Stay-Alive/Capacitors for 12vDC

[Simon G]

Getting back to what the OP asked, and following the failure of my Plan A, here is Plan B!.  Thanks to the posters who informed us that you can now buy a 1 farad capacitor that is sufficiently small to fit in some locos, I have produced a circuit which might just work.  The 1F capacitors are rated at 5.5V, so rather than daisy-chaining them for a higher voltage, I intend to use just one.  This is because the stalling issue generally only occurs at low speed (and therefore low voltage) and for a short distance on points, so the circuit does not need to drive the motor at speed or for very long.

My circuit will charge the capacitor while the motor is running, up to approx 5.5V, then when the power cuts, it will discharge approv 4.6V to the motor, taking into account a 0.7V voltage drop across a diode such as a 1N4001.  Assuming that the motor will continue to run with a voltage of 4.6V, this circuit has a chance as far as I can tell.
R1 and R2 need to be the same resistance effectively a potential divider to reduce the track 12V down to 6V, then 5.3V through diode D1 to the capacitor.  I would suggest a resistance of approx 100 ohms for R1 and R2 and a rating of 0.5W.

If anyone has any comments or views, I would be most interested (even if it is to say that it wont work!).
The cost of the whole thing is about £5, with the capacitor being approx £3.60 of that.

 

 

[Dagworth]

As soon as you turn the controller the opposite direction you'll let the smoke out of the capacitor. Your circuit is quite an effective one-shot smoke generator but not much else...

 

Andi

[richard-g8jvm]

You will also find those caps are designed for memory back-up, hence the ESR,

electrical series resistance, is high, so the current it can supply is low.

 

Richard

[jdp298]

Getting back to what the OP asked, and following the failure of my Plan A, here is Plan B!.

They're right, it's not totally brilliant. Those things from Maplin will stand up to just over 6v, but 12 will probably do them in. Nil Desperandum, though. There is a bit of a bodge you can use where you back-to-back electrolytic caps. So in place of D2, put another C1, but have both of the positive sides facing outwards. This'll get you 12v well enough, but halve the capacitance. You won't need the rest of the components either, so this is a proper old-school jury-rigged 'hang on for the ride'.

 

That's not actually the worst thing though. The high ESR will prevent too much coming out of the capacitors too quickly, so you'll get a slightly slower let-down. Hopefully it'll be enough to get you over a stalling section.

 

Rough numbers. Energy stored running at 5v with 0.5F total = ~ 12J. Assuming you need 0.5A for 1 second at 5v = 2.5J. Once we allow for all sorts of inefficiencies and not being able to use the last few Joules from the cap as the voltage runs down, I reckon you're in with a chance. Give it go, see what happens.

[Crosland]

Getting back to what the OP asked, and following the failure of my Plan A, here is Plan B!. 

 

 

Please, do not try this at home, as they say

 

Andrew

[Simon G]

Thanks for the feedback on Plan B!  The general consensus is that it is a complete non-starter, so I wont bother going to the expense of buying the 1 farad caps.  I did say earlier in this thread that my electronics skills were limited, and I think I have proved that beyond all reasonable doubt

[Robin2]

Of course the other short term energy storage device is a flywheel. And it has much the same properties as a capacitor.

 

...R

[richard-g8jvm]

Hi

I'm glad you didn't try the 1F cap, I dont know what the dielectric construction of them is,

but the back emf off a motor is large, so you would be reverse biasing it each time the brushes lost contact with commutator.

Electrolytics have a vent panel to limit to explosion, but the damn things can still go off with quiet a bang, and leave a mess .

 

I 1F caps are sealed, which makes them problematic if when the are over voltaged or reverse biased they produce gas, most thing getting hot will do.

The greater the gas pressure the bigger the bang.

An example is the 3V lithium button cells, they must never be charged, the normal configuration for battery back up is via steering

diode, so current can only flow from the battery to the circuit load, should that diode fail and go short circuit , there will be a current flow

in to the battery and the resultant gas build up is enough to blow a hole in a GRP board and through an aluminum heat sink 1 cm thick, excluding the fins, I've seen that several times in some very expensive test equipment.

Also, if they were using aluminum foil for capacitor construction, one of the chemicals used on Ali. to stop , I think, oxidation is cyanide.

Its definitely used on Ali-alloy castings in industry.

 

If one of these batteries explode inside a loco, its probably bye-bye loco and anything else close to it.

