Paralleling 9V batteries?

On Tue, 21 Dec 2004 18:27:51 +1100, T. Ryan wroth:

If the batteries are ordinary alkaline or carbon/zinc types, then paralleling with no extra circuitry is perfectly all right with no potential problems regardless of their state of charge.

If the batteries are rechargable, NiCad or Lithium, they can be paralleled with no extra circuitry if both batteries are new and both are charged to the same state before being paralleled.

Jim

Not! I second the six standard elements approach =)

Two diodes will do the trick. But you'll loose voltage (=>power=>efficiency)...

/Anders

They can also have more voltage drop than 0.2V when large currents pass. For ex., an SR304 rated 40V 3A drops about 0.43V with 3A of current.

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I'd like to add that Schottky diodes have significantly higher reverse leakage current. No such thing as a free lunch. :)

A 'good' way is to add a a diode (or "rectifier" depending on current used) in series with each battery, so the higher voltage (and more fully charged) battery will provide the most current, and no current (other than a little reversed-bias diode leakage, insignificant) will flow from one battery to the other. If near-full battery voltage or high efficiency is important, the

0.6V drop of regular silicon diodes can be reduced to about 0.2V by using Schottky diodes.

If this is a one-off project, the above should be fine, but if it's a production product I would think the solution is a bigger single battery (I have never ever seen a product that had two batteries in parallel) or string of cells in series, such as six AAA or AA 1.5V cells.

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I need longer battery life than a single 9V provides.

What is the conventional wisdom on wiring two or more in parallel, particularly since any two could not be expected to have exactly the same charge?

Advisable or not? If not, any way around it by adding certain passive components.

Thank you,

Tom Ryan

Batteries connected in series last longer though you're getting less Ah. The parallel connection drives current through each other when not operating and this tends to destroy them earlier. You though need to take into account though the costs of the 6 AAs against the 2 9V's.

Hardly easier to change.

You can get battery holders that hold 6 AA cells and use the same snap connector as a 9 volt cell.

Philmore BH3634, $1.19 at Frys (or cheaper at All Electronics).

Radio Shack, for some reason, only sell ones that have 4 or 8 cells.

Mark Zenier snipped-for-privacy@eskimo.com Washington State resident

Ever take apart a nine volt battery? It is six little cells wired in series. Nine volt batteries are costlier by the watt-hour than buying cells and putting them together in series yourself. Any cells from AAA to D offer better power to the dollar than the nine-volt package.

can.

use

in article snipped-for-privacy@f14g2000cwb.googlegroups.com, snipped-for-privacy@yahoo.com at snipped-for-privacy@yahoo.com wrote on 12/25/04 10:28 PM:

Yeah, but the cost of the sockets detract from the savings.

I read in sci.electronics.design that snipped-for-privacy@yahoo.com wrote (in ) about 'Paralleling 9V batteries?', on Sat, 25 Dec 2004:

NiCd batteries have seven cells. 7 x 1.2 = 8.4, which is considered near enough to 9 V for marketing.

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And the reason that 9 volt batteries are not being used in new designs is that AA cells offer significantly better power density.

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I've seen 7.2 and 8.4V versions, but the 7.2, made from six slim cylindrical cells is more common. The 8.4 is seven button cells.

It's pretty much a waste though, to power a 5V system from 9V, especially if it draws any significant current. Switchers help, but there are low current ranges where the linears are more efficient than the switchers.

Not the ones I've owned - they were 7.2V, made from 6 cells. But then again, I haven't bought a new 9V NiCd in a few years since the few things I own that need a 9V battery, should have alkalines installed due to the low drain nature of the products, such as alarm clock back up, DMM batteries, smoke alarms, etc. Even the newer Fluke DMM's now use AA's.

Only once.