Battery powered/Radio controlled locos

[davetheroad]

Ah, I hadn't spotted that one!

Did you spot my reply "good point about power requirements" !.

 

I suggest everyone checks out emerging battery technologies and then we can speculate about what battery capacity/recharge times will be potentially available in a few years time.

 

If all these news reports are to be believed a typical 1000mAh mobile phone battery will be rechargeable in a very short time, presumably without exploding the phone and burning the house down.

[Robin2]

 I personally hope that the technology can be miniaturised for use in the smaller scales in the future.

How much smaller do you want it? Earlier posts here have shown that N-Gauge BPR/C is perfectly feasible now.

 

 

The "Just by improving technology, we should be able to recharge a 3 Amp hour battery in one minute" really got to me.

But let's not dismiss the whole concept just because there are occasional misguided expectations.

 

That sort of statement is an opportunity for you to explain things to the poster.

 

...R

Edited November 8, 2014 by Robin2

[davetheroad]

How much smaller do you want it? Earlier posts here have shown that N-Gauge BPR/C is perfectly feasible now.

 

 

But let's not dismiss the whole concept just because there are occasional misguided expectations.

 

That sort of statement is an opportunity for you to explain things to the poster.

 

...R

Indeed, much better than giving a 'lecture' in an apparent attempt to rubbish the whole topic.

 

Back to that 3000mAh battery. Using my 0.3amp Eflite charger it would take 10 hours to recharge that battery. If i had a 3amp charger It may recharge in 1 hour. That would power my locomotive for 14 hours which would last for up to a year for my loco use. Using 3 amps to charge a 3amp battery should be no problem as that is only '1C'. Rates of at least 2C or 3C are possible with the latest batteries so we could be recharging in say 30 minutes with a 6amp charger.

 

Actually my charger has 4 independant charging circuits so if I used 4 x 750mAh batteries connected in parrallel I could recharge in 2.5 hours

at 1C and 1.25 hours at 2C.

 

Apparently some new battery technologies use different materials which give more efficient chemical reactions which generate less heat, allowing faster recharge rates.

 

Other technologies claim to recharge a phone battery to 70% in 2 minutes. That is 700mAh for a typical battery. That would give me over 3 hours use. If I used 4 batteries in parrallel I am up to over 12 hours use with a 2 minutes charge by using 4 chargers.

 

OK, it is not a sub minute recharge but getting pretty close!

[Simond]

Do be a little careful - AFAIK the multi channel "balancing" chargers are intended for cells in series, and may cause short circuits if connected to a battery comprising parallel connected cells.

 

Charge rates should be specified in the cell documentation, do not exceed them, and monitor the cell temperature whilst charging.

 

For those not familiar with the term "C-rate", it is the ratio of the current through the cell (charge or discharge) to its capacity, thus a 2Ah cell supplying 4A current is being discharged at 2C.

 

Best

Simon

[raymw]

If you have a 1Ah battery, and can charge it in one minute, you'll need a connector capable of carrying 60A, and most likely some interlocking to prevent disconnecting when charge current flowing.

[davetheroad]

Do be a little careful - AFAIK the multi channel "balancing" chargers are intended for cells in series, and may cause short circuits if connected to a battery comprising parallel connected cells.

 

Charge rates should be specified in the cell documentation, do not exceed them, and monitor the cell temperature whilst charging.

 

For those not familiar with the term "C-rate", it is the ratio of the current through the cell (charge or discharge) to its capacity, thus a 2Ah cell supplying 4A current is being discharged at 2C.

 

Best

Simon

True but my eflite charger is only suitable for single cell lipos. I can recharge 4 single cells at the same time and the charger will be using a maximum of 1.2 amps or 4 x 0.3 amps. Plug those recharged batteries into the appropriate wire harness and you have a 1S 4P battery pack.

 

i actually use a series wiring harness so 3 batteries gives me 11.1V with a 3S 'battery'

[davetheroad]

If you have a 1Ah battery, and can charge it in one minute, you'll need a connector capable of carrying 60A, and most likely some interlocking to prevent disconnecting when charge current flowing.

