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Discussion Starter #1
I haven't posted or visited the forum for quite some time now, because I my health went south on me for a spell and I had to have surgery to correct a problem and have been recovering, however I am feeling fine now and better everyday.
I have been back at my drafting table, designing some possible layouts for the space I have to work with. I have also been doing some research into power options and I believe I will go with battery power instead of track power, as I will not have to worry about track connections or constent track cleaning.
I have come across a place to purchase lithium-Ion or lithium-polymer batteries in voltages from 3.7 volts to 30 volts with weights from 3 oz. (3.7 v) to 6.61 lbs (30 v), I am thinking of using a 26.25 volt lithium-ion battery weighing 4.85 lbs. and lasting 6 hrs. at 5amp constant current draw, I figure that if a GP 38 loco would draw a constant 2 amps, then I should have approxiamately 15 hrs of constant run time.
However I am very knew to large scale and my calculations may be wrong, any corrections or help would be greatly appreciated.
Oh! the battery company claims that this particular battery can be recharged numerous times and will last for 5 years and the cost is around $135 for battery and charger.
 

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Your math is essentially correct but your approach is an error very common to beginners. You are building a nitro fuel dragster to go get bread and milk. From someone who has done literally hundreds of install conversions over the last 15- 20 years, the standard which is fine for 95% of users, is 14.4 volts or very close to it. A small number of users that wish to go faster use 19 volts or even 22-24 volts, but that is max. Your proposed nominal voltage of 26 will peak charge to near 30 and that is either over the limit or uncomfortably close to the limit of most garden rail electronics and sound.
The USA gp38 and other similar units run at a very fine scale speed with excellent power at 14 volts.
Likewise , the current capacity is far larger than most need. Everyone has different operating methods and stamina, but there is no need to haul around all that excess weight (power) , unless your operating sessions will achieve 10-15 hour duration. Remember, you will not operate at max speed except rarely, so the excess voltage will be burnt off as heat in the throttle. Llikewise, a geep will run for a few hours on 3000 mah to 5000 mah. This can easily be fitted inside the loco, to aid traction and allow running without an added trail car. Since Lithium can be part charged at any time , whether empty or not, having days worth of power is an unusual parameter. Alternately, design your system to allow battery quick change, and run as long as needed with one pack on charge while the other pack is used.
In planning for the future( more locos) you could find it advantageous to standardize on a battery pack that will fit most engines, can be easily charged with a standard charger, and can be easily interchanged between units, for max flexibility.
Technology has developed greatly in just the last few years, and it is very easy now to design conversions that outlast most afternoons - or users legs- and still avoid the overkill factor.Remember, the larger the pack, the longer it will run, but the longer it will also take to charge, even with a smart charger. Much better to adapt your hardware more closely to your actual needs.
In general, the claims stated about the battery are essentially true, provided good maintenance practice and use. The price is ok, about average for the hardware, but more specs on the charger would be a help.
jonathan
 

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I agree with Jon re the voltage required for most locos.

It is also quite possible to have reasonable capacity on board batteries and a wiring circuit that permits the one port to both charge and double as a port for auxilliary batteries carried in a trail car. Just extra batteries not the main batteries.
This will permit the loco to run light engine until you have a train with the extra batteries in the trail car which can be plugged in. Doing so disconnects the on board batteries.
Then you can run as long as you like without worrying about how long the loco mounted batteries are going to last.
 

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I'm one of those users that likes the higher voltages. Still, I agree that the pack you describe is way too much. The packs I built/build are of 16 1.2 volt cells for 19.2 volts nominal. That is plenty. I don't neccessarily run fast.. really, I do run slowly most of the time. I just find the higher voltage gives me a better response from the throttle at low speeds using PWM.

Recently I've been using tool battery-packs removed from their case. They are 15 1.2 cells for 18 volts nominal. These work fine for me
too.

--
craig
 

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Craig.

Why don't you adjust the acceleration rate to a faster setting?

That way you will save the energy wasted when you use a higher volatge battery but never run at full speed.
 

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That way you will save the energy wasted when you use a higher volatge battery but never run at full speed.



Actually, not wasting as much as you'd first think. Most RC systems, including RCS are pulse width controlled. All he's doing with higher voltage is lowering the throttle setting he runs at, narrowing the pulses. But yes, 26.25 is way more than you need for a loco. Look at more like 16.

When you have a high voltage, you're only using the bottom part of your control's speed range, so a lower voltage battery would spread your loco's operationg over more the the controler's range, giving you finer control, or, as Craig points out, slower starting as the throttle ramps through the loco's dead band