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How to test your Glue Pot heaters to see if they are bad?

 

All glue pots on edgebanders have heaters.  They mostly have cartridge (pencil shaped) heaters, but some of them have plate heaters also that are usually mounted to the bottom of the glue pot.

 

If your glue pot is supposed to heat up in 10-15 minutes, but you noticed lately that it takes 25-40 minutes, you most likely have burnt out heaters.  Heaters burn out like a light bulb, they are either working, or they are not.  Usually there are several cartridge type heaters in the glue pots, usually between 4 and 6, and sometimes there are also flat plate heaters on the bottom of the pot. 

 

There are also cartridge heaters near or inside the glue roller.  Sometimes there is one, and sometimes two.  If there are no heaters working by or in the glue roller, you are DOWN.  Because the glue roller will not get hot enough to apply a proper glue bond.

 

Additionally there is a temperature probe inserted into the glue pot, usually nearer the front to measure the glue pot temperature.  Sometimes there are two temperature probes, one to measure the glue pot and one to measure the glue roller temperature.  Unless your edgebander has two temperature readouts, you will only have one of these.  I only mention this probe so as not to confuse it with a heater. 

 

Often times the heaters in the glue pot are of different wattages.  Sometimes they are different diameters and different lengths as well.  You do not want to mix up these sizes and wattages because you will have problems.  Electrical contactors in the control cabinet automatically turn off and on depending on what the temperature control is telling them to do. 

 

Typically there is between 1 and 3 contactors connected to 4-6 heaters.  The particular heaters these contactors are connected to are very important because they are sized properly for the different amperage of the different heaters.  So, when replacing the heaters, you must mark the wires and the locations where they go so that you hook them back up to the correct contactors.

 

Now, here is how you test the heaters.  First MAKE SURE MACHINE IS TURNED OFF, and then you have to find where they hook to the contactors in the control cabinet.  Sometimes on newer machines all the heater wires, (and usually the temperature probe wires) are routed to an external multi pin plug that plugs into a receptacle on the machine.  This makes it a little bit easier to check, but you still have to use caution to not mix up the wires.

 

Either way, ONE AT A TIME, disconnect the heater wires from the plug or contactors.

There will be two wires per heater, almost all of the heaters these days are 220 volt single phase.    Now, with the wires disconnected, use your volt ohm meter set on ohms to check resistance of the heater.  So you place one probe on one wire of the heater, and the other probe on the other wire of the heater, and if the heater is good, you should read a resistance number.  For example, if the heater you are checking happens to be a 500 watt heater, you should read resistance of around 97 ohms.  That means the heater is good.  If the circuit is open (No resistance) then the heater is bad.  Just make sure you know you are holding each probe on one wire of the same heater.  If you get mixed up and hold the probes on two different heaters your test is invalid, and you have not learned anything.

 

Now I will explain and show you the calculation for determining what wattage heaters you are checking once you have read a particular resistance.

 

Let’s let

 

I  = current, (which is amps)

V= voltage, (usually 220 volts)

R= resistance

W=watts

 

Important point:  Most heaters on edgebanders are running on approximately 220 volts.

Important note:  MAKE SURE THE MACHINE POWER IS OFF WHEN DOING THIS CHECKING.  IF NOT YOU COULD GET SHOCKED!

 

Ohm’s law

 

I = V

      R

 

Volts X Amps = Watts

 

V x I = W,    So

 

watts (W)                    =         volts (V)

volts (V)                                 resistance (R)               So,

 

 

watts (W)                    =         volts (V)  x  volts (V) 

                                               resistance (R)                   So,

 

 

watts (W)  = Volts (V) (squared)                                  

                      resistance

 

 

                             Or,

 

resistance (R) = Volts (V) (squared)

                           watts (W)

       

So, if we know from looking at the schematics or looking at the heater that it happens to be 500 watts, and we multiply 220 volts x 220 volts, which equals 48400 volts, then when we divide by the resistance we read on the meter, (which should be 97 ohms approximately,) then we know that the heater is good, and that it is a 500 watt heater.

This can help us in case we accidently mix up the wiring.

 

Next, if we try another one and get a reading of 242 ohms as resistance, and we divide (220 volts x 220 volts) which equals 48400 volts by 242 ohms, we get 200 watts as the size of our heater.  Again, this reading proves the heater is good and is a 200 watt heater. 

 

But now if we try another, and get zero ohms, and we are sure that one probe is on one wire of the heater, and the other probe is on the other wire of the heater, then the heater is bad and needs to be replaced.

 

IMPORTANT NOTE:  As I said before, you must disconnect the heater wires from the plug or contactor or you will get a false, (incorrect reading)

 

To replace the heaters you will most likely have to heat the glue pot up some, and see if there are any set screws holding the heaters in place.  Sometimes there are, and sometimes there are not.  Sometimes the heaters pull out easy, and some times hard. 

 

So, hope this helps, more tutorials coming in the future.   Please don’t forget to check out our New Edgebanders for Sale Page.

           

                   

 

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