# 22v DC to 12v DC of Charger

#### piBoss

Joined May 22, 2021
9
Okay, I'm a EE who never worked in the industry and finished school in 1988 so please keep the laughter to a minimum lol.

All is DC
I have a battery charger from a Hoover Vacuum that puts out 22v, 2A. I desire to use it as a 12v charger. Is this as simple as placing a 5 Ohm resister in the positive output line or am I missing something?
I ask because of never hearing about the use of such a high Ohm resister and because of my introductive statement.

Thanks everyone and it's nice to meet a new group!

#### ElectricSpidey

Joined Dec 2, 2017
2,436
The simple answer is...no and yes. (compound question)

But, I have two questions.

1. How did you come up with the 5 ohm value?
2. Why do you think 5 ohms is a high value resistor?

#### BobTPH

Joined Jun 5, 2013
6,546
Battery chargers are more complicated than that.

We need to know what battery chemistry and capacity for starters.

bob

Last edited:

#### ErnieM

Joined Apr 24, 2011
8,356
Well... probably not if you have a 12V battery and want to put the resistor in series with the 22V and the battery to limit the charge current to 2 amps. What's gonna happen is the battery is still getting the 2 amps at 12 volts so it continues to charge up until all the magic smoke and other nasty stuff comes out.

If you have an inline series charge regulator meant for 12V then again I doubt this simple thing will work as the smoke this time may come from the charger.

#### dl324

Joined Mar 30, 2015
15,536
Welcome to AAC!
I have a battery charger from a Hoover Vacuum that puts out 22v, 2A. I desire to use it as a 12v charger. Is this as simple as placing a 5 Ohm resister in the positive output line or am I missing something?
This is a common bad newbie idea; another is to try to use a voltage divider. Ohm's Law tells us that the voltage dropped by the resistor depends on current through it, so this is almost always not a proper way to get a stable 12V.

A voltage regulator would be the most obvious solution. Before we can answer your question, we need to know the load and voltage regulation requirement for whatever you want to power. If it's actually to be a charger, we need even more information.
I'm a EE who never worked in the industry and finished school in 1988 so please keep the laughter to a minimum lol.
For my own edification, where did you get your degree?

#### Ian0

Joined Aug 7, 2020
7,513
Is this as simple as placing a 5 Ohm resister in the positive output line or am I missing something?
Yes, but you must remember to turn it off as soon as the battery has charged. If not the type of disaster that will ensue is dependent on the battery chemistry - it can range from ruining the battery (Nickel types) making loads of hydrogen which explodes at the first spark (lead-acid) or burning your house down (Lithium).

#### crutschow

Joined Mar 14, 2008
32,089
Summary questions:
What type of battery do you want to charge?
Do you want to charge at the full 2A?

#### piBoss

Joined May 22, 2021
9
The simple answer is...no and yes. (compound question)

But, I have two questions.

1. How did you come up with the 5 ohm value?
2. Why do you think 5 ohms is a high value resistor?
1. The 2A x 5-Ohm = 10v drop from 22v over the resistor yielding 12v.
2. I looked at buying one and the mentioned uses were high voltage components, may very well have drawn an incorrect conclusion, night be fine.

#### piBoss

Joined May 22, 2021
9
Battery chargers are more complicated than that.

We need to know what battery chemistry and capacity for starters.

bob
I didn't know the complexities. I'm was wanting to tie three-four power supplies (of 12v) together in parallel to use for;
1. Charging a car battery 2. For powering a car CB.

#### piBoss

Joined May 22, 2021
9
Battery chargers are more complicated than that.

We need to know what battery chemistry and capacity for starters.

bob
A new card battery and was going to power a car CB from placing 2-3 12v power supplies together in parallel. The 4th one is at 22v and thus was thinking I could bring it down to 12v. As I said..I B New (newbie).

#### piBoss

Joined May 22, 2021
9
Well... probably not if you have a 12V battery and want to put the resistor in series with the 22V and the battery to limit the charge current to 2 amps. What's gonna happen is the battery is still getting the 2 amps at 12 volts so it continues to charge up until all the magic smoke and other nasty stuff comes out.

If you have an inline series charge regulator meant for 12V then again I doubt this simple thing will work as the smoke this time may come from the charger.

Is the regulator to keep the voltage at 12v. So s power supply, say for a cell phone, is "matched" to the load and load capacity?

#### piBoss

Joined May 22, 2021
9
Yes, but you must remember to turn it off as soon as the battery has charged. If not the type of disaster that will ensue is dependent on the battery chemistry - it can range from ruining the battery (Nickel types) making loads of hydrogen which explodes at the first spark (lead-acid) or burning your house down (Lithium).
In other words, power supplies, say for AA batteries, monitor how full they are so as to taper down to off as the batteries approach full charge? And therefore this would be like putting a locked-on gas station nozzle in your tank and walking away... Poof go the batteries if not monitor for full capacity?

#### piBoss

Joined May 22, 2021
9

#### Ian0

Joined Aug 7, 2020
7,513
In other words, power supplies, say for AA batteries, monitor how full they are so as to taper down to off as the batteries approach full charge? And therefore this would be like putting a locked-on gas station nozzle in your tank and walking away... Poof go the batteries if not monitor for full capacity?
I guess so - over here the nozzles don’t lock on.
But it would be more like staying right next to it as it overflows and lighting a cigarette.

Have a look at SGS-Thomson’s PB137 IC (if it is lead-acid that you are charging) for an easy solution.

#### piBoss

Joined May 22, 2021
9
Welcome to AAC!
This is a common bad newbie idea; another is to try to use a voltage divider. Ohm's Law tells us that the voltage dropped by the resistor depends on current through it, so this is almost always not a proper way to get a stable 12V.

A voltage regulator would be the most obvious solution. Before we can answer your question, we need to know the load and voltage regulation requirement for whatever you want to power. If it's actually to be a charger, we need even more information.
For my own edification, where did you get your degree?
Cleveland State University. Am a member of Tau Beta Pi Engineering Honor Society (had to boost my esteem a little after such an introduction lol)
I guess so - over here the nozzles don’t lock on.
But it would be more like staying right next to it as it overflows and lighting a cigarette.

Have a look at SGS-Thomson’s PB137 IC (if it is lead-acid that you are charging) for an easy solution.
Thanks, shed I will. Yeah I guess the locked-on mode faded away in the 80''s.
Here's the thing: I do enjoy learning by hands on, have tons of power supplies and was just wondering if I could put some in parallel to charge a car battery and maybe power a car CB. And I have one power supply that puts out my mentioned 22v 2A and was going to bring it down to 12v to put in the parallel group.