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8th November 2018, 07:42 #1
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Fuse Amperage Determination Circuit
Hi
I need to build a 12V circuit which can determine the amperage of various automotive fuses.
In other words, a circuit which can show at what amperes the fuse blows out.
Any starting point tips, shall be appreciated.

8th November 2018, 08:06 #2
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Re: Fuse Amperage Determination Circuit
Hi,
May the test trip (destroy) the fuse?
If yes, then build a current source. Slowly increasing current. Detect the trip event. Measure the current at the trip point. With this you may determine the fuse current rating.
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8th November 2018, 08:26 #3
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8th November 2018, 08:44 #4
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Re: Fuse Amperage Determination Circuit
O.K., it's clear that the test will destroy the fuse. The actual tripping current will however strongly depend on the current ramp time and be probably 1.5 to 2 times the nominal current. You'll know if you reviewed fuse specifications.

8th November 2018, 09:13 #5
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Re: Fuse Amperage Determination Circuit
Yes.
The actual tripping current will however strongly depend on the current ramp time and be probably 1.5 to 2 times the nominal current.
But I couldn't get "....tripping current would be 1.5  2 times the nominal current"
You'll know if you reviewed fuse specifications.

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8th November 2018, 10:05 #6
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Re: Fuse Amperage Determination Circuit
Hi,
But I couldn't get "....tripping current would be 1.5  2 times the nominal current"
* hold current (depends a little on ambient temperature)
* trip current (depends on time, heat spreading and a little on ambient temperature)
I don´t think you can directly measure those values on a bare metal sheet and apply for it a finshed fuse.
All the other metals will spread heat, the plastics will add other "errors".
This is for quality control?
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8th November 2018, 10:32 #7
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Re: Fuse Amperage Determination Circuit
But I couldn't get "....tripping current would be 1.5  2 times the nominal current"
https://www.littelfuse.com/~/media/a...lade_fuses.pdf

8th November 2018, 17:38 #8
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Re: Fuse Amperage Determination Circuit
Yes, I want to be sure of the ratings of the pretrimmed alloy sheets each for the designated fuse ratings.
Okay, now I got some idea of the holding and the tripping current. But that brings me to a question: Is the rated current same as trip current current?
As far as my required circuit is concerned, I am thinking of some singlebuttonpushoperation. I just want to be sure that when current ramp is applied at some fixed rate the fuse blows at its rated current. Of course, some tolerance has to be considered in such crude circuit design.

8th November 2018, 17:54 #9
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Re: Fuse Amperage Determination Circuit
Hi,
Okay, now I got some idea of the holding and the tripping current. But that brings me to a question: Is the rated current same as trip current current?
You want to produce fuses but you dont know the specification?
Did you read any similar fuse´s specification like mentioned by FvM in post#4?
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8th November 2018, 18:54 #10
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Re: Fuse Amperage Determination Circuit
Is the rated current same as trip current current?
Time to reconsider.

8th November 2018, 22:25 #11
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Re: Fuse Amperage Determination Circuit
I do have similar specs of some other for my reference. As I mentioned earlier, I want to be sure that the prepunched alloy sheet which I bought for a specific amperage is actually rated for those amperes.
So basically, the circuit which I am looking for would be having 2 parts:
a) a current ramp source which to begin with a push of button
b) current measurement such that the analog or digital ampere meter retains its readings even when the fuse has blown.

8th November 2018, 22:44 #12
Re: Fuse Amperage Determination Circuit
b) is a sample and hold. I guess that's probably to do with an ADC that has a latching/hold feature that can be triggered when the other end of the "fuse" no longer presents a current/voltage to whatever is used to sample it, be that a current shunt monitor, a comparator, etc.
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