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Very hot fuel pump wires


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Hi all, please bare with me.  Long story short, was going to take the car out today and it wouldn’t start, realised pump wasn’t coming on, stripped out boot for access and slowly worked my way back to the beginning {eye roll).... loose connector in the ignition switch by looks.   Anyway as I was putting everything back together to take it out for a spin the fuel pump wiring join pictured (three wire one more so), was incredibly hot to the touch.  It cooled down when power was off, but gets hot when pump gets power.  Is this normal?  
 

PS.  I’m a rookie, so if anyone has any technical electric advice, say it like I’m 5.  

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Apart from undersize wires, if it is actually just the connection getting hot it is probably a dirty joint.  Pull them apart and clean up the bullets with fine emery paper.  Do the same with the inside of the receptacles and pinch the tubes slightly with pliers to tighten them up,  then push it all back together.  

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You don't need a new loom. Mine's wired up as per the diagram at the end of Egil Kvaleberg's article here:

http://www.visanova.com/t2000/t_pi.html

For the power feed I used the heaviest gauge wire I could find in my wiring box directly connected to  the positive  battery post- others may be able to supply a gauge recommendation.

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Once you have sorted out the connector, check how hot the wires themselves get. If they stay cool, they are big enough and there's no need to do anything. It depends on what fuel pump you have as it appears some replacement types take more current than do others, which is why some owners have found it necessary to use heavier gauge wires. 

Edited by RobH
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As others have said the wiring to the pump needs to be reasonably heavy duty. On my TR6 (1970) there is a connector box on the LHS of the engine compartment that I believe was a legacy from the TR5. This has 3x heavy duty 30A connectors that are unused and perfect to wire (through a fused relay and inertia cut-out switch) directly to the pump. Don't forget that the earth has to be of the same rating and it is worth having a local dedicated earth near to the pump. 

It is not good that the connectors are getting that hot and it could be a sign of the pump beginning to fail. I measured 11A+ to my failing fuel pump - that would get your connectors warm! For this reason I re-wired with 30A cable.

I previously posted details of the wiring on this forum, a quick search will get them.

My suspicion is that the new Bosch pumps take more current than the old Lucas one? Does anybody know?

Good luck 

All the best

Tom

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19 minutes ago, Tom B said:

I measured 11A+ to my failing fuel pump - that would get your connectors warm!

No it shouldn't - that is well within the capability of a bullet connector provided it is clean and making good mechanical contact.  

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13 hours ago, Tom B said:

As others have said the wiring to the pump needs to be reasonably heavy duty. On my TR6 (1970) there is a connector box on the LHS of the engine compartment that I believe was a legacy from the TR5. This has 3x heavy duty 30A connectors that are unused and perfect to wire (through a fused relay and inertia cut-out switch) directly to the pump. Don't forget that the earth has to be of the same rating and it is worth having a local dedicated earth near to the pump. 

It is not good that the connectors are getting that hot and it could be a sign of the pump beginning to fail. I measured 11A+ to my failing fuel pump - that would get your connectors warm! For this reason I re-wired with 30A cable.

I previously posted details of the wiring on this forum, a quick search will get them.

My suspicion is that the new Bosch pumps take more current than the old Lucas one? Does anybody know?

Good luck 

All the best

Tom

11 - 12 Amps draw for a Bosch pump is expected according to this.  https://www.ehow.co.uk/list_7554610_bosch-fuel-pump-specifications.html

 

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Thanks Blue, interesting - according to a previous poster in this forum (I should have looked!) the original Lucas fuel pump (according to member JohnC): "The Bench Test specs say the pump should draw 5.0A-5.5A with the PRV set to 100psi."

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The Lucas pump is a terrific item.  The pump part that is.   The adapted electrical wiper motor that drives the mechanical pump is the let down.

Peter W

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  • 2 weeks later...

I wish that I had not looked at this post - I am getting obsessed with the current carrying capacity of bullet connectors.

In my work I am used to seeing connectors with current capacities for each pin and a maximum stand-off voltage. Having trawled the net I have been unable to find a specification for the bullet connectors. Anyone who know differently please let us know.

I did an experiment - I made up a double bullet connector with stout copper wires (into one side only) and measured the resistance (across two joints) this came out at 3.5 mOhms. I did a proper 4-wire measurement at 3.6A with current reversal (yes, I am a scientist IRL).

