Old BMS Hardware Thread

[GregsGarage]

Thanks for the pic and congratulations on it all working. I will be doing some bench testing next week.

[dillond666]

I am still trying to iron out my interference problem. I thought the slaves were playing up but now I'm not so sure. The master bus is much improved by the addition of a low pass filter, but still I get interference if I give the throttle a good stab. It always seems to be battery 13 that throws up the error but that is a symptom of the master code as the error bit is set in the for next loop.
I tried the ferrites on the slave leads instead of the master bus and all seemed good...........but then I put on the charger and it all went haywire again. As the BMS had previously been happy charging I can only assume that the low pass filter is not playing nicely with the charger. FYI the charger looks much noisier on the scope than the zilla, yet the charger worked with no problems and the zilla needed filtering.....weird eh?
Here is some pics of how my installation is at the moment as mentioned before I have made numerous errors of design so this set up will get fixed but will be replaced with a MK2 version of my own in the future.
http://www.dillond1.pwp.blueyonder.co.uk/front.jpg
http://www.dillond1.pwp.blueyonder.co.uk/rear.jpg
http://www.dillond1.pwp.blueyonder.co.uk/master.jpg
I have a suspicion that the main cause of my problems is the distribution of my batteries in the car necessitating long cables on the BMS.
I have ordered one of these chips with the hope of sorting things out as I read that the bessel filter is better for square waves than most of the other filter types.
http://uk.farnell.com/jsp/search/produc ... 7423EUA%2B
It's a 3v part though, but it'll do.
I also ordered one of these to play with.......
http://uk.farnell.com/avago-technologie ... /dp/327750
So MK2 will be multi slave board x2 and new master linked with nice fibre optics

Derek

[retepsnikrep]

Try some of the varistors I used and add some zeners to stop voltages going over 5v etc.

[GregsGarage]

I am still trying to iron out my interference problem. <snip>

<snip>I have a suspicion that the main cause of my problems is the distribution of my batteries in the car necessitating long cables on the BMS.

Derek

Also try and keep your main traction battery cables close together. For example if you have 2 cables going to a rear battery box route them next to each other rather than having one going along the left sill and one going along the right sill. You can even twist them together like CAT5 cable, twisted pairs aren't just for small wires.

Also if you are using shielded wire for the master and slave bus only connect one end of the shield to earth.

EDIT: One last thought, add fuses at each battery connection, they should be rated or tested to open at pack voltage not battery/cell voltage. Any sort of short circuit on those wires or slave board and they could start a fire.

[dillond666]

Thanks for the excellent suggestions gentlemen. Seems to be working now. Simple 5.1 zener from picaxe input pin to ground. and no RC filter!
Just for the science of it, i'll scope it tomorrow and report my findings.
The noise coming from the controller didn't seem to be as high in amplitude as the serial comms but was much higher in frequency so I didn't think a zener would have helped.
I'll have a play with the filter chip when I get it anyway.

BTW any of you think digikey seem really expensive? and they charge £12 postage for orders< £50. Farnell won this time! (free post £20 min order). I still like Rapid electronics though.

Derek

[retepsnikrep]

I've never used digikey.

I in UK I use, farnell, RS & Rapid and e-bay.

Well done on sorting the interference issue. I have to say on the two multislave installations I have done now i havent had any interference issues whatsoever. It's so reliable I even removed the "Alarm count" code (which allowed a certain number of errors before triggering an alarm) from the software and I'm thinking of going back to my original single cell slave setup car and converting that to a multislave boards as i have some made up spare 16 cell ones available.

[dillond666]

I don't believe it!
Just tried it again and it's flakey using the charger and needs the RC filter to run the controller.
The scope shows the same interference it did before. Did I just dream it was fixed? Will definitely need to try the filter chip.

The controller interference looks like regular spikes at controller switching freq (I presume). Amplitude of the highest spike is about 0.5V higher than serial squarewave even when clamped with the zener.
When I switch on the charger the phase of the squarewave shifts and there is a noisy fattening of the peaks and troughs of the squarewave. This stuff is beyond my level of experience so It's going to have to be a lot of best guesses and trial and error unfortunately.

Derek

[retepsnikrep]

OK

Is the interference on the slave or master bus? You could add another layer of opto isolation right next to the master using a small dc-dc converter to power the slave side of the master bus.

Do you have any temp sensors on the master routed to the pack. These lines will need checking as well. I had to use varistors etc on my analog temp sensor lines.

Are you using screened cables?

What filtering do you have on the power supply for the master?
I have used a small 12V DC-DC converter to fully isolate the master supply from the car in the past.

In fact on master v3 I will probably do away with the standard linear voltage regulator and specifiy a small dc-dc to get rid of any supply interference, plus they are much more effcient.

Make sure master is located away from any RFI sources try putting it in a tin box.

[dillond666]

Put in a 690 ohm pulldown on the master instead of the 4k7. Put 14v varistor between gnd and data and +ve and data. Also put varistor on the charger relay lead.
I can still see interference on the scope but the master isn't playing up now.
I'm using cat 5 twisted pair but I'll need to check when I get home that I am actually using the correct pairs......just in case
Slave bus looks fine on the scope.
Current sensors are also clean.
I,m going to remove the zilla speed control thingy from the master and make up a separate board for that duty. I've not run the (long) cabling for it and I think it might be inviting trouble to include it in the master.
I like the idea of a 12v-12v converter as I am running from a separate battery just now, but when I join the BMS gnd to the Zilla/chassis gnd I get extra interference.
I'm still unsure about the various grounds, I mean they all ultimately go to the chassis ground in the end unless you run a 12v-12v converter. But then, what ground do shielded wires and enclosures connect to? Very confusing

Derek

[GregsGarage]

I'm still unsure about the various grounds, I mean they all ultimately go to the chassis ground...

Except for your traction pack, that should be isolated from the chassis for safety reasons.

Sounds like your making progress, thanks for the update.