Mister Kool
Member
do you test bad coils by testing the resistance on the coil???
what should the resistance be (high/low)??
thanx Mister Kool
magnetic coils resistance
- Thread starter Mister Kool
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do you test bad coils by testing the resistance on the coil???
what should the resistance be (high/low)??
thanx Mister Kool
If it's a coil from a typical AC contactor, it won't have much resistance.
do you test bad coils by testing the resistance on the coil???
what should the resistance be (high/low)??
thanx Mister Kool
Probably the best you can get from a DC measurement is continuity.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090526-1210 EST
Mister Kool:
You need to know the nominal resistance of a good coil. If your measurement of a particular coil differs by maybe more than +/-5%, then it may not be good. Also it could read correctly at room temperature and not be OK under operating conditions.
If the resistance is higher than it should be, then maybe a bad internal connection. If the reading is near infinite, then an open coil.
If the reading is lower than nominal, then there is likely a short between turns.
There is the possibility that a coil that reads good at room temperature might internally fail at elevated or lower temperatures.
.
Mister Kool:
You need to know the nominal resistance of a good coil. If your measurement of a particular coil differs by maybe more than +/-5%, then it may not be good. Also it could read correctly at room temperature and not be OK under operating conditions.
If the resistance is higher than it should be, then maybe a bad internal connection. If the reading is near infinite, then an open coil.
If the reading is lower than nominal, then there is likely a short between turns.
There is the possibility that a coil that reads good at room temperature might internally fail at elevated or lower temperatures.
.
Mister Kool
Member
thanx a lot
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
more than a few coils used with AC have a bridge rectifier in them; 1.5V meters won't QUITE overcome 2 diode drops to indicate. Be sure your meter uses (usually 9V) enough to handle that.
I had one customer when I was in sales return his new coils because all were open ... they worked fine.
I had one customer when I was in sales return his new coils because all were open ... they worked fine.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090527-2233 EST
An AB 709COD #2 starter with coil 72A86 120 V 60 Hz has a room temperature DC resistance of 40.1 ohms.
This can be easily read on a Simpson 260/270.
.
An AB 709COD #2 starter with coil 72A86 120 V 60 Hz has a room temperature DC resistance of 40.1 ohms.
This can be easily read on a Simpson 260/270.
.
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