Point-1 Lipo BMS

Hello

Well I have now modified 2 of the point-1 lipo packs and have observed something about them. The BMS appears not to control charge of each cell? I assumed that it did, it appears that the whole pack is charged in series with 42V right down the pack and each cell is monitored during the charge process, so if any cell goes out of balance it simply stops charging by cutting the negative feed to the pack.

It also monitors each cell during discharge and will do the same if any cell goes out of balance, I dont know too much about charging lipo cells but it seems to work, however I think I will test both BMS boards off the pack to make sure they are working properly.

With this in mind it would be relatively simple to use something like a crouzet millennium controller to manage the pack, you could disconnect the internal BMS and toss it, they do an 8 channel PLC we use them at work, you could monitor the volts of each cell in the same way and use the scrolling display to keep an eye on out of balance cells, nice thing is when running more packs you can use extension modules on the controllers and we get them cheap through my place of work as we use 100s of them.

The software is great as well, all you would need then is 1 x ssr for the whole feed when running 72V, it would cut the pack completely and identify the out of balance cell, you could then charge it on its own or change it for a new pouch in needed?

Just an Idea, I dont trust the cheap BMS too much, I have smoked 2 of them already, that said the actual pouches have been great.

I can get the 8 I/O controller very cheap indeed and the program is easy. You could also use one of these controllers to make your very own programmable drain brain as they also offer pid loops as well, you can pwm modules for 0-10v as well or 4-20ma, nice for control not ideal for the casual ebiker more of a project for mad tinkerers like me!!

You can also implement over temp cut off, the only thing would be over current protection, I guess you would have to rely on a fuse or fit a shunt, shunt would be ideal, just an idea.

Cheers

Knoxie

I use PLC's at work also. The packaging doesn't lend itself well for an E bike.
Especially if you want to maintain the stealth look
There are lots of microcontrollers that can do the job and are easy to program. I also have a lot of experience programing dedicated motion control computers for industrial robotics.

Basic stamp or the C stamp with 12 A/d converters and 41 I/O channels is cheap in low quantities

this chip looks good allso

http://www.jrkerr.com/icproducts.html

Once you go down the design road you will be endlessly updating and improving the design which has its up side and down side depending on how much time you have.
These days I only embark on a new design if I feel there is money to be made. Otherwise if I figure out my hours and what my time is worth its never less expensive to do it myself.

There must be a better BMS you could use in your pack that does all you want. If not maybe thats the design route you should take because when you are finished you will have a product that fills a market need and a salable product

Mark

The BMS appears not to control charge of each cell? I assumed that it did, it appears that the whole pack is charged in series with 42V right down the pack and each cell is monitored during the charge process, so if any cell goes out of balance it simply stops charging by cutting the negative feed to the pack.

Click to expand...

Bummer as range will suffer since such a system won't correct an out-of-balance pack, only prevent it from self-destruction. You could just alligator clip a single-cell charger to bring up the laggers after every 10 rides or so.