9 Volt battery power supply.

[Squire99]

The last time I did anything with electronics was to build a Mullard Stereo amplifier many many years ago! So bear with me. I need to power an LED torch (UV) for 12 hours.* It is currently powered by six 1.5 volt rechargeables which have a run life of three hours before dimming. I was hoping to use maybe a drill battery ( for Bosch/ deWalt) of 18 volts output and voltage split. Anyone got any suggestions how to do it or alternative method/s.
* It is for a moth trap.

 

[rjenkinsgb]

The torch will already include the LED current control, so all you need is something that provides around 7 - 8V, roughly mid range battery voltage.

A small switch mode "buck converter" power supply module would do the job.
Something like one of these from ebay should do, set to around 7.5V before connecting to the torch.

Pardon our interruption...

That will then run from anywhere from 11 or 12V up to 30V or more. An "18V" power tool battery would be fine.

You can buy battery holders for some types on amazon or ebay, intended for adapting tools to take different batteries; or if you have a 3D printer some designs can be downloaded from such as Thingiverse. I've designed one to use the batteries Aldi sell in the UK.

 

[rjenkinsgb]

However the voltage on the industry-standard 9-volt battery is, obviously, 9 volts.

er, No. That is a common misconception.

Dry cells start out at somewhere near the nominal rated voltage, but the voltage steadily drops in use, over the life of the cell/battery.
The end point when they are considered totally flat is at around 1V per "1.5V" cell; 6V for a 9V battery.

And also the OP stated his torch was working on rechargeables, which are nominally around 1.2 - 1.3V per cell, so mid range in that graph.

 

[JimB]

Sorry rjenkins, but you just spent time replying to a spammer.
The blue word "voltage" in their post is a link to a website.

JimB

 

[rjenkinsgb]

Doh..

 

[Squire99]

Many thanks R Jenkins - advice much appreciated. Just one more thing please - I am assuming that the middle two terminals on the battery are back to the drill to a low voltage cut off? Should I be replacing the drill control with an in line one after the buck converter?
Many thanks, Squire 99.

 

[rjenkinsgb]

I am assuming that the middle two terminals on the battery are back to the drill to a low voltage cut off?

What battery are you planning to use? Each make used different connections.
Some have the battery protection built in, others do not.

If the low voltage cutout is external, it's inline with the power connections. Auxiliary battery terminal are usually for such as temperature sensors or capacity coding, on typical large "block" type packs.