How to see if battery or charger is broken?

All,

Recently my battery has not been charging. It is a 36v 20a LifePO4 battery. When I connect the charger, the charger's light does not turn red (indicating that it's currently charging), it turns green (indicating that it's charged) but the battery is definitely not charged. If the battery is connected to the motor, it does operate the motor... but I can't actually use it because it's very near empty.

Can anyone help me with how to test which is broken, what I need to test, how I test it, etc? I have a multimeter but have never used one and dont know what I'm doing.

Here's a picture of the battery before months ago when I purchased it and before I installed it. When testing it with multimeter, what will I do with the negatives? There are two negatives, one which goes to the controller, and the other which goes to the charger.

Thank you so much for any help.

The negative that goes to the controller (and the positive that goes to the controller) is known as a discharge wire because it is used to discharge (take energy out of) the battery. You don't need to mess with either discharge wires.

The first step is to test if your charger is outputting the correct voltage, or any voltage. Plug your charger into the wall, but do not plug the connector into your battery. You can put your battery to the side, you won't be needing it for this test. Now, turn your multimeter to the DC voltage setting. Place the black probe on the outside metallic part of the charger connector, the barrel part. Hold it there. Now very carefully touch the red probe of the multimeter to the pin in the center of the charger connector, being sure you don't also touch the probe to the barrel or the black probe. If your charger shows a voltage like 43, 58, etc (depends on what voltage your battery is) then your charger is fine. If it shows 0 volts, the charger likely is either blown, or you've simply broken a wire that connects to the charging tip.

It is also possible that your BMS has fried, but the charger is more likely. The best quick test to see if it is the charger or battery is to use a different charger. I'm guessing you don't have one, but if you have a friend with the same voltage charger or even a local ebike shop that can just plug your battery in real quick to see if it charges on their charger, then that will do it.

Hey tmb41! Looks like you got some learning to do. We were all green at one point so don't worry about that. Just be careful not to fry anything while you are learning what to do.

First things first......


Ok, some chargers will put out full voltage when plugged in, some will need a load, like a drained battery before it starts charging. To test your charger you need to put the positive probe of your meter to the positive part of the connector, and the negative probe of the meter to the negative part of the connector. If this is a mystery then watch the video below. It is long but thorough, so grab your favorable non-alcoholic beverage, put your feet up and absorb as much as you can.

You might find shorter vidios on the net, but make sure you are sure-enough about what you are doing so you don't cross your probes with electricity going through them or you will get a sparking-surprise!

[youtube]ZBbgiBU96mM[/youtube]

As for the two black wires from the bms, one of them goes to the negative on the charger and the other is for the discharge side of the wiring harness. Look at the bms and see if their is a letter where the black wires connect to the bms. Do you have any letters like P- or B-? The markings on the bms will tell you what wires go to where.

Also pictures of how it is all hooked up now would be helpful. Just keep the .jpg's under 500kb so you can post them here.

Can you give us a close-up of that BMS?

yes, take that cardboard shield off the BMS and take a close up so we can tell you where to place the voltmeter probes. do not leave the probes touching anything on the battery while you are twisting the dial to the voltmeter setting. use 20V DC scale to measure the cell voltages on the BMS where the sense wire plug is soldered on.

I now have a Multimeter and I'm trying to test my Charger. However, I'm not getting any reading from the device at all. I'm clearly doing something wrong because I'm not getting a reading even when I try to test a wall outlet.

The charger and battery are for 36V.

Can anyone help with what I may be doing wrong?

For AC voltage like your wall outlet you measure with the knob turned to V~ 200.
For DC voltage like your 36V battery you measure with the knob turned to V= (= means top line solid -, bottom line dashed ---) 200.

mark5 said:

For AC voltage like your wall outlet you measure with the knob turned to V~ 200.
For DC voltage like your 36V battery you measure with the knob turned to V= (= means top line solid -, bottom line dashed ---) 200.

Click to expand...

I tried both and I'm still not getting any kind of a reading on the device. The device has battery installed, and the backlight button does work... but I never get any kind of a numbered reading

is it possible that you used the ohmeter scale or the amp scale before you tried the volts scale? if you turn the dial through those scales while it is connected to a voltage source it can be bad. but it should blow the fuse, maybe. so think if that coulda happened. happens to all of us at least once, or twice in a lot of our cases. i am up to four meters killed now.

Is the meter saying anything?

