26 replies to this topic

[Dan]

Yes, a glass cartidge fuse labelled by its continuous current rating is essentially not an automotive fuse. There are fuses of similar design and size intended for use inside machinery and equipment which are labelled with their continuous current rating but these tend to be slow blow fuses (fuses designed not to overheat in a large segment of their slow blow phase so they don't melt through plastic fuse holders, another thing I've seen happen with the wrong fuse in use). They should not be used at all even if you should find some which pysically fit, the failure characteristics are completely different. And as I said there appears to be a company selling automotive glass fuses labelled with their continuous rating, it will cause fires and worse in some people's cars no doubt and eventually British Standards will catch up with them. So buy proper fuses from a reputable source, and use the recognised values.

[firefox]

is this it dan

http://www.theminifo...rt#entry1706469

interesting read, and also i have some 7.5 amp fuses, need to get my head around this, thanks bud

Edited by firefox, 05 May 2012 - 09:02 AM.

[firefox]

Am i right in thinking, 2 wires to one fuse, say for example heated screen and heater motor, put a multi meter across the fuse to earth and switch the items on, say it pulls 15 amps you need 7.5 plus a little more, so fit a 10 amp blade fuse
Hypothetically

[Dan]

No, if a circuit is running at 15 amps continuous it needs a fuse capable of suppying 15 amps continuously. So it needs a 15 amp blade (thinking about it it's more likely a 20 would be the right choice) or a 35 amp glass cartridge. If it's an inductive load or anything else with a high inrush or startup current (think air horn motor and that sort of thing) then you need to consider how long it might be running at higher than its continuous rating when selecting a fuse. This is what the fuse curve can help you with. When the wiper motor starts up for example it draws considerably more than its usual running 14 watts, and if the blades are stuck or the screen dry it will do so for some time. So the circuit wiring and fuse should be capable of supplying the stalled current to the motor for a number of seconds or else it will fail all the time which will be irritating. But the fuse should fail at the stalled current before the motor or switches are damaged by the increased current, so if for example the blades are frozen to the screen and the motor stays stalled for some time the fuse will protect it properly by failing in a slow blow mode before the motor burns out. Proper electrical design is a lot of maths, people think its easy because it's 12v but in reality it's much harder to do properly because there aren't pre-prepared tables and calculators to use like there are for power installations.

Edited by Dan, 05 May 2012 - 09:46 AM.

[firefox]

Thanks for that bud, i found this, http://www.littelfus...alogs/OE101.pdf
might make more sence to you, and might be helpfull to others, dont know if it is product related
or generic

[Abs]

Anyone that understands all this made a list of the fuses from glass to blade for the mini? So us non electric people can just go out and convert?

I would like to convert mine to one box under the bonnet as I have quite a few inline fuses over the years.

Edited by Abs, 18 October 2014 - 06:28 AM.

[Dr s]

Personally I'd suggest that changing out fuse boxes to sort loom problems is not a great approach. Perhaps sorting wiring out and a fresh loom would be more effective than cutting in a new fuse box?

[dklawson]

There are online tables that spell out the differences and conversions.  I am providing a link to one such table below.  

 

You will probably find most fuse conversion tables on U.S. sites because when we (over here) see glass fuses in the parts store, they are of the Bussman (AGC) type which are rated like the modern blade (ATC) type, NOT rated the same as the Lucas glass fuses.  It was very common in the 1960s and 1970s for people to install a Bussman fuse in place of a Lucas fuse of the same numeric value only to see their wiring melt.

 

In the absence of a table, use the conversion factor of...

Lucas Glass Fuse Rating x .6 = ATC (Blade) Fuse Rating... then go to the next smaller value.  

For example Lucas 35 Amp x .6 = 21 Amps.  There is no 21 Amp fuse so use a 20 Amp ATC fuse.  See the page linked below for more info.

http://www.drooartz....dex.php?page=29

The "Randall table" on the page reflects what most of us in the U.S. have followed for years.  You will notice that the .6 multiplier I mentioned works with Randall's table except for the 50 Amp fuse.

Edited by dklawson, 18 October 2014 - 01:17 PM.

[ryomini]

Good stuff

still like one poster said a list of glass fuse ratings and the converted blade fuse rating would be nice

 

Just putting in a decent blade fuse box without changing all the wiring keeps things tidy

and makes checking and changing a blown fuse a little easier

or as another poster said keeping the plastic fuse holders up to condition and swapping in new ones when the old ones get too worn out

personally a couple of decent blade fuse boxes would be tidy - that will be one of my projects if my car ever gets to run

I will then post what I did. 

thanks for the 0.6 conversion factor a big help

[dyshipfakta]

Wired by Wilson makes a plug and play kit that looks the mutts with all the work done. Will be purchasing when I have the spare dollar and an mot

[minimat]

You could just measure the current bring drawn by a circuit using an ammeter available from somewhere like maplins then fit the appropiate size fuse egif the circuit is drawing 13 amps the fit a 15amp fuse etc.

 

http://www.maplin.co...axi-blade-n48cy

[Spider]

A couple of things I'll say here to no doubt add to the confusion!

 

Fuses are not over-load 'devices' but there for short circuits. Not to say they won't work for over-loads, but not very good at doing that.

 

Fuses (and most Circuit Breakers) have a Time / Current Characteristic. The more Current Drawn through them, over their rating, the less Time before they blow. There's published curves for this eg;-

 

 

Which to most people tinkering around with auto electric, is probably as useful as pockets in a singlet!  But it can also show why you can sometimes get away with a smaller fuse. It could also be that the bigger fuse fitted is simply over-rated, which is most likely. Remember, they are Short Circuit devices.

 

Eg, the 5 Amp Fuse in those curves, can be run at 5.75 Amps (over-load yeah?) however, it will take almost 3 hours to blow. When a short circuit occurs, many hundreds of amps will flow through that short and coming back to the same fuse, under these conditions, it will blow in less than 0.1 seconds (more likely 0.001 seconds in fact).

 

When doing these conversions, I use the commonly available 6 Blade Fuse Holders that have a clip on cover. I know CBS for one supplier has these and others. Well worth a look.

 

I also have the same Ammeter that minimat has linked up ^ and found it very helpful BUT don't try to use it for fault finding, they are only rated to 20 Amps. They are for measuring health circuits of less than 20 Amps. They do have a fuse, but it's still easily possible to damage them especially on shorted circuits.

Edited by Moke Spider, 19 July 2016 - 09:02 PM.