ALCO LGB motor loading/runtime question

[CoggesRailway]

Thanks to a helpful centralist I am reconfiguring a dodgy battery set up in one of these locos. There has been no operational issues but I am concerned I might have caused a potential issue in the future so she is on the bench at he mo.... long story...

I have just nicked the batteries out of my kids tanks 4.5mah nimhs. (Easy as stealing a batteyr from a baby funnily enough) These fit so much more neatly into the Alco leaving potential room for RC/Sound if I ever wanted to change them it critter control.

My question is this: With a ballasted LGB Alco (in good working order it seems) with 25 bogie wagons on, minimal gradients and R5 loop what (very approximate worst/best case) runtime migh I look for. This is the loco which does all the heavy hauling when the long train thing takes me....

From my electrickery lessons in Ruritainia I was thinking perhaps 1amp and then double it for ballast/long train which would mean about two hours. Before I complete the theft I just wanted confirmation...

 

[Neil Robinson]

From my electrickery lessons in Ruritainia I was thinking perhaps 1amp and then double it for ballast/long train which would mean about two hours. Before I complete the theft I just wanted confirmation...

That would seem to be a reasonable ball park estimation to me.
I suggest you fully charge the batteries, do a temporary installation (but please don't forget a fuse) and then run the train to get a practical test result.

 

[beavercreek]

Is this load to include pulling one of your little 'uns on a flat bed? If it is then maybe.....5 mins

 

[CoggesRailway]

Thanks chaps. ha ha Mike no he is too big now and the smallest one can't sit still long enough!

 

[beavercreek]

Maybe try the missus?.............only joking!!

 

[gregh]

Please take this as constructive criticism. Your question is really in the realms of ?how long?s a piece of string??
But similar things have been asked many times before.
Neil Robinson?s suggestion to do a test is a good one, if it's possible.

But if you want to find out before you ?pinch? the batteries, another way is to measure how much current your train takes.
And for this you need a multimeter that has a 10 amp range. I picked up this one last week for $7 here in Australia so you must be able to get one for under 10 quid in the UK.

Now I believe that anyone owning an electric GR can?t exit without a multimeter for fault finding and if you?re planning battery conversions it is a MUST.
For those who haven?t used one, here?s a description?
If you?re still operating your train on track power it?s super easy to test ? you just disconnect one of the leads from power pack to track and insert the multimeter.

Note that you must plug the red lead into the 10A socket on the meter AND select the 10A range.
Now make up your desired train, put your throttle on a suitable speed and just watch the ammeter readings as the train moves around your track. It?s pretty easy to ?sort of average? out the readings as it goes around different curves and grades.

As an aside try varying the throttle setting (speed) and notice that the current doesn?t vary much. The current depends on the train load not the speed (voltage)!

Also as another exercise, add another (2nd) loco to the same train and again notice that the current doesn?t increase much ? it certainly doesn?t double.

Now while you?ve got the meter out, set the throttle on your preferred speed and measure the track voltage. You?ll probably be surprised at how low it is. I?ve never found I needed more than 15V and 12V is usually plenty for most locos.

Anyhow, now you?ve got your ?average? current needs, you can calculate the size of battery you need for a given run time. This simplest calculation will always err on the high size.

[h1]Battery size in mAh = avg amps x hours required[/h1]
BUT there?s a bit more, if you want to be a bit more exact..

If you?re using a battery with a higher voltage than the max you require for top speed AND you?re using a PWM controller (and usually you are) then you?ll get run time increased by a factor: Battery volts divided by max speed volts. So the whole equation is:
Battery size in mAh = avg amps x hours required x max speed volts / battery volts

Or rearranging..

Run time= battery mAh / avg amps x battery volts / max speed volts.

Example:

Say you need 0.9amps = 900 mAh, with a 15V battery but will usually only run at a max 12V and you want 2 hours run time?
Battery mAh=900 x 2 x12/15 = 1440 mAh


Another little hint:
If you?ve already installed the battery and would still like to measure the current, my way is to connect the amp meter across the loco on/off switch, in the off position. This means you are shorting the open switch with the amp meter, so it is turning the loco on. Then tape up the meter leads out of the way and put the meter in an open wagon and walk alongside to read the current.

 

[beavercreek]

Darned good advice Greg, as usual.
I will be using the battery size calculations from this thread for when I eventually 'battery-up' a couple, or so, of my locos with the Aristo Revolution wireless system.
We are so lucky to have the likes of you and Neil on this forum (other members are also available). It is like have electronics mentors at your shoulder!