Bike cutting out when battery on 3 bars

[matthewslack]

So essentially the balancing was only a temporary fix and the same series being the issue again suggests either BMS/bleed resistor/bad cell issue?



I haven't done any wiring with the bike - do I need much equipment for it, and a new type of meter?
Is it quite advanced?
It would be nice if there was an easy way to test the controller and it was a cheap fix, but seeing as the same battery series is still lower than the rest it indicates it's a battery issue and not controller?

You can get some idea of what is going on by letting the battery sit with no load connected, and measure the cell group voltages at intervals to see if they change. Do this twice, from fully charged, once with the bms plugged in, and a second time after recharging, with it unplugged.

As soon as fully charged get a baseline set of measurements, then every hour or few hours, depending on how fast anything changes, remeasure.

If all stable with bms attached, give it a really long time say a day before testing again. If no change then probably not the bms.

If it DOES drift down faster on cell block 11, then continue the test long enough to be sure what you are seeing, then recharge to full, then unplug bms, and repeat the observations.

If different, then bms problem. If not different, then probably not bms problem.

nce with if plugged in. Start from the same condition each time, i.e. fully charged.

 

[Nealh]

So essentially the balancing was only a temporary fix and the same series being the issue again suggests either BMS/bleed resistor/bad cell issue?

Balancing can be a temporary or a permanent fix when a BMS is fitted, those who don't use a BMS rely on it all the time as a manual way of keeping the cells good.
As has been mentioned charging then letting the battery sit with BMS sense wires disconnected might show a different result but it depends if you are able to open the battery and do this.
In most cases BMS work well but occasionally they fail, I had a 48v pack that was fine one week at storage voltage then 5 weeks later or so when checked was only fit for scrap as all the battery groups drained to sub 1v.

 

[bikemerchant]

Thanks guys.
Attached are a few photos of what I think is the BMS, how would I go about unplugging it?

 

[matthewslack]

That big white connector. Pull that out, with the usual caveats about not shorting anything out. One side of it goes to the cell groups, the other to the bms .

 

[bikemerchant]

Tested rows just before fully charged and again at fully charged.

Just before - total 54.8V.
All series were 4.22V apart from 10 (4.21V) 11 (4.12V) and 12 (4.20V).

Fully charged - total 54.9V.
All series were 4.22V apart from 11 (4.12V) and 12 (4.21V).

Should I now let the battery sit and test it every few hours with the BMS still attached (I didn't know just letting it sit would drain it - I could try riding it a bit)?

 

[matthewslack]

Tested rows just before fully charged and again at fully charged.

Just before - total 54.8V.
All series were 4.22V apart from 10 (4.21V) 11 (4.12V) and 12 (4.20V).

Fully charged - total 54.9V.
All series were 4.22V apart from 11 (4.12V) and 12 (4.21V).

Should I now let the battery sit and test it every few hours with the BMS still attached (I didn't know just letting it sit would drain it - I could try riding it a bit)?

Don't ride it.

Then only something internal is responsible for any change you see. We track down the culprit by eliminating other possibilities.

We don't know if just letting it sit will run it down, that's what these tests should find out. It should not run down if bms is ok, but if the weak cell group does run down, then it points to the bms being the issue.

 

[bikemerchant]

6 hours later - total 54.6V.
All series were 4.2V apart from 11 (4.12V) and 12 (4.19V).

 

[matthewslack]

Ok,

6 hours later - total 54.6V.
All series were 4.2V apart from 11 (4.12V) and 12 (4.19V).

Ok, I suggest leave if overnight, measure again in the morning, if no change then the bms looks ok, and there is no parasitic drain.

I would then want to set up a low drain test, say 100 watts, and measure voltages every hour to see if 11 drops faster than the others under a low load.

 

[bikemerchant]

This morning - total 54.5V.
All series were 4.19V or 4.2V apart from 11 (4.11V).

How do I set up a low drain test? Change settings on my multimeter and then hold the probes to the battery end connector?
Attached is a photo of my multimeter.

 

[Nealh]

Low drain means attaching something that will apply a small current load, typically some 12v bulbs attached in series.

 

[bikemerchant]

Requires some wiring but not soldering?
I found a few videos of doing it off a single cell, unsure if this would be the same.

Would the series rebalancing probably do the trick to keep me ticking over for another month or so?
I could try to do it myself this time if it will be a regular necessity.

 

[matthewslack]

This morning - total 54.5V.
All series were 4.19V or 4.2V apart from 11 (4.11V).

How do I set up a low drain test? Change settings on my multimeter and then hold the probes to the battery end connector?
Attached is a photo of my multimeter.

I use a 2kW panel heater, connected via a spare battery connector.

Basically a big resistor, which at 48V instead of it's normal 230V consumes a bit over 100W on a fresh battery and 70 or so at cutoff.

I used to use bulbs, but I had a few blow, and car headlamp bulbs are expensive. I ran out of old H4s with one element blown. The heater will never break used like this.

