Using a solenoid-type battery isolator as a heavy-duty relay?

Submitted: Monday, Jan 26, 2015 at 09:31
ThreadID: 110877 Views:1809 Replies:5 FollowUps:11
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I'm in the process of installing a air "system" in my Chev Silverado and have decided to use the large Ironman compressor I've been carrying around in the Landcruiser for several years. It is still practically new as I've always had good service from the "Air-On-Board" belt-driven compressor under the bonnet.

However, I want to hard-wire this compressor up to the bank of 3 batteries in the back of the Chev and attach it (via a 3 foot stainless steel braided hose) to a 18 litre receiver tank.

The sticker on the side of the compressor says it draws 45 amps, so I can't use a regular 40 amp relay.

Instead, what I've decided to do is use a 100amp battery isolator solenoid and a 60 amp manually re-settable circuit breaker. The solenoid will be activated by a wire connected to the tail lights.....the Chev's lights come on automatically every time I start her up, although there is the ability to then turn them off if I wanted to. That would mean that whenever the engine is started the compressor will ensure the tank is full to 100 psi. I have installed a 70/on ...100/off pressure switch as well as a safety blow-off valve, so it's all good and safe.



So, the only thing I'm not 100% sure of is whether the 100amp solenoid would be okay to act as a large relay.....as far as I know they do the same job.

Thanks in advance.

Roachie
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Reply By: Allan B (Member, SunCoast) - Monday, Jan 26, 2015 at 09:44

Monday, Jan 26, 2015 at 09:44
The solenoid you propose would work fine Roachie.
Regular automotive relays can be had for 60A and even 150A but your solenoid would possibly be more reliable.
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Allan

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Reply By: Member - DOZER - Monday, Jan 26, 2015 at 10:00

Monday, Jan 26, 2015 at 10:00
Should work fine Roachie, it is effectively a 100a relay. The only thing to consider is how you plan to keep the compressor running after the brake light goes out? ie, the compresser will stop as soon as the brake light is extinguished unless you have it wired up in such a way as to retain.

b4 you bag me out, walk a mile in my shoes, then your a mile away and have my shoes :)

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Follow Up By: Frank P (NSW) - Monday, Jan 26, 2015 at 10:04

Monday, Jan 26, 2015 at 10:04
Dozer,

He says he's wiring it to the tail lights, which are always or nearly always on when the key is on, not the brake lights. It should be ok.

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FrankP

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Follow Up By: Roachie.kadina.sa.au - Monday, Jan 26, 2015 at 10:46

Monday, Jan 26, 2015 at 10:46
yep....that's right....tail lights, not brake lights.

I should have added that the reasons for the air "system" are:

* quad air horns
* ability to use a blow-down gun for cleaning dust etc.
* tyre inflation (of course).

Roachie
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Follow Up By: Allan B (Member, SunCoast) - Monday, Jan 26, 2015 at 10:55

Monday, Jan 26, 2015 at 10:55
And of course, the blow-up doll? LOL
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Follow Up By: noggins - Monday, Jan 26, 2015 at 12:14

Monday, Jan 26, 2015 at 12:14
The relay you propose draws a few amps for it self.
Maybe a better idea to activate this relay via a standard 40A relay that's activated via the tail lights when the ignition is turned on .
But :-
Why don't you just activate by 40A relay direct from the accessories at the ign switch .
That way your not going in circles just to activate a relay or 2



ZZ
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Follow Up By: Roachie.kadina.sa.au - Monday, Jan 26, 2015 at 18:58

Monday, Jan 26, 2015 at 18:58
Noggins,

I'm trying to keep the wiring REALLY simple.....so I won't be installing any switch in the cabin.

One small "gripe" (if I can even call it that) with the big Chev is that are NO (zero, zilch) spare switch blanks like the Nissans and Toyotas I've owned in the past have.

There is one accessory switch in the cab (for the driving lights), which is one of those ARB-type press button units with double sided tape...so no holes drilled anywhere.

I take your point about the possibility that the solenoid might draw more amps than a relay....I did already think of that, but given that all the tail lights are LEDs, I *think* I will be okay to power the solenoid's switch from the brake lamp relay itself. Having a relay to control a solenoid would seem a bit excessive.... ;-)

Roachie
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Follow Up By: Frank P (NSW) - Monday, Jan 26, 2015 at 21:14

Monday, Jan 26, 2015 at 21:14
Ahh, there's a thing Roachie.

In new vehicles you have to be careful where you draw power from.

