#7 Fuse ... How hot it gets ...

[nkemp]

A couple years ago I noticed the number 7 fuse had melted the fuse panel. So I installed an inline fuse as the general consensus is that the fuse panel has poor connectors. Problem solved? Not so fast.

The day before leaving for DCS 14 I noticed that the new fuse holder was showing signs of heat. So I took my infrared thermometer to DCS and took a few readings as I drove. The highest recorded temperature was 265F! Way hotter than it should be. I attempted to read other fuses but I'm not sure what I actually was pointed at. Regardless, I picked up some temperatures in the 110F range. Even that seems a bit high for a fuse panel given that the cabin temperature was in the 70's or 80's. Note that these readings were with the panel cover off and as such may have cooled them a bit by giving better ventilation.

It may be worthwhile to take a road trip with someone else to take and record temperatures. Driving and taking temperatures does not work well and is not recommended. The temperature may not be a problem for short hops around town but on longer trips it gets a chance to rise. I cannot tell how long it takes to rise to that temperature. Another option would be to use a data logger and monitor multiple points in the fuse panel. Anyone have a data logger handy?

FWIW there is the 3 second test that is sometimes referred to as the UL 3-second touch test. I'm not sure that it is related to UL but the test is useful anyway. It simple states that it is safe if you can touch it for 3 seconds. That temperature usually implies something in the 120F - 130'ish range. My #7 is twice that temp.

Clearly the problem is not with the fuse holder/socket. That may aggravate the problem but eliminating or replacing it does not solve the problem. Also, the WUR was unplugged when it reached the 265F.

As part of resolving the problem, I'll install a dedicated 12Vdc line to the fuel pump (which is on the #7 fuse) and control it via the exiting fuel pump wiring and a relay to take that load off the circuit. Operating as is is not helping and may be hurting the pump. BTW .. I'm not sure what the fuel pump is. It was replaced by DMCH 5'ish years ago and I presume it is not a factory pump.

Another option is to trace out each wire and check/improve the connection and ground. Most likely there is a poor ground, poor connector or a wire that has broken strands likely near a connection. Or the replacement pump draws a lot more than original but that I believe is unlikely.

I just thought I'd add that bit of data to the DeLorean knowledge base. Feel free to add more info to this thread. A data logger file would be real interesting.

Related posts but not covering fuse temperatures:
- http://dmctalk.org/showthread.php?5911-Dedicated-fuel-pump-circuit
- http://dmctalk.org/showthread.php?8624-Isolated-Fuel-Pump-Circuit&highlight=fuel+pump+saver

[DMCMW Dave]

Clearly the problem is not with the fuse holder/socket. That may aggravate the problem but eliminating or replacing it does not solve the problem.
.

#7 powers only the fuel pump and the Lambda ECU. So if you move the load off the pump to another circuit (assuming you fused that one too) you are just moving the problem to a different fuse (unless the power consumption of the ECU is higher than I'm guessing). Compared to the fuel pump, the lambda computer and RPM relay circuit use relatively low power to operate (would be interesting to measure those though).

Too much resistance in a circuit does not cause the current to go up, it goes down (per ohms law). Resistance at points like fuse contacts, connections, ground contacts etc. will cause heat AT THOSE POINTS not anywhere else. You can see this as brown connectors on the ignition coil, ballasts, and circuit breakers.

So there are really only two things that can cause a fuse to run hot without blowing:
---too much current in the circuit, i.e. running a 20-amp circuit at 19 amps continuously will overheat heat the fuse. This could be a failing fuel pump that is running slower causing current draw to go up;
---resistance at the fuse contacts themselves. I know they were new but here's a thought on this.

You get a compound effect because as soon as the fuse connection degrades from being run hot due to too much current, the terminals corrode and get resistive which adds to the problem.

Have you measured the operating current in that circuit?

[nkemp]

I have not measured current yet.

The fuses come installed in the pigtail fuse holder and they are very tight from the factory implying a solid connection. That does not mean that the connection is still clean and good. I'll pull the fuse and check the connection. While open I can check the current draw.

[Bitsyncmaster]

The stock type fuel pumps draw about 7 amps. If you check currents be sure the engine is running so the voltage it normal (about 14. 4 volts). From memory the lambda ECU draws less than one amp and my guess the FV draws about the same one amp.

A fuse will get hot if your running above 80% of the rated current. All a fuse is, a metal that melts when it gets to hot.

The relay compartment does get hot if your running a long time closed up. I would do a measurement but mine runs cooler than stock will all solid state relays. Whats left is the voltage drops over the wires that generate heat in the wires.

[David T]

Fuse #7 also powers the warm-up regulator aka control pressure regulator. Not uncommon for them to burn the wiring up inside. It can burn so as to ground and draw current. I would open it up and see what is going on inside and measure the current to the fuel pump. Those are the two main causes for overloading #7. When the fuel pump nears the end of it's life, it's current draw starts to go way up. Good practice is to never draw more than 80% of a protective device's rated current continuously and that is at 70 degrees. As it gets hotter you must further derate the load. The fuse is there to protect the wiring NOT the devices being powered. The wiring is supposed to be sized so that the fuse is capable of handing all of the intended load of the current carrying conductor AND having sufficient capacity to power the devices. Lucas never did it well, the whole electrical system is undersized and the grounding is totally inadequate especially when you consider what time has done to all of the connections.

