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What Ampage fuse for fuel pump wiring.

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Hey guys.  I had some wiring problems where some dick decided to hard wire my fuseable link for my fuel pump. I am going to install a different fuse type, but I don't know what ampage fuse was originally there.  I can't find anything on it.  Someone suggested it would've been around 100 amps, but that sounds a bit high to me.  I  running an after market fuel pump, but I don't know what brand it is.  Is there a way of figuring out the ampage I would need?

 

Cheers

 

Scott

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ROFL 100 amps.....

 

That's more than what the stock alternator would put out by almost 3 times.

 

It would be best to know what brand and model of pump you have and use their recommendations for fuse and wire gauge.

 

Most electric fuel pumps will run on a 10 amp fuse. The thing to make sure of is that the fuse you are using is not a higher rating than the current capacity of the wire.

 

The use of a fuse is to protect the car, not the equipment it is attached to. The fuse should blow if there is a short in the wire or a malfunction of the equipment that it is attached to. This is why you will find fuses generally nearer the source of power than at or near a component. The exception is aftermarket equipment where they install a fuse in the equipment, but the purpose is the same, to protect the car, by blowing the fuse in the even that a problem occurs inside that piece of equipment.

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Yeah as above you'd need to know the size of the aftermarket pump Scott. Can you see the last three numbers on the code stamped on the outside. Hopefully its a Bosch.

 

10A is usually pretty safe.

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About 90% of cars on the road have fuses from 10-15 amps max. With 100, the car would burn up to save that fuse from blowing.

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lol yeah, I thought the same thing.  Awesome, thanks guys, that makes things easy since I already have the fuse holders and fuses here, so I dont have to go and buy more.  Would it be worth reading the ampage output from the pump and say raising the amps by 5-10 from normal for the fuse?

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So, I installed some blade fuse holders and used 20 amp fuses and they didn't blow when I tried to start the car (it wont start at the moment).  I put the multimeter on the fuel pump and it read 13 amps, so is 20 amps overkill, would 15 or 17 better? 

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That seems like a lot of amps. I'd be tracking down your 12V feed and see how thick the wiring is and where the source is from.

If your losing voltage somewhere youre amps will be higher.

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How did you check the current draw, are you sure it wasn't 13volts? I don't think my wiring would handle 20amps as its pretty small gauge and you want the fuse to burn out before the wiring... Maybe try smaller fuses until it blows then use the next size up.

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Is your zed using the original wiring for the fuel pump (large solid green wire) ? Or did you run your own wiring?

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well, thats the problem, I haven't done any of the wiring.  I am crap at it.  At the moment, the car is in getting fixed.  should have it back Monday.  I'm not sure about the reading, I followed the instruction manual on how to measure amps and all I had flick up was 13 for just a split second then nothing.  Its the only reading I could get out of it, so even though I had the multimeter set on amps, could it possible show a reading in volts or something.  It was just a flash, no longer than half a second.  Once I get it back, I think Ill just drop the fuse size until it blows as above, that seems like the next best thing.

 

I am concerned it wont work for the Nationals next weekend though, its creeping up very quickly now.

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from someone who has built a few wiring looms in his time...

 

 

If you are measuring the amperage draw on the pump, you need to set the multimeter to the AMPS setting, on the highest amperage range selectable, then place it IN LINE of the power wire (or earth wire)

Its important that all the current MUST flow through the multimeter, so not just resting the probes against two terminals, but physically disconnecting the wire and placing the multimeter between it.

Bear in mind that measuring in this way often requires some consideration of what you expect to see. No point having a multimeter thats only rated to a maximum of 20A and trying the same thing with the alternator output or starter motor, Clearly that sort of load will cause it to melt/break/explode ect.

If you have an Inductive Amperage meter, then its heaps easier, just clamp around the wire and measure, they are kinda expensive but they'll measure up to hundreds of amps....