 

[Nealh]

The manual balancing is a pain but yes one can keep balancing the cell group every so often, 0.01 or 0.02v out of balance isn't worth worrying about but a full 0.1v is. To save opening the battery all the time the best option is to wire/solder up a separate balance lead to the cell groups only and have fed out to the exterior of the battery, then if balance falters one simply uses it for diagnosis and repair. The BMS remains connected and intact and still deals with the bottom and top end discharge but obviously with a flaw in the circuitry, the more capable amongst us would simply swap out the BMS if it was suspected.

 

[wheeliepete]

Would the series rebalancing probably do the trick to keep me ticking over for another month or so?
I could try to do it myself this time if it will be a regular necessity.

Not really, unless you do it on a daily basis. I think it's been established that your pack obviously contains one or more bad cells, which will continue to throw it out of balance. Do you have pedal assist on your bike, as I've only read you mention a throttle? Using this at lower levels will nusre your battery a little, limit the voltage collapse and cut outs. If not you could cut the current draw on the throttle with the C5 setting on your display.

 

[bikemerchant]

I use a 2kW panel heater, connected via a spare battery connector.

Basically a big resistor, which at 48V instead of it's normal 230V consumes a bit over 100W on a fresh battery and 70 or so at cutoff.

I used to use bulbs, but I had a few blow, and car headlamp bulbs are expensive. I ran out of old H4s with one element blown. The heater will never break used like this.

Thanks but I'm still struggling to visualise how I would do this with my battery pack. I don't think I have a battery connector (had to google what it looks like), I can send a photo of the ends of the pack if that would help.
Can't I just connect the battery to the bike and ride it a bit to drain it?

Not really, unless you do it on a daily basis. I think it's been established that your pack obviously contains one or more bad cells, which will continue to throw it out of balance. Do you have pedal assist on your bike, as I've only read you mention a throttle? Using this at lower levels will nusre your battery a little, limit the voltage collapse and cut outs. If not you could cut the current draw on the throttle with the C5 setting on your display.

Nope I use it as an electric motorbike (it's 40kg).
Is it safe to presume that the bad cell is in series 11?
If so would an option be to purchase 6 new high quality brand cells (one series) and try to find someone to replace them?

 

[matthewslack]

Thanks but I'm still struggling to visualise how I would do this with my battery pack. I don't think I have a battery connector (had to google what it looks like), I can send a photo of the ends of the pack if that would help.
Can't I just connect the battery to the bike and ride it a bit to drain it?



Nope I use it as an electric motorbike (it's 40kg).
Is it safe to presume that the bad cell is in series 11?
If so would an option be to purchase 6 new high quality brand cells (one series) and try to find someone to replace them?

The aim of a small load is to see if the problem is only under heavy load, or under a light load as well.

I use Anderson powerpole connectors for my 48v battery, so I have a double socket with cables to a powerpole connector, and just plug it all together. I'll put up a picture when I get home from work.

 

[matthewslack]

The aim of a small load is to see if the problem is only under heavy load, or under a light load as well.

I use Anderson powerpole connectors for my 48v battery, so I have a double socket with cables to a powerpole connector, and just plug it all together. I'll put up a picture when I get home from work.

As simple as that. The live and neutral on the back of the socket are connected to the white and yellow powerpoles (I had run out of red and black). Plug battery into socket, then any purely resistive load into the socket, and there you are.

Just for posterity I had better say out loud that this is a standalone socket not being used for its normal purpose so that no one fries themselves in years to come!

A 2kW 230V heater on mains 230V draws 2000/230 = 8.7 amps, so its resistance is 230/8.7 = 26.4 ohms.

So on 48V, it draws 48/26.4 = 1.8 amps, which is 48 x 1.8 = 86.4 watts.

 

[bikemerchant]

Thanks - do I have to unwire the ends of my battery to expose the red and black wires?
I'll put up a photo of the battery ends now.

I don't own any plug sockets with wires coming out of it - did you need to wire these up yourself, or if not what's the name of the plug socket I should buy?
I also don't have powerpole connectors.

Would turning C5 down to 1 still be too much load for a small load test?

 

[matthewslack]

Thanks - do I have to unwire the ends of my battery to expose the red and black wires?
I'll put up a photo of the battery ends now.

I don't own any plug sockets with wires coming out of it - did you need to wire these up yourself, or if not what's the name of the plug socket I should buy?
I also don't have powerpole connectors.

Would turning C5 down to 1 still be too much load for a small load test?

That first picture of yours looks like an Anderson 50a connector - or a clone of it. So one if those would be best ,then you don't need to modify the battery wiring. Ebay etc. For those.

The socket is a standard mains plug socket, cheapest you can find will do, b&q, screwfix or any DIY store.

This test only draws 2 amps through the 50a connector, so with care you could just jam the stripped wire ends into the battery sockets. Maybe the wedge end of a wooden clothes peg as a jammer.

It does not matter which goes to which pin of the plug socket, polarity does not matter for simple resistive loads like the panel heater.

The C1 etc.. settings are as yet outside my experience, my kit build is still in its box!

 

[bikemerchant]

The C1 etc.. settings are as yet outside my experience, my kit build is still in its box!

I can half the maximum current by changing the C5 setting if that is a small enough load?
Obviously I can also manually
1 - put it into first gear
2 - not turn the throttle the full way
3 - put the bike on its side so it has no resistance