Today’s Dumb Battery Question

[Ralphmp]

“If AA and AAA NiMh rechargeable batteries both have a nominal output voltage of 1.2 volts, what is the benefit of using AA over AAA?”

I’m sure the answer is obvious to experienced battery folk, but unfortunately not to me (other than the AA cells weigh more so can aidtr@ction).

Thanks

 

[JimmyB]

Current, amp power, i.e. real terms haw long the battery will last under the same usage, or how much it can drive.

 

[dunnyrail]

“If AA and AAA NiMh rechargeable batteries both have a nominal output voltage of 1.2 volts, what is the benefit of using AA over AAA?”

I’m sure the answer is obvious to experienced battery folk, but unfortunately not to me (other than the AA cells weigh more so can aidtr@ction).

Thanks

I would certainly stick to AA, but if you have space limitations AAA can get you out of problems at the cost of slightly less running time. My use of AAA has been with smaller locomotive conversions such as my Piko 25 tonner for example, here the difference in running time is not noticed between this and larger machines. Of course more AAA would give you higher top voltage if you felt the need.

 

[Ralphmp]

Current, amp power, i.e. real terms haw long the battery will last under the same usage, or how much it can drive.

OK, so is there any REALLY simple way I can work out likely running time for a single motor LGB Ballerina using AAA cells and AA cells? I apologise if this is another stupid question but having spent the past couple of days reading up on battery capacity, discharge rate, what other people have done, etc., there seems to be a large number of case studies that say "this is what works for me so this is what I'd do" without any clear indication of how the solution was devised in the first place. Please be assured, I'm not being critical here - I imagine the answer is so obvious that only a dimwit like me can't get there!

 

[Greg Elmassian]

amp hour capacity: for smaller batteries expressed in smaller units: mah, milli amp hours, 1/1000 of an amp hour.

AAA nimih are typically 800 mah or 0.8 amp hours, and AA nimih are typically about 1800 mah (there are MANY exxagerated claims for higher numbers)

from physics to move anything takes power over time or watts over time. (watt-hours)....

So you need to know how many watts your train takes. There is a simple way to do it, run your train and measure the amps and volts it takes... just try to get the average of running around a loop... say that is 1/2 amp at 12 volts..... (this is an example, lets not go nuts on this!)

Now that is 0.5 times 12 = 6 watts... (amps times volts)...

Your AAA battery is theoretically 0.8 watts for one hour (amp hours) at 1.2 volts

You want tor run a train for one hour, 6 watts for one hour is 6 watt hours... (simple watts per hour)

you want AAA batteries to supply 12 volts for one hour, you need 6 watt hours, ok, so 10 AAA in series is 10 * 1.2v = 12 volts

each battery is 0.8 watt hour, so 10 are 8 watt hours in that configuration. (10 times 0.8 watt hours).

So 10 AAA will give you 8 watt hours at 12 volts. go a bit slower and you can get you 5.6 watt hours with 7 batteries, i.e. you can run about an hour with 7 batteries.

It's not exact but will get you in the neighborhood only using what you measure on your loco and published specifications of volts and amp hours.

The major step is to measure the actual usage of your loco, the battery calculations are pretty easy.

Greg

warning: I have not had any coffee yet, so there may be some errors, so check my math... also note that AA are more than double the amp hours of AAA so your runtime will more than double.

 

[PhilP]

I agree with Greg, except I think he is being (slightly) pessimistic, about the capacity of AA cells..
The caveat being I use LSD (Low Self Discharge) cells.

Just think of the battery as a 'container' for the energy (fuel)..
The AA cell is a bigger 'tank' of 'fuel' for your loco.
Same as your car: bigger tank, longer range, before you have to fill the tank (recharge your battery).

PhilP

 

[Ralphmp]

Thanks guys - this helps me both understand and realise I was making things in my own mind much more complex than it actually is. I have data on amps used by the loco and I pretty sure that my Massoth kit puts 22V out to the tracks so I'll rework Greg's example with my info and see what comes out.

 

[PhilP]

Something else, if you are going battery:

How often do you run your loco's 'flat-out'?
Crudely speaking, if you only run with the controller turned half-way up, you are running at (roughly) 12V.
It is worth experimenting, as you can save weight (and money) but not 'over-batterying' your loco. - You also have the full-range of your speed control, rather than using only part of it.

PhilP

 

[Greg Elmassian]

I did the calculations on the "low" side of batteries, as I states many manufacturer/dealer claims are wildly exaggerated. The proof is to test yourself. Also LSD (low self discharge) nimih cells have less capacity as do the "regular" ones. I've tested many rechargables, the big names (samsung, sanyo, etc) tell the truth. The junk on ebay and amazon, not usually.

No implication of "flat out", maybe that is a response to the data on amps on the loco from the manufacturer.

1. The data is probably not accurate
2. it is probably some average
3. As PhilP states (effectively), you need to measure your voltage and current for YOUR running conditions.

I did say run it yourself and measure your voltage and current... that will give him his REAL usage data. Again, that is the key to this helping again as I clearly stated.

Now, you are talking DCC for the first time, you need to test this on DC, not DCC.... if you have a decoder in the loco and will keep it, you can measure this way, that would be best... also you almost certainly do not have an accurate DCC amp meter that can measure accurately down to tenths of an amp... without that precision, you are wasting your time.

Please ask more questions if I have not been clear...

Greg.

 

[Ralphmp]

Sorry, should have mentioned I do have a DCC decoder installed and will be keeping it. Also, I never run my locos past speed step 14.

I'm assuming that the decoder will need a constant supply voltage from batteries similar to what it receives via track power, so around 22V. To date, I have converted 2 dual motor LGB locos, both with decoders, and used battery packs with 16 NiMh AA cells. This appears to work fine (all decoder functions operate as expected - lights, sound, uncouplers) and I'm getting 3 or more hours' use of the locos from a full charge, which is fine for me.

