does a voltage spike from a 60amp load dump(engine starter) have enough power to blow a surface mount medium speed fuse?
https://www.mouser.com/datasheet/2/54/Bourns_SF_1206HIA_M_datasheet-1892140.pdf

since the original idea of resettable fuse didn't work, i will use a regular fuse so the TVS hopefully protects the circuit from spikes but the fuse will blow if unit is hooked up to excess voltage. this will give me proof of excess voltage so the dummies can't say it wasn't their fault.
would a slow blow or quick blow be better?

i will also use a slow blow for the main circuit just as a precaution. please check new circuit design.
thanks

 

Can't believe I stumped the pros here.

 

does a voltage spike from a 60amp load dump(engine starter) have enough power to blow a surface mount medium speed fuse?

I doubt it.

since the original idea of resettable fuse didn't work,

it does work. It just requires either an accurate knowledge of the interference signal, or sufficient patience to try a variety of devices to get the optimum.

 

it does work. It just requires either an accurate knowledge of the interference signal, or sufficient patience to try a variety of devices to get the optimum.

2 different scenarios here, 1 is catching voltage spikes which seems to be working fine.
the other is trying to trip the fuse when continuous input voltage goes too high.
when the voltage goes up high enough that the TVS starts conducting, the TVS burns up before the fuse trips.
i've tried smaj26, smaj24, and smbj26. they all burn up before tripping a resettable fuse.
i have quick blow NON resettable fuses ordered to see if they will work.
thanks for your reply.

 

A few big-fat-Capacitors solves the problem.

There are many highly inductive Loads in an Automotive-Environment.
Capacitors are more expensive than some of the other available protection/damping solutions,
therefore the manufacturers go with the cheapest solution that solves the problem adequately.

I have 4 large Capacitors hidden in various (cool) places within my Truck, ( NOT under the Hood ),
I have zero noise/spike problems.

Some Alternator-Voltage-Regulators are slow to respond, sometimes causing issues.
.
.
.

 

when the voltage goes up high enough that the TVS starts conducting, the TVS burns up before the fuse trips.

What voltage are you testing at? What is the current rating for the PTC fuse and the part number?

 

What voltage are you testing at? What is the current rating for the PTC fuse and the part number?

voltage range from 12v to 38v.
finally got the result i wanted.
i used a non resettable quick blow 1 amp fuse(vishay MFU1206FF01000P1) with a smbj24 tvs.
https://www.vishay.com/docs/28747/mfuserie.pdf
tvs starts getting hot at 36 volts but it lasted long enough to blow the fuse.
the smbj is rated at 600 watts.
i think if i used one rated at 1500 watts, it would work ok.
the 1 amp fuse blew before it reached 1 amp, around 700mA. what's up with that? maybe the amps went up faster than the power supply could report.
another concern is the first 2 fuses failed just from soldering. one was reflowed and the other was hand soldered with iron.
the circuit still works after i replaced the fuse.
i may try a resettable fuse with the 1500 watt tvs. i can't decide because if the fuse resets, i don't have proof of excess voltage.
i have 3 - 10uf caps in the circuit.
can't believe something so simple is so much trouble.
maybe it's not worth the effort? i just don't want the tvs catching fire from excess voltage.
thanks everyone.

 

What PTC fuse didn't work?

 

What PTC fuse didn't work?

1.1 amp
https://www.mouser.com/ProductDetail/530-0ZCF0110AF2A

 

"A voltage spike from a 60 amp load dump is a rather inadequate description of a real system. It has been obvious to the automotive OEMs for many years that voltage spikes can occasionally do damage. A fast-blow fuse along with a fast clamp diode can usually provide adequate protection. But that protection comes with the expense of needing to replace the surface mounted fuse each time.
Providing an adequate series inductance along with a fast clamp diode can do very well at protecting against spikes damage. A clamp scheme alone is not enough because there is often a low impedance drive of that spike, meaning that it can deliver some current. So the series impedance is very important, and offers a second benefit of tending to block noise as well.

 

"A voltage spike from a 60 amp load dump is a rather inadequate description of a real system. It has been obvious to the automotive OEMs for many years that voltage spikes can occasionally do damage. A fast-blow fuse along with a fast clamp diode can usually provide adequate protection. But that protection comes with the expense of needing to replace the surface mounted fuse each time.
Providing an adequate series inductance along with a fast clamp diode can do very well at protecting against spikes damage. A clamp scheme alone is not enough because there is often a low impedance drive of that spike, meaning that it can deliver some current. So the series impedance is very important, and offers a second benefit of tending to block noise as well.

very interesting...i hadn't thought of that.
in case you don't know, i'm an electronics idiot.
and if you haven't read all this thread, i'm trying to do 2 things with one tvs.
trying to catch spikes and trying to trip a fuse if supply voltage is too high. this may not be possible???
what value inductance should i use?
do i just put it in series before the tvs?
so a resettable fuse is not fast enough to protect against excess voltage even with a 1500 watt tvs?
thanks

 

The inductance should go between the voltage source and the load. Probably after the fuse.
To protect the load against a just plain over voltage, connect an adequately rated zener diode across the load.
OR look up the classic over-voltage SCR crowbar circuit. Those circuits place a triggered SCR across the load if the voltage exceeds some limit value. That either pops a fuse or activates a current limiting function.

