PowerFlex 4

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You would really want to look at suppressing transients and inductive kick from the load, which is easier to do for a DC control voltage.

If there's no noise or inductive kick from the load across the switch contacts, just a switching a transistorized circuit, it's probably built and rated for at least 1/2 million cycles. If you're switching the coil of another contactor and not suppressing the inductive kick, the small interposing relay is going to be fragile. The pitting and carbonization on the contacts can make it look electrically open even as it still mechanically closes.

Can be very hard or time consuming to trace and find if there's a lot of them in series, like a safety circuit. Suppress the switching noise from the load if you want the contacts to last forever.
 
Might have read that too fast. The load is the interposing relay coil? The tiny coil is going to have a lot less inductive kick compared to a contactor. Probably not a problem for a large sample of same installs, but there will still be some non zero early failure (due to noise and inductive kick at the switching contacts).

If you have a lot of them, they do fail, intermittently. Mechanically they're still working but the pitting and carbon on the contacts, resistance, can be too much.
 
__dan said:
Might have read that too fast. The load is the interposing relay coil? The tiny coil is going to have a lot less inductive kick compared to a contactor. Probably not a problem for a large sample of same installs, but there will still be some non zero early failure (due to noise and inductive kick at the switching contacts).

If you have a lot of them, they do fail, intermittently. Mechanically they're still working but the pitting and carbon on the contacts, resistance, can be too much.
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Yes, the load is an interposing relay. We are getting an alarm that the VFD is not in RUN, when we can see it is in fact, running.

Grrrr. I’m slow. :slaphead: There is a reason we put in that easily replaceable Relay. :dunce::ashamed1:
 
It's one of those things that make me go aghhagahagaga. You'll see a long series loop of similar devices, Omron ice cube devices in a safety circuit, looping through everyone's equipment. Somewhere in the circuit there's a small control contactor coil load that is blowing out the contacts in the ice cube device, 50 ft away in someone else's control cabinet.

But it's intermittent and may latch on the next power cycle. Otherwise it could be anywhere, or on someone's very expensive safety circuit board. It can be difficult to find, but when you do one look will tell you, someone should have suppressed the inductive kick off the control contactor coil load.

If there's only one, socket mounted, and you know where it is, you're golden.
 
The inductive rating of the built-in relay on a PF4 is 0.5A and it is designed for 200,000 operations for a DC inductive load, 300,000 for an AC inductive load.

One thing I have run into however is that there is a MINIMUM current rating at well, it needs to be "whetted" at a minimum of 10mA, otherwise a film builds up on the contact surfaces and it eventually increases the resistance to where it stops current flow. This isn't usually a problem with AC coils on the output, but it is with low voltage DC coils and circuits.
 
Jraef said:
The inductive rating of the built-in relay on a PF4 is 0.5A and it is designed for 200,000 operations for a DC inductive load, 300,000 for an AC inductive load.

One thing I have run into however is that there is a MINIMUM current rating at well, it needs to be "whetted" at a minimum of 10mA, otherwise a film builds up on the contact surfaces and it eventually increases the resistance to where it stops current flow. This isn't usually a problem with AC coils on the output, but it is with low voltage DC coils and circuits.
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Is a 10ma load turn on surge sufficient, or does it need 10ma continuous load? Is that why it is usually OK with AC coil loads?
 
GoldDigger said:
Is a 10ma load turn on surge sufficient, or does it need 10ma continuous load? Is that why it is usually OK with AC coil loads?
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The issue is that when the contacts OPEN, there needs to be sufficient arcing to burn off the film. So that would be 10mA of continuous load.

One place I have run into this is when the relay contacts of the VFD were being used to feed safety relay status inputs at 24VDC, where the load current was (in my case) only about 5-7mA. We could NOT get the contacts to reliably keep working, we had to drive interposing relays that then had gold flashed bifurcated contacts going to the safety relay inputs.
 
Jraef said:
The issue is that when the contacts OPEN, there needs to be sufficient arcing to burn off the film. So that would be 10mA of continuous load.

One place I have run into this is when the relay contacts of the VFD were being used to feed safety relay status inputs at 24VDC, where the load current was (in my case) only about 5-7mA. We could NOT get the contacts to reliably keep working, we had to drive interposing relays that then had gold flashed bifurcated contacts going to the safety relay inputs.
Click to expand...

My load side interposing relay for the VFD relay only drew about 5 ma. We put a snubber across the coil of it and increased the current to about 25ma.

We will see.
 
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