# Forced Fuse Blow -- Oh Sh*t button???



## jddcircuit (Mar 18, 2010)

I have a dumb question.

I was watching the EVTV video yesterday and it was Jack putting redundant contactors in series with contactors that already exist inside the motor controller for redundancy and safety.

I also recall some high power racers putting a pull bar in there cockpit to break the current flow in run away situations. Apparently breaking high current flows without welding the contactor shut can be a challenge.

Here is my question:
In these extreme situations and in a last resort kill attempt would it make any sense to intentionally increase the pack current by shunting the pack terminals to force the pack fuse to blow. I would assume that some inductance could be built into this switch to limit the rate of current diverting if it was necessary for the switch to function properly.

My logic is that the fuse has a purpose and this sounds like it might be one of those situations.

Regards
Jeff


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## frodus (Apr 12, 2008)

use a DC rated breaker with a cable pull to disable it.

Fuses aren't cheap when you're in high power levels, neither are breakers, but they're good for many uses.


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## Yukon_Shane (Jul 15, 2010)

frodus said:


> use a DC rated breaker with a cable pull to disable it.
> 
> Fuses aren't cheap when you're in high power levels, neither are breakers, but they're good for many uses.


This is what I've used in my build (recommended by Randy at CanEV) and I'm curious why you don't see this setup more often. It seems simple and foolproof; pull the cable and the breaker opens.


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## Ziggythewiz (May 16, 2010)

It's all about price and availability. A breaker can cost much more than a fuse for a rated voltage and current, and if you aren't expecting to ever need it anyway, sometimes you go cheap.


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## dtbaker (Jan 5, 2008)

Ziggythewiz said:


> It's all about price and availability. A breaker can cost much more than a fuse for a rated voltage and current, and if you aren't expecting to ever need it anyway, sometimes you go cheap.



the oh Sh*t button is not the place to cheap out!

besides a manual pull circuit breaker is very handy to flip on and off when you are working on the car or have it parked at a show, or doing a show.n.tell to people that might stick fingers where they shouldn't.


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## Ziggythewiz (May 16, 2010)

By cheap I mean use fuse instead of breaker. Protection is still there, but just for a single use, which hopefully is more than you need.


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## dtbaker (Jan 5, 2008)

Ziggythewiz said:


> By cheap I mean use fuse instead of breaker. Protection is still there, but just for a single use, which hopefully is more than you need.


my point is that if you have a $200 breaker you can (and should) use it lots more than once... rather than blow a $50 fuse by shorting your main traction pack on purpose and risk melting other things and damaging batteries/controller, etc.

much safer to OPEN a circuit than to short it and count on a fuse to protect components.


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## Ziggythewiz (May 16, 2010)

well, shorting the pack was a self-admitted dumb question...

Mine also has a $20 shroom stop ($140 if american branded) that i use for maintenence disconnects and reprogramming the charger


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## bjfreeman (Dec 7, 2011)

tongue in cheek, Knife switch with a rip cord, whats a few sparks among friends.


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## dtbaker (Jan 5, 2008)

Ziggythewiz said:


> well, shorting the pack was a self-admitted dumb question...
> 
> Mine also has a $20 shroom stop ($140 if american branded) that i use for maintenence disconnects and reprogramming the charger




hhhmmm, I don't know of any 'shroom stops' that are rated for 120v at 500amps. while this may work under no load, you might get a surprise if you hit it under full-load.... it might NOT break contact due to gap or lack of magnetic blowouts.

check your ratings, and do not skimp on emergency manual circuit breaker!

if you have found one, post source/vendor, I'm sure lots of people would consider over the typical GE or airpax units....


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## Ziggythewiz (May 16, 2010)

Was posted here 2 years ago. It's only rated for 80V 250A continuous, but was sold elsewhere at the time as an albright with a peak of 150V and higher amps.


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## greif (Jun 26, 2010)

Ziggy
Were do you get a $20 shrum?
Thanks
Gary


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## PStechPaul (May 1, 2012)

I have designed, modified, and repaired circuit breaker test sets, including some DC units that have a nominal output of 4000 amps and peak currents as high as 40kA. I even worked on a special DC test set that could produce continuous current of about 12kA at 20 volts. Here are some videos:

http://youtu.be/DRAOeTs7JIM (various test sets)
http://youtu.be/Xr713ZUsJws (4000A DC test set in operation up to 20kA)

I have also seen videos of circuit breakers compared to fuses, under short circuit conditions with various available fault currents. Circuit breakers are typically limited to 10,000 or 20,000 interrupting capacity, while fuses are often rated at 100k to 200k. They are also current limiting, so they will clear even before the full potential fault current is attained. And the fuses opened up with just a small puff of smoke, while the circuit breaker, at its interrupting rating, was severely damaged, but met specification because it cleared the fault. Above its rating, it exploded violently, and in some cases exhibited an arc flash that continued for some time, due to the metal parts being vaporized as a conductive plasma. Here is an example of what can happen:
http://youtu.be/Cup5fMGaE2g (reverse polarity incorrect installation)
http://youtu.be/-iClXrd50Z8 (480 VAC breaker short circuit arc flash)

The lesson to be learned is that the primary protection should be a fuse, and after the fuse a circuit breaker can be used for on/off control and overload protection.

