Melting-Alloy Motor Overload Protector (heater) Test...

[turbokinetic]

<span style="font-family: Calibri;">Here's a video where I verify the function of a motor overload relay, which uses a melting alloy. There is a ratchet wheel soldered to a shaft, which holds the switch in the ON position.</span>

 

<span style="font-family: Calibri;"><span style="font-family: Calibri;">Around the shaft is a heating element. The current supplying the motor is passing through this heating element. If the motor draws too many amps, the heater will heat up the shaft, melting the solder.<span style="mso-spacerun: yes;">  </span>Once the solder melts, the ratchet wheel is free to turn. Once freewheeling, the ratchet will release the switch from the ON position, stopping the current.</span></span>

 

<span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;">The resistance of the heater element is used to calibrate the tripping current. This one is from a General Electric refrigerator compressor. It is a 1935 model, with the fridge thermostat and the motor protector built into the same device.</span></span></span></span>

 

<span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;">Due to the safety nature of this device, I wanted to verify it worked before putting the control to use. The control knob was broken off and a new one was fitted. I wanted to be sure that during this repair, the overload function had not been accidentally compromised.</span></span></span></span></span>

 

<span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;">I<span style="font-family: Calibri;">n real life, the glow was very obvious but not as bright as it seems in the video. The camera must be more sensitive to infrared and near-infrared colors; than my eyes are.</span></span></span></span></span></span>

 

<span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;">Interestingly, the CK Monitor Top fridge this came from has TWO overload protectors. This one in the thermostat; and then a second, auto-reset bimetallic one built into the motor start relay. I guess if the bimetallic failed and welded, this one would be a last-ditch second chance at life.... Normally the bimetallic trips first.</span></span></span></span></span></span></span>

 

<span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;">This one was built in by GE into this control. You can get these stand-alone for other motor applications. The Allen-Bradley and Cutler-Hammer manual motor switches have a similar mechanism in them.</span></span></span></span></span></span></span></span>

 

<span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"><span style="font-family: Calibri;"></span></span></span></span></span></span></span></span></span>

 

[toploader55]

Always Educational.

Always Exceptional.

Thank You.

 

[rp2813]

David,

 

Your knowledge of every system involved in the operation of mechanical refrigeration is truly impressive. 

 

If I knew what you know, I can't imagine the number of appealing refrigerators that I'd have rescued and revived by now.  It's clear that you enjoy what you do.  I would too.

 

Ralph

 

[combo52]

Melting Alloy Overload Protectors

Very cool demonstration David it is truly amazing the cool mechanical devices engineers came up with before we had computers and better manufacturing processes.

 

Some on this site may also know that Frigidaire Unimatic washers and their matching dryers used this type of overload protector. The Push-To-Reset button on the machines was this type of control, in fact FD used these through the 1966 models on their washers.

 

The down side to these controls was poor sensitivity, higher cost of building and shorter life span, fortunately of most appliances the overload does not get used often and durability is not a huge factor.

 

Great demonstration David, keep the cool videos coming.

 

John L.

 

[turbokinetic]

Hi John, interesting about the washers using this type of protector as well!

Honestly I haven't had to deal with too many of these. Maybe had to replace 2 or 3 failed in motor starter buckets, where Captain Reset had been at play. As for old appliances, I restored one Frigidaire belt drive condensing unit where the alloy was gone. I am partially convinced that was a result of corrosion from SO2 leaks more than anything else. The alloy had turned to a bright blue crystalline substance.

 

In the starter buckets; the melting alloy material was displaced from the soldered joint. I think it comes from someone repeatedly banging the reset button again and again before it has cooled down. The failed ones I've seen had little beads of the alloy material in the bottom of the enclosure, and the wheel would freewheel even with the device cool.