[Elecraft] K3 Power Supply Question

[James Bennett]

I put my DMM leads on the front terminals of the 4545 and with key down, no change at all: 13.9V, so it appears that MFJ gets a pass on this one.

To do my testing I had run the 4545 directly to the K3 and not through the Rig Runner. However, to do that I had simply hooked the cable from the 4245 that used to go to the Rig Runner into the end of the cable going to the K3, basically taking the Rig Runner, Power Gate, and Boost Regulator out of the picture. This gave me two cables, total of about 10 feet, with three APP connectors.

Thus the connection went from the 4245 through a five foot cable and some ferrite donuts into another five foot cable to the back of the K3. The voltage dropped to 12.5 on the K3 meter. With some work, I pulled the cable out of the K3 and connected the 4245 cable with the ferrites directly into the K3. With this combination (only ONE cable and Power Poles at the K3 end) the voltage dropped from 13.9 to 13.1. This means that a second five foot length of cable and two APP’s caused a loss of .6 volts.

So, what does all this mean? Since I am not using wimpy, skinny wire I have to conclude that perhaps the APP’s might be the cause of some of this voltage drop. With the original configuration I had using the AGM battery, Power Gate, Boost Regulator, and Rig Runner, there are a bunch of APP’s in the circuit, in addition to several feet of wire. I “could” simply connect the 4245 directly to the K3 and settle for a drop of .8 volts (13.9 to 13.1), but that kinda defeats the purpose of having a solar / battery backup system and a power distribution system. I thought this issue would be solved by replacing the MFJ PS with something else, but it is looking a LOT more complex at this point. Crap - what is one supposed to do? 

Jim / W6JHB






> On Mar 9, 2017, at 5:23 PM, Don Wilhelm <donwilh at embarqmail.com> wrote:
> 
> Jim,
> 
> Get your DMM out and make the same measurement at the power supply terminals.
> If you see a substantial voltage sag during transmit there, you can blame the power supply.  But if the voltage stays close to constant, the problem is voltage drop in the power cabling.
> 
> The RigRunner will contribute some drop due to the extra contact points and even #12 or #10 wire has some resistance.
> 
> If the power supply is good, run a power cable direct from the power supply to the K3 and run another power cable to the rigrunner.  Run the accessories in the shack from the rigrunner.
> 
> 73,
> Don W3FPR
> 
> On 3/9/2017 8:09 PM, James Bennett wrote:
>> Hi All -
>> 
>> Haven’t had any issues with the above configuration. Until today, when I happened to punch the K3 DISP button, changing it from reading my VFO B frequency to the other various bits of information. One of them was the rig voltage. Sitting there on 17 meters in CW mode receive it was showing a nice 13.8V. Cool. I hit the key and - wait a minute…… it dropped way down to 12.4v. Huh - not so cool. My first thought was that the Boost Regulator was not doing it’s job. But I decided to start trouble shooring at ground zero - the MFJ 4245. I disconnected it from the Power Gate and ran it directly to the K3. Key up = 13.8V. Key down = 12.0V. Yikes! I think (IMHO) calling this poor regulation (15%) would be a gross understatement.
>>