12v DC to 12v AC 50Hz

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Gwylan

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I need a little black box to take the 12v d.c. on board and make it into 12v 50Hz a.c. with a reasonably sine wave form. Need about 10 watts power

This is out of my competence zone and I just need to find said black box to do the job.

Of course it is not what I wanted to do at the start of this project, but this is the softest fix I can look at right now to get the project done, at least until next year when a service interval means we get a chance to exchange the offending component.

Constructive suggestions much appreciated.
 
Twelve volts AC? Odd voltage. Do you have a source for 220V 50Hz AC power? If so you can get a step down transformer to easily drop the voltage to 12V.

If no AC supply then you'll have to get an inverter to make AC from the DC but off the top of my head don't know of one that makes 12V which would be a bit of a specialized gear. Unless someone can point you to one that makes 12V AC the best option is in two steps. A small, sine wave inverter that makes 220V, 50 Hz AC from your 12V battery supply then take the 220V inverter output to a small, stepdown transformer to get the 12V AC. Since you only need 10 Watts you can use the smallest inverter you can find. Whole bit should be $200 or less.
 
skipmac said:
Twelve volts AC? Odd voltage. Do you have a source for 220V 50Hz AC power? If so you can get a step down transformer to easily drop the voltage to 12V.

If no AC supply then you'll have to get an inverter to make AC from the DC but off the top of my head don't know of one that makes 12V which would be a bit of a specialized gear. Unless someone can point you to one that makes 12V AC the best option is in two steps. A small, sine wave inverter that makes 220V, 50 Hz AC from your 12V battery supply then take the 220V inverter output to a small, stepdown transformer to get the 12V AC. Since you only need 10 Watts you can use the smallest inverter you can find. Whole bit should be $200 or less.
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A very weird corner I painted myself into.
Your suggestion is a route, but there is no 220v. Mostly practical and safety reasons.
Anyway, said device needs to fit in a very small space! Oh and be weatherproof, replacement will require the entire set up to be de-constructed - probably with a chain saw or similar.

It all seemed so easy at the outset. Not carefully reading the spec on a key and irreplaceable component leaves me with this last gasp attempt to snatch chaos from the jaws of monumental failure
 
Gwylan said:
A very weird corner I painted myself into.
Your suggestion is a route, but there is no 220v. Mostly practical and safety reasons.
Anyway, said device needs to fit in a very small space! Oh and be weatherproof, replacement will require the entire set up to be de-constructed - probably with a chain saw or similar.

It all seemed so easy at the outset. Not carefully reading the spec on a key and irreplaceable component leaves me with this last gasp attempt to snatch chaos from the jaws of monumental failure
Click to expand...

How small is the space? You could mount the inverter remotely, run 220V AC to the space and just mount the transformer there?
 
People might die if there was 220v around. Or I might need much bigger batteries.

We already blew the budget on this one.
Now I am hemorrhaging time and money. I have 5 days to fix it - and a few other related issues. Oh and the project is 1000 miles away and being [not so well] remotely managed.
 
What are you needing to power with low voltage AC? Most equipment with AC input will not need it internally.
 
Discrete sealed component that needs 12v 50Hz - how did I ever miss this? Bloody light bulb, that now has an expensive machined fitting to contain it. Really do not have time before hand over to make a change.
Too much is built around this component to change things at this late stage.
 
1. How clean a sinewave must the 12V AC be? Could it be a square wave (lots of odd harmonics, but depending on the application may not be an issue).
2. What frequency? Although they say 50Hz, isn't always always essential. Have you any idea why it needs to be 50Hz?

Of course you may not have a spec, but it's possible that the light bulb, if a halogen, is not at all fussy. I have some halogens in the bathromm and kitchen that run off 12V AC, but it's from a small 'transformer' box which actually delivers a square-wave at several kHz.

PS: Did you try DC? Not a daft question: it's hard to envisage an electronic design for a bulb which would mind. A 50Hz transformer is a big and heavy thing, so almost nothing these days uses one. Instead almost all devices convert to DC immediately on input, and then convert again, if need be, with a 'switch-mode' circuit running at some tens or even hundreds of kHz. These circuits will accept sq waves up to some kHz, and in fact many will accept DC at their inputs.
 
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I'm fascinated by what this device might be. Here's my speculation ...