[Elvis]

Many moons ago I made a therad with pics that showed how hot the fuses get,
especially #7 and the ones for the head lights. Back then we also found out,
that you guys are running darker head lights then our standard over here.

My suggestion was (in addition to new clean contacts) to use a higher rated
fuse to keep them colder, I proved it with pictures.


Yeah well, I still remember well how I got bashed for that suggestion :-((((
oh - BTW - my car still runs great and is not burned....


What I also learned is - use a good working crimping tool when replacing the contacts.
Meanwhile I always also solder the wires on.

As a crimping tool I got this one from a friend and bought it myself yesterday:
HERTH+BUSS 90942241
looks like the cheapo $2 shit but this one is the good stuff and more like €30.

[nkemp]

What is the link to the thread?

[robvanderveer]

i'm just venting an idea here, please correct me if i'm wrong:

Could it be that the pump is drawing too much current, because it is working too hard? years back i had issues with my car stalling because of a clogged fuel filter. this caused fuel starvation at high rpm. it ran fine on idle. Also my #7 melted back then (the PO already bypassed the inertia switch because of a melted connector). I cleaned the fuel system, replaced the filter, and it never got hot again since.

[NightFlyer]

i'm just venting an idea here, please correct me if i'm wrong:

Could it be that the pump is drawing too much current, because it is working too hard? years back i had issues with my car stalling because of a clogged fuel filter. this caused fuel starvation at high rpm. it ran fine on idle. Also my #7 melted back then (the PO already bypassed the inertia switch because of a melted connector). I cleaned the fuel system, replaced the filter, and it never got hot again since.

Makes sense to me - good point!

[nkemp]

The question it raises is why the fuse holder gets hot? Why not the other connection? That said maybe they do and we just don't know. Or maybe there is enough air flow at the tank connection to keep it cooler.

I'm generally of the opinion that connections heat when there is insufficient contact area for the current flowing. That can be aggravated by high(er) resistance connections.

FWIW ... I tried to remove the fuse from the pigtail fuse holder and cannot. I pulled on it with a pliers and it is not coming. A different pliers and more force may break it loose but I want to keep the car running.

So here is the idea I'm floating to resolve teh hot terminals at fuse #7. Why not use a screw terminal 20A circuit breaker? Same function, better terminal connections.

[Bitsyncmaster]

What I think causes all the fuse block problems is the design of the terminals in the fuse block. They were just to low tension to keep a solid connection. The DMCH new fuse block has very nice terminals with a spring loading design.

One of the first things I noted when I first got my car was how easy the fuses pulled out.

[nkemp]

What I think causes all the fuse block problems is the design of the terminals in the fuse block. They were just to low tension to keep a solid connection.

But the connection of the pigtail fuse holder seemed REALLY tight. Maybe the point of contact was very tight but very small.

[Bitsyncmaster]

But the connection of the pigtail fuse holder seemed REALLY tight. Maybe the point of contact was very tight but very small.

Yes those add on pigtail fuse holders grip the fuse really tight (you do need pliers to pull them). I wonder if the molding rubber adds to that problem.

[nkemp]

So here is more to the story ...

I was driving the other day and let some of the smoke out of the wires in the relay compartment. Since I was driving I was not sure which one it was but suspected the #7 fuse. BTW ... I would drive a bit and turn off the car and roll a bit and repeat until I was home. Luckily I was close to home. Note that I drove from the Minneapolis area to DCS and back and no smoke was released on that trip but I did see temps as indicated above.

The fuse showed damage so I cut it out and removed the rubber socket cover to see what was going on. The fuse is melting, the contacts look terrible but the fuse is not blown. This fuse holder has only been in a couple years and was "flying" to help dissipate heat. Here is the picture:

28762

The fuse was installed at the factory and was, and still is, VERY TIGHT. There seems to be good surface area contact. The crimps look good. I seriously doubt that you can get a better contact using these types of connectors.

I'm posting this mostly to add to the knowledge base and for future readers. I have not made any amp readings yet (waiting for a shunt to arrive).

Additional note: This is not unique to DeLoreans. If you search many car marques show up.

[robvanderveer]

that fuse is deep fried. :jawdrop:

[nkemp]

That fuse is now replaced with a 20A circuit breaker. The connections to it are lugs and the nuts are tight.

The original fuse holder melted but not nearly as bad as the replacement (shown above). Being 0 for 2 I think it is time to try something else ... especially since that is the fuse with the fuel pump... a rather important part for happy motoring.

I run an Optima battery and I think those have less out-gassing and out-gassing is one of the suspects causing corrosion on the contacts in the relay compartment. The fuse in the connector was tight from day one but maybe the contact area is too small for the current. I'm not really sure I'll ever know the answer to that given the fuse holder's condition.

