Li-ion Rewiring Battery Help!

[nixie]

I've just bought a second hand hope vision HID battery (14.8v, 2400mah), mainly for the casing, but also to turn into a 7.2v 4800mah battery for my hope vision 2 light. I've got it apart and have a question about rewiring it. At the moment the 4x 18650 cells are configured in 2 blocks of two, each connected to its own pcb (Giving 2 sides of 7.2V 2400mah). The two pcbs are then connected is series neg -> pos by a small resistor to give 14.8v across the whole lot.

Now to rewire this do I need to

a) Split the two pcbs at the resistor and wire the two sides in parralell

b) Wire the batteries in series so they form 2x 3.6V 4800mah pairs and connect both pairs to one of the pcbs pcb as if they were a single cell?

If that's not very clear I'll do some wiring diagrams to explain more.

 

[herulach]

Wirein parralel after the PCBs, or, if you want to get better balancing, take one of the pcbs off & wire it all to one PCB. Thats always assuming the PCBs are there to act as protection circuits.

 

[wildwood]

Hi nixie,
are you sure its a resistor and not a fuse?

make sure both sides are the same OVC before you link them across then just use the one PCB.

then there should be 5 wires to:
+ve cell
-ve cell
Centre tap
+ve out
-ve out
just make sure you have the outputs on the right ones. (-ve cell & -ve output)

Should be a polyswitch there somewhere too?

 

[nixie]

Thanks. Its definitely a resistor, has r100 written on it. I think the polyswitch is attached to the negative flying lead.

So to confirm this is how it should be wired

http://www.flickr.com/photos/27324215@N02/3004338557/sizes/o/

Battery photos (if they help)

http://www.flickr.com/photos/27324215@N02/3004340279/
http://www.flickr.com/photos/27324215@N02/3004339841/
http://www.flickr.com/photos/27324215@N02/3004340045/

 

[nixie]

Helps if I link the images properly!

 

[wildwood]

thats pretty much it.
Just make sure you get the -Ve's the right way round. -ve cell to the second pad in on the left and -ve output first pad on the left. the +ve's are ok as both +ve cell and output are same pad.
I'd put the polyswitch back on the -ve cell and use the other side of it to solder a wire onto the the protection circuit board (remember to insulate it underneath tho).
You wont need the R100 resisitor or diode either.
Another good idea is to wrap the pcb in tape before you pop it back into the gap of the cells. this prevents any solder tag rubbing or scratching through the cell sleeving.

 

[nixie]

Thanks.

You mention above about OVC, I presume this is making sure all 4 cells are charged to the same level before joining it all up. Is there an easy way of doing this. Hopefully they will already be at the same level as the are used as a set.

 

[wildwood]

I'll pm you nixie

 

[Nubo]

Thanks. Its definitely a resistor, has r100 written on it.

I think you'll find that is a thermal breaker, to open the circuit in event of overtemperature, especially overcharge or overdischarge situations (such as a short). I ran across a similar component when I rebuilt my NiMH pack for Light&Motion HID system. A small resistor wouldn't make much sense in that location. At the current draw of the light, a small resistor there would burn up. The R100 designation could mean a 100 degrees Celcius cutoff.

From what I understand, the thermal switch should be placed in contact with the battery, near the center of mass of the pack, so that it properly detects a thermal situation.

If this really is a thermal switch, then you should retain it, and make sure after your mod that it's wired in such a way that it breaks the circuit for the entire pack (not just one pair).

Mine looked something like this:

http://www.master-instruments.com.au/products/58124/ER475A-06.html

There are many other forms

http://www.master-instruments.com.au/category/Thermal_Protectors/1240

 

[wildwood]

hi Nubo, its a R100 sense resistor. The polyswitch (thermal breaker) you question is welded onto one of the cells

 

[nixie]

Right I did the changes last night. Seems to be ok. The light powers up and the battery charges . Now just need to check it for run time. The cells were quite empty (wouldn't power the light till I charged them), just hope they hadn't got too empty.

Thanks to all that replied and a very large thank you to wildwood for answering all my pm questions.

 

[eddyesi]

Has anyone manage to create a Hope epic battery pack from 18650's, assume its 2p2s to create a 7.2v 4800mAh pack. Idealy want to create one that can charge from the hope charger as a pack, this possible? have a dying standard hope 2 cell to use as a basis (PCB/Connector)

 

[Doh!Nut]

No... but
I used some 18650s to make a USE Exposure 7.2v 4800mAh pack
But not 100% success initially:candle:
I bought the pack as spares/repair and saw a trace had come off the protection board.
I soldered the trace back on the board and all looked good, but when I came back to the project a few days later one side of the battery was completely zero volts

So I replaced the batteries with some from an old laptop and wired them up with an All-battery circuit board and it has been working fine.

So if your batteries are just tired and circuit board is fine then you will be ok