[Shop-talk] Mystery of the blown transformers

[Jim Juhas]

The cold current calculation (with V = I * R) will be higher than the 
running current, and this failure occurs after it's been running for a 
while.  The P = E * I is a better indicator of what you are working with.


John T. Blair wrote:
>
> Next you'll want to disconnect the wires from the xformer and using the Ohms
> setting of your multi meter measure the resistance between the 2 wires.
> This will tell you what the cold resistance of the wire & 2 bulbs is.
>
> >From that you can calculate about how much power you need to supply.
>
> V = I * R ,  You'll now V = 24, the Resistance of the bulbs is R, so
> I = V/R.  Now you know the current that you'll require.  Then I'd go
> with a safety factor of 2 or 2 times as much current as the calculations
> say.
>
> The other possibility is, are the bulbs marked as to how many watts they
> are?  If so, then Power = V * I.  So if we assume the bulbs are 20w each,
> you are using 40W of power.  So I = P/V, or 40/24V is approximately 2 amps 
> of current. Again, double the 2 amps and find a 24V xformer that will handle 
> 4 amps.
>
> I think you'll find that your bell xformer is rated at either 250 or 500 ma
> or 1/4 to 1/2 amp max.  So you are trying to get it to output at least 4X
> what it can handle.
>
> John
>
>
> John T. Blair  WA4OHZ     email:  jblair1948 at cox.net
> Va. Beach, Va             
> Phone:  (757) 495-8229
>
>           48 TR1800    48 #4 Midget    65 Morgan 4/4 Series V (B1106)
>      75 Bricklin SV1 (#0887)    77 Spitfire    71 Saab Sonett III
>                        65 Rambler Classic
>
> Morgan:    www.team.net/www/morgan
> Bricklin:  www.bricklin.org
>
> If you can read this             - Thank a teacher!
> If you are reading it in English - Thank a Vet!!
> _______________________________________________
> Support Team.Net  http://www.team.net/donate.html
>
> You are subscribed as james.f.juhas at snet.net
>
> Shop-talk mailing list
>
> http://autox.team.net/mailman/listinfo/shop-talk
>
> http://www.team.net/archive