Battery Pack Selection

[Elmtree Line]

I am looking to convert my USA diesels to battery operation, the battery pack would be housed in a boxcar behind the loco so space is not a real concern.

The loco's draw 1-2 amps, they are known to be amp hungry.
Current would have to be 18 or 20volts.

Can anyone suggest what sort of rechargeable battery would be up to the job, I know some are fast drain, others slow, others won't provide the ampage.

I have looked around and its a bit of a minefield.

 

[nicebutdim]

I was just about to start a thread about batteries, I was checking all the old posts to ensure I wasn't asking a same question!!!! If it is ok, I would like to add a quick question to this thread?
I'm running sub c packs that I made up myself from old tamiya packs (all matching mAh) and have noticed I can get the same capacity in aa size. What is the difference except for size? Why have 2800mAh sub c size and 2800mAh aa size?
Tim

 

[Westcott]

My Bachmann Annie runs off 2 x 9.6V 2600mAh AA packs, £11 - £12 per pack
http://shop.ebay.co.uk/i.html?_nkw=2600mah+9.6v < Link To 9.6V battery packs on Ebay

If you are happy to buy from China/Hong Kong, I've seen 7.2V 5000 mAh packs for a similar price.
You might also consider a single 22.2V 5200mAh 20C LiPo pack for about £30.

 

[steven large]

I am looking to convert my USA diesels to battery operation, the battery pack would be housed in a boxcar behind the loco so space is not a real concern.

The loco's draw 1-2 amps, they are known to be amp hungry.
Current would have to be 18 or 20volts.

Can anyone suggest what sort of rechargeable battery would be up to the job, I know some are fast drain, others slow, others won't provide the ampage.

I have looked around and its a bit of a minefield.

mr spockie is the expert in radio controlled..drop him a line..wink

 

[gregh]

Sorry if this is a bit technical, but maybe the background can help you out of the minefield.

Before you start selecting batteries, can I suggest you get yourself a multimeter, with a 10A scale.
Put a typical load on your train and measure the actual current being taken and somehow try to average this over your run. I know thats a bit unscientific, but you can watch your meter's max and mins and guess at the average.

Then select your max speed that you want to run at and measure the voltage on the track near the loco. I'd be surprised if it's more than 15V. I've never found I need more than 10 NiMH cells or around 15V. Remember that track power sometimes seem to need higher voltages because of the voltage drop from controller to train. There's none of that drop with a battery loco.
You don't say what type of controller you plan to use.

Now you can start selecting batteries.
NiMH are fine - just see the comments further down about their reducing capacity at high loads. I have 14 locos with NiMH batteries ranging from 700 mAh to 2400 mAh, in connections of from 4 to 12 cells.
LiPo are even better, just remember to use the special charger AND you need an undervoltage shut off in the loco. If you overcharge them beyond 4.3V/cell they catch fire. If you discharge below about 3.3V/cell they are DEAD FOREVER.

Voltage....
If you go for NiMH, just divide the required voltage by 1.2 to get the number of cells. (NiMH will be about 1.3V/cell when charged and 1.2V/cell when discharged - but this depends on the current you are drawing.)
If you go for LiPo, you have to select in multiples of 3.7V. eg They are referred to as 3S for 3 in series.

Capacity......
Theoretically you just multiply the average current by the hours you want to run and that gives you the mAh capacity of the battery.
But batteries, especially NiMH aren't all that efficient so you need to 'add a bit more mAh'. How big that 'bit more' is depends on the ratio of the battery capacity to current draw. There's no mathematical equation that I know of for it.

If you're drawing a current equal to the capacity, theory says you get one hour running. But more likely only 1/2 to 3/4. If you're only drawing 1/3 of the capacity, you'll get probably 2 1/2 hours, instead of the theory 3 hrs.

My recommendation would be that you need a capacity (mAh) at least twice the current draw. That should give you more than 1 hours running time, maybe 1 1/2. Go to a capacity of three time the current and you'll be getting closer to 3 hours running time. So let's say your average is 1.5 A. Go for a MINIMUM 3000 mAh battery.
None of the above really applies to LiPo. You can have a 500 mAh battery and still take 3 amps from it with no loss of capacity. (but it will only run for 10 mins)

Other considerations....
While we usually talk about capacily in mAh, it's really the energy stored that's important. This is just the product of the capacity (mAh) times the voltage, measured in watt-hours.
Now if you have a PWM type controller, you can use a higher voltage battery than you need and you will get a longer run time, than the straight mAh/mA would suggest. The PWM controller acts like a transformer.
Lets say you've decided on a 3000 mAh, 24V battery, but you only run your loco at 16V and it takes 1.5A. The loco is using 1.5A x 16V = 24 watts. The battery has a capacity of 3A x 24V=72 watt-hours. So the loco will run for 72/24=3 hours, instead of the 2 hours the 3000mAh/1.5A would suggest.
If you don't have a PWM controller and just connect the battery to the loco motor, it will zoom around at 24V, for 2 hours. Using a resistor or transistor controller (not PWM) to slow it down will still only give you 2 hours (slower) running.

 

[gregh]

After writing my previous response I thought maybe I'd better give a few more practical recommendations.

To start, my webpage here has some info on my experience....
http://www.members.optusnet.com.au/satr/battery.htm < Link To http://www.members.optusn..com.au/satr/battery.htm

But I'd just suggest you buy some 2400 mAh NiMH cells, stick them in a holder and give them a go.

Now some pros and cons...

