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Fuses in'66 B

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19_again

19_again

Jedi Warrior
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I've already searched the archives to find an answer to what I felt was an obvious question, taint there! My bib benmtlay book states that I should have two 35A fuses, one for Aux.Ign. and one for just Aux. The PO has a 20 amp in the top position 1+2 and an unknown in the bottom 3+4 position. There is one spare that is a 35A Lucas continous, but that's it. The car starts, the lights, blinkers, wipers work. What's the actual required fuse rating for this car (18GB-U-H.)
Also is distilled water really the best for the cooling system?
Thanks,
Mike
 
I would definitely use distilled water, it doesnt have alot of the crud tap water has in it. Make sure you mix in coolant too, it will increase the boiling point of the distilled water.

My Robert Bentley book says the current tating is 17 amps (35 amps blow rated) Not too sure if that helps at all.
 
If the operating rating is 17 amps that would explain why car runs using only a 20 amp and presumably another 20 even though I can't be sure, but given the fantastic reliability of the dark master, I would prefer to use what he calls for.
what page in the bentley has that info you referred to?
Thank you,
Mike
 
Oh shoot, I was looking at the '71-74 part of the Bentley. Your profile says you have a '66 so check it out on page 12. If Im wrong and its a 71-74 then check out page 33.
 
This was my response to a recent question on the Spridget Forum. Dave is an electrical engineer, and knows of what he speaks.
Once again, sincere thanks to Dave.

Bob, regarding your fuse question, this information was provided courtesy of Dave Russell. Dave is about the "Guru-est of gurus" in these parts.

"If you are wondering, you can replace Brit fuses with US fuses. Due to different rating systems, Brit fuses & US fuses will have different numbers for APPROXIMATELY the same ratings.

Brit (Lucas)--------US (SFE AGC)
5-----------------------3
10----------------------5
20---------------------10
25---------------------15
30---------------------15
35---------------------20
50---------------------25
Later Lucas fuses are dual marked to eliminate some of the confusion. An example is the 17/35. In this case the 17 is the approximate continuous current carrying capacity & 35 would be the fast blow rating.
This means that a single marked 35 or a dual marked 17/35 amp marked Lucas fuse is about the same as a 20 amp marked BUSS fuse.
D
Edit:
The US ratings are the continuous current carry ratings. In this case the Lucas fuse marked 35 or 17/35 would have a continuous rating of 17 & the US 20 rating would be close with it's continuous rating of 20.
D "
Thanks, Dave!
Jeff
 
To expand on the previous reply, the fuses our cars originally came with are "slow blow" fuses. As explained above, a 35-amp slow blow fuse will sustain 17 amps and blow at 35 amps. However this also means that if your car is pushing 25 amps through the circuit, it won't blow the fuse but will weaken it over time. For this reason it's good practice to replace slow blow fuses if there has been any suspect voltage issues in the car's electrical system. Some people even replace slow blow fuses periodically as preventative maintenance.
 
Hi 19_again, Since you have only two fuses of the same value to worry about. It is safe to use the equivalent US values in the table provided.---Fwiw-Keoke
 
No Steve that is not the case. There is a variable in the fuse design "T" = Time. If the fuse carries a significant amount of its rated must blow value for a significant period of time. Then the same amout of heat will be produced in the fuse and it will blow. Most fast blow fuses interrupt at their must blow rating within five minutes. Th table provided defines fast blow fuses---Keoke
 
Isn't that basically what I described? You're saying that carrying 25 amps for a certain amount of time will blow the fuse, once significant heat has built up. Now assuming 25 amps is put through for less than that amount of time, but dozens of times over, it seems safe to assume the fuse will be somewhat weakened. I don't have scientific proof to back this up, it's just what I've read and what I've been told by the "old timers" over the years.
 
Thanks to you all. It's a great forum that consistently delivers quality information. Soon I'll be able to answer a question myself.
 
Hi Steve,
The attached graph shows the actual time to blow vs current for a typical simple fuse such as found in our cars. It also shows the comparison between a Brit rated fuse & a USA fuse.

It is true that repetitive overloads are cumulative on the simple fuses. The typical simple fuses under discussion are considered fast blow fuses. The higher the overload or the longer the time, the sooner it will blow. This DOES degrade the original fuse rating & fuses that are subject to overloads should be periodically replaced before they blow at less than their original rating.

In some applications, such as electric motor starting, there are slow blow & other variations of time delay fuses that do not degrade as much with repetitive overloads. As you say, even these are often replaced as preventive maintenance.
D
 

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Steve_S said:
Isn't that basically what I described? You're saying that carrying 25 amps for a certain amount of time will blow the fuse, once significant heat has built up. Now assuming 25 amps is put through for less than that amount of time, but dozens of times over, it seems safe to assume the fuse will be somewhat weakened. I don't have scientific proof to back this up, it's just what I've read and what I've been told by the "old timers" over the years.
Click to expand...

I doubt that the fuse will be weakened. This is because the automobile designer counts on the wire harness resistance to limit the transient type current to his fuse. This simply says that current in the non inductive circuit can not go from zero to infinity in zero time as it is limited by the wires resistance. For inductive type circuits; motors, solenoids etc, they should use a slow blow type fuse. But that's another issue.--Fwiw--Keoke
 
Added the fuse info to the BCE WIWI.
 
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