 

If using this type of component check the manufacturers data sheet before use, and check the construction material.

 

And dont ask the guys in Maplin if something is OK to use

 

Richard

[Titan]

What about a small rechargeable battery? You would have enough power to last a few minutes and it would keep itself topped up when on the juice as it were.

[Crosland]

What about a small rechargeable battery? You would have enough power to last a few minutes and it would keep itself topped up when on the juice as it were.

 

The problem when you have too much stored energy is that you can get runaways, e.g. when you expect a loco to stop on an isolating section.

 

Andrew

[DCB]

I rather thought the whole point of on board capacitors was to get a smooth stop rather than stay alive per se.   That said I cannot see enough physical space in an oo loco, especially a "Pug" or similar for a meaningful amount of capacitors, bearing in mind with electrolytics you would need one set for forward and one reverse.   A capacitor generated auto stop would be a good way of getiting protypical stops, just turn the power off and let it glide to a halt.

 

Personally witn one annoying exception I fin peco live frog points kept clean to be essentially stall free, the exception is the long diamond crossing and the Wrenn 8F where the flanged front and rear driving wheels are exactly the same distance apart as the rail gaps and they sit on their flanges with the wheel tyres clear of the metal rails.

 

Im have never blown up a model railway capacitor but well remember a Lucas 12 volt motorcycle which went "Bang" very impressively showering my leg with what I assumed was acid, it taught me a valuable lesson, don't use genuine Lucas motorcycle electrical parts, use the local electronic components shop.

[Crosland]

 use the local electronic components shop.

 

Is this the same shop trying to rip you off by trying to sell you a resistor with every LED? I wouldn't trust them if I were you.

 

Andrew

[richard-g8jvm]

Here is a page from NEC referring to the super capacitors, these are up to 200F 2.5 V

Note the comment on using in ripple systems, applicable to electric motors, on series connections, and soldering

It has wrapped on pasting , but its still readable

 

●All specifications in this catalog and production status of pro

ducts are subject to change without notice. Prior to the purcha

se, please contact NEC TOKIN for updated product data.

●Please request for a specification sheet for detailed product d

ata prior to the purchase.

●Before using the product in this catalog, please read "Precaut

ions" and other safety precautions listed in the printed versio

n catalog.

2013.06.19 9565SCAVOL13E1306H1

38 Super Capacitors Vol.13

10.

Notes on Using Super Capacitor

(Electric Double-Layer Capacitor)

1. Circuitry design

1.1 Useful life

The electrical double layered capacitor (super capacitor) uses electrolyte and is sealed with rubber etc. Water in the

electrolyte can evaporate in use over long periods at high temperatures, thus reducing electrostatic capacity which in turn will

create greater internal resistance. The characteristics of the super capacitor can vary greatly depending on the environment

it is used in. Therefore, controlling the usage environment will ensure prolonged life of the part.

Basic breakdown mode is an open mode due to increased internal resistance.

1.2 Fail rate in the field

Based on field data, the fail rate is calculated at approx. 0.006Fit. We estimate that unreported failures are ten times this

amount. Therefore, we assume that the fail rate is below 0.06Fit.

1.3 Voltage application when maximum usable voltage is exceeded

Performance may be compromised, and in some cases leakage or damage may occur if applied voltage exceeds maximum

working voltage.

1.4 Use of capacitor as a smoothing capacitor (ripple absorption) in electrical circuits

As super capacitors contain a high level of internal resistance, they are not recommended for use as electrical smoothing

capacitors in electrical circuits.

Performance may be compromised, and in some cases leakage or damage may occur if a super capacitor is used in ripple

absorption.

1.5 Series connections

As applied voltage balance to each super capacitor is lost when used in series connection, excess voltage may be applied to

some super capacitors, which will not only negatively affect its performance but may also cause leakage and/or damage.

Allow ample margin for maximum voltage or attach a circuit for applying equal voltage to each super capacitor (partial

pressure resistor/voltage divider) when using super capacitors in series connection.

Also, arrange super capacitors so that the temperature between each capacitor will not vary.

1.6 Outer sleeve insulation

The outer sleeve wrapped around the super capacitor indicates that it is sealed, however the outer sleeve is not guaranteed

for insulation purposes. Therefore, it cannot be used where insulation is necessary.

1.7 Polar characteristics

The super capacitor is manufactured so that the terminal on the outer case is negative (-). Align the (-) symbol during use. Even

though discharging has been carried out prior to shipping, any residual electrical charge may negatively affect other parts.

