63v limit for SP4 FETs question

[Thuktun]

How reliable is this? If I put a 14s battery on here which can charge to 58.8v would that be safe? That's not a lot of leeway.

I'm going over options for building a battery, leaning towards 18650 cells with no BMS. I'm going to use voltage alarms on each group of batteries while riding and charge them with a balance charger. Maybe. But if I go with 13s most chargers are 6s (the one I have now) but I can get an 8s charger easy enough. So either 2 packs of 6s (charged in parallel) and basically be riding little more than a 36v setup or 2 packs of 6s and one of 1s that I somehow have to charge separately or 2 packs of 7s charged in parallel? Or a 13s battery with a BMS and save myself the trouble lol. Or get 13 chargers and use one on each if I wanted to be really goofy about it. I may just get an 8s charger, do 6s on my current charger and the other 7s on the new charger. That would be the cheapest and easiest solution. Any suggestions?

*Side note: I have read up on 18650s and how much current each type can deliver and I've bought some and done my own tests for capacity and voltage sag. Still crunching numbers to decide which way I want to go, a smaller, lighter, lower capacity (8-10Ah) battery with high current or a larger, heavier but much higher capacity (20-24Ah) battery with the same current. They would cost about the same. I only need 18A. I've had a meter on my bike for a week, the most I've drawn is 19.56A. Do I want the extra weight when I usually use 2.5-3Ah each way on my commute and can charge at work and home? Is it worth it to be able to ride 40-50kms once in a while? Decisions decisions.

This is my winter project, it's for next spring. Lots to learn yet still before deciding on a direction and spending money. For now I just want to know is that limit reliable.

[Bikemad]

The 58.8V shouldn't be a problem as the GM LiFePO4 battery is 58.4V fully charged and there are plenty of customers using those.

I have even tested the MP4 controller on 15S (63V fully charged) to confirm it worked OK, but I did not ride it for very long as the pack was only thrown together just for the test.

I have used 14S LiPo on all of my Magic Pies and Smart Pies without any problem whatsoever (apart from one modified MKI Magic Pie internal controller that didn't survive for very long on 97 Amps!)



I use an iMAX B8 Charger to charge the two 7S packs in parallel with a home made balance lead adapter:



Changing from series to parallel (and vice versa) can be a pain, and it is quite important to remember to unplug the balance lead adapter before connecting the two 7S packs in series, unless you really like seeing lots of sparks and having to replace damaged connectors.

A battery that you can simply plug in and charge without having to swap wires around (or monitor the charging process) is a lot more convenient. 

Alan
 

[Thuktun]

Agreed. I was changing all the connections on my SLA setup every time I charged or rode until I installed 3 switches. One way they are in series, the other in parallel. I was thinking I would do something similar except I would only need one switch. And label it lol, the second day I had the 3 switches in I flipped them the wrong way and fried my charger. Replaced a capacitor and it was fine but not something I want to do again.

I do have a 13s BMS but I have no idea who made it or what current limit it has. I was told it came off an ebike. Not even sure how to connect it to be honest. The balance connections and charger and all that are obvious but there are 2 4pin connectors on it that I'm not sure what they are for. I'd post a pic but it's home.

[Thuktun]

What about regen braking? I live on top of a big hill, I normally don't go that way but if I did I would use almost no power for at least 2kms and right after leaving home so at the full 58.8v and if I didn't brake would be doing 70-80kms an hour. The hills leading to downtown St John's are STEEP. Is there something to keep the voltage from spiking too high or would I have to ride around a bit first or take the long way?

[Bikemad]

If you set the "Overvoltage protection value (V)" to 58V it should prevent any overcharging, but you may find that the regen won't work very well until the battery has been used slightly, so make sure your mechanical brakes are working properly to stop the increased overall weight.

It might be a good idea to have a volt meter (or cell checker connected to some of the cells) for the first few rides to make sure the voltage does not rise too high.

Alan
 

[Thuktun]

I have a voltmeter on the handlebars already spliced into the wires to the motor. Whatever battery I connect would go to it.

Here's that BMS. Any ideas what the 4 pin jacks are for? One has N/A, 0-,SW_0 and Vbat+ written by each pin and the other GNDD, SCL, SDA and v3.3.