I needed to replace the Headway pack in W2. I didn’t design it for battery replacement. It’s a pain. It needed to be replaced because I was overseas in Asia for a month. Someone came to my house to feed the dog while I was gone. They moved the chair and left it turned on. Not only turned on, but put some things on top of it, which were on the joystick, holding it slightly applying throttle against a wall for three weeks until the Roboteq shut off at 8 volts.
I recharged, balanced, and capacity tested. No bueno.
Sooooo…..
I think this is the third pack I’ve built using RJ Lithium cells. Not the cheapest but best I’ve tried. Grade A virgins. Buy once. Cry once. FYI – Shipping was $588 plus $55 Paypal fee. Took about two weeks.
Very well packaged
All connected in parallel to charge/balance to 3.6v prior to assembly. That’s a piece of Romex 12/2 household wire I stripped. This took three days. That’s 1400ah worth!
Making the bus bars from .0625 x 1 inch oxygen free 101 copper. Overkill but what I got.
https://photos.smugmug.com/photos/i-ZKCQskf/0/5ed0d57c/1920/i-ZKCQskf-1920.mp4
How you have to pick them up when you’re a gimp that can’t reach the floor. I need a copper magnet.
Short video machining them
https://photos.smugmug.com/photos/i-gJJQBkv/0/7bd8efce/1920/i-gJJQBkv-1920.mp4
All wire ends properly crimped then lightly soldered to reduce resistance. All bus bars were thoroughly sanded to remove oxidation, cleaned with acetone, and coated with heavy duty red Lucas grease as they were installed. Copper will oxidize in minutes, causing major issues later on. We use this same grease on our 5th wheel hitches at work. It comes factory on the big tractor truck battery bus bars. It’ll still be there airtight on the bus bars years from now.
Care must be taken though. This grease will destroy many plastics over time and is electrically conductive. It will cause shorts! It’s also messy.
Balance wiring. All equal length. There’s a sheet of .031 inch thick buna n rubber between each cell.
These two bronze studs on the end will be the positive/negative connections.
Almost ready for install
That’s the BMS on the front. More on it later.
The thoroughly beaten Headway pack awaiting a viking funeral. These chairs are used hard. Actually, what to do with these old cells?
The Headway pack was 60ah. It's being replaced with 100ah.
Snug fit! Hard to see but the pack is surrounded by 1/8” thick buna n rubber sheet.
And a layer on top. An 1/8” plastic layer went on top of this. Only the battery connections are exposed. They’ll be covered.
The BMS I used is a JK B2A24S. This is not an advertisement for them. It’s the only BMS I’ve even remotely considered since building my first pack in 2012 or so. I probably still wouldn’t use one for 8s or less. Charging 14s is a bit more challenging though.
It balances/charges up to a 24s pack, balances at 2 amps, and is good for up to 200 amp continuous discharge. It also measures ah used and so far seems to give a pretty accurate battery percentage indicator. I’ve gotten a display working with it. Haven’t quite figured out how or if I’ll use it. The phone app is capable.
You must set everything up correctly. All of the necessary settings are there.
You can turn the charging, discharging, and balancing off/on
So far, it balances fast while charging and properly does no balancing below whatever volt you choose. I have it set to turn the balancing on above 3.45v.
Balancing at 2 amps
Pulling out 2 amps. From testing, it appears to pull energy out at up to 2 amps to fill its capacitors, then dumps that energy into the lowest cell. So, on paper it’s moving two amps, but that works out to 1 amp over time I guess when you consider both directions. Still much better and much more efficient than dumping the extra energy into a resistor as heat to balance.
I tried testing how quickly it responded by connecting the charger at 8 amps with the high voltage protection at 3.6v after the pack was fully charged/balanced t0 3.55v. It reacted withing ten seconds and cut the charge current down. No cells got over 3.62v. Very good.
Within one minute
Within two minutes
Within five minutes all cells were back down to the 3.55v target. Supply voltage isn’t super critical. Set it 2 or 3 volts over the max pack voltage. I was worried it couldn’t resist overcharging if the supply was over the max full pack voltage. It cuts it back fine. It cannot add voltage. The pack won’t charge if the volts aren’t slightly over.
Real time view of pack amps being pulled out. -20.2 amps. It refreshes about once every second. So, not really easy to see spikes.
So far I’m pleased. Time will tell if it’s good. It’s nice being able to disable the entire electric system with one tap. That alone will prevent this pack from being over discharged.
It can also be set to disconnect at a certain voltage x time. Ie – if the pack is below 42v for 60 seconds it will disable.
