Power cuts out

[chris_m]

Hey folks,

I installed a KT36/48SVPR-20A with a 48V battery on an old Wisper bike with a BFUN8 250W, and it's been running great until the other day.
Suddenly (after my wife used the bike to pull a heavy trailer) the power cuts out as soon as the load increases slightly.
I noticed this happens both on throttle operation and PAS. But it happens only when the bike is on level 5 of PAS (max). On throttle it occurs regardless of power level set.

If I pedal (on 5) it cuts out pretty much right away. On throttle I can ease it into running if I increase it very very carefully, but as soon as it's not flat or I pull it just a little too fast it cuts out right away. I then have to release the throttle and start over.

What could be the problem? (I've pulled heavy loads with the bike before, but probably more carefully than the wife may have done - I mention this as I have nothing else to go on that may have caused the problem, but not sure this is related to the heavy trailer)

Some suggestions I have had earlier:

1. Battery
It seems unlikely to me as it's a quite new battery Hairon 48V 14.5ah with LG cells. I should mention the battery was in storage for about 18 months before being installed. It has been running flawlessly for 6+ months though, and charges up to 54.9V.

2. Damaged wires to the motor
I have not found any.

3. Damaged FET(s) in the controller after overheating due to pulling heavy load.

I am sortof "hoping" it's the controller, as this is way cheaper to replace than the battery, but if eveything points to the battery, maybe it's not worth buying a new controller?

Thoughts anyone?

Thanks

chris

 

[flat tire]

It sounds like you are drawing too much power and something is tripping. Without more information I would suspect your battery BMS. That's the component most like to cause an actual cut-out. The controller will just limit itself transparently.

 

[amberwolf]

Suddenly (after my wife used the bike to pull a heavy trailer) the power cuts out as soon as the load increases slightly.
I noticed this happens both on throttle operation and PAS. But it happens only when the bike is on level 5 of PAS (max). On throttle it occurs regardless of power level set.

If I pedal (on 5) it cuts out pretty much right away. On throttle I can ease it into running if I increase it very very carefully, but as soon as it's not flat or I pull it just a little too fast it cuts out right away. I then have to release the throttle and start over.

1. Battery
It seems unlikely to me as it's a quite new battery Hairon 48V 14.5ah with LG cells. I should mention the battery was in storage for about 18 months before being installed. It has been running flawlessly for 6+ months though, and charges up to 54.9V.

(above Snipped down to essentials)

The most likely issue is the battery itself. Either cells damaged from overheating by too high a load for too long, or drained down too far under the high load and now badly unbalanced.

The latter can be tested by leaving it plugged into the charger at least overnight, and if that's already been tried do it for days or longer. If it recovers even a little bit then this may fix it by doing this as often and as long as possible.


If it doesnt' change at all, then you may wish to try measuring the voltage sag under load, first of the pack, and then if it seems excessive, the cells themselves.


A 48v controller probably has a 42v-ish LVC, so it would cutout without blanking the screen, if the battery dropped below that. It would recover immediately if the battery stops sagging (when the load is removed by it cutting out).

If the display actually shuts off, then the battery is cutting out at the BMS, which is usually from a cell-level LVC low voltage cutoff.

If the latter isnt' happening, then to verify the problem, you can measure the voltage during a ride during cutout (easy if there's a voltmeter on the screen, otherwise you have to put a voltmeter or wattmeter where you can see it), and if it's dropping down to the 42v range, then the former's probably what is happening.

 

[Butch1]

Check the connections from the battery mains to the controller, is it a setup that involves metal contact strips typical on some removable battery setups?. With a poor connection and the heavy load imposed by acceleration the controller gets "starved" for current and shuts down. Mine would do this going over big bumps until I found the problem and fixed it.

 

[chris_m]

Hey, thanks for the very helpful responses!

The most likely issue is the battery itself. Either cells damaged from overheating by too high a load for too long, or drained down too far under the high load and now badly unbalanced.

The latter can be tested by leaving it plugged into the charger at least overnight, and if that's already been tried do it for days or longer. If it recovers even a little bit then this may fix it by doing this as often and as long as possible.

Great. I will try this, hopefully that will be it! But in order to balance cells, would I have to discharge the battery a bit before charging again, or just keep it plugged in for many days, and it could potentially balance itself?

