quote:

So what is it exactly about the CW-80's "internal resistance" that should be causing me concern

Wolverine --

The internal resistance of a power supply (or any supply, originally batteries) is a characterization of how the supply's ability to provide its rated voltage as the current load increases, but below the supply's capacity (where the resistance increases sharply and ultimately goes infinite). Note that this metric is independent of the supply's ultimate current handling capacity.

The supplies we use in O vary a great deal in this regard. I'm running Z1000s and 180 power bricks on my layout now; with the same 4 amp load (i.e., 33% below the Z1K's capacity and a whopping 60% for the 180), the 180's voltage drops more than twice (2.3 volts) as much as Z1ks (0.75 volts). I've measured three different CW80s over the past few years and their drops were all on the order of my 180; i.e., over two volts for 3 or 4 amp loads. I don't have one handy to compare in the house though.

I'm sorry for the MRC fans out there, but all MRC supplies i've measured are poor in this respect.

There is substantial sample-2-sample variation in this metric, but all of my Z1ks (of differing vintages) are quite good.

Does it matter? For conventional, emphatically "no" for all practical purposes. One simply turns the handle up more.

Things are trickier for command with cruise. Simply put, voltage drops require current increases to maintain speed under load. Amps are heat, heat is bad. In addition, DCS doesn't work all that reliably under 14 volts or so; thus an extra volt, volt-and-a-half, can be important. There are losses at track joints, through the roller, etc., so 16-17 at the supply may put you in the 13 range as measured by the PS2 electronics. TMCC may be a more robust to voltage drops (or less so; i just don't know), but the amp vs volt / heat phenomenon is unavoidable.

Bottom line: for conventional use, i am the first to agree that this characteristic is largely irrelevant. It may not be so for many command implementations, and can be important.

-- gary ray

This message has been edited. Last edited by: gearbox,

Gary (gearbox),

Thank you for your detailed explanation. I know that a lot of members use DCS, TMCC, or other fancy systems. I personally run conventional only, and although I admire versatility* in any device, I had not considered this factor in the context of this thread. If I understand you correctly, this need not concern Demo at this stage of his participation in the hobby, but might be something to consider in the future.

*As long as complexity doesn't compromise reliability.

>

I thought I was going to read about Optimus Prime playing with trains.