Step down 18v power tool battery to 12v

Support Product Questions
1

I’m new here so maybe dumb question but

I’m after a step down buck regulator to reduce from 18v power tool battery to 12v-10a.

I want to pull the regulator inside an old battery charger so size is a issue.

Could someone recommend the best buck regulator. I am looking at the
DC-DC Step Down Buck Converter (15~24V to 12V/12A)

Thank for the help

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Hey there, @Graham317900, and welcome to the forum. Glad to have you here.

This would be the right sort of module if you were going to be doing this work, buuuuut

I’d want to confirm your battery details and chemistry before saying if this would be a good match. Could you provide a couple more details of your battery?

I’d also say that while it’s theoretically fine, at 12 V10 A, that’s going to get hot, especially in a cramped charging enclosure so you’re really going to want to make certain you’re dissipating that heat correctly. This unit has a thermal pad and I’d recommend you use it.

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Hi

Thanks for your reply.

The battery is a Ryobi 18v lithium. 4/5ah

I was going to use this setup to power 12v fridge and have a handy 12v power for when I needed it.

I’ve seen ready made ones but I like to make my own..

So you would highly recommend attaching a heat sink,

Thanks again Graham

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Hi Graham
A bit of an add on here from Jane’s request would be info on that fridge. The Ryobi battery might be struggling a bit to give you any meaningful operating time.

An important number would be the inrush or start up current requirement. A fridge by its very nature will stop and start up pretty frequently and this could be pretty hard on any battery. I think a 12V fridge would commonly be used in a vehicle, motor home or caravan etc where the battery is charged while the vehicle is moving and runs the fridge over night when stopped. This battery could be between 100Ahr or even 200Ahr to run the fridge between charges.
Cheers Bob

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Hi Graham,

Sweet project!
A quick aside, if the fridge is also rated for operation up to 24V (most camp fridges are), you’ll be able to run it directly from the battery itself.

Good point Bob, but on the contrary, if the fridge is mostly full (and well insulated), and contents are cooled - the smaller battery ought to keep it at temperature for a good while. But too many variables to make any promises.

Liam

6

Hi Liam

There are a hell of a lot of “ifs” in this lot.
Like:
“IF” the fridge is of the compressor type the start up or inrush current could be many times the running current, Possibly up to 10 times.
But
“IF” the fridge is a 240VAC, 12VDC and gas type it will probably have a heating element (yes it gets hot to make the fridge cold) in it which would have no where near the compressor inrush but there will be some as the cold resistance of a heating element will be quite a bit less than the operating resistance.

The size of this fridge should also be considered although this would be reflected in the power requirements.

Don’t forget the battery is relatively small @ 4/5Ahr.
Cheers Bob

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