Motor contactor "black box" 1

[gtwy]

I don't post here often, but enjoy reading the posts concerning motor and controls- I've spent the last 40 yrs on low voltage D.C instrumentation........

Had a customer call the other day complaining that his Eaton Cutler Hammer size 6 contactor would not pull in- he gave a model no.A10JN0-C1. From what I could conclude from his description, there must be a rectifier within. He stated that there was a "black box" in the line between the coil input terminal and the rectifier (another box!)

I tried several internet searches but found nothing. I've had numerous black box descriptions thru the years that turned out to be capacitors, power supplies, relays etc, Any idea what this "black box" is? Perhaps a fuse holder?

It seems as though he was ohming things out and stated that there was 5k ohm across this "box".

 

[melspuds]

gtwy
I believe I have the latest eaton parts book and can't find that #. It could be rc snubber if the coil is feed from solid state device. You need the coil voltage, ac or dc and the contactor #. On that size contactor, I have seen rectifiers used also.
good luck
Dave

 

[ScottyUK]

Economy resistor perhaps, to reduce the coil burden once it has pulled in? Very common on large contactors with DC coils.

 

[gtwy]

Thank you for the responses.
I will see if I can obtain more info i.e. a good p.n. and the control voltage used.
He said that the coil is marked 110 a.c 50/60 hz, 110 d.c. From what he described it sounds like there is an internal rectifier, with a "small blck box" between one of the coil terminals (A1 or A2) and the rectifier. Don't know whether or not the box is holding the coil out- he thought it might be a fuse.

 

[jraef]

No, not a fuse. Almost all large contactors like that were made with DC coils, especially if using 115V controls, because a DC coil will have less "inrush" and thus not burden a control power source as much. So rather than require a DC control power source, the contact mfrs built the unit with a rectifier. But the down side of a DC coil is that after pulling in, it wants to consume the same amount of power, even though it takes much less once that has been accomplished, which made the coils over heat and swell, leading to failure. So the circuit included that "economizer" ScottyUK mentioned. Every manufacturer had their own version of that circuit depending on the characteristics of their coil and the entire circuit was often complex (I don't have Cutler Hammer's diagram). But if any component in that string has failed, it would not work. Unless you have the internal diagram of that contactor, it may be difficult to troubleshoot. I looked around, I couldn't find one.

That contactor was obsoleted before the age of the internet, so documentation on it is going to be paper, if it still exists.




"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

Cutler Hammer supplies a two wire On-delay timer for series connection. The application is starters up to size 2. For a model C320TDN3000 you may have to wait up to 30 minutes for the starter to pull in.
However, I don't think that the timer is usable on a size 6 starter and not useable on DC. (No ratings are given)
All current large CH starters use a two winding coil and special shorting contacts. When the starter pulls in the shorting contacts open and place the holding coil in series with the pull in coil. This is the arrangement I have seen the most often with DC coils.
Is it really a size six starter or did the customer make a mistake there?
how large is the motor and what does it drive?
Your customer may not be the first person to see this starter since it failed.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

A10J is actually a NEMA size 7 IIRC. H was Size 6, J was Size 7. So 600-800HP at 480V.
C-H stopped selling these 20 years ago (yes, it's been that long...!).


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

Do you know if they used a series resistor back then, Jeff? If so, there may be connections to a shorting contact missing.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

I know it had an economizer circuit, almost all of the big NEMA contractors do/did, so that would have involved the resistor, yes, but some designs also used caps after the coil was pulled in. At the time I was playing with those things in the late 70s, I wasn't savvy enough to dissect them yet. Had I broken one and had to pay for it, I wouldn't have been able to afford to eat for a week or so.

Come to think of it, that may not have been a bad plan to lose some weight. Should have thought of that...


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[gtwy]

Thank for the responses.
I did not realize that these contactors were that old, or early obsolescence due to failures like this? Absolutely nothing on the web (provided that the part number he gave me is the right one). I may try to call Eaton and see if they have old schematics available on line. He was firm on the size 6, 540a/ 400 h.p.
Just curious, does anyone have a ballpark guess as to the va burden from the coil of a contactor such as this- on the a.c. side if fed from an a.c. source?

 

[jraef]

Only a few mfrs still make true NEMA Size 6 or 7 contactors now, most have gone to using their IEC contactors de-rated for NEMA standards, then use electronic coils. Of the remaining true NEMA designs they use line voltage coils and an interposing relay. Allen Bradley still makes one for example (509-GOD) and it uses a line voltage coil + interposing relay, but the coil inrush is 4860VA, sealed is 254VA, which would be the same regardless of voltage, it's just that 4860VA at 120V is a lot of current... That Citation contactor was likely similar.

But if it has the DC coil and rectifier / optimizer circuit, there is no inrush, that's why they used it. So it will be in that 250VA range from an AC draw standpoint. When you order thre A-B version with the DC optimized coil, it comes with a 250VA CPT as part of the assembly to power the coil.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[gtwy]

Perfect- that's where I was heading- what size CPT might be required!