Regarding the single motor Ballerina, the Amps data I was referring to is that shown on my Navigator when running the loco on track power with nothing else active (no lights, signals, other locos, etc.). This indicates the loco is using around 0.3 amps. So, if I plug my raw data into Greg's workings above, it seems a 16 cell AAA battery pack will give me around 12.8 watt hours and, as my loco appears to use 6.6 watts per hour, I should get just under 2 hours of continuous running.

By the same token, the calculations indicate a 16 cell NiMh AA pack would give about 4 hours of continuous running for the Ballerina and this extrapolates to the results I get with my twin motor locos.

So whilst I don't have the precision measuring tools needed to get the data needed to perform the calculations to a very high level of accuracy, I now do have an indication of the difference in likely run time between AAA and AA batteries that I was after.

Thanks for the help on this.

 

[dunnyrail]

My view is that you can try to over think this completely. You may get x hours running but as Phil says will it be flat out? Sound and DCC on can be sucking power but not entirely sure that will be in sync with thinking. So my view is, if you can get 12 AA quite high MaAh batteries fitted you may or may not get 6-7 hours out of a DCC G scale loco circumnavigating your line continuously. I defy anyone to prove me right or wrong on that.

 

[Greg Elmassian]

OK, need to answer another question... are you going to run this loco from DC, or are you going to add some remote control system....

For example, an R/C system that can output DCC to the decoder? In the USA we have AirWire, Crest Revolution, and other systems that will drive a DCC decoder IN DCC MODE.

Your post does not explicitly say, but IMPLIES that you are running DC, but then constant track power makes no sense.

So, in the 2 locos you have converted, what is powering the track and how do you control speed?

Greg

 

[Ralphmp]

My converted locos can run on either DCC track power (I use Massoth central station and Navigator handsets) or battery power (I use Fosworks components to interface with the Massoth decoder and an OMNI controller to operate them on battery power). A DPDT switch controls which power source feeds the decoder.

My reason for the original question about AAA cells is that I’m finding it a bit challenging trying to squeeze in all the necessary components to do the same type of conversion into my Ballerina. My thinking was that by using AAA instead of AA I could create more space and simplify the overall installation, however I wanted to understand the trade-off between saving space and reduced capability when running on batteries.

Thanks to the help from Philp and yourself I now have a better grasp on this trade-off and can more confidently decide how to proceed.

 

[JimmyB]

My converted locos can run on either DCC track power (I use Massoth central station and Navigator handsets) or battery power (I use Fosworks components to interface with the Massoth decoder and an OMNI controller to operate them on battery power). A DPDT switch controls which power source feeds the decoder.

My reason for the original question about AAA cells is that I’m finding it a bit challenging trying to squeeze in all the necessary components to do the same type of conversion into my Ballerina. My thinking was that by using AAA instead of AA I could create more space and simplify the overall installation, however I wanted to understand the trade-off between saving space and reduced capability when running on batteries.

Thanks to the help from Philp and yourself I now have a better grasp on this trade-off and can more confidently decide how to proceed.

When space is a premium, lithium will give you "more bang for your buck", but if you are already set up for NiMH batteries then it would mean having two different set ups.

 

[Ralphmp]

When space is a premium, lithium will give you "more bang for your buck", but if you are already set up for NiMH batteries then it would mean having two different set ups.

I did wonder about a lithium experiment - I guess the electronics don’t care where the power comes from as long as it meets the necessary “specs”? - and if I can’t figure out how to cram everything in using NiMh I may go down that route.

Biggest concern is I would need to invest in another battery charger (the one I have is NiMh only) and I suspect a multi battery-type charger won’t be cheap.

 

[PhilP]

I suspect you would find 12 x AA (14.4V) would be adequate for your needs..

That would be 4-cells less, to find the space for.

Worth mocking something up, and trying it?

PhilP

 

[Ralphmp]

I suspect you would find 12 x AA (14.4V) would be adequate for your needs..

That would be 4-cells less, to find the space for.

Worth mocking something up, and trying it?

PhilP

I’ve already mocked up 16 AA cells and have found one possible way to fit everything in, but that solution relies on having the battery pack “suspended “ from the top of the boiler right above the decoder and DCC interface board, and I can’t help worrying about what would happen if it broke loose and dropped onto the two boards!

I will try a 12 cell mock up - only concern is will it deliver enough oomph to drive my uncouplers? These are attached to the +22v outputs from the XLS board and the Massoth manual indicates they should have full track power to work correctly. It may be the 16 cell pack would also be insufficient to drive them in which case I guess it’s time for a lithium experiment. Know anyone who can advise on this?

 

[PhilP]

With Lithium, you would be looking at 5-cells (which is a little less commonly available).
You would also need a charger, possibly something like an Imex B6 (you would, most likely, end-up with a 'clone', but they seem OK).

You can get Li-ion cells, in the same physical size, as AA (known as 14500) but I think you would be better with the larger 18650 cells. - If you didn't know, the numbers give you the physical size of the cells:
14500 are 14mm diameter, 50mm long
18650 are 18mm diameter, 65mm long.

PhilP

 

[dunnyrail]

It should also be said that it is not good practice to leave Lithium Cells charging and go away and forget them. I would go for as many AAA as you can and ditch the Auto Uncoupling's, at best (IMHO) a gimmick add on.

 

[JimmyB]

It should also be said that it is not good practice to leave Lithium Cells charging and go away and forget them.

I would agree, but we all do it with toothbrushes, phones, and even leaving laptops plugged in. As far as my locos are concerned, I may leave the room, but never the building whilst charging.