Getting 24V AC efficiently

[Sverige]

I have a device which uses 24V AC, which I’m currently powering from my LiFEPO4 solar charged battery via an inverter (to 230V AC) and then transformer to drop down to 24V AC. It works, but it bugs me that it’s inefficient, so I’m wondering if there’s a more direct way to convert 12V DC to 24V AC for a device with a total draw of no more than 10W?

 

[mikefitz]

No simple solution unless the device can accept a square wave, what is the unit that needs 24v ac?

Mike

 

[Sverige]

It’s an underfloor heating controller. It connects to thermostats (white cables) in each room and sends 24V AC to solenoids (grey cables) which open each circuit of a manifold to allow warm water to flow through pipes built into the floor of each room.

Living in a country with -20C winters, it’s kinda important this stays working reliably, so although I’m interested in running it more efficiently, I’m not sure I want to take any chances.

 

[Noday]

I've used some PowerStream PST-INV1224 to drive industrial devices from a 12V battery backup, they accept 12 VDC as input and produce a 24 VAC "pure" sine wave output. They tend to get hot so I did enclose them inside a metal box with forced ventilation.

I don't consider this as a "simple solution" though, since you already have 230 VAC available and you are actually transforming the 230 VAC to 24 VAC with an isolation transformer, I'm not sure you will be getting more efficiency by using instead an electronic trasformer to pull up from 12 VDC to 24 VAC. You will probably have a less overall efficiency and more points of failure.

 

[acdoctor]

There are lots of diodes on that board. Maybe check the output signal to see what it really is. And you can get 12 volt thermostats. Maybe even change solenoid coils.

 

[Don B. Cilly]

It works, but it bugs me that it’s inefficient,

Well, how inefficient can it be? How much does that thing draw? Is it really worth worrying about?
In the end... is it worth the hassle? Because if you're only "losing" a few Ah a day through "inefficiencies", unless you're in a situation where "every milliamp (really) counts"... well, me, I just wouldn't bother :·).
-

 

[Sverige]

I've used some PowerStream PST-INV1224 to drive industrial devices from a 12V battery backup, they accept 12 VDC as input and produce a 24 VAC "pure" sine wave output. They tend to get hot so I did enclose them inside a metal box with forced ventilation.

I don't consider this as a "simple solution" though, since you already have 230 VAC available and you are actually transforming the 230 VAC to 24 VAC with an isolation transformer, I'm not sure you will be getting more efficiency by using instead an electronic trasformer to pull up from 12 VDC to 24 VAC. You will probably have a less overall efficiency and more points of failure.

Thanks!

 

[Sverige]

There are lots of diodes on that board. Maybe check the output signal to see what it really is. And you can get 12 volt thermostats. Maybe even change solenoid coils.

I measured around various pins on those headers and could only get 0V on a DC voltage range and 24 across a few pins on the AC voltage range. I agree there’s a few diodes, not sure what to make of that. I think the centrally located bigger diode and capacitor are deriving DC to power a relay which switches the pump output on and off, via the header connector at the lower side of the board next to the big grey transformer. (Labelled with triangle symbol)

 

[Sverige]

Well, how inefficient can it be? How much does that thing draw? Is it really worth worrying about?
In the end... is it worth the hassle? Because if you're only "losing" a few Ah a day through "inefficiencies", unless you're in a situation where "every milliamp (really) counts"... well, me, I just wouldn't bother :·).
-

You’re undoubtedly right, and I should probably leave it alone. I have a kind of pathological OCD about reducing our energy usage and even before dabbling in solar have got our annual electricity consumption down from around 12,000kWh to 5,000kWh. We have electrical heating (rock source heat pump).

But anyway, finding everything greater efficiency becomes an obsession and it’s not always rational.

 

[acdoctor]

What about this?

inv-12dc-24vac | PowerStream

www.powerstream.com

 

[Sverige]

What about this?

inv-12dc-24vac | PowerStream

www.powerstream.com

Looks great, but price and availability here in Europe might be an issue. Plus I’m tending towards thinking this is a problem I should just leave alone, as adding a further device with its own quiescent consumption is maybe not even better than simply driving the existing transformer using my 230V inverter which is already on, driving other loads.

I guess the main reason for starting this thread was to discover if there’s an easy (simple / cheap / high efficiency) way to get low voltage AC from DC and I think I’ve discovered there probably isn’t.

 

[efficientPV]

All those diodes are likely there to absorb back EMF of the solenoids. That means the solenoids are DC and everything else is too. Time to pop that grey cover off.

 

[acdoctor]

I thought the inverters only reason for running was the power this.
Most inverters efficiency band is in the middle.
If you are running out anyway it may improve efficiency.