It looks like the problem wasn't caps after all. Or the time delay
relay.
While poking around inside the electrics enclosure and putting
number labels on wires so that I could remove the contactor I found a
female spade connector just hanging behind the contactor coil spade
terminal.
It's really hard to see the coil connections because it is buried
pretty deep and a lot of wires are in the way. So I pushed the spade
connector back on and it just slipped on real easy. Too easy. I pulled
it back off and wormed the wire through the others and could see that
the female connector was open too much. Maybe years of vibration
loosened it. So I closed the connector some with pliers and when I
tried pushing it on again it was quite tight.
After putting the rest of the wiring back in order I tried
starting the RPC (Rotary Phase Converter) and it started normally,
which is essentially instantly.
Now I have another question. Since the spade connector was loose
could this have caused a high resistance connection which in turn
caused the contactor to barely pull in which then made for another
high resistance connection between the starting caps and the motor?
I know that at least some types of relays have a higher pull in
current than the holding current. So that once they pull in less
current is required to keep the contacts closed. In other words a
curve of the current required is shaped like a hill, with the holding
current past the crest a little.
But I think that maybe contactors for motors may work differently
because they have so much more travel in the solenoid after the spring
loaded contacts first make contact, unlike "regular" low current
relays. And since the current required to pull in the contactor
remains the same even a slight decrease in current would cause the
contactor to drop out. And maybe a low current situation could cause
the contacts to make only a light, high resistance, contact.
Anyway, thanks for reading all these posts and thanks for the
advice given. While writing this post I have started the RPC 6 times
and each time it has started normally.
Cheers,
Eric

On 26/08/2017 7:52 AM, wrote:
It looks like the problem wasn't caps after all. Or the time delay
relay.
While poking around inside the electrics enclosure and putting
number labels on wires so that I could remove the contactor I found a
female spade connector just hanging behind the contactor coil spade
terminal.
It's really hard to see the coil connections because it is buried
pretty deep and a lot of wires are in the way. So I pushed the spade
connector back on and it just slipped on real easy. Too easy. I pulled
it back off and wormed the wire through the others and could see that
the female connector was open too much. Maybe years of vibration
loosened it. So I closed the connector some with pliers and when I
tried pushing it on again it was quite tight.
After putting the rest of the wiring back in order I tried
starting the RPC (Rotary Phase Converter) and it started normally,
which is essentially instantly.
Now I have another question. Since the spade connector was loose
could this have caused a high resistance connection which in turn
caused the contactor to barely pull in which then made for another
high resistance connection between the starting caps and the motor?
I know that at least some types of relays have a higher pull in
current than the holding current. So that once they pull in less
current is required to keep the contacts closed. In other words a
curve of the current required is shaped like a hill, with the holding
current past the crest a little.
But I think that maybe contactors for motors may work differently
because they have so much more travel in the solenoid after the spring
loaded contacts first make contact, unlike "regular" low current
relays. And since the current required to pull in the contactor
remains the same even a slight decrease in current would cause the
contactor to drop out. And maybe a low current situation could cause
the contacts to make only a light, high resistance, contact.
Anyway, thanks for reading all these posts and thanks for the
advice given. While writing this post I have started the RPC 6 times
and each time it has started normally.
Cheers,
Eric


I would guess that the connector was moving a little each start until it
finally came out. The last few times it would make up with the previous
start. Generally contactors either buzz - vibrate or close, no in between.