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# what transformer to power my 24v drill with 240v mains power? Answered

i use a dewalt 24volt allday at work and every now and then it would be handy to be able to use 240volt mains mainly when i forget to charge the batterys.i have a collection of old unuseable batterys to use as a body but cant work out what transformer and or circuitry it would need. any ideas?
cheers dave

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think il just buy a cheap 240v sds drill!!! lol!!! or just remember to charge the batterys in the first place.

according to the dewalt site it has a power output of 300 watts
300watts/24volts =12.5amps if im correct!!!

You are correct !
And now into a large TR unit that costs £93 to buy outright.

Two 6lb Triad F-400U control transformers will deliver the Power you need.

im not sure what the current draw is. its not stated on the drill or the battery.il have to have alook on the dewalt site.

Potentially, its very high, 20-30 A or maybe more when you're flogging it.

IF it runs on less then 1.5 amps here is an unregulated simple
2 amp Transformer Rectifier circuit schematic for you.

A

How does an 18VAC output from the transformer get rectified up to 24VDC? Especially when there will be a slight voltage drop at the rectifier.

As in "Why does 18 x 1.414" = 24 (only on no load), or if C is very big and I is modest.

As in 18VAC going into the rectifier will end up being 16.5VDC coming out. right!?

Sorry 18 vac x 1.414 = 25.5 vdc - 1.5 vdc = 24 vdc

A

Depends on the load, the capacitor and the transformer. On NO load, the open circuit voltage of the transformer is likely to be considerably higher than the "plated" output - the cheaper the transformer, the higher the output volts.

For something like this, I'd expect around 30V Open Circuit from the transformer.

After rectification (OK, drop 1.2 V on full load), if there is no load, the voltage on the cap will be transformer (AC volts x 1.414)-1.2V
As load increases, the voltage across the capacitor will ripple more and more. If C is very large, then V won't droop as much as the load increases.

I would assume the drill will be putting a considerable load on the circuit so an 18V transformer wouldn't be enough.

I have never come across the ideal 22v transformer and that assumes
a normal mains supply which could also be 15% lower.

Ultimately the very best way would be using a standard 24VAC
transformer 24 x 1.414 -1.5 = 32.5VDC supplying a LM317 regulator
to hold the output @ 24VDC where Davey's drill wants to run.

There is a concern of exceeding the mains by +15% and breaching
the maximum 40vdc supply voltage.

All this because sometime our man forgets to charge his drill :-D

What's the maximum current it can draw ?