Relay vs. Solenoid - Electrical Question for ya!

[CoreyPerez]

Hey guys,



I've got a technical electrical question and hope you may be able to answer it for me.



Here is the application:



I'm wanting to install work lights (6 total 12volt lights & 1 small 12vlt "lamp" near the ramp loading area on the side of the trailer) these are like KC Day lighters and what not, I'm wondering if I should use a constant duty solenoid for all 6 lights, or if I'd have to use 6 separate relays for these.



Also,

I'm wanting to install 2 reverse lights on my Car Hauler. Same thing. What would you suggest. Both applications I'd like to have a manual on/off switch. I'm not sure if a Solenoid would offer this or not. Also, they would be semi-exposed to the elements. Mostly under the hood situation. The on/off switch will be located in the passenger compartment. Included with all of this, I'd like some LED's inside of the engine compartment to tell me when the lights are on.



Now, for an interesting "switch". I'm considering installing a relay that would (when activated) illuminate the work lights when the reverse lights come on. Granted this is like having a bunch of reverse lights, but this feature would only be activated with a flip of a switch, or could be overridden by shutting off the switch.



All of these questions stem from past wrecker driving experience. I liked the setup that the wreckers have.



If you have any suggestions thanks.



Corey

 

[LSMITH]

Corey, personally I would use one relay sized for all of the lights you want to use per switch, and use illuminated rocker switches instead of LED's. If you want LED's you can run the LED off of another set of contacts on the relay. I would fuse each light individually, coming off of a bus type distribution as close to the light as possible. Then you only have one wire per light system (sized accordingly of course) going to the bus making routing and protection much easier, not to mention troubleshooting them if you have a problem.



Tying into the back up lights is simply using a wire that is hot in reverse on the relay coil as well as your switch lead. For overriding this "feature" you will need a switch to open the reverse circuit to the relay coil.



I do not see where a solenoid would tie into this at all, solenoids are used to start, stop or reverse flow of a gas or fluid. A relay is used to switch loads of electrical power that a control circuit cannot handle. Same operation but different media controlled.



One thing to be aware of though is the power loading of all of your lights is going to be quite high, a real battery killer if the engine is not running. You could also switch each light at the bus in the trailer to allow you to use only the light that is needed, or maybe gang them so you have two sets of three lights. Hope this helps, let me know if you need more info.

 

[THerman]

I see where the solenoid reference comes from... "starter solenoid"



I agree with Corey. If you can get the specs on the lights (current draw) get a realy big enough to handle that load. The rest is just how you wire the relay coil as far as How it operates.



Oh, before I forget... the starter "solenoid" is nothing more than a large relay... SPST (single pole, single throw)



Tod

 

[LarryB]

Could it be that "solenoid" refers to mechanical switching/action of some sort? The starter solenoid mechanicaly engages the starter motor to the flywheel, at the same time switching on the starter motor (sometimes called a "solenoid relay"). Solenoid valves mechanicaly switch fluid or gas. Relays only switch power? Mmmm... that makes sense... I guess. .

 

[THerman]

Actually, if I were to nitpick, I would say that relays are also solenoids... . (the coil is the solenoid, moving the contacts)



Getting very picky here!!!! javascript:smilie('')

roll eyes (sarcastic)



Tod

 

[CoreyPerez]

First, before I get too far into this, my application is a 18' Car Hauler w/Dove tail. Just so you know what the lights are going on, and when I'm talking about light reflecting off a vehicle...



As far as the solenoids I only really know them from Starters, Electric Winches & Dual batteries. One of the common types of setups for Dual batteries if you want to Isolate them is using a Solenoid. I don't know how accurate this is, just something I thought I knew.



As far as the setup, I think I have it down. I'll try and get it drawn in and see how it looks to you guys.



If I remember my drawing correctly, its setup so that when the truck is in reverse the trailer reverse lights will come on (by the way, are our trucks already setup with this in the plug?) I've got it so that the work lights will come on also. The truck & Trailer work lights can be overridden and the work lights can be shut off (if the light is reflecting off a vehicle and not allowing me to see behind the trailer). But, I can also just turn on the work lights with out the reverse lights coming on. I was planning on using the center pole of the 7pin connector for this feature @ the hitch. As far as the LED's, I wanted to use the multi-color LED's. Something like Yellow if they are on alone, or Red if they are working together. Just so I would know during the day time if the lights were on or off. (plus it would be pretty cool!)



Currently I'm considering mounting the switch & lights on the dash next to the O/D switch. I've got a 94 and if I got 2 SMALL switches & 2 Small LED's I think they would fit neatly in the small area of the stock non-used switch hole. I had planned on using another O/D switch in the place of the non-switch and use it for the work lights, but I really think I'll need 2 switches.



Like I said, I'll try and get my idea drawn and posted. Granted I don't know a lot of the actual symbols, so I'd have to explain what some of them mean to me (vs. what the symbol actually should be)



Thanks guys!