In the case of a DC system, the destructive arcs are caused by breaking the current to an inductive load, like a DC motor. It should be possible to install a big, fast rectifier from the load to ground so that the current has a safe place to go as the inductive energy is dissipated. Sometimes it's even better to add a series resistor sized such that the maximum short circuit current will generate no more than 600 volts or so.


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## dtbaker (Jan 5, 2008)

PStechPaul said:


> I have designed, modified, and repaired circuit breaker test sets, including some DC units that have a nominal output of 4000 amps and peak currents as high as 40kA. I even worked on a special DC test set that could produce continuous current of about 12kA at 20 volts. Here are some videos:


entertaining as as it is to see stuff vaporize, what are you saying applies to this thread?

I would HOPE that people have fuses in main traction pack... the discussion as I see it is what is the most cost effective/safe way to build a manual 'kill' of the expected EV scenerio under load.... say 144v at 500amps.

circuit breaker to open circuit better than shorting to blow a fuse?

...assuming that a shroom kill button rated for 80V 250A continuous is totally risky.


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## EVfun (Mar 14, 2010)

Ziggythewiz said:


> well, shorting the pack was a self-admitted dumb question...


It's not dumb, it even has a name -- crowbar. You short out the load and have a suitably rated fuse between the pack and the shorting contactor or SCR. I have not seen it used in an EV, but with some of the extreme packs being built I could see this becoming more practical than trying to open them into the inductive load of a motor after a controller fails.


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## PStechPaul (May 1, 2012)

Here are contactors that might be up to the job, but inductive loads may be a problem:
http://relays.te.com/datasheets/ev200.pdf
http://relays.te.com/datasheets/ev500.pdf
http://www.hubbell-icd.com/icd/contactors/files/42264.pdf


A snubber or vacuum arc tube across the contacts may help:
http://relays.te.com/kilovac/power/direct.asp

The freewheel (or flyback) diode may be the best option:
http://en.wikipedia.org/wiki/Flyback_diode
http://www.crydom.com/en/Tech/Tips/DC relays-technical guidelines.pdf (for SSRs, but good discussion)

It should be fairly easy to simulate its effect. Just use a single battery and a 12 volt DC motor (like a starter motor), and add a fast high current diode across it. Use a contactor or a circuit breaker and observe the contacts, especially in a darkened room, or with a storage oscilloscope. To simulate worst case you can use a motor with a locked rotor and close the breaker, which should trip almost instantly at several hundred amps.

You can extrapolate to the case with a high voltage battery pack and a big EV motor, and choose components accordingly. 

A diode module such as the following should work. It is 1200V 50A but can handle a 1000 amp transient and recovery time is less than 1 uSec. Cost is about $60, and some may be available on eBay for much less.
http://www.pwrx.com/pwrx/docs/cc241250.pdf
http://www.newark.com/powerex/cc241250/rectifier-module-1-2kv-50a/dp/09B2164


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## JRoque (Mar 9, 2010)

Hi.


dtbaker said:


> entertaining as as it is to see stuff vaporize, what are you saying applies to this thread?





PStechPaul said:


> The lesson to be learned is that the primary protection should be a fuse, and after the fuse a circuit breaker can be used for on/off control and overload protection.


Didn't he answer that right there? A little resume boasting as a prequalifier to a statement doesn't hurt either.

In case of an emergency I would much rather have a fuse open than relying on my finding and hitting a cutout button. I could be busy crashing or trying not to.

As previously mentioned, a crowbar inline with a fuse is the sure way to go. Circuit breakers risk welding "on". A crowbar stops the motor.

JR


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## jddcircuit (Mar 18, 2010)

EVfun said:


> It's not dumb, it even has a name -- crowbar. You short out the load and have a suitably rated fuse between the pack and the shorting contactor or SCR. I have not seen it used in an EV, but with some of the extreme packs being built I could see this becoming more practical than trying to open them into the inductive load of a motor after a controller fails.


"crowbar" sounds good

thanks
Jeff


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