Battery powered Bachmann K27

[DGE-Railroad]

The Johnson bar is done. I'd hoped to use a linear servo. That thing is tiny! It worked okay but was a bit noisy and the servo motor got pretty hot. I wasn't happy with it so opted for a standard micro servo in the cab

Animated Johnson Bar

I quite enjoy the speed and endpoint setting part of things, it's quite fun!

I've tidied up the loom a bit and run everything back ready for tender connection.

The last job I think is going to be to make a shield for the flywheel. Why its exposed is beyond me, given the amount if wiring around this area. Even with everything strapped down, the slack needed to allow boiler removal means theres some flapping around, to close for comfort



Its surprisingly busy in there!

 

[Paul M]

n, the slack needed to allow boiler removal means theres some flapping around, to close for comfort

It all looks very tight in there, perhaps they know you like to live dangerously

 

[DGE-Railroad]

So something interesting happened on the maiden run, which I want to try and understand..

I normally have the smoke unit set up for main smoke chuff with the cylinder steam on a DCC function. The result is the cylinder steam heater and fan only draw current when the function is activated. The main smoke also comes in with its function and idles unless a chuff is triggered.

I had left both functions switched on when I started up and didn't have the chuff trigger for the main smoke. The result was that both cylinder and main smoke units ran full at the same time.

The ESU is also running two micro servos a 12v dc fan plus sound. I had no lights on at the time and the train wasn't moving, so no motor current.

About a second after starting up, the Revo handset reported an overload condition and correctly shut down the power it supplies to the decoder. Once I switched the smoke functions off and restarted the Revo, all was fine. Turning the smoke functions on individually was also fine.

I was surprised that the Revo overload protection was triggered though. Its a 5A peak, like the ESU XL, but I was expecting my 3A fused supply from the battery to blow first, which I'm using as a safety.

I may look at putting a realtime current monitor in there to try and figure out why it's happened but was just curious and wondered if anyone had any thoughts about it. I can only surmise the Revo has a current overload protection below 3A.

To recap my electrical config:
18v 2ah battery through a 3a glass fuse to the Revo DCC reciever
That is connected to an ESU XL4 decoder which is connected to
Smoke unit
Motor
Speaker
Servos
Bachmann power distribution board (which operates the fan via an onboard regulator)

 

[PhilP]

A '3Amp' glass fuse will have a rupture current of about twice the fuse rating - so 6 Amps.

It takes time to heat/blow a metallic fuse, so it does not surprise me the 'electronic' trip fired first.

instantaneous current through the heaters, motor-windings, bulbs will be pretty high, but very transient. You also have the decoder electronics, any 'keep-alive' all near-instantly coming on-stream.

The electronic cut-off, would likely be, single-digit milli-seconds.. A wire-fuse wold be 100 milli-seconds plus, probably..

 

[DGE-Railroad]

Ah.... JK at Revo tells

A '3Amp' glass fuse will have a rupture current of about twice the fuse rating - so 6 Amps.

It takes time to heat/blow a metallic fuse, so it does not surprise me the 'electronic' trip fired first.

instantaneous current through the heaters, motor-windings, bulbs will be pretty high, but very transient. You also have the decoder electronics, any 'keep-alive' all near-instantly coming on-stream.

The electronic cut-off, would likely be, single-digit milli-seconds.. A wire-fuse wold be 100 milli-seconds plus, probably..

Ah!!!
Thanks Phil, that probably explains it then.

Possibly something like a poly switch would be a better safeguard then regular fuses?

 

[Greg Elmassian]

Yes, also the electronic circuitry acts fast, so a short duration of higher current will often trip an "electronic" breaker, while you have to have it long enough to melt the fuse wire, and as was stated, most "fast blow" fuses blow at 200% of rated current...

Your decoder just does not have enough current capability. I forgot how your smoke unit is connected, but is it possible to give it a separate power? I think the only hope here would be a SUSI interface between the main decoder and the smoke unit...

Greg

 

[DGE-Railroad]

JK at Revo also explained theres a 'base station power' value tucked away in the config menus that can be used to tweak the overload value as a percentage...

 

[DGE-Railroad]

Yes, also the electronic circuitry acts fast, so a short duration of higher current will often trip an "electronic" breaker, while you have to have it long enough to melt the fuse wire, and as was stated, most "fast blow" fuses blow at 200% of rated current...

Your decoder just does not have enough current capability. I forgot how your smoke unit is connected, but is it possible to give it a separate power? I think the only hope here would be a SUSI interface between the main decoder and the smoke unit...

Greg

Thanks Greg. I had thought I would be sailing close to the wind trying to run the smoke unit from the common power source but the same setup seemed to work on the Mikado, so I was reasonably comfortable.

I guess I am only just beneath it and the differences in this install such as the servos and fan have pushed it right up to that limit.

I'll see what the Revo cut off is set to and then look at cutting a few features, or running a second battery for dedicated stuff

 

[PhilP]

Ah.... JK at Revo tells



Ah!!!
Thanks Phil, that probably explains it then.

Possibly something like a poly switch would be a better safeguard then regular fuses?

Polyswitches will still 'rupture' at about twice their rated-value.. But, a lot quicker!

An 'electronic' trip, will win everytime.

 

[DGE-Railroad]

Polyswitches will still 'rupture' at about twice their rated-value.. But, a lot quicker!

An 'electronic' trip, will win everytime.

Something like one of those blade-fuse style push button circuit breakers instead of the glass fuse then if I wanted to include my own safeguard Phil?

 

[PhilP]

What I meant was:
The electronics, will safeguard the 'system' most of the time..
A 'fuse' (glass, poly, rest-of-choice) will safeguard the wiring, and model, from a major meltdown..

I tend to use Polyswitches.. Possibly more than 'just' as soon after the battery as possible? - I might use lower ratings on the motor-feeds, and perhaps smoke sub-system?
I would ALWAYS fuse a supply leaving the loco. - Out for vehicle lighting, for example.

 

[Greg Elmassian]

phil, I have to disagree with you about polyswitches, they are slower than a fast blow fuse.

For those reading the thread who do not know, clearly a fast blow fuse is a thin metal strip that melts and parts given too much current.

The Polyswitch (that is actually a brand name by Ray-Chem I believe) is a material that melts under heat (caused by current flow).... when melted it does not conduct (much) and when it cools, it goes back to a conductive crystalline form.

The reason that some people believe it is fast is that while a 3 amp polyswitch will indeed trip at 6 amps, at 3 amps there's enough heat inside already to be on the threshold of melting and "opening".

There are also faster "blow" polyswitches that have a bit more tightly controlled specs, but still sloppy, and still way slower than an electronic overcurrent sense, which can be microseconds.

All that said, I too use polyswitches, as they protect from gross overages and self reset. They are not good for protecting sensitive electronics.

Greg