Im thinking about adding the dark green pack to my new MJ872 pack (bright green) then do away with the volt read out.

Possible or stupid. I know where to solder etc what what cables to join. Is this stupid? do people do this?

or If I dont do this, can I just do away wit the volt read out? is that all the top circuit is?

If you run cells in parallel, you’ll get twice the capacity but it will take twice as long to charge.

The top circuit may be part of a cell voltage balancer ?
(Any new series/parallel combinations may require new voltage balancing circuits to prevent one or more cells over charging.)

why?

Edit: I thought you should know I own one of these and I’m interested, so no offence intended.

The little PCB at the top of the batteries is your protection circuit for the pack (the cells themselves will be un-protected). To the best of my knowledge these in general are designed for the specific size of the battery pack so a 7.4V 5.2Ah battery will have a different protection circuit to a 14.8V 5.2Ah battery. It is not quite as simple as just soldering on the extra 4 cells to increase the capacity of the pack.

Thanks Rusty Mac, I was thinking this last night. I may well just chop the plastic volt meter off then.

Edit – or what if I keep the protection circuit on both and still join them?

Is it not easier to just keep them separate and swap them over when one runs out? You could run the cables into a switch to avoid having to faff about in the cold/rain. You would be able to use two chargers then to maintain the same charging speed.

I’m struggling to see what the benefit chopping them about is going to give you?

Is the little PCB not for balancing the individual cells since they are Li-ion?

In the end ive just taken the volt readout off. just snipped it and resoldered the cable.

Paul – you are right. “Is it not easier to just keep them separate and swap them over when one runs out” YES.

Yes you can add the first pack to the second to increase the run time.
The current packs are 2S2P
two cells in series (2*3.6volts = 7.2volts) and
two cells in paralell (2*2200mAh = 4400mAh)

The new pack should be 2S4P
two cells in series (2*3.6volts = 7.2volts) and
four cells in paralell (4*2200mAh = 8800mAh)

You would also have the option of making two packs one biggish using 6 cells (2S6P) and one mini using 2 (2S1P)

This link may help. It also shows how to connect balancing leads to be used with a balancing charger. It should be noted that the circuit boards are protection circuits preventing overcharging and over discharging of individual cells but does NOT make sure that all cells have the same voltage ie are balanced.

Sorry slight Highjack.

I have one of these batteries. The LCD output reads 8.4 Vols when fully charged.
How is this possible when it has 4No 3.6 Volt batteries inside, obviously 2 in series 2 in paralel. Still doesnt get to 8.4 Volts though.
Am I missing something?

The nominal voltage is 3.6 volts but the peak voltage after charging is 4.2

Same as a NiCd is known as 1.2v nominal but might be 1.4+ volts hot off the charger

I finally made my mind up, been a bit busy today.
I put the packs in parallel which should make – 14.4volts 8800mAh, while keeping them protected. 🙂
This will fit nicely in my rear jersey pocket. Although I need to get something more substantial to cover the pack. Lecky tape is not preferred.

You will either have 7.2v and 8800mAh if you did them in paralell or you will have 14.4v 4400mAh if you did them in series.

not 14.4v 8800mah

Just a thought – are you going to use it with a magicshine?

I am not sure what the input voltage limit is, but all the components are speced to the absolute minimum and are unlikely to have 100% headroom.

Nick

If you use a 14.4v battery pack with a light that orginally came with a 7.2v battery pack then you will at minimum make the protection circuit cut in on the batteries, but more likely screw the processor thingy that regulates the voltage/amps to the LED’s.

It will be 7.2v and 8800mAh then as connected in paralell.

Thanks for your help.

I blasted the light on full power last night, hanging out of the window.

It lasted for 3 hours on full beam and went on to red. So obviously lasted twice as long. cool stuff.