Battery not charging, charger shuts off. help please

Batteries, Chargers, and Battery Management Systems.
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R6bbie   1 mW

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Battery not charging, charger shuts off. help please

Post by R6bbie » Jul 17 2018 2:24pm

I have a newish system that has been working great, now it will not charge, the charger starts up then stops, over and over till I unplug it. The fan kicks in then off with no charge.

I have a 4amp charger, fuse is fine.
52v 20ah battery

Thanks for any help.

999zip999   100 GW

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Re: Battery not charging, charger shuts off. help please

Post by 999zip999 » Jul 17 2018 2:37pm

Do you have a multimeter or volt meter put it on a high enough setting and let us know how much volts the charger is putting out.

R6bbie   1 mW

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Re: Battery not charging, charger shuts off. help please

Post by R6bbie » Jul 17 2018 2:54pm

999zip999 wrote:
Jul 17 2018 2:37pm
Do you have a multimeter or volt meter put it on a high enough setting and let us know how much volts the charger is putting out.
I do but I'm in Spain and all my bike stuff is in USA.
On vacation for 10 more days but If I need to order a new charger, I want to get it before I get home.
My battery still reads 52v on my LCD3

Could it be my BMS?

If I buy new charger will it fix my troubles?

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Re: Battery not charging, charger shuts off. help please

Post by 999zip999 » Jul 17 2018 4:13pm

Step one voltage of your charger. It never hurts to have a backup charger for work or ? Just buy the right one.

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amberwolf   100 GW

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Re: Battery not charging, charger shuts off. help please

Post by amberwolf » Jul 18 2018 2:06am

If the battery is fully charged already, it sounds like the charger is just turning on and off to balance the battery; shutting down as current drops below it's shutoff threshold.

However, it could also be the BMS that is shutting off and turning on repeatedly due to a cell that's too high, so the BMS has to drain it down a bit before it can reallow charging.

Does the bike run normally? If it does, then run the battery down just a bit, a minute or two of riding around, for instance, and then retry. If teh charger still cycles on and off immediately, then something else is wrong--either the BMS is not allowing charge or the charger has a problem.


Problems generally start with wiring and connectors, so check those first.

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Re: Battery not charging, charger shuts off. help please

Post by 999zip999 » Jul 18 2018 12:39pm

It could be a bleed resistor turned on and just draining that one cell and that is turning on the charger. I had a signalab bms with led and one channel got stuck on. It was easy to tell because the lied on the bms was stuck on. I sure love the singing with the LED on each channel for balancing. If this is happening the battery would never keep a full charge.

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Re: Battery not charging, charger shuts off. help please

Post by R6bbie » Jul 18 2018 1:15pm

amberwolf wrote:
Jul 18 2018 2:06am
If the battery is fully charged already, it sounds like the charger is just turning on and off to balance the battery; shutting down as current drops below it's shutoff threshold.

However, it could also be the BMS that is shutting off and turning on repeatedly due to a cell that's too high, so the BMS has to drain it down a bit before it can reallow charging.

Does the bike run normally? If it does, then run the battery down just a bit, a minute or two of riding around, for instance, and then retry. If teh charger still cycles on and off immediately, then something else is wrong--either the BMS is not allowing charge or the charger has a problem.


Problems generally start with wiring and connectors, so check those first.
Thank you, just what I wanted to hear. Thank you for taking your time to explain some of the possibilities.

The bike runs great, I do most of my charging when my battery is over half full, I think.
My gauge LCD3 tell me my volts and it reads around 52-54v currently.

I have ran it a few times after this issue and it still didn't charge and did the on and off over and over without charging the battery.
The charger has acted up before, I am not sure if it is the bms. My battery (52v 20ah) is from Unit Pack Power and I have 50amp BMS. My batter shuts down/turns off at 48V if I am still riding hard, I get 30 miles easy running it very hard before it shuts down. Not sure if any of that information I gave you is helpful but that is what I have, again...thanks!!

What happens if my BMS is bad? How would I fix that issue?

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Re: Battery not charging, charger shuts off. help please

Post by 999zip999 » Jul 18 2018 3:05pm

You ask the battery supplier if he will send you an exact duplicate BMS so you just unplug the multi wire connector and re solder about 4 wires.

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Re: Battery not charging, charger shuts off. help please

Post by amberwolf » Jul 19 2018 1:46am

R6bbie wrote:
Jul 18 2018 1:15pm
I have ran it a few times after this issue and it still didn't charge and did the on and off over and over without charging the battery.
Does it do this if it's not connected to the battery at all?

