12 vdc relay controlling 24 vdc?

Thread Starter

duncan mccallie

Joined Apr 2, 2015
10
Newbie question here:
I’ve been switching a small 24 vdc engine fuel solenoid with a continuous duty 12 vdc solenoid.
It has run very hot but that is apparently is normal. Yesterday it overheated and failed in the closed position along with strong burned plastic smell.
I’m searching for another, less volatile, solution.
Since the load is small. My guess <1 amp., I’m looking at a 12 volt Bosch style relay cube, switching the 24vdc load. Is this viable?
I’d appreciate any guidance.
Thanks in advance!
 

MaxHeadRoom

Joined Jul 18, 2013
18,869
Two solenoids? 24v and/or 12v?
There are plenty of automotive 12v relays around, I get a handful from the local wreckers yard.
Max.
 

Thread Starter

duncan mccallie

Joined Apr 2, 2015
10
Two solenoids? 24v and/or 12v?
There are plenty of automotive 12v relays around, I get a handful from the local wreckers yard.
Max.
Thanks for the quick response.
As this 24 vdc load is sometimes “on” for days at a time, I need a continuous duty relay.
After studying specs for small relays, I’m unable to tell if it’s OK to switch the small 24 volt load ( an integral fuel solenoid) with a 12 volt unit?
 

crutschow

Joined Mar 14, 2008
23,157
The relay possibly failed due to inductive spikes from the fuel solenoid causing pitting and welding of the contacts.
To minimize that, add a diode (e.g 1N400x) across the solenoid coil (cathode to +).
 

crutschow

Joined Mar 14, 2008
23,157
I’m unable to tell if it’s OK to switch the small 24 volt load ( an integral fuel solenoid) with a 12 volt unit?
The 12V is the coil rating, not the contact rating.
As long as the contacts are rated for more than the load current (at least 50% higher), you should be okay.
 

MaxHeadRoom

Joined Jul 18, 2013
18,869
If it is on for days at a time, I would not think the present problem is caused by BEMF, but it does not hurt to add the rectifier anyway.
That is a trivial load for an automotive style.;)
Max.
 
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