Fuel Pump Relay blowing the running switch fuse.

[Sluggo]

Having a problem with the Fuel Pump Relay set up from Duncwarw's site.

http://www.paultaylorimaging.com/VW/Relays/Relays_3.htm

The blue Voltage Regulator wire used for a running switch keeps blowing it's fuse. I have a 5 amp fuse there (the pump is 4 amps). I was told by Duncwarw not to fuse the wire and to put a fuse there by steponmebbbboom. Should I have a higher amp fuse since it's not feeding the pump but is feeding the relay?

http://images.thesamba.com/vw/gallery/pix/290144.jpg

[Adventurewagen]

I would think you'd want the fuse to be on terminal 30 and not 87.

Switch comes in to 85 and then tells the relay when to work which pulls power from 30 and sends it to 87 which turns on your fuel pump.

You should be protecting the relay instead of the fuel pump. This would also probably figure why you'r burning up 5A fuses since when you kick the switch you are sending more like 15A to the relay.

Just an idea? What do you think about that?

[Sluggo]

I would think you'd want the fuse to be on terminal 30 and not 87.

Switch comes in to 85 and then tells the relay when to work which pulls power from 30 and sends it to 87 which turns on your fuel pump.

You should be protecting the relay instead of the fuel pump. This would also probably figure why you'r burning up 5A fuses since when you kick the switch you are sending more like 15A to the relay.

Just an idea? What do you think about that?

Terminals 30 - battery, 87 - pump & 85 - VReg are all fused with 5 amp fuses. Your sending higher amps to all wires I believe. The fuse amp that should be used is based on the draw not what's being sent IIRC. When I ran it straight from the coil I used a 5 amp fuse and it did not blow. When I tried to run the pump straight from the V-Reg it didn't run at all. Does the relay draw power itself? Aside from what it's sending to the pump.

[Adventurewagen]

Yes, but I'm not sure how much.

Can you measure the current off 87 to the pump and see what it's spiking at without a fuse?

Let me check on the regulator and see if there is anything I can find on that.

[Adventurewagen]

It looks like the Bosch relays have a 75ohm coil or .16Amps of draw.

Not much. Check out this link though, more info on relays than I really ever wanted to know :) Kind of also explains why you'd want the fuse off 30 and not off 87, just like you said the pump pulls the current, not really the battery pushing it.

http://www.bcae1.com/relays.htm

[Amskeptic]

Having a problem with the Fuel Pump Relay set up from Duncwarw's site.

85 is the relay's solenoid supply, the signal wire terminal.
86 is the solenoid's ground wire terminal.
30 is power supply which contacts
87 which drives your pump.
Some have an 87A, an extra output if you will.

The relay 85/86 circuit does not need a fuse, and does not want a fuse.
The wire leading to 30 must be fused. I use an 8 amp. 87 side is not necessary to fuse.

Safety is driving sensibly first, if it gets too anticipatory of too many contingencies, what the hell, let's all stay in a rubber room with helmets on.
Colin

[chitwnvw]

It's like your speaking Latin, I can't wait to delve into the electronics.

[Amskeptic]

It's like your speaking Latin, I can't wait to delve into the electronics.

Let's begin:
VW uses the common German terminal #s amongst all German cars.

30 hot
15 ignition
50 start
85 relay solenoid*
86 relay ground*
*if diode is present otherwise polarity not important
87 switched
4 twentythousand + volts out of coil
1 primary

there are many more. . .quiz on Monday
Colin

[Sluggo]

Having a problem with the Fuel Pump Relay set up from Duncwarw's site.

I would expect so. The diagram is labelled wrong. 85 is the relay's solenoid ground. 86 is the live signal terminal.
30 is power supply contacts to 87 which drives your pump.

The relay 86/85 circuit does not need a fuse, does not want a fuse.
The wire leading to 30 must be fused. I use an 8 amp. 87 side is not necessary to fuse.
Colin

Are you sure that 85 is ground and 86 is switch? I'm looking at 2 sites (Duncwarw's and the other posted earlier) and both say 86/ground 85/switch. I'll give it a shot and see what happens. I'm not using Bosch relays. Maybe that's the problem. I have several. But I used ones I found with securing tabs built in.

[Adventurewagen]

Relay brand "shouldn't" matter. Bosch decreed years ago what each connection was supposed to be. Unfortunately I've found two places that contradict the same thing you've run into but it shouldn't be a problem.

30 = 12V power
87 = accessory output

86 = Ground or Switch
85 = Ground or Switch


We do know that 30 is power and 87 goes to your accessory.

85 and 86 connect to either side of the coil (inside the relay) and all the coil needs to operate is a difference in potential, so applying the power to 85 OR 86 shouldn't matter if you ground the other.

check out this image, it shows it nicely.



Bosch relays usually also have an 87A terminal which is basically just powered when the other is not and could maybe be used for something, just don't know where or for what yet.

[Amskeptic]

Let's pretend that I am not an idiot.

Aw what the hell, it's too late.

You MAY use 86+ /85- if you do not have a discharge diode which we do not.
My fuse suggestions still stand, so there.

I am going to go correct my erroneous posts now. . . . . . .
Colin
(and thank-you for your sharp minds, I used to have one)

[Adventurewagen]

You MAY use 86+ /85- if you do not have a discharge diode which we do not.

I need some explaning on this one and how a diode could fit into the picture? You've gone beyond my knowledge of the relays and how things work at this point. I knew there was a circumstance when current flow direction was important, but this is where I get lost. I've been reading about quenching/suppression diodes trying to figure it out which I think is the same thing as what you call a discharge diode but I just don't get it.

I read that you want one of these diodes to be put in paralell with the coil so that when you take power away the reverse energy flow that happens gets absorbed by the diode (or possibly a resistor). Lets say I have a standard Bosch relay, in what instances would I want to insert a diode when sending power onto some power unit downstream? Or maybe the diode is only to protect the relay?

Either way I'm lost on the whole diode in parallel and explaining to myself how you'd know if you needed the flow to be important. Basically I'd like to be able to prove to myself or KNOW why I'd hook positive to 85 over 86 and why.

On another note I still think we should start subdividing forums whether sub forums or not into problem areas. Electrical comes to mind as a really good sub forum topic. Regardless of VW model and year we would all benefit from having a very technical electrical section I think.

[Sluggo]

I belive it does have the diode. Little silver wire with a bubble in the middle between 86 & 85?

[Sluggo]

Now that the VR isn't working, the fuse from the blue VR switching wire doesn't blow but the fuse for the starter switching wire does. Are you saying neither of these should be fused? I have everything fused except the ground.

[Amskeptic]

I read that you want one of these diodes to be put in parallel with the coil so that when you take power away the reverse energy flow that happens gets absorbed by the diode (or possibly a resistor).
in what instances would I want to insert a diode when sending power onto some power unit downstream? Basically I'd like to be able to prove to myself or KNOW why I'd hook positive to 85 over 86 and why.

On another note I still think we should start subdividing forums whether sub forums or not into problem areas. Electrical comes to mind as a really good sub forum topic. Regardless of VW model and year we would all benefit from having a very technical electrical section I think.

Diodes are found in later cars with electronic circuits that do not want surges when the solenoid retracts in its windings. The FI double relay has a diode to prevent back feeding through the fuel pump circuit