View Full Version : Installing / Wiring up extra fuel pumps- need help/advice
Hi, I plan to install two new fuel pumps to my car, while keeping the original in place as well. Forg provided a bit of help IN THIS THREAD HERE (http://board.performanceforums.com/forums/showthread.php?s=&threadid=67145161) , but I'm just chasing perhaps a different alternative to consider.
A standard relay would normally have the following, right? Well, thats what mine has anyway.
(a)12v input from battery
(c)output to pump
(d)output to something else, ie, std pump (?)
This is what Forg said :
An easy way to wire up what you've got would be to run a relay's trigger circuit off the power supply to the pump you've already got mounted, and run the power for the second pump through the relay (and a fuse).
From my understanding, that would install a new relay, with the output to pump (c) from the first relay becoming the input (a) for the second relay? correct?
What I was wondering, is it possible to get a relay which can supply power to three different pumps to get rid of the first relay??
output to pump 1
output to pump 2
output to pump 3
I'm worried about voltage drop affecting the operation of the pumps.
11-03-03, 05:34 PM
I've never seen a relay that closed three circuits. If you were using a stockish relay I imagine the power sapped by three pumps would be significant enough to go close to burning the stock fuse.
I'd just leave the stock one there and use it to trigger the new relay. Less hassle, and easily removed.
Always fuse, always use heavy gauge wires, solder everything, shrink wrap everything. Do it once, do it right :)
A relay usually has two completely different circuits;
(a) +12V input from the circuit you switch from (eg, ignition)
(b) Earth for (a)
(c) Terminal 1 for the circuit you want to connect
(d) Terminal 2 for the circuit you want to connect
For (c) & (d), there's no polarity; you can wire it up either way. Think of it like a switch, but instead of it going on when you flick it one way & off when you flick it the other, it goes on when you put +12V at (a) and off when there 0V (or no voltage) at (a).
Does that make sense? I hope so, 'cos I'm going to go on. :)
The way you want to wire it up is like the following;
Let's have two relays; with
(a1), (a2) +12V input from the circuit you switch from (eg, ignition)
(b1), (b2) Earth for (a1) & (a2)
(c1), (c2) Terminal 1 for the circuit you want to connect
(d1), (d2) Terminal 2 for the circuit you want to connect
You already have (a1), (b1), (c1), (d1); that's your existing relay. Relay '2' is the one you add.
So, just connect (a2) to (a1), and (b2) to earth; or connect (b2) to (b1), it is an earth.
Then connect (c2) to a juicy power supply lead or the battery, through a fuse; and (d2) to the newly-added pump.
Does that make sense? Draw it out, if it doesn't make sense at first.
There is another alternative, however. You could use the +ve of your existing pump as the +12V that runs the second relay. So, (a2) connects to the wire that goes to your existing pump's +ve, (b2) goes to earth. (c2) & (d2) wire up as I described above.
The only difference here is that you're using a different location as the trigger for the relay.
As for having one relay; to do what you want to do, it would have
You probably can buy these.
Truth be known, you could also go with a single relay, as long as it handles the current your pumps pull; just put a 'T' intersection in the wiring at point (d). It is current draw that is important, the relay could even catch fire if it can't handle enough current; and also, if you do it with one relay, you'd be best still to have a separate fuse for each pump.
There, babble over. :)
hehe, I need a minute after reading that I think.. It makes A LOT more sense when you actually have the relay sitting infront of you.
I think using the 12V output from the first relay will be the best option.. I THINK..
Thats the relay I'll be using. I gather that 87 can be used to supply power to 2 pumps?
I'm thinking 85 will be the 12V which was going to the original fuel pump. 86... Can 86 supply power to the original pump now or will it have to be ground??
What about 30? feed from the battery?
I think I've got it sussed, what do u reckon?
I think they are labelled 30 85 85a 86 87
30 is feed from the battery.
