[Milsurplus] PE-73 Dyno starting solenoid running hot

[Bruce Gentry]

Laura and Jim wrote:
> I had my BC-375 up and running for about 45 minutes yesterday trying to check into the west coast MRCG net and noticed "a hot smell" toward the end. I shut down and found the starting relay on the PE-73 too hot to touch. Really stunk up the shack when I pulled the cover. Everything else on the dyno was normal, temperature-wise (warm, but not HOT). Never sounded funny. Bearings seem OK. DC from the PSU is clean when I scope it. I measure 28VDC at the input for the solenoid itself, 28 across the main power lugs on the business end. "ON" switch on the 375 did not feel unusually warm.
>
> Is this normal? Should I be shutting down between transmissions? Couldn't find any trouble-shooting or resistance/voltage references in my copy of the famous 1943 manual, so I don't have a base line to compare against.
>
> I want to blame it on a partially shorted starting solenoid winding drawing too much current, and/or cruddy contacts. 
> Or is it just a loose nut behind the mic again...........?
>
> 73 DE JIM K6FWT
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>   
There are  three likely possibilities. First, find out if the coil 
itself is overheating or if cruddy contacts are the cause. If the big 
terminal studs are  cool to the touch after running the dynamotor for a 
minute or so, the contacts are probably fine.  The coil may be partially 
shorted. A few turns short out, and the heat causes more to heat up and 
it becomes a vicious circle. The solenoid may have been designed for 
intermittent duty only, but that seems unlikely. Someone in the past may 
have replaced it with a 12 volt solenoid so they could use the dynamotor 
on 12 volts to make 600 volts for some other rig.  24 volt solenoids 
with  continuous duty coils are frequently used in floor scrubbers, so 
you should be able to find one  that will easily handle the load.   A 
mounting adapter plate can be made so a new solenoid can be installed in 
place of the orginal without hacking anything up.  Good luck..

  Bruce Gentry, KA2IVY