 

The inductance should go between the voltage source and the load. Probably after the fuse.
To protect the load against a just plain over voltage, connect an adequately rated zener diode across the load.
OR look up the classic over-voltage SCR crowbar circuit. Those circuits place a triggered SCR across the load if the voltage exceeds some limit value. That either pops a fuse or activates a current limiting function.

i like the zener voltage regulator idea but i had bad luck with those.
i used them with a transistor to turn off the control pin on the driver chip.
the zeners would go bad from spikes or something and turn the chip off.

the driver chips i'm using have a 40 volt limit.
i've been using a SMAJ26 without a fuse for quite a while with good luck. i think it catches most spikes.
i think most catastrophic failures are caused by defective charging systems.
some use stators and rectifiers. the rectifiers burn out and put AC or something bad on the circuit.
what's best way to stop damage from that?
and if i can't stop it, how can i prove their problem damaged it?
thanks

 

i like the zener voltage regulator idea but i had bad luck with those.
i used them with a transistor to turn off the control pin on the driver chip.
the zeners would go bad from spikes or something and turn the chip off.

the driver chips i'm using have a 40 volt limit.
i've been using a SMAJ26 without a fuse for quite a while with good luck. i think it catches most spikes.
i think most catastrophic failures are caused by defective charging systems.
some use stators and rectifiers. the rectifiers burn out and put AC or something bad on the circuit.
what's best way to stop damage from that?
and if i can't stop it, how can i prove their problem damaged it?
thanks

Not a zener voltage regulator at all. A zener voltage sensor that triggers an SCR that short-circuits that power circuit to the common.

 

Not a zener voltage regulator at all. A zener voltage sensor that triggers an SCR that short-circuits that power circuit to the common.

remember, i'm an electronics dummy.
will this idea stop AC or whatever comes from stators and defective rectifiers?
it needs to stop anything higher than 38 volts DC.
do you have a way to post a schematic here?
if i can see it, maybe i'll understand?
thanks

 

OK, and no, I am not able to post a circuit. The good news is that an SCR over-voltage crowbar circuit is a classic that has been around at least 50 years. That means that there are many published versions available, some of them with good explanations of how they work.
I suggest studying a bit and learning a bit more about circuits and then about components and how they work. The more you know in this field the better the chances of making correct choices and having things work the first time. And that adds a lot to the enjoyment.

 

the problem with crowbar circuit is a blown fuse that has to be replaced unless a resettable will work.
i don't want to buy more boards just to test and i don't have enough board space anyway.
think i'll just stay with a quick blow fuse after the TVS so it won't melt or catch fire if voltage is too high.
the quick blow fuse has 400mohm resistance. will that inhibit the TVS protection?
i'll put a resettable fuse on the main circuit just as a precaution.
see any serious problems with this design?
thanks

 

Exactly how bad can your Car's Electrical-System be ?
Or any Car's Electrical-System for that matter ?
Millions of products easily survive the usual Automotive-Electrical-Environment
millions of times per day,
so why is your situation so "special" ?

If You need less than ~10-Volts for your device,
a FET and a couple of Resistors, and a Zener-Diode solves all
common problems in an Automotive environment,
and ~95% of the serious freak-accidents,
like driving around in the Car with the Battery disconnected.
.
.
.

 

Once again we are dealing with a question without an adequate amount of information about the problem.
As far as the disconnected battery comment in post #18, back in 1968 we drove all over in an old Rambler American with a battery so weak it would only light the dome light. It had a manual trans and so we would always push start it. We drove it all all over around New Orleans that way for many weeks, and the lack of battery never allowed any damage to the radio.
So what sort of electronic device is the TS complaining about others saying was damaged by an starter motor load dump?
I do see a circuit of a three light flasher in the first post.

 

Once again we are dealing with a question without an adequate amount of information about the problem.
As far as the disconnected battery comment in post #18, back in 1968 we drove all over in an old Rambler American with a battery so weak it would only light the dome light. It had a manual trans and so we would always push start it. We drove it all all over around New Orleans that way for many weeks, and the lack of battery never allowed any damage to the radio.
So what sort of electronic device is the TS complaining about others saying was damaged by an starter motor load dump?
I do see a circuit of a three light flasher in the first post.

it's not a flasher, it's a regular LED light with option to turn on 4 or 6 LEDs.
it's used on cars or boats.
boats have multiple batteries and require 36 volts to run some equipment such as trolling motors.
i originally wanted to protect the driver chips from voltage higher than 24 volts but after testing, the chips survived 42 volts.
so now all i want is to protect against voltage spikes and add a fuse in case the TVS shorts.
i don't know if the fuse with 400 mohms resistance would inhibit the TVS?
thanks