Alkaline batteries in parallel?

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?

  1. 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.

Reply to
George
Loading thread data ...

Usually if you parallel batteries of identical type the internal resistance is enough to prevent them from "doing bad things to each other". You could rig up a belt pack to supply the needed voltage at greater capacity.

Tom

Reply to
Tom Biasi

Don't mixed used and new batteries when paralleling. Use all new identical batteries (same size and brand). No problemo. I took apart a 9 volt battery once. It has six individual cells, wired in series. It's kind of cute, they look just like the A type batteries but much smaller. Cute, but inefficient. The nine volters cost far more per unit energy than a single cell "battery" (misnomer, a single cell is not a battery of cells). I calculated it and you get way more bang for the buck (calculted per joule) with single cells. You were contemplating weighing yourself down with more nine volt batteries in parallel, but you would do better in my opinion to put six single cells in series, AAA or whatever you want. Clip it on your belt and run some 20 or 22 gauge wire to the mic. Get a 9 volt connector clip to connect to the mic.

Reply to
gearhead

You might want to try a 9V lithium battery.

formatting link

Ed

Reply to
ehsjr

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

Reply to
Bob

Connecting batteries in parallel isn't a good idea, if you do it make sure they are with the same date code and both new and replaced as a pair.

If you are going to strap batteries on the outside . . . go to radio shack and get a holder for 6 AA batteries with a 9V snap on the case and use that. That would increase the capacity by about 3.5X

A 9V battery should last a good while in the transmitter.

The alkaline 9 V should have a capacity of about 700 milliamp hours and at 38 ma that's 18 hours . . .

A single AAA has a capacity of about 1.25 amp hours or should last around 24 hours . . .

Maybe the switches are being left on?

Reply to
default

-snip-

Thanks very much for all the suggestions. I had to interrupt my battery-life test, but at 15 hours both the transmitter and receiver were still working. With the power on, the 9V was at 5.47V and the AAA was at 1.20V.

What I was trying to find was the voltage at which the circuits stop working, since of course that could have a substantial impact on how long the batteries will last. And so far the numbers are better than I expected.

I'll finish the test, but I think if I need better life than provided by alkaline batteries, I think using lithiums is the best option rather than adding on external packs.

Reply to
George

Yup, those are AAAA cells --- as far as I know, they're only ever found inside 9V batteries...

--
   Wim Lewis , Seattle, WA, USA. PGP keyID 27F772C1
Reply to
Wim Lewis

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.