1.8 Use next to heat emitters

Useful life of the super capacitor will be significantly affected if used near heat emitting items (coils, power transistors, and

posistors etc) where the super capacitor itself may become heated.

1.9 Usage environment

This device cannot be used in any acidic, alkaline or similar type of environment.

●All specifications in this catalog and production status of pro

ducts are subject to change without notice. Prior to the purcha

se, please contact NEC TOKIN for updated product data.

●Please request for a specification sheet for detailed product d

ata prior to the purchase.

●Before using the product in this catalog, please read "Precaut

ions" and other safety precautions listed in the printed versio

n catalog.

2013.06.19 9565SCAVOL13E1306H1

Super Capacitors Vol.13 39

1.10 Super capacitors fitted with pressure valves

HV series super capacitors are fitted with pressure valves Make an opening in the top of the pressure valve to avoid any

damage to the super capacitor when the pressure valve is in use. Allow at least a 2mm opening for models with a diameter

of

φ

18mm or less, and at least a 3mm opening for models with a diameter of

φ

22mm.

2. Mounting

2.1 Mounting onto a reflow furnace

Except for the FC series, it is not possible to mount this capacitor onto an IR / VPS reflow furnace. Do not immerse the

capacitor into a soldering dip tank.

2.2 Flow soldering conditions

Keep solder under 260

°C

and soldering time to within 10 seconds when using the flow automatic soldering method. (Except

for the FC and HV series)

2.3 Installation using a soldering iron

Care must be taken to prevent the soldering iron from touching other parts when soldering. Keep the tip of the soldering iron

under 400

°C

and soldering time to within 3 seconds. Always make sure that the temperature of the tip is controlled. Internal

capacitor resistance is likely to increase if the terminals are overheated.

2.4 Lead terminal processing

Do not attempt to bend or polish the capacitor terminals with sand paper etc. Soldering may not be possible if the metallic

plating is removed from the top of the terminals.

2.5 Cleaning, Coating, and Potting

Except for the FM series, cleaning, coating, and potting must not be carried out. Consult us if this type of procedure is

necessary.

Terminals should be dried at less than the maximum operating temperature after cleaning.

3. Storage

3.1 Temperature and Humidity

Make sure that the super capacitor is stored according to the following conditions: Temp.: 5

～

35

°C

(Standard 25), Humidity:

20

～

70% (Standard: 50%). Do not allow the build up of condensation through sudden temperature change.

3.2 Environment conditions

Make sure that there are no corrosive gasses like sulfur dioxide as penetration of the lead terminals is possible.

Always store this item in an area with low dust and dirt levels.

Make sure that the packaging will not be deformed through heavy loading, movement and/or knocks.

Keep out of direct sunlight, and away from radiation, static el

ectricity

, and magnetic fields.

3.3 Maximum storage period

This item may be stored up to one year from the date of delivery if stored at the conditions stated above.

This product should be safe to use even after being stored for over a 1 year period. However, depending on the storage

conditions, we recommend that the soldering is checked.

4. Dismantling

There is a small amount of electrolyte stored within thecapacitor. Do not attempt to dismantle as direct skin contact with the

electrolyte will cause burning.

This product should be treated as industrial waste and not is n

ot to be disposed of by fire.

 

Not something to be played with unless you know what you are doing

Richard

[Crosland]

As with any component, there are super caps and there are super caps. The user needs to choose appropriately. A look at http://www.rapidonline.com/Electronic-Components/Capacitors/Memory-Backup-Capacitors will show that you get what you pay for.

 

The cheapest has an internal resistance (that determines current rating) many orders of magnitude greater than the more expensive. The kinds of ripple current found in a model loco are well within the ratings of the more expensive components, but the price may put you off. There is a reason why the Lenz Power-1 costs what it does (or did, Lenz USA list it as discontinued but that may be a US thing).

 

Andrew

[richard-g8jvm]

If you really want to play with super capacitors. read the sections I highlighted.

 

They are particularly sensitive to heat hence the 3 secs soldering limit .

 

they do not like ripple, look at the waveform of a DC system with something like a Gaugemaster controller,

All they use is a bridge rectifier across an AC 50 Hz supply, so you get a raw un-smoothed 100 Hz ripple,

thats why people like them good slow running control.

Look at the other designs that have appeared on this forum , and they make use of the ripple on the un-smoothed

supply to get slow running performance.

