Emergency power cut switch

Rolf Hayes · Dec 13, 2018

We have a battery operated device that needs to operate when there is a power cut, in effect like an emergency light fitting would.

Can any one help with a switch that will be triggered when power to the property is lost so that the battery operated device will run the frost protection device. Have thought about rigging up a bit of a homemade setup with a relay and just have the battery wired through NC so that the relay will be on all the time there is power to the property.

Shoei · Dec 13, 2018

The question needs more information, what voltage, how much power how long should it hold up for? The usual solution would be a UPS.

Toneyz · Dec 13, 2018

Do you have a lot of power cuts in the winter then? What are you protecting from frost plants?

Rolf Hayes · Dec 13, 2018

Thank you Shoei

The voltage and power would only need to be sufficient for a low voltage trace heating, so something like 24v for a trace heating of 10W/m, a total length of 15m.

A UPS system was concidered but thought to be too much for what is required.

It is expected to hold out only when it is below 5 degrees outside (was going to have a mechanical frost stat for this) and when there is a power cut.

Trust this helps and grateful of your help.

Rolf Hayes · Dec 13, 2018

anthonybragg said:
Do you have a lot of power cuts in the winter then? What are you protecting from frost plants?

We are needing a contingency in place for some external pipework to a heat pump where we haven't been able to add glycol or antifreeze to the system.

I have to agree that power cuts at the same time as a cold winter for long enough to freeze water that has been at 30 degrees is almost unheard of but the client is adamant that the protection is needed.

westward10 · Dec 13, 2018

So this trace heating is only required during power cuts to prevent the stationary liquid freezing?
Surely the best way is a UPS with 230v output to a power supply with the 24v output. Batteries do not seem a good idea as you will have to have some charging facility for them.

Shoei · Dec 13, 2018

Have you identified the float charger and battery? If the charger has a charge status signal it could be used to operate a relay which connects the heater. If there's no charge signal, a diode and relay could be used to do the same thing.

Deleted member 26818 · Dec 13, 2018

Is the frost protection intended to be dual fed, or is just intended to be used during power cuts and fed from the battery?

Rolf Hayes · Dec 17, 2018

spinlondon said:
Is the frost protection intended to be dual fed, or is just intended to be used during power cuts and fed from the battery?

Frost protection is only to be fed during power cuts.

rapparee · Dec 17, 2018

Rolf Hayes said:
We are needing a contingency in place for some external pipework to a heat pump where we haven't been able to add glycol or antifreeze to the system.

I have to agree that power cuts at the same time as a cold winter for long enough to freeze water that has been at 30 degrees is almost unheard of but the client is adamant that the protection is needed.

You know we used to make heat pumps and we always had antifreeze in the system, are you sure this won't be possible?

Rolf Hayes · Dec 18, 2018

rapparee said:
You know we used to make heat pumps and we always had antifreeze in the system, are you sure this won't be possible?

We aren't able to put antifreeze in as some of the fittings and materials used contain a rubber that can be degraded with propylene glycol and we aren't able to add ethylene glycol as is has potential to come in contact with the hot water cylinder coil, being against regulations and health/safty standards.