Problems with batteries

About a year ago I built my esk8 and it was great, I went for a pretty cheap first build with options to upgrade. But there’s one problem I can’t seem to solve ever since the start: When the board was running, for some reason, only one cell from one battery emptied (got to 1.7v once) and the board became too slow to ride after that. I contacted Hobbyking and they sent another battery, and when I sautered and connected the new one, a different problem appeared - power is only withdrawn from one battery until each cell is around 2.7V and the board gets too slow to ride. The batteries I’m using are two of these:

They’re connected in series using this connector: The connections I’m using are XT90’s which I soldered to the batteries and the esc. Also using an anti-spark XT90 loop key: So my question is what is causing this? can I fix it or do I need to get another battery? I don’t think its likely that I would get 2 faulty batteries in a row. I can post pictures and a more detailed explanation of the parts and how they are connected if it’s needed. Thanks

Are you charging/discharging through a BMS?

No, through a normal IMAX charger:

Using the cable that came with the charger, and soldered the XT90 connector to the other side, thing is, the cable is pretty thin, can that be a problem?

It happens during discharge, not charge so the charging cable is not the problem. What esc are you using?

if getting a VESC will solve it, ill buy one right away, i was thinking of getting one for a while now

You are connecting two 5 cells batteries in series which is 10 cells to a 6 cells esc? Connect them in parallel

Edit: though it was 5 cells.

Any other ideas?

Got the same lipos and connector (though I am using 4). No issues.

I would measure the output voltage to see if it is 6S if the lipos are fully charged. Keep measuring the output voltage when you apply throttle. Does it drop suddenly? What happens? What if you move the cables?

how do i check the voltage? usually to check the cells i use my charger, do i need something else for that?

Take a voltmeter and see that the series cable is ok first. Are you sure you are getting the power of 6s and not only 3s? you can say by the speed.

volt meter or multi meter. With a multimeter, you can also measure the resistance of the cables, thus check if they are ok.

this is a physical problem. if both batteries are connected there is NO way they are not discharged both

I weigh about 80kg and i get at least 20kph so Im pretty sure its all 6 cells

Alright, so what do you suggest i do? resolder everything?

dont really have one lying around lol ill just get one on ebay

Checking the resistance is a good idea as @telnoi suggested. You can upload a photo of the soldering job you did, we might spot something.

I can post pictures of the connections if needed, not at home right now though edit: i will in a few hours

too high resistance anywhere from the battery that is not getting discharged.

please provide gearing ratio, wheel size for calculating maximum speed so we can see if your value is correct

wheels are 90mm, need to check about the gears

You should never discharge lipo under 3.2 volts

1 Like