mikep2002

iTrader: (10)

First off I hate electrical junk... Let me ask the probably stupid question...

People who run a hobbs switch for there secondary fuel pumps why is a relay used?

Just curious why would you not just run a direct feed from alternator to hobbs switch and then to the fuel pump and add an inline fuse? The pump would not get power till the hobbs switch activated.. Just dont understand the relay in this case...

(edit)Here is the hobbs switch that I run... Doesnt give an amp number but it looks pretty stout..
http://napaautoparts.com/Search/Resu...word&Nty=1&N=0

fastassls1maro

iTrader: (22)

its normally due to the fact a hobbs switch is not rated for the amount of amps that a fuel pump will pull, thus burning up the hobbs switch.

mikep2002

iTrader: (10)

I am not quite getting it.. The relay is hooked to a trigger wire off the ignition. So if the car is running is there power to the hobbs switch hot side?

Pocket

iTrader: (22)

It can go on either the power or ground legs depending on the situation

Im running this

mikep2002

iTrader: (10)

Pockets, thanks looking at the schematic.. It looks as if the hobbs switch is being used to complete the ground and activate the relay? And you also mention it can go from the power or the ground. If you would use the power side as you mention what is the purpose of the relay?

Like I was saying if you use the power side of the relay on the hobbs (meaning there is power on one side of the hobs switch) what is the purpose of the relay? When I look at this diagram in this thread appears to be on the hot side... https://ls1tech.com/forums/fueling-i...g-diagram.html

fastassls1maro

iTrader: (22)

relays are basically designed to use a low amp wire(small in size 18g-22g) to activate a circuit using higher amp wire(8g-12g). So there wouldnt be a need to run 8g to your hobbs switch and then back to the pump. All factory cars are designed with relays for this reason. Hope that makes a little better sense.

Pocket

iTrader: (22)

Yes, mine is on the ground side

The 12v leg can be used instead like the link you posted. Id suggest using the PCM to engage it instead of any 12v IGN

Mike52

iTrader: (1)

Mike, please don't take this the wrong way, it seems you don't understand the purpose of using relays in an electrical system. It's not as easy as connecting power to a wire or switch to turn on a device. In simple terms, a relay is similar to putting a dam in a river, it stops the heavy flow yet allows enough thru to do the job. Here is a great reference for using relays. I hope it helps.

(Another) Mike

nodrok

Here is the most lay mans way I can be put. A relay allows you to power heavy amped components without the need to run heavy amps threw your switch.

They due this for several reasons. One you dont need heavy wires to run up to you dash switches. (allowing for smaller switches,alot less wire, or weight)

Lower amp switches are cheaper, lighter. so weather its a head light switch, interior dimmer or a hobbs switch you dont need to run 15 amps threw it. Also makes them last longer in my experience. Hope this help. The question I have is im running a bypass regulator ( obviously return style system). Why do guys run the second pump on a hobbs switch? why not just let it go back to the tank. Sorry for the hi-jack.

mikep2002

iTrader: (10)

Just to help a brother out... Most run the second pump on the hobbs switch to try and keep the fuel a touch cooler. I run both pumps at the same time and have a 3rd pump on a bypass/hobbs switch more for safety than anything else. Now I have dual tanks so I dont worry as much as some with warm fuel because my fuel is cycled back to a static tank if you will. Then it is jet syphoned back to the other tank where my fuel pumps are. This is giving it time to cool if you will. (being it doesnt get dumped directly into a tank with warm pumps and it is being mixed with cooler fuel before heading to the primary tank...)