I apologize if this is the wrong forum to ask this ...
I built an electric skateboard for my son with parts form a little Chinese scooter. It works great - for about 30 seconds and then the power cuts out and I am clueless as to why. Perhaps I wired something wrong..
The battery is a second hand LIFEPo4 24V 30ah from VPower. It is one of those duct tape specials. Originally it was the size of a cement block. I was able to unwrap it and open it like a book. I split it into 2 halves and reconnected it so it would fit under the mountain board. It came with a BMS that is still connected. My DMM reads 25.8 volts. When I connect the smart charger to it - it always reads full - or at least the green light stays on.
The 24v thumb throttle ($10 from ebay) has a led power meter on it and seems to work fine. It reads full power until it cuts out.
The motor ( my1016) and controller (xrk2000-24 G) I took from the old scooter. Most all the extra wires from the controller - like to brake, signal lights and stuff - are still connected but taped off to prevent shorts. I may remove most of them once I'm more confident that it won't screw something else up.
It is possible I bought a bad battery, but don't know how to test it. I would really appreciate any suggestions. I'm a novice to this stuff.
Thanks!
Your battery is NOT fully charged! Voltage at full charge should be over 27 volts, typically about 29 volts, fresh off the charger.--Are you using the correct charger for the lithium battery?-Bob
Robert M. Curry
thanks Bob,
I think you're right.
The VPower website list the voltage for their 24 volt LIPO packs at 26.7 volts.
Of course thats still more than I'm reading at the battery. The charger is a brand new smart charher from Battery source.
http://www.batteryspace.com/smartcharger30afor256v8cellslifepobatterypackstandardfemaletamiyaplug.aspx
I tested the charger's output and I think it read about 29 volts, so the charger is probably OK. I had to change the plug to a 3 pin deal to fit the board. I thought perhaps I wired that wrong and bypassed the plug to the wires leading from the charger receptical and it still shown a green light (full charge)
Since I think the charge goes through the BMS, could the problem be there? Is it dangerous to or can I bypass it?
Do not bypass the BMS unless there is no other way. The BMS keeps the cells safe.
You have a voltmeter it seems.. the next step is to measure voltage of each cell. It's possible one of the cells is bad.
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
Thats kind of a worst case scenerio...
Are you saying that I have to pull out the battery - 2 blocks of cylindrical LIPOs- strip off all the F'n duct tape again and measure the individual voltage on each of the individual cells? What should the voltage be and what would a bad cell read on the multi meter?
When I first got this battery and strated stripping it of tape, 2 or 3 of the metal tabs came loose. Finding a spot welder was a problem, so I used a mixture of "liquid electrical tape" and powdered graphite to re attach them where they came loose. It seemed to make a solid connection, but what do I know...
I probably should have suspected a problem with the battery as the seller tried to rip me off.
Well, this is a learning experience for me :-)
Thanks
You DEFINITELY have a problem if the cells are not properly connected! "Liquid tape and powdered graphite" will NOT do the job! Clean/remove all of that, find a business, such as "Batteries Plus" that can properly spot weld the cell connectors! These connections absolutely MUST be direct metal-to-metal connections! Normal soldering would work, except the amount of heat, and the TIME required to do the job, would be very likely to cause shorting or damage to the cells, and possibly create a small disaster, from the shorted cell overheating, and possibly exploding!-Bob
Robert M. Curry
OK Thanks... I've got my work cut out for me. And I thought I was being soo clever with the conductive liquid tape stuff... dam! You're pretty sure thats a problem?!
!^%^$#** should of used a good old gasoline motor...russin fussin!