12V DC to 24V AC mini converter for Xmas lights

[Jules]

I have a basic set of outdoor Xmas lights which I want to power away from any AC supply. The lights need 24V AC at 6 watts to power the 6 light sequences, and there are 4 separate light strings in total, not a single string, so I can't just cut the transformer power lead off and connect directly to a 12 V battery. I want a simple DC - AC converter, powered from a 12volt lead acid rechargeable battery. There must be a simple schematic around. Any help please? I'm guessing some form of oscillator circuit using power transistors?

 

[panic mode]

what type of lights? are you sure they wouldn't work on 24VDC too?
maybe all you need is one more 12V battery...

 

[Jules]

24V AC from DC converter

They are standard small filament bulbs, but wired in 4 strings from a "control box" with 6 possible flashing patterns. I guess the need the AC component in the current to activate this. I tried connecting the power lead (which should fit into a 24V AC transformer) to a 12 volt lead acid battery, and nothing lit up, so am pretty sure that it would work using 24V AC if I could get it. Need a 6VA supply

 

[hotwaterwizard]

You could make an inverter to do the job. I think you may even be able to do it without a transformer.

A variation of this circuit may do the job.
https://www.aaroncake.net/circuits/6-12conv.htm

 

[hotwaterwizard]

Here is a Unique one using car amp.

 

[hotwaterwizard]

Ommit the transformer on this one.

 

[Jules]

mini DC to AC converter

Thanks for the suggestions. I will try both of these circuits and let you know how I get on. From first glance it looks lie each could give about 24V AC, which isn't too critical. 20V - 28V would most likely work fine. The frequency wouldn't need to be exactly 50Hz either.

 

[stevez]

Jules - have you actually tested the lights on 24 vdc and 24 vac? I may have missed something but it looks like you described a test at 12 vdc. My concern is that you'll do all the work to generate 24 vac and find it still won't work. You refer to a control box - I wonder if there could be a transformer in there suggesting a requirement for AC. As already suggested, if 24 vdc will work then another 12 v battery might be an alternative. I know at the local surplus place here I can buy a 12 volt, 7AH gel cell for $6 (US). A larger auto battery is about $29.

 

[Jules]

12V to 24V AC inverter

The lights came with a transformer, which gives 24V AC at 6VA.
Nothing happens if I apply DC to the input power connector - must be some blocking rectifier diodes or something. I can't just buy a simple string of low voltage bulbs here - low voltage lights are supplied with a 24V AC transformer, and have a control box and lots of wiring to 4 different light strings.

 

[Nigel Goodwin]

Re: 12V to 24V AC inverter

The lights came with a transformer, which gives 24V AC at 6VA.
Nothing happens if I apply DC to the input power connector - must be some blocking rectifier diodes or something.

You didn't really answer the question, have you tried applying 24V DC, and not just a lower DC voltage - in fact you would probably need more than 24V DC, because the 24V AC will give nearer 36V when rectified.

Usually the unit will have a bridge rectifier inside, which as well as rectifying the AC from the transformer will also accept a DC input (of either polarity) and 'steer' it accordingly.