Weining Grinder contactor heater

Discussion in 'General Electronics Chat' started by oellasawandtool, Apr 4, 2007.

  1. oellasawandtool

    Thread Starter New Member

    Apr 4, 2007
    1
    0
    We have a 460 3 ph machine that I just switched to 230, I swithced the jumpers at the block and the jumpers at the transformer, ran for 3 minute sthen shuts off-

    I think the problem is the heaters are being overloaded and tripping. An electrical guy helped me figure they are in fact underated now that I am running low voltage, here is my question: Should I just replace the contactors as the heaters are 58 bucks each, i need 6 because there is a grinder motor and a pump motor- Or should I get a step up transformer, or 2 new cutler hammer starter contactors with a higher amp rating?

    If you have time to ponder and give input it would help- If you are in Maryland and you want to trade your time for woodworking tooling: shaper cutters, router bits etc. let me know!

    Thanks
     
  2. wireaddict

    Senior Member

    Nov 1, 2006
    133
    0
    You need to change the connections on the motors for 230V also, assuming they're dual voltage, like you did the transformer. Running them at half the voltage doubles the current they need, hence the overload heaters are now too small. $58/heater is quite high; I'll bet this is an old machine & the heaters & motor starters are nearly obsolete to justify that price. Check with your nearest Square D, Allen-Bradley &/or Cutler-Hammer distributors for prices for new motor starters & heaters [3 per starter]. Be prepared to give them the full-load current at 230V & the coil voltage for them. You'll have to compare prices between the right size heaters, new starters with heaters & a step-up transformer to find the best price. Also make sure the tranny is big enough to run the machine; multiply the sum of the 480V full-load currents of the motors times 1.25. That's the current it needs to be able to supply so it doesn't overheat. BTW, if you want to buy a house in the Flint, MI area let me know!
     
  3. phillip.casten

    New Member

    Nov 21, 2008
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    WHAT IS THE PURPOSE OF A MOTOR STARTER HEATER
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,039
    287
    It limits the current in the motor while it's coming up to speed. It's just a resistor and a time delay contactor.
     
  5. awright

    Well-Known Member

    Jul 5, 2006
    84
    7
    KL7AJ, I beg to differ. The motor starter heater is a fault-current sensor that causes the contactor to open if the motor current is too high for too long a time period. It is not a current limiter, but an overload current sensor with a built-in thermal time delay. The thermal time delay prevents the motor starter contactor from opening during the normal motor starting inrush current, but will shut off the motor if there is a sustained overload condition that could burn out or damage the motor.

    The heater is wired in series between the power source and the motor. It reacts to motor current by getting hot. If the motor current is too high for too long a period, the heater gets hot enough to melt the low melting-temperature alloy inside the thermal element. When the alloy melts, a tiny ratchet that was spring-loaded when you last "RESET" the starter is freed to rotate. When the ratchet rotates, it releases the force holding the contacts feeding power to the motor closed, shutting the motor down and hopefully saving the motor from burning out.

    This function does nothing to LIMIT the motor current except in the sense that if the current is excessive, the contactor switches the motor off. It acts like a resettable fuse.

    There are other devices designed to limit motor starting current by means of series power resistors that drop line voltage during starting, but their function is to reduce the voltage initially applied to the motor thereby reducing stress on the machinery, not to get hot. These starting resistors (rarely if ever seen on an ordinary machine tool motor of one or a few HP) are heaters only in the sense that they get hot as a side effect of their voltage dropping function, not as the primary purpose of the resistors. Conversley, the PURPOSE of the motor starter heaters is to get hot if the current exceeds the heater rating, thus releasing the contactor.

    Grainger's (www.grainger.com) heaters are listed at about $13 each. Of course, you have to match the heater exactly to your starter model and the motor characteristics. Why are you getting such high quotes? They all do about the same thing. Shop around. In my area we have an electrical supply house that handles used/salvage/surplus electrical supplies. Not junk, but perfectly good materials that were disposed of by contractors, retailers, manufacturers, etc., who did not need the materials any longer. It's called Ace Liquidators. (510)-522-7622 http://www.aceliquidating.com/index1.html. I'm sure they have an assortment of motor starter heaters. They generally sell at half of list price.

    awright
     
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