Capacitor size for coach led strip ?

beavercreek

beavercreek

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I have a set of Aristocraft aluminium streamline passenger cars. It is the latest type that they did before going belly up. It has the clear windows, detailed interior and long coach length rigid strips for led lighting.
The other evening I was running them and they were flickering as the track had become a wee bit dirty. I usually fit capacitors as anti flicker aids when I am adding lighting to rolling stock, so I inspected one of the streamline car strips.

It does have a capacitor but is only 100uF (25v). It is obviously not doing the job.
Would a 1000uF being over egging the pudding for about 5 secs of back-up (to anti flicker for closely spaced consecutive 'dirty spots).

Also, would it be best to use low impedance capacitors due to the load that the 6 cars would place on the power as they charge up the capacitors?
 
beavercreek said:
I have a set of Aristocraft aluminium streamline passenger cars. It is the latest type that they did before going belly up. It has the clear windows, detailed interior and long coach length rigid strips for led lighting.
The other evening I was running them and they were flickering as the track had become a wee bit dirty. I usually fit capacitors as anti flicker aids when I am adding lighting to rolling stock, so I inspected one of the streamline car strips.

It does have a capacitor but is only 100uF (25v). It is obviously not doing the job.
Would a 1000uF being over egging the pudding for about 5 secs of back-up (to anti flicker for closely spaced consecutive 'dirty spots).

Also, would it be best to use low impedance capacitors due to the load that the 6 cars would place on the power as they charge up the capacitors?
Click to expand...

Here's the basic equation for capacitor size. You need to know the current all the leds take.

C in Farads = current x time / voltage drop while no supply.

So as an example if you can handle the voltage to the leds dropping by 2V while the power is off for 5 seconds, and the total led current is 100 mA then
C= 0.25 Farads ! or 250,000 uF.

So your idea of 1000 uF is way too low (if the above example is close to reality)
Admittedly, you maye be able to tolerate a voltage drop of 10V while you're on dirty track and not notice the led brightness vary much. Then you'd only need 50,000 uF.

Low impedance capacitors would be worse. Don't worry about the inrush current - your power supply won't notice it. But if you want, put a resistor between the wheels and capacitor of value around 1/led current. The capacitor is always 'partly charged' except at initial turn-on, so the inrush is not all that much.
 
Thanks for the input Greg.
I have some 2.5V 4F caps that I was using to make back-up blocks for LGB sound modules (cheaper than buying the LGB jobbies).

I took one and temporarily hooked it up to the coach LED strip. I powered up using the 1amp LGB controller input set to about 12V.
I also had a loco on test rollers taking power form the feed line to see how much of the power would be sucked by the cap.
As the LGB controller is only 1 amp there isn't much spare power available beyond what the loco needs.

Anyhow, the cap did take quite a lot of the power while it was charging up and the loco was barely crawling on the test rollers. Once it was charged the loco went back to a 'normal' speed for the voltage input.

I broke the feed line to the LED strip with the cap...and the LEDs stayed lit for about 10 minutes. Of course they were not at full brightness (as the cap was only 2.5v) but stayed on they did.

I only need the 5 secs or so of back-up so a 25v or 35v cap of about 10,000uf might be ok?
 
Yes have seen it in the distant past. It's not compatible with DCC (but then you don't need it as the DCC power is in the track all the time anyway for the stock to pick up).
 
A new lighting solution is not really relevant here.
I am looking for the ideal cap for 5 secs or so anti-flicker with the Aristo led strips in the streamline coaches.
As the track power will be either from DC or from DCC and the strips already have built in rectifier, all I need is the right amount of capacitance.

But new lighting solutions are always interesting............... ;-)
 
what you want is a memory or super capacitor used a memory backup capacitor in PC's

http://www.members.optusnet.com.au/nswmn/flicker_free_JB.htm
 
As I posted above, would a 10000uf 25v cap be enough?

I stated that I had tried a 2.5V 4F supercap (at low voltage...12v) and it lit the leds for many minutes.

I do not need that long... only a max of, let's say, 5 to 10 secs.... but at 22v max....... so a 25V 1F might be a bit of overkill (let alone a bigger lump to hide in the roof)
 
10,000uf might be bit small, id try a 20,000 at 25v, but id go for a high temp version
 
I tried a 10000uf 35v cap and it did hold the illumination for a second or so.......so it looks like a larger one may well be necessary.
One problem..........the size!
Trying to hide a large capacitor in a passenger car is going to be challenge...let alone the cost of them!
 
http://www.rapidonline.com/Electronic-Components/22000uf-35v-85deg-Hc-Snap-in-Capacitor-11-3109

I put mine in the post vans or freight cars , run 3 or 4 four wheel coaches with a 3019 post van or a box van
 
beavercreek said:
As I posted above, would a 10000uf 25v cap be enough?

I stated that I had tried a 2.5V 4F supercap (at low voltage...12v) and it lit the leds for many minutes.

I do not need that long... only a max of, let's say, 5 to 10 secs.... but at 22v max....... so a 25V 1F might be a bit of overkill (let alone a bigger lump to hide in the roof)
Click to expand...
How did you use a 2.5V capacitor on 12V?
Did you put it straight across the leds?

I am assuming you have pickup from the wheels, up to say 25V, then a bridge rectifier, then some sort of regulator to a lower voltage??? to run the leds (via resistors).

If you're putting the cap right after the diode bridge, so it sees track voltage, you could use 2 of these:

http://www.hobbyking.com/hobbyking/store/__17100__Turnigy_Voltage_Protector_783333uf_3sec_.html

Connect the 2 in SERIES to give a rating of 30V and a capacitance of 190,000 uF
 
Well lads...this is how it has gone.... and thanks for the input, it was very much appreciated.

