I knew this 48v 40ah pack was too big the moment I got on the bike with it. And now that a string has gone bad I finally have the impetus to split it into smaller packs. I guess basically what I want to know is how the 18650 cells are connected in series in those duct tape packs. I know the basics of the parallel connections in that they are connected by spot welds on metal strips, but I don't really know the details of that arrangement either. I'm planning on cutting the pack into two 15ah sections and one 10ah section and hoping all the bad cells are confined to one section. Then I can get 2 smaller 48v batteries and one 36v battery out of it. Problem is I don't have any ability to weld and have only been soldering for the past few months, so I'm hoping I can do this by just cutting. And if I'm lucky maybe I won't have to do any BMS re-wiring on the first pack. At the very least I could cut it into two 36v 20ah packs right? Then maybe a 12v SLA booster will be the ticket.
Cutting a battery down to size.
- Thread starter Rifle
- Start date
That is a LOT of work. To do it you'll have to:
-cut the pack apart completely
-rebalance the cells (i.e. charge them all to the same voltage)
-reassemble the cells (you'll probably need a welder; soldering generally won't cut it)
-add a BMS or two (a 48 volt BMS generally won't work with a 36 volt BMS)
-cycle a few times and look for bad cells; replace from your spare pile (after rebalancing)
It's basically the same amount of work it would take to build them from scratch, plus you have to take the old pack apart first.
-cut the pack apart completely
-rebalance the cells (i.e. charge them all to the same voltage)
-reassemble the cells (you'll probably need a welder; soldering generally won't cut it)
-add a BMS or two (a 48 volt BMS generally won't work with a 36 volt BMS)
-cycle a few times and look for bad cells; replace from your spare pile (after rebalancing)
It's basically the same amount of work it would take to build them from scratch, plus you have to take the old pack apart first.
kilowatt
1 mW
I don't know who built your pack but Cammy_CC (V-Power) built my 36 Volt 20 Amp pack. My pack was configured as a 2S19P configuration and when I unwrapped it I found 2 each 18 volt 20 amp packs series connected and folded together into one big brick. I think you will find two 24 volt 40 amp packs the same way. I don't think you will be successful with this. I ruined my pack; over 100 cells spot welded and you will have double that. When you lift a spot weld, you need to solder it so in your case, in order to make those various configurations you want you will need to take the battery too far apart and without a welder, almost impossible to manage. Leave it alone and build a battery trailer or; the battery would be great for a trike with a rear basket.
Kilowatt
Kilowatt
Little-Acorn
100 W
- Joined
- Oct 15, 2009
- Messages
- 130
Cammy_cc and Vpower are the same thing?kilowatt said:
full-throttle
1 MW
Expect a lot of hot glue when you take it apart, but its of a lower quality and chips off easily.
I have successfully reassembled a rectangular v-power 16s9p 18650 LiFePO4 pack into a triangular shape. Its not too difficult. The trick is to cut the tabs halfway between the cells (don't pull the tabs off the cells) and re-solder them using tinned shim cut to strips using low-temp silver solder.
I have successfully reassembled a rectangular v-power 16s9p 18650 LiFePO4 pack into a triangular shape. Its not too difficult. The trick is to cut the tabs halfway between the cells (don't pull the tabs off the cells) and re-solder them using tinned shim cut to strips using low-temp silver solder.
Ypedal
100 TW
Well, if you have one bad string in there, nothing to loose by trying to open it up ! ( other than shocking yourself and burning something down :lol: .. lol.. but you know that already ! soooo... moving on . :wink: )
First thing to do is to remove all the duct tape, the first few layers are not so critical, but the last layers stuck to the cells you want to be carefull with, try to pull the tape in the same direction as the bus bars, if you pull in the other direction the strips edges pull up and this is where most of the spot welds get yanked.
Sharp blade knife with fresh blades, don't try to save the duct tape shell, cut it off in sections and throw it out.
Take note of how the BMS is currently hooked up so that you can re-wire it later on ( or if you loose track, someone here will know how to wire it back up lol.. thank god for this place ..) Usually the - side starts on one end or ther other and followed by the next wire in series.. i bet you nick or cut or mangle at least one ballance wire during the process so better to just remove them all and solder thicker gauge and known to be good leads after you take it all apart.
You will need a method to charge a single series group at a time to manually ballance, single cell charger or adjustable RC type charger..
Only way to know how yours is wired up is to expose it, nothing consistent with these DT packs, it's only a guess until you get there.. " hopefully " it is build in 20ah blocks..
I would go with 24v 20ah bricks, but that depends on what bike you want to run them on.
Take your time, work on it for a bit and take a break, can't say this enough, but no jewelry and work in a clean space with lots of light. liquid butane Zippo fuel works pretty good at cleaning your hands..
And Take Pictures !!!!
I was up until 1am last night putting the page together:
http://www.ypedal.com/cammycc/Index.htm
First thing to do is to remove all the duct tape, the first few layers are not so critical, but the last layers stuck to the cells you want to be carefull with, try to pull the tape in the same direction as the bus bars, if you pull in the other direction the strips edges pull up and this is where most of the spot welds get yanked.
Sharp blade knife with fresh blades, don't try to save the duct tape shell, cut it off in sections and throw it out.
Take note of how the BMS is currently hooked up so that you can re-wire it later on ( or if you loose track, someone here will know how to wire it back up lol.. thank god for this place ..) Usually the - side starts on one end or ther other and followed by the next wire in series.. i bet you nick or cut or mangle at least one ballance wire during the process so better to just remove them all and solder thicker gauge and known to be good leads after you take it all apart.
You will need a method to charge a single series group at a time to manually ballance, single cell charger or adjustable RC type charger..
Only way to know how yours is wired up is to expose it, nothing consistent with these DT packs, it's only a guess until you get there.. " hopefully " it is build in 20ah blocks..
I would go with 24v 20ah bricks, but that depends on what bike you want to run them on.
Take your time, work on it for a bit and take a break, can't say this enough, but no jewelry and work in a clean space with lots of light. liquid butane Zippo fuel works pretty good at cleaning your hands..
And Take Pictures !!!!
I was up until 1am last night putting the page together:
http://www.ypedal.com/cammycc/Index.htm
full-throttle said:
I had to look up what a shim was
. Could you tell me what sort you used and where one might buy some? Sure would be nice if I could cut the pack into like 5ah chunks to isolate where the bad cells are and then put the good chunks back together into a nice sized pack or 2.Ypedal said:Well, if you have one bad string in there, nothing to loose by trying to open it up ! ( other than shocking yourself and burning something down :lol: .. lol.. but you know that already ! soooo... moving on . :wink: ) .
...
I would go with 24v 20ah bricks, but that depends on what bike you want to run them on.
Take your time, work on it for a bit and take a break, can't say this enough, but no jewelry and work in a clean space with lots of light. liquid butane Zippo fuel works pretty good at cleaning your hands..
And Take Pictures !!!!
I was up until 1am last night putting the page together:
http://www.ypedal.com/cammycc/Index.htm
Thanks a bunch! Since I got the pack for 400 I've been thinking I might be able to sell it someone who wants to salvage it for around that, but I guess if I can't manage to pull this off it might be about as easy to find someone to buy the bare cells and BMS. If I do pull this off though it would be impossible to get anywhere near this many watt hours for that price. I've got to get something that is at least 36v due to the LVC and smaller than a 48v 20ah battery so I can physically lug it around on a consistent basis without irritating the injury that caused me to get an electric bike in the first place. 48v is much preferred since I already have a 48v 5amp charger.
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