 

These devices are referred to as cells, and you can not use them back to back , so you can't make a bipolar cap by using a pair

back to back.

This is due to the very thin dielectric measured in Amstrongs, ( probably mis-spelt that), Lithium Titanate is used by most manufacturers

in construction.

The main application types :_

battery back up capacitors

and Mass storage for automotive/ solar energy storage , these will deliver high current, but they are large and very expensive.

 

The battery back caps are low current Hi ESR devices intended for holding CMOS memory, the hi quality ones used in aircraft black boxes

they are designed to supply current in microamps and are unsuitable for motor supply with peak currents of several hundred milliamps.

1 uA = one millionth of an Amp, 1 mA = one thousandth of an Amp.

 

More and more countries are banning battery products containing lithium from their postal systems, super caps use Lithium Titanate.

They are banned due to their explosive nature. hence the ban on posting batteries in the UK

 

Listing the Rapid site to give info, there is none there , its a sales site for the consumer,

industrial companies will use Farnell, RS and the many others like it who will give a direct link to data sheets on devices, or links to manufacturer's sites for further info.

If you check the Samwha website you will find the product info in shortform on their super caps, the full data sheets are in Korean, and you will need to load the character set to be able to view the pdf files.

The Wima site is easier to navigate and you can find the same data as their competitors NEC, which I poster a page from their data sheets.

Their super caps are designed fro the power market, they are large, and expensive.

There are super caps designed for the audio market for the output coupling of amplifiers, Audiophiles like to have good low frequency performance right down to a few hertz.

As a result there are 10F caps designed for it, but they do not withstand reverse bias, there are a few U-Tube videos of idiots blowing them up wit car batteries , these caps are expensive and look to be about an inch or two in length, but note the explosive power.

 

The argument will be made that car batteries are capable of more current for a short term, but the explosive power is from the build up of gas internally, if you are charging your cap up off the track supply, the gassing will still continue if reverse biased , it will build up slowly, but still likely to reach the point where it goes bang.

 

Before using them find out who the manufacturer is and ask the tech support if the device can be used for your application.

The big well known companies will reply, if you don't get a reply ,I wouldn't use that manufacturer.

Dont ask tech support at the sales outlet or distributor, their job is to sell to you,

 

Richard

[SHMD]

"Scale boiler explosion" anyone?

[richard-g8jvm]

May be if in a cast white metal body or brass, but loco destruction on a plastic body

Richard

[Crosland]

Sigh.

 

It doesn't take long with google to show that a three second soldering limit is nothing special, among quite ordinary components, and certainly not unique to supercapacitors.

 

It doesn't take long to see that the Rapid site includes links to the manufacturer data sheets.

 

I'll ignore the rest of the straw men.

 

Andrew

[richard-g8jvm]

Oh please get yours facts right

 

The Rapid site only has links to to manufacturers sites, you then have to search for data

 

It is very clear that you are one of those people that every list has , who has to nit pick his way though anyones posting to try and find fault..

 

May be you feel so insecure you have to try and prop up your self importance..

 

Sad really, If you like I could post the urls or some of the helplines you may find useful.

 

Richard

[Gordon H]

Oh please get yours facts right

 

The Rapid site only has links to to manufacturers sites, you then have to search for data

 

Don't know where you think you were looking, but I found plenty of data sheets for these at the Rapid site itself.

 

http://www.rapidonline.com/Electronic-Components/Samwha-High-Capacity-Condenser-Capacitors-519710

 

Perhaps you should get your own facts right before complaining too loudly.

[richard-g8jvm]

ONE PAGE SHORTFORM SPECIFICATION SHEETS !

R

[jdp298]

I think we've gotten into 'analysis-paralysis'. Too much worrying and over thinking. As model makers, do we not use rotary, unguarded machines that can cut our fingers off, knives sharper than the average kitchen carver, materials like white-metal with a high lead content, and all the time peering as close as we can? Letting a bit of the magic smoke out means you're actually trying something, which in and of itself is to be applauded.

 

We should be trying to help, not generating endless data and links. Pick out the right ones, suggest a way to use them, make it useful information and knowledge. At the moment we're not getting anywhere.

 

So, this circuit, with the right resistors, will work for 5.5V 1F cap. In fact you could have it shoreside on DC and it'd work, but we're talking stalling correction here.

 

 

It's a lot of components I grant you. There's probably a way to use a latching relay that does the remembering direction of travel for you and cuts down on the components but I didn't do that part of the design as someone else had used one and I was experimenting on something new.

