Large Scale Central

Batteries 101

Electronics Power and Sound
#1

OK so some battery theory needed. Lets just say I want to operate a small loco at 7-8v. Light load very small loco, nothing but the motor and a LED light. This will be operated by an R/C unit and battery power.

Now producing 7.4v with rechargeable Lithium Ion batteries seems easy enough. At 3.7v each it would take two in series to produce 7.4v correct? This would be the right voltage. To achieve this I could use two aaa size lithium ion batteries. That just doesn’t seem like enough. Am I missing something like amps. Does amp hours or miliamp hours increase with size of battery?

Someone explain batteries to me.

#2

Milli Amp Hours. MaH

I have 5600 MaH lithiom batteries in my K-27 and have had it running all day without a recharge.

Now don’t ask me to explain what Mah’s are, I have no idea, but there’s plenty of guys on here that do.

#3

Quick read on the net and I think I understand a little more. Forgive my analogies but this is how I have to do it to make sense. Voltage is the horsepower, how much work can get done at any given moment. aH or MaH (1 amp equals 1000 miliamps) is the gas tank how long said work can get done for. Am I right so far? So lets say a particular battery produce 3.7v at 2600 Mah. It will power a motor requiring 3.7 volts and drawing 2.6 amps for one hour, correct? If same said battery is paired with another equal battery in series I will double voltage while maintaining the same duration of use; twice the power for the same period of time. If I take the same two batteries in parallel I will get the same power as one battery but twice the operating time.

2- 3.7v 2600 Mah in series = 7.4 v for 2600 Mah

2- 3.7v 2600 Mah in parallel = 3.7v for 5200 Mah

Now if I have that right then by wiring two sets of two batteries in series and then wiring each set parallel I should double voltage and amp hours.

2- (2- 3.7v 2600 Mah in series = 7.4 v for 2600 Mah) wired in parallel = 7.4v 5200 Mah.

Did I get that right?

#4

Now if I did get that right and I want to power my little loco at 7.4v then how long could I expect it to run on 2 batteries producing 2600 Mah and 4 batteries producing 5200 Mah? I realize no one can really give me an exact answer but half hour, hour half day, all day, a month etc.

#5

Ken Brunt said:

Milli Amp Hours. MaH

I have 5600 MaH lithiom batteries in my K-27 and have had it running all day without a recharge.

Now don’t ask me to explain what Mah’s are, I have no idea, but there’s plenty of guys on here that do.

Ken,

that I think answers my question about operation duration. My critter running at 7.4v and 5200 Mah should give me a long run time. If I were to drop that to 2600 MaH wonder if could get say even four hours of run time. This will be a micro layout. I can’t imagine needing to run very long before it gets turned off and recharged.

#6

Devon.

Provided you know the current consumption of the driven load (motor, LED and carriages), you can work it out yourself.

Just divide the drain in MA (milli-amps) into the battery capacity in MA.

EG (roughly) Batts being say 2,600 ma by 1,000 ma (1 amp) will yield about 2.6 hours.

Say the load is 500 ma (1/2 amp), you would double the run time.

#7

It is all going to depend on how many Amps the motor draws and how much weight it will be pulling which is drag or friction. If this is going to be a little small quary type engine and cars, you probabbly will be able to run it for about 8 hours before charging. I run a Standard off the shelf Bachmann Big Hauler pulling 4 passenger cars or 5 Freight Cars all with Metal wheels and I can run for about 6 to 7 hours with a 14.8V 3200 MAh Battery pack.

Dan S.

#8

Devon you are on the right track with your analysis. But the missing variable is how much power does your locomotive draw. If it draws .5 amp, then 2.6 amp hours (2600 mah)will give over 5 hours of run time. Maybe a but less since the voltage will drop a bit toward the end. Using the same draw, with 5.2 amp hour (5200 mah) you should get over 10 hours of run time. If your critter draws more then you will get less, if it draws less then you get more. And I am talking run time, time sitting at the station while you go potty or grab a sandwich doesn’t count.

But also to be figured into this is how much current does your RC equipment draw? How much power is lost on the RC driver board. So, as with many things in the hobby, your mileage may vary.

#9

Your analogy is OK, but simpler for me is water. Voltage equates to pressure and amperage equates to volume. You can also compare wire to pipe. The bigger the pipe (or wire) the more gallons (or amperage) you can flow through it in a given amount of time.

Buy your LiIon batteries in packs. Much safer than wiring up yourself and more efficient than using the single cells with built-in PCB.

LiIon cells come in various capacities. You can get a 3.7V 4400mAh pack with only two cells for just under $20. That should power your little loco for a long time. You would need to know the current draw of your completed loco to know for sure. I use a 14.8V 2200mAh pack in my 2-truck Shay and get more than a few hours run time. I never run it for more than that so I’m not sure how much more.

