Overcurrent on Autocalibration

[Britannia Builder]

I installed an 8-TXS decoder in my 8P Duke of Gloucester TTS loco yesterday. This is the last of my steam locos to be upgraded, and I did so mainly in order to get the better chuff rate and the AFC sounds, despite the fact that there's no DoG sound file as yet. I used the Tornado profile, which has 3 cylinders and a decent chime whistle similar to the DoG. Perhaps Hornby will migrate the DoG TTS sound profile in due course - its sounds are very good.

The installation went well, although I had to reset the decoder with the Bluetooth password at the outset. However, when I came to run the auto-calibration, the loco did not move and I found that the overcurrent warning was showing in the app. I reloaded the profile as advised in the app, although I wonder if this was strictly necessary. The loco then ran well, but I didn't try autocalibration again.

I wonder if the decoder's overcurrent detection is too sensitive? Autocalibration seems to apply instant maximum voltage to the stationary motor, which will draw a much higher momentary current than normal acceleration from a standstill. I suppose it's possible that there's a genuine fault with the loco, but it's only a few years old and not heavily used so that seems unlikely. The overcurrent protection could at least reset itself in a user friendly way when the high current draw has been cleared.

Regards, John

[96RAF]

Auto-cal was only working from DCC. I can’t recall if it was fettled on the app or not.

[SteveM6]

Rob, we are still waiting for autocal to be fettled on the app. Android that is - can’t speak for iOS.

BB - the TTS profiles cannot be ‘migrated’ to HM7K, they need to be built from the ground up as they are significantly more complex.

[Britannia Builder]

I did trigger the autocalibration from DCC (Railmaster) after setting CV149 to 0 in the app, by turning on F28 (which also turns on F0). This is how I've always done it. The loco didn't even twitch, which suggests that the overcurrent triggered instantly. I haven't tried it again because reloading the profile gets rather tedious.

I suppose my hope of a DoG TXS profile was rather optimistic.

Regards, John

[96RAF]

I used the Brit profile in my DoG.

Try using F0 not F28.

[Britannia Builder]

Yes I thought about using the Britannia profile but that is 2 cylinder rather than 3, and the Tornado does have decent chime whistles on F3, like the DoG. The only very minor gripe is that AFC uses F2 whistles as its moving-off sound - in an ideal world AFC could be set up to use F3 instead of F2.

I've always used F28 to turn on F0 and hence trigger autocalibration, because I have F28 and not F0 on my set of 6 Railmaster small-throttle buttons. It does work, as proven by the overcurrent!

Regards, John

[96RAF]

Maybe F28 does work but the reason for suggesting using F0 the prime control is to rule out or identify any bug if F28 is used.

[Brew Man]

I used the Brit profile in my DoG.

Try using F0 not F28.

 

 

I'm confused. F0 is for lights surely. Should that not be F1?

[96RAF]

I used the Brit profile in my DoG.

Try using F0 not F28.

I'm confused. F0 is for lights surely. Should that not be F1?

 

 

No - in the self calibration procedure F0 is used as the trigger.

[Brew Man]

I used the Brit profile in my DoG.

Try using F0 not F28.

I'm confused. F0 is for lights surely. Should that not be F1?

No - in the self calibration procedure F0 is used as the trigger.

Ah, OK. I'm currently working my way through the Manual but haven't got to that bit yet. Thanks for the clarification.

 

 

[Britannia Builder]

I'd be happy to do more tests to pin this problem down, and I can certainly change my Railmaster setup to allow me to trigger F0 directly, although I've used F28 successfully many times before with other locos. I think the interesting test would be whether a lower setting for VHigh would remove the overcurrent, and if so how high a voltage it could tolerate.

The main barrier to doing this is the apparent need to reload the profile and then reset all the customised CVs in order to clear the overcurrent error shown in the app. This just too tedious to contemplate! Is there any other proven way of clearing the error?

Regards, John

[SteveM6]

When I have seen that message it has been cleared by switching everything off and on again. That includes the app and tablet/phone.

[Britannia Builder]

I tried it again, with pretty disastrous results.

I started by autocalibrating with F28, and it worked! I tried a couple of times more to be certain, and ran the loco successfully, and then I thought I'd better try using F0, and it failed with the overcurrent. I'm sure that this is nothing to do with F28 versus F0, but just some randomness in the overcurrent mechanism.

So following Steve's advice I powered off the track for at least 5 minutes (the loco has no power bank) and I rebooted the iPad, but this unfortunately didn't clear the overcurrent. The loco responds to sounds and makes chuffing noises but the motor doesn't turn.

So I reloaded the profile, which cleared the original fault yesterday, but even this didn't clear it this time.

Is there anything else I can try before sending the decoder back?

Edit: I've also now tried a CV8 reset, and that doesn't help.

Regards, John

[LTSR_NSE]

Since the issue appears intermittently repeatable - have you performed a stall test on the loco recently?

If it is marginal at the upper range of the decoder’s capability, that could account for your experience?

Otherwise if loco’s stall current is nowhere close, then personally I would contact Hornby, as decoder might benefit from health-check?

