Topic: Custom Lithium Battery Pack

[gtkid94]

Hey Everyone,

I was trying to fit a new LED headlight onto my 1972 CB500 the other night, and I'm pretty sure I over-discharged the Lithium Battery I installed (Second one I've wrecked).

I'm super frustrated with how electrically fragile these Lithium battery packs are. Also after taking one apart I found that it was actually just a plastic case around 8 circular batteries, and a very basic balance charge circuit(no charge/discharge protection). I feel like that's a very lazy electrical design and from a space standpoint also super inefficient.

Has anyone out there tried making a custom battery back for their bike? I'm going for a minimalist brat-style look, and hiding the battery seems to be a big design issues on these. It seems to me like it would be pretty simple to build a battery back into the seat with a very slim form factor, and better charge/discharge protection than Anti-Grav is putting in their packs?

I'd appreciate any insight/advice!

[pjlogue]

You can coax a LI battery back to life if you know what you are doing.  These batteries have a voltage sense circuit that detects a minimum voltage it will allow charging and when the battery voltage falls below this point the charging circuit is shut down.  If you can bypass the volt sense circuit and do a low current charge directly to the battery pack you can coax them back.  I limit the charge current this way to 1/10 of the normal charge current and keep the battery pack outside in a safe place while charging.

If the battery (or pack) has only discharged once below the threshold I will charge it like this.  for a pack that has gone below the point more than once I would not attempt it a second time.

There is a good reason we still have lead acid batteries.  They are pretty simple and they work like they should if taken care of.

-P.

[dazemc]

If you're battery is getting discharged then wouldn't it be your charging system that is the problem? I have a 500 and these things do not put out a lot of amps, especially at idle. Besides that LED headlight, what else have you done? You could install a circuit to protect the battery but that will consume power that you might not have. Just don't want you to be disappointed when you do all this work and find that your battery protect circuit is constantly keeping your battery disconnected.

Sent from my SM-N950U1 using Tapatalk

[gtkid94]

@pjlogue -  The first battery I ruined, I did take it apart, and attempted to put it on a balance charge I had sitting around, but 6/8 of the cells were too far gone. That battery had a small circuit board which was for balancing the cells only, it didn't have any other kind of built in protection, which was pretty disappointing. I haven't gotten around to taking the second battery apart yet, but maybe there's a chance I can still bring that one back to life.

@dazemc - The first battery failed because I was still running the old regulator and rectifier, which is a well known no-no (I discovered after the fact). After upgrading the regulator/rectifier and getting a new battery, I ran the new battery for a few months just fine, then when I went to replace the headlight over-discharge the battery while installing it. I wasn't even running the bike. You do have a point though about the available current. The stock headlight is spec'd at 40W I believe, and the one I was trying to install was like 70W, so it was already over-sized, which is a lesson learned. As far as a battery management system, the digital circuits are super low draw, so I don't think they'd be any problem for even the 500s available current.

[The Duke]

I have been considering making a custom battery pack, to keep the size down.  I am considering removing the starter motor, so the biggest current draw would be negated.  It would for sure need some sort of BMS, which could be pretty small for a 4 or 8 cell battery, and like you mentioned, the stock reg/rec would need to be changed.
I did some research about lithium battery packs for an e-skate project I wanted to do, and learned a lot about BMS (battery management systems) whcih are used to balance charge, and protect from over-discharging; I think that could be the remedy.
I actually just made myself a spot welder for building my own battery packs, have not tested it yet though.