Car Battery Charger

[dan091]

Hi Guys,

After my last post about the ups system I have an idea of whats required sorta of. Does anyone have a working circuit layout for a car battery charger. The thing is I am trying to figure out whether its worth building one or buying one. I am looking at around 40-70amps charging capacity because it would be used for a ups system I have setup and I need more power for around 500+ watts of power.

Any ideas?

 

[Resqueline]

Neither way is going to come cheap.
Iron transformers of that size has a hefty price tag as well as a hefty weight, but can be used for a DIY project.
A switch-mode supply will cost a bit too, but it's nothing you build yourself (usually).
I believe there are 500W dual-conversion UPS's on the market but I don't know their price.

 

[dan091]

Resqueline,

Thought so. I'm trying to find a way around this. I have a couple of basic questions though before I decide:

1. Would using a 500watt computer psu provide enough power to use a 400-500 watt inverter on the 12v output?
2. I have had issues with our breaker tripping due to the amount of machines we have. If I were to use a psu's 12v output onto an inverter would that work the same as a car battery charger. I have tested 4-5 machines on the battery charger > inverter idea and the rcd didn't trip however I could only get 240 watts out of the 20amp charger . I believe although I might be wrong that the car battery charger uses an isolater transformer.

The only way around this currently is to buy a bigger car battery charger say 50amp which would provide 600 watts of power. Basically I am after a way of making a bigger car battery charger without the huge cost if possible.

Any help would be appreciated.

Daniel

 

[Resqueline]

1. Yes, barely, and a modified one at that, with only little to spare to recharge the batteries. You'd have to adjust the voltage up to 13.8V and also rewind the transformer to put all its available power on the 12V output. Not too easy to do.
2. That's due to their heavy duty mains input filters with cap's to ground. Medical PSU's don't have these as they are not allowed as much ground leakage currents. Yes, nearly all transformers also acts as isolation tranformers.

I can't recommend that you modify the PSU's and remove their ground filter cap's, or that you disconnect ground to the 'puter outlet strip..

 

[(*steve*)]

I believe there are 500W dual-conversion UPS's on the market but I don't know their price.

I had a 3kVA unit. About the size of a largish PC case.

It had 12 x 12V 7AH led acid batteries in it (in series) which consumed most of the volume inside.

It was "transformerless" but had quite a number of large inductors inside.

It could operate in "standby" mode if required (in overload conditions and on startup) but after running its diagnostics would normally switch to dual conversion.

It was an incredibly complex piece of equipment, and 144V DC source inside deserved to be respected as it had the potential to kill you faster than you could say the first "a" in Aaaaaaagh!

I worked in an emergency services control room that was completely powered by a dual conversion UPS (with diesel backup) That made my 3kVA unit look tiny.

One of the serious issues is the ability to provide (say) 50A, and not cause the batteries to be recharged too fast or overcharged whilst still responding to load changes. It may be a delicate balancing act.

 

[dan091]

Thanks guys for your replies. Steve that story sounds interesting. 99.99% of the time the psu would be providing the power to the inverter, if mains power went off the deep cycle batteries would take the load. I am still pondering over a few things as to safety and if its all going to work as I needed. Obvouisly I'll need to test things etc.

I'll let you guys know even if it doesn;t work too great. Either way its a learning curve.

Daniel

 

[dan091]

I've decided not to go down the computer psu route. I'll probably build a few systems or look for a really big charger.

Daniel