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Batteries Or Super-Capacitors ?
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 Posted: Tue Mar 30th, 2021 10:05 pm
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bobquincy
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And the 2.7F super-capacitor powering the 200 mA motor,

will drop 66% of it's voltage in about 5 milli-seconds.

boB





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 Posted: Wed Mar 31st, 2021 07:42 am
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Helmut
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@bobquincy

NO, Sir!

Let's assume you use a 2.7F capacitor @2.3V 
The charge is C*U=6.2Cb
If you discharge that at 0.2A, the time to zero is 31seconds.

For convenience, let's say the motor stops at 1.5V,
then you still have 11seconds run-time.


Two electrolytic capacitors back-to-back, will NOT explode or whatever.

To extend their useful life, you can bypass each of them by an anti-parallel diode,
to make sure that they do not see any reverse-charging current.




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 Posted: Wed Mar 31st, 2021 01:27 pm
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bobquincy
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I stand corrected:

T (seconds) = R*C

In that time the voltage of the capacitor,
will drop to ~ 37% of the initial charge voltage. 


If the capacitor is at 2.3 V and the motor draws 0.2 A (about 11 Ohms),
the T is 11 * 2.7 or about 30 seconds to 0.85 V.


Your calculation of 11 seconds run time appears to be good.  :)

boB




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 Posted: Wed Mar 31st, 2021 05:23 pm
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Helmut
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Okay, now that we've settled that,
there remain two drawbacks of direct buffering in analog operation:


1. Such a huge capacity in parallel to the motor,
will make it virtually uncontrollable with a standard controller,
because of the stored charge.

Your controller has to be of the four-quadrant-type,
i.e. actively discharging the capacitor to the set voltage.


2. Supercaps AFAIK do not respond well to the simple circuit Si. featured.
You have to use diodes, too.
The simple circuit needs double the number of capacitors.




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 Posted: Wed Apr 7th, 2021 12:12 pm
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Steve Soar
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The use of capacitors to store energy and "keep things running" is well proven,
but not very easy to implement on analogue.

Has anyone any experience of using an inductor between controller and rails ? 

I have been considering this,
and as it is not on board the loco, there is no problem with size and weight.

I am thinking about an iron cored inductor with air gap which will store energy,
according to how much current is flowing, and the value of inductance.

If the current to the loco is suddenly reduced, due to dirty track,
the inductor tries to maintain current, by increasing the voltage at the dirty track,
this voltage can be quite large.

Does anyone have any experience of this technique ?  

I intend to do some trials,
but if it is a non-starter I don't want to waste my time.

Regards to all

Steve


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 Posted: Wed Apr 7th, 2021 01:39 pm
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Helmut
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An effective method, and taking up less space,
was the RF-ionizer once sold by 'Relco' in the UK.

I still have one of these,
and it is rather effective in bridging dirty spots.


Excerpt from their website:

In the late 1970s the first consumer product utilizing RF technology,
was developed and marketed – The 'Relco Track Cleaner' for model railways.

This product was demonstrated on the BBC TV programme “Tomorrows World”,
consequently it became hugely popular between model railway enthusiasts,
within Europe, North America and Australia.


BUT there are caveats:

They bake the dirt onto rails and wheels if you don't do regular cleaning maintenance.
They will damage DCC decoders and coreless motors, due to the 50V RF voltage.


Now imagine what your proposed ignition-coil circuit will do to your locos!




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 Posted: Wed Apr 7th, 2021 03:17 pm
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Steve Soar
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Very pleased for the info,  
yes I can now see the problems.   

Ah well, back to the drawing board.

Thanks for your input.

Regards

Steve


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 Posted: Thu Apr 8th, 2021 10:06 am
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Steve Soar
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Back to super-capacitors.  

There seems to be two basic types, one of which is the EDLC,
this has symmetrical electrodes and construction, so although marked + & -
I wondered if they can be used in a bipolar circuit.  

So I have connected 3 off 0.47F 5V capacitors in series,
and mounted them on a running loco chassis (see photo). 





Polarity is correct  when running forwards, but is reversed when running in reverse.  
This appears to work well on my dirty tracks, and will run down to a much lower speed,
with the capacitors connected than without capacitors.  

Forwards or reverse is ok,
but I don't know if running in reverse will eventually damage the capacitors.  
I have run this in reverse for over 1 hour with no problems.

When running at higher speed (10V) and supply is switched off,
then loco continues to run for approximately 1 metre forwards or reverse.
Running on my uncleaned tracks is much improved especially at creep speed.

The super-capacitors were bought off ebay  0.47F  5V

I will continue to run for longer periods.

Regards

Steve



Addition :

Now completed 4 hours running in reverse, all working well,
still giving 1 metre run when supply switched off (from a 10V rail voltage).


I have also tested capacitors on a power supply,
and they appear to work well with reversed voltage.  

Not seen any degradation .... yet!


Testing to date has been with a linear DC controller.  

I have just tested with a PWM controller,
and as expected this needed a small ferrite-inductor in one of the rail supplies.

All looking very promising, I have not cleaned this track in months,
but loco is now running very well, even at very low speed (a big improvement).


There is a problem with emergency stops from high speed,
the super-capacitors run the loco for over 1.5 metres before stopping.  
 
So if a quick stop is required, then it could be done by shorting out the rails... !! 
(after switching off the supply) 



Regards
Steve


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