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

Thread Starter

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?
DC, since it was originally powered by a battery.

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).
 

Thread Starter

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?
 

Thread Starter

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
 
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.
 
Top