6 AA vs 8 AA

Put a dummy cell in the 8-pack and get 8.4v. Either buy on (Google) or DIY with some dowel, a couple of pins and a piece of wire.

But don't try and charge it!

Sounds like a crap product then unless it records the information by hacking chunks out of a large tree trunk. Decent GPS logging devices should last a few days of continuous use.

How much longer?

I guess the small PP3 9v batteries are about 200mAh so you should get

Diodes in series with override switches for low battery might work but it is hard to predict how tetchy the device will be about >9v.

It might extend the lifetime a bit but it really depends on how well the device tolerates overvoltage and undervoltage. You need to know what current the thing draws and at what voltage it stops working.

Freshly charged the terminal voltage is something like 1.4v per cell so

Some moderately high current devices can be awful on rechargeable batteries and only work properly on alkaline primary cells. The low voltage protection circuit triggers early on NiMH - long before the cells are exhausted. It is very annoying. Typically one weak cell in a block of 4 or 6 scuppers it and the others will slowly kill it.

A typical silicon diode drops around 0.6V, so a full 8-pack feeding the logger via such a diode should give a pretty accurate 9V.

SteveW

not really. at any current it can be up to a volt.

so a full 8-pack feeding the

A fresh alkaline cell has a voltage of over 1.6 making that 9.6 too. But then fresh NiMH are about 1.3v. ;-)

I'd be most surprised if it caused a problem.

Ive used 7 Nicd to replace PP9s at least.

Thats a nominal 8.4v..nearly ten on full crack going down to around 6 or

Anyone wishing to convert from dry cell to rechargeable should browse te online model shops where chargers and packs of all sorts are available

- and replacing the actual battery connector with a suitable plug is a cinch..

Almost certainly not. There is always a slight risk, but many things that also work off car or mains supplies are pretty accomodating on voltage. What they don't like is reverse voltage and large spikes.

Brian

The logger can't be taking much current, if it runs for 2 hours on a PP3.

SteveW

What about a zena diode and a transistor to set the voltage.

...and what you get with one hand you are taking away with the other.

It is a bit nonsensical to add in an extra cell for more power and then throw away most of that additional power dissipating in a diode or any sort of linear regulator

or even a Zenner diode

or even a zener diode B-)

Or even a Zener diode.

Zener warrior diode?

Or even a Zener diode?

Zena warrior, dude.

I'll stick with Zena - it's the leather...

Isn't it Xena?