generic relay question...

Gris · **Posted:** Tue Jan 30, 2007 4:46 pm

Using your standard 12v relay, ie...

pins 85 & 86 are your switch power and ground and pins 30 & 87 are your "battery" passthru...

Will pins 30 & 87 pass a ground signal instead of a battery signal assuming the switch is still set up like it should be?

Reason I'm asking is because I want to use a relay to pass ground instead of battery and want to know if I need a specific relay.

I'm thinking it will work fine as all the switched part does is close the circuit so "whatever" passes from 30 to 87.

N / A · **Posted:** Tue Jan 30, 2007 6:01 pm

id have to play with one but it should be possible

W3CSX · **Posted:** Tue Jan 30, 2007 6:19 pm

Yes that will work. It doesn’t matter to the relay where the current comes from. As long as there is no power thru contacts 85/86 the electromagnet inside keeps contacts 30 and 87 separated.

You can not keep a content power thru terminals 85/86. Whenever this half of the circuit is complete. Power will flow thru 30/87.

Jason

Gris · **Posted:** Tue Jan 30, 2007 6:36 pm

That's what I needed to confirm.

Thanks Jason!

circuit will be setup as such...

85 - trigger ground
86 - trigger power

30 - ground from compressor
87a - ground pass-thru with trigger off
87 - ground pass-thru with trigger on

87a will go to one side of the 105psi pressure switch, then from the other side to chassis ground.
87 will go to one side of the 200psi pressure switch, then from the other side to chassis ground.

so in essence, if the relay has no power, it will pass the compressor ground thru the 105psi sensor and shut off the compressor at 105psi.

is the relay DOES have power, it will pass the compressor ground thru the 200psi sensor and shut the compressor off at 200psi.

SO...

I throw a switch in the back with my compressor. when off, the system runs at 105 PSI to charge the ARB without worrying about damage.

If I choose to turn that switch on, it will kick the system into 200PSI mode for refilling tires and what not.

sound right?

W3CSX · **Posted:** Tue Jan 30, 2007 6:55 pm

I hate to say it Craig but I do not think that will work. The pressure switch should be in the control wire leading to terminal 86. This way power feeds thru the switch on your dash then thru the pressure switch. If pressure is high the pressure switch will keep the relay off when you drop to 85lbs the switch closes thus closing the circut thru 86/85. The relay power then feeds from the battery and terminal 30 thru terminal 87 to the pump.

Power from 30 to 87a is ALWAYS ON. It does not matter what position the switch is in. When the pressure is down to 85psi the pump will kick on. Unless you have the main power switch in the line from the battery thru terminal 30 which is a no no. This overrides the whole purpose of have in the relay allowing full current to flow thru the both switches. Also the full 30-35amps is flowing thru the pressure switch. Most of the pressure switches out there will not handle that kind of current.

Gris · **Posted:** Tue Jan 30, 2007 6:59 pm

I'll find a schematic of the relay to show ya. 87a is ON when the trigger is OFF, if you give the relay trigger power, 87a loses it's connection and 87 gets it.

as it is now, the compressor ground goes through the 200psi pressure switch. cutting the ground seems to work just fine.

when I get home later tonight, I'll photoshop my intended schematic to show ya.

W3CSX · **Posted:** Tue Jan 30, 2007 7:11 pm

Ok here is how it make it happen. You said you have switch in the back to control which pressure switch is on line.

Battery to terminal 30. Pump to terminal 87. Terminal 85 to ground. Forget about terminal 87a we will not use it. Run the control line to both pressure switches. If you have a switch on the dash to control the whole thing run the wire off this switch to both pressure switches. From the pressure switches feed to a double throw switch one pressure switch to post 1 the other to post 3. Then wire post 2 to terminal 87 on the relay.

EDIT: Mis-typed post 2 on the double throw switch goes to 86 on the relay.

By using the double throw switch you select what input from the pressure switches supplies the relay.

W3CSX · **Posted:** Tue Jan 30, 2007 7:17 pm

Gris wrote:

I'll find a schematic of the relay to show ya. 87a is ON when the trigger is OFF, if you give the relay trigger power, 87a loses it's connection and 87 gets it.

Correct this is why you will always have power. When the relay is activated the power thru 30 is moved from 87a to 87. Without a switch inline to 30 you will still have power to 87a when the system is off.

Give me a call if you can.
Jason

Gris · **Posted:** Tue Jan 30, 2007 8:02 pm

I'll give you a call in a few...

here's the wiring diagram I whipped up and the pin-out for the relay I have.

Kniggit · **Posted:** Tue Jan 30, 2007 11:34 pm

That would work. I'm an electrician, I know. But make sure you have a heavy duty enough relay. That compressor motor could draw quite a bit.

K

JimJ · **Posted:** Wed Jan 31, 2007 12:06 am

Question?
Is the 105 psi switch normally closed with pressure below 105?
Is the 200 psi switch normally open with pressure below 200?

Gris · **Posted:** Wed Jan 31, 2007 1:05 am

Jason and I talked about it. He didn't realize the the pressure switches were rated to handle 20amp each.

Kniggit, the relays I use are 30amp. The compressor Viair claims the compressor maxes at 19amp at full load. I currently have a 30 amp fuse inline to the compressor. I'm going to change that to a 20amp tomorrow and run it 100% for 1.2 hour or so to see if it ever gets hot enough to pop the 20amp fuse. If it does, then i'll rethink this. If it doesn;t pop the fuse, then the sensors should be fine.

Jimj, both switch have an open and closed state. the 200 psi one turns the compressor on at or below 165psi and turns it off at 200psi. the 105psi one turns it on at or below 85psi and turns it off at 105.

generic relay question...

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