Electrical guru's....reverse a battery charger

Can your reverse a batery charger into a power inverter?
110V-12V for charger then somehow reverse it to 12V-110V?

Any info appreciated. Thanks.


(mod's, move thread if needed)

Not entirely sure I understand where you are coming from..

But the heart of a battery charger is a transformer.. Which works on the principle of coils, and can transform voltage up or down depending how it is wired.

So, basically the answer is yes. But it's slightly more complicated to do what you want than just "reversing" something.

Okay, a battery charger takes an AC source, and turns it into a DC source. On top of that, it employs a current limiter which makes sure the batter doesn't over charge.

The way it converts AC to DC is through a Bridge Rectifier. Typically 4 diodes intended to shunt electricity in one direction. Feeding DC current back through it would NOT create an AC phase.


If you want to take DC voltage and step it up to another DC voltage, then by extracting the transformer from it and using it by itself, you can step the voltage up, but you will not get an AC power source out of any of the components in a battery charger.


If you like building stuff yourself, then this is what you will want...
www.uoguelph.ca...

Otherwise, you'll want to buy a DC to AC Inverter pre-made.

... or, you could also have a little fun and try to make a commutator... but that's old school... VERY old school.

reply to post by adjay


Just to clarify.....

Battery Charger. 110V AC in, 12V DC out

Can it be reversed with minor changes (diodes, circuit change etc)
to act as an inverter (still a transformer) to hook 12V leads to a battery and get 110V at AC plug?

Thanks!

Not possible.
To go from AC to DC requires a very simple circuit, but to go from DC to AC requires a lot more electronics, simply "reversing" a battery charger will not do it.

Yep, thats what I thought you were asking. As per my first post, no, you won't get an inverter out of a battery charger.


An AC to DC transformer (like your battery charger) employs the use of
1: A transformer coil.
2: A Bridge Rectifier.
3: Capacitors to smooth the signal.
4: A current limiting circuit to stop overcharging.

The transformer is pretty universal, you can use it backwards, but all it's going to do is step the voltage up or down, sacrificing or amplifying amperage depending on how you use it.

The Bridge Rectifier works by allowing electrical current to move in only one direction. Think of it like a one way valve. You can push water back and forth through a pipe, but it will only exit the pipe in one direction.
The bridge rectifier uses 4 diodes typically, (unless it's a half wave), as the AC wave moves in one direction, the current is allowed to move through the next part of the circuit via 2 of the diodes... as the AC wave moves in the opposite direction, the other 2 diodes send current in the same direction as the last two. Meaning all current is now traveling in one direction, instead of back and forth like in AC.

The capacitors then are used to smooth the current into a nice smooth DC line. Otherwise, you would have end up with pulsed DC, which would fry computerized electronics or anything with logic gates.

After that, you have a current limiting circuit, which checks on the current passing through the battery to determine when it has reached its full potential. At which point it opens the circuit (turns the DC half off) so that it doesn't overcharge your battery causing damage, heating, loss of battery acid and corrosion.



The only part of this you could use in a DC to AC inverter is the coil. Depending on what you want to use it for, and the capacitors to smooth the edges of the created wave out.

You still need to create a timed trigger in both directions, and use a relay to switch the output of the coil at 60Hz.
Your capacitors would be used after that to eliminate the jagged edges on it after that, otherwise, you end up with a square wave.
(Which can also do some serious damage to most household electronics.)

To bring people up to speed were Battery Chargers have come technologically in the last 10 years most of them now contain switch mode control of the voltage because it is cheaper and lighter than the older transformer types.

This is basically done by rectifying the voltage as per the second comment using a simple rectification bridge but instead of stepping this voltage down by using a step down transformer they now employ more complex methods.

By high speed switching of this DC you can modulate it back into a form of AC by turning off the output before it reaches its maximum AC value and holding it off longer with triac's so that when you re-rectify it back to dc again you have a 12.4V DC equivelent output after some smoothing.

To properly answer what you are asking you can't modify an existing battery charger without extension surgery to perform as an invertor.

You can buy invertors that do this and they are pretty chep.

[edit on 9-7-2008 by mazzroth]

Ok guys, Thanks for the electrical clinic! Greatly appreciated!