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Batteries Or Super-Capacitors ?
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 Posted: Sun Mar 7th, 2021 06:46 am
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davecttr
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Rod Hutchinson wrote:
Helmut,

Is the input voltage to the Supercap from Track or Battery?


I imagine the power is from the track,
as if it was from a battery, there would be no 'dead spots' to worry about!

The idea is very interesting though, well worth watching.

There is also a topic on RMWeb,
where someone is experimenting with using supercaps in DC locos.

The only things on that diagram I understand are the RX6 and the 'Pololu'.







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 Posted: Sun Mar 7th, 2021 07:13 am
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Rod Hutchinson
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davecttr wrote:


" I imagine the power is from the track,
as if it was from a battery there would be no 'dead spots' to worry about! "


5v seems an unusual voltage. 

Is that normal for TT scale?

Rod




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 Posted: Sun Mar 7th, 2021 07:55 am
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fallen
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It looks to me as if the power for the RX6 receiver and motor comes,
either from the track if it is powered, via the 1N4001 diode at the top,
or from the supercap via the 'Polulu' if there is no track power.

There is no battery, just the supercap.


The 5v is because the max voltage the supercap will take is 5.5v
The 7805 regulator reduces the track voltage to 5v, to safely charge the supercap.

The 'Polulu' steps the 5v from the 7805 regulator and supercap, back up to 9v,
to feed the RX6 receiver and the motor.


An interesting idea, worth watching.
Must get some supercaps!


Frank


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 Posted: Sun Mar 7th, 2021 12:52 pm
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Helmut
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The track voltage is a constant 12 to 14V DC from a switch mode power supply,
or should you be so minded, 15V DCC.

In my case, I operate the RC locos together with the standard DCC on module meetings,
in order to be independent of tethered walkaround controllers and DCC address management.

The supercap's only function is to keep the loco alive at contact loss.

Battery operation is covered here




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 Posted: Sun Mar 7th, 2021 08:27 pm
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Rod Hutchinson
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Helmut wrote:  
The track voltage is a constant 12 to 14V DC from a switch mode power supply,
or should you be so minded, 15V DCC.

The supercap's only function is to keep the loco alive at contact loss.


I misread the circuit. 

On closer inspection it now makes more sense to me.




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 Posted: Mon Mar 8th, 2021 10:48 am
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Steve Soar
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Hi

I have done some further testing on the Poover PP3 Li-Ion battery,
the inbuilt protection circuit works well, and protects from over discharging. 

I have now simplified my circuit and omitted the ON/OFF switch.

So, a bridge-rectifier off the rails charges the battery (or supercaps),
the boost circuit is connected to the battery, and the 12v from the boost,
goes to the receiver, and then its output to the motor.

Charging is still the same on a powered section of track (I use 1 metre).  

The supercap version charges in a few seconds, 
the battery needs a few minutes depending on how big the circuit is,
then it gets a top up charge every time it runs on the charge track section.

I have now ordered some prototype PCBs,  
they measure 61 x 26 mm, and include the receiver.

Best wishes to all

Steve

:2t:


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 Posted: Mon Mar 8th, 2021 01:03 pm
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davecttr
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Supercaps would be better as they can recharge very quickly?

For example, one of my passenger locos at 60mph scale speed hauling a passenger train,
would only be in the 1 metre charge zone for 3 seconds per circuit.

The locos power requirement demands a 2-cell Li-Po battery and voltage booster.
Would this be difficult to achieve without 3 wires to balance charge?

Still utterly confused over this, but it appears four 2.5V 15F supercaps in series,
would have the  equivalent of about 10mAh and give 10V ?

The loco described above would need about 3mA per circuit?




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 Posted: Mon Mar 8th, 2021 03:09 pm
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Helmut
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A set of 4x15F supercaps in series, stores a charge of 37.5 Ampsec. @10V

Without a step-up regulator, the usable charge is much less than that,
because the voltage drops continuously with discharge.

Now let's assume you have one and its cutout voltage is 3V,
the usable charge would then be ~26 Ampsec,
which gives you roughly a running time of 100sec @ 200mA motor current,
and a COP of 0.8 for the step-up.

In order to recharge, you have to put these 26 Ampsec back in.

A charge current of 1A maximum is possible only at very good contact conditions.
Intermittent contact may cause some detrimental arcing on wheel treads.

So if you limit the charging current to 500mA,
you need ~ 1minute to top it up after a complete use of available charge.




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 Posted: Mon Mar 8th, 2021 04:21 pm
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davecttr
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Thanks for the clarification Helmut.

It looks like the idea won't work unless you pause on the powered track,
every circuit to give the caps time to recharge.

So no trains running around the continuous run,
while you are happily moving wagons in the freight yard.

It might be doable if you have say 4 trains that do one circuit in sequence.
For example

- long through freight
- express passenger
- local pickup freight
- local passenger

Each of the storage loops would need its own powered track?

Might be just as easy to fully charge the batteries before the running session,
which for me is up to 30 minutes run time per loco in a 2 to 3 hour period.




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 Posted: Mon Mar 8th, 2021 04:27 pm
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Helmut
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A supercap of ~1F suffices for the purpose it is ideally suited for:
Keep the loco running for up to say 1sec over a stretch without contact.

There you can keep recharge time short,
and space requirements for necessary components and circuitry are manageable.




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