# I want to convert a battery operated device to work from power outlet without electrocuting myself

#### Deem

Joined Jun 8, 2018
3
Hello.

I bought an electric string trimmer (weed trimmer) without batteries on a yard sale with the intent to convert it to a corded device. I know little of electronics and need your help.

My initial questions are:
1. Would this work at all?
2. What kind of transformer would I need if the device was originally powered by 18-Volt NiCad battery (Model BP91001)?
- Should it be 18v output AC to DC or just AC?
- How can I figure out the amps of the transformer?

#### crutschow

Joined Mar 14, 2008
25,446
1. Would this work at all?
Probably.
But it could add a fair amount of weight.
2. What kind of transformer would I need if the device was originally powered by 18-Volt NiCad battery (Model BP91001)?
- Should it be 18v output AC to DC or just AC?

It should be a switching type AC to DC supply to minimize size and weight, such as used to power laptops, but likely larger.
- How can I figure out the amps of the transformer?
Measure the current using a DC power supply.

Determine the running time specification using the battery and calculate the current by dividing the Ah of the battery by this time (in fraction of an hour).

#### Sensacell

Joined Jun 19, 2012
2,598
You can, but it will cost more than a new weed trimmer.

Do it only if the exercise pleases you, not to "save money"

#### ArakelTheDragon

Joined Nov 18, 2016
1,350
Or just buy a new battery of similar type. You can use 1 battery instead of 2.

#### Deem

Joined Jun 8, 2018
3
You can, but it will cost more than a new weed trimmer. Do it only if the exercise pleases you, not to "save money"
The new trimmer of this type costs around \$90. Surely it can not be that expensive to attach a transformer, can it?

#### MrChips

Joined Oct 2, 2009
21,890
Go to a second hand store and find a 18-19V laptop charger. Not much to lose if it doesn't work.

#### Deem

Joined Jun 8, 2018
3
Go to a second hand store and find a 18-19V laptop charger. Not much to lose if it doesn't work.
That's is my plan for now. I already have a couple with these specs:
Type: AC to DC Standard
Input: AC 100V - 240V 50-60Hz
Output: DC 18v 3 amp max

#### MrChips

Joined Oct 2, 2009
21,890
That's is my plan for now. I already have a couple with these specs:
Type: AC to DC Standard
Input: AC 100V - 240V 50-60Hz
Output: DC 18v 3 amp max
Try it and see if it works. Get the polarity correct.

#### KeepItSimpleStupid

Joined Mar 4, 2014
4,224
I did the following. I looked at a NiCd cell about the same MaH and got this datasheet. https://media.digikey.com/pdf/Data Sheets/Panasonic Batteries PDFS/Ni Cd Catalog 2002-03 v1.pdf#page=67 the pack is going to be a series connection of similar cells rated at the same MaH at 1.2 V.

So, that's like 2 hrs at 1.2 A looking at the discharge curves.

So, a rule of thumb 4x-5x current wise a laptop charger would seem to be ideal. e.g. http://www.powerstream.com/AC-A0407.htm

You could probably devise a way of putting the pack on your waist

So, anyway, Mr. Chips idea is a pretty good one. Batteries will generally allow a large surge current.

I bought a 3/8 VSR drill with adjutable torque settings, Makita drill a long time ago and it's been my "go to drill" every since. I got no case and a charger. I generally have two pscks.

NiCd is falling out of favor and I've been replacing hem with NiM-H especially in phones for greater capacity. NiCd chargers seem to work fine. I even got 5-7 year life on a phone.

For the BIG JOBS, I have a Dewalt stud and Joist Drill. The best use of that is indeed stud and joist. e.g. drilling holes in the footer with a flex drill bit for low-voltage wiring.

Then there is the Dremel tool.

#### ArakelTheDragon

Joined Nov 18, 2016
1,350
Trim for 8 hours 1 day and you will never need a trimmer again.