LED Flicker

[Tim-1207899]

I have a DC layout using a gaugemaster controller to run trains. I also have a separate Hornby R965 controller using the 12v output just for LED plaza lights which I like as I can use the knob to vary the output/brightness, and I use the 16V accessories output for the older type colour signals used with R046 lever switches. I`ve just increased the plaza lights from 2 to 4, and added another colour signal to a total of 6. Now when I move a switch I get a strong flicker from the plaza lights as I go from on to on with any switch, and this did not happen before the addition. So I would appreciate any help thanks.

[Chrissaf]

Is the R965 embossed with 'Made in Margate' or 'Made in China'.

The Margate made version uses a power transistor output to control voltage. This means that the output is a sort of DC albeit electrically noisy.

The China made version uses a 'SCR' Silicon Controlled Rectifier output. This means that it controls current rather than voltage. The output seen on a scope is a series of spikes and the electrical circuit is optimised for the supply of higher currents than LEDs typically draw. When low currents are drawn, measured spike voltages can peak at up to 20 volts. Neither of these controllers are really a suitable way of powering LED lighting. But the China made version is less suitable than the Margate one.

Typical output of a China made R965

To be honest, model rail DC controllers rarely give out anywhere near a proper DC voltage.

Note this also, the early R406 dual aspect signals used red and green incandescent bulbs. Whereas brand new ones you can buy today [and probably going back about 3 years or so] are now built with LEDs not bulbs. Both are compatible with AC AUX supplies. Although Hornby are now using LEDs [which are DC] in the R406, they have designed the internal circuit with reverse bias diodes to protect the LEDs from the adverse reverse voltage affects of the AC voltage supply. Hornby in their infallible wisdom decided to keep exactly the same R406 stock code number and not even call it a MKII. There is no easy way to tell the difference just by looking at them.

If some lights are bulbs [signals] and others LEDs [Plaza] and they are both in effect connected ultimately to the same primary input supply of the R965. Then the mismatch between bulb and LED electrical characteristics on a supply not ideally designed for that use, could very well be the cause of the flicker. The R406 with bulbs will drawing a lot of current relative to the LEDs, so when you switch the R406, you are going through an 'off state' on the switch. This means that the current drawn will fall and rise. This lack of current stability would appear to be affecting the more sensitive LEDs.

I suggest that you need to separate your supplies. One to power LEDs and another different one to power bulbs.

If all 6 x R406 signals are built with bulbs, then these combined are likely to be drawing a total current close to the maximum the R965 can supply. A R406 bulb is likely to draw about 60 - 80 mA each. So any sudden change in current draw i.e operating a R406 signal switch to change aspect, could very well cause the supply to the LEDs to dip and look like a short burst flicker.

[Going Spare]

I read the post as the R965 being used to control both the plazza lights and the colour light signals, with the Gaugemaster unit purely having a track connection.

[Chrissaf]

G.S

After several read throughs I now see the error I made. I read the Accessory output as being the one on the GM. I have edited my previous reply to match.

[ColinB]

If I understand this right, I am assuming you are only using the Hornby supply to power the Leds. So why not put a 10 uF across the outputs of the 12 volts, that will smooth the output so it doesn't flicker. As it is a 12 volt supply that can go positive or negative it might be better to use a bridge rectifier followed by a 10 uF capacitor, exactly how you power the lighting strips in a carriage.

[Chrissaf]

Colin, he says it only flickers as he throws the switch to operate the R406 signal. There is no indication I can see in his text that infers that the LEDs are constantly flickering the way I think you are interpreting it - if I understand your reply correctly. I believe the flicker to be more like a brief change of LED intensity as the current load changes as the signal switch is thrown. I'm thinking that perhaps the word 'flicker' might not have been the most optimum description term to use.

[ColinB]

Sorry Chrissaf, I must admit I had difficulty figuring out what was actually going wrong. I just assumed he had put more leds on so it was drawing more current to cause the flicker. A capacitor might help either way, although it might slow down the response of the led. I must admit with the modern tower leds I tend to use, the light output seems to be a bit digital, they only seem to change their brightness significantly when I put stupidly low currents down them.

[Tim-1207899]

.... I believe the flicker to be more like a brief change of LED intensity as the current load changes as the signal switch is thrown. I'm thinking that perhaps the word 'flicker' might not have been the most optimum description term to use.

 

 

Thanks for your reply, and your interpretation of my `flicker` is more accurate, it`s as though there is a very short power surge to the led lights when I throw a switch. My unit is a China edition so probably concurs with your `spike` comments. I`m thinking the best option is to use a separate power unit for the LEDs.

[Chrissaf]

Yes, Tim ... I think a separate supply for the LEDs that provide a better [smoother] DC output would be a wise prudent choice. There are model railway layout lighting controller products out there that provide dimming controls [not made by Hornby].

[Chrissaf]

TIM - Your post to which this post replies, got lost for some inexplicable reason. But at the end of the day it is the answer that is important rather than the question. For other readers, the lost question was along the lines of Tim using a voltage convertor between the output of the R965 and the Plaza LEDs, the convertor suppressed the flicker. He was asking whether I thought it a suitable permanent solution.

From your product description it sounds like a 'Buck Convertor' you are using. I bought half dozen or so of those for my tools box. To be used for various electronics projects. I have found them very good at cancelling electrical noise from a noisy power supply before feeding the more stable power output they produce into a secondary connected circuit. So yes, I do think that is a very reasonable alternative [if it is a Buck] as you can then also use the convertor adjustment to perform your dimming function.

As I said in my original reply, trying to read a meaningful accurate voltage on the output of the 'China Made' R965 is a waste of time. Getting a 20 or 20 plus volt reading is to be expected. The way the SCR output works on the China R965 doesn't produce a steady voltage in the traditional sense. Any reading you get will be the reading device [meter] just trying to make a best stab in the dark as to what it is seeing.

[Tim-1207899]

@Chrissaf

Yes it is a 'Buck Convertor', so seems a reasonable solution, thanks again for your advice.