12V DC to 12V AC convertor

[bruce_c]

Does anybody have any suggestions how to do this:

I need to create 12V AC (max 2A, probably closer to 1A-1.5A) from a 12V DC source (big ex-UPS storage batteries).

My thought was to run a 555 timer (or such like) in astable mode, passing through a couple of decent power transistors and then onto a 1:1 ratio isolating transformer.

I realise this would not produce a very nice waveform and would probably result in the output being a little under 12V and I am not sure if the voltage regulation would be any good.

So does anybody have any better soultions for this?

thanks in advance.

[Buckey29]

Look for an inverter circuit. I found one with a quick Google search and found this:
http://www.aaroncake.net/circuits/inverter.htm

Instead of the xformer they show, use a 1:1 as you stated for isolation.

[Miami Mike]

There's always the simple consumer appliance solution. Buy a small inverter that produces AC at your country's standard mains voltage (220 VAC, is it?) and step it down to 12 volts with a small transformer.

Maybe you could even use the inverter circuit from the UPS you robbed.

[vintage1]

Why is the AC needed? This is important, becauyse you don't stipulate the frequency, and as you have discovered, waveform can be critical..

Let us know what the application is - there's millions of ways to skin this cat depending on exactly what you want.

[bruce_c]

Why is the AC needed? This is important, becauyse you don't stipulate the frequency, and as you have discovered, waveform can be critical..

Let us know what the application is - there's millions of ways to skin this cat depending on exactly what you want.

It is to run a midge/mosquito machine. http://www.mosquitomagnet.com
The machine comes with a 240vAC to 12V AC adapter (I have checked that it is outputing AC not DC).
Now this is intended to run off a mains supply - which we do not have at our flying site, but what we do have is more 12v DC than we will ever need.
-coming from a set of solar panels float charging a 160Ah st of UPS batteries.

Now the machine is US made but has just been bundled with a UK spec mains adapter, so I guess it is happy with 50 or 60 Hz.

I am not 100% sure that it NEEDS AC. I suspect it may be rectified immediately and used as DC. Is there an easy+safe way to check this without taking it to bits?

[vintage1]

well 12V AC is almost certainly being rectified to produce about 14-16vDC.

If its a full wave rectifier it willl probably work direct off a car battery anyway.

Oherwise you can build an inverter - you need a 50hz oscillator, and I would go simple and get a car audio amp chip and use that...its hard to say.

Any chance to open the gadget up and take a look at what is inside it in the power area?

[Dan Baldwin]

Often when a piece of consumer electronics uses an AC output adapter, it is because the AC is needed to make other necessary DC voltages. Perhaps it needs 24 VDC as well as the primary supply of 12-14 VDC, or maybe it needs a negative supply as well as the positive supply.

Dan

[Aethertek]

Most easily available inverters are designed to convert low voltage DC 12-24 v to 120v AC.
Can you use one of these & then just replace the 240vac to 12vac transformer with 120 to 12

[Acetronics]

I am not 100% sure that it NEEDS AC. I suspect it may be rectified immediately and used as DC. Is there an easy+safe way to check this without taking it to bits?

;) Reading the maintenance page of the site it appears a battery has to be unplugged inside your mosquito BBQ ...

It ( the battery ) surely needs a charger , and then an up to 12 vDC source ...
Might be the simple reason for the 12 v AC input ...

I guess you could have a look inside the machine to confirm that ...

Alain

[Miami Mike]

Most easily available inverters are designed to convert low voltage DC 12-24 v to 120v AC.Aethertek, please try to think more globally.

[Aethertek]

Aethertek, please try to think more globally.
Fine get a 220v inverter, sheesh

[bruce_c]

Aethertek, I should probably have said, that to try it out we were using a 12V DC to 240V AC inverter (true sine wave type). The reason we dont want to go this route is because of the power wasted by the inverter.
Basically why step 12V up to 240V just to step it back down to 12V.

I measured a current draw of 2.56A on the batteries by the whole system (with inverter), whereas the machine itself consumes less than 2A from its 12V feed. This this basically comes down to a greater than 20% power wastage which is undesirable when you are trying to run things off solar power+ storage batteries..

I guess the easiest way to find out what it needs fed with is to open it up and have a look inside...

[vintage1]

I think so. Chances are it just needs 12vDC and actually has a rectifier, capacitor and regulator to achieve just this.

Those warts are basically a way to allow kit to be made cheaper: Instead of a bunch of mains stuff which has to be tesetd and comply with safety standards before it gets sold, these cheapo bits of kit are designed to work off low voltage AC and the wall warts are produced in volume and tested for compliance as a separate item.