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G-Scale 'Big Boy' - Via WiFi
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 Posted: Thu Jul 12th, 2018 03:22 am
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dan3192
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Steve,

The "normal" minimum is around 3V, but I've seen protection boards touting 2.5V, a bit too low for me. My DelTang receivers shut off at 3V for a 1S arrangement, 6V for a 2S arrangement, etc.

Voltage drop-off with Lithium type batteries is a little worse than with NiMH types, which is why I prefer using a voltage regulator to maintain a constant voltage. IMO, since batteries have more capacity today than just a few years ago, I think performance is more important than the 10% or so loss in efficiency because of the regulator.

A 2S arrangement I'm using with Pamasonic 18650 x 3400mAh batteries (and 12V step-up voltage regulator) has 3 wires out to the side of the trailing (passenger) car. I use this connection to both slowly balance charge the batteries and occasionaly check cell condition. It is NOT recommended to fast charge batteries using the balance wire connection. eBay has several battery checkers that will do the job, around US$3-4.

Dan

Last edited on Thu Jul 12th, 2018 03:29 am by dan3192

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 Posted: Thu Jul 12th, 2018 03:44 am
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dan3192
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Steve,

Here's the performance curve for the 26650 battery.
If you know how much power your engine uses, you can estimate run time.
The slower the drain on your battery, the less it will heat up, which promotes longer battery life.  

Dan





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 Posted: Thu Jul 12th, 2018 06:54 pm
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Steve P
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Dan,

Getting close...

I am using an MTH Track Interface Unit that is rated for 18v nominal, 24v max, 10 amps max  input.
6 x 4.2 = 25.2. TOO MUCH.

So I am thinking about getting one of these:
https://www.jacobsparts.com/items/DCMOD-C/

Setting the output to 22v,
setting the under voltage protection to 20.4v (6 * 3.4v),
and current limit to about 5 amps.
I will also fuse the output where it exits the boxcar.

Does this sound about right?

update:
battery & holders arrived, batteries about 3.6v each,
put together a 6S strip, total 21.8v

Runs my HO BigBoy quite nicely.  :rah:

Steve P



Last edited on Thu Jul 12th, 2018 08:37 pm by Steve P

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 Posted: Fri Jul 13th, 2018 08:57 pm
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dan3192
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Sounds good to me. At least it gets you started and you can make modifications later.

You may want to keep in mind the 6S2P arrangement Tony mentioned earlier, in view of the steep grades you anticipate.

Give us an update when you can. I'm particularly interested in battery performance under load.

Dan

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