Interesting figures when some innovators are claiming that you can recharge a typical phone battery to 70% in 2 minutes. That is 21Amps and the normal ring main socket is 13amp? The figures don't add up.

 

Sub minute recharges are not needed for model trains anyway. Fifteen or thirty minutes is fine which would only need 4 amps?

[Simond]

You can easily get 21A or indeed, a great deal more, from the 240V13A mains, provided you have a transformer to reduce the voltage.

 

If you don't know what you're doing, don't play with it.

 

Anyone attempting to charge a lipo at 60C will get a surprise, probably a dangerous and nasty one.

 

Best

Simon

[davetheroad]

You can easily get 21A or indeed, a great deal more, from the 240V13A mains, provided you have a transformer to reduce the voltage.

 

If you don't know what you're doing, don't play with it.

 

Anyone attempting to charge a lipo at 60C will get a surprise, probably a dangerous and nasty one.

 

Best

Simon

I have no intention of 'playing with it'. as i wrote elsewhere i will only be using commercial products. Maybe in the future there will be products that can recharge 1000mAh in a couple of minutes. Meanwhile my modest requirements of no more than a 500mAh battery can be met with existing equipment.

 

The other part of the requirement, 'remote' control is already doable in 00 scale and even 'N' if you have the fingers and eyesight to handle it!

[Andy Reichert]

Interesting figures when some innovators are claiming that you can recharge a typical phone battery to 70% in 2 minutes. That is 21Amps and the normal ring main socket is 13amp? The figures don't add up.

 

Sub minute recharges are not needed for model trains anyway. Fifteen or thirty minutes is fine which would only need 4 amps?

 

You've also missed the voltage part part of the power requirements.

 

If we assume the motors used in battery remote control remain the traditional 12 V dc type, and the battery cell used are simply connected in series to also supply 12v, then the charging power is a little over 12 volts times the charging amps.

 

If you charged, even momentarily at 2 amps, you are putting roughly 25 Watts into the battery compartment, assuming 100% efficiency. (which it isn't) .

 

I don't know if you've tried holding your hand around a 25 Watt light bulb, while it's on, but the heat going into your small 00 or N scale locomotive, with nice, meltable plastic body and parts, will be the same.

 

It's possible that the "new" technology will cause all "model trains" to end up with 3V or even 1.5 volt motors, just for this reason. But I don't see that incompatibility with existing models happening very quickly. And low voltage motors will use more current when they are running.

 

Andy

[fallen]

If you charge your LiPo at 2 amps and it is still charging, ie absorbing the charge and storing it, then the energy goes into the chemistry not heat and it does not get hot. If it reaches full charge and so can't absorb any more, then it gets very hot very quickly. So not overheating the battery depends on the charger detecting that the battery is fully charged and switching off in time. If the current is high it has to be very precise and very fast. If the current is low it is not so critical. Moral - charge slowly.

 

Incidentally, many modern locos already have motors that work very well on much less than 12 volts, so the system can run with a single cell or only two cells, not three. This reduces the space required. And they also take much less current as they are more efficient, which again reduces the space required for the battery.

 

Frank

[davetheroad]

You've also missed the voltage part part of the power requirements.

 

If we assume the motors used in battery remote control remain the traditional 12 V dc type, and the battery cell used are simply connected in series to also supply 12v, then the charging power is a little over 12 volts times the charging amps.

 

If you charged, even momentarily at 2 amps, you are putting roughly 25 Watts into the battery compartment, assuming 100% efficiency. (which it isn't) .

 

I don't know if you've tried holding your hand around a 25 Watt light bulb, while it's on, but the heat going into your small 00 or N scale locomotive, with nice, meltable plastic body and parts, will be the same.

 

It's possible that the "new" technology will cause all "model trains" to end up with 3V or even 1.5 volt motors, just for this reason. But I don't see that incompatibility with existing models happening very quickly. And low voltage motors will use more current when they are running.

