Generic relay questions (24V-12V)

[clinto]

I am designing a portable converter box for trailering operations and I have some relay questions.

I need a generic relay, capable of say, 20A. I want it to be triggered using a 24V source, but control the flow of a 12V circuit (I think the diagram I have posted below explains this more clearly than I can verbally).

I know such relays exist, but I have NO idea of what to look for on ebay. When I do a search for relay, 24V relay, etc., I literally get thousands of results.

Can someone point me to a high quality relay (vibration and moisture resistant/protected) to search for? I want something reasonably priced, as right now this is an experiment. I still haven't figured out how to make a setup that is 100% portable from any truck to any trailer that includes trailer brakes. So for now this is an exploratory thing.

Does someone have experience with such an item?

Thanks

C

 

[Speddmon]

Clint,

Try Amazon...24 volt automotive type relay...Less then $10 each, it's going to have one "normally open" and one normally closed" contact with a common between the two, but will do exactly what you need it to do. Feed the 12 volts on the common and use the "normally open" contact just like in your drawing.

Sealed and moisture "Resistant"...nothing is waterproof anymore, unless you really want to pay a lot of money for it.

 

[Westech]

Clint I have seen a ton of 24V relays starting at $7.00 or so. I just did a Google search. But you can with out a problem run 12V in the high amp side and not 24. You will need to run 24V throu the low amp side (actuating side). Thats it my friend I know what your up to and I have thought about that many many times. There was a member who made one just the way you are thinking and he said it worked great.

 

[mikew]

Here's the 24v relay I used to operate 12v trailer lights.

24V 20 AMP 5 PIN RELAY REPLACE BOSCH. 0 332 209 203 : eBay Motors (item 140296447207 end time May-16-10 12:27:40 PDT)

It's a standard automotive relay, "water resistant" but not water proof. Water proof ones are hard to find. You can use 1/4" spade connectors or a socket (I'd bet NAPA has the sockets).

I purchased these 12v relays, they were cheap, just to get the sockets!

12V/12 VOLT 30/40A SPDT RELAY w/ SOCKET & WIRE HARNESS : eBay Motors (item 320349922777 end time May-08-10 12:08:47 PDT)

 

[cranetruck]

THIS is a relay (as Crocodile Dundy would say). The 25 amp relays I have installed for turn signals and head lights on the 8x8 (image #1). Makes you wonder where they compromise when producing commercial relays...

The switching action you are looking for is SPDT (Single Pole Double Throw) as shown in image#2, a 3 amp relay shown, hermetically sealed.
For a mil spec relay check this: LEACH BALANCED-FORCE RELAY, P/N KCL-D2A-002 : eBay Motors (item 120559563315 end time Apr-27-10 13:30:00 PDT)

 

[clinto]

Thanks to all for the replies. Like I said, I am still planning this out and I still can't figure out a easy way to actuate electric trailer brakes while still having a converter box that is 100% transportable. Plus, it's adding up quickly in price (24-12 converter, 3 relays, 4/7 pin receptacle, 10 pin military trailer harness, etc.

But I do have one question: In the ebay auction for the balanced force relay, what are the "hooks" for-is that where you attach the wires? I have never seen connections like that before.

 

[cranetruck]

You solder the connections (wires) to the hooks, help make a mechanical connection before soldering.

Consider having a 12-volt battery on the the trailer for all your trailer needs.

 

[papakb]

Clint,

If your planning on controlling the full range of taillights on your trailer you're going to need a relay for each of them. It's easier to calculate the current draw for each light string and put a set of dropping resistors inline with each 24 volt circuit. Using Ohms Law; R=E/I;
to drop 24 volts down to 12 with a current draw of 1 amp the formula is R=12/1 or 12 ohms. You calculate power for the resistor with P=IE or P=1 x 12 or 12 watts. So a 1 amp circuit will need a 12 ohm, 12 watt resistor. Resistors with higher wattages will work just as well so if you find 12 ohm 20 watt resistors they're fine too. If your current draw is 2 amps, calculate the proper resistance and make sure to double the current ratingof the resistor in watts.

The commonly available "sand block" power resistors are cheap and can be found at most electronic supply places for a couple of dollars.

No moving parts or fancy circuits, just a resistor inline with each set of bulbs.

Make sure you mount them securely and they will heat up in use so put them in a place where they can be cooled by the frame or on a heat sink.

Kurt Lesser

 

[gpp111]

I own an M818, want to find an adapter for the NATO 12 pin connector to a 7 pin connector on a tag along trailer. I realize I need to change the bulbs to 24 volt, but is there an off the shelf adapter I can use to connect the two electrically?

 

[gimpyrobb]

Gpp111, contact Ferro, he had some.

 

[gpp111]

Is this the fellow?

Ferroequinologist

 

[gimpyrobb]

Is this the fellow?

Ferroequinologist

You got it! I call him Ferrogynecologist.

 

[Chevytruck]

http://www.steelsoldiers.com/5-ton-up/32440-m818-24volt-12volt-trailer-lights.html

 

[kastein]

You can use common 12 volt relays quite easily with the addition of some one or two watt resistors. Measure the resistance of the coils in your 12 volt relays, then add a resistor in series with the coil that is approximately the same resistance, probably several hundred ohms. Make sure they are rated for the power they will be dissipating, use P = V²/R where V = 15 for a bit of safety margin.

Another thing you could do is swap the bulbs in the trailer to 24 volt ones, though this would be a real pain if you pull trailers that aren't yours frequently.

 

[gpp111]

adapter

appreciate the information. One of the steel soldier members is sending me an adapter and then I will change the bulbs on the trailer to 24 volt.

This should work for me. Just had the DOT inspection done on the M818. Will use this to pull my halftrack to events.

thanks

Geoff

 

[sterlun]

Clinto,

This is exactly what I'm trying to do. From my research, it appears you're on the right path. Unless we're both on the wrong path!

The relay set-up appears to be the favored one due to their ability to resist vibration and low heat. From what I gather you just need a 24 volt DC relay. 5 pin I think. I'm not interested in the electric brakes but for either set-up you would need 4 relays. I would have all 4 in my converter box. You would probably have one of yours in the cab for the brake controller and the brake lights would operate eventually off that power source. I guess for full portability you'd have to fabricate a harness going back from the box to the brake controller and maybe use molex to plug it in.

I found what we want here: SEC America LLC

Called today. $580 for that bad boy. I think I threw up in my mouth!

I'm buying all the stuff to do mine but I'm having a problem finding a NATO 12 pin male plug with the cover. I actually have found one source but it's price is incredible. I wonder if any of you guys can help me with this. Maybe from something being parted out or whatever.

Please post your progress. I need the edumacation.