Wood boiler UPS

[bpk]

I have a customer that has an outdoor wood stove/boiler to heat his house. The stove has a small circulating pump to keep the hot water heating loop flowing. In the event of a power outage and the pump stops they can build enough pressure to blow the relief valve. The stove installer said he has seen people use an automotive battery and 12v to 120v inverter with a contactor used as a transfer switch to keep the pump running for a little while until the stove cools down. It sounds to me like they are basically makeing a type of homemade UPS. Do any of you know of a small UPS (already assembled) that would work well for this application? The only ones that I have seen are built more for computers and servers and have built in power conditioning with surge supression, ect. The pump is very small 120volt and around 1 amp.

 

[mxslick]

Yes, there are a variety of commercially made UPS that can handle this pump motor. You'll need one rated at least 250va (preferably 350 va to allow plenty of runtime). Even though they are desigend for computers, a true sinewave UPS can do the job.

The important thing is this: The UPS MUST have a "true sinewave" output and it will handle the motor just fine. A normal, lower-end UPS has a "stepped sine wave" or quasi-sinewave output and MAY not work with the puimp motor.

A true sine wave UPS usually brags about it in the product cutsheet and adverts. Check the specs on any one you consider before buying.

Some makers to look at are APC (one of the best around) Tripp-lite, Belkin and a few others.

All a UPS really is, is a fancy packaging of the setup you mentioned.

 

[benaround]

He could pipe the relief valve into the fire box and it would put the fire out !!

 

[mdshunk]

That man should also double check that the firebox damper is fully closing during a power outage.

 

[coulter]

bpk -
As mx discussed, runtime may well be an issue. Ask your customer how long this pump need to run - 1hr, or 10hrs. 10hours is going to take 200AH (battery capacity) or so - likely well past what a canned (integral batteries) UPS is going to do. Even if the required time is only an hour, I'd recommend sizing the inverter by the battery capacity at expected load. You may have to get one that will take external batts.

Last one of these I did, the customer wanted 10 hours. He had installed a second smaller pump in parallel, to run off of an inverter - had not bought the inverter yet. I convinced him to change the small pump to a 12VDC unit. It only drew about 2.5A but it was just enough to keep minimal heat in the house and the boiler from over-pressuring. Turns out the same pump (the small one) was available in 12VDC - easy changeout.

With a 12VDc pump, no need for an inverter. Used a battery charger and a battery. Turned on the small pump with a power fail relay. For 10(+) hours, he went with an inexpensive 60AH deep discharge sealed bat. Just had to make sure the battery charger was one that would shut off when the batt reached full charge and not keep cooking it.

carl