Re: !956 Power window electric motor

Posted by HH56 On 2016/3/7 15:56:08

The Packard reversible motors have two field coils which are reverse wound. One coil is used for forward and the other is used for reverse. Both coils are connected together at one end and use that point to provide power to the armature which places it in series with whichever field coil is being used. The other wire from armature is internally tied to ground. In this arrangement, whenever one coil is used, the opposite coil does nothing. The switch takes the power and feeds one of the coils depending on direction needed and the armature sees the different magnetic polarity caused by the different winding direction of field coil and moves accordingly.

Modern motor fields are for the most part permanent magnets so no field coils. The magnetic polarity in relation to the armature never changes. In order to reverse direction on those motors the armature has to reverse polarity. Since there are only the two armature wires brought out either the switch has to do the reversing or in our case, because the Packard switch only has one voltage wire out for each direction those wires would operate relays -- one for each direction. The two relay combinations of N.O and N.C. contacts would switch the positive and negative going to the armature. A motor wire would see voltage for one direction and ground for the other.

Biggest problem with going with solid state relays is polarity and price. Since 55 and 56 have different grounds the solid state relay would need to be configured accordingly and would also be susceptible to damage with an accidentally reversed battery. Most SS relays capable of the current requirements the motor needs are fairly expensive.

A common Bosch style or cube type relay with 40 amp contacts is less than $5 and is not polarity sensitive. All it would take between 55 and 56 is hooking up the Packard switch to operate the proper relay so up and down was correct. If the battery is reversed, the worst that would happen is the window would go opposite to the switch until the battery was corrected.