DIY EV Part 42 - More BMS Wiring

[@FrankGraffagnino]

glad to see you are making progress!!! I took some flack online for soldering our BMS wires... apparently using crimp connectors holds up better to vibration... so, something to consider for the future. We are still going to use our soldered connections for our BMS wires as I'm not going to redo them all, so we'll see if it becomes a problem for us. But in the future I'll try to use crimp connectors if it is wires that will have vibration on them.

[@alibro7512]

Thanks mate. If done properly Soldered connections are fine, especially on thin bms wires where crimped connections would be too bulky. Some people love to tell you that your doing it all wrong but don't actually do anything themselves. The other thing is it is easy to badly crimp a connection and not realise it, especially when doing 192 of them. It's easier to ensure all the solder connections are good.

[@andybp840c]

Sometimes it's just easier to start again I'm also currently sorting out my bms wiring and if it's any consolation I'm hating every second of it 😁

[@alibro7512]

Sorry nope! That just makes me happy I'm not the only one. 😋

[@Popeyes66]

I admire that you have not given up this major headache of a project Ali. I can only wonder about the red tape you will face when attempting to legally register your glorious creation with Government pen pushers that work from home . I wish you well.

[@alibro7512]

Thank you. I'm confident that because I've not changed anything except the engine and fuel type it should be relatively straight forward. In the UK there is a points system for modified cars and as I have original steering, transmission and haven't modified (drilled or welded) the chassis (the entire monocoque body) I should be OK.

[@Popeyes66]

Can't wait for you to be using it as your daily driver and proving any naysayers wrong. I have watched your previous ebike projects in the past and enjoyed watching your highs and lows during the process. I myself have bodged together an ebike using a washing machine motor converted to DC and modifying the rear wheel with another free wheel and sprocket. It worked fine but was temperamental at times. I am currently using a Razor E300 scooter which i gutted and swapped out the OEM 24V motor and squeezed in a 36v motor & controller with slight frame welding adjustment. It runs great but i am always weary of the boys in blue who are not that overjoyed with my projects. All the best Ali,and God speed with youe EV

[@alibro7512]

@@Popeyes66 Thanks mate

[@ianlighting100]

Did you need to consider the wire thickness between the separated front and back battery packs? Or did you keep it all the same? Sorry if I’ve missed this answer, but is the split of modules between front/back where that extra negative was in the original Leaf BMS wiring (48 from memory from your earlier video?) Thanks. I’m binge watching but possible reaching saturation point!

[@alibro7512]

If I were using the bms correctly the thickness would matter but it turns out I can only turn the bms on when off load. In other words when not driving. This is because of the resistance between cells 40 and 41. When driving cell 40 shows wildly out of balance because of the voltage drop between the packs. When unloaded it is fine.

[@ianlighting100]

@@alibro7512 thanks for the answer. I have to admit I don’t fully get what you’re saying ( sure that’s my lack of understand rather than your explanation) so maybe I have a bit more binge watching to do before I get up to speed with the end of your journey.

[@ianlighting100]

I should explain, I’m at the first step of a conversion (Resolve-EV VCU with full leaf motor), so still in absorbing mode in terms of what questions to ask, and then what the answers mean when I get them. I do intend to split my battery modules front and rear, hence my original question.

[@alibro7512]

@@ianlighting100 If you can split them 50/50 then do it although it won't be perfect it will help and make life easier. . TBH I'm not sure how others handle split packs. Good luck with your build.

[@alibro7512]

​@@ianlighting100 I tried to answer this but Pootube lost it. A bms has the positive of every cell connected to the neg of the next, so the voltage shown for each cell is in relation to the previous one. That is OK when the resistance between each cell is the same but if some idiot puts 5m of cable between two cells it will have a resistance, even if it is 50mm2. There will be a few mV voltage drop which skews the reading for that cell.