Rewiring The Gp2x To Run 2 Lithiums In Parallel?


alkaline

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Feb 4, 2008
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Hi,

I was wondering anyone has rewired the GP2X to run 2 lithium AA cells in parallel to increase battery life?
This shouldn't be too hard to do and can give you 5000 MAH batteris that has little or no discharges like Nimh.

Here is the battery I'm looking at:

http://www.atbatt.com/product/3443.asp

This should fit the AA compartment, know all that needs to be done is to rewire the circuitry to run in parallel.
Also a small volt meter could be attached to have an auto cut-off at 2.8 volts as to not damage the battery. But you could probably increase your usage life by 3x that of NIMH.
 
I'll check but I have been using rechargeable lithiums for my rc plans for quite sometime... if these don't work I'm sure I can find some AA sized rechargable li-ons.
 
Putting batteries in parallel is a perfectly good idea, it doubles the mAh while keeping the voltage the same; however the cells have to be the same brand and type otherwise you will get issues with better cells trying to recharge worse ones, unless you use a diode.

Normally Li-ion cells are a different size to normal batteries so you don't accidentally try to recharge normal cells in a Li-ion charger.

Make sure the Li-ions have built in circuit protection, or your charger does, otherwise you will have a hand grenade (explodes violently and catches fire).

Only issue I see is if 3.6v is too high as the GP2x normally expects 3v.
 
bacteria said:
Putting batteries in parallel is a perfectly good idea,"
I have to agree here. There is nothing wrong with this. I was actually considering doing this myself but it's hard to do cheaply without making the GP2x as thick as a brick.

bacteria said:
it doubles the mAh while keeping the voltage the same;


Yes, however you MAY notice that you don't get exactly double what the batteries would give you in pairs. At lower current drains, batteries exhibit different properties, so you may find that, say, 2 x two batteries in parallel won't last *quite* as long as 2 sets of the same batteries (because when you run them in parallel, each battery is only supplying half the current is was before, but for longer). The mAh that you see printed on batteries are measured at very specific current drains, so at lower/higher currents you may or may not get the same value.

For example, a 2000mAh battery cannot necessarily supply 1000A for 0.002 hours or 1micro-amp for months etc.

bacteria said:
however the cells have to be the same brand and type otherwise you will get issues with better cells trying to recharge worse ones, unless you use a diode.
Yes, I'd echo this. The batteries used in parallel will also deteriorate at different rates so as they get older they will appear to "die" quicker because they will be recharging each other if you don't have a diode in there.

bacteria said:
Only issue I see is if 3.6v is too high as the GP2x normally expects 3v.
Firstly, if you are using diodes, you're conveniently going to have a (0.7v-ish) voltage drop on them that would bring it into the realm of a normal set of batteries. One to stop a battery charging it's partner, one to bring the voltage down? I'm sure with experiment you might even be able to get away with just the first but I'd do the maths or measure it first.

Secondly, I believe the GP2x runs on 3.3v, which is regulated upwards in the case of batteries. Although I may be wrong, it may just be that only the external power-adaptor is regulated down to that. Again, this is one of the reasons that your GP2X with 2500mAh batteries won't exhibit perfect performance and performance will vary depending on the abilities of a particular battery (which is why some 2500mAh batteries die quicker - they can supply 2500mAh but only at particular voltages/current drain).

So it doesn't seem like a bad idea. However, if in any doubt, just make sure you thoroughly compare the voltage given off by your usual two batteries and that given off by your finished product. There's a page somewhere on the GP2X wiki concerning measuring battery with software, that I believe has a reference table of voltages at which the GP2X considers the battery fully charged/dead. It would be a good idea to stay within those parameters.
 
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I actually checked the gp2x's current consumption a good while ago and found that across a range of provided voltages (2V->4V in 0.1V steps), the gp2x used less wattage at 3.7V than the typical 2.4V provided by a pair of rechargeable cells (or 3V provided by a pair of non-rechargeable cells). Note that I said 'wattage' not 'amperage', which would obviously drop as the voltage increased.
 
Here is what I am thinking:

1, Safety of the Lions:

Lions can be charged up to 4.0 Volts max/cell
Lions should not go below 2.8 Volts/Cell during discharge

LIONS CAN NOT CHARGE EACH OTHER like NIMH, they have be be invidually charged and monitored. Also while in parallel configuration they do not balance each other out like NIMH.

For my plan I will do the following:

Install a 2.8 volt cutoff inside the GP2X, whenever the voltage drops below 2.8 volts the system will turn off. Then use my lithium battery charger to charge the cells. I have a great planes lion charger that would work great.

I should be doing this mod probably next week or so and will update you guys with pics, if it works, it would increase the battery life by about 3x that of the highest NIMH. I see 3x because the self-discharge of the LIONS is only 1% a year while NIMH self-disharge around the neighbourhood of 30%/week.

The mod will be nice and clean, and I think the GP2X will handle 3.6 Volts happily after all NIMH fully charged are almost 2 volts/cell :ph34r:
If not it should be easy to install a small 3 volt regulator inside the GP2X.
 
Good information here on batteries and charging, but not applicable for the batteries in question. Those are non-rechargeable lithium cells, not lithium ion. I'm not positive, but pretty sure, you're not going to find a standard AA size high capacity lion cell...
 
Ah yes, of course - I wondered why the cells in question were the same size as an AA (unusual, for the reason I posted in my last post). This means you could easily put these lithium cells in your GP2x and make them parallel (only needs a couple of wires, plenty of space) but the cells are expensive to buy in comparison.

Yes, I have had poor experiences with NiMH batteries in my projects, they drain too quickly when not being used; that is why in my Universal Console System (forthcoming project) I am going to use two Li-ion camcorder batteries, 7.4v, 5200mAh each - nice and chunky, rechargeable and 10400mAh in parallel (I just bought a special charger for them).
 
Actually, I'm toying with the idea myself of just attaching some 5000mAh or 10000mAh C or D NiMH cells to the GP2x... not cheap (£10-15 each from Rapid Electronics) but easy to charge, same voltage (so you can just connect directly to the AA battery contacts inside the GP2X), more capacity (approx 2-4 times that of a good set of AA's), doesn't stop you using AA's (so in a gaming emergency, you can still just plug in your normal batteries, or you could mess about trying to make a nice parallel connection so the AA's work in conjunction with the C's/D's), and if you position the batteries correctly they'll work as a nice hand-hold on each side of the rear of the machine.

That's my idea of modding - not pretty, but it works. If I want it to work nicely, I'd probably invest in some AA-blanks (they are battery sized but literally just a piece of plastic with a strip of conductor running through them) to run the leads off (so you install the AA-blanks in the GP2X and the C's/D's connect to the strip in the middle of them). It also makes it easier to charge if you are going to "fix" the C/D cells... you can just plug the AA-blanks into your normal charger!

Only thing is I need to check to see if I can source some cheaper 10,000 mAh D-cells. If not, I'll only buy two.
 
Any news? I'd like to install lithium battery. Has anyone modded a gp2x f200 to increase battery life?
 
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