Electric current draw exposure

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Jun 10, 2008 | 04:40 PM

sdetweil

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From: Pflugerville, tx

Electric current draw exposure

So, I am finishing up the wiring, and need to add one more circuit and don't want to run another wire.

I need a switched 12v source, and I need to run

Fuel pump
occasional, short duration air bag valves. MAYBE once a drive.
and the trigger side of the relay that will power the air bag pump. the main line of the air bag pump will come direct from the battery.

Is there any reason I can't use the fuel pump wire for that?

the valves are .5 amps when triggered (10-20 seconds maybe),
the relay is milliamps.

the fuel pump is on a 15 (? have to check that)amp circuit and draws 2 amps steady, 7.5 start.

these three devices are all in the same general area together.

Any reason to be concerned?

I have to run 2 wires for the airbag valves tho, these will be ground leads.

Sam

Jun 10, 2008 | 05:35 PM

tip49

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From: Alberta Canada

Sam;
The load doesn't seem to be an issure does your fuel pump operate through any safety device ie: inertia sw or other that might affect how you actuate your air bags, it would prevent them from operating inder these conditions?

Tom

Jun 10, 2008 | 06:47 PM

sdetweil

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From: Pflugerville, tx

If I am upside down, or after an accident, it is unlikely I would be operating the bags!

Sam

Jun 10, 2008 | 10:34 PM

cmoritz

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From: Westminster,Md

But you may start some crazy new upside down,suspension/air-bag dance fad.....
Seriously though, ..total amperage draw on a circuit exceding the fuse will blow the fuse, at least you want it to..and as you stated Sam,you will see a jump or rise in current draw as any consumer is initialy operated, then current settles down.
That initial spike is what usually blows the fuse. If the air-bag valves don't draw but .50 amp,or maybe even a full amp (x2) , your at 2 amps and 7.5 amps for the fuel pump.
Sounds like things "will" work. From a layout/diagnostic view..they need to be seperated though, the problem shows itself when you need to fix something and need to track it down...you now have a fuelpump and 2 relays in series and have combined two different systems...Yeah,yeah,I know you wrote that down somewhere, and probably even drew a schematic in a note-book you keep in the glovebox, but what about the next person behind you? Just my own opinion of course....
I would keep the fuel system all by itself...simple, and I would keep the airbags in their own circuit.
Another option would be to wire up a junction-block, and run seperate fused circuits from that....still have to run a new B+ to the valves though.Your project is coming along nicely...keep at it! Good Luck!

Jun 10, 2008 | 10:52 PM

sdetweil

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From: Pflugerville, tx

Ok, as I have to run 2 wires for the valves, I'll put another back in the fusebox (switched) and run it to the back as well..
(I hate it when you get all logical on me!)

then I'll run the separate line from the battery to the air pump relay, etc.
the pressure switch on the tank will control ground to the relay control circuit, and fire the relay to switch the main line.

Sam

Jun 10, 2008 | 11:06 PM

cmoritz

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From: Westminster,Md

The relay "coil" side requires very,very small amout of current to operate. Your "load" should be on the contact/swx side.
Dont know how much your airpump draws either.Do you plan on using a controller for ride height? Will it power the valves or ground them at the control unit?

Jun 10, 2008 | 11:20 PM

sdetweil

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From: Pflugerville, tx

air pump draws about 18amps running, 25 start. It will have a 30 amp fuse.

yes, the waterproof relay will just switch this circuit, direct feed from the battery.
battery to fuse to 30, pump on 87
ground to pressure switch to relay 85
new power lead switched to 86, coil

No controller for the ride height, just one SPDT momentary rocker switch (rear is shared air between two bags).. this will switch ground. (two new wires to be run)
Constant (switched) power will come from the new wire to be run.
it will drawing .5 for one valve, and the draw for the main lead relay control side. way less than 1 amp total.

I have enough valves to do them independant, but don't see the need.

The valves, fill & dump control will hang off the bed cross member.
pump under the bed on the passenger side, front corner, outside the frame.
3 gal tank under the passenger door (where the battery was)
all connections (in, out and pressure switch) to the tank on the back side, a drain petcock on the front lower side (due to the truck stance).
Sam