Re: Alkaline batteries in parallel?
- From: Bob <bob9@xxxxxxxxxxxxxx>
- Date: Fri, 25 Jan 2008 07:56:23 -0800 (PST)
On Jan 24, 5:21 pm, George <gh424NO824S...@xxxxxxx> wrote:
I just bought a dirt-cheap wireless lapel microphone with
transmitter and receiver. But, I think there may be a problem with
battery life.
The transmitter is powered by a 9V alkaline battery, and I rigged it
up to test the current draw, which was 38 ma. The receiver is
powered by a single AAA battery, and it draws 52 ma. In both cases,
that's with the power-on LED indicators disconnected to save power.
Back in the day I've used an external battery pack to extend the
life of a digital camera which didn't operate well on rechargeables.
The pack was just a Radio Shack holder for four C cells, plugged
into the AC jack on the camera, to take the place of the usual four
AA's. The C's lasted a long, long time, at not much more cost than
four AA's, but at the cost of "wearing" the battery pack in some
position.
With the wireless mic, there may be times when I want to use it over
an extended period of several hours without having to stop and
change batteries, and without having to wonder if it's gone dead.
In the case of the receiver, I could attach a twin AA holder to the
back, and power it from that, but with the holder wiring modified so
that the batteries are in parallel. That would give me two AA's in
the place of the one AAA, which should significantly extend the
life.
The transmitter is a bit more of a problem. The best I can think of
is to mount two external 9V's on the back, probably with tape, and
wire the connectors together in parallel, possibly also leaving the
internal 9V still connected, which would give me three 9V's in
parallel.
Well, I have a couple questions:
1. Is there a better way to do this?
2. Is connecting the batteries in parallel going to cause any
problems? They will remain connected to each other even when the
power switch is off. Will the batteries do bad things to each other
connected that way for extended periods even when no current is
flowing to the external circuit?
I don't know yet how much voltage drop the devices will tolerate and
still operate. I'm testing that now. The answer might give me
other options.
Why don't you run the reciever from a mains power supply?
A single D cell would be better than paralleling two AA's.
For the tx there are lithium PP3 batterys with more than
twice the capacity of a typical alkaline PP3. A few suppliers
have PP3's they specifically recommend for long life in
radio mikes.
Personally I prefer rechargable batterys. Since I have a suitable
charger (and take precautions just in case they do catch fire
while on charge) I'd use three 18650 cells and a couples of
diodes to drop the voltage a bit as 11V from a full charge
might be a bit high, a little polyfuse in case the wires get
shorted and insulate the whole thing in heatshrink.
That would not be much more bulky than a single extra external PP3.
2200mAH 18650 cells would in theory give 58 hours at 38mA drain.
18650 cells are used in most laptop battery packs, cheap and
high capacity but you have to charge then properly and not short
circuit them so I'm allways slightly hesitant to recommend them
for projects.
Bob
.
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