Does anyone know if it would be practical to geta 24V ac 50 Hz power supply from a stand-by battery?
I'd think there'd be an inverter involved but are these easily available for this output? The aim is to run an electronic device during power failures, but getting a different device might be easier than getting 24V ac.
if you make your own invertor. Or you could buy a 24v dc to sine mains invertor and add a 24v transformer onto it.
no
quite likely. But your 24v ac device will most likely run quite happily off 24v x 1.41 - 3v = 31v dc. Sometimes theyll even accept a range of voltages. I cant think of too many 24v appliances that would need ac.
Dont ask electronic questions on ukdiy. You can, but its at your risk, this isnt a tronics group, theres little expertise here on it.
NT
I would be tempted to see if the electronic device can be modified to feed it DC (since there is a fair chance it converts its AC input to DC at some point anyway).
Failing that an invertor will do the trick, although many will produce
240V not 24. A change to their tansformer may fix that however depending on the design.
What is it? Maybe it will run off DC too?
Apart from that, finding a cheap inverter may be difficult. Probably easier to buy a 24VDC -> 230VAC inverter (v. cheap) and a mains power supply for it.
Christian.
Do you have any means of running it at present? If so, you presumably have a
240v/24v transformer which you power of a battery to mains inverter. Having said that, most cheap inverters require 12v DC input rather than 24v. What is your battery?
It should run on dc without modification. As the OP didnt think to tell us what it was, we can only guess.
I made a mistake earlier, it'll want 24x1.41 = 34v dc, so 36v lead acids should do fine.
NT
It's a BMS outstation, a computer type device intended to monitor & controls heating & stuff.
On the pcb, it has an encapsulated transformer 0-24V pri/0-18V sec, adjacent to the power input. The power is from a 24V ac mains transformer. Also 4 electrolytic capacitors, but nothing I recognise as an rectifier. There's a small battery on the pcb, but it's just to maintain the RAM & programmed settings. The device fails if the 24 Vac goes off. I'd like to monitor inputs and keep the alarms working. The control valves are also 24 V ac, but I wouldn't intend maintaining the power supply to these.
You could probably achieve what I want with PLCs but I'd have to learn how to programme those, so that's relegated to plan B!
In that case, use the *same* mains transformer running from an inverter - like I suggested earlier.
You are proving the point I assume?
Going through an inverter will be much less efficient than direct DC injection. There MUST be a rectifier; almost certainly the secondary of the traffo will be connected straight to it (maybe via a fuse) so trace the pcb tracks. If you can't find it just disconnect the secondary of the traffo and connect your DC feed to wherever the secondary previously went - the rectifier may run a little warmer but this is very unlikely to be a problem - and if it DOES get too hot you'll be able to find it ;)
If you want this as a back-up system , rather than replacing the mains supply, you'll need to find the rectifier and connect the new DC supply to its output via a diode.
Dave
You are assuming it has a full wave bridge rectifier on its input... (fair assumption certainly, but not guarenteed).
Thanks all. There is a small fuse tucked out of sight above the transformer. I'll dismantle one and see if I can follow the circuit & measure some voltages.
24v ac solenoids will generally run happily on 12v dc.
NT
No I'm not.
NT
Yes, you are. A device with (for example) a transformer in the input circuit, as this one turned out to have, will simply blow fuses if you connect DC to it.
No solenoids. All are modulating motorized control valves, 24V ac power supply with a 0-10V control signal.
No battery at present, besides the coin-sized one on the pcb.
No, I wasn't, thats why I said I wasn't. Its not hard to run through the various possibilities and see that what I said is consistent with them. Note I said 'should' not 'will'.
The possibles:
full wave rec: ok on dc. Most likely option, until we knew it was tf input. half wave: again dc fine ac loads: some ok on dc, some not, but these comprise a very small percentage indeed of 24v electronic loads.
So clearly we can say a 24v ac input box of tronics should run on dc - but not will, as there will be the ocasional one that wont.
of course. Just think the options thru.
NT
Obviously a well researched bit of work. Of the dozen or so devices I have immediately to hand which require 12-24VAC precisely none will run off 12-24VDC (or any other DC supply of any voltage).
It will? Of those dozen or so devices I have none would "blow a fuse" if used on DC. None of those with transformers would blow a fuse. About half would probably be damaged though including many with transformers which would not blow a fuse.
Actually, there's rather a lot.
A most unusual situation. Of all the low v kit in this house that takes ac from wallwarts, not a single one is unable to run happily off dc.
NT
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