When you turn it on, it should at least read 0.00V when the probes aren't touching anything but air. If the display isn't doing anything at all, it's probably got a dead battery...

mlt34 said:

Is the meter saying anything?

When you turn it on, it should at least read 0.00V when the probes aren't touching anything but air. If the display isn't doing anything at all, it's probably got a dead battery...

Click to expand...

Meter is absolutely blank and has been since I purchased. I have yet to see it even put up 0.0. It's not a dead battery because I just put a brand new battery into it, and the device is brand new as well. The battery is working because if I press the top right button (backlight), the LED does light up.... but never any actual readings.

Also, I'm putting the black wire which comes with the device in the COM socket, and the red in the middle. That's what the directions say to do, at least.

In that case the meter is broken or you've blown a fuse. You should be getting readings of 0.00V at least. I'd return it to where you got it.

If you're still near the university, consider swinging by the engineering lab and just asking to borrow a multimeter.

Did you put your probes in the right sockets? The black one should be in the "com" one and the red probe in the one next to it.

d8veh said:

Did you put your probes in the right sockets? The black one should be in the "com" one and the red probe in the one next to it.

Click to expand...

Even without probes at all, he should still be at least getting a zero value reading. In some way or fashion, the meter is messed up.

I'm pretty baffled. At this point, I'm buying a new charger since I will ultimately need one anyway (I cut off the end at some point during this whole process). If that doesn't fix it, I'll know it's the BMS or battery.

tmb41 said:

I'm pretty baffled. At this point, I'm buying a new charger since I will ultimately need one anyway (I cut off the end at some point during this whole process). If that doesn't fix it, I'll know it's the BMS or battery.

Click to expand...

While it is wise to have a backup charger, the charger whos plugs you seemingly cut off isn't trash. Consider replacing the plugs with something like anderson powerpoles. Strip the wires from the charger and crimp, pretty easy (search for some videos)

It seems funny to me to ponder how to test if a battery for your multimeter is working without a working multimeter, put your tongue to it? Haha!

Anyway, to me, having a functioning multi-meter doesn't seem optional, you should make that happen.

tmb41 said:

I'm pretty baffled. At this point, I'm buying a new charger since I will ultimately need one anyway (I cut off the end at some point during this whole process). If that doesn't fix it, I'll know it's the BMS or battery.

Click to expand...

You mean you had cut off the charger output plug as previously shown in the picture. But you still have that plug end and could reuse it?

You could go to Harbor Freight--there should be several in your area--and buy their cheapest $6 multimeter which would work fine.

I'm going to buy a new charger and a bunch of anderson powerpole connectors. I'm also going to return the multimeter I purchased (~$35) and get one from harbor freight for $6.

Will post an update after that.

Update: I now have a new charger and everything soldered correctly. Unfortunately, the battery still does not charge. In fact, the light on the charger does not light up, almost as if it does not recognize it has been plugged into anything.

How do I determine what BMS I may need and replace it?

did you check continuity between the charger and the battery?

You're just stabbing around in the dark. You need to be methodical in finding the cause of your problem. It really is simple and should have been sorted out in 5 minutes. Changing connector and chargers won't solve anything and neither will changing the BMS.

You only need a voltmeter to find the problem:

• Switch it on, set it to volts DC and test that it's working by sticking the probes on your car battery . You should get about 12v to 13v.
  
  Now that you know the voltmeter is working, switch on the charger and measure between the two wires. It should be 43.8v.
  
  Before connecting it to the battery, you need to make sure that you have the wires the right way round. Put the black probe on the wire you're going to connect to the black battery wire and the red to the other one. The read should be 43.8v. If it says -43.8v, you're the wrong way round. If you connect the wrong way, something will pop.
  Now check the battery wires: Red probe to the red wire and black to each black so that you get two results. Both need to be at least 30v.
  
  Check that the charger connector goes to the right battery black wire, which is marked C- where it connects to the PCB.
  
  Connect the charger and put the red probe on the red battery wire connection and the black one where it joins the PCB (marked C-). You should get somewhere around 30v to 35V. If it's 43.8v, something is wrong.

That's it. Those steps will almost certainly point to the cause of your problem. Don't change anything until you know what it is. There's further simple tests that you can do to get the solution after you've done the above tests to find where the problem is.

Is the new charger dual voltage 110V/220V? Make sure it's set to 110V.

Guys!

It's finally charging again! I had a bit of a loose connection on a solder. I now know how to use a voltmeter, which is a plus!

Thank you everyone that commented and helped!!