The expected reading will be dependant on several factors, How big the pump is (how much it flows), how high the rail pressure is and often the pump is used.

Suffice to say, you should expect around 6-8 amps.

It will peak higher when it initally turns on, this is normal.

Even then, it'll only peak an amp or two over its nominal range.

Most Automotive pumps will be fine on 10-15A fuses.

Pretty much ALL the aftermarket pumps i have set up, i have used a 15A fuse.

While your doing that, it pays to ensure you have a good earth too, either measure for continuity to the chassis from the

pumps negative terminal (should be as close to 0 ohms as possible, 1-2 ohms is acceptable) Or physically remove the ground point and clean it.

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:-\  As the purpose of the fuse is to ensure that the wire being used does not overheat & burn out would it not seem reasonable to check the amount of amps the wire being used can carry given that there is only 13Volts to push the amps thru this wire. Then try three quarters of this figure for the fuse itself. You may be able to apply OHMs law theory if you can find out a bit more about the fuel pump itself.

 

                                                            Regards : Alan.  :D

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Heya

 

Basic electrical theory is that Power (P) = Voltage (V) x Current (I)

 

=> P = VI

 

By example, if the power of the device you are running is known (eg 90/130W head lamps), then max total power is 130 x 2 (lamps) = 260W.

 

So, 260 = VI

=> 260 = 12V x I

So, I = 260/12 = 21.7 Amps

 

So, in the case of a high beam headlamp fuse, you would run a 25A fuse minimum. I use heavy gauge wire in my installation, and use 30A fusing, which works fine, and will protect the wiring from a short.

 

As one of the other contributors mentioned, the fuses are there to protect the wiring, NOT the device. Shorts are caused most frequently through short circuits (eg wiring abraided and shorts to earth) OR through a device failing (eg fuel pump short circuits, effectively conducting power through the pump with no resistance in circuit). In these cases, if the fuse does not blow, the wiring will heat up and potentially cause a fire and/or damage the wiring. By blowing, the fuse protects the wiring from this outcome...the device is already stuffed, hence the fuse is not there to protect it.

 

Bottom line: The fuse needs to be 'big' enough to sustain the maximum current draw of the device when under load (including start up current), but small enough to blow BEFORE the wiring gets hot and fails. Hence, you need to know the power requirement of the device, and the power/current capacity of your wiring to design your fusing.

 

Cheers

 

Jamo

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;) Just to add a little more info, according to a wiring chart I looked up (AWG)    #6 wire gauge carries 37Amps                      / #8 24Amps /#10 15AMPS.

 

  * AWG: American wiring gauge.                                                           

                                                                          Regards: Alan.  :D

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;) Just to add a little more info, according to a wiring chart I looked up (AWG)    #6 wire gauge carries 37Amps                      / #8 24Amps /#10 15AMPS.

 

  * AWG: American wiring gauge.                                                           

                                                                          Regards: Alan.  :D

 

Over what length?

 

As the wire length gets longer, the resistance goes up, reducing potential current transfer.

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;) These figures would be suffice to cover the max length used in most vehicles.It stands to reason that the longer the wire more volts are reqd to force the reqrd Amps thru.

 

                                                        Regards: Alan.  :D

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;) These figures would be suffice to cover the max length used in most vehicles.It stands to reason that the longer the wire more volts are reqd to force the reqrd Amps thru.

 

                                                        Regards: Alan.  :D

 

That's not how electricity works though.

 

If there is too much resistance in the wire the current will go up, which causes the wire to heat up, which causes increased resistance, which causes the current to rise, which causes more heat.....

 

Including the wire length in the spec "max current capabilities" of wire gauge is very important. There are some wire lengths in vehicles that are only a few inches, while others are several feet long, which can change the required wire gauge drastically.

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mate your car has a aftermarket loom autronic from memory and they have a 15a fuse for the fuel pump for a 044 style pump .but if you have a lift pump as well you should run a separate relay and fuse or you may have a problem

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