# Question on ATC fuse specs.

Discussion in 'Automotive Electronics' started by geekoftheweek, Jul 21, 2016.

1. ### geekoftheweek Thread Starter Member

Oct 6, 2013
45
2
I'm looking to possibly use ATC type fuses instead of shunt resistors for a project. I found this http://www.littelfuse.com/~/media/a...cle/blade-fuses/littelfuse_atof_datasheet.pdf which gave me the idea in the first place. In the chart on the right it gives typical values for voltage drop across the fuse. Are the voltage drop values what to expect at the fuse's rated current? If so is there any sort of curve to consider or will it be a simple ratio to convert the measured drop into a current value? Say with 5A through a 10A fuse would I expect to measure around a .055V drop or is there a curve to work out? Since the values are listed as typical I'm assuming there's a little wiggle room which I can handle a small amount of. The more accurate it is the coolness factor goes up, but as long as I can be within 1 amp after calculations it will be good enough.

2. ### geekoftheweek Thread Starter Member

Oct 6, 2013
45
2
So I went and did what I probably should have done first before asking my question. I took an old tail light bulb and connected both elements to power inline with a 10 amp fuse and shunt. I put power to it, took measurements, and found when calculated out the measurements of the fuse was always around a half of an amp lower than the calculations from the shunt. I'm going to dig through the drawer tomorrow and find more bulbs to string together and measure and calculate... and try some different fuses to see how repeatable it is.

I guess I'm just hoping for a little real world knowledge from anyone who's tried this.

3. ### #12 Expert

Nov 30, 2010
16,656
7,296
In any one fuse, it's just Ohm's Law. In a batch of fuses, there will be a small variation. Modern manufacturing technology will probably make that variation very small.

4. ### crutschow Expert

Mar 14, 2008
13,469
3,356
There may be a difference in resistance between different fuse manufacturers for the same fuse.

#12 likes this.
5. ### bwilliams60 Active Member

Nov 18, 2012
734
94
Not all manufacturers are created equal. I have put 30 amps through a 10 amp fuse. It was an offshore fuse company. The name brand companies usually get it right and #12 is right, ohms law prevails every time so if your voltage doesn't change and you increase amperage, the voltage should rise in proportion.

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6. ### geekoftheweek Thread Starter Member

Oct 6, 2013
45
2
As always thanks everyone!!

I more or less assumed variances between manufacturers, and to some extent between lots by the same manufacturer. My thinking was along the lines of fuses being cheap and easily replaced if things go wrong. The circuit is already protected by a fuse in the source, and if I go a step higher than what the source is supposed to be the fuse should be immune to failure. The variable is the source since it won't always be the same one, and I don't have control over what they do to their equipment (the most important variable and the biggest headache with this idea!!)

My new goal more or less is to eliminate the shunts from the circuit. That would eliminate the design headaches involved and the possibility of magic smoke due to an over current situation. I never considered using fuses until I read something in another forum a couple weeks back that more or less sparked the idea. The fuses would also give me a bigger voltage difference than the shunts I have which will work to my advantage.

Maybe I should start looking into circuit breakers instead and see where that takes me...

Last edited: Jul 24, 2016
7. ### geekoftheweek Thread Starter Member

Oct 6, 2013
45
2
So I did some more research. I've decided some simple automotive circuit breakers will probably be my best bet in the end... I just have to figure out what to expect from them. If not then it will be fuses. Either way I'll just have to include some form of calibration function and offset calculations in the program.

I've never done anything with fuses and circuit breakers but change them so I didn't realize they had other useful properties to consider.

Maybe I should have done some more research before asking (the answers were just a few more tries on google away). Maybe someone will see this and it will spark their own imagination...

Last edited: Jul 24, 2016