Help with charger for Urban Mover UM44 (kl3688cr3 BMS)

[UnclePuncher]

Hi all,

I have an Urban Mover (24v). I bought it from a neighbour without a charger. Battery still has charge and works (I've been using it with my electric chainsaw). But I need to sort out the charger.

I bought a new 24/28v ebike charger on ebay but could only find one with a 3 pin plug (mine has a 5 pin plug). So I've ordered a new 5 pin plug to fit onto the charger. Happy to solder the new one on.

Edit: my original list wasn't terribly clear. I know the polarity of the battery output. I don't know the polarity of the charger input (to the battery). The 5 pin plug in the photo is for charging only. Battery output is in a separate port.

My issue is I don't know which pin on my battery (charger input) is positive and which is negative. On my battery (see photo below) only the two pins on the left hand side (not the lower central one) are connected to anything. Both go to the BMS but I can't tell which is positive. No markings on the BMS.

BMS is a kl3688cr3 which I believe is fairly widely used. But I can't seem to find a circuit diagram. I've no reason to believe its not working but can replace if needs be (I've done this before). Photo of the BMS is nabbed from somewhere else online but I've highlighted where the charger cables go to (red highlight - lower right hand corner). There are 4 pins but they're soldered together on the other side in 2 blocks of 2.

Thanks.

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[amberwolf]

I have an Urban Mover (24v). I bought it from a neighbour without a charger. Battery still has charge and works (I've been using it with my electric chainsaw).
<snip>
My issue is I don't know which pin on my battery is positive and which is negative.

If you don't know which is which, how did you use it with your chainsaw?


To find polarity on any voltage:
Set your multimeter to 200VDC.
Put red lead tip to one of the two possible connector pins you know is connected internally.
Put black lead tip to the other connector pin.
If the meter reads negative - in front of value, then you have them reversed. Swap them, and if it reads the expected voltage with no - sign, then whichever one the red lead is on is positive.


BTW, it's not uncommon for stolen bikes / etc to be sold without chargers (because the charger wasn't with the bike when they took it), so unless you know for sure the bike was theirs....you might have bought stolen goods. (it's happened to people here before).

[UnclePuncher]

I know the polarity of the battery output but I don't know the polarity of the input (from the charger). Battery output is at the other end of the battery, the photo is just of the charger connection. Obviously I know the polarity of the charger too but not which way round it should connect to the battery.

I bought the bike from a neighbour. It's not stolen. But thanks for your concern.

[UnclePuncher]

Also it's a chainsaw. If I connected it the wrong way round it'd just spin the wrong way. Pretty easy to see and correct it.

[E-HP]

Sounds like you got all the info you need. Make sure to maintain safe practices while charging!

[UnclePuncher]

Sounds like you got all the info you need. Make sure to maintain safe practices while charging!

Does it? As yet I've got no new information.

I still need to know how to determine the polarity of the charger input to the BMS. That was my original query and I'm no closer to an answer unfortunately.

Tempted to buy a new BMS and install it. But afaik there is nothing wrong with this one. I just don't know how to charge it. No markings on the board and can't find a circuit diagram online.

[fechter]

It's a little hard to see in the picture of the BMS, but it looks like there are two spade lugs labeled OUT+ and OUT-. Were there wires hooked up to these?

All of these small BMS units have the positive side wired straight through. The positive battery connection goes right to the output. Switching happens on the negative side. If this is a single port (sort of looks like it), you charge through the same pair of wires as you discharge. Then it's a matter of tracing the wires back to the connector.

[E-HP]

Does it? As yet I've got no new information.

You asked this

My issue is I don't know which pin on my battery (charger input) is positive and which is negative. On my battery (see photo below) only the two pins on the left hand side (not the lower central one) are connected to anything.

amberwolf responded with this

To find polarity on any voltage:
Set your multimeter to 200VDC.
Put red lead tip to one of the two possible connector pins you know is connected internally.
Put black lead tip to the other connector pin.
If the meter reads negative - in front of value, then you have them reversed. Swap them, and if it reads the expected voltage with no - sign, then whichever one the red lead is on is positive.

You got the information you were asking for.

[UnclePuncher]

I didn't though.

They're telling me how to measure a voltage.

My issue is not with measuring a voltage but which way round the charger input should be.

[UnclePuncher]

It's a little hard to see in the picture of the BMS, but it looks like there are two spade lugs labeled OUT+ and OUT-. Were there wires hooked up to these?

All of these small BMS units have the positive side wired straight through. The positive battery connection goes right to the output. Switching happens on the negative side. If this is a single port (sort of looks like it), you charge through the same pair of wires as you discharge. Then it's a matter of tracing the wires back to the connector.

Thanks. That's actually useful. I'll get the BMS out tonight or tomorrow and have another look. Should be able to get some better photos too.

[E-HP]

I didn't though.

They're telling me how to measure a voltage.

My issue is not with measuring a voltage but which way round the charger input should be.

Read it again. The procedure determines polarity.

[amberwolf]

I didn't though.

They're telling me how to measure a voltage.

My issue is not with measuring a voltage but which way round the charger input should be.

No, I told you how to determine polarity (in a safe and easy way), which is what you need to determine.