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.
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.
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.
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.
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.
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"
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 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".
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.
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?
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.
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.
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.