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RE: [T3] Electric/Mechanical Brake Switch

On 5 Oct 2005 at 11:30, Steve Jackson wrote:

> Actually, that is not how it works.  If it is rated for 240V/2A then it
> would be 24V/20A or 12V/40A.... because 2A * 240V=480W s0 12V*40A also
> is 480W.

That's usually not what those limits mean. It's not a wattage rating, because 
the switch is not expected to dissipate significant power. It's a SOA (safe 
operating area) definition: You're okay as long as you don't go above 240 V or 
2 A. This is probably just the AC rating, however.

DC current ratings are generally lower, because there are no zero crossings to 
quench any arc.

Now that I look at this, this 240 V/2 A rating is really VERY small on the 
current side. Most of the smaller form factor microswitches are rated for 5A 
and some are rated at 10A. If this is really rated at 2A AC, then it may not 
last long here; those brake lights may actually take more than 1 A each, and 
the DC rating is likely to be less than 2 A.

OTOH, maybe this is a heavy duty switch and 2A IS the DC rating.

I just checked a few that we have here, and the large form factor ones like 
John used were marked 250 VDC/1/4A  125VDC/1/2A, with much larger currents for 
AC. It's reasonable to assume that with lower voltages the rating might keep 
going up, but it looks like this could still be a problem.

Jim Adney
Madison, WI 53711-3054

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

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