12vDC to 12vAC? Running a 12vAC bathroom extractor from a 12vDC source

[MooChaqa]

Hi there,

My name is Paul and I am new to tinkering with electronics.

That said, I have successfully installed a 280 watt Solar array in a small single room habitation in France. It works quite well and currently feeds 3 fluorescent bulbs, a 24' flat screen, a small Eeepc netbook and charges numerous USB devices. Great stuff, I am enjoying myself and even learning a little as I go!

However, now I wish to add further items to the system which do not run from the native 12vDC supplied by my batteries.

My manifesto is simple: High efficiency, low power/low watts without having to entirely compromise luxury.

I would like to install a small PIR sensor to turn on both a light in the shower room, and an extractor fan. All low power extractor fan's I can find that are designed to extract humidity from a shower room are all 12vAC.

I guess the question in short is: What is the most efficient way for me to transform the 12vDC from my battery into a supply suitable to turn on a 12vDC bulb and a 12vAC fan from a single PIR switch?

Many thanks and hi to all!

 

[MikeMl]

Are you sure they are 12Vac? More likely 120Vac. Why not use a 12VDC Muffin Fan like in a computer?

 

[MooChaqa]

Hi there,

This fans electrical requirements are:

12 Vac 50/60Hz AC Voltage.
16 Watts.
1.7 Amps.

Most low power extractor fans in the UK are 230vAC and come with a supplied transformer that converts to 12vAC. The low voltage allows them to be installed directly in the splash zone of a wet room shower. With the transformer installed remotely. Which is what I wish to do. It gets pretty darn steamy in there right now!

I think the humidity level and the possibility of splashing rules out a modified 12vDV PC fan also.

 

[tronitech]

The cheapest, although not most efficient, way would be to buy an inverter to convert 12VDC to 120VAC(230VAC) and put a 120VAC(230VAC) to 12VAC transformer on the output?

 

[MikeMl]

It is simple to create a 12V square wave drive to the fan using an H-bridge driver IC chip. A clock to run it is as simple as a NE555 astable. I dont think that the fan would care if it is driven with a sinewave or a squarewave.

 

[JMW]

Try your local auto parts or marine dealer. The local truck parts distributor could also be a source. Problem is, these don't move much air. Therefore they won't do much.

 

[KeepItSimpleStupid]

You just need to find the the right transformer. (Right ratio)

I did a drive for a 120 VAC synchronous motor using a center-tapped transformer (Secondary) to a 120 V primary. Just switched the primary and secondary roles. Forget what I used for transformer. A 50% duty cycle 555, and inverter stage and 2 output transistors. Guy used it for a telescope drive.

 

[dr pepper]

Have a closer look at the motor, or even just try it on 12vdc with an indicator bulb in series, if its a brushless motor it probably just has a rectifier on the input which would work on dc, if its a brush motor then it might be fine on dc, if its a synchronous motor which is possible being a larger motor then it wont work on dc, if the latter is the case then you might be better off looking for another extractor.

 

[MooChaqa]

Hi all,

Many thanks for the replies.

I was really hoping it would be possible to just switch 12vDC to 12vAC and bingo! Am I barking up the wrong tree? Is this not the easiest/cheapest method? Granted I can't find anything on the market that does this!

@ tronitech
This looks like the simplest route as everything required can be bought off the shelf. Things is, I really want to keep efficiency at a maximum even if it means a little extra work now.

@ JMW
The extraction rate on this fan is: 60 m3/h (19 l/s. While low it should be suitable for the job in question as the shower room is very small. I want it set to run on entering the room and quit perhaps 5 mins after exiting.
(Although this will probably change once I realise just how many times I enter the room without requiring anything to be extracted!)



Cheers!

 

[ronv]

If you are handy with a soldering iron the suggestion made by MikeMl is the most efficient. You could use an IC like the L298 - though there are better ones - and a 555 timer IC to make 60 Hz.

 

[KeepItSimpleStupid]

And that's what I said too. When I built mine, for 120 VAC there were no H-bridge drivers. You just have to figure out the right Center tapped transformer to use. +12 goes to the center and two tranistors/FETS drive the outer legs 180 degrees out of phase.

Now you need 12 V out, but your driving the secondary (usually primary) with .about a 22-24 V peak to peak signal. 12 V is a 33. V peak to peak signal. So you need a center-tapped xformer with a ratio of 24/32 or 0.75 or 1.33 and possibly run it backwards with the right current ratings.

Hopefully, I did that right.

 

[Bob Scott]

Oh, it's a FAN!
I just had to see the messages behind this thread's title. I just saw "Bathroom Extractor" and thought to myself "That sounds painful. I have to read this!"

 

[MooChaqa]

Hi guys,

Thanks to all for the replies although unfortunately, I think I am floundering in the deep end. I was hoping that this wouldn't require as much knowledge as appears to be required, and I think is beyond me at this point.

Anyone wish to make a couple of quid and make me a 12vDC to 12vAC transformer that I can just sit between my battery and fan? Pretty please?

 

[KeepItSimpleStupid]

I found a solution for you: Take this https://www.powerstream.com/inv-12dc-24vac.htm 12 VDC to 24 VAC converter which is 40 W

We would just need to select a transformer that would work: e.g. https://www.rapidonline.com/Electrical-Power/Toroidal-Transformer-500va-0-50v-0-50v-88-3840 I'm not saying that this will work without checking some calculations. It's probably overkill.

In this case 115 to 50 is nearly a factor of 2. This is what you need, but the currents need to be worked out. I'm not in the mood to do so, right now. If the fan takes 10 VA, you might need a 100 VA transformer to make it work.

In any event, if it's within you cost constraints and the FAN takes less than 40 VA we can go from there. You may need a case too. Custom is always possible: **broken link removed** even at quantity =1/