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Thread: UPS for Boiler

  1. #1
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    UPS for Boiler

    I do a lot of work with a heating contractor that has asked me to install a UPS in line with his gas boiler at his house. He wants this because during a recent power outage his generator was feeding power to the boiler burner and on more than one occasion the boiler quit and had to be reset. I don't know anything about the burner except it is fairly new and very effecient. He wants the burner to get cleaner power than his generator will deliver. I would suspect the most the burner and circulator pumps would draw would be 4-5 amps. The circp pumps are very small. I imagine I have to consider starting current on the burner motor.

    I don't have any idea where to begin to buy or even size a UPS for this. The only experience I have with UPS's are the little ones that plug in for a desktop computer or commercial ones that fill a large room that I did not select. Any feedback would be appreciated.

  2. #2
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    Quote Originally Posted by mkgrady View Post
    I do a lot of work with a heating contractor that has asked me to install a UPS in line with his gas boiler at his house. He wants this because during a recent power outage his generator was feeding power to the boiler burner and on more than one occasion the boiler quit and had to be reset. I don't know anything about the burner except it is fairly new and very effecient. He wants the burner to get cleaner power than his generator will deliver. I would suspect the most the burner and circulator pumps would draw would be 4-5 amps. The circp pumps are very small. I imagine I have to consider starting current on the burner motor.

    I don't have any idea where to begin to buy or even size a UPS for this. The only experience I have with UPS's are the little ones that plug in for a desktop computer or commercial ones that fill a large room that I did not select. Any feedback would be appreciated.
    Perhaps you can separate the motor from the control circuit and only UPS to control circuit.


    I know what I don't know, and I know where to go to find it!

  3. #3
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    Even if you can separate the controls from the motor loads, many electronic furnace control systems will not like the output of a cheap UPS.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  4. #4
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    Quote Originally Posted by Strathead View Post
    Perhaps you can separate the motor from the control circuit and only UPS to control circuit.
    I would only do that if I had to. This customer doesn't care what it costs, I just don't know how to size what to get

  5. #5
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    Quote Originally Posted by don_resqcapt19 View Post
    Even if you can separate the controls from the motor loads, many electronic furnace control systems will not like the output of a cheap UPS.
    I wasn't thinking cheap. I will pay whatever is needed to do this right

  6. #6
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    Quote Originally Posted by mkgrady View Post
    I would only do that if I had to. This customer doesn't care what it costs, I just don't know how to size what to get
    If the burner runs from 120 volt single phase at less than 15 amps, just drive the burner through a Kill-a-Watt (TM) meter to collect peak power and average power usage numbers over a representative period of time. The only thing it will not give you is the motor starting surge. Fluke, among others, makes a good meter for that.

  7. #7
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    It sounds like the Owner wants a 'power improvement' device, not a 'power backup' one. Very few small UPS's actually provide power quality improvement.

    You might want to look into what we used to call a Power Conditioner. These transformers provided constant voltage and noise filtering.
    Just because you can, doesn't mean you should.

  8. #8
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    Quote Originally Posted by GoldDigger View Post
    If the burner runs from 120 volt single phase at less than 15 amps, just drive the burner through a Kill-a-Watt (TM) meter to collect peak power and average power usage numbers over a representative period of time. The only thing it will not give you is the motor starting surge. Fluke, among others, makes a good meter for that.
    Not sure what to do with that info. I would think tuning on the burner with all zones calling would give me the same info with an amprobe. Let's say I find the FLA to be 7 amps or 840 watts. How would I go about selecting a UPS for that?

  9. #9
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    Quote Originally Posted by mkgrady View Post
    Not sure what to do with that info. I would think tuning on the burner with all zones calling would give me the same info with an amprobe. Let's say I find the FLA to be 7 amps or 840 watts. How would I go about selecting a UPS for that?
    For selecting the output capacity of the UPS you need to know the VA consumed. But for sizing the battery and looking at run time you need to know the actual watts. Your Amprobe will not give you the PF information. But I agree with Jim that just a UPS, even one which delivers clean sine wave output, will not have the run time that he will need and will not give any advantage when he is running the generator anyway.
    An alternative to a power conditioner would be a dual-conversion UPS in which the output is always driven by an inverter, with the DC to the inverter coming either from the AC line or from batteries. Unlike a power conditioner, that would let him stop the generator from time to time without killing the boiler. This is the sort of equipment designed for servers rather than home computers and is priced accordingly.

    The basic design decision on a UPS is threefold:
    1. Can it deliver the maximum continuous power output needed? Look a the VA and watts of the load.
    2. Can it deliver any motor starting surge?
    3. How long can it deliver the average power output needed? Look at the watts consumed and compare to the watt-hour capacity of the batteries to find the run time.
    A UPS will typically specify the run time at various load levels rather than watt-hour capacity, and for above ~25% load the relation is close to linear. If a UPS can deliver 1Kw for 1 hour, and you need 500 watts average, you will have a run time of 2 hours.

  10. #10
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    Quote Originally Posted by mkgrady View Post
    Not sure what to do with that info. I would think tuning on the burner with all zones calling would give me the same info with an amprobe. Let's say I find the FLA to be 7 amps or 840 watts. How would I go about selecting a UPS for that?
    For an intermittent load, like a burner which cycles or a refrigerator, the total-over-time capability of the Kill-a-Watt is a big advantage. It saves you the work of timing the cycles over a 24 hour period to calculate the average load!
    One caution: Although it will read watts, VA and PF and do a pretty good job for displacement power factor loads like motors, it can give wildly wrong numbers for non-linear loads like LEDs and CFLs which have a poor distortion power factor.

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