85 / 85a is the output to the device, in this case the fuel pumps
86 is from the trigger eg ignition ON
87 is the earth for 86
13-03-03, 11:58 AM
Most relays have 2 ouputs, 85 and 85a, use these to power the 2 pumps, i have run a carter and a bosch motorsport of the one realy for years and never had a issue, i always use 8ga wire to the realy and then 6mm wire from relay to pumps, voltage loss is a killer, use the biggest cables that are practable
Oh OK, I've not seen relays with two outputs like that, although they're obviously around. All the standard ones on my car that have two "output" terminals have it set up so that one is off when the other is on, & vice versa.
But yeah, the drawing of that relay looks like it might do what you want ... although I wouldn't swear on it 'cos the numbering seems different to 10sec_rx7's experience [actually, it looks a bit to me like the relay switches OFF when you send juice through the trigger, rather than ON ... but that's just a quick look at the drawing].
This stuff makes a lot more sense when drawn. :)
The ones you seem familiar with are what I refer to as a 'changeover' relay. You would use these in a situation such as switching foggies off when you switch to lowbeam, and vice versa.
If you buy a driving light set from anywhere, the relay you should get will be the one I described, with 2 outputs.
To reduce the voltage drop in my Z, I used 10amp 3-core domestic cable (like you make extension cables from) - able to run a VL-turbo and a lift pump off the same relay.
OK, I've got it sussed now :D
Forg, I think you were right with the switch closing. Double checked the relay I already have installed, and its been bridged.
OK, IGNITION signal comes in through 86
When there is 12V, switch flicks completing the circuit so power can flow
Between 85 and 30 has been bridged so will not flick on/off (?)
30 supplies power to 87 & 87
Should the following happen??
RELAY 1 - Signal from ignition 86
- 12V goes through 87a and 87b
- 87b currently supplies 1 pump
- 87a provide input to RELAY 2 (through RELAY 2 pin86??)
- 30 & 85 goto a fuse, then to ground?
RELAY 2 - 86 gets signal from 87a of RELAY 1 (?)
- 87a & 87b will provide power to new pumps
- 30 & 85 will goto GROUND (?)
Hope I'm on the right track. I'm not 100% on what to do with the wires coming from 30/85.
This is a diagram of how it'll be set out.
In the setup you've got, 85 and 30 are connected to the same power (battery) source. 86 is connected to ign, and switches current to earth when the ign is switched to ON.
Or its using the switched power to power the device - very inefficient!
It would be simpler if 30 was connected to +12V, and 85 was connected to earth. Then when ign -> ON, power flows into 86, through a coil winding and out 85 to earth.
When 85/86 switches, the coil causes throws an arm that causes the connection to be made between 30 and 87, allowing battery power to travel to the device, in this case the fuel pumps.
Quite simple really. The setup is drawn on the relay casing (at least on the Bosch ones, and I think on the Hellas).
The other 87 output could be used to trigger a second relay, or you could branch off relay1's 86 to the second relay's 86. But realistically, I've had 2 pumps running off the same relay (the relays are rated at 30 amps). You want both pumps to work at the same time, so run them off the same relay. If you want to be able to switch between them, then you will need a switch (on / off / on) that directs the switching current to the 86 of 2 different relays.
Alright, now I'm confused.
Cheers, that makes a lot of sense.
The diagram for the switch was posted before (http://board.performanceforums.com/gallery/data/500/1017relay.jpg)
So let me see. When power flows through 30 and 85 (which is to GROUND) it goes through 86, and as power goes through 86, it'll also flick the switch between 30 & 87, correct?
So, Ignition in relay 1 goes into 86. 85 is ground. 30 is battery. 87a goes to Pump 1. 87b goes to relay 2
relay 2, 86 gets source from 87b of Relay 1. 85 is still ground. 30 gets feed from battery. 87 are outputs
should that work??
Undo the (external) connection between 30 and 85.
Then everything should work OK.
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