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MOTOR CAPACITOR RATINGS

Hey Bill,

Most P ermanent S plit C apacitor motors have different windings for the main and auxiliary windings. The auxiliary windings usually have more turns of smaller wire with the cap in series. Due to the phase shifting we were talking about, the current in the auxiliary winding peaks before the current in the main winding, giving a rotating field effect which causes the rotor to turn in a direction determined by the relative polarity of both sets of windings.

One other point. . . with PSC motors (single speed), the two windings are connected end-to-end, as though they were in series, but the AC line is connected to the centre-tap and the end lead of the main winding. The capacitor is connected between the two end leads(main and auxiliary). That way the current has to pass through the capacitor (Simplified, pentagrid!) connected in series with the auxiliary winding in order to get back to the other line (connected to the centre-tap). They are only reversible with four leads, as the relative polarity of the auxiliary winding must be reversed in relation to the main winding in order to run in the opposite direction. Variations include the multi-speed direct-drive furnace fan motors, which use a multi-tapped main winding to get the various speeds. The more turns there are in the main winding, the weaker the motor is at the same applied voltage, therefore the slower it runs when loaded. An important point. . . the motor is still trying to run at it's theoretical speed (determined by the number of effective poles and frequency of applied current), it just isn't strong enough to maintain that speed. It has a greater percentage of "slip". These motors are usually intended for direct-drive air-handling equipment. They will overheat if used to supply mechanical power without auxiliary cooling.

Regards,

Dave D.

Wild Bill wrote:

Reply to
Dave D. via CraftKB.com
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Multi speed PSC motors. . .

The auxiliary winding is connected across the high speed tap of the main winding. That way, if a lower speed is selected, the volage applied to the auxiliary is also dropped by the proportion of the lower speed tap to the high speed.

I don't want to try to draw any more pictures using punctuation. Did any one get more than the first diagram in the previous post in any logical form? When I go back to read it now, it doesn't line up.

Dave D.

Reply to
Dave D. via CraftKB.com

Dave,

I have numerous 3-lead PSC motors that are reversible, so the statement about requiring 4 leads to be reversible, isn't accurate.

For an example, look at some Oriental Motor PSC wiring diagrams. BTW, the OM PSC motors are capable of being run at continuously variable speeds, by using the OM speed control modules.

Some manufacturers utilize a method of changing the value of the capacitance to provide different speeds, as in low-med-high, by using a dual capacitor of 2uF and 4uF (to be able to connect a capacitor value of 2, 4 or 6uF).

WB metalwork> Hey Bill,

Reply to
Wild Bill

You have a 2 phase motor of the first type with two identical windings 90 deg apart. It is optimised for easy reversing and good starting torque ("good" means a bit better than lousy!). The penalty is that it needs a large value run capacitor.

Looking at it drawn with the windings connected to form a Vee, with the capacitor bridging the top open ends of the Vee. Supply to Vee base and LH top gives forward rotation. LH Vee is the main winding, RH Vee is the capacitor phase.

Moving supply high from LH Vee to RH Vee gives mirror image operation. The motor reverses. The RH Vee is now the main winding and the LH Vee is the capacitor phase.

Jim

Reply to
pentagrid

According to Dave D. via CraftKB.com :

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1) Use a fixed-pitch font (such as Courier), not a proportional pitch font (such as Times Roman or Helvetica or whatever your system offers).

This is because differing systems have different ideas of how much the spacing of different letters varies -- and some systems make it very difficult to use proportional spaced fonts in a newsreader anyway. Remember -- not everyone uses the same computer here.

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While you are about it -- make sure that each line is ended with a hard return. If your program folded the line for you as you typed in, it *may* be sending it out with each paragraph as a single long line, and the chances of it being mangled more on other systems is greater.

4) Always remember to remind others to switch to a fixed pitch font (with Courier being a good suggestion as it is almost alway available on systems with multiple fonts), or *their* variable pitch setting will distort things anyway.

And yes -- it was mangled when I saw it, and I *always* use a fixed pitch font for newsreading rather than switch back and forth, which is a pain on my system.

Be aware that anyone who quotes your ASCII graphics will probably distort it -- sometimes beyond recognition. :-)

Enjoy, DoN.

Reply to
DoN. Nichols

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