If it doesnt' change at all, then you may wish to try measuring the voltage sag under load, first of the pack, and then if it seems excessive, the cells themselves.

A 48v controller probably has a 42v-ish LVC, so it would cutout without blanking the screen, if the battery dropped below that. It would recover immediately if the battery stops sagging (when the load is removed by it cutting out).

If the display actually shuts off, then the battery is cutting out at the BMS, which is usually from a cell-level LVC low voltage cutoff.

If the latter isnt' happening, then to verify the problem, you can measure the voltage during a ride during cutout (easy if there's a voltmeter on the screen, otherwise you have to put a voltmeter or wattmeter where you can see it), and if it's dropping down to the 42v range, then the former's probably what is happening.

Display does not shut off. It does have a voltmeter, so I will see what it shows and report back.

Thanks again!

 

[Hwy89]

I have had the same experience with one of those batteries. Mine was very out of balance. This was a result of always taking it off the charger as soon as the light turned green. Since I had the battery open at that time I manually balanced it with a single cell charger. When they were fairly close I plugged in the charger and verified that the BMS was trying to balance but it is painfully slow. My solution has been to leave it on the charger for a few extra hours every time I charge and giving the BMS time to do it’s thing.
The downside of this is that this unattended charging needs to be done in a fire safe place and I’m still trying to figure that out.

 

[amberwolf]

Great. I will try this, hopefully that will be it! But in order to balance cells, would I have to discharge the battery a bit before charging again, or just keep it plugged in for many days, and it could potentially balance itself?

IF it has a balancing BMS (they don't all) then just leaving it plugged in whenever it is not in use will improve the balance, but this is often a temporary fix, because imbalance is usually caused by:

--mismatched cells; not all the same capacity or capability

--damaged or defective cells

--damaged or defective cell interconnects

--damaged or defective sense or balance wiring or channel components in the BMS

All of those will eventually lead to imbalance, some of them soooner than ohters or under different conditions, requiring periodic rebalancing.

 

[chris_m]

Ok. It definitely sounds like an imbalance problem then. How do I manually rebalance cells? Aren’t they soldered together? Which kind of charger should be used to charge single cells?

I’ve now left the battery plugged in for a week. I’ll see if this helped in a few days.


Thanks again!!



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[amberwolf]

Ok. It definitely sounds like an imbalance problem then. How do I manually rebalance cells? Aren’t they soldered together? Which kind of charger should be used to charge single cells?

If they dont' rebalance doing it with the charger and BMS, it means that either the problem is really bad, and the pack is going to need repair to fix the problem causing it, or the BMS is not a balancing type.

If it's the latter, then using a single cell charger would work to do it, but you'd need to setup the system so you can do this "frequently", meaning as often as necessary. So you would want to add a balancing connector that you can access without opening up the pack.

The single cell charger would be exactly that, like many of the ones that show up here:
https://www.google.com/search?&q=single+cell+charger&oq=single+cell+charger&
Many these days are made for 18650 cells, so you could either wire in a permanent set of leads to hook to your groups of paralleled cells in the pack as needed, or use alligator clips to hook to the contacts in the charger (if possible), and then to the cell groups in the pack.

Or you could get an RC charger, and make a cable for it to attach to "banks" of cells, to rebalance several at a time.

The quick and dirty way is to use a celphone charger (5v) to bring up really low cells, but you have to stay right there and monitor voltage the whole time so it doesn't go over full charge, which happens pretty fast once you get close to full, especially with high-resistance cells (ones that typically have problems like this).


But first, you should check to see if it actually *is* a balance problem. If the leaving-pack-on-charger doesn't change anything, and you want to do the manual balance, you'll have to open the pack up to do this anyway, so you should first check cell group voltages. If they are all about the same, within a few hundredths of a volt, then you'd need to test them under load to see if some sag a lot more than others, because it's not just a balance problem at that point.

 

[chris_m]

Ok. So tried the bike after a week of keeping the battery plugged into the charger.

Seems like there is no difference. Still cuts out at high load on pas 4 or throttle. Voltage does not seem to drop at all. Display shows around 52v when it cuts out.

Next step I believe would be to see if the bms is a balancing type? But how would I check that?

Thanks

Chris



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[john61ct]

If your BMS has no means of displaying per-cell/group voltages

You need access to those posts / leads, and ideally a clamp-type ammeter.

 

[goatman]

hailong battery case, have you looked at the contact blades/prongs where the battery slides into the base.

 

[fechter]

If the battery had a problem and the BMS was tripping, the bike display would go blank and you'd have to cycle power to turn it back on. Doesn't sound like a battery issue to me.

If you had a bad hall or phase wire connection, the motor could possibly be drawing enough current to trip something. I've also seen the solder job on the shunts inside the controller go bad too. If you can't find anything else, I'd take apart the controller and carefully inspect everything inside. Sometimes the problem is obvious.

 

[amberwolf]

Ok. So tried the bike after a week of keeping the battery plugged into the charger.

Seems like there is no difference. Still cuts out at high load on pas 4 or throttle. Voltage does not seem to drop at all. Display shows around 52v when it cuts out.

If there's no voltage drop, and the display doesn't shut off, the battery isn't cutting off power from an imbalance. (so while there could be an imbalance, it isn't the issue here).

You could have a connection problem from the battery to the system.

Or possibly the motor phase wire connections are high resistance (or one of them is), so it causes the controller to shutdown to prevent damage when it detects the imbalance in current flow, or some other problem.

 

[goatman]

heres a thread on it

https://endless-sphere.com/forums/viewtopic.php?f=3&t=91925&p=1340872&hilit=hailong+battery+bms#p1340872

 

[chris_m]

heres a thread on it

https://endless-sphere.com/forums/viewtopic.php?f=3&t=91925&p=1340872&hilit=hailong+battery+bms#p1340872

Thanks. I checked the connectors but they look good. Also wouldn’t a bad connection cutout occur more randomly? My problem always occurs very predictably (throttle operation or pas 5)

So battery imbalance is ruled out then?

Is it possible to check for resistive leads to the motor? If so how?

It sounds like this may be the only suggestion not yet ruled out?




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[goatman]

its pretty easy to open up a hailong case ,8 screws and youre in, you can peel back that paper and with a dmm check the voltage of each group just to be sure. if I remember right there might be some bullet connectors in there you might want to look at. another pack I had, someone else was in there rewiring things, you never know what youll find.

 

[chris_m]

its pretty easy to open up a hailong case ,8 screws and youre in, you can peel back that paper and with a dmm check the voltage of each group just to be sure. if I remember right there might be some bullet connectors in there you might want to look at. another pack I had, someone else was in there rewiring things, you never know what youll find.

Right. I’ll open it up when I get a chance and report back.

Thanks everyone for your input.

If imbalance is ruled out it seems resistive motor leads are the next (and only?) remaining suspect then?




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[fechter]

One other remote possibility is a bad throttle. If something is shorting it could trigger a fault.

 

[E-HP]

What type of connectors are you using between your battery and controller? I had some weird cut out issues that I traced to a bad crimp.

 

[ADVBiker]

The most likely issue is the battery itself. Either cells damaged from overheating by too high a load for too long, or drained down too far under the high load and now badly unbalanced.

A 48v controller probably has a 42v-ish LVC, so it would cutout without blanking the screen, if the battery dropped below that. It would recover immediately if the battery stops sagging (when the load is removed by it cutting out).

If the display actually shuts off, then the battery is cutting out at the BMS, which is usually from a cell-level LVC low voltage cutoff.

Thank you for the information. I am having a similar issue. I have a 48v 24.5Ah battery in a Hailong case (bought it from a known UK seller quite recently) and its been good untill the other day when it cut out at around half the range I had been getting.

I have no display on my bike but just like OP i could lightly feather the throttle and it would go but trying to put any kind of load and it just shuts down, the only way to get it back being to turn the battery off and on. When it comes back on the throttle voltage display still reads green (full) and when I checked the voltage it was at 51.4. It charges normally to 54.5.

Does this sound like a faulty BMS?

 

[amberwolf]

YOu have to test the pack to find out if it's cells or BMS. But it's rarely the BMS. See this post I just made in another thread:
https://endless-sphere.com/forums/viewtopic.php?f=3&t=106773&p=1564274#p1564274

But first, just like in this thread, if the system's display/etc stays on, it's not the BMS or the battery, because when those shut off, the display/etc stops working and shuts off because there's no power to it.