[Captain Slough]

Mainline Peaks (class 45) have a LOT of space in them and all the power pickups are on the trailing wheelset

20 years ago I built a circuit that fitted inside one of them (using a mix of 1980s and 90s components, what I had to hand more than by design). In short..  3 small DPDT relays were wired across the traction power supply, one direct, the other two with a diode in series so only one of them would come on, depending on the direction of travel

 

The relay without the diode was connected so that if track power was intrrupted the power to the motor was switched from pickups to a PP3 9v battery. The other 2 relays were connected between the first relay and the motor and controlled the polarity of power from the battery

 

the clever part was each of the 2 directional control relays had a 100 microfarad capacitor across their coils which kept the correct direction engaged for about 10 seconds after the track power was lost.  If neither relay was under power there was no electrical route from the battery to the motor

 

End effect - if the power to the Cl45 through the rails was lost, first one relay clicks and connects battery to motor, after a few seconds the directional control relay drops out and the unit returns to track power.  Net effect was that it would jerk slightly and move forward a few inches. Could never make it run smoothly but it did tend to get through bad track sections, and was my unit of choice for dragging a Hornby track cleaning wagon.

 

Obvious downside was it wasnt possible to do an emergency stop if something got in its way, and starting it up meant 2 relays clicking into place, which also caused jerkiness

 

JDP298's circuit diagram above does essentially the same as my mechanical relay circuit but is much more elegant and should react faster thus causing less jerkiness

[Dagworth]

Mainline Peaks (class 45) have a LOT of space in them and all the power pickups are on the trailing wheelset

 

20 years ago I built a circuit that fitted inside one of them (using a mix of 1980s and 90s components, what I had to hand more than by design). In short..  3 small DPDT relays were wired across the traction power supply, one direct, the other two with a diode in series so only one of them would come on, depending on the direction of travel

 

The relay without the diode was connected so that if track power was intrrupted the power to the motor was switched from pickups to a PP3 9v battery. The other 2 relays were connected between the first relay and the motor and controlled the polarity of power from the battery

 

the clever part was each of the 2 directional control relays had a 100 microfarad capacitor across their coils which kept the correct direction engaged for about 10 seconds after the track power was lost.  If neither relay was under power there was no electrical route from the battery to the motor

 

End effect - if the power to the Cl45 through the rails was lost, first one relay clicks and connects battery to motor, after a few seconds the directional control relay drops out and the unit returns to track power.  Net effect was that it would jerk slightly and move forward a few inches. Could never make it run smoothly but it did tend to get through bad track sections, and was my unit of choice for dragging a Hornby track cleaning wagon.

 

Obvious downside was it wasnt possible to do an emergency stop if something got in its way, and starting it up meant 2 relays clicking into place, which also caused jerkiness

 

JDP298's circuit diagram above does essentially the same as my mechanical relay circuit but is much more elegant and should react faster thus causing less jerkiness

Whereas the circuit that I posted and proved in the topic I linked to way up the top of this thread does what you describe but much more elegantly and with variable speed options from the battery when traction power is lost, in that the loco will continue at approximately the speed it was doing when contact was lost and will gradually slow to a halt if power is not restored, whereas just using relays will result in full battery power being applied to the motor on loss of pickup power, and a dead stop when the relay drops as the cap discharges.

 

Andi

[Captain Slough]

Whereas the circuit that I posted and proved in the topic I linked to way up the top of this thread does what you describe but much more elegantly and with variable speed options from the battery when traction power is lost, in that the loco will continue at approximately the speed it was doing when contact was lost and will gradually slow to a halt if power is not restored, whereas just using relays will result in full battery power being applied to the motor on loss of pickup power, and a dead stop when the relay drops as the cap discharges.

 

Andi

 

i got a bit lost and baffled chasing thru the web of links....

 

I take it your circuit is the one with the latching relay? if so yes, congrats, thats clearly better.

I posted my remarks more as a relevant thing that may be of interest than from any desire to provide a better solution

 

Eventually I got fed up with the clicky, jumpy 'Peak' that was only any use for a track cleaning train and ripped out the relays, replacing them with a bridge rectifier and 7809 voltage regulator. Then when I needed the tracks cleaned I put it on there, light engine, and fed 50 volts AC to the rails. Worked a treat, like a psychotic and highly dangerous RELCO unit, one or two circuits of the line and the rails werent just clean but shiny.