In the other side of the double bullet connector I inserted a temperature sensor and measured the temperature with 3.17A over a period of a few minutes the temperature rose from 23.6C to 29.6C (difference 6C). This was noticeably warm (finger test) even with such a low current.

A simple thermal model of a single barrel connector with rubber casing and an appropriate heat transfer coefficient to air gave a temperature rise of 10.1C for the same input power. The agreement is not great but at least in the right ball park. I would note that the rubber case is an effective thermal insulator, keeping the heat in.

The problem is that the power goes up with the square of the current - the model predicts an inner temperature of 145C with 11Amps. What would constitute a failure? Solder melts at 216C but the casing will soften nearer 180C (if it is a rubber compound). With 11A the connector will get hot - the joint that I made is new - an older joint will corrode and inevitably have a higher resistance. Similary an old connector may lose its spring, the contact force will be lower and the resistance higher. Also the connector can be behind a carpet where any heat generated can not be dissipated. There are many variables.

Given all this, I don't think I would be happy with a current greater than 5-8 Amps in these connectors. At the higher end it would be best if the connectors are installed in an area with good air circulation. There are probably many sage people reading this saying that we knew all this anyway.....

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Interesting experiment but I think you are being over-pessimistic with your model extrapolation Tom. I also find it difficult to believe you got a 6 degree rise from a dissipation of only 45mW. 

I have just carried out a quick-and-dirty experiment by passing 5A through a rubber-shrouded bullet connector pair and measuring the temperature inside, using a thermocouple meter over a number of minutes.  There was no more than an initial 0.5 degree rise in the connector after which it stabilised (but the resistor I used as a load became smoking hot of course!) I couldn't detect any difference in the connector by touch.

The contact area of a bullet connector is comparable to that of a 6.3mm spade connector and those are adequate for 30A. I think a bullet connector is quite capable of carrying the same and your fears are unjustified. 

Edited by RobH
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Hi Tom,

look at it from a different angle.   

How many of these high loads on a TR6 are there in the world = 1000's

How many are going up in smoke - probably some but very few.  The few may well have other issues as well - old/corroded/knackered bullet socket etc.

Keep it on good condition and all will be well.

 

Roger 

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Hi Tom,

interesting experiment indeed.

Did the bullets have a proper (tight) fit in the female connector? I found some have an iffy fit and the females sometimes are made from materials not stiff enough.

Cheers,

Waldi

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Hi Tom

I suspect any connectors of any design will have a resistance even gold plated ones. As Roger says keep them clean and I suspect they will do a good job if you want a bit of extra security then solder the bullets and ensure the wire is free of oxidation. I find that if I can't solder the wire its time to change it.

Andy

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24 minutes ago, PodOne said:

I suspect any connectors of any design will have a resistance even gold plated ones.

No need to suspect it Andy, it is a physical fact. 

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Thanks for all the replies. My main take is that there are a large number of variables. The point about keeping the connectors in good condition is a good one. There is a reasonable temperature rise with small input power because of the insulating properties of the rather thick rubber(?) jacket.

Waldi - clearly the fit wasn't as good as it could be - I just pulled an old one out of the drawer. I am not sure how representative it was. But I doubt many people would check the joint.

RobH: good experiment - I used a lamp as a load to limit the current. 

RogerH: I may be wrong but I think we are only talking about the replacement Bosch pump on the TR6 that can take 11A - the only other high current application - the headlights with an H4 bulb (headlight) is ~60W / 5A so not an issue. The original poster (if we can remember that far back) had an issue with the bullet connectors on the fuel pump - if he has a Bosch type fuel pump then I am not surprised that the connectors are warm/hot. They won't burst into flames (and as you note there is good evidence for that!) but under the circumstances I don't think that there is enough margin in the design to be comfortable.

 

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Hi Tom,

for various odd reasons I needed to Join the brown wire coming out of the 40+ amp alternator on my TR4 - some idiot cut it short !!:wacko:

The normal inline crimps look flimsy for a possible 30 amp feed so i used a 1" length of copper tubing to suit the cable (big) and crimped that then insulated it.

No way of testing any temp rise once it is bound into the loom but the joint would be classed as industrial compared to the rest of the loom. 

 

Roger

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