Hello group,
I have a Bluetooth serial plug, working with an AC converter that outputs 5V
800mA.I would like to use the device without the AC supply by using batteries. A Google search didn't get me nowhere. Can someone help me with this ? Ideally, I would use the smallest possible rechargeable battery with an autonomy of 10 hours.
Many thanks
Jacquelin Hardy
Hi, If you connect four 1.2 volt NiCd or NiMH batteries in series(end to end) you will have 4.8 volts which will probably work. If the rating per battery is 600mA hr( you can get better ones) it will theoretically run for one hour with 600mA drain or a bit less with 800 mA drain. To get 10 hours of runtime at 800 mA you will need a battery that will output 800 mA for 10 Hrs. That works out to 8000 mA. For that you will need an 8 amp hour battery. You will have a problem finding such a thing in a small package. Maybe someone else has a suggestion.
Rod
It's tough to get 800ma for one hour out of a 800mAH battery. They're rated for longer discharge times where they are more efficient. I'd double your numbers to allow for some degradation over time. Fully charged batteries can be 6.4V, although I've seen more. Fully discharged will be closer to 4.0. I think I'd do some regulation.
Another issue is that the average power drain of the device may be a LOT lower than the marketing/regulatory number written on the supply. You have to measure it. If it's really drawing that much current, you should look into alternative solutions to your problem...or get a wheeled cart to lug the batteries around. mike
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The Bluetooth won't draw 800 mA - you can't use the power rating of the AC adapter to figure out the battery size needed. According to the datasheet here:
Assuming 200 mA for 10 hours, a pack made up of 4
2100 mah AA cells seems like it might work.Ed
The easiest way is to steal 5v from a keyboard, joystick, mouse, or USB socket.
for batteries you're going to need want something like a 7.2V battery and a
5V regulator.
it's probable that the device doesn't use all of the 800ma that's available from the converter. so it's be hard to pick the right battery capacity without measuing it's power consumption first.
Bye. Jasen
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