I have another recent thread on this issue, but I want to come at it from another angle.
My complaint is my three Intermountain HO scale F3A locos run too slow at the maximum speed setting.
All three locos have Digitrax DZ143PS decoders. At the time, the DZ143PS was the recommended decoder for the F3A by Intermountain.
I wrote to Intermountain about this speed issue and, and in their reply, they said that no one at Intermountain could recall the gear ratio for the F3. I thought that was strange. Their suggestion was to remove the decoder and do a speed test “in a DC environment”. Easier said than done. They went on to say that normal performance can be achieved between 14 and 15 volts for DC or DCC. My DCC output is 14.7 volts. So, that response from Intermountain was not helpful.
On the previous thread that I had started, it was suggested that I turn off BEMF. I reset the values of CV54 (switching speed) and CV57 (BEMF) to zero, so both were turned OFF. Still, no difference in maximum speed.
So here is my question. Instead of the DZ143PS, would the other recommended Digitrax decoders for this loco, DN163PS or DH163PS, provide greater maximum speeds? Or would there be no difference?
I have a question for You. That output of 14.7, do you know for a fact, that the motor, is running on 14.7, or is the decoder, giving the motor less than that? Can you turn the throttle all the way up and measure, how many volts the motor is actually getting? If it is infact running on the whole 14.7, already, how many more volts will it stand before it burns up? Back to the gear ratio issue again.
Frank
Edit: Something to take a look at, if you want to take the time;
That 14.7 volts is the reading of my DCC output voltage to the track, as measured by a RRampMeter, a circuit board that reads DCC voltage output.
I do not have a voltage reading to the loco motor or a reading under load.
I only mentioned it because of the reply that I received from Intermountain. I really don’t care what voltage is reaching the motor. All of my locos have HO scale or N scale decoders installed and run a lot faster at maximum speed than these three Intermountain locos which are equipped with Z scale decoders.
My question is whether an N scale decoder will cause a loco to run faster than a Z scale decoder and whether an HO scale decoder will cause a loco to run faster than an N scale decoder.
. I really don’t care what voltage is reaching the motor. All of my locos have HO scale or N scale decoders installed and run a lot faster at maximum speed than these three Intermountain locos which are equipped with Z scale decoders.
I don’t understand your statement. If the others are getting more voltage to the motor, would that not make them run faster, than the one that is getting less voltage? Why do you have N-scale and Z-scale decoders in a HO-scale engine, for size?
It’s not getting less voltage to the motor because it is a “Z scale” decoder. The Intermountain motors are seeing the same peak voltage that any other loco is seeing, unless you’ve set a speed table or set CV5. The difference is either the motor that Intermountain uses, or the gearing, or both. A scale designation on a decoder is little more than a physical size reference, and sometimes a current capacity indicator, though many “Z scale” decoders have the same current ratings as a similar “HO scale” decoder. The big large scale decoders, those often have a 4 amp or higher rating. The motor drives of most any decoder I’ve ever heard of are all the same, transistor H bridge switching rectified track voltage to the motor, so the peak voltage that the motor gets is really set by the DCC system’s track voltage. Peak can be reduced by setting a speed curve or adjusting CV5, but that’s it. BEMF can possibly ‘reserve’ a bit at the top end to allow it to increase motor power under load, even if already at full throttle. Switching speed is extremely obvious - when engaged, default uses F6 on Digitrax decoders, it runs the motor at half speed, and also reduces any momentum effects in CV3 and 4 by half.
Frank, yes, the Z scale decoder was recommended by Intermountain for space reasons, although a comparable N scale decoder would fit as well. An HO scale decoder would be a tighter fit.
What I meant by my reference to voltage is that I only measured it since Intermountain raised it as a potential issue. But, as Randy confirmed, the voltage reaching that particular motor should be similar regardless of whether the decoder was Z, N, or HO.
If the DZ143PS is putting full track voltage (minus H-bridge rectification losses) to the motor, how will using a different brand of decoder be able to put more than full track voltage (minus H-bridge rectification losses) to the motor?
Sure, there may be some minor difference in those rectification losses due to different components used by the different manufacturers, but I don’t think it would be nearly as much as what you’ve described with your F3’s vs. your other locos.
As an example, I have 18 Atlas GP’s of various vintages that have Digitrax decoders in them: DH123PS’s, DH163A0’s, a DH163IP, DN135PS’s DZ123PS’s, and DZ125PS’s - Whatever was cheap and/or on-hand at the time.
Now we KNOW that all those different form factors use different H-bridge components, yet all those locos run close enough to the same speed that I haven’t bothered to speed match any of them.
