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Old 4th Jul 2010, 4:36 pm   #1
Radio_Dave
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Default Vintage Limit Fan

Hi,

I've just brought my first vintage fan. It's, obviously, made by Limit but can anybody identify the model and year of manufacture?

Any tips for dismantling and reassembling the motor? The last photo shows the rear view, is that screw on the top to allow lubrication?

Again on the last photo the nuts holding the motor together seem to have been painted after assembly. Should the motor be painted whilst in parts or assembled and then painted?

TIA
David
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Old 7th Jul 2010, 6:56 pm   #2
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Default Re: Vintage Limit Fan

Okay, I dismantled, cleaned up and reassemble the AC motor. Trouble is it's drawing 600mA, at mains voltage. I calculate this to be 144 watts which is far higher than the 35 Watts quoted on the motor.

Could I have reassembled it incorrectly?

David
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Old 7th Jul 2010, 7:15 pm   #3
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Default Re: Vintage Limit Fan

A lot of that current could be reactive. Unless you have a meter that can read watts and VARs the simple but hazardous way to check is with a dual trace scope and a small resistor in the neutral. You can measure both voltage and current this way and see how far out of phase they are. You really shouldn't attempt this without an isolating transformer.
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Old 7th Jul 2010, 7:49 pm   #4
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Default Re: Vintage Limit Fan

If you do the resistor-in-the-neutral thing, you can use the variable setting to get the two traces the same height and then put the scope into X-Y mode. A perfectly resistive load will give a diagonal line; a perfectly reactive load will give a circle. A mixed load will give a slanting ellipse, whose width will indicate just how reactive it is.

Always use an RCD when working with live mains like this -- and if a partner is working on a computer elsewhere in the house, have them save it before you start. Otherwise, don't expect any sympathy from them for the electric shock that caused the power failure that trashed an important document!

If you don't feel safe doing this, then most plug-in energy monitors can show the power factor of the load as one of their display modes. Some electricity boards might even send you one for free.
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Old 7th Jul 2010, 8:00 pm   #5
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Default Re: Vintage Limit Fan

Just pointing out that the procedure AJS recommends is hazardous. In practice it's usually fine, provided you know what you are doing. The correct method is to use an isolating transformer so that the scope can stay safely earthed.

I likethe idea of making a lissajous figure to show the relative phase of V and I.
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Old 9th Jul 2010, 5:40 pm   #6
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Default Re: Vintage Limit Fan

I have just plugged a similar (10" blade dia) model into one of the energy monitors referred to above - 32 watts, 49VA.
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Old 9th Jul 2010, 6:28 pm   #7
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Default Re: Vintage Limit Fan

Quote:
Originally Posted by ajs_derby View Post
If you do the resistor-in-the-neutral thing, you can use the variable setting to get the two traces the same height and then put the scope into X-Y mode. A perfectly resistive load will give a diagonal line; a perfectly reactive load will give a circle.
A perfectly reactive load, actually, will generally give an ellipse; it will only be a circle if the X and Y sensitivity controls are set appropriately.

However, this ellipse will always be either on its side or one its end; it'll never be at a slant, which is (just as ajs_derby says) the case for a 'mixed' load.
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Old 10th Jul 2010, 12:20 am   #8
Lucien Nunes
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Default Re: Vintage Limit Fan

So Nick's fan uses 49VA, that sounds much more reasonable than 144.
Possible causes for David's motor eating too much current:

Shorted turns in winding
Incorrect connection of taps if multi-speed
Rotor not properly located within stator lamination stack
It's a 110V model!

I've discounted stiffness as I'm sure David wouldn't have fired it up until he was happy that it ran freely. If it starts looking like there are shorted turns, perhaps the winding resistances could be compared with Nick's one?

Lucien
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Old 10th Jul 2010, 11:58 am   #9
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Default Re: Vintage Limit Fan

Quote:
Originally Posted by Lucien Nunes View Post
So Nick's fan uses 49VA, that sounds much more reasonable than 144.
At the time of my post I didn't understand the difference between inductive and resistance loads. Hence my mistake of using ohms law to calculate the current drawn.

Unfortunately I do not have an isolating transformer, so I cannot take the reading as advised, but the fan does run freely, the windings look ok and there's no smell of burning. There is some tremendous end float, but I doubt this would cause problems.

It's been running for about 3 hours this morning and it seems to work well, although the motor does get a bit hot, but I imagine it would be?

