Solid state relay derating for motors
 

I have a 25A SSR that is spec'd "motor load 7.2 FLA". What is it about
motor loads that require such drastic derating?

It is a zero-crossing relay, if that makes a difference.

Thanks,
Bob

Solid state relay derating for motors
 

When a motor starts up, it takes a lot more power than it's rated run power.

Think of it like revving your car up to a nice steady 4000 rpm and dumping
the clutch.

Although a fuse wire will take a little while to melt, a P-N junction in a
semiconductor will snap like an axle when you exceed it's rating.

Typical electric motors draw 3 to 5 times more power when starting from a
stalled condition.

Hope this helps,
Peter

"Bob Engelhardt" wrote in message
...
I have a 25A SSR that is spec'd "motor load 7.2 FLA". What is it about
motor loads that require such drastic derating?

It is a zero-crossing relay, if that makes a difference.

Thanks,
Bob

Solid state relay derating for motors
 

Technically speaking, it takes very little real power to start a motor.
However, it does take lots of current , 5-10 times the FLC, depending on the
motor design. Since SSR's are VA rated devices, that is why it is derated
so much for motor control duty.

Randy

"Bushy Pete" wrote in message
...
When a motor starts up, it takes a lot more power than it's rated run
power.

Think of it like revving your car up to a nice steady 4000 rpm and dumping
the clutch.

Although a fuse wire will take a little while to melt, a P-N junction in
a
semiconductor will snap like an axle when you exceed it's rating.

Typical electric motors draw 3 to 5 times more power when starting from a
stalled condition.

Hope this helps,
Peter

"Bob Engelhardt" wrote in message
...
I have a 25A SSR that is spec'd "motor load 7.2 FLA". What is it about
motor loads that require such drastic derating?

It is a zero-crossing relay, if that makes a difference.

Thanks,
Bob