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Testing heater strips — Parallax Forums

Testing heater strips

NickSrNickSr Posts: 7
edited 2009-06-15 14:26 in BASIC Stamp
Hello,

I·have a BS2 application that measures temperature of wood material as it is heated in a large chamber. We are using a 480V stepup transformer.·the BS2·controls a 3-phase 25 amp SSR for the fan·and two 3-phase 50 amp·SSR's for the heater (twelve 4150 watt fin strips). Our first 3·heats·came to temp (140 deg F) pretty quickly. About 12 hours. Each of the next·heats has·taken successively longer. We know·from the electric company meter reading that the most recent heat used only 344 KWs over a 26 hour period and we are not up to temp yet. Shouldn't we be using 49.8 KW's per Hour? Unfortunately there are no meter readings available from·those first 3 heats.·

Our fan is working as well as it did when we started.

I am wondering how we can record information as to how the fin strips are working. i.e. measure the current going through each fin strip. We think they may be degrading somehow, or possibly not working. How does a fin strip "burn out"?? The temperature of the heat sinks that the relays sit on was about 110 deg F.· The heater load is 480V 3-phase as is the fan.·

Any comments or suggestions would be very helpful!!

Thanks!

Nick

Comments

  • UnsoundcodeUnsoundcode Posts: 1,532
    edited 2009-06-10 00:17
    Hi, you could put a clamp meter on each of the legs from the relays to measure the current or you could kill the power and do some resistance checks.

    The results would depend on how the heaters are configured. It looks like you would expect each relay to have 3 heater pairs connected in parallel in a delta configuration to produce ~50KW. Your observations suggest they could possibly be connected as 3 heater pairs connected in series as a "Y" configuration which would produce ~13KW. I'm not 100% on those figures but it seems right.

    Heaters usually do work or don't but they can burn out although from what you say it seems unlikely.

    Only other thing I can think of might be some serious voltage drop at the transformer.

    Don't forget LOTO

    Jeff T.
  • NickSrNickSr Posts: 7
    edited 2009-06-12 22:05
    Jeff,

    Thanks for your help. As you suggested, we put a clamp meter on the three load Wires for each SSR. Found that one SSR was fine and·one SSR had failed. Probably due to heat from the heavy load in an enclosure with no air vent or circulation. We used the good SSR to control the much smaller loads of two new mechanical contactors that controlled the heavy loads of the heaters. Seemed to work well.

    Thanks again for your help!

    Nick

    What's SOLO?
  • UnsoundcodeUnsoundcode Posts: 1,532
    edited 2009-06-12 22:34
    Hi Nick, sounds like you resolved everything, the SSR to contactor should work well I'v seen both forms of control.

    LOTO is an acronym for lock out tag out , it's a recognized standard saftey procedure of ensuring equpment is de-energized from mechanical and electrical energy.

    It was just my way of saying take extra care with 480v

    Jeff T.
  • NickSrNickSr Posts: 7
    edited 2009-06-15 14:26
    Re: LOTO

    Thanks Jeff,

    just checked with HR and our ops mgr. We have LOTO procedures on our other equipment and they will put one together on this one.

    Nick
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