Old BMS Hardware Thread

[hohisilver]

Just a quick update on my progress:

Finally attached the slave board to my 25S pack yesterday. First relief - no pyrotechnics! So time to attach the master and see what I get. Powered up the master, get half a screen and - reset But after the reset, screen comes up and reports pack voltage of 84.63V

Can't understand where the reset came from, but it seems to do it every time when attached to the pack but not in my workshop attached to AAA cells. More debugging needed methinks

Also finished making up the current sensor board yesterday, so a test is imminent Greg!

[retepsnikrep]

Does it give a hard reset or an error screen then back to start?

Add a pause at start of master program say 2-3 seconds and report back.

[hohisilver]

This is running my C rewritten master code Peter - I'm not using the watchdog chip but have the internal watchdog enabled so I think something is causing too long a delay from a hard reset, but a soft reset seems to work ok for some reason. The comms to the video chip are interrupt-driven but I don't have a very large buffer - it has to wait if the buffer is full so that's my prime suspect at the moment. I've enlarged the buffer to see if that helps.

I hope it's not a noise problem already - the only noise was from my stereo in the garage!

I'm going to get everything installed in the scooter before I do any more testing, So I'll report progress then

EDIT: I don't have the master reset jumper in place so it won't be a reset from the watchdog, but I was wondering if I should have some sort of pull-up/down on that line to the PIC?

[GregsGarage]

The external watchdog chip will allow over a minute without a pulse from the master before it will reset. This means you don't get resets while in menus (unless you stay on a menu screen for over a minute), or when first starting up. Maybe try disabling your internal watchdog and see if that helps.

I have finally got my noise issues sorted.

Final solution was to move the front slave inside the car, seems the engine bay was too noisy for reliable slave and master comms. Might have been able to get away with 2 of Peters isolated bus tricks, but in the end I am just running the master with an isolated bus, 3 AA batteries a 220R resistor and 1 opto. The noise spikes that I was getting in the previous post turned out to be a problem after all. Tip for prototyping/testing, I got a small breadboard from Rapid and stuck it next to the master. They come with an adhesive back and it makes it easy to try different things.

[GregsGarage]

EDIT: I don't have the master reset jumper in place so it won't be a reset from the watchdog, but I was wondering if I should have some sort of pull-up/down on that line to the PIC?

I am not sure about this, best to check the data sheet for the pic. It will specify if the pin can be left floating or not.

[hohisilver]

Ok, from the datasheet it appears when that pin is configured as ~MCLR it has an internal pullup, so that's that question answered

[retepsnikrep]

I think it's only a weakpull up though you might be better with a 10k tied to +

[GregsGarage]

Drove my Matiz home today. Car feels good, got it up to just over 60mph,, but mostly did 50-55mph on my trip home. Used 16ah for 11 miles, this would suggest a range of 82 miles and around 220wh/mile. I am hoping to improve on that with some Michelin LRR tyres, tracking and streamlining the underside. I will try and get an MOT on it this week (trade plates if you are wondering) and then get it taxed. The 16ah consumed would suggest that my Zivan NG3 would take a bit over an hour to charge, which it did, so that gives me around 10 miles per hour of charging, a useful figure to know if you are planning a journey and need to opportunity charge.

Still lots to do, first thing is to get a charger cutoff relay. Can't decide on the best way to go. I could get a solid state relay off of ebay, but I also have three 48V supplies that I intend to wall mount. These are 3 phase and will charge the pack at 20 amps, so I could simply open the contactor I fitted mid pack which would stop either chargers (or both for really quick charging ). Any thoughts on this?

[retepsnikrep]

You need to control the mains inputs to the chargers IMO not break the output circuit under load as that may damage them anyway and would be wasteful. I used some cheap20A 240v solid state relays from e-bay, one works fine for my Zivan, needs to be bolted to some metal (not much) though as does get warm when 3kw is passing.

Nice to hear car is on the road sort of

Get the tyres pumped upto max sidewall pressure + 5-10psi

I run the Insight tyres at 55psi

[GregsGarage]

Got the Matiz MOTed today. All together I put 52 miles on the car between going to get it MOT, and other essential road testing. That wasn't all on one charge, I kept topping up between journeys as I am trying to gently run in the batteries. A report from a converter in Australia was noticing some cell failures on new packs and found that by doing some initial shallow discharges the problem was solved. Next step is a trip to Edinburgh to get it taxed.

I've ordered a SS relay off of ebay, I splurged and got one with built in heatsink.

Experimenting with the load cut in voltage this evening while charging. I set it to 3.40 volts and let it stay there until all the cells where at least 3.40 and then bumped it up to 3.45. The plan was to keep doing this, gradually working the voltage up and gently nudging the cells into line. I actually stopped charging not long after a couple of cells reached 3.50 volts, as I have to switch off the charger manually at the moment until my relay arrives. Really most of the cells are quite well balanced, cell 6 always leads with it's voltage being some 10s of mv above average and cell 26 bringing up the rear, being some 10s of mv behind. When I disconnected the charger cell 6 was 3.50 volts, a small number of cells had gone above 3.5 and turned on the loads and cell 26 was at 3.40 volts. I am quite pleased with this. The cells where sitting around for over a year before I did anything other than occasionally check voltages. Self discharge rate is obviously extremely low.

My current tyres are at 40psi., they are old, cheap and of various brands so I won't push my luck by over-inflating them that much. I have ordered some Michelin energy 145/80R13 to go on the car. They are on back-order at the moment, so not sure when they will come.