Thanks
David
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Old 10th Jul 2010, 1:57 pm   #10
Lucien Nunes
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Default Re: Vintage Limit Fan

Checking the current immediately on first power-up as you did is a good idea and I too would be concerned that it is so high. Nick measured a real power of 32W and an apparent power of 49VA, i.e. his motor has a power factor of 0.65, which sounds OK for a small shaded pole motor under load. Yours is rated 35W, yet from your current measurement consumes 144VA apparent power, which (if the real power is actually 35W) corresponds to a power factor of 0.24, which seems too low. So my hunch was that the real power is actually greater than 35W, indicating a fault of some kind that would manifest as overheating.

Another good quick test, where a motor has two or more identical coils, is simply to compare their resistances. It is so long since I took one of those Limit fans apart, I can't actually remember what their motors look like inside.

Lucien
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Old 11th Jul 2010, 6:55 pm   #11
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Default Re: Vintage Limit Fan

DC resistance 367 ohms on Hi speed and 439 on Lo. To complete the picture, indicated power draw on Lo speed is 20 watts / 35VA.

I also have a Frost fan and both are in regular use - especially in this weather!
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Old 11th Jul 2010, 7:53 pm   #12
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Default Re: Vintage Limit Fan

Thanks Nick,

Mine measures a very disappointing 175 ohms on high and 231 on low
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Old 11th Jul 2010, 9:33 pm   #13
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Default Re: Vintage Limit Fan

Quote:
Shorted turns in winding
Incorrect connection of taps if multi-speed
Rotor not properly located within stator lamination stack
It's a 110V model!
Looks as though the last possibility may be the correct one!
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Old 11th Jul 2010, 11:13 pm   #14
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Default Re: Vintage Limit Fan

Nope, the plate clearly states 240 to 250V.

I suppose the million dollar question is, what do I do with it? I've had it running for hours and it seems to be working perfectly, albeit a bit hot. Should I keep using it?

David
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Old 11th Jul 2010, 11:29 pm   #15
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Default Re: Vintage Limit Fan

Actually got round to looking at the plate on mine and it is rated at 25 rather than your 35 watts. It does run warm, almost hot, as does the Frost. FWIW I'd say carry on using it but, like any old electrical gear, don't leave unattended.
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Last edited by Dave Moll; 12th Jul 2010 at 10:39 am. Reason: unnecessary to quote preceding post in full
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Old 13th Jul 2010, 9:35 am   #16
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Default Re: Vintage Limit Fan

Dave, if its been running OK for three hours without any sign of burn-out, then I would say that everything is correct with this fan. The motor will always dissipate some heat, this is normal. I would tend to suspect the meter, this could well be at fault. Do try one of those energy monitors, that would give you a definitive reading.
Neil
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Old 14th Jul 2010, 1:41 pm   #17
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Default Re: Vintage Limit Fan

I have an early GEC and that gets hot.Just dont leave it unattended.
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Old 14th Jul 2010, 1:48 pm   #18
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Default Re: Vintage Limit Fan

Thanks for all the replies.

Since my last post I've re-painted and polished it up. It looks great now!

I've had it working, regularly, for hours on end without any problems and the new paint isn't showing any signs of peeling, so I guess it can't be getting that hot

David
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Old 16th Jul 2010, 11:01 pm   #19
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Default Re: Vintage Limit Fan

Quote:
Originally Posted by ppppenguin View Post
A lot of that current could be reactive. Unless you have a meter that can read watts and VARs the simple but hazardous way to check is with a dual trace scope and a small resistor in the neutral.
If you don't have a shuftie-scope, you could do it by connecting a suitably-rated capacitor ('X'-rated) in series with the fan and an ammeter and measuring the supply voltage, the voltage across the fan (a combination of Xl and R), and the voltage across the capacitor.

As the capacitor is a known value and you have a voltage and a current, you can obtain a reactance (neglecting any small capacitor losses), and assume a -90 degree angle WRT to the current phasor. You will also have the impedance of the fan, from the voltage dropped across it divided by the current. The supply voltage is the vector sum of the voltage across the capacitor and the voltage across the fan.

You now have three sides of a triangle, but no angles. Using the Cosine rule, the angles can be obtained. The triangle you end up with can be split by a horizontal vector representing the resistive component, and the voltages dropped across the resistive and inductive components can be deduced using trigonometry.
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