If you tug is all CANBUS, it may NOT be a good idea to try to draw power directly from the tail lights, especially for a solenoid that may pull half an amp or more for the coil.

If you don't know for sure already, you need to get advice as to whether or not you can add a load the tail light circuit. You may have to find another source.

"Try it and see" is not a good option. If it blows a body control module you will be in deep, expensive ka-ka.

And you may be off the road for some time while a new BCM is located.

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FrankP

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Follow Up By: Roachie.kadina.sa.au - Tuesday, Jan 27, 2015 at 05:43

Tuesday, Jan 27, 2015 at 05:43
Thanks Frank....the use of a relay to activate the solenoid is looking more attractive now!

Roachie
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Reply By: pop2jocem - Monday, Jan 26, 2015 at 12:23

Monday, Jan 26, 2015 at 12:23
Roachie,

As said should work just fine, although I'm not sure why you wouldn't just use an accessory feed that goes live to operate your solenoid when the engine fires up. With of course a separate switch to turn the compressor off when not required.
Not being familiar with the electrics on a Silverado, (bloody nice vehicle by the way) are the tail lights conventional incandescent or LED? If LED it might be an idea to check what current draw is involved with the holding coil of your solenoid. That feed circuit may be a little (no pun intended) light duty.

Cheers
Pop
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Follow Up By: pop2jocem - Monday, Jan 26, 2015 at 12:25

Monday, Jan 26, 2015 at 12:25
noggins beat me by "that much" LOL
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Follow Up By: Roachie.kadina.sa.au - Monday, Jan 26, 2015 at 18:59

Monday, Jan 26, 2015 at 18:59
Thanks Pop....I have responded to Noggins.....
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Reply By: Member - kev.h - Monday, Jan 26, 2015 at 12:25

Monday, Jan 26, 2015 at 12:25
Hi Roachie
I did similar and wired the solenoid control wire through the pressure switch on the compressor that way you only have the solenoid alive when the tank is down otherwise with the compressor isolated with the pressure switch the solenoid has power going it for no reason
Can send you a wiring diagram of mine if you need
Kev
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Follow Up By: Roachie.kadina.sa.au - Monday, Jan 26, 2015 at 19:03

Monday, Jan 26, 2015 at 19:03
Thanks Kev, but no need for the diagram.....that was how I was going to wire it anyway. It's a beefy compressor so under normal circumstances it should be working for more than a minute or so.

However, when I'm re-inflating the tyres (to their 60 psi recommended pressure!!!), it will be working for a longer period of time.

I think what I might do when the solenoid arrives (from ABR) is bench test the current draw of the internal circuit to see how much stress it will place on the tail light circuit.

Roachie
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Reply By: wholehog - Monday, Jan 26, 2015 at 21:01

Monday, Jan 26, 2015 at 21:01
Seems like a lot of work for a tin can air storage facility of 18 litres.

Your running 123/126 rated LT tyres on the Chev right..and spare/s..?

Sure wire up a good compressor, a spare tyre is your reservoir, more useful capacity than the 18 litre steel can unit, which is replaced/inspected every when..?..should be 10 years industrially.

Make a hose fitting to use your inflated spare (when you need compressed air to clean filters etc) with a air nozzle.

Do you think a 18 litre water capacity tin can at 100 psi is going to transfer (after you have pumper it up) sufficient air volume and pressure to inflate a tyre or 2 quicker than just using the compressor directly to each tyre?

Quad x Air horns..?..every time you use them the big compressor is gunna rattle off to top up the 18 litre can.

There would be some beaut electric ones available to run off your bank of batteries in the back...stored energy waiting to be used..not transferred inefficiently into a piston compressor to squeeze air into a can with thermal losses/inefficiency along the way to then be piped into a 4 x fart tubes.

C'mon Roachie.
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Follow Up By: Roachie.kadina.sa.au - Tuesday, Jan 27, 2015 at 05:51

Tuesday, Jan 27, 2015 at 05:51
I am under no false illusions about the 18 litre can's capacity to re-inflate even one tyre....it can't and I know it.

I have the same set-up on my current 100 series except for the pump (which is currently a "kit" revolving around a air conditioner-type compressor which is extremely efficient). Unfortunately, there is no "kit" available for the Chev's Duramax donk, so I will just have to settle for a big electric compressor.

The compressor is going to be mounted at the rear of the canopy; some 4 meters from the driving position..... I won't hear the pump doing its work!! hahaha


Roachie
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