Afternoon all, just joined and been having a read through, all interesting stuff. Right to the question. I need a reliable constant 12 volt source and I have an inverter which is 12v to 240v. Can that be reversed? I do have a very small 240v to 12v converter but its too small to do anything more than run a couple of lights. I have 240v mains supply.
Thanks

 

No, this can not be reversed.

There are plenty of SMPS you can buy that will give you 12V constant. How many Amps do you need on the 12V side?

 

500 watts minimum would do the job. How about a 12v Battery charger? Would that work? I seem to remember not was the case due to something in the design of a charger that stopped it discharging through a circuit other than a battery?

 

500 watts minimum would do the job. How about a 12v Battery charger? Would that work? I seem to remember not was the case due to something in the design of a charger that stopped it discharging through a circuit other than a battery?

Pmin = Imin*V

Imin = Pmin/V = 500/12 = 41.67 A

That's not going to happen with a battery charger. Do you mean milliWatts?

 

Get a battery.

or A 12V adaptor

 

you can buy one, but it aint cheap.
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2094961_-1

 

500 watts minimum would do the job. How about a 12v Battery charger? Would that work? I seem to remember not was the case due to something in the design of a charger that stopped it discharging through a circuit other than a battery?

A battery charger is absolutely not the answer for many reasons, one of which is the output voltage. It's not 12V and depending on the charger could be as high as 17V.

A SMPS might work, but it's hard to judge unless we know for sure what you are trying to operate and how much current is required.

 

Think about it: a battery charger is designed to deliver current into a battery, and continue doing so as battery voltage rises until it reaches its maximum on-charge value.

The result is going to be a long way from a steady 12V independent of load current.

 

The numbers of 12V power supplies out there are huge, though they actually tend to go for 13.7VDC for automotive accessories like radios. You can buy any amperage you want. Personally I would go for a cheap battery holder and D cells, unless you need large current values (didn't see any stated). I also saw a tiny SLA (sealed lead acid) for $10 the other day, which would do nicely.

 

Bill...he said 500 watts in post 3

500/12 = 41.666amps

 

Sorry about that, missed it. However, at the Ham Com I did see a 50A 12V power supply. They are out there. This was in no way a battery charger though.

 

a 500 watt+ computer power supply will deliver 25+ amps at 12 volts. if you find a dual rail put the 12 volt rails in parallel and double the amps

 

500 watts minimum would do the job.

Why don't you explain what it is you're trying to do first. There may be some solutions available that you haven't considered. A 500 W load at 12 V requires a lot of current; generally, it's preferable to run things at higher voltages and lower currents if possible because it reduces the size of the needed wiring.