On Apr 12, 9:43 pm, "Harold E. Johnson" wrote:
"wb5kcm" wrote in message

ups.com...

My Ranger is blowing the 5 amp primary fuse every once in a while when
I turn it on. I have checked for any kind of intermittent short but
unable to find anything. I am now suspecting inrush current. My Ranger
has all the power supply mods. Solid state HV and LV power supplies
with 330mfd LV cap and 165mfd HV cap. At first did not suspect inrush
current due to having choke input filters but I suppose with the solid
state rectifiers and the large caps it maybe happening. Does anyone
have any suggestions to limit this inrush current in the Ranger. Also,
does anyone know what the Ranger's nominal current consumption is from
the 117 VAC source under full load? Any info is appreciated. 73, Randy

You probably would find a varistor in the primary of the transformer to be
of help. It also improves the life of the power on-off switch at the same
time.
We used one in the primary of the Signal One transceivers after having
measured an one cycle inrush current in excess of 50 Amperes! (Hypersil core
transformer) You can purchase them that exhibit a hundred Ohms or so when
cold that drop to 4-6 Ohms hot and essentially remove themselves from the
circuit after the first few moments of operation. They don't help at all if
you turn the radio off after a period of use and immediately power it back
up whilst the varistor is still hot, but it takes the edge off the inrush
curent in "normal" operation. About the size of 3-4 nickels stacked together
with a radial lead off each face.

W4ZCB

Thanks for the info Harold. I think that is the way I want to go is
with the ICL Thermistor or Varistor. The only thing I need is to find
out which one to use. Looking at them in the catalog, it seems the
deciding factor will be the maximum sustained current from the Ranger.
If I need a 4 amp Thermistor then it may only provide about 10 ohms
resistance depending on the current. Would 10 ohms do enough inrush
suppression? It seems the higher current models have the lowest
resistance. I will need to do a little more research into this and try
and pick the right one. Possibly two of them in series will do the
job? I have read where someone used a Thermistor p/n CL-90 on a
Hammerlund receiver with good results. This CL-90 has a 120 ohm
resistance and a 2 amp current rating. I would be concerned that this
2 amp rating would not be enough for the Ranger. Would 2 of these
CL-90's in parallel give me 60 ohms @ 4 amps??
If someone has not already tested for this. I want to check the AC
current on my Ranger at maximum AM, 100% modulation transmit. This
should give me a good idea about which ICL Thermistor to look for.
Thanks for everyones input, it is very helpful.
73, Randy, WB5KCM