# Relay Chatters with a Blown Capacitor

#### lmei

Joined May 31, 2022
7
Please refer to the diagram below.

• BX is +110v or 0v. (not sure DC or AC)
• NX110 assumes -110v. (Maybe 0v? not sure DC or AC)
• Y2T is 110v DC relay with a part number of KUP-14D15-110. Its operate voltage is 82.5v.
When BX is 110v, the relay coils pick up. Why the relay chatters when C1 is blown? How does this circuit function?

#### sghioto

Joined Dec 31, 2017
5,391
D1 and the capacitor C1 form a DC supply for the relay. If the capacitor is blown the relay is operating on half wave AC voltage.

#### MisterBill2

Joined Jan 23, 2018
18,584
This is not a new sort of problem, I dealt with this sort of relay chatter back in the late 1950's. A DC relay fed rectified AC will be noisy if there is not enough ripple filtering.
The wiring diagram does not even show the relay coil in the circuit, and so no good evaluation is possible, only guesses. And the item marked "NV" we have no mention of what it is, and that may matter.

And the information that a DC relay fed unfiltered half-wave power will buzz. Relay Chatter is different.

#### sghioto

Joined Dec 31, 2017
5,391
The wiring diagram does not even show the relay coil in the circuit,
The relay coil is Y2T shown connected between 1 and 6 on TB2-2. I also believe R2 is a 4.7K resistor since the coil resistance of the relay listed is 10K.

#### lmei

Joined May 31, 2022
7
D1 and the capacitor C1 form a DC supply for the relay. If the capacitor is blown the relay is operating on half wave AC voltage.
Thank you for replying. Do you mean that the voltage supply is AC?
The reply is chatting/noisy then BX is 0v tho. Is there any references/formulas I can use to calculate the DC voltage generated by D1 and the capacitor C1?

Thanks again. I dont come from a EE background.

#### lmei

Joined May 31, 2022
7
This is not a new sort of problem, I dealt with this sort of relay chatter back in the late 1950's. A DC relay fed rectified AC will be noisy if there is not enough ripple filtering.
The wiring diagram does not even show the relay coil in the circuit, and so no good evaluation is possible, only guesses. And the item marked "NV" we have no mention of what it is, and that may matter.

And the information that a DC relay fed unfiltered half-wave power will buzz. Relay Chatter is different.

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#### lmei

Joined May 31, 2022
7
The relay coil is Y2T shown connected between 1 and 6 on TB2-2. I also believe R2 is a 4.7K resistor since the coil resistance of the relay listed is 10K.
R2 is indeed a 4.7K resistor.

#### sghioto

Joined Dec 31, 2017
5,391
Is there any references/formulas I can use to calculate the DC voltage generated by D1 and the capacitor C1?
It depends on the size of the capacitor and the load which in this case is the relay. But assuming no load and a 10uf cap it's appx = 1.414BX or
110 x 1.414 = 155.54 volts DC. Hence the reason for R2, the excess 45 volts is dropped across R2.
EDIT: Yes the BX supply is AC.

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#### lmei

Joined May 31, 2022
7
It depends on the size of the capacitor and the load which in this case is the relay. But assuming no load and a 10uf cap it's appx = 1.414BX or
110 x 1.414 = 155.54 volts DC. Hence the reason for R2, the excess 45 volts is dropped across R2.
EDIT: Yes the BX supply is AC.
Why -110v is used here? The replay is chatting/noisy when BX is 0v

#### sghioto

Joined Dec 31, 2017
5,391
Depends on how you are measuring the voltage.
From the schematic the AC voltage should be measured from NX to BX. Not sure exactly but I think the NX represents the neutral wire of the 110 volt AC supply which is also the negative side of the DC.
.

#### MisterBill2

Joined Jan 23, 2018
18,584
OK, now the part with the relay coil is clear. That is not a JIC symbol for a relay coil, and so it was not obvious to me.
And indeed the capacitor voltage is at least 155 volts, which is certainly far too close to the rated voltage of the capacitor. Evidently the series resistor (R1, 330) was intended to limit the capacitor voltage, unfortunately reality does not work that way. But the series resistor does reduce the filtering function quite a bit.
The relay coil should have a standard intended operating voltage that should be marked on it some place. A filter capacitor for this circuit should be rated for at least 250 volts DC.

The simple way to stop the relay buzzing is to add a suitably rated diode across the relay coil, connected to oppose the applied voltage. This will allow the collapsing magnetic field to keep current flowing during the half cycle when the supply voltage is reversed. I have used the trick to quiet a large contactor and it works well in every instance. It works for both large and small relays. Unfortunately many electricians do not recognize that.

Joined Jul 18, 2013
28,698
This is not a new sort of problem, I dealt with this sort of relay chatter back in the late 1950's. A DC relay fed rectified AC will be noisy if there is not enough ripple filtering.
Not ALL by any means, I have used DC relays with just full wave rectification and no smoothing for Many decades with no problems.
Even large DC brakes on industrial machinery and cranes do not filter the DC, and if any would be prone to chatter, it would be these.

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#### eetech00

Joined Jun 8, 2013
3,958
Thank you for replying. Do you mean that the voltage supply is AC?
The relay coil is supplied a half wave AC voltage thru diode D1. This (ripple) voltage rises and falls above and below the 82.5 must operate voltage of the relay. The C1/R1 combination filters (smooths) the ripple voltage so the voltage across the relay remains above the relay's 82.5 must operate voltage. If C1 is blown (open) then the relay will chatter as it attempts to operate with the rising/falling ripple voltage.

#### MisterBill2

Joined Jan 23, 2018
18,584
Not ALL by any means, I have used DC relays with just full wave rectification and no smoothing for Many decades with no problems.
Even large DC brakes on industrial machinery and cranes do not filter the DC, and if any would be prone to chatter, it would be these.

CERTAINLY full wave is the fix. No question on that. In addition, a full wave bridge provides that same function as I described, except it has 2 diodes in series..

#### sghioto

Joined Dec 31, 2017
5,391
The fix is to replace the capacitor with a higher voltage rating.
A full wave rectifier would require three additional diodes.

#### MisterBill2

Joined Jan 23, 2018
18,584
The fix is to replace the capacitor with a higher voltage rating.
A full wave rectifier would require three additional diodes.
Certainly you are correct. And I suggested a 250 volt capacitor replacement back in post #11.
And I am wondering what this circuit is part of.

#### lmei

Joined May 31, 2022
7

#### lmei

Joined May 31, 2022
7
Certainly you are correct. And I suggested a 250 volt capacitor replacement back in post #11.
And I am wondering what this circuit is part of.
It is part of an Emergency Trip System

#### eetech00

Joined Jun 8, 2013
3,958
The fix is to replace the capacitor with a higher voltage rating.
A full wave rectifier would require three additional diodes.
Or replace the relay with an AC version ( KUP-14A15-120) of the same series, and remove C1,R1,R2, and D1.

#### MisterBill2

Joined Jan 23, 2018
18,584
Certainly AC versions are available.
In this instance the reduction in parts count will improve reliability.
An emergency system of any type needs to be reliable.