I have an old Janitrol furnace that used the old gas valve which opened at approximately 22 Volts. I am up-dating the furnace with a new 24 volt gas valve. My problem is that when I hook up a standard 120 volt to 24 volt step down transformer the transformer is popping, smoking, and shorting out after 120 volts are applied to the primary. This process takes several minutes. I have tried the standard 40 VA transformers. Any suggestions?

 

How do the current ratings (or coil resistances) of the two valves compare? Is the new valve AC or DC?

 

What is your mains rating ?

 

dear check out the transformer name plate..... rated values will be written there. for rated current.. n coil resistance.... and rated frequency...
And..also check out the output connections also....

 

Starting with a new transformer I would connect it to the 120 VAC supply, leave the secondary open and check the secondary output voltage, just letting the transformer sit there. Then I would connect the secondary to the system and monitor the under load voltage, I assume you have a meter. The secondary voltage should not drop other than maybe a volt or two. If the secondary voltage drops way down close to zero volts either the gas solenoid is shorted or something to the gas solenoid is shorted. Finally I assume 120 VAC 60 Hz mains power and a transformer rated for the same.

Oh wait a min, I just saw where you were updating the gas valve. My slowness this early. Make sure you are not operating a AC coil gas valve solenoid with DC. Then too transformer secondary is AC and solenoid should be AC.

Ron

 

Oh wait a min, I just saw where you were updating the gas valve. My slowness this early. Make sure you are not operating a DC coil gas valve solenoid with AC.
Ron

The DC version would be much higher in resistance so I would not expect any where the same load for a DC coil?.
Max.

 

how about the diode across the coil of a dc solenoid? half wave short on ac.

 

How do the current ratings (or coil resistances) of the two valves compare? Is the new valve AC or DC?

I have not even tried hooking the new gas valve into the 24 volt transformer circuit. I can NOT get the transformer operational because it blows out..shorts out after a few minutes

 

Wired backwards!?
Max.

 

dear check out the transformer name plate..... rated values will be written there. for rated current.. n coil resistance.... and rated frequency...
And..also check out the output connections also....

If I am blowing out the primary of a 120 volt circuit could it be surging more than 120 volts to the primary?..And why does it take several minutes for the transformer to blow?..I have not tried hooking the new AC gas valve up..because I can not keep the transformers from blowing.

 

dear check out the transformer name plate..... rated values will be written there. for rated current.. n coil resistance.... and rated frequency...
And..also check out the output connections also....

I just need a 40 VA ..120 Volt stepped down to 24 volts secondary..I have shorted TWO NEW ONES OUT..w/o even hooking up the secondary..to the new AC gas valve..

 

What is your mains rating ?

What do you mean by 'Mains Rating'?

 

The DC version would be much higher in resistance so I would not expect any where the same load for a DC coil?.
Max.

I did manage to get that backwards. Thank you Max.

Ron

 

If I am blowing out the primary of a 120 volt circuit could it be surging more than 120 volts to the primary?..And why does it take several minutes for the transformer to blow?..I have not tried hooking the new AC gas valve up..because I can not keep the transformers from blowing.

No way you are applying 120 VAC to the transformer secondary is there? Meaning primary and secondary backwards.

Ron

 

measure the AC you are connecting to. if secondary is open, I can only see over voltage causing this. be sure it is 120 and not 240.

 

most of the transformers sold for hvac use have two black wires and two screw terminals. the screw terminals are the 24 volts and the black wires are 120.