Convector heater motor cuts out.

[Phil.cc]

 I have two convector room heaters in the pool enclosure, one at each end, they have been working perfectly for about twenty years, but one of them now cuts out after about ten minutes, then comes back on about twenty minutes later.

The heaters are about five feet long, with two long vents at the front, one at the top and one at the bottom. Behind the bottom one is a rotary cylinder fan unit and motor, there are three cylinder fans that rotate freely via a steel rod, two on the left then the motor and one on the right, air is sucked in from the lower vent, it goes through a car type radiator above and warm air expelled through the top vent.

To me, it sounded like a faulty thermostat, (this is adjustable), it's not needed so I bypassed it completely, which means, the same power supply to the two heaters via two switches, that didn't work as it still cuts out. The motor gets hot, I changed the capacitor, no difference, I have a spare, brand new un-used heater unit, I swapped it, and there's no difference. The vents have foam filters, to stop dust etc, if these were restricting the airflow, then that might cause the motor stopping...so I removed the foam, the motor still cuts out after about ten minutes and comes back on after about twenty minutes, the other heater works fine.

Any ideas please?

 

[ProDave]

My guess is the bearings have gone stiff and the motor is struggling to turn the fan and hence it is getting hot and bothered.

Put those thermostats back into circuit.  They are a safety feature to stop the heater overheating and catching fire if the fan stops.  As above I suspect the fan is rotating too slow so it is getting too hot hence the thermostats are cutting out.

You might try just lubricating the bearings first to see if you can get it spinning freely.

 

[Evans Electric]

You might try just lubricating the bearings first to see if you can get it spinning freely.

That was my thought when I read it .    Squirt of WD40  at the ends of the rotor  .    As Dave says ,  the fan speed keeps the element from overheating . 

 

[Phil.cc]

Thanks dave but the motor runs free and at full speed, as I mentioned, I changed the whole fan and motor unit for a brand new un-used one, it has sealed for life bearings, I could try a squirt of WD40 into the motor bearings as although it is new and has never been used before, it's been stored for about eighteen years.

 

[Phil.cc]

I squirted WD40 into the bearings and run it, it cut out after about twenty minutes and the motor a very hot!

This unit originally had a three speed switch, it was always on the fast speed but a few years ago it burnt out so I bypassed it, but strange how it burnt out. My other heater on the other side of the room still works perfectly, the two units are on the same power supply.

 

[Geoff1946]

I don't recommend WD40 as a bearing lubricant. It dries out quickly and becomes sticky. For bearings use a light machine oil like 3 in 1 or a bit of what you top up the car engine with. I'm not saying that's your present problem though as WD will work in the short term.. Are you sure you got the connections right when you took out the speed control switch?  Does the whole assembly spin freely by hand?

 

[Phil.cc]

There's four wires, the black, blue and red (neutral) are connected together, the white is live, the brown is tucked away and not in use, the other two are to the capacitor which is new.

The whole assembly spins easily by hand, just a very slight resistance, I think due to the three fans, which is the same on the old unit I took out.

BTW, I see you are in Blackpool, I lived there for three years in the mid 60's when I payed in a few bands

 

[Geoff1946]

There's four wires, the black, blue and red (neutral) are connected together,

Well that seems odd to me but without seeing the original wiring arrangement before the speed control was removed, I couldn't say if it's right or wrong. Is there a schematic in the manual?

 

[roys]

If they are sealed for life bearings it probably means that the bearings have rubber grease shields on them so oil probably won’t be able to penetrate to lubricate. As said above I would have suspected faulty seized bearings as well. However a bit hesitant after you said it spins freely. Although the unit is broken just now anyway so I would give it a bearing change. At least then that is that possible fault eliminated which on an old heater motor has to be suspect, bearings are only about £4 each anyway.

Wild guess is that the bearings might have a number on them like 6202RS, the rs stands for rubber seal or if it is say 6202zz which is metal shield covering the ball race. This is what makes it sealed for the life of the bearing not the life of the motor or hearter.

 

[Geoff1946]

I'm very suspicious of your wiring modification when you removed the speed control.  A common way of speed controlling a small motor is with three tappings on one winding.  One tapping is connected to supply at a time, to give slow, medium, or fast.  If you have connected any two tappings together that shorts out part of the winding, which WILL then get hot.

I'm attaching a generic wiring diagram of a three speed fan. This is NOT your unit and wiring colours may be different but it may illustrate my point.

 

[Phil.cc]

Thanks for the replies, later I will check my other heater, first to compare the fan/motor spin to see if it's the same as the problem one, then, I'll make a note of the wiring, this one has the three speed switch and stat connected, the three speed switch with the faulty one had burnt out so I bypassed it and the stat, however the stat can be re-connected.

 

[ProDave]

I share the concerns of others. Only 2 of the motor wires should be connected.  If you have them all connected it will simultaneously be trying to run at 3 different speeds and each winding will be fighting another hence the motor getting very hot.

 

[Phil.cc]

SOLVED !

As suggested, I've just tried single wire connection and I'm getting slow, medium and fast speeds, I've run the unit fot forty minutes and everything is fine, what's more, the motor is just warm, so thanks all for the input and to Geoff1946 for the wiring suggestion and info

Phil

 

[Geoff1946]

Thank you for reporting back.

 

[Evans Electric]

SOLVED !

As suggested, I've just tried single wire connection and I'm getting slow, medium and fast speeds, I've run the unit fot forty minutes and everything is fine, what's more, the motor is just warm, so thanks all for the input and to Geoff1946 for the wiring suggestion and info

Phil

Great to arrive at a successful conclusion .     Nice one  from Dave  & Geoff 

 

[Phil.cc]

I now realise that when the three speed switch blew (I don't know why, it might be down to condensation) I bypassed it, but didn't thing that each of the three wires went to a different winding

 

[NozSpark]

... that big fan heater in Zone 1 !!!!!!!