18v Power tool battery?

droffset · Posted: Wed May 03, 2017 3:12 am Post subject: 18v Power tool battery?

Hello awesome people.
Does anyone have an opinion on using an 18v rechargeable tool battery as a power supply?

It seems like you should be able to put together a regulated +/- 12v supply from one of these and have enough juice to run a small system for a while.

It would give me a chance to 3D print a housing, always looking for an excuse to 3D print something...

What do you think?

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batt18v by S G, on Flickr

Grumble · Posted: Wed May 03, 2017 3:59 am Post subject:

The big advantage of using batteries as a power source is the absence of hum (line frequency) and/or noise from other equipment on the same power line.
For the power supply of a "better" synthesizer its a big nono to use switching power supplies, because they are inherently noisier as an analog regulator.
That said: using a 18 volt accu it is only possible to construct a dual voltage power-supply when you use a switching power supply (boost).
So, is it possible to use a 18 volt battery to construct a +/- 12 volt power-supply? Yes, but only if you use a switching regulator and you have to do a lot to get rid of the noise.

PHOBoS · Posted: Wed May 03, 2017 9:27 am Post subject:

For a -/+12V you would indeed need to turn it into a switching supply.
However, since they contain seperate cells inside you could probably
use it as a -/+9V supply.

droffset · Posted: Wed May 03, 2017 10:41 am Post subject:

This is really about a fear of mains voltages.
The answer may be to just purchase a synth power supply and make some modules already.

That said:

Grumble
Great explanation, thanks. Those 7912s will have to make themselves useful some other way. Smile

PHOBoS
It never occurred to me to open the thing up, very cool idea.

In that case though, what about rechargeable 12v Lithium Ion batteries? I think I'm going to try it.

PHOBoS · Posted: Wed May 03, 2017 4:08 pm Post subject:

One thing I was just thinking about is that if you would use a 18V battery for a dual 9V supply it will most likely drain the
internal cells differently since modules often don't have a symmetrical current draw. I don't know if this could cause any
problems with charging or if it just evens out since the cells are connected in series.

2 12V Lithium Ion batteries should work fine but make sure they have some decent protection and a good
charger as they can explode, although I think they are pretty safe these days.

If fear of mains voltages is the problem you could also go for a supply using an AC wallwart, as I have done for my euro-rack modular.

gdavis · Posted: Wed May 03, 2017 5:20 pm Post subject:

The voltage of a battery will drop as it is discharged. A fully charged 12V battery may put out more or less than 12V fully charged (depending on chemistry) and will gradually drop throughout it's charge range. This will affect the synth if some sort of regulation isn't used. So unless you just want to power some sort of noise maker or something where stability isn't necessary, I wouldn't power directly from any battery without regulation.