Power Bank

[Britannia Builder]

I installed an 8-TXS decoder in my Hornby 3-car class 101 DMU last week, and found that it frequently stalled on points and then went through all its start-up sounds before moving off again. This wasn't a surprise because the DMU only has pickups on one of its bogies, and the carriage lights that I fitted used to flicker on points with the old non-sound decoder, although the motor carried on with no apparent interruption.

I had the same problem with a TTS decoder on my Peppercorn A1, which I solved by fitting pickups to the tender wheels.

Now with the TXS decoder I've been able to buy and fit a Power Bank, which solves the problem completely. The train will run for maybe 10 seconds with the track power switched off, and if the train is stopped the sounds will play on for ages. Interestingly the carriage lights, powered from output HF03 on the decoder, still flicker on the points - they are obviously not driven by the power bank capacitors, presumably to save all the power for the motor.

Having the option of the plug-in power bank is a great step forward!

Regards, John

[96RAF]

The power bank simply applies its stored voltage to the decoder to prevent it browning out. There is no priority logic involved. Whatever is switched on will still try to pull its load from the power bank under track fault conditions.

An analysis of the decoder wiring schematic versus the power bank schematic would be required to confirm where any prioritising happened if at all.

[Wayne-in-Oz]

It might be that the Power Banks would be 12v and your track is 15V. I have made up quite a few "Stay Alives" using 4 x 3V Super Capacitors so pretty much the same as the Hornby ones (just lots bigger) and they rate at 12v charged . So the quick flicker might just be the 3v drop for a split second.

[Britannia Builder]

That's an interesting point that you make about the voltage of the power bank, Wayne, but I think that the power bank must be feeding into the decoder circuitry after the point at which the HFnn feeds are taken off - if I cut the track power, the carriage LEDs on HF03 go out completely while the motor and sound carry on for 10 seconds. The schematic in the manual suggests that the HFnn feeds come directly off the bridge rectifier.

If so, it seems an entirely sensible design decision to reserve all the power bank power for the motor and sounds. It might be worth updating the manual to clarify this?

Regards, John

[96RAF]

Not sure if your deduction is correct BB as when I kill power to my track after a running session the locos with lights on slowly dim out as the power bank store is consumed.

[Britannia Builder]

How strange! I should have said HF03 rather than HF01 in my previous post - I've edited it accordingly.

Regards, John

[96RAF]

HF03 on an 8-pin being the green wire. Not convinced there should be any difference in response from how the HF01/02 directional lights behave with a power bank.

[Britannia Builder]

Yes, the LED strips are wired to the blue and green pins on the decoder socket, with a suitable resistor - 3 LED strips in the 3 coaches, joined by fine wires between the coaches.

It would seem rather strange if HF01/02 and HF03 behave differently with respect to the power bank. Anyway, it's no big deal.

Just tried the auto calibration out of interest - the train shot off like a scalded cat, but luckily stayed on the rails! The result is perhaps slightly smoother, although there was nothing much wrong with it beforehand.

Regards, John

[96RAF]

Auto-cal is the next step if the speed profile imported by the download for that loco type is not satisfactory. In the event that is not enough then you get to stage 3 fiddling with PID values by way of CVs, not for the faint hearted. RTFM about that.

A likely scenario would be putting the Hornby settings into a Bachmann loco, then use auto-cal to fettle any irregular running - akin to switching CV150 regimes in a ~tTS decoder.

[Britannia Builder]

I think Wayne is after all correct in his post #2 above to say that it may be a voltage difference between the 15v DCC track voltage and the voltage of the power bank. In fact the power bank appears to contain 3 supercapacitors, not the 4 that Wayne uses, so I think will only have a voltage of about 7-9 volts? This may well be enough to keep the motor going, but my carriage LED lighting has a resistor in series to reduce the voltage across the LEDs to keep the lighting fairly dim and reduce the power consumption. So the power bank probably does feed HF03, but its lower voltage causes the voltage across the LED strips to drop below the minimum needed to light them.

Regards, John

[Fishmanoz]

Suggest it would need to be a very large resistor to reduce the voltage across the LED to less than the couple of volts needed to turn it on, even at 7-9 volts.

[Britannia Builder]

I think the 12v LED strips are wired with groups of 3 LEDs in series, so the minimum voltage to light them will be something in the region of 6-7 volts.

