humble dave

Sudden cut off. Stop turn battery off then back on and it runs again. The battery pack shows nearly full charge and will be reading @47 volts. The individual cell packs in the 13s 48 volt battery read evenly @3.9 volts when testing with my volt meter on the kitchen table. Do you suspect the bms is bad or have my 18650 cells lost their ah capacity? Why would it drop out when showing a fair amount of voltage?

Doc_Wui

47 volts on a 18650 based lithium battery is about half charged (3.6V).. . A basic BMS will shut off if any individual cell group dips below 2.5v, while the ebike controller will trip when the battery voltage falls below its LVC, around 41V, Battery sag could cause either to happen, Maybe a broken contact on one group. Maybe a bad contact if you built your own battery using the spring based connectors instead of spot weld. If they are all even though, it's not contacts.

How many amps can your controller pull?

I've been riding more and more when it's below 45F, sometimes at freezing, and it does seem like I an getting more voltage sag when it's cold. I have a bike with the LCD3 display that shows voltage, so I can watch it,

.

2old

FME, and it occurred a couple of times with a suspect company, the problem is the batteries are sagging. This doesn't happen unless there is a load on them. Could be something else, but I'm betting it's the batteries. I changed the battery on my system and the problem disappeared.

humble dave

I can't tell what amp draw the controller handles. Nothing I can see on it. The bike came with a 500watt rated rear hub motor and a 48 volt 8 amp hour battery. The dealer sent me a free replacement battery 48 volt 10 ah and with the replacement battery it has not cut out. I am right now charging the old battery and plan to test it with the bms bypassed running the battery negative straight to the controller. I shall see if it continues the cut out problem. If it doesn't I will get a new bms.

humble dave

Ok, I charged it. It started at 51.7 volts and the charger just cut off at 53.9 volts. reading 4.1 volts an each cell bank except 2 at 4 so now I am chickening out about running at battery volts straight thru to controller and plan to reassemble with bms as factory and try a test ride.

I did the test ride and it cut out just like before. Showing 52 volts on the lcd at rest now. It cut out while it was showing 49 volts under mild up hill pedaling in assist level 3 @250 watts.
An amp meter would probably tell more to me or a watt meter? The volt read out seems to mean nothing.

chas58

BMS (and controllers) cut out at a certain voltage. It would be good to know the current capacity of your batteries (C rate), and the current draw of your controller (it really should say – and the vendor should be able to tell you). A 1C 8ah battery isn’t going to have much headroom to pull much current.

48v x 10amps = 500 watts. You probably are not pulling too much current (certainly not at 250 watts).

Remember watts = Amps x volts (referring to your meter question)

Your controller or your BMS could be flakey…