# Examples of Add On Capacitor Motor Run Time



## wvgca (Jan 21, 2013)

I did a simple experiment today, demonstrating how much additional run time is gained by using add on capacitors ..

I used three different capacitor energy sizes ..
1] single standard electrolytic,4700uf ... large in size, low cost, impossible to fit in tight locomotives
2] an array of three 0.33 coin or button style super caps in series, rated here at 16.5V, 110,000 uf
3] an array of three 1.0F coin or button style super caps in series, rated here at 16.5V, 333,000 uf

There are capacity ratings for some commercial style of these super cap arrays / modules, in an easy to read reference chart, at this page :
https://sites.google.com/site/markgurries/home/decoders/keep-alive-compatibility

For motors on this test, I chose a new old stock blue box Athearn with flywheels, and an inexpensive can motor without flywheels rated at 16V operating ...the tests were done with 12V applied to the caps, and motor, and were allowed to run for about one minute to make sure the caps were fully charged, no charge current limit resistor was used. The Athearn drew around 150ma at 12V free running [no load applied], and the can motor drew around 30ma under the same conditions. For each of the following videos, the power supply was unhooked, and the motors ran only on capacitor reserves, no blocking diode was used.

The purpose behind these tests is primarily to help determine what capacity of add on capacitor may be needed to add a DCC stay / keep module, either commercial or 'home made'

























Video YouTube links are below

The Athearn with a 4700uf..





This one is a bit misleading, the voltage dropped very quickly, but the motor spun longer due to the weight of the flywheels, less noticeable with larger capacitor values

The can motor with the same 4700uf..





The Athearn with 3x 0.33F super caps





The can motor with the same 3x 0.33F super caps





The Athearn with 3x 1.0F super caps





and last, The can motor with the same 3x 1.0F super caps





this test was terminated early, the motor was still spinning fast enough that I couldn't see the black magic marker stripe on the motor shaft
enjoy


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## Bwells (Mar 30, 2014)

Very interesting. It tells me two things, first would be that a can motor is way more efficient than the open frame pancake motor even with flywheels and second that the supercaps store a lot for their size and that a single 1F should get the loco across any dead spots. Good test a superbly done!


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## wvgca (Jan 21, 2013)

Bwells said:


> Very interesting. It tells me two things, first would be that a can motor is way more efficient than the open frame pancake motor even with flywheels and second that the supercaps store a lot for their size and that a single 1F should get the loco across any dead spots. Good test a superbly done!



thanks 
the can motor that I used was a cheap generic, I would assume a name brand, or a rare earth magnet style would be even better, but I don't have any to try with ...
from what I could 'guesstimate' probably somewhere in the range of 0.1F TO 0.2f [total] would be more than sufficient for most HO scale applications


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## Bwells (Mar 30, 2014)

What is the difference between wiring caps in parallel versus series? Parallel would increase the size of the gas tank but what does series do? Possibly slow the discharge rate?


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## gregc (Apr 25, 2015)

Bwells said:


> What is the difference between wiring caps in parallel versus series?


wiring caps in series reduces their combined value. N 1F caps have a values of 1/N F.

wiring caps in series is necessary when the individual capacitor voltage is smaller than required -- two 10V cap allows operation with voltages up to 20 V.

larger voltage caps are larger in size.


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## gunrunnerjohn (Nov 10, 2010)

What you should consider is some tests in a real locomotive with a track power light showing so you could see how far it goes after the power is removed.


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## wvgca (Jan 21, 2013)

gunrunnerjohn said:


> What you should consider is some tests in a real locomotive with a track power light showing so you could see how far it goes after the power is removed.


I did try before, using a 3x0.22F array, roughly two seconds, enough to get it through a longer #6 dead frog okay ..
but it wasn't a really good test, an old athearn switcher with a fairly high draw motor, and an old command 2000 driving it ..
the foot switch and panel meter show up for my resistance welder project so that is probably next on the bench ..
and time to get machinery ready for harvest, if the ground actually dries up .. 
i may actually have to do some real work for a change


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## wvgca (Jan 21, 2013)

just realized that the videos would have been better if i would have had a light or something to indicate when the power was shut off, and the capacitor took over .. oh well,
might do some more next month ...


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## gunrunnerjohn (Nov 10, 2010)

Yep, that's why I mentioned the track power light, I wasn't sure when the power dropped, so it was hard to judge how effective the caps were.


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## gregc (Apr 25, 2015)

A while back i purchased a few supercaps to experiment with. So I wired them in series, wired an led/resistor across them, connected a meter across them, charged them up. 

