Looking for a relay with 120v trigger but 12v circuit

[Dale M.]

Get simple automotive 12 volt 30 amp relay and power it by a 120 volt AC input/12volt DC output transformer... I have picked up many a 1000/1200ma (1amp) out put 12 volt transformer at resale shops or garage sale or junk bins....

Dale

[eggsalad]

Let me try another tactic...

If you got a 120/120 relay (that is, a relay triggered by 120v and the outputs are rated at 120v) well, 120 volts is a lot more than 12 volts. The output is just a switch. If the switch contacts are rated to 120v, surely they'll handle 12v just fine.

[Hennesseystealth]

Let me try another tactic...

If you got a 120/120 relay (that is, a relay triggered by 120v and the outputs are rated at 120v) well, 120 volts is a lot more than 12 volts. The output is just a switch. If the switch contacts are rated to 120v, surely they'll handle 12v just fine.

Understood.

[H.A.]

Let me try another tactic...

If you got a 120/120 relay (that is, a relay triggered by 120v and the outputs are rated at 120v) well, 120 volts is a lot more than 12 volts. The output is just a switch. If the switch contacts are rated to 120v, surely they'll handle 12v just fine.

Of course keep within the current rating of the relay contacts, what btw are typically printed for both AC and DC upon the housing of most relays.
The current rating is typically lower for DC. (notice upon the Potter Brumfield relay exampled earlier)

[kludge]

You don't need a 120VAC trigger.

Any old 12VDC coil relay will work.

Put the coil on the output of the Converter but before the contacts of the relay.

The Converter will turn on when AC is applied and give you 12V on the output. The output from the Converter will power the relay coil, the contacts will close connecting the battery, and the battery will charge.

Let me know if you need a picture.

A picture might be nice,
As I envision by your description, What happens when 120vac is removed from the charger ?
Will the battery back feed thru the closed contacts to keep the relay coil energised ?

Further, Many of these 'smart chargers' wont switch on its charging output until it first measures a correct polarity voltage from the battery.
Its a safety feature what prevents its output from becoming energised if for example its output leads are shorted to each other or connected in reverse polarity.
I expect the small constant battery drain previously mentioned is related to this voltage measuring circuit.

Here's a sketch of what I was thinking:



But you're right, the battery will feedback through the contacts and keep the relay energized. And if you placed a diode there the battery might not charge correctly (it may or may not, I don't know for sure with your converter). If there is a separate sense wire, that may satisfy the reverse polarity detection.

As someone else suggested a small DC "wall wart" could run the relay.



But this still doesn't address the issue of the voltage sensing being the cause of the battery drain... so... if that is the case, this should work... or if there is no separate sense wire, and the sensing connection is internal, it will be OK too.