2004 F350 6.0
Where is the best place to hook into for a 30Amp ignition switch controlled power source.

I am replacing my air compressor with a higher rated unit and heavier cable.

Currently is hooked to a blade fuse tap on the fuse box (left under steering wheel) but I am not comfortable with this power source for the uprated amp requirement.


As always, from you knowledgeable people any input greatly appreciated.


Mark

 

You could use a relay hooked to a battery for the power (pin #30 on the relay) then use a 10amp fuse in slot #42 (think that's the "Customer Accessory" fuse number) in the under-dash fuse box to route power to the relay's #85 pin. That way when you turn the IGN on it will cause the relay to energize pin #87 and the relay handles the amperage and not the steering column.

Very crude wiring diagram of how a 30 amp relay works:

 

I don't suppose this compressor has a remote option? Amps for car stereo's normally have straight shot out of the battery to a filtering capacitor to the amp. When you turn the radio on a Remote wire (normally blue with white stripe) sends the signal to amp to energize. This allows a small dash ignition source to power the huge amps. No matter where you put this circuit for this compressor you may want to consider putting a filtering capacitor on the compreesor.... that way the starting surges don't beat the crap out of battery and or alternator.

 

30amps is a lot to pull through any of the ignition-switched switches all ready in the truck. A relay is clearly the way to go. a/c current motors often have a " start" capacitor but I think you can get away without it on a d/c motor like this. I think I read there is a switched relay pre-wired behind the glove box, but I may be thinking of the trucks with the "up fitter" switches.

 

Is the Bosch relay already on the truck or do I need to get one a d wire it in. Is this the one shins the glove box referred to above

Mark

 

The start capacitor that AC motors have is normally to prevent excessive current through the windings of the motor itself not to prevent damage to the circuit/power source. I was talking about the capacitors used in cars (normally stereo's) to prevent damage to the VEHICLE. It minimized the peak current as the motor first starts. ALL ELECTRIC MOTORS have some sort of starting current (normally it is approximately 5 times run current). If you have a 30 amp motor it could be peaking at 150 amp spike which over time can damage batteries and or alternators. A properly rated and installed capacitor can cut this spike in demand down from 150 amps to about 50 -60 amps peak spike...

 

Never seen a cap on a wiper motor or fan motor in a car before. On some vehicles the fuses on those circuits are 20-25-30 amp. I admit that's a little less than what were talking about here. If he's pulling power for the relay directly from the battery + terminal, doesn't the battery itself provide significant capacitance? I've seen some car stereo's with 1 or even 4 caps as big as an old style ignition coil lol! Maybe I'm misunderstanding but I thought that was to protect the relatively delicate MOSFET components on the audio equipment power and audio amps?

 

I'd have to do a little research. Maybe someone will post up and beat me to it What year is you truck? Do you have the up fitter switches?
As you can see above we will soon figure out if you need a capacitor <----grin.

 

Yes and no. A capacitor opposes a change in Voltage.,,, it does this by charging and discharging Power to maintain a set voltage (basically a low charge rapid fire battery.) A battery is a chemical source of electricity. A perfect example of this is starting a car/truck. When a Load starts on a system there is a drop in voltage till the battery has a chance to recover the system voltage. This is why a charged battery is 12.5 volts but can drop down to 11.5 to 12.0 volts when turning over. The larger the load the larger the demand. the lower the voltage drops. Once the car starts a alternator kicks in and charges at 13-14 volts to recharge the battery. In the case of the stereo equipment there is a large load splike when the bass hits. This causes voltage to drop just like turnin a large compressor or the starter on. This can cause multiple problems.

1) the mosfets etc can be sensitive to voltage.... like some other things that come to mind.... FICM.

2) a large enough load acts similar to a starter in its drain on the battery. All batteries are rated a number of charge/discharge cycles.... if each start of compressor cuts into this... why not minimize the impact. Our trucks are rough enough on batteries (why else would Ford install 2 of them) the capacitor could be the difference between 5 years of battery and 2 years..

All in all. While not required I sugeest it (sorta like while not required pepps on this forum suggest a coolant filter

 

2004 and no no up fitter switches.

Mark

 

Some great info in this thread. https://www.ford-trucks.com/forums/3...-location.html Post #14 has a link to the Ford body builders guide that shows a couple of places you could pick up an (ignition) switched power source for your relay but it looks to me like you'll have to add the relay yourself. The upfitter relay control panel has 4 relays to use for whatever you need but they are 10, 15, and two 30 amp relays in the factory panel so not big enough for what you need.

 

metmop,
Thanks for the insight, I see where youre going now. Anything to help the charging system out is a good deal in the long run.

 

Ok one thing that was missed about a filter.
They also keep electrical noise from going back
up the wire. Compressors are very electrical
noisy and they will give things fits back up the line.
I can think of two reasons for the filter. Do you listen
to AM trafic radio? You may not be able to with the compressor
running. When it shuts off it WILL make a voltage spike as the
magnetic fields collapse. Sort of like a baby EMP. The truck
electronics will be unhappy over time.

Sean

 

All of this although most helpful refers to the 2005 and up models. Mine is a 2004 so don't think that the upfitter switches will fit or work. Or am I wrong.
If they dont, any ideas on where to fit the relay and where to power it from.

Thanks Mark

 

That is correct, Upfitter switches are a '05 and up option only. But there is quite a bit of room under the steering column for relays. I've got three under mine (high-idle, mirror heat & fog lights) and they're safe & clear of the actual column. I've got the F650 dash in my truck for some "upfitting" of mine own.