26 replies to this topic

[firefox]

I have searched the site looking for fuse box changing, and people are saying that you need to half the fuse rating for converting to blade fuses

this site http://www.autoelect...xes/Blade_Fuses

shows that the glass fuses blow at double the amp rating, the same as blade, so who is right, i am confussed now, the auto electrician i bought the fuse box off also told me that the same rated blade fuse would be ok, for the safety of members and Mini's bursting into flames, can someone with the knowledge point us in the right direction please

Edited by firefox, 03 May 2012 - 09:26 PM.

[Bungle]

i down graded mine by 1/2 and haven't blown a fuse

smaller the fuse the better

[tiger99]

Yes, about half is somehwere near correct, and close enough to avoid any fire hazard. Old-style car glass fuses (doesn't apply to anything but cars!) were rated for "instant blow" current (ok, no such thing as instant, it may mean under 1 second, or something like that) while all modern fuses are rated for continuous current carrying capacity.

Converting to blade fuses is a very good idea, as the connections are far more reliable. The glass ones were always prone to dirt and corrosion.

[matt615]

Converting to blade fuses is a very good idea, as the connections are far more reliable. The glass ones were always prone to dirt and corrosion.

That seems to be a common misconception amongst Mini owners. They have problems with their fuse boxes, and automatically think it's because glass fuses are rubbish and they must upgrade to blade fuses.

In reality Mini fuse boxes cause problems because they have been fitted to the car for 20 or so years, and corrode and go dirty inside. All that's needed is to fit an original type replacement, and it will give several more years reliable service. A blade fuse box would cause the same kind of problems if it had been fitted to the car for 20 years.

[firefox]

I did not start this thread to debate which is the most reliable fuse, the point i am trying to make is that fuses need to be rated correctly to avoid any problems
all the debates on this site looks like guess work, there must be an auto spark on here that can explain the ratings, my therory is near to what Bungle has said
start at the lowest fuse rating and then increase if they blow, i think the rule of thumb is 1,5 to 2 amps over the blow load, as for glass fuses the reason i have changed to blade is supply, when you are stuck it is easy to buy blades, and i think also more reliable

[pierres]

So what about the continental ceramice fusebox and how do the ceramic fuses compare to glass fuse ratings

[firefox]

So what about the continental ceramice fusebox and how do the ceramic fuses compare to glass fuse ratings

Good point i am waiting to learn

[adam_93rio]

Fuse ratings are the same now matter which type of fuse it is, the fuse rating is what current flow that fuse will blow at.
Current generates heat and drawing more current through the same piece of wire/cable will cause more heat.
This is the basics of how a fuse works, a 10amp fuse will get hot if 10 or more amps is drawn through it and therefore will melt. No matter which type of fuse it is.

If people half the current rating when "upgrading" to blade fuses, then there is also no reason why you wouldn't be able to lower the glass fuse rating in the same fuse box.

Hope this helps and makes sense!

Ps. Just to clarify, blade fuses are no more reliable than glass ones. The only reason I could see someone changing them is because they seem to be more readily available. So fair point there

[pierres]

think you best buy a fire extinguisher

Edited by pierres, 04 May 2012 - 03:19 PM.

[tommy13]

According to this site,
http://www.vehicle-w...fuses/fuses.php

the original glass fuse was referred to as a 35 amp fuse which is the amperage at which it would blow, and was designed to cope with 17.5 amps continuous.
The modern blade fuses for example a red 10 amp will take 10 amps continuous and blow at 20 amps.
There is no exact blade equivelent of the glass type.
To make matters more interesting, your original fuse box also acts as a junction box with as many as 4 wires on each terminal.
The blade type fuse box has only one terminal per fuse, which makes for difficult connections. I have found that the best solution is to use a 6 or more blade type fuse box and join together 4 of the input terminals by soldering a brass strip along the back of the terminals. the white wires can then connect to these and the 3 or 4 green wires to the other side of the fuses, which means that wipers, heater, brake lights etc each have their own fuse.
Similarly join the remaining 2 input terminals for the permanent live fuse and the purples on the two outputs so you have seperate fuses for horn and interior light.
If you do this, each fuse will need to be considerably smaller in amperage. I used all 10 amp with no problems.

