitance, plus the lead capacitance, plus the probe capacitance, it can be as much as 100pF on a cheap probe - it can do a lot of damage on a high frequency high impedance signal!

Edit - just worked it out ~800R impedance on a 2MHz signal!
My probes are certainly cheap, and when I was testing previously, lots of configurations didn't work at all when probes were connected.

Just made up the inline boards. They seem pretty secure. I'll coat the back in hot glue then heatstrink. Hopefully the cables still reach!
PXL_20220709_134501366.jpg
Pete9008
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Re: New BMS for bq76PL455A based batteries

Post by Pete9008 »

Looks good, the loop of cable should help improve the robustness a lot.

TBH even good quality 10x probes aren't great and all of them will load the circuit to some degree. For any precision stuff at high frequencies you really need FET input probes, trouble is they are expensive, have limited voltage range, are easy to kill and either need a compatible scope to power them or a separate power supply. Very good performance though!
Pete9008
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Re: New BMS for bq76PL455A based batteries

Post by Pete9008 »

Just thought of a potential issue. While the Ethernet transformer is isolating it doesn't have a specified working voltage (a hipot test is specified but not quite the same thing). Ethernet networks are usually all at the same potential (mains earth) so it's not an issue, the isolation is there to break earth loops not to allow the equipment to float at HV!

In this application it's not providing safety isolation (the dual redundant caps are doing that so definitely keep them!) but it is likely to have a significant voltage drop across it for extended periods or time. It will probably last like this quite happily long term but then again it might not :(

If you do end up re-spinning a board it might still be worth thinking about putting an isolated interface on it.
Volkmar
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Re: New BMS for bq76PL455A based batteries

Post by Volkmar »

Hi,

I am completly new in this forum and I am afraid, I am a coding fool :-(

I have purchased for my homemade electric vehicle a complete Volvo XC90 hybrid battery and I have a SimpBMS for Tesla modules at home. Do you think there is a possibility to use the Simp BMS with the Volvo Batteries?

Just to clarify: I am really a complete novice in the area of programming and electronics. I'm good at steel construction and can also design a chassis, but I just can't get my head around the electronics. So please excuse my question!

It would be wonderful if you could help me!

Thank you in advance and best regards from Austria

Volkmar
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Volkmar wrote: Mon Sep 12, 2022 11:52 am I have purchased for my homemade electric vehicle a complete Volvo XC90 hybrid battery and I have a SimpBMS for Tesla modules at home. Do you think there is a possibility to use the Simp BMS with the Volvo Batteries?
Sorry I didn't reply sooner. Can you confirm exactly what batteries you have? Do you have a photo?
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catphish
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Re: New BMS for bq76PL455A based batteries

Post by catphish »

Pete9008 wrote: Sat Jul 09, 2022 3:49 pm If you do end up re-spinning a board it might still be worth thinking about putting an isolated interface on it.
I built a new batch of these boards for Silent Classics this week. I updated the board to have 2 x battery interfaces and an Ethernet transformer integrated. I haven't tested this yet, but the performance should be the same as my external transformer setup.
Screenshot at 2022-09-21 22-51-13.png
PXL_20220920_155222472.jpg
Volkmar
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Re: New BMS for bq76PL455A based batteries

Post by Volkmar »

catphish wrote: Wed Sep 21, 2022 9:48 pm Sorry I didn't reply sooner. Can you confirm exactly what batteries you have? Do you have a photo?
Now I have to say sorry for my late reply! :?

I have bought the complete battery pack of a Volvo XC 90 Plugin Hybrid from 2017.

I will send you detailed picture tomorrow, when I am back in my Workshop.

Have a nice weekend
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catphish
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Re: New BMS for bq76PL455A based batteries

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Volkmar wrote: Sat Sep 24, 2022 5:22 am I have bought the complete battery pack of a Volvo XC 90 Plugin Hybrid from 2017.
I've been wanting to know for a long time where these batteries come from, so thanks for confirming what car yours are from. It's good that you got the whole battery pack, because assuming it's the same pack as mine, it should come with a really high quality set of fuses and contactors. Are you running the full 3 x strings of 6 modules?

It certainly makes sense for you to use my BMS if you're using these batteries, however this isn't really an "off the shelf" product, so there are a couple of things you will need to consider.

Firstly, I do not have any boards with integrated transformers. If you read through the recent posts on this thread, you will see that the BMS requires a transformer between the BMS and the first module in each parallel string, so if you'd like to use it, you have 2 options:
A) Use an older board I have in stock, but you will need to build transformer adapter boards as shown above. This is how my car works.
B) Order a new batch of BMS boards with integrated transformers. I can provide all the design files, but it'll probably cost around £250.

Secondly, you will need to consider how you will do charging. In my car, I have a second board that interfaces with the BMS, with the charge socket, and with an Elcon compatible charger (this includes Ovartech and Dilong chargers). If you're doing the same, you can use one of my boards, but if not, you will need to think about integrating the BMS into whatever charging setup you have using its CAN protocol.
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