# bridge rectifier circuit putting out wrong voltage

Discussion in 'General Electronics Discussion' started by Dave RV, Apr 26, 2013.

1. ### Dave RV

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Apr 26, 2013
I have group of AC relays with a DC controlled coil. The rectifier/capacitor circuit fried on one of these relays. The others are getting 110vAC in and putting out 110vDC. I built another. The new one is putting out 160vDC current. Why? Old circuit specs are 200V, 4amp bridge rectifier, 160V, 22 uF(M) axial capacitor. It works fine, output is 110vDC. New circuit specs are 200V, 4 amp bridge rectifier, 160V 22 MDF radial capacitor. Output on this one is 160vDC. I am not an electronics guru. Just a guy willing to take a stab at this on his own to fix a problem. Please help.

2. ### Harald KappModeratorModerator

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Nov 17, 2011
AC 110V means RMS. The peak value of the signal is Vpeak=sqrt(2)*Vrms=1,414213562*110V= 155,6V.

The question is not why the new circuit delivers 160V. The question is why the old circuit delivers only 110V. That is not plausible unless there's some other component in the old circuit that you haven't listed. Maybe some votage limiting varistor or a series resistor between the rectifier and the capacitor?

Compare every component between the two circuits and also every connection. Show us circuit diagrams for more informatrion.

3. ### Harald KappModeratorModerator

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Nov 17, 2011
Maybe the original circuit uses only one half of the rectifier bridge so the voltage can drop every second half cycled thus reducing the effective output voltage?

4. ### BobK

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Jan 5, 2010
Or maybe the capacitor is blown in the original circuit.

Bob

5. ### Dave RV

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Apr 26, 2013
BobK Nailed it!

I just pulled the other circuit that is putting out 110dc. THe capacitor is burned up. Now the question is what do I go back with? The dc coil on these relays is max input of 125 DC. Just got off the phone with the MFG. They are rated at 110. Do I even need the capacitor? Why did they put them on in the 1st place if the voltage output is beyond the safe limit of the relay? These are the things that make me go hmmmm.

6. ### Dave RV

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Apr 26, 2013
You nailed it. Thanks.

7. ### Harald KappModeratorModerator

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Nov 17, 2011
If the relay works with the original circuit (including the blown capacitor), you may just leave out the capacitor in the new circuit. Just observe whether there is noticeable hum from the relay without the cap. If the hum is too strong, you may want to put the cap back into the circuit and add a series resistor instead to limit the current (and consequently the voltage) to the relay.

8. ### Dave RV

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Apr 26, 2013
Ya'll(a Texasism) are awesome! There is no hum on any of the other 3 circuits so I"m going to go with no capacitor for now. I am quite thankful. I was able to accomplish in 30 minutes here what was impossible for 3 days with the original manufacturer of this RV. Have a great weekend.

9. ### Dave RV

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Apr 26, 2013
Just wanted to let ya'll know. The system is restored, cut out all 4 failed caps, no noise from the relays, new inverter installed and functioning with no backfeed. Hitting the road with it tomorrow. If either Harold or Bob are ever in Texas, look me up. I'll buy you a beer.

10. ### Harald KappModeratorModerator

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Nov 17, 2011
Sehr schön (Germanism)