# Minimum redundancy



## migreig (Aug 5, 2011)

Hi all,

Just curious, what should be considered the "minimum redundancy" for safety systems in a basic electric car? I'm building a 96V forkenswift style Chevrolet Sprint.

My plan is to fuse the main cables, use one contactor, anderson connector with cable disconnect. This seems sufficient when coupled with the fact that my car retains the clutch to prevent runaway if all else fails. Any thoughts?


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## conaman551 (Nov 12, 2012)

I'm from New Zealand and these are the guidelines we have to follow.


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## kennybobby (Aug 10, 2012)

In rocket town we consider redundancy as a solution for meeting failure-tolerance requirements--how many failures can occur in which you must continue to operate. 
The New Zealand LVV standard indicates only that the systems must fail in a safe manner, so that implies zero fault tolerance with no redundancy required to allow continued operation. 
In life-or-death critical systems it is necessary to examine how likely a particular failure may occur and what are the consequences if it did to determine fault-tolerance and redundancy. 
In the EV world i would fear a failure of the traction system while pulling out into traffic or crossing a highway, but an ICE has that same issue. The consequences are high, hopefully the likelihood is low--not many vehicles have backup engines... 
If you must continue to operate even with a failure then you will need redundancy, otherwise the LVV standard seems to have good safety guidelines to follow.


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## Roy Von Rogers (Mar 21, 2009)

migreig said:


> Hi all,
> 
> Just curious, what should be considered the "minimum redundancy" for safety systems in a basic electric car? I'm building a 96V forkenswift style Chevrolet Sprint.
> 
> My plan is to fuse the main cables, use one contactor, anderson connector with cable disconnect. This seems sufficient when coupled with the fact that my car retains the clutch to prevent runaway if all else fails. Any thoughts?


Use a proper main fuse, to a main high voltage manual disconnect, to two 12v main contactors, one for positive one for negative. Run both negative 12v sides of contactors through a slap switch that can be reached quickly from drivers position, from there use an automotive fuel shut off switch (impact switch) in series to the negative side going to contactors.

Roy


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## PStechPaul (May 1, 2012)

Perhaps it would be a good idea to wire the seat pressure switch and/or seat belt switches to the interlock system that trips the contactors. You could add a bypass switch, but have an extra contact that flashes a warning light when bypassed.

Fuses are the most reliable battery and harness protection, but they only work quickly in the case of a huge overload or short circuit, and with low voltage battery packs and high current controllers and motors, a sufficient current from a short circuit may be unlikely if it results in arcing or welding through a resistive path such as the vehicle frame.


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## EVfun (Mar 14, 2010)

migreig said:


> Hi all,
> 
> Just curious, what should be considered the "minimum redundancy" for safety systems in a basic electric car? I'm building a 96V forkenswift style Chevrolet Sprint.
> 
> My plan is to fuse the main cables, use one contactor, anderson connector with cable disconnect. This seems sufficient when coupled with the fact that my car retains the clutch to prevent runaway if all else fails. Any thoughts?


You will be fine with that equipment, it is one more level of safety than I consider strictly needed. I figure you should have 2 ways of cutting power to the ground, and fuses don't count because they are too slow to blow unless the current is 10x their rating. You are proposing a main contactor, a remote openable manual disconnect, and a clutch to separate the power from the ground. I see 3 and call it great. 

You should have a fuse in each battery box, so 1 if the pack is together, but more if you have it in several locations. They are for fire protection much more than runaway protection.


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## migreig (Aug 5, 2011)

EVfun said:


> You will be fine with that equipment, it is one more level of safety than I consider strictly needed. I figure you should have 2 ways of cutting power to the ground, and fuses don't count because they are too slow to blow unless the current is 10x their rating. You are proposing a main contactor, a remote openable manual disconnect, and a clutch to separate the power from the ground. I see 3 and call it great.


Thanks for that. I'm going to stick with what I have for now. I can add to this over time but priority 1 for the time being is getting the thing on the road!


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## Roy Von Rogers (Mar 21, 2009)

be careful with those Anderson connectors, better to direct connect to cells.

Roy


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## migreig (Aug 5, 2011)

Roy Von Rogers said:


> be careful with those Anderson connectors, better to direct connect to cells.


I don't get it, can you explain?


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## Duncan (Dec 8, 2008)

Hi Migreig

I have:
A contactor in each battery line - I read the NZ standard as requiring this
A manual disconnect (Oh Shit Handle)
A 400 amp fuse

Additionally the brake pedal shorts out the throttle signal

BUT I am direct drive so No Clutch


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## dougingraham (Jul 26, 2011)

Duncan said:


> BUT I am direct drive so No Clutch


If you still have a transmission you could just force it into neutral.


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## Duncan (Dec 8, 2008)

dougingraham said:


> If you still have a transmission you could just force it into neutral.


No gearbox - just a short propshaft from the motor to the diff


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## EVfun (Mar 14, 2010)

dougingraham said:


> If you still have a transmission you could just force it into neutral.


There are a great many transmissions out there where you would break the shift fork before you could force the gearbox out of gear under 100+ ft-lb of input torque.


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## favguy (May 2, 2008)

Have to agree with the above, it's almost impossible to shift to neutral with the gearbox under load without a clutch. ( I'm clutchless also) Best to not rely on this as a safety back up!


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