[ausev] switching the mainline power

[jefoy at mindspring.com]

A simple explanation may be in order here.. 

For switching alternating current it is a fairly simple matter - break the circuit with enough spacing between contacts to prevent the voltage from arcing across. Since the voltage is alternating, the potential is going to 0 sixty times a second, effectively quenching any arc that forms between contacts. For switching DC it is an entirely different matter. At the moment the contact breaks, the potential across the gap ionizes the air and continues conducting across, using the ionized air as a conductor. Look at the rating on a typical switch or relay and you will see something like "125 VAC/32 VDC", meaning it can safely switch up to 125 volts AC but only 32 volts DC..

Switches and relays designed for DC are either contained in a vacuum to eliminate the air that can ionize or they are magnetically quenched meaning there is a strong permanent magnet contained within the switch or relay such that the field will shunt the ionized air away from the contacts when the switch or relay opens.

For safety reasons, any switch used on the main battery pack of an EV must be capable of interupting the circuit at full system voltage and current. It is an unfortunate fact that the electronic devices used to regulate the motor current typically fail "on" when there is a catastrophic failure.

Jack Foy

-----Original Message-----
>From: Rush <Rush at ironandwood.org>
>Sent: Nov 7, 2006 7:32 PM
>To: info at easystreetrecumbents.com, AustinEV News Announcements and General Discussion <ausev at austinev.org>
>Subject: Re: [ausev] switching the mainline power
>
>We *all* use a HEINEMANN #GJ1-B3-DU0250-01C...Single section w/toggle handle...compact...160 VDC max...For controller systems up to 800 Amps...3 lbs 
>http://www.kta-ev.com/catalog/index.html or equivalent. Sometimes 2 in series if the V is larger than 160 vdc.
>
>Rush
>Tucson AZ
>www.ironandwood.org
>
>
>Mike wrote - 
>
>
>> Does anyone know of key switches that can be used to switch the main 
>> power line on an EV?  I mean something that can handle big DC volts and 
>> fairly high current?  I know I can find relays that will do this, but 
>> they require their own power.  I am looking for something can just be 
>> manually switched and locked.  Any tips? 
>> 
>> If it is necessary to clarify, I am not looking to switch the thing on 
>> and off while the amps are flowing, but something that can handle having 
>> the current pass through it when it is on.
>> 
>> -- 
>> Mike Librik, LCI #929
>
>
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