 

Andy

none of my locos so far use anywhere near 2 Amps. The most power hungry is 0.17 amps and some are near 0.1 amps, even pulling a normal length train. Some of the locos use a 3S battery configuration with up to 3 x 220mAh batteries connected in series. The charger can charge 4 of those without problem at less than 1C. the charger even handles little 70mah batteries which is theoretically 4C but the batteries and charger are designed for each other with the same micro connector. The battery plugs into the charger, the red light goes on, some time later it starts blinking. When the blinking stops the battery is at 4.2V.

[davetheroad]

If you charge your LiPo at 2 amps and it is still charging, ie absorbing the charge and storing it, then the energy goes into the chemistry not heat and it does not get hot. If it reaches full charge and so can't absorb any more, then it gets very hot very quickly. So not overheating the battery depends on the charger detecting that the battery is fully charged and switching off in time. If the current is high it has to be very precise and very fast. If the current is low it is not so critical. Moral - charge slowly.

 

Incidentally, many modern locos already have motors that work very well on much less than 12 volts, so the system can run with a single cell or only two cells, not three. This reduces the space required. And they also take much less current as they are more efficient, which again reduces the space required for the battery.

 

Frank

Luckily my steam era freight locos don't need to go any faster than a scale 40mph so i find that a 2S 7.4V battery works fine. I was surprised to find my Bachmann 3F 0-6-0 freight loco would pull its expected maximum load at scale 35mph for over 40 minutes with 2 x 70mAh batteries. that is less than 0.1Amps. The 3S batteries are for the passenger locos where i have a minimum scale 60mph speed requirement.

[billbedford]

It's possible that the "new" technology will cause all "model trains" to end up with 3V or even 1.5 volt motors, just for this reason. But I don't see that incompatibility with existing models happening very quickly. And low voltage motors will use more current when they are running.

 

Or even use a regulator that gives 12v output with a 3.7v input.....

[raymw]

Maybe it would be worth while having a read of this http://en.wikipedia.org/wiki/Lithium_polymer_battery

 

With today's lipo batteries, there are chemical limitations to fast charging, but super caps? http://cleantechnica.com/2014/11/07/energy-storage-slam-dunk-graphene-carbon-nanotubes/

 

Lipo's voltage tails off as it discharges, so ideally you need a voltage regulator. May as well get one that boosts (micrel make 2A chips with 98% efficiency, iirc, for example http://micrel.com/_PDF/mic2601.pdf). In that case a standard 12V motor will run fine on a single lipo cell.

 

However, if you want a fast charge, you need heavy currents, and connectors to match.

[davetheroad]

I now have a layout of sorts on which to run my BPRC locos, Pengarigg by name and totally wire free, honest!. I am now buying receivers and buying rolling stock etc etc.

 

I have spent many hours thinking about the run time needed for the locos and worrying about battery capacity. I need many hours between recharges don't I? No i don't!, thinking about how I 'play trains' reveals that in a typical operating session a loco is unlikely to run for more than about 15-20 minutes. By standardising on small single cell micro 'Eflite' type batteries plugged into a 2S or 3S harness I can just pop the batteries on the charger after running the loco. No need for balance charging and no worry about batteries becoming unbalanced during discharge as they will still have 40%-50% of their charge left. No need for complex accounting and book keeping either.

 

These little lipos are available in several capacities up to 220mAh, all with same connector, a larger connector gives capacities up to 550mAh. My Eflite charger has 4 independant charging sockets, each delivering 300mAh.

 

i have started endurance testing the locos under typical loads and to avoid terminal boredom as the train goes round and round and........!. i have bought some little 70mAh batteries. theoretically one of these will provide 1Amp for 4.2 minutes. the results can then be scaled up for larger capacities.

