In addition to the comprehensive reply from Larry.
Your 7.2v draws a nominal .22 amps at 7.2v and your 6.3v draws a nominal .15
amps at 6.3 volts. At 12v the 6.3v will draw double that, which is getting
on for double the standard nominal 12v 2.2W bulbs current of .18 amps. I.e.
double the current through your wiring, rheostat and switch.
A 6.3v bulb cannot be expected to last very long at 12v. In fact it is
worse than that. Because the reason that nominal 12v bulbs are actually 14v
is that 14v is the running voltgage of the car, not 12v.
However the reduction of life of an actual 12v bulb against an actual 14v
bulb (i.e. 12v nominal) would be small enough to make them worth while, I
would have thought, particularly if they are noticeably brighter.
In the UK we have none of these funny numbers, all bulbs and packaging are
marked with voltage and wattage.
PaulH.
http://freespace.virgin.net/paul.hunt1/
-----Original Message-----
From: Mike Lishego <mikesl@tartan.sapc.edu>
To: MG List <Mgs@autox.team.net>
Date: 01 April 1999 07:07
Subject: New dash light debate...
> I got a bulb from the dash and tried to get a similar voltage
>and amp rating. Instead of the #50 7.2 volt bulb, I got a #40(I
>think) with a 6.3 volt rating. The amps on the #50 were .22, while
>the amps on the #40 were .15. These new bulbs seemed brighter, but
>I could be wrong. Any electrical wizards care to explain how long
>these bulbs will last and if they're better or worse for our
>application?
> Here's the breakdown again, in table form:
>
>Bulb # Volts Amps
>50 7.2 .22
>40 6.3 .15
>
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