Loco slower on hm7000

[sir john]

Hi all

I have just fitted a decoder to my hornby lemberg. When I was running it in on dc it ran a lot faster than it now does on dcc is this normal I have looked at the manual but most of it just goes over my head

[P-Henny]

Is this normal? .... IMO Yes.

[Bulleidboy]

How fast do you need to run them? I only did it once, but on full speed one of my HM7000 equipped steam loco's left the track on a curve (greater than fourth radius).

[sir john]

BB

I dont run the very fast at all just that I noticed a difference twixt the two just wanted to make sure all was well, I haven't had lemberg on the track yet only on the rolling road

John

[ColinB]

They should still run at the same speed. I must admit I have never measured to see if there is a difference. I did find though that some decoders do slow the loco down, HM7000 wasn't one of them.

[Rallymatt]

Would any of this be that via a decoder the motor only sees a maximum of 12v but on DC with some controllers, it could be slightly more?

I spent a little time with a scale speed calculator to establish max realistic speeds and then adjusted CV5 to match that. I have a table of what throttle results in what speed. 🤓

[Rog RJ]

There are very few decoders that limit the motor supply to 12volts.

Post amended

[ColinB]

I have been testing different decoders in the same locos for a while and yes some work a lot better than others. That is why I tend to use Zimo ones as I found them to be the most reliable and work with most motors. On a lot of my 0-6-0 locos when I convert them to DCC I have found some of the 6 pin varieties are terrible when applied to OO locos. I must admit the only issue I found with HM7000 was it has a tendency to reset itself on pieces of track where the DCC signal is not that great, other than that no real issues. The V2 software is a lot better at curing this but not perfect.

[sir john]

So I have finally got lemberg on the layout . I was quite disappointed in the performance as comparing her to my other A3's I needed a far larger throttle opening to keep lemberg going at the same speed as Doncaster

[5Dublo2]

Possibly an explanation:

Using DC the max speed of the loco just depends on the applied voltage (ignoring PWM for simplicity) and is therefore limited by whatever maximum voltage the controller can deliver or whatever voltage causes the motor wiring to get too hot (and eventually burn out) - which ever of these two comes first ;)

Using DCC the decoder itself limits the maximum speed based on a CV value

Each decoder manufacturer sets the max speed (voltage) to a default value (and the default may not be 100% of the possible voltage for a given decoder model)

Similarly (and I haven't checked this point) but for the HM7000 decoders, Hornby may set a different, less than 100% default for each loco profile that you could apply to the decoder - this being done to make different classes of loco have realistic maximum speeds

Based on the above there is a good chance that unless you check and tweak the CV settings then a DCC fitted loco will have a slower max speed than the same loco running with a blanking plug fitted on DC

[sir john]

Colin I was comparing two dcc fitted locos one with a lenz decoder one with the hm7000 I will take on board what you have said about cv's and check next time I'm in my train cabin

Thanks

[P-Henny]

I second 5Dublo2's suggested last para explanation and is precisely why I wrote my earlier reply quoted below:

Is this normal? .... IMO Yes.

[sir john]

Paul I understand what your saying but my A3 doncaster is much faster at 60 speed steps with a lenz decoder than lemberg with the same speed steps with the hm7000 decoder I'm just looking for a plausible explanation

John

[P-Henny]

5Dublo2 & my comments relate to comparing the same loco with and without a decoder i.e comparing its DC running to its DCC running characteristics, which was the query raised in your original starting post. You have now moved the 'goal posts' by comparing one DCC Loco against another different DCC Loco. This is something completely different.

[ColinB]

There will be a difference between locos speed because all motors run at slightly different speeds but it shouldn't be that much. The PWM from the HM7000 should be roughly the same at a particular setting as this will be determined by software. As I said before I would expect the loco to run at roughly the same speed on DC as DCC, I suppose there could be a difference in maximum voltage depending on the source. Most DC controllers are PWM based, but your DC controller may not drop as much voltage across its drivers as the HM7000 does. I only test on DC to check that the loco runs so most of my experience is between different types of DCC decoders. I may have missed it but have you tried swapping the decoders over and see if the difference in speed moves. On a totally difference subject I did find "stay alive" lasted longer on a Zimo decoder than a Train O Matic, so it does prove not all designs are the same and the difference was quite noticable.

[sir john]

I only test on dc then fit a decoder, I have 6 A1/3's lemberg is the only one that ran slower after fitting a decoder all the rest showed no conceivable difference when running in on dc and after fitting a decoder so paul I have not moved the goal posts as you suggested I was merely saying there was a marked difference with lemberg and the others when fitted with a decoder but no difference when run on dc

[ColinB]

@Sir John have you tried moving the decoder to another loco to see if the fault moves. I recently had an issue with a Zimo decoder where the loco ran a lot slower. Replaced it with another one and it fixed the issue. The offending decoder was new when I fitted it but when I came to running the loco a year later it suddenly didn't run properly. These devices fail in many different ways.

[96RAF]

Paul I understand what your saying but my A3 doncaster is much faster at 60 speed steps with a lenz decoder than lemberg with the same speed steps with the hm7000 decoder I'm just looking for a plausible explanation

John

 

 

You would have to investigate the speed curve settings and the values applied to CVs 2, 5 and 6. If the basic speed curve is in play then those CVs rule the roost, but if a complex speed curve has been invoked by CV29 then it’s anyone’s guess as to the curve settings. HM7K steamers use the complex speed curve to help regulate chuffs.

[sir john]

@Colin b Colin I have interchanged the decoders twixt Doncaster and lemberg now the problem has reversed lemberg is faster than Doncaster on the same speed step settings must just be an idiosyncrasy of the decoder

[sir john]

@ Raf

I am running it with "out of the box" speed settings haven't changed any

[sir john]

Problem solved (well sort of) running with my nce power cab it's as fast as my other A1's so must be a Bluetooth issue not the decoder

[ColinB]

That is really interesting sir john, it doesn't surprise me. I only ever use the bluetooth to load the profile and check it works, I then revert to DCC. I wonder what the issue is?

[sir john]

Collin That's what I will do from now on I have deleted the app then reloaded it no difference

[ColinB]

I am surprised that the testing team didn't do that test. It will be interesting to see if the same issue arises with the dongle when it eventually gets released. It could be that they have designed the product to work with the standard Hornby power supply driving the tracks, with no DCC controller in the way, whereas you are using a DCC controller, so the voltage will be slightly lower. I suspect you will get the same result using the Elite.

[sir john]

Well it's a complete mystery to me. Can't see why it would make any difference. On my rolling Road the difference twixt the two at the same speed step is really unbelievable