Relays

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It will eventually make contact at the relay and close. Just sometimes it takes several shots.
 
What is the difference of a 50va General Purpose Transformer and 50va Control Transformer
 
According to the spec in previous listing, it says coil current rating is 10Va. I would then guess that 50 va shouls be enough.
 
It's just you stated you changed from 15 kva (15,000 va) to 50 va. I thought the lower power output of the 50 wouldn't have been enough.
 
wmeek said:
It did work. I changed from a 15kva transformer to a 50va control transformer to get my 240V.I am trying to control a contactor to de-energize a 480V panel which feed 4-welders and a 15KVA transformer that feeds a 120/240v Panel. This is all installed on a Tractor powered Generator. I have 240V off of a 50VA transformer rated 480/240 volts.
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15 kva to 50 va is a huge decrease. Perhaps under load its no making it
 
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Also what else is on this 50va, is there any other control that activates when this contactor closes, if so voltage drop from the draw of these controls, or even the contactor it self may be enough to drop your voltage to an unacceptable level.
 
The 50Va supplies power to frequency monitor, which has a set of normally open contacts, which close when generator supplies correct frequency. Then it goes to a pushbutton which inturn feeds the control relay. Also on one set of normally open contact the same 50va feeds the contactor which supplies power to 480V panel .
 
wmeek said:
What is the difference of a 50va General Purpose Transformer and 50va Control Transformer
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A control power transformer has better voltage regulation. Control power transformers are designed to supply the inrush current while maintaining the 85% voltage required for a coil to fully pickup.
 
What is the frequency that the gen is supplying.

How does the 50va recieve power before the monitor closes the circuit for the gen?
 
The generator produces 60Hertz. The 50va transformer receives power from the line side of contactor that is fed from generator. After coming off the 50va it goes to frequency monitor that has a Low and High range setting for the frquency. Once generator gets up to the required setting on monitor it closes a set of contacts on frequency monitor. Which sends powewr to pushbutton which when oushed closes relay with a set of normally open contacts that feed contactor.
 
After I have thought about it, When frequency monitor closes a set of contacts it lights up a pilot light which lets the operator know when to push the pushbutton. Then you push the pusbutton to energize the relay which has two sets of normally open contacts. One set for maintaining contact for pushbutton, the other for contactor feed. The contactor feed is the set of contacts that chatter. They arc
pretty good. If you keep pushing the button it eventually stay close. They then stay close until the generator is powered down causing frequency monitor to open its contacts for the controls
 
What powers the contactor? (The big one, not the relay.) If it's also powered from the 50VA xmer, quite likely when the relay contacts close, it causes a large voltage drop, resulting in undervoltage to the relay coil, which opens the relay contacts, and with the load now off, the voltage builds back up, closing the relay contacts, dropping the voltage..... All this happens very quickly, hence the buzzing of the relay.

The reason you see an arc across the contactor control contacts is due to the larger current needed by it's bigger coil. Any AC coil draws a large inrush, then much less when it's sealed in. When you hold the pushbutton down, eventually the big contactor seals in, thereby reducing it's current to a level the 50VA xmer can handle.

A general purpose xmer can't come up with much surge current, a control xmer can. The control xmer has more iron in it's core, thus it's heavier.

If this is the case, you'll need to grossly oversize a general purpose xmer, or get a control xmer that can handle the big contactor.
 
So what size control transformer would be needed. Would a 50va control transformer work. I know the control rating current of the relay is 10va. I do not know about the contactor. It should not be that much i wouldn't think.
I am not sure how to figure the proper size transformer.
 
Control power transformers (CPT) need several pieces of information to be sized correctly, the sealed and the inrush VA's and the allowable % voltage drop (well techincally the output voltage regulation).

CPT are labeled based on their sealed VA. But there is no standard amount of inrush capacity and typical ranges range from 8 to 14x nameplate so you really need to check with the manufacturer's literature.

However, as a rule of thumb, for 85-90% voltage regulation most CPTs are actually applied only by adding the sealed VA of all of energized starter/contactor/relay coils and then picking the next larger size.
 
OK
I have 26va(Sealed)& 310va(Inrush)on this contactor coil.
I have 10Va on a relay 240v coil. So are you saying that if I add 26Va(contactor coil) and 10Va (relay coil) that I could use a 50VA Control Transformer. I was trying to use a 50Va General Purpose transformer, but it would not pull in relay coil. Or should I go up to a 100Va Control Transformer.
 
wmeek said:
OK
I have 26va(Sealed)& 310va(Inrush)on this contactor coil.
I have 10Va on a relay 240v coil. So are you saying that if I add 26Va(contactor coil) and 10Va (relay coil) that I could use a 50VA Control Transformer. I was trying to use a 50Va General Purpose transformer, but it would not pull in relay coil. Or should I go up to a 100Va Control Transformer.
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You need a transfromer capable of supplying 310+10=320VA while maintaining a voltage regulation of at least 85%.

For 85%V, a Square D 50VA CPT (#9070T50---) is capable of supplying 339VA @ .20PF and only 282VA @ .40PF.

Personally I would use a 100VA transformer, but you should really check with your transformer manufacturer.
 
I did use a 100va CPT. It worked like a charm. I want to thank everyone for all their suggestions and help. I have learned alot from this project, I hope I can retain it for future projects.


Thanks
 
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