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# Looking for a specific transformer

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#### Electric-T

Jun 4, 2017
212
you cannot put 10 - 0V at 10A through a potentiometer it will smoke instantly
you will need to use a DC-DC buck converter
Is the amperage too high?

#### BobK

Jan 5, 2010
7,682
Potentiometers are not power devices, they are not used to reduce voltage at anything beyond milliamps. At typical potentiometer is rated at 1/2 W.

You still haven't stated what battery chemistry you are trying to charge, so I will assume lead acid. These require roughly 14V for charging.

If you start with 30V and reduce it to 14V with anything other then a switch mode DC to DC converter (buck converter, as davenn called it), then, at 10A the potentiometer would have to drop 16V at 10A. That is 160W. Think how hot a 100W light bulb gets, now multiply that by 1.6. You will not find a 160W potentiometer. If you do, you will not be able to afford it.

But let's go back even further.

Can you tell us what you are trying to accomplish with a "variable voltage" battery charger? Have you wondered why you don't see "variable voltage" battery chargers commercially available? What is the problem you are trying to solve?

Bob

#### Electric-T

Jun 4, 2017
212
Potentiometers are not power devices, they are not used to reduce voltage at anything beyond milliamps. At typical potentiometer is rated at 1/2 W.

You still haven't stated what battery chemistry you are trying to charge, so I will assume lead acid. These require roughly 14V for charging.

If you start with 30V and reduce it to 14V with anything other then a switch mode DC to DC converter (buck converter, as davenn called it), then, at 10A the potentiometer would have to drop 16V at 10A. That is 160W. Think how hot a 100W light bulb gets, now multiply that by 1.6. You will not find a 160W potentiometer. If you do, you will not be able to afford it.

But let's go back even further.

Can you tell us what you are trying to accomplish with a "variable voltage" battery charger? Have you wondered why you don't see "variable voltage" battery chargers commercially available? What is the problem you are trying to solve?

Bob

#### kellys_eye

Jun 25, 2010
6,514
This thread is going to go on for dozens of pages if the OP doesn't start stating what he wants from his idea. One/two word answers don't cut it and we can't keep going by volunteering tiny bit after tiny bit based on 'nothing'.

Might I suggest you get yourself a list of requirements that you want from the charger - if you don't know what the requirements are (other than variable voltage which has already been explained as not being something chargers actually do) then you will never get a resolution to your problems.

We've offered loads of help so far but seem to be in the same place we were when we started!

#### Electric-T

Jun 4, 2017
212
This is purely an idea for a project. There is no immediate need for it. Im just exploring electronics. After studying theory for a while then experimenting on my breadboard, i figured it was time to try and design/build something. I
This thread is going to go on for dozens of pages if the OP doesn't start stating what he wants from his idea. One/two word answers don't cut it and we can't keep going by volunteering tiny bit after tiny bit based on 'nothing'.

Might I suggest you get yourself a list of requirements that you want from the charger - if you don't know what the requirements are (other than variable voltage which has already been explained as not being something chargers actually do) then you will never get a resolution to your problems.

We've offered loads of help so far but seem to be in the same place we were when we started!
I had an idea of a battery charger that charge 12v all the way down to those rechargeable 1.5v battery. Variable voltage is the only thing i want out of it. I understand amps have to be considered. I dont see why everybody seems to want more information i already got the answer i was looking for. I was asking if a certain transformer even exists. Turns out it does. Solved. This thread is going nowhere now haha. Thank you all for your input. Hopefully next time i post on here it doesnt turn into a mess like this has.

#### davenn

Moderator
Sep 5, 2009
14,261
Hopefully next time i post on here it doesnt turn into a mess like this has.

it wont if you are clear and precise in your information you give up front

i already got the answer i was looking for

OK then, we can close the thread

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