OT question for any electricians out there.
term1te
Posts: 1,462
Is it possible/safe to run an electric motor off a light dimmer switch?
We have an open fire that has a built in fan that blows air behind the fire and out the other side, heating the room. Its great, saves some of the heat that would have been wasted up the chimney. The on/off and fan speed switch got snapped off a while back. I glued it back on, but it’s been snapped again, and the broken end has gone missing. I took the whole thing apart today; looks like Edison built it himself. The broken bit is a rotary switch which has 5 wires all leading to different heavy duty resistors, then on to the motor.
The motor says its 220V and 95W, similar to a light bulb. So is it safe just to replace the existing components with a light dimmer switch? There are no markings on the broken switch to identify what it is, so finding a replacement won’t be easy. I guess the whole thing is about 30 years old.
Many thanks!
We have an open fire that has a built in fan that blows air behind the fire and out the other side, heating the room. Its great, saves some of the heat that would have been wasted up the chimney. The on/off and fan speed switch got snapped off a while back. I glued it back on, but it’s been snapped again, and the broken end has gone missing. I took the whole thing apart today; looks like Edison built it himself. The broken bit is a rotary switch which has 5 wires all leading to different heavy duty resistors, then on to the motor.
The motor says its 220V and 95W, similar to a light bulb. So is it safe just to replace the existing components with a light dimmer switch? There are no markings on the broken switch to identify what it is, so finding a replacement won’t be easy. I guess the whole thing is about 30 years old.
Many thanks!
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Comments
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I'm no electrician, but I'm pretty sure it depends on whether its wired into the lighting circuit or the the mains (plug socket) circuit. if it goes into the lighting circuit, then yes, it should be safe because its designed to cope with the lower loading of the lighting circuits, but if it's the mains, then no. You'd have to trace the wiring, though, to see which loop it went into.
You could maybe get around it by trying to find a heavy duty dimmer switch, or a fused switch. I think the fuse would go before the switch itself burnt out.
Like I said, I'm no electrician, but I think that it's the fuse that's important when wired into the mains. Imagine, you can have lights and all sorts of devices that use those small electic motors running off the mains circuit. We plug them in every day, but they are not wired directly into the circuit, and they have a fuse in the plug to take care of any problems.
Hope that helps.0 -
Some of those "resistors" may actually be "capacitors" - so, if you get it wrong there may still be a large charge sat in there (even if isolated from the mains). :shock:
...so be VERY careful!
Are the 5 wires connected via slide-on connectors, or soldered? If you can (SAFELY) remove the switch, you could take it to Maplin & see if they have something suitable to replace it with. Tape over the loose ends as you go.
***do at your own risk***Cycling weakly0 -
The dimmer will be designed to run on the 5A lighting circuit. If you wire the motor into the lighting circuit it will want to draw more than 5A, so will trip the light circuit out before you get up to full speed. If you were to wire the dimmer into the mains, the current at the motor's higher speed will potentially cause it to burn out.
You will be able to get a suitable rotary switch from the likes of Maplin, but for anyone who has not messed around with electronics I'd recommend that you find someone who is capable of doing a proper electical repair. It will take unsoldering the resistors before removing the old switch and resoldering them back onto the new one, keeping them in the right order.To err is human, but to make a real balls up takes a super computer.0 -
He said the motor is only 95W so it can run off a lighting circuit (why you would do that I don't know!!). Photo would help us
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The motor may only be 95W but what is the ampage, that is the important part, I agree with the capacitor comment, check first.0
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The amperage will be 0.4A, maybe 1.5A Surge tops.. Sill that doesn't answer his question of if a dimmer switch will work. My guess is not as they don't like inductive loads.0
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volvicspar wrote:The amperage will be 0.4A, maybe 1.5A Surge tops.. Sill that doesn't answer his question of if a dimmer switch will work. My guess is not as they don't like inductive loads.
This is correct, also a motor is more likely to produce an overload if it fails than a lightbulb. If a lightbulb fails, it generally instanltly goes open circuit. But if a motor seizes it can suddenly draw a large current, before whatever device is protecting it operates.
As a motor is an inductive load, in a fault condition it may cause damage to the dimmer, or worse cause the dimmer to get very hot.
It is the same principle that prevents dimmers working on flourescent fittings because the choke is inductive (a coil).0 -
The last two posters are correct. I am not sure if tebbit is a troll or an idiot.
If you can find a massively overspecified dimmer, then it might hold together for a while. You should be able to pick up a rotary switch and a bunch of appropriately rated resistors from somewhere like Maplins.0 -
Alternatively you can attach the fan to you turbo trainer and voila 2 fold heating
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Ummm, can you not just buy a replacement switch that is designed for purpose rather than chancing it with a light dimmer switch? Dimmer switches can work in two ways, chopping or pure resistance. If you don't know what you're looking for better find someone who can physically inspect the switch and offer sage advice.
Connecting a chopping dimmer to a motor doesn't bear thinking about. No idea of the consequence but I doubt it's the right solution.0 -
Hi, thanks for your comments. I'll see if I can clarify the problem. The motor has a label saying it is 220V and 95 W, so I guess the current must be 0.43 A. It is already wired in to the mains circuit, not the lighting ring. The wires from the switch, do go to the strange devise, which at first I thought was a transformer, but as there is only one wire in, one wire out of each section I guess must be a bank of resistors. They don't look like capacitors, unfortunately no markings to suggest either way. There does appear to be something that could be a capacitor on the back of a mounting board, but it is fixed in place and you can't really see it. It seems if I have an inductive electric motor that a light dimmer switch is not a good idea, if however it is a standard motor it will be OK. Any ideas on how to tell which sort of motor it is?
I'll try to take some photos this evening.
Cheers0 -
All readily available (what you call standard) motors are inductive. They contain a coil which when rotated inside a magnet will produce a current (hence a motor works by applying a current to the coil and the motor rotates). The ratings of the motor are irrelvent, its the principle that is the issue here.
I will give you some very clear advice. DO NOT CONNECT THE MOTOR THROUGH YOUR LIGHTING CIRCUIT VIA A DIMMER.
If you do choose to go this route, when it is completed and wired up please make sure your smoke alarms work and your family knows how to escape when your house fills with smoke. You might also want to let your insurance company know in case they want to pull your cover.
While MBA007 is absolutely correct about chopping dimmers, a resistive dimmer will control the speed of the motor through increasing the resistance on the circuit. The natural result of this is heat. The item you are describing may be a choke. If you do not know what a choke is or does, then I suggest that you proceed no further.
Please don't think I am being an @rse. It is wiring faults that cause most house fires after smoking.0