I'll be installing a shunt so that I can run a digital display of Volts & Amps. That will be installed in a couple weeks. The display can be installed permanently or removed as desired. On eBay, search for "volt amp digital 50 30 shunt" and you'll get a few examples. The 50 & 30 in the search string results in devices that are 50 Amp & 30 Volt devices. Other volt and amp ranges are available,

[nkemp]

Just for the nuts of it I measured the resistance through that narly mess and it is 182 Ohms. Granted it has seen better days but I'm still curious what causes those connections to develop a resistance across the connection in the first place. I wonder if it is dissimilar metals and a bit of galvanic action. There are very few reasons for a solid connection to develop resistance.

Also ... everything runs cool with the circuit breaker installed.

[Bitsyncmaster]

Just for the nuts of it I measured the resistance through that narly mess and it is 182 Ohms. Granted it has seen better days but I'm still curious what causes those connections to develop a resistance across the connection in the first place. I wonder if it is dissimilar metals and a bit of galvanic action. There are very few reasons for a solid connection to develop resistance.

Also ... everything runs cool with the circuit breaker installed.

My guess it that black rubber must oxidize the copper wire. I have seen other info on copper wire with black insulation would oxidize the copper much faster than other colors of insulation. I wish they would spend the extra money to use plated wire.

[nkemp]

My guess it that black rubber must oxidize the copper wire. I have seen other info on copper wire with black insulation would oxidize the copper much faster than other colors of insulation. I wish they would spend the extra money to use plated wire.

I looked with a 10x loupe and you can also see in the photo that the copper looks sorta good. What is really bad is the spade connections, one side looking worse than the other... which both are also under the rubber boot. When checking resistance, there is no resistance between the copper wire and the outside of the crimp.

Does anyone listening still have the original Irish fuses installed? What are their spades made of? What do they look like? Do they look different than current production? Without looking, I recall that the original female connections have a brass colored surface. Many newer surfaces have that dull grey color.

[Bitsyncmaster]

I looked with a 10x loupe and you can also see in the photo that the copper looks sorta good. What is really bad is the spade connections, one side looking worse than the other... which both are also under the rubber boot. When checking resistance, there is no resistance between the copper wire and the outside of the crimp.

Does anyone listening still have the original Irish fuses installed? What are their spades made of? What do they look like? Do they look different than current production? Without looking, I recall that the original female connections have a brass colored surface. Many newer surfaces have that dull grey color.

Nice work looking for the failure.

The dull grey color is tin plating. They tin plate pins and wires to provide better corrosion resistance. You can usually solder to tin plated wires even corroded. Corroded copper will not solder at all. The original fuse holder pins are tin plated and have 4 "fingers" contacting each pin of the fuse. There was not much tension on my original fuse holder pins. The fuses could be pulled and inserted with very little force. The new DMCH fuse block has much better pins. The pins have a metal spring clip to hold the fusees tight.

[NightFlyer]

Does anyone listening still have the original Irish fuses installed? What are their spades made of? What do they look like? Do they look different than current production? Without looking, I recall that the original female connections have a brass colored surface. Many newer surfaces have that dull grey color.

Most of mine are original, with the exception of #17, which was replaced due to the original one blowing because the cigar lighter shorted out against the console. They're indistinguishable from modern replacements as far as I can tell anyway.

Tension on my fuse block's holders feels pretty good - nothing is loose or wiggly and it requires some force/effort to remove and install a fuse. The female holders are brass/copper colored.

While battery out-gassing is definitely a suspected cause of corrosion/degradation of the fuse/relay area in general, another biggie is moisture infiltration of the interior, which is exacerbated with outdoors storage/keeping of the car.

[Bitsyncmaster]

The female holders are brass/copper colored.

That is interesting. I thought my fuse block I replaced was original and it has tin plated female holders (sockets). My old fuse block had a little heat damage on fuse #7 but was still working.

[nkemp]

Mine are tin colored as well. They have an "appropriate " amount of retention but could be a bit stronger... if that helps :-) Some of the other connections in the car, such as the diodes, are brass colored.

[NightFlyer]

OK, I just double checked mine, and they're tin. When #17 blew, it burned/darkened the holder's metal, which is why I thought they were all brass/copper.

My fuse block says Pressac on it.

[D Knight]

I just replaced my old pressac block with the new DMC one. Big difference in the connectors tension on the fuses. The new terminals have an extra "spring" built in to aid in the reliability


-D Knight-

[robvanderveer]

Replacing the fuse box is on my list somewhere in the future. But the wiring is already very short and I'm terrible at crimping.

[D Knight]

For anyone wondering about the connectors here's a pic of the spring on it vs an original. 2889828899 might be hard to see but it surrounds the terminal and puts a little tension on it. Feels solid when inserting fuses. Took maybe an hour to install the new fuse block. Not hard, but you will want to get a ratcheting crimper for open barrel or weatherpack terminals. Makes the job cake. 28900


-D Knight-