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Circuit protection

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tio_rafael

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Hi,

Does anyone here can tell me if an overload protection circuit is necessary for an equipment that will be connected directly in the battery of an car or truck?

Which is the best solution?

The circuit cannot be off...
 
Of course it does or the battery will explode if it's short circuited.

The best possible solution will depend on the load which you haven't given any information about.
 
The load is an small tracker circuit. It needs 5,5V and almost 200mA. The circuit is composed, basically, by an PIC16F877A and one GPS/GPRS module.
 
I would use an LM7805 which has built-in overcurrent protection.
 
I'm using this voltage regulator...

Perhaps I have not expressed me correctly. I want to know if I can put my circuit, that already have an voltage regulator (LM7805), directly in the battery of an car or truck, or if I need some type of protection circuit. Can you help me with this?
 
I would recommend it should be rated to 3A, that way it won't blow if the output to the regulator is shorted (some LM7805s can pass >2A before they cut out).

If you don't want to worry about replacing a fuse you can buy resettable circuit breakers or you could even use a polyfuse.
 
My boss understand nothing of electronics but he insists that he wants a protection circuit (named TER0608) for the circuit already mentioned here (car tracker). I have to tell him how the circuit works, but I dont even know some components in the circuit. Somebody can tell me what components are in the circuit?
 

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Some fuses look like that.

Are you an electronics engineer? If not then perhaps you should get someone else more experianced in your company to advise you and your boss.
 
I think the label should be enough....
Anyway, here is the photo. It is not that good.

Yes, I'll need a few more years to be an electronic engineer, but thats not the problem. If you want some explanation... in my company nobody knows nothing of electronics so I really appreciate your comments, they are very helpful....

PS.: My boss is crazy, he doesn't even know who made this circuit..... but thats the reason they had invented the trainees...:eek:

Thanks!
 

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The balck cylinder with a stripe round one of the ends is a diode.

The yellowish square things could be either capacitors of polyfuses but the look like poly fuses to me. You can test this using a multimeter, if they're capacitors they'll read open circuit, if they're polyfuses they'll read short circuit, Polyfuses provide overcurrent protection, they are an example of a positive temperature coefficient resistor, the hotter they get the higher their resistance gets until they barely pass any current. When your circuit is operating normally the low current running isn't enough to heat the polyfuses enough for their resistance to be significant, if there's a short circut a huge current flows the heating in the polyfuse causes it to get hot causing its resistance to rise which causes more heating until very little current flows. If you want more information look it up on Wikipedia.

If you're really confident that this thing won't blow up if it's short circuited then tell your boss that he can trust you and if it doesn't feel that way then shoudn't have given you the task in the first place.

If you're not confident, then explain to your boss that you don't yet have enough experiance to work on this and he should get someone else to look at it even if it means hiring a contractor from another company.

Are you going to college at the moment? Perhaps one of your lecturers might be able to help you.
 
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Yes, I'm going to college. Starting third year (of five) of electronic engineering. A lot of math, physics and cauculus and a few electronics practice. I already had basic digital, and electronics but discrete schmitt trigger isn't helping me right now... But i'll get there.:D

You solved my problem, the component really is a polyfuse (resettable fuse). I made some tests yesterday and I tested de short circuit, sorry I forgot to mention that important thing. I just couldn't make it open circuit because I don't have a good source to do that at the moment.

So thank you all for your time and helpful coments!!
 
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