Re: 9v battery min voltage

chuck wrote:
ehsjr wrote:

lerameur wrote:

chuck wrote:

Well, you will have to lower the supply voltage to your project by steps
to determine the approximate voltage at which it fails to operate
reliably (or at all) and then set your warning light (comparator) to a
voltage somewhat higher than that.

Chuck



yes thats good, thanks


No - not good. The project may keep working, but
discharging the cells too far risks damaging them.
When the cells discharge to 1.0 volts per cell,
it is time to recharge, regardless of whether your
project is working.

Watch out for "9 volt" rechargeable batteries.
They are really 7.2 volts. There may be
exceptions to that - I don't know.

Ed


Ed has pointed out yet another design parameter. The problem is not that the batteries would be damaged:

The problem most certainly *is* that cells may be damaged.

See "Discharge Termination" in the Energizer
Battery Application Manual, pages 14 - 16.
http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

Ed



every charge/discharge cycle decreases battery capacity somewhat.

Discharging below 1.0 volts causes greater decreases.

One's purpose in life, however, is usually not the preservation of battery capacity.

As the designer, you get to choose whether you want to keep the batteries for as long as possible, at the price of frequent recharges; or you want to recharge less frequently because it's a pain, with the knowledge that your batteries might not last for as many recharges? as many years? etc., etc.

Electronic design is full of tradeoffs. Haven't even mentioned alternative battery chemistries, charging techniques, voltage regulation, etc., all of which will affect battery life; and the appropriate cost-benefit analysis. ;-)

Chuck

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