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Author Topic: USB battery  (Read 9018 times)

BalefireX

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Re: USB battery
« Reply #20 on: October 15, 2005, 06:48:29 PM »

Parallel = same voltage, more current
Series = more voltage, same current

you want Parallel.
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trials_modder

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Re: USB battery
« Reply #21 on: October 15, 2005, 07:06:29 PM »

OK, I shall try testing the charger again, this time with two 9V batteries inside wired in parallel.
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linear

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Re: USB battery
« Reply #22 on: October 15, 2005, 09:50:43 PM »

Have a gander at a datasheet for a typical 9V battery:
http://www.duracell.com/oem/Pdf/new/1604_US_Ultra.pdf

Pay special attention to the "discharge curves" section. There's not a linear relationship between load current and service hours. So it's not strictly correct to say that paralleling 2 batteries will double the run time.

The thing that is getting me is that 9V are about the worst possible choice for your application. You are forced to dissipate 4V* your load current in the regulator. That's just money you are throwing away. Make a 7.5V pack from 5 D cells if you want longer life. If you use rechargeables, they only have a 1.2V nominal voltage, so you'd need a 6-cell pack to get 7.2V.

9V batteries are specifically targeted to low load current applications (think transistor radio).
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BalefireX

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Re: USB battery
« Reply #23 on: October 15, 2005, 09:59:03 PM »

The thing that is getting me is that 9V are about the worst possible choice for your application. You are forced to dissipate 4V* your load current in the regulator. That's just money you are throwing away. Make a 7.5V pack from 5 D cells if you want longer life. If you use rechargeables, they only have a 1.2V nominal voltage, so you'd need a 6-cell pack to get 7.2V.

Agreed.  Everyone has a 7.2v rechargeable battery pack laying around somewhere, steal it from your little brother's remote control car for a trial if need be.
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trials_modder

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Re: USB battery
« Reply #24 on: October 17, 2005, 07:53:24 PM »

Yes, but then I have the problem of recharging the rechargable battery in the USB battery charger.

I think the USB charger is recharging the Zen micro, then drops to a certain current that triggers the Zen to think its plugged into an active computer and start its fancy glow-while-charging feature. Will two 9V at say 7V produce more current than a full power single 9V?
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BalefireX

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Re: USB battery
« Reply #25 on: October 17, 2005, 10:55:16 PM »

Batteries aren't magic eternal energy sources.  If you DONT go rechargable, you will have to buy new batteries every time you recharge your device.  Recharge it 4 or 5 times, and you've already spent far more for 9v batteries than you would have on a rechargable pack and charger.
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trials_modder

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Re: USB battery
« Reply #26 on: October 18, 2005, 10:00:16 AM »

Yes, but I don't know if the NiMH 9V rechargables i got are == powerful to a normail 9V. Maybe I'm charging it wrong, but it doesn't last nearly as long in other applications that the 9V alkaline.

p.s. this topic is on FIRE
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BalefireX

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Re: USB battery
« Reply #27 on: October 18, 2005, 10:12:45 AM »

A NiMH 9v cell (ie, the size you'd put in a smoke dectector) is going to have less capacity than an alkaline 9v cell of the same size.  This is why we are suggesting a 7.2v pack made from 6 x 1.2v NiMH AA size batteries, like one you would use on a remote control car.
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trials_modder

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Re: USB battery
« Reply #28 on: October 19, 2005, 10:20:07 AM »

I've had a remote control car before, but never a battery pack. How would I keep one of those charged?
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BalefireX

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Re: USB battery
« Reply #29 on: October 19, 2005, 10:47:45 AM »

They come with a wall charger.  You'd charge it before you wanted to use it.
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