#10

Tony and Dan,

That’s the one down side to this equation. I don’t know the amp draw of my motor. It is an older Lionel (?) DC motor block I got from Stan. I know the loco will be small and light and it will pull little light cars and no more than two or three. The only other element in the equation will be a little LED so no real draw there.

But I think I am getting my answers. At least to the length of operation. I am thinking 7.4 @ 2600 Mah should give me enough operating time to be happy. This loco will be very tight on space, saddle tank, no tender so everything has to fit in a small space. Thanks to Tony’s very small ESC if I only need two aaa size Lithium ion batteries I think I can get it all in there will some ideas I have floating around.

#11

Oh and if you want to shop. Cheap Chinese Tenergy packs of all varieties from All-Battery.com or high quality packs from Cordless Renovations (an LSC sponsor) for a bit more money. I’m cheap (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif)

#12

some real-world observations:

HLW Mack wired to factory lamp and straight to battery will run about 8+ hours with an 7.2v unknown ah Ni-Cad from about 8 years ago (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-cool.gif)

I have a Bachmann 50 Tonner Side-Rod Block under a scratch-built “Toby” Tram (Plywood const) that is powered by 3 AA alkalines -He CREEPS along at a very real speed and will go for a few hours as well (No lights or sound-no roof either) (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-laughing.gif)

#13

The Panasonic/Sanyo AA size Li-Ion cells are claimed to be 850 mah.

I doubt you are going to get AAA size Li-Ion batteries with a greater capacity than that.

#14

I run 8 Sanyo Eneloop AAA 850mAH (9,6v) in a Bachmann Indy (the space availabe for batteries is tiny) and it gives me about 2 1/2 hours running, pulling a train of one Newqida and two Bachmann coaches, all with metal wheels and on a layout where the ruling grade is about 60 feet of 3 1/3 %. As Tony suggested, I couldn’t find any AAAs with more capacity than that.

#15

Well I will be the first to admit I could be wrong on the size. You all know more than me. I am fresh meat. What I did see was 3.7v li-ion @ between 2200 and 2600 MaH but they must be bigger than I thought. Will need to make sure of that before I buy.

#16

Yeah I see where I went wrong the battery I was looking at was considerably bigger. So that makes sense. At any rate at least now I understand the theory and can find a solution that works and fits. Thanks for catching that.

#17

A 5600 MaH battery is a pretty good sized battery, but the K’s tender is a pretty good sized tender. You can also split the battery pack in half and wire it up in parallel to fit in 2 side tanks or in the corners of a tender or inside a boiler. I have 2 Annies where the packs are in 2 pieces and fit in the back corners of the tender.

Here’s the size of a 5600 mah pack in the K’s tender:

#18

Annie Tender

There’s my first Install. The Annie Tender with RCS and Sierra Sound… note 2x 7.2v NiCads.

2010…has it really been that long ago? (Still runs like a champ btw!)

#19

Thanks for the pictures, I am a visual guy. After receiving all of your suggestions, thoughts, experience, and expertise I have decided that I need the 7.4 volts but somewhere in the neighborhood of 2000 MaH.

When I say space is a premium I mean a serious premium. This will be very similar to the LGB Iron Mountain “Helena”

The only major difference between what I am making and this loco is I am adding a rear area that will hold the wood. Like below.

A combination of the two. If I can find a way I need to cram Tony’s smallest RX/ESC and batteries in it. I have a plan in my brain if I can work it out. The ESC and motor will pretty well occupy the boiler. That leaves the tank and the wood storage area for batteries. I am thinking that I might be able to make the saddle tank into a battery pack. Thanks to some good tutorials and batteries with tabs already in place (I wont solder on a battery, I will blow it up) I think I can do it. Not sure yet but i am investigating the idea.

#20

If I end up trying to put a round peg in a square hole there is always the option of a battery car. I am just being stubborn in wanting to stick it in this little loco.

Edit:

Changing my thinking around may have offered a solution. Addressing the largest item first meant finding a spot for the battery and trying not to re-invent the wheel. There are a few 7.4v 2000MaH +/- battery packs available. I found one (I am sure that there are more than one) that will fit in the boiler pretty nice between the motor and the front of the smoke box. Length on the side by side packs is not an issue at all its the width and height that are limiting, fortunately they have rounded corners. The end for end types are to long. That leaves finding a spot for the ESC which I think maybe able to go where the wood bin is going to be.

Thanks for helping out guys, and letting me ramble along and work this out.

One of the things I love about this site is the vast knowledge base and the willingness to share it. I am a way more advanced modeler than I could have ever hoped to be without it.