AC to DC converter from transformer.

[sledge21]

Hi all.
I got my hands on a HUGE transformer, the input is 220v and output is 13.7v or 12v or 36v but all outputs is AC and I would like to charge some 12v car batteries with it.
The max amps that I have tested the output from the 13.7v are 43A .
Is it possible to build a simple circuit to use one of these AC outputs to charge a 12v car battery witch is normally 14.7V fully charged.
It will be used on standby batteries for the extractor fans at a acid plant. (110Ah p battery and there is 16 of them total =1760 A/h.)
Thanks for any help...

 

[Ian Rogers]

14.7V fully charged.

Chargers for car batteries usually run at 13.6 volts.... 14.7 is way too high for a 12 volt battery.

How did you measure the 13.7 volts... RMS meter? If you put a decent sized bridge rectifier on the 13.7v output, what would be the DC output?

Of coarse, I'm talking about a car charger ( where the rest of the car is still in circuit ).. As these are being used else where, overchargeing may not be as big a problem.

 

[sledge21]

Yup, I went and had a look; I am charging some of the batteries with an Intelli charger (Radio control charger for lipos and pb and so on) When charging 12v Pb batteries the charger get them to 14.7v , but those that has been charged shows 13.2v to 13.5v when disconnected.
Its my bad I was referring to the rc charger.
Is it possible that the transformer conversion with bridge rectifier will over charge?

 

[ronv]

It's a little more complicated to properly charge a lead acid battery. A 3 stage charger will limit the current to the battery's C/10 level. In your case 11 amps per battery. This is called bulk charge.
At about 80% charge the charge is constant voltage. This would be your 14.7 volts.
Once the current drops to a few percent of the capacity rating it should switch to a float or maintenance voltage of about 13.6.
If you want to skip all of that you can most likely use the float voltage (13.6) for the whole thing (constant voltage charger) This will be slower to charge the battery but easier to build. If your charger now does not shut off after a while it will boil your batteries dry.

 

[sledge21]

Thanks "ronv".
How would I protect my batteries from over charging then?
I found a rectifier (MB150) more than enough amps on this thing I just added a cap for smiles.

 

[sledge21]

I found this circuit, but it charges at 2.2A max. Is it possible to use more of the LM315 s in parallel to get higher amps.

 

[MikeMl]

Read "how to charge lead sealed acid batteries" on this page. This applies to flooded lead acid batteries, too.

 

[ronv]

Something like that circuit would work. It won't be super fast to charge but since its for backup it probably doesn't matter. So should we try to come up with one like above but for 11 amps maximum charge current or are all your batteries in parallel?

The circuit shown protects the batteries by making the maximum voltage 13.6 volts. They won't overcharge at that voltage.

 

[sledge21]

Hay "ronv"
Sorry for getting back to you now, I was in an accident over the weekend, but all is well now. I would really appreciate it if you can help me with the design of the circuit since I am not all that of an expert. In the above circuit, can I only use more than one in parallel of the 317 s to get more amps or do I have to build another circuit, or is there a better option ?
Oh yes; the batteries, It consists of 2 banks of 8 batteries in parallel so it is 2 banks of 12v batteries with 880A/h each.
Thanks again man!

 

[schmitt trigger]

880AH?
Charging them at C/10 would mean 88 amps of DC current.
This will not be achieved with a simple LM317 circuit, you cannot parallel that many.

Large battery chargers always use SCRs as the power control elements. I had a schematic for such a large charger somewhere. Let me see if I can find it.

 

[sledge21]

Hay man that would be awesome!! The transformer can deliver more amps than I have tested , but my amp meter only goes to 50A and so I tested it at 43A for about 2 hours and it was luke warm.... Like 47 deg Celsius. The rectifiers can do 100+ amps.
I would like to adjust the current if possible for smaller batteries if necessary.

 

[schmitt trigger]

With the proper feedback loops, yes indeed, current and/or voltage can be adjusted.

As I mentioned, the schematic must be somewhere along hundreds and hundreds of books, papers and magazines.....let me see if I can find it at home.