Its the Missile telemetry control unit on Kim Jong Un's next missile firing - fits most of the clues provided !
 
Bloody LED, encapsulated and no way to modify it.

Tried 12v d.c.. Lamp flickers on and goes off. Thought it was a circuit fault and spent hours searching for the fault.

Eventually read the box for the lamp and found the fact that it needs 12v a.c. Suspect any alternating voltage would do. Have to get a data sheet and see what shape wave it will cope with.

Getting a lab power supply to site is not going to happen. Trying to pick up an equivalent lamp locally to run some tests and bodge an inverter. An off the shelf item would be very nice.
 
Cannot see an easy way of doing this without the use of an small inverter then dropping down to 12vac, this could be using a small 240vac to 12vac wall wort adapter, these are easy to find. Have you looked at how the sealed component actually uses the ac and looked if it can actually use dc as well, many can
 
superheat6k said:
I'm fascinated by what this device might be. Here's my speculation ...

Its the Missile telemetry control unit on Kim Jong Un's next missile firing - fits most of the clues provided !
Click to expand...

Please don't say things like that. People in a Gloucestershire town get quite excited and I do not need to have them on my case too!
 
Gwylan said:
...it needs 12v a.c. Suspect any alternating voltage would do. Have to get a data sheet and see what shape wave it will cope with
Click to expand...

If it can indeed use a sq wave then it's v easy indeed to make a circuit (from scratch with resistors, capacitors and two small (14 or 16 pin) ICs, but only 'dead-bug' style construction is needed) which will toggle solid-state switches. As the LED is presumably not grounded it should be ok to swap the pos and neg in a break-before-make manner. For roughly 50Hz one can make a relaxation oscillator. This brings me to the question: what current does it take?

PS: one of these would do: http://www.robotshop.com/uk/cytron-...MI2fDl6oqF1gIVjrztCh1lOwsuEAYYASABEgKM3fD_BwE

Capable of switching up to 30V at up to 20kHz. You'll just have to feed it with the ~50Hz control signal. It costs only £12.81
 
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Gwylan said:
People might die if there was 220v around. Or I might need much bigger batteries.

We already blew the budget on this one.
Now I am hemorrhaging time and money. I have 5 days to fix it - and a few other related issues. Oh and the project is 1000 miles away and being [not so well] remotely managed.
Click to expand...

It's not the volts that kill, it's the amps. Use a very small inverter and

1. It won't make enough amperage to kill anyone
2. It will only draw an amp or so from the batteries.

Also, you mention this is to power some kind of a light bulb. Did I understand that correctly? If it's a standard incandescent bulb it's just a plain resistive load and won't care if it's being feed AC or DC as long as the voltage is right. Of course if there's anything else on the circuit, it has a chip or ballast or other complication then the DC won't do.

Never mind the above suggestion for DC. Just read the later posts.

I'm back to a small inverter, run a small wire from the inverter to the gadget and put a small transformer (wall wart will do great if you can find one the right output)
 
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pvb said:
Some ideas here? https://www.instructables.com/answers/cheapest-way-to-convert-dc-to-ac/
Click to expand...

Thank you. Did look at this and dismissed the idea - but nothing better has come along. So, this is the way to go.
Only 10 watts, even at 50% efficiency that will not be a lot of heat to cope with. Will be at ambient - on a boat that's 20C, nearer 10 this season.
Do not need to step up or down the voltage - the supply side is already stabilised at +-5%. Goodness knows why on a sailing boat, but there we are.

Off to Maplins in the morning, they are open and nearby.
Could pot the entire device or maybe just hide it under the headlining. Someone is going to wonder why there is a 12v a.c. supply to one circuit.
Hope there will not be too much RFI - the VHF, AIS and GPS are all in the vicinity.

Onward and upwards
 
Ok,bit late to this game but...

OI you lot, quit harping on about 240V (yeah, I know its easy... lazy buggers). 12V 50Hz is audio!. Think sine wave generator and audio amp.

and another thing... without upping the volts, you cannot make 12Vac from 12Vdc! (its an RMS thing, innit?) That may well be why the lamp barfed at 12Vdc.
So, you need a 12V -> 24V buck converter and the audio gubbins run from that, all done as jdb says "dead bug style"

edit add: use 24V as these buck converters are common vehicle kit.
 
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