Auto relays

sallylillian

sallylillian

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Falmouth, Cornwall
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Palace Liner 90LO
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2011
A question for auto electricians. I have a 24vdc chassis and the driving lighting circuit is 24vdc. I have installed a LED light bar up under the rear to supplement the reversing lights. I am also installing a radio controlled fob so I can use it as a work light/ intruder defence.
The light bar is 9-32 vdc. I have spliced in a trigger wire from the reversing light and intend to use that on a relay.
So I have a choice of feeding the main power to the light as either 12 or 24vdc if my understanding of a auto relay is correct and the 2 sides are isolated. If I have a 24v 40amp relay can I use the 24 v trigger on the coil side but have 12v being connected through. So 24 v on 85 & 86 and 12v on 30 & 87.
Reasoning is if I wanted to use the work lamp for an extended time then feeding from the 12v house bank is more logical.
 
It's quite normal to have different voltages on the coil and the switch contacts of a relay. For example, a 12V coil to switch a 240V light, etc. Just read the details of the relay to make sure it can take the voltage. If it says 12V coil then you can only use 12V on the coil, but any voltage on the switch contacts.
 
Thanks both. I want put a fuse on the trigger wire from the reverse light to the coil. Its a 24vdc 40amp relay, what would be an appropriate size fuse?

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sallylillian said:
Thanks both. I want put a fuse on the trigger wire from the reverse light to the coil. Its a 24vdc 40amp relay, what would be an appropriate size fuse?
Click to expand...
To energise the relay is minimal I would "guess" a 2amp fuse should be fine, but as autorouter said just check the details on what ever you use/buy
 
I wonder if Jim should moderate this thread, I am not an expert but wonder if some potentially lethal wrong ideas are being posted.
 
68c said:
I wonder if Jim should moderate this thread, I am not an expert but wonder if some potentially lethal wrong ideas are being posted.
Click to expand...
I wonder if you meant to post that here as you have posted exactly the same on a thread discussing 240v and earth bonding.
 
No, posted here in error. I went to see if I had an answer on the other thread and could not find it.......thought I had forgotten to save it. Do not think anything in this thread will kill you.

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Last edited:
68c said:
No, posted here in error. I went to see if I had an answer on the other thread and could not find it.......thought I had forgotten to save it.
Click to expand...
Just so you know I went ahead with using the 24vdc 40amp relay, taking 24vdc from the reverse light loom to the coil and 12vdc through the switch via a 40 amp fuse, plus a 40amp wireless relay with a fob for switching as a working lamp. All fine works a treat.
 
Make sure you seal everything.

I had a watertight LED strip fail fitted low down on the step. All others have been fine, no idea how the water got in. I sealed it with silicone on the cut end but it failed at the factory fitted waterproof end. :-(

Would hate for you to do all the work to have it fail a few months later.
 
This is the bar, Siberia Light Bar
Its IP-class IP67/69K, the 69K bit is serious stuff. The cable is factory fitted and not cut and is run in one length through conduit and a boat water tight gland into my electric locker where the relays reside.
So yes hopefully watertight!
 
Wow!

That’s a nice bar. :-)

I think you have it covered then. Ha ha
 
How much Seks do you get to the £ ? :giggler:

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