I expected to see the charged voltage bleed off but saw a dramatic drop in voltage after disconnecting them from charge source and they seems to remain charged longer than I expected.

i don't understand why there was an initial drop in voltage. Any idea?


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## gunrunnerjohn (Nov 10, 2010)

You apparently have low quality caps with high leakage. I just pulled out a 5V SuperCap, the ones that I use for battery replacements in PS/2 3V locomotives. I connected it to a power supply and let it charge until it was fully charged. When I pulled the power supply off the cap, the voltage dropped .01 volts after about a second. After ten seconds, it had dropped .05 volts. I suspect the 1meg impedance of the meter is very slowly discharging it, they should stay charged for a very long time if there's no load.


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## wvgca (Jan 21, 2013)

gregc said:


> I expected to see the charged voltage bleed off but saw a dramatic drop in voltage after disconnecting them from charge source and they seems to remain charged longer than I expected.
> 
> i don't understand why there was an initial drop in voltage. Any idea?


Depends to some extent on how many caps you had wired in series, apparantly load balancing is recommended when over three in series are used, to prevent over voltage in any one seperate capacitor .load balancing mount PCB's are readiy available for higher energy storage applications like using super cap arrays for replacing standard automotive batteries .. I have watched some videos on this on YouTube .. On commercial cap arrays for DCC stay alives I have not noticed any load balancing, but they seem to work, perhaps because of the relatively low energy storage

Or perhaps just a bad batch?? I usually buy from ebay based primarily on price, and have been lucky so far ..

From what I have read, a super cap will lose around fifty percent of it's stored energy in a month because of fairly high internal drain, some attribute this to the organic seperator layer.. 

Some time ago I found a helpful web page on super caps, and bookmarked it ..decent write up .

http://electrical-engineering-portal.com/super-capacitors-different-then-others-part-2


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## gunrunnerjohn (Nov 10, 2010)

Load balancing is pretty simple, the folks that built the BCR used Zener diodes.

Here's a 9V BCR clone, this is how I build them. The heatshrink in the background is what I use to encase them after construction.

Before anyone asks, the red going to the negative pole of the cap array is correct. Remember, I'm using a 9V battery clip as the "battery", so the polarity has to be reversed to be correct for the external circuit.


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## wvgca (Jan 21, 2013)

gunrunnerjohn said:


> Load balancing is pretty simple, the folks that built the BCR used Zener diodes.
> View attachment 217666


When I look at commercial DCC stay live images, I don't seem to notice any type of load balancing [ on images that show the actual pcb] .. and many use five or six super caps in series ..
Any idea why? maybe just a dumb question?


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## gunrunnerjohn (Nov 10, 2010)

Perhaps they think the caps are matched? Maybe they're just cutting corners? I really can't say. It's cheap to add a few Zener diodes, they don't have to be high current models, they can be small and cheap.


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## gregc (Apr 25, 2015)

finally had a chance to look at this again. It's been hot and humid here in Jersey and I still have a challenging enough day job.

I have 3 supercaps in series and connected an LED/resistor across them. Charged them up to ~13 V thru a 80 ohm resistor.

i see the voltage drop to ~7 V within 1 sec. But it takes 6-8 sec to then drop to 6 V.

looks like these caps are rated a 5.5V and I'm charging 3 to close their rated voltage?

could this be high internal resistance?

thanks for the explanations and experiments


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## gunrunnerjohn (Nov 10, 2010)

I can't imagine that being an issue, if you look at my example, I was charging a 5V one to 5V, 100% of it's rated voltage!


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## wvgca (Jan 21, 2013)

gregc said:


> f
> 
> I have 3 supercaps in series and connected an LED/resistor across them. Charged them up to ~13 V thru a 80 ohm resistor.
> 
> i see the voltage drop to ~7 V within 1 sec. But it takes 6-8 sec to then drop to 6 V.


You don't mention what size of super caps that you are using, but a rough guess with the 80 ohm resistor that you are charging them around 150 ma .[initially, then lowering].
If you have a series of three 0.22F caps, charge time would be [I think], some where around 20 seconds or so ..
Just wondering if possibly that you weren't charging them for a long enough time period for them to get close to the input voltage potential?


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## gunrunnerjohn (Nov 10, 2010)

Good point, I connected mine directly to the power supply and then gave them enough time that the voltage stopped changing.


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## Cycleops (Dec 6, 2014)

Where's ED-RRR? Or is this the lull before the storm!


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## gunrunnerjohn (Nov 10, 2010)

Shhhhhh! Don't wake a sleeping giant.


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