How tricky is it to repackage a LIFEPO?

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jso123
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How tricky is it to repackage a LIFEPO?

I am buying a used 24v 30Ah battery ( from Sangesf on this forum) for use on a home made skateboard. It is made of cylindrical cells and made by a company called V-Power.

The size of the battery pack is 5.5" x 10.5 ". I would really like to take it apart and reassemble it into a flatter package that would fit under the skateboard instead of above it. I believe the battery pack is one of the China "duct tape specials". I have basic soldering skills but am a noobie to most of this battery tech. I haven't even received the battery yet, but does anyone know how difficult or easy this might be?

thanks all!

Scott

moveon70
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Re: How tricky is it to repackage a LIFEPO?

Short answer: not that easy, but with patience and a soldering iron, you can do it.

I have unwrapped a 48V 20ah LiFePO4 battery from Vpower.
THey are made up of 18650 cells instead of larger cells.
http://cgi.ebay.com/New-Lifepo4-A123-18650-1000-1100mah-battery-Cell-15-Pcs-/220636265773?cmd=ViewItem&pt=LH_DefaultDomain_0&has...

They are spot welded together with Ni tabs, very similar to the pack I made with 18650 LiCoO2 cells.
http://visforvoltage.org/forum/9318-re-use-18650-li-ion-laptop-cells-build-battery-pack

You could change it by cutting the Ni strips and re-soldering.
BE CAREFUL! there is not protection at that level. YOu could easily shunt out a whole bank and melt it down.

30Ah is a bit large for a skate board. I guess your dimetions are 270mm x 140mm x 150mm? and about 10kg?
I would probably do ~10Ah to keep size a weight down. 24V 30Ah would give >10mile range.

I hope it works out for you.
-Mark

jso123
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Re: How tricky is it to repackage a LIFEPO?

Thanks - especially for the links.

It looks like you too have discovered every "fun" project turns out to be about double the time and expense originally thought. However - you do get bragging rights when done ;-)

I'll carefully unrap the battery pack when I get it and decide then if I'm brave or foolish enough to rearrange the cells.

Thanks a lot for your help!

Scott

jso123
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Re: How tricky is it to repackage a LIFEPO?

Thanks - especially for the links.

It looks like you too have discovered every "fun" project turns out to be about double the time and expense originally thought. However - you do get bragging rights when done ;-)

I'll carefully unrap the battery pack when I get it and decide then if I'm brave or foolish enough to rearrange the cells.

Thanks a lot for your help!

Scott

jso123
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Re: How tricky is it to repackage a LIFEPO?

I got the used battery in the mail today. I haven't tried it out yet. I'll need to repackage it into a flatter shape before I can use it. However, before I spend a lot of time on this project, is there a relateively easy way for me to test it and make sure it still as as much life as "advertised"?

I have a $3 multimeter and the ability of a competent 6th grader.... :-)

Thanks!

jso123
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Re: How tricky is it to repackage a LIFEPO?

Hi Mark,

I need your expert advice..

I began to unwrap the duct tape from this beast and am worried.
There was a lot of glue gun used to assemble this thing. One of the metal strips already came loose from 3 cells and I've only unwrapped one corner. Perhaps I was not too careful pulling off the tape. Dam ! Not sure how to best to reattach it. I don't have or want to build any special welding equipment just for this project.

To make this work the way I hoped, the battery pack has to end up being be no more than 3 " or 76 mm thick. I could probably build a frame with battery clips and copper tabs like http://endless-sphere.com/forums/viewtopic.php?f=14&t=17912 , however not sure how to connect the bms to it.

Perhaps if I use a heat gun on the remaining duct tape, it will come off easier and do no more damage. What do you think?

moveon70
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Re: How tricky is it to repackage a LIFEPO?

Ooops!
Actually, I am surprised that you pulled a tab off. If they are properly welded, they are really hard to pull off. The fact that it came off so easy is concerning.
The reason spot welding is done, is because if you solder, it will get the end of the battery hot enough to likely reduce its life span. That said, in a pinch, you sold solder one cell, and probably not notice the difference. The tabs are made or nickel and solder nicely.
I like the option of building a box and applying pressure, but I think it would be hard to do write. Since you plan to pull a lot of current, it is really going to test the contact resistance. Raw copper will oxidize too fast. Best off coating with tin, cadmium or gold. I had considered building a box like that for the same reasons: replaceable cells, but decided it would be hard to do and pull high current.
Still, my favorite is spot welding, but I agree.....its a whole other project just to build a spot welder. I live in San Jose, CA. You could borrow mine if you live around here. Or you could try to find a shop that has one. Other than that....the quick solution is to solder it. Use a hot soldering iron so that the battery does not have time to soak up the heat and degrade. You could consider replacing just that single cell with another one that all ready has tabs welded onto it, and then solder onto the tabs. That way you have a fresh batt that will not get too hot when you solder.
As for the hot melt glue....yeah, a blow drier may help. The one I took apart also had hot melt glue, but not as much as what you describe.
And for the BMS....just keep track of where the wires are hooked up. Usually, there is one thin wire between each group of cells.
Well, you are in it now....let me know if I can help more.
-Mark

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