Regards, John

[Britannia Builder]

Just as a footnote to this, the relatively low voltage of the power bank does cause some speed hesitation when running over points with poor pickup. I believe that the power bank is less than 9V - it contains 3 supercapacitors each rated at I think 2.8V (from memory - the power bank is now tucked away in the loco's cab). It depends on the weight of the train - my Hornby 3-car DMU is relatively light and carries on without noticeable slowing down, but my Bachmann 3MT Tank with 3 coaches is heavier and slows down momentarily to a crawl before the 15V track power cuts in again. If I cut the track power, the 3MT comes to a halt within a foot or two, but its sound carries on for ages.

I shall have to get the track rubber out and give my points a good clean!

Regards, John

[Fishmanoz]

Rob, it shouldn’t behave like that should it?

[96RAF]

Rob, it shouldn’t behave like that should it?

 

 

I wouldn’t have thought so. I would have to check what the boffins say the PP output is but it has to be high enough to power the decoder and run the motor for a good few seconds.

[Britannia Builder]

The other point to bear in mind is that the power bank does take a couple of minutes of running to charge up (according to the decoder manual). If the train sets off from rest at the start of a session and immediately hits duff points at the end of the platform, the power bank doesn't help. It's not clear for how long the supercapacitors retain their charge when the loco is sitting at rest on powered track, but hopefully some minutes. I can understand why they've chosen to only charge them when on the move, to preserve the programming track functionality, but in the new world of changing CVs from the app it's a mixed blessing.

On the plus side, when the loco loses its DCC communication at speed and the only way of stopping it quickly is to cut the track power, the power bank doesn't send it crashing through the buffers!

Regards, John

[96RAF]

Feedback from Hornby confirms the output voltage from the PP is quite low compared to track voltage, but they emphasise the design purpose of the device it to cater for the low track speed scenario such as when a short loco crosses duff points. In that case the decoder is kept alive for the few short seconds necessary to clear the dead track. The design was not to support high speed running across an isolated track section, although I was almost caught out when I had my bridge open and a PP equipped loco travelled well into my safety dead zone before the Hand of Dog stopped it.

This is why a loco without power will run at modest speed for a few seconds but the sound and lights drawing less current will sustain for ages.

As to the lack of static charge scenario, I wonder if running the loco up against the brakes (F27) will charge the PP.

[Britannia Builder]

Thanks Rob, it's good to have that confirmed. If the charge-only-when-moving is a software rather than hardware feature of the decoder, perhaps in the future it could be changed to also charge when the sound is turned on? This would still allow the charging to be turned off when on the programming track, but would keep a sound decoder charged when at rest in the station.

Regards, John

[96RAF]

John

Looking at both the PP and decoder schematics in concert it is a hardware feature. Whether it can be made switchable in software is another question for the boffins.

[Peter-351502]

I’ve fitted a 21pin Bluetooth decoder to a Bachmann class 21

it runs fine once the power bank is changed.

but really bad before it charges

What is the best method of charging the power bank (ideally without moving the train)

[96RAF]

What is the best method of charging the power bank (ideally without moving the train)

………….

There isn’t one unless you have a rolling road or can run the loco with the driving wheels off track or slipping.

[Brew Man]

Yes, you could place the loco upside down on a foam cradle and place the track wires from your controller on two of the wheels and run for a while like that. However, if it runs as badly as you say pre-charge, maybe your track needs some attention.

[SteveM6]

I agree with the last post, it sounds as though your track and the loco wheels and pickups need cleaning. The power bank is there to help over points but is not a substitute for a decent cleaning regime.

[Britannia Builder]

I decided to check how long the power bank retains its charge when stationary on powered track. I've seen circuit diagrams of other stay-alives which have a high-value resistor across the capacitors to gradually drain them, so I was concerned that it might lose its charge after a few minutes in the station.

So I ran the loco for 3 minutes to ensure the power bank was fully charged, then left it at rest on powered track with the sound on. I briefly flipped the track power off for a second or two every minute or so to check that the power bank kept the sound going.

I'm pleased to report that the power bank was still going strong after half an hour, so it seems that if you can get across the first set of points after moving off at the start of a session, you should be good for the rest of the session!

Regards, John

[riverlagan]

Might have missed this just looking to confirm the Power Bank dimensions.