NiMH
are heavier than LiPo - could be an issue in a trailing battery car.
Have short shelf life - quoted as losing 10% of charge per week, so you need to recharge the day before you run. Latest 'LS' types may be better. I have bought some but not used yet.
Are better for 'tailoring' your voltage to suit. Just choose the number of cells you want and buy a holder to put them in (or solder them yourself)
Can be charged in 3 hours but this shortens their life. I alway charge overnight at about 1/10 of capacity.
The higher the current you take out, the less the capacity is.

LiPo
Cell voltage is nominal 3.7V (4.2V charged) so less scope for choosing the exact voltage you need.
Have unbelievable current supply capability. They are made for model aircraft fliers who take 50A for 15 minutes and then recharge in another 15 minutes! Our applications are a piece of cake.
Are much lighter than NiMH
Retain their charge for months and months. Just grab your loco off the shelf and go!
Can be recharged 'slowly' and 'safely' in a couple of hours.
You need a special charger to ensure they don't overcharge and catch fire. Plenty of horrific stories but actually no problem for our low current usage.


Here's a 5000 mAh LiPo battery for only 40USD ex Germany.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11024 < Link To http://www.hobbyking.com/...em.asp?idProduct=11024

or a 3000 mAh for 30USD
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10189 < Link To http://www.hobbyking.com/...em.asp?idProduct=10189

and here's a suitable LiPo charger for 23USD: (you'll need a 240V/12VDC plugpack too.)
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7028 < Link To http://www.hobbyking.com/...tem.asp?idProduct=7028

For completeness, I've added my comments on lead-acid types here:
HEAVY - about 3 times as heavy as NiMH and five times LiPo. Not good for trailing battery cars.
BIG - for similar capacity, twice as big as NiMH and 3 times LiPo.
Cannot be fully discharged without damaging (my reason for replacing). Lead-acid are not meant to be deep cycled, so a given Ah rating cannot be achieved. ie my 7Ah battery was really only 5 Ah.
Have good charge retention - mine lasted for 6 months without charging.
Are easy and forgiving to charge.

 

[jetomlin]

Don't disregard a sealed Lead Acid battery...Maplins sell both 12v and 6 volt types I have both running on my railway and perform very well!The 12v can be charged by my car battery charger!
They will fit in a following van or in the case of my Caledonia, I added a coal bunker to house the 6volt battery!

 

[Doug]

I run a USA trains power block in my boxcab. It has 9 subC cells, each are 4300mAh. I get about 4 or 5 hours run out of them (normally get bored before then) running about 30 axles trains. Runs at a reasonable speed, a couple more cells would give you a very good speed.

 

[gregh]

Don't disregard a sealed Lead Acid battery...Maplins sell both 12v and 6 volt types I have both running on my railway and perform very well!The 12v can be charged by my car battery charger!
They will fit in a following van or in the case of my Caledonia, I added a coal bunker to house the 6volt battery!

Good point, I neglected mentioning Pb-acid.
I started off with them 10 years ago in 2 locos but have replaced with NiMH (1) and LiPo (1). They were the cheapest available then. But not now.
So I've added my comments on them by editing my previous post - that keeps everything together.

However. Select a Lithium ION or LI fe type for greater safety.

Sorry ROSS, we'll have to agree to disagree. My friends have been using LiPo in aircraft for 10 years and trains for five. LiPO are just fine if treated properly.

 

[Del Tapparo]

Greg - Excellent job on explaining things! (But please folks, don't forget get to invert Greg's results by 180 degrees if you live north of the equator )

 

[whatlep]

Greg - Excellent job on explaining things! (But please folks, don't forget get to invert Greg's results by 180 degrees if you live north of the equator )

I can't add much to Greg's splendid explanation, other than to say his calculations certainly correspond with my newly-earned appreciation of battery power this year. Even with my awful 1 in 20 (5%) gradient, 10 cells at nominal 12 volts has been fine (remember, battery locos have no skates or power "bullets" acting as brakes!). Ten 2100mAh cells have permitted me to run an LGB Schoema with an extra 1Kg of weight, hauling a standard LGB van as battery trail car plus 7 LGB hoppers for 3.5 hours non-stop. Up and down that 1 in 20 slope, round radius 1 180 degree curves at each end of the line, no problems at all.

One small point. I strongly recommend that you go for low self-discharge (LSD) NiMH batteries rather than ordinary NiMH cells. Uniross Hybrio or Sony Eneloop seem to be the most common brands in the UK, though make sure that you get the 2100mAh type, not the 700-800mAh ones which are sold temptingly cheaply on eBay and Amazon. Over 6-8 weeks the amount of discharge appears to be negligible: that 3.5 hour run came after my cells had been sat charged on a shelf for well over a month. By contrast, when I tried to use my (theoretically) more powerful 2600mAh conventional NiMH cells after a similar fallow period, they had virtually no power at all. OK, if you are organised and a regular battery user, you'd probably have cells more commonly available. However, for those of us who get the sudden chance of an unplanned 10 minute running session, the LSD batteries are manna from heaven, albeit at extra cost.

 

[gregh]

Greg - Excellent job on explaining things! (But please folks, don't forget get to invert Greg's results by 180 degrees if you live north of the equator )

Thanks Del. I'll be in Ft Collins in a couple of months and hope to see you again.

I can't add much to Greg's splendid explanation, other than to say his calculations certainly correspond with my newly-earned appreciation of battery power this year. ..

One small point. I strongly recommend that you go for low self-discharge (LSD) NiMH batteries rather than ordinary NiMH cells. ....

Nice to hear you have the same ballpark results, Whatlep. I agree about LSD types, now that they are available. It is the main drawback of NiMH. I've bought a set of LS types from Hobbyking and have them sitting on the shelf 'testing' before I instal.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10456 < Link To http://www.hobbyking.com/...em.asp?idProduct=10456