 

Summery of the first few tests are:

 

1 - Hornby Midland compund 4-4-0 Railroad range second hand

2S 70mAh battery 7.4 volt

load 8x Hornby Railroad Mk1 coaches

test speed 60mph

result - loco started slowing after 42 minutes

top speed was 66mph

loco draws approx 0.1amps under normal operating load

 

2 - Hornby Railroad Duke of Gloucester 4-6-2

3S 70mAh battery 11.1 volt

load 9X Railroad Mk1 coaches, 2x Dapol LMS coaches, 1x 12 wheel dining car

test speed 60mph

result - loco started slowing after 25 minutes

top speed was 78mph

loco draws 0.17amps under normal operating load

 

3 - Hornby Railroad 'Jinty' 0-6-0 second hand

2S 70mah battery 7.4 volt

load 2x Railroad Mk1 and 1 open wagon (to carry the battery)

test speed 30mph

result - loco started slowing after 37 minutes

top speed was 52mph

loco draws 0.12amps under normal operating load

 

4 - Bachmann 3F 0-6-0 tender loco

2S 70mAh battery 7.4volt

load 4x railroad mk1 coaches

test speed 35mph (loco normally hauls freight)

result - test abandoned after 50 mins due to boredom!

top speed was 47mph

loco draws 0.085amps

ps the loco will haul 9X railroad Mk1 without any problem.

 

I find these results very good, especially that Bahmann 3F.. There will be no problem with any of the locos reaching their run times. The3F would be happy with the 70mAh batteries but they are just for testing and a set of say 160mAh is cheaper to buy!.

 

Only 12 more locos to go -so far.

Another 2 locos tested, First bought second hand and had to rebend the coupling rods etc to make it work properly. The tender needed the application of a hacksaw to get rid of the tender drive mountings.

 

5 - Hornby Railroad Illustrious Patriot 4-6-0

3S 70mAh battery 11.1 volt

load 8X Railroad Mk1 coaches, 1x Dapol LMS coach (test rig)

test speed 60mph

result - loco started slowing after 28 minutes

top speed was 78mph

loco draws 0.15amps under normal operating load

 

6 - Hornby Duchess of Gloucester 4-6-2 (the blue engine)

3S 70mAh battery 11.1 volt

load 9X Railroad Mk1 coaches, 2x Dapol LMS coaches, 1x 12 wheel dining car

test speed 60mph

result - loco started slowing after 25 minutes

top speed was 94mph

loco draws 0.15amps under normal operating load

[Simond]

Please remember that the cells have an internal resistance (impedance) and the heating of them (in Watts) is this impedance (in Ohms) multiplied by the current (in Amps) squared. Typical impedances are between 10 and 50 milliohms per cell, but may be outside this range. Doubling the current will thus increase the heat generated by four times.

 

It is simply NOT TRUE to say that Lithium batteries don't generate heat during charging, or only at the end of charge. The ohmic heating occurs whenever a current is flowing through the cell. Please be careful about comments like this - someone may misinterpret, and end up with a melted model, or worse. Just about every commercially available power tool battery has a temperature sensor built in, specifically to prevent overheating during charging. Some power tools also monitor temperature during discharge too, and will inhibit use if the temperature rise is significant. Models rarely have this level of protection.

 

Hot is a relative term. The electrolyte in lithium cells starts to degrade at temperatures as low as 50C. This is likely to only result in reduced life expectancy (of the cell...), but as temperatures rise above 70C, things are likely to become considerably more exciting.

 

Lithium batteries are very useful, but as potent energy stores, they need to be treated with appropriate care and respect.

 

Simon

[StuartM]

Well said Simon,

[davetheroad]

Please remember that the cells have an internal resistance (impedance) and the heating of them (in Watts) is this impedance (in Ohms) multiplied by the current (in Amps) squared. Typical impedances are between 10 and 50 milliohms per cell, but may be outside this range. Doubling the current will thus increase the heat generated by four times.

 

It is simply NOT TRUE to say that Lithium batteries don't generate heat during charging, or only at the end of charge. The ohmic heating occurs whenever a current is flowing through the cell. Please be careful about comments like this - someone may misinterpret, and end up with a melted model, or worse. Just about every commercially available power tool battery has a temperature sensor built in, specifically to prevent overheating during charging. Some power tools also monitor temperature during discharge too, and will inhibit use if the temperature rise is significant. Models rarely have this level of protection.

 

Hot is a relative term. The electrolyte in lithium cells starts to degrade at temperatures as low as 50C. This is likely to only result in reduced life expectancy (of the cell...), but as temperatures rise above 70C, things are likely to become considerably more exciting.