Corey

 

[LSMITH]

Sounds good Corey, get the drawing up and we can help with that as well. I have some software to draw electrical schematics too, I would be willing to help out in that way too.



I stand corrected on the solenoid thing. I am used to the industrial electrical side, relays switch power and solenoids are only used for gas/fluid/actuators.



Digging in my reference material a solenoid uses an energy source to create motion and a relay switches electrical loads, in the most simplistic terms (and I need them sometimes ).

 

[NETim]

Solenoids?

Actually, there are no more Solenoids. Dr. Who soundly defeated them in Episode 42,

"Battle of Hysteresis. "



Tim

 

[LarryB]

No. . No. . No Tim!

That was Hemoroids... er ... asteroids? Ahh. . Same thing!

 

[illflem]

Actually solenoid just refers to the electrical coil part of a relay switch, valve or actuator. The old type starter solenoid is an actuator/switch combo, that's probably why it's still called a solenoid even though the new ones are really just a relay.



You can buy large relays to handle your lights but often times starter solenoid is cheaper than a high amp relay, that's probably the reason they are used on electric wenches. I think you are better off to use several small relays to control your lights.

 

[CoreyPerez]

Ladies & Gentlemen,



The long awaited drawing by your non-electrical idiot on the forum. I've changed my method of madness. Here is the newly created idea.



Tell me what ya think!



The Solenoid will be a Ford Starter Solenoid, and should beable to handle MORE than enough voltage / amperage.



Here it is!



#ad




Corey

 

[LSMITH]

Corey, you currently have all or nothing. The lights are going to be on when you hit the switch whether you are in reverse or not. You are going to want a seperate switch to either lock out the lights in reverse or to turn them on. Put a switch in the solenoid coil line from the reverse that has a seperate switch in it and connects to the solenoic coil "downsteam" of the manual switch. That will leave your manual control effective yet let you not use them in reverse if you choose to, both switches off means they do not come on at all.





One more thing, and it is kinda nitpicky but here goes. A plug and socket where you go out to the trailer is like this ---->>------, the ---l l----- you have is a contact.



I think you are well on your way. Good luck.

 

[tgbol]

Because I am not at work I don't have the part number, but Bosch makes a 70 amp relay that is the same size as the ones we are all familar with. The connectors are 3/8" wide. We use them on the accessory side of the ignition switch to power the controls on the bucket trucks.

 

[CoreyPerez]

LSmith,



I updated the picture to reflect your correction thanks. One question I do have. The way I understand, or atleast THINK I understand the setup I've got, when the truck is put in reverse, the truck's & Trailer reverse light will come on. Also, there will be a "sense lead" sent to the work light that trigger the solenoid to power on. Although, I did just re-look at the drawing, and the lead from the trailer lights would have to be after the switch BEFORE the solenoid or the reverse light would always run off the battery, regardless.



I guess I still have a little thought that needs to go into this. I may see about getting my original drawing up sometime. Its quite a bit more indepth and complex.



Gotta go to work!



Thanks guys,



Corey

 

[Rotty]

Excuse me for jumping in late here.

Solonoid is an older term, relay is probably more appropiate, both terms work just fine. What ever you do, DON't use a starter solonoid. It is rated ONLY for intermittant duty. There are relays that are rated for continuous duty that look like (god for bid, ford starter solonoids). :--) Your local auto parts dealer should be able to help you. I personnaly like the bosch 30-40 amp relays. They are avaiable at all auto part stores (nice if they fail on the road). But definatly size the relay to the max current load or larger.

If you have any questions, email me at -- email address removed --

 

[BV]

solenoid

Hey Corey - I have been very happy with the solenoid made by Tekonsha which they market as a battery switch and rated for continuous use. I have put them on 3 pickups now to isolate the vehicle battery from the RV battery while the engine is off and also used them to run a some driving lights and backup lisghts. Most RV supply stores/shops have then for less than $30.

 

[CoreyPerez]

I don't suppose you have the information about the relay you are discussing? Is it available at most/all auto parts stores?



How about part numbers?



Thanks,



corey

 

[tgbol]

COREY

I said that the relay is a Bosch but I couldn't find the number tonight. We have a new parts system and sometimes it is hard to track down. BUT, here is the HELLA number for the same relay p/n 87110. We buy them from a commercial truck light supplier in L. A. If you prefer the Bosch relay give a couple of days to locate the ones in the garage. I just moved and it is a big pile.

Tom

 

[CoreyPerez]

Tom,



Thanks. I think with either the part number or atleast with the ideas I may beable to find a part that will work for this application. The part stores around here are idiots, I even got so tired of it I started working at one so that I could go in and look behind the counter with out being bothered. The bad part was I only tied working a few days a week and everytime I went in they bugged me about working for somebody else. So now, instead of getting crappy service from some idiot with an ASE badge on his sleeve, I was getting bothered to work!



Ya just can't win...



Thanks again guys, I'll let ya know how it goes!



corey