Resetable Fuses

Thread Starter

RodneyB

Joined Apr 28, 2012
697
I am trying to fit a reset-able fuse to protect a Charger I have fitted into a car. I think I was having a problem with a "Load Dump" destroying the circuit so I fitted an MOV across the supply.

The whole circuit draws 2 Amps at peak current draw. However when using a blade type Auto fuse I had to fit a 15 Amp fuse otherwise it just blew.

I want to protect my charger but at the same time dont want to be changing fuses all the time or having to do repairs because of the load dump.

I have attached the drawing of my proposed circuit I am looking for some advice so as to be able to make sure I have everything covered.

In the Load Dump i read on line about excess voltage and current in Alternators causing damage. I am assuming this is the problem.
 

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bwilliams60

Joined Nov 18, 2012
1,248
Fuses are made to blow instantly unless you use slow acting fuses. Try a circuit breaker instead. They are made to withstand current surges. Go to Littlefuse website for more info on size etc.
 

crutschow

Joined Mar 14, 2008
24,125
Load dump only occurs if the battery is suddenly disconnected when the alternator is charging so I doubt that's your problem.
Try a slow-blow fuse.
 

Alec_t

Joined Sep 17, 2013
10,746
The whole circuit draws 2 Amps at peak current draw. However when using a blade type Auto fuse I had to fit a 15 Amp fuse otherwise it just blew.
:confused: Clearly the peak current was much greater than 2A. Have you considered an inrush-limiter NTC varistor?
 

Thread Starter

RodneyB

Joined Apr 28, 2012
697
Both of these directions to information is very informative. I now understand how a NTC works in theory, now the big challenge is to put it into practical use,

I have looked at the datasheet of several and see they have an Imax at 25 degrees. My question is how do I select the correct NTC when my temperature ranges between 25 and 35 degrees. My full load current is 2 Amps.

Is there any additional circuit required to putting the NTC in series to the load
 

dl324

Joined Mar 30, 2015
9,625
I have looked at the datasheet of several and see they have an Imax at 25 degrees. My question is how do I select the correct NTC when my temperature ranges between 25 and 35 degrees. My full load current is 2 Amps.
I use an Ametherm SL10 10004 and it doesn't specify any derating other than max current at 65C or less:
upload_2016-3-17_8-39-59.png
Is there any additional circuit required to putting the NTC in series to the load
Generally the thermistor is sufficient unless the resistance at the nominal current is too high. Then you use the same technique that would be used for a simple resistor limiter; switch it out after the inrush event.
 
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