I have seen several discussions in the past about the current draw of “older” versus “newer” locos. I recently ran some tests for my own curiosity and thought I would share the results as they may be of interest to others. I realize the results may vary somewhat under different test conditions, but I figured these numbers could at least serve as a baseline for some.
Test Setup:
9’ of Atlas Nickel/Silver Super Flex Track (unsoldered, used alligator clip
leads to connect power)
MRC Tech 4 280 Dual Throttle
Fluke 77III Multimeter (DC 10 Amp Range)
Athearn PA1
0 - 50% throttle - .35A
50% throttle .34A after roll out
100% throttle .60A nominal
Athearn PB1
0 - 50% throttle - .30A
50% throttle .27A after roll out
100% throttle .71A nominal
Athearn GP-35
0 - 60% throttle - .67A ( barely moved at 50% throttle)
60% throttle .63A after roll out
100% throttle .97A (.77A after roll out)
IHC Alco Century 415
0 - 50% throttle - .08A
50% throttle .08A after roll out
100% throttle .13A nominal after roll out)
IHC Premier Series Alco C-628
0 - 50% throttle - .23A
50% throttle .18A after roll out
100% throttle .40A (.28A nominal after roll out))
Atlas Classic Series Alco C-424 PH1
0 - 50% throttle - .20A
50% throttle .17A after roll out
100% throttle .51A (.28A nominal after roll out)
Bachman Spectrum Series EMD SD-45
0 - 50% throttle - .28A ( moved very slow @ 50% throttle)
50% throttle
John, your information shows that just about any small Z, N, scale Decoder Rated 1 to 1.5 amps could be used in HO Locomotives without trouble.
Still check the wraw on Iron core motors before using a Z or N scale Decoders.
The limiting factor is stall current which is not what you are testing. What you are checking is unloaded current draw which will vary by design, wear on components , lubrication and many other factors.
John, I think the variation in current draw refers to the old open frame motors versus the newer style can motors. The open frame motors generally drew up to an amp or more of current and higher still when stalled.
I apologize, I made it painfully obvious that I am new to this forum posting stuff and neglected to include a lot of pertinent information. I even missed mentioning I am talking about HO scale locos. The good thing is your responses made me realize the things I left out.
Nos. 1, 2 & 3 are older locos, the rest are newer. What I was trying to show was that the older ones do draw more current than the newer ones, but for the most part, not enough more to prohibit converting them to DCC with decoders.
John’s (jsoderq’s) comment about stall current is correct, however, my understanding is that stall current can easily damage or even destroy motors in just a few seconds, so it would be advisable to avoid stalling a motor if at all possible.
My further understanding is that there are two ways to measure stall current, the theoretical method, where you simply measure the resistance of the motor windings and use ohm’s law (I = E / R) to calculate the current, and the mechanical method where you actually, physically stall the motor and measure the current draw. But again, this could damage the motor very quickly. As John also stated, these measurements are dependent on a lot of variables.
Ultimately, I am just trying to give something back to this forum which has given me so much over the last 2+ years.
Thanks, John
John, please don’t think of any of the questions as criticisms. They are simply requests for clarification. Your efforts are appreciated. I apologize if there were any misunderstandings on my earlier comments.
You seldom truely stall a locomotive anyway. Most of the time they slip. Your actual “running” ratings are very helpful. I have installed z-scale decoders(Digitrax) in Ho locomotives and haven’t experienced any problems. But then I don’t sit on them and ride them around the track.
I have ammeters wired in series with my throttles (guess this is only possible on traditional DC throttle systems). They are analog meters with a range of -2 to +2 amps, therefore not as precise as John’s measurements (do you have a digital ammeter, John?). I do have some older locos with open frame motors and they do draw more than my cans, but nothing gets dangerously close to the 1-amp mark.
But my real point is stall current. I just don’t consider that to be the practical limiter or maximum because as John says of his own locos, I am never going to physically stall my locos. If one has been given more tonnage than it can handle, it starts to slip. My observation has been that the current draw peaks out when the loco is going upgrade, struggling with the tonnage, and just prior to slipping, i.e. the current draw actually drops a tad when it starts slipping. For this very reason, be wary of adding too much weight to larger locomotives; if you add so much weight that they can’t slip, can motors will burn out in not much more than the blink of an eye. Its not a problem with smaller locos because you can’t physically add enough weight to keep them from slipping.
John - good show! That cleared things up for me. Thank you for the data - may come in handy for converting my old kato to dcc. Thanks for your efforts!
I have ammeters wired in series with my throttles (guess this is only possible on traditional DC throttle systems). They are analog meters with a range of -2 to +2 amps, therefore not as precise as John’s measurements (do you have a digital ammeter, John?).