[96RAF]

ADCC/ABC testing has shown these decoders can be sensitive to voltage change on track resulting in spurious reaction to grubby track thinking it is a diode induced stop/reverse, hence a sensitivity setting is being introduced via CV128, however whether this will affect over-current tripping is yet to be considered.

The sensitivity setting will be introduced in a future profile update, possibly v4.0.

[Britannia Builder]

I tried the decoder again this morning and it has magically recovered after a good night's sleep! Very strange, after a complete power down for 5 minutes yesterday didn't clear the overcurrent condition, and nor did a profile reload or a CV8 reset. I shall never use autocalibration again after this experience. Applying maximum voltage to a stationary motor just seems too vicious.

@LTSR, I can't do a stall test because I don't have a DC controller, and from reading up about it stall testing does seem to risk damaging the motor unless done very briefly. If I were to remove the decoder again I could check the resistance across the motor drive wires on the decoder socket, which would presumably give the stall current by Ohm's law.

Regards, John

[SteveM6]

John, glad you got it sorted. Even though you gave it a good five minutes yesterday, I guess it wasn’t quite enough.

Don’t shy away from the autocalibrate facility, it is a very useful tool to have in the box. The TXS decoders are ‘tuned’ to suit the motors that Hornby currently use - consequently an older loco or one from another manufacturer may not run as smoothly as they could. The autocalibrate will rectify this and provide superb performance over a range of manufacturers.

You said that you used F28 as a trigger - as that is the AFC command which also triggers a number of other sounds eg whistle, steam cocks and chuffs, I wonder if that created a higher than usual current draw on an already marginal loco? Stick to F0 as Rob described and you should have no issues.

[Britannia Builder]

Thanks Steve. It would be good to know how the overcurrent protection works - what current triggers it and over what time measurement, and how it gets reset. Is the advice in the app to reload the profile a red herring, and it just resets after a suitable period of power off?

I thought about whether F28 would put an additional load on the decoder with the sounds starting, but in fact F28 only caused 1 overcurrent out of 4 recalibrations, whereas F0 caused the overcurrent on the one time that it was used directly. It could be that the F28 sounds divert a bit of power away from the motor drive, and hence slightly reduce the protected motor current? It's clearly right on the limit of the overcurrent protection.

I agree that autocalibration is useful, and I've used it many times previously without problems, but I wonder why it needs to use maximum motor voltage? Surely the back emf characteristics of the motor could be determined with a lower voltage?

Regards, John

[SteveM6]

I don’t believe the reload is necessarily a red herring but I question whether it is the reload or the power cycling done as part of the process that is the solution. Personally I have found that a full power cycle has cleared the occasional issue for me, having never had to reload a profile to clear this issue. I wonder if there is some latent memory in either the decoder or the tablet that retains the error and that your five minute shutdown wasn’t quite enough? I have left mine powered down for an hour or two when it has happened - not based on any advice received but based on experience after I had an issue, powered down then had to go out for a while - all good when I got back later. I just use that as my default process now.

You must also take into account that this advice I sent offered by someone who still considers electronics as a form of witchcraft.

[teiger]

Hi

I wasn't doing autocalibration, but I too get this message about Motor Overcurrent. My Bachmann Class 37 is on a DC track. The profile and everything loaded and I got sounds. However the loco didn't move. When I tried to reload the profile, after completion, I got the overcurrent message and the App has lost connection to the decoder (Bluetooth). Nothing I do seems to get it back. Is that the end of the decoder.

Sorry if this is all a newbie question.

Steven

[SteveM6]

DC track? How is the track powered i.e. What is the power supply?

Is the track powered by a Hornby endorsed PSU as shown in the compatibility table in the sticky posts at the top of this part of the forum or is it some other kind of supply.

Be aware that using an incompatible supply can destroy the decoder.

Not all DC supplies are created equal.

[teiger]

OK so it looks like I blew it. (Literally) I have an HM2000 power supply! Is there anything to salvage? (Apart from the speaker).

[SteveM6]

OK so it looks like I blew it. (Literally) I have an HM2000 power supply! Is there anything to salvage? (Apart from the speaker).

 

 

Hornby have flagged the HM2000 as incompatible as shown in the table of compatible controllers in the sticky thread at the top of this forum section.

Your decoder is probably no more than a desk ornament now.

[Fishmanoz]

Steven, might I suggest that next time you have a problem, rather than adding a post to a topic that is different to your problem (by your own admission), you start your own topic to find your answer.

For your current problem, a title like “Solution to Motor Overcurrent Message” would have been the way to go.

Then, before you go any further with HM | DCC and HM 7000 decoders, you might also read the pinned sticky at the top of the forum on Compatible Power Supples.

Finally, despite this problem seeming to be of your own making, I suggest you contact Hornby to see if they might do a warranty replacement for you.

[teiger]

Yes thank you. I found the forum after I read the leaflets enclosed with the decoder. There is not a strong enough warning there IMHO.

I will, in future start a separate thread. Thank you for your patience and understanding.

Season's greetings.