BMS Selection Help

[Senecio]

Sorry, new to the forum and wasn't sure how to title this post.

I have completed a small frame Vespa electric conversion and built an 18S8P battery using Samsung 30Q cells with a 100A BMS that was supplied to me. I'm wondering if I should change the BMS for something that could offer me more control.

Here's the issue I'm facing. Fully charged the battery will measure at 75.6V or 4.2V per cell which is perfect. Once I discharge the battery down to ~35% charge remaining my Vespa starts to lose power. I can still maintain 50Km/h on the flats but as soon as I encounter any sort of hill it really struggles. At this 35% charged state the battery still measures ~64V or 3.55V per cell. I'm wondering if my BMS is being overly conservative with its low discharge voltage protection. I would have thought that I could safely take these cells down to 3.2V or even below? At the moment I'm getting about 32Km of range before the loss of power. If I could take the cells a bit further safely that could give me up to 40km of range that would make my commute so much less stressful.

Do you think it could be my BMS? If so, does anyone have a suggestion for a quality BMS that might allow me to configure the low voltage protection to get a bit more range from the battery pack without doing damage.

 

[amberwolf]

The BMS will completely shut power off if any cell were to exceed any limit (HVC, LVC, overcurent, etc); it's all it's hardware is capable of. So if you were hitting a BMS limit of whatever type, your Vespa would just stop running entirely.

If your system still works but not as well as it should, it means the controller's setup is doing the limiting, *or* there is simply not enough power to do the work needed for the particular conditions.

18 x 3.55 = 63.9v. Is there anything in the controller programming setup that begins to limit power output around that voltage?

 

[Senecio]

Thank you. I don't know too much about the controller. I converted my Vespa using the kit from Retrospective but had to build the battery myself. I'll have to open up the black box that house the controller, DC-DC converter etc... to find out more about it and too if I can adjust its programming.

 

[amberwolf]

Before opening it, why not contact the people that sold the kit--if it is programmable they should know, and be able to supply you with the programming cable, software, etc.

Even if you open it, you'll still need those things to do anything with it, and you'll have to get the software specific to that model and brand of controller. (the cable might be a standard usb-serial, but some use specific wiring, voltages, etc, on the serial side at the controller end, and using a non-OEM cable might not work).

If the manual for the kit doesn't provide all of it's specifications and limitations, then the kit sellers should have all of this info they should be able to tell you. If they can't, they should be able to give you the manufacturer contact info and the model of controller so youc an then ask the manufacturer.

 

[Senecio]

Thank you. I will contact the kit seller.