# Fuse Amperage Determination Circuit

1. ## 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.

2. ## 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.

Klaus

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3. ## Re: Fuse Amperage Determination Circuit

Originally Posted by KlausST
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.

Klaus

The tips, I was expecting were how to measure, hold and display (analog or digital) ampere reading. As soon as the fuse will blow, the amperes will drop to zero immediately.

4. ## 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.

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5. ## Re: Fuse Amperage Determination Circuit

Originally Posted by FvM
O.K., it's clear that the test will destroy the fuse.
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.
What I get is, the slower we ramp the current, the accurate will be the reading.
But I couldn't get "....tripping current would be 1.5 - 2 times the nominal current"

You'll know if you reviewed fuse specifications.
Actually, I need to verify the ampere ratings of the trimmed zinc sheets before using them in fuse blade assembling.

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6. ## Re: Fuse Amperage Determination Circuit

Hi,

But I couldn't get "....tripping current would be 1.5 - 2 times the nominal current"
With fuses there is
* hold current (depends a little on ambient temperature)
* trip current (depends on time, heat spreading and a little on ambient temperature)

I donīt 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?

Klaus

7. ## Re: Fuse Amperage Determination Circuit

But I couldn't get "....tripping current would be 1.5 - 2 times the nominal current"
Before you understand why, you would want to review fuse datasheets, e.g. the below one. It shows that tripping time for 2*In can be as high as 5 sec.

8. ## Re: Fuse Amperage Determination Circuit

Originally Posted by KlausST
This is for quality control?
Yes, I want to be sure of the ratings of the pre-trimmed 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 single-button-push-operation. 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.

9. ## 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?
How do I have to understand this?
You want to produce fuses but you dont know the specification?

Did you read any similar fuseīs specification like mentioned by FvM in post#4?

Klaus

10. ## Re: Fuse Amperage Determination Circuit

Is the rated current same as trip current current?
It isn't, therefore a fuse isn't allowed to blow at its rated current. In case of the automotive blade fuse, it's guaranteed that it won't blow at rated current + 10% before 100 hours. Assuming a reasonable test duration, you'll apply considerably more than rated current to make the fuse blow.

Time to reconsider.

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11. ## Re: Fuse Amperage Determination Circuit

Originally Posted by KlausST
You want to produce fuses but you dont know the specification?

Did you read any similar fuseīs specification like mentioned by FvM in post#4?
I do have similar specs of some other for my reference. As I mentioned earlier, I want to be sure that the pre-punched 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.

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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