Hello all welcome to another video.
I've got a children's Razor MX350 electric motorbike that needs a new battery.
By default it comes with two 12V 7AH lead acid batteries.
They are 59 on eBay Australia.
Today we're going to go one better and i'm going to build my own lithium-ion battery pack.
I've already harvested 18650 cells from laptop battery packs.
Next I've gone through and charged them all.
I've discharged tested all of them and written the capacity on the side of the battery
Then I left the batteries to sit for about a week to see if they'll hold a charge.
Any self-draining cells should be discarded.
Fortunately for these, they were all good.
You can sort them in banks based on mAh, but all of these are so close I'm not even going to bother.
Next we have these battery boxes I ordered from AliExpress.
These are the same dimensions as sealed lead acid 12V batteries.
These ones come with battery holders.
Because I need 24V I have to use two.
I'm going to glue them together and use a BMS for both batteries together.
As you can see there's plenty of room inside for a BMS and wiring.
I did plan on using this battery spot welder but it failed.
It blew up a mosfet and it's passing almost no current at all.
We'll have to revisit that later.
So for this battery build i'm going to solder all the connections.
First I'm going to glue the battery boxes together.
Marking out holes for the bus bars.
And I'll drill them.
Next I have to go through and solder both ends of all the batteries .
I find most cells don't need any prep work.
I carefully watch the blob of solder until it bonds with the battery.
I don't want one single cold solder joint.
All done can you spot the one I missed.
Now let's solder on some copper wire.
Here I'm making 6S 7P.
That'll work out about 24.6 volts.
Stop! I need 7S not 6S
My DIY power wall is 7S,
I want to be able to charge it from my solar panels
and the easiest way to do that is if i make this battery 7S as well.
I can just connect it directly from the charge controller.
So I took all that off and I'm going to change it to 7S 6P.
It'll work out to about 28.7V.
Slightly over voltage for a 24V motor, but a much longer range.
It can drain down to about 21V with no problems.
You won't get that out of 6S or lead acid.
For 7S I had to change the cell layout, they go a different direction.
I'm soldering the bus bar directly to the bottom.
On the top i'll use fuses.
I've cut wires to join the two battery halves together.
Now I'm soldering them on and we can put the two batteries into the box.
It looks a bit messy with all the wires but my solder joints are good,
and once it's in the box nobody will know.
I have to cut out a bit more plastic for the top bars.
So far so good I'm happy with that.
Next we've got the top bus bars and fuses.
Let's put it back in the box and see how it fits.
Too close for comfort, so I'm going to bend the top bus bar around the bottom one.
If I had to make one of these again, I'd take out the whole side, or cut slots all the way down.
A quick double check of my voltage to make sure there's no mistakes.
Now I'm soldering on the last bus bar.
I cut out a slot for an XT60 connector.
This goes to the BMS, it's the charge port and also load under 60A.
I'm also connecting both sets of spade terminals directly to the battery.
If it turns out i don't need them later i'll cover them up.
Now I'll connect the battery negative and charge negative to the BMS.
And finally the BMS wires, these connect to each of the seven banks of batteries.
The BMS's job is monitoring the individual voltages.
If the voltage in one bank of cells is out of balance,
or if the overall voltage is too high or too low it'll cut off the charge or output.
This particular BMS is a JBD-HP08S001
It's 7s60 amp. I actually made a video where i repaired this BMS.
Previously I'd used it on my DIY power wall.
That's all done, one last check I've got everything in the right place and I'll plug it in.
I'm putting silicon on these loose wires to make sure they don't go anywhere.
A bit of an adjustment there.
That's it, time for a test.
There it is I plugged it in, it's working. Sorry for the shaky camera.
Now I'm sticking it together with super glue.
And finally silicon for a bit of waterproofing.
And here it is working.
Well that's it for this video.
Overall I'm happy with how the battery turned out.
If you got any questions, feel free to leave them in the comments.
We'll revisit this little motorbike in a future video. It needs brushes and maybe a replacement motor.
Thanks for watching.
Don't forget to like and subscribe, it really helps me out.