Modifying 24v Inverter to Battery Charger

Thread Starter

davidm2232

Joined Dec 31, 2015
21
I have a spare 2000w 24v inverter. I have a ~600AH 24v battery bank connected to 800w of solar. I would like to supplement solar charging when my generator is running. Is there a way to make a charger out of the inverter? It should have a transformer to step 120v down to 24v, correct? I just purchased a 100A bridge rectifier. Would it be as simple as hooking the transformer to 120v, through the rectifier and then to the battery bank? I would like at least a 50A charge current that does not need to be automatically controlled. I can switch it on and off manually as needed. The biggest store bought chargers I have found are around 20-30A and cost upwards of $250. Seems like a lot for just a simple charger. Any ideas or links to people who have done this before? Thanks
 

Dodgydave

Joined Jun 22, 2012
9,685
A simple charger would be a transformer, bridge rectifier, the current output would be limited by the transformer capability, any 24-30V AC transformer should be ok.

You cant reverse the process of the inverter, as it uses high frequency pwm.
 

Thread Starter

davidm2232

Joined Dec 31, 2015
21
Doesn't an inverter use mosfets to get 60hz AC in this case at 24v then use a transformer to go from 24vac to 120v ac? Or is it done a different way?

So in a perfect world, if I use any transformer rated at say 1200w (50A at 24V) going through a 100A bridge rectifier, the transformer should self regulate to it's maximum capacity and the rectifier should put out DC current suitable for battery charging? Just trying to avoid letting the blue smoke out haha.
 

Dodgydave

Joined Jun 22, 2012
9,685
Yes that's a simple 50/60 hz mains inverter, you can use the transformer from that to make your charger, you would only need two diodes for a full wave bridge, like this circuit...



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Last edited:

tcmtech

Joined Nov 4, 2013
2,867
Even if it does have a low frequency iron core transformer in it it wont put out the correct voltage when ran in reverse.

To properly charge a 24 volt battery you will need ~28 - 29 volts whereas a typical low frequency transformer based inverters low voltage winding is only good for about 1/2 - 2/3's of that at best.

Your best option would be to buy or find a properly designed 24 volt battery charger unit for it. They're not hard to find if you go looking.
 

Thread Starter

davidm2232

Joined Dec 31, 2015
21
Even if it does have a low frequency iron core transformer in it it wont put out the correct voltage when ran in reverse.

To properly charge a 24 volt battery you will need ~28 - 29 volts whereas a typical low frequency transformer based inverters low voltage winding is only good for about 1/2 - 2/3's of that at best.

Your best option would be to buy or find a properly designed 24 volt battery charger unit for it. They're not hard to find if you go looking.
I have been looking. I can't find a simple manual style charger. They are all electronic/automatic chargers at low amps. I was worried about the transformer not outputting the correct voltage. That's really unfortunate.
 

tcmtech

Joined Nov 4, 2013
2,867
I have been looking. I can't find a simple manual style charger. They are all electronic/automatic chargers at low amps. I was worried about the transformer not outputting the correct voltage. That's really unfortunate.
Google searches too hard to do? o_O
I found hundreds of them that way. Many pretty cheap too. :oops:

Also, most decent automotive battery chargers can be easily modified to put out 24 volts at half the rated amps. Or a matching pair of 12 volt units can be wired up in series to work as a single 24 volt unit.
 

Dodgydave

Joined Jun 22, 2012
9,685
I gave you one in post#5, here is another one with a full bridge rectifier, just get your transformer for the desired voltage output.



e84f6f5212491aa9995cd4cf86558a9f.jpg
 

Thread Starter

davidm2232

Joined Dec 31, 2015
21
Google searches too hard to do? o_O
I found hundreds of them that way. Many pretty cheap too. :oops:

Also, most decent automotive battery chargers can be easily modified to put out 24 volts at half the rated amps. Or a matching pair of 12 volt units can be wired up in series to work as a single 24 volt unit.

I must be missing something then. Here are Mouser results for a 36v transformer. The transformer alone is $325. Where are these cheap chargers?
 
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