[tommy13]

Sorry please ignore my post above unless you have the Mk1 or 2 type fuse box with only 2 fuses

Edited by tommy13, 04 May 2012 - 06:54 PM.

[Dan]

If people half the current rating when "upgrading" to blade fuses, then there is also no reason why you wouldn't be able to lower the glass fuse rating in the same fuse box.

No. This is the problem, and it's boring having to keep re-explaining it but it is important people get this right. A fuse rated to fail at a certain current will fail at that current as said. The labelling is very different between glass and blade fuses though as also said above. Glass fuses are labelled with their instant blow current (failure will occur within 5s at this current). Blade fuses are labelled with their continuous safe carrying capacity (failure will occur after an impractially large number of hours at this current), which as also said is more or less exactly half the instant fail rating for almost every type of fuse. There is a make of glass fuse out there which is labelled in the same manner as blade fuses, which is not to the BS rules and is causing confusion. It is essential to use the right fuse for each circuit.

The suggestion above to use a low rating and keep increasing until it appears to hold is also dangerous. Between the instant fail and continuous current ratings for any fuse there is a scale of increasing fail time, this is the slow-blow region for that fuse. It's a curve. Along that curve are ratings that will cause a fuse to fail after months of use, which to all intents and purposes would look like the fuse was holding in this sort of testing. This is dangerous, in this region the fuse itself can generate considerable heat. These low fault currents often cause fires in under specified wiring and I have seen this happen because someone thought a slightly lower rated fuse would be fine in a given circuit. It didn't fail so it seemed to have worked, later that day the car was on fire. This is why the proper fuse must be selected by design not by near random experimentation. Once when someone suggested I was just making this up, I found and posted the curves for various blade and glass cartridge fuses, so they will be here somewhere if you poke around. All manufacturers have the charts for their fuses available if you look. This is not guesswork, it's published and easily researched fact. You can't just select a fuse because it's a 10A fuse or whatever, you have to know and consider what that means. There are other things to consider too, like the fact that blades are open air fuses while glass fuses are sealed. That makes a difference to their response times and ratings too if the strictest rules are applied.

I personally don't know how ceramic type fuses are rated but their charts will also be available from the manufacturer.

Incidentally, Bungle is an electrician.

Edited by Dan, 04 May 2012 - 09:21 PM.

[Daviewonder]

Interesting thread, learnt a few things from it

[tiger99]

Dan is correct. As it happens, I design high reliability electronics for a living, so I do know what I am talking about. Dan has provided a more full explanation than my attempt. You really do need the fuse to be able to carry the load current safely and continuously, but blow before the wiring is in danger of seriously overheating and catching fire.

I would take issue with the person who suggested that glass fuses are as reliable as blades. In my industry it is common knowledge that you have to stick to certain rules for reliable contact design if you expect them to be reliable. The standard Mini fuseholder has very poor wiping action, and the contact faces are not gas-tight. You get both wiping action and gas tightness of the mating faces with a well designed blade. Contact pressure comes into it too. But in terms of professional quality stuff, the very best electrical fittings used on cars are trash, it is just that some of them are more trashy than others, and glass fuses are way at the bottom of the pile as regards good design, if they are going into standard car-type fuseholders. There are ways of using them reliably, which naturally cost a lot more than what Rover were paying for the fusebox..

NEVER use those horrid ceramic fuses with the pointed ends which were common on things like Opel Rekords in the 1970s. I don't know where else they were used, as I never had another car with such a trashy electrical system. The fuse element is completely exposed, and can give your finger a very nasty burn if it blows while inserting the fuse, as it will if there is a fault. They are a fire hazard and seriously violate the rules of correct contact design.

[firefox]

QUOTE

There is a make of glass fuse out there which is labelled in the same manner as blade fuses, which is not to the BS rules and is causing confusion. It is essential to use the right fuse for each circuit.

Dan is that the continuous glass fuses ?? , very interesting read and needs some thought, i will have a search for the fuse ratings and see if i can work it out
thanks so much for your input Guys