There are up to 20 5mm leds with their own resistors on the Aristo passenger car strip (depending on type of car). Interestingly there is a rectifier circuit but no regulator on the strip and the leds can be fed up to 22V

Tried the following on the test bed ...

1) Four 10F 2.5V in series (I already had a few of these for making 10V LGB sound module back-up packs) and 11v fed to the car (9v reaching the caps) .....kept lights on at full brightness for ....a very very long time......45 minutes!!...would need a regulator in the circuit....could try to source some 1F 2.5V and try those

2) Three 4700uf 25v in parallel (also had a few of these hanging around) .....kept the lights on at full brightness or 1 second before decay for enough brightness for 2 seconds...a possibility but still would show a 'variation' in brightness in real world use

3) Two 10000uf 35v in parallel (bought these to try as they were fairly cheap and were the last step in dimensional size before the caps got too big!)....kept lights on full brightness for about 2 seconds before decay through enough brightness for 4 seconds...would show a variation in brightness in real world use but better than solution 2

There is another two capacitors (which rapid did not have in stock when I visited), 22000uf or 33000uf 25V which would probably, when paired in parallel, give full brightness for maybe the 5 seconds I was aiming for but be dimensionally just that bit bigger than the 10000uf 35v jobbie (30 to 35mm wide as opposed to 25mm), and that would make it visible below the roofline where they will be slung longitudinally.

Upshot is..
I could try to get some 0.5F 2.5V caps and use them in series with a regulator..or...

that I do have the solution of either a fully hidden solution for shorter brightness-time or an ideal one time-wise that could be seen hanging below the window line of the cars........ there isn't another place to store the caps in the cars out of site...I promise, have checked everywhere.
As the cars are pretty sweet looking, I would prefer not to spoil the effect with two whacking great 'tanks' hanging over the passengers heads.. :o

I could also try more to find a make of 33000uf 25V cap that is cheap and also 25mm wide
 
By real world I was also including the possibility of 'gaps' in track pick-up that may closely follow each other so that the caps do not have the time to charge after they have already discharged.
I notice this 'gapping' in pick-up happens more after a long running session, on a now dewy evening, where perhaps a Bachmann loco has been working hard and left its black deposit on the rails (due to the imperfect pickup wheel surfaces)

Also the 2 seconds full brightness before decay (that I measured for the paralleled 10000uf 35v caps) might have been a bit on the optimistic wishful side of my recording!

What I am really saying, I suppose, is that I do not want any 'pulsing' of the light.....and yes there may be those who say that even in 1:1 scale the carriage lights do flickers at times, but in scale world it is a bit distracting.....at least to me that is.....

I have just found a 22000uf 25v cap that is 25mm in diameter made by Cornell Dublier (CDE)...but it is only available in the USA and Farnell will only ship them over to UK in batches of 100!
 
ROSS said:
Spend the day......

https://www.google.co.uk/search?newwindow=1&site=&source=hp&q=22000uf+25v+capacitor&oq=+22000uf+25v+cap+&gs_l=hp.1.0.0i22i30.3911.3911.0.5675.1.1.0.0.0.0.96.96.1.1.0....0...1c..64.hp..0.1.94.5p-y_tITj3A
Click to expand...

Wow..... Google......who would have thought.......... ;D

I have already used it extensively Ross and it is the 25mm width that is hard to find as most of the 22000uf 25v caps, as I said in me posting, are 30 to 35mm in width
Also I have already stated that I have been to Rapid (who are just around the corner from me) and they do not have 25mm sized ones............

...but I have now found a couple more than the CDE branded 25mm ones....now to see what the postage is as some companies have a flat rate no matter how small your order (eg. Mouser charge £12 for any order less than £50)
 
Nothing suitable on ebay? (I can't check @ work) I quite often find I can get singles of stuff that RS etc. only really want to do in packs. I find there are sellers out there who are obviously breaking packs and reselling with more appropriate postage charge. You pays a smidge more per item but it's convenient.
 
ntpntpntp said:
Nothing suitable on ebay? (I can't check @ work) I quite often find I can get singles of stuff that RS etc. only really want to do in packs. I find there are sellers out there who are obviously breaking packs and reselling with more appropriate postage charge. You pays a smidge more per item but it's convenient.
Click to expand...

I had checked on ebay many, many times ( I always go there first anyway, just in case).............cheapest 22000uf 25v which is 25mm wide is about 18 squids for 5...I need 10 of them
I have found them at Mouser for £2.11 (10 and above) each, but unless I bump my order up to £50 I have to pay £12 shipping....

So it looks like I need to find things to add to the order to do this very thing....
A real shame that Rapid do not do them as they are just around the corner....
 
http://www.ebay.co.uk/itm/5x-UVZ1E223MRD-Capacitor-electrolytic-THT-22000uF-25V-25x50mm-Pitch12-5mm-/191595314467?hash=item2c9bf87d23
 
sparky230 said:
http://www.ebay.co.uk/itm/5x-UVZ1E223MRD-Capacitor-electrolytic-THT-22000uF-25V-25x50mm-Pitch12-5mm-/191595314467?hash=item2c9bf87d23
Click to expand...

Cheers Sparky....with the shipping they work out at £40.08 for 10 (if it is the came shipping cost for multiple purchases)
Mouser are £2.11 each for 10 so £21.10......plus the £12 shipping (if order is under £50) so total of £33.10
I think I will go with Mouser and add stuff to bump the order up to £50 and get the free shipping......now, what do I need?........Hmmmmmmmm
 
it's sometimes crazy for components, I needed 4 rf diodes to fix my MFJ anyalyser, common fault, cheeper to buy a reel of 50 than four individulay, so if there's any fellow Hams in here that have blown the sniffer diodes in there MFJ, I have some
 
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