So I agree with Randy that it’s probably either the loco’s gearing, or you have a CV setting that’s limiting top speed.
Stevert, I was not saying that using a different brand of decoder would deliver more than full track voltage to the motor. My understanding of Randy’s comments is that any size decoder, Z, N, or HO, will deliver the same voltage to the motor and no more than the track voltage.
What I then asked was whether another brand of Z decoder might provide a higher speed at maximum setting than the Digitrax Z scale decoder. It has been suggested that Digitrax decoders may run slower due to their CV configurations and values. For that reason, I am asking whether a different brand of Z scale decoder would result in the Intermountain loco running faster than with the Digitrax Z scale decoder installed.
My last comment… If both engines, the fast and the slow, are getting the exact same voltage to the Motor, the slower one has a different gear ratio, than the faster one. What else is left?
I think that it was Randy in my other thread who mentioned that at least some Digitrax decoders run slower than other brands with comparable decoders. If I recall correctly, it is because of the way that Digitrax uses CVs. i am hoping that Randy will have something more to say in this regard.
No, nothing different about Digitrax - most decoders that have BEMF will reserve a little bit of the top end if BEMF is turned on - otherwise is the load increased while at full throttle, it wouldn;t be able to increase motor power at all. However, BEMF at high throttle is more of a crusie control than anything, that’s why I like TCS, since the BEMF turns off above a certain speed step. But turning off BEMF would eliminate that.
Also, with the previous Digitrax sound decoders, the microcontroller just isn’t powerful enough to play multiple sounds AND calculate BEMF, so when you hit thehorn, they would slow down - unless you turned off BEMF. Totally different issue.
Randy, I have a question, even though it does not really seem like one at all, and would like your opinion on it.
Back when I was first getting into DCC, about 1999, we had a gentleman in the club who was a beta tester for Digitrax. We had been putting some DZ12x’s, can’t remember if 121’s or 123’s into some HO loco’s, mostly P2K geeps, and we noticed that after a period of time, 6-10 months, the decoders started acting up. They would then eventually fail.
We asked our Digitrax buddy why this was happening, and this is what he said. That while the Z-scale decoders had the same rating as HO decoders, the Z-scale decoders heat sink couldn’t get rid of the heat generated by the electronics fast enough due to its size as opposed to heat sinks in larger decoders. The Z-scale decoders were literally cooking themselves into failure. I know that even Soundtraxx recommends that you attach an extra heat sink to their TSU-750 decoders due to this.
We replaced the Z-scale decoders with DH123’s and they have been fine since “upgraded”.
I went back and looked at the replies to my previous threads on this issue. In one reply, a remark was made that full voltage may not be getting to the motor due to lighting, circuit board, decoder settings, CV values, etc.
Stevert, I am not saying that a different brand of decoder will make the loco run faster. I don’t know. Since I am no expert on this issue, that is why I am asking the question.
All I can say is that my observations and conducting speed trials around the layout tell me that these three Intermountain locos are running considerably slower than any other loco on the layout. To me, it is either the decoder or the gear ratio on the loco. What else could it be?
i’m no expert either, but not all 12V motors run at the same max speed at max voltage. There may be a trade off between speed and torque. See the 12V RPM column on the NWSL motors catalog page.
It’s possible, since they are amsller. But if you weren’t exceeding the rating, they shouldn;t fail. The only Digitrax decoders with an actual heat sink are the heavy duty large scale ones, none of the others have a heat sink of any sort under the shrink wrap. In the early days, there were soem runs of P2K E units and/or PA’s that had the wrong motor installed and drew somewhere north of 3 amps, which would fry even HO decoders. Never heard of the Geeps getting that motor though. The TSU-750 is just a bad design, rated at less than 1 amp and it still overheats unless plenty of airflow is provided ot the thing is held against a large heat dissipating surface. The Loksound Micros are significantly smaller and have a higher current rating, and do not overheat. Part of it has to
No, no, yes, yes, no, and sorry that you have become such a wiseguy. You seem determined to ridicule my basic question on this thread. Reply after reply by you has mis-stated what I have asked since my initial post.
Is this decoder connected via an 8 pin plug? If so, just wawap one of your others. Don’t care if it doesn’t physcially fit, just run it with the shell off. That will clear up any doubts about the decoder. I still say it is simply that hey have geared them down more than the others, though ti could be a different RPM motor as well, or both. No amount of decoder tinking will change that.
To reiterate, there is nothing about the Digitrax DZ series decoders that would make them put less voltage to the motor compared to a similar series DN or DH decoder with the same settings. And they do all take the same settings across the line, ie, all Dx125 use the exact same CVs and values, the only difference is physcial size and number of functions.