 

Lithium batteries are very useful, but as potent energy stores, they need to be treated with appropriate care and respect.

 

Simon

I agree, use only well known branded chargers and FOLLOW THE INSTRUCTIONS

 

Now i am confused. If my battery has an internal resistance of 50 milliohms and i use a 0.3amp charger there will be 0.015 watts of heating?

 

hardly enough to worry about maybe!.

[raymw]

no, it's less than what you said - it's I*I *R for power.

Edited November 12, 2014 by raymw

[Simond]

Dave

 

If your charger is limited to 0.3A, and if your cell has an impedance of 50 mO, then the heating effect would be 0.3 x 0.3 x 0.05 W which is 0.0045W, which, as you say, is unlikely to cause a problem, particularly if your charger is voltage sensing, and switches from Constant Current to Constant Voltage at an appropriate voltage level (probably around 4.2 V but dependent on cell chemistry), and even more so if the cell is sitting on a tray on your workbench. If it's inside your loco, with no convective airflow, it might get mildly warm, even with this limited heating effect.

 

There are suggestions on this thread of "charging in a minute" which implies absurd currents, and you earlier suggested using a 3A charger to charge a 3000mAh (=3Ah) battery at 1C, in one hour, which is not unrealistic, provided you monitor the temperature.

 

The heating effect at 3A on the same cell would be 3 x 3 x 0.05 = 0.45W which is still quite low, but at this point, you will find an appreciable temperature rise, particularly over an hour, and with the cell in closed container such as a loco body. Will it get to 50C or above? You would need to check preferably with a grain-of-wheat bulb or a resistor rather than a cell. Does your charger have a temperature sensing connection? It may, but I doubt it.

 

If you again increased the charging current - let's say a relatively mild 2C, you would then be putting 6 x 6 x 0.05 = 1.8W into your loco. It might get hot enough to cause problems in around a quarter of the time, but your charge time has only reduced by half.

 

There are cells that will accept C rates above 10, but in all cases, performance is limited & controlled to ensure safe temperatures are maintained.

 

HTH

Simon

[davetheroad]

Thanks Simon, lots of useful information there.

 

My E-flite charger has 4 independant charging circuits, each capable of 0.3 amps. I simply plug in a compatible battery and a red light goes on, eventually the light starts blinking and the 'blinks' gradually get longer until the light is only occassionly blinking on. Remove the battery and test it and it is 4.2V. I guess it is doing the job properly.

 

At the moment I only use small E-flite compatible batteries connected in series and the batteries are recharged when they are no more than 60-70% depleted.

 

For the little tank engine i was hoping to use a voltage regulator and parallel connected batteries permanently installed with a 440 mAh capacity. I will take your advice about heating into consideration. i could pop the body off and stick it in front of a fan?

[Andy Reichert]

If charging from the track, then the intelligent charging regulation and limitation has to be in each (and every) loco.

 

if not, then every loco has to have a charging plug and cable, or a removable battery and some sort of way to access and remove/replace it.

 

Andy

[fallen]

Andy,

 

I charge in the loco with a small charging socket usually mounted under the loco out of sight. I arrange the switch so it switches the battery between the radio chip ("on") and the socket ("off/charge"). I charge at about 1C and as I don't run the cells fully down it takes less than an hour to charge, sometimes less than half an hour depending on the state of discharge. I charge after I have used the locos and they are ready to go next time. Works for me!

 

Frank

[Rabs]

The hardware for charge management is very small, particularly if the supply voltage to the tracks is regulated to 4.2V.  Basically you need a BMIC and a back to back FET package.  These can be as small as about 1mmx1mm each.  If the track voltage available is 12V or DCC then you also need a rectifier (already in the circuit somewhere) and a regulator, so add another 1mm^2 for a linear or ~2.5mm^2 for a switch mode. 

It's not an easy hobby solution, but it would be very achievable if someone like Deltang wanted to add the functionality into their receivers.

Edited November 13, 2014 by Rabs