If so, then there's rpobably a break in the wiring from charger to battery somewhere (anywhere in the path, from inside the charger to inside the battery).

If not, then either the charger is just flaky, or the BMS is not allowing it to charge.

If the former, a different charger will work. If the latter, a different charger will also not charge it.

if you can connect the charger to the output (controller end) of the battery, it will bypass the BMS charge port, so fi the BMS is stopping the charge then the charger will now work normally.

If it does not change teh charger behavior, then the rpoblem is more likely in teh charger itself, and trying a known good charger would verify this.


If the BMS isn't allowing a charge, it could be the cells, or it could be a wiring fault (balance wires most likely), or it could be a cell or group problem (cells or interconnects). Or it could just be a bad BMS.



The charger has acted up before,
Exactly how has the charger "acted up"? If it's teh same as this problem, and you knwo it was the charger then, then there's no need for any questions, just a new charger or a repair of the existing one.

If you don't know for sure it was the charger then, then you'd still need to do troubleshooting as you don't know that the charger was what was acting up or not.


What happens if my BMS is bad? How would I fix that
Replacing it is the only way that's easy. Otherwise you'd have to do compnent-level truble shooting and repair on the BMS. If you don't have electronics experience, it could take a while to track down and repair the problem.

But first, you should test the other things.

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Re: Battery not charging, charger shuts off. help please

Post by 999zip999 » Jul 19 2018 2:14pm

A.W. I like the just charge before the bms or straight to the battery to moitor charger Behavior. Plus.check charger voltage first. As these test don't cost anything.

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Re: Battery not charging, charger shuts off. help please

Post by Pete1961 » Jul 21 2018 6:45am

I have had this problem a couple of times, ie battery will run the bike but not accept charge afterwards. Both times it proved to be one of the little positive multi plug wires detaching from its cell. To best detect this I removed the multi plug from the BMS. I taped a sewing needle to the pos probe of my multi meter (to best get into the connectors on the multi plug). Set meter to DCV above the max V of the batt. Test across main bat neg & multi plug individual wires. The first little wire on this plug is a neg, after that you have 1st pos, 2nd pos etc, - so you read say 3.2v, 6.4v etc. If one reads 0v then this is the detached wire to follow back to its cell pos. Restoring this has allowed all to run again - twice. Obviously the charger is not connected nor the bike motor when making the above test. I thought my BMS had failed but not so.
Vibration from tree roots under the blacktop is my enemy - need to look at a better termination of these little wires


I have a home built Li Po4 pack - pouch cells & smart BMS from bmsbatts.com. I did flag each little wire 1st pos etc, at the time of assembly - for future probs. Battery builds have rather moved on since I did this one - but test method also good for Vruzend batt etc. I am a mech guy & struggle with electronics

R6bbie   1 mW

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Re: Battery not charging, charger shuts off. help please

Post by R6bbie » Aug 12 2018 4:07pm

Great news (best it can be)

It was the charger and unitpackpower did replace it after 3-4 months of use. That's great customer service for a China store/factory. I will buy again

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Re: Battery not charging, charger shuts off. help please

Post by R6bbie » Aug 12 2018 4:08pm

and how do you fix a broken charger? I would love to know.

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dogman dan   100 GW

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Re: Battery not charging, charger shuts off. help please

Post by dogman dan » Aug 14 2018 6:47am

Depends on how broken of course. The number one fault is a loose or broken wire on the plug, AC side sometimes but usually on the DC side because the wires are thinner there, and sometimes not the right kind of wire to bend back and forth much. So presto, after a while the strands start breaking off at the plug. Easy fix

The other fairly common charger fault is the inrush limiter frying. This is the first thing on the AC input side, and it tones down the rush of current into the capacitors when the charger is plugged in. Sometimes this heats up too much, is defective, or whatever, and it is obvious when you look that it cooked itself. Also fairly easy to diagnose and fix.


The third most common charger fault is the one I have done a lot :roll: :lol: , and been too uneducated and unskilled to fix. This is where I fix problem one, f it up, and then plug it in with the polarity wrong. Smoke comes out and its done. FWIW, really good chargers have a protection circuit to prevent that from damaging the charger.

Some good info on the forum about charger repairs was posted by former member Dnmun. Hard to dig up old posts here, but his are good ones to look for. His posts can be found here. search.php?author_id=6548&sr=posts

But for current answers to specific questions, Amberwolfs might be the best info on the forum. Others just as good, basically you want to ask the engineers here, not dumb carpenters like me.

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