Discharge box for bicycle battery

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PRINTERMON
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Discharge box for bicycle battery

Postby PRINTERMON » Mon Feb 25, 2013 9:24 pm

Hello,
I use a rechargeable battery on my bike front light, the battery is 8.4V, 6400mAh, the led is a Cree T6. During lighter nights, when the light is not required, I have been charging and discharging the battery ( via the led) to maintain battery life. I would like to build a discharge unit in order to do this without using the led as this gets very hot whilst stationary.

The lamp will burn for about 3 hours on the highest setting, I think the set up is 4 x 18650 batteries.

Any ideas what I would need to build one?

Cheers

xanthic
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JoinedCOLON Fri Jun 29, 2012 10:03 am

Re: Discharge box for bicycle battery

Postby xanthic » Tue Feb 26, 2013 9:35 am

You shouldn't need to cycle lithium batteries in the same way you would for Ni-Cads. The memory effect is much less. If anything, you are possibly reducing the working life of the batteries. You don't cycle the battery in a laptop for instance and a decent charger will sense the battery state and recharge it properly.

I'm honestly not going to recommend anything here. Lithium batteries should be handled with care and a mis-handled cell can vent gas or even explode. Have a read of this forum, a couple of interesting stories of when lithiums go bad - http://www.candlepowerforums.com/vb/forumdisplay.php?107-Smoke-and-Fire-Hot-Cells-and-Close-Calls-The-dangerous-side-of-batteries

PRINTERMON
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Re: Discharge box for bicycle battery

Postby PRINTERMON » Tue Feb 26, 2013 10:09 am

Hi xanthic,

Thanks for the info - The light I am running now is a new set up, I had a similar light ( an SSCP7 led ) on a similar battery pack, and in the users info, it advised to charge and discharge at least once a month if not in use. (The light was a Raleigh RSP product) .I failed to do this during the summer and when I came to use it again in the winter, I found the battery was running out very quickly. After no improvement through charging, I made my own pack using Senybor batteries which my dad is still using now with my old light. Do you think this problem was due to poor batteries to start with? I've read quite a bit about sub standard batteries being used in this type of product.

Many Thanks

xanthic
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PostsCOLON 87
JoinedCOLON Fri Jun 29, 2012 10:03 am

Re: Discharge box for bicycle battery

Postby xanthic » Tue Feb 26, 2013 11:06 am

Lithiums should be stored charged up and in a cool place if possible. All batteries will naturally discharge over a period of time (how long depends on the type). It'd be worth draining them off and recharging after about 3 months. Poor batteries could be an issue,but a poor charging unit will also reduce battery life. I've seen lots of recommendations for the Pila charger,but at £40, one of the more expensive out there.

faariwasi
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Re: Discharge box for bicycle battery

Postby faariwasi » Thu Nov 13, 2014 6:10 am

Little update on this, at long long last I've built a small dimmer circuit. Nice and simple, hopefully very cheap to build and I'd like to put it in a kit. Only breadboarded at the moment so I'll solder one together and have a play with it so we can run it with a 12V setup and see what sort of current we can run through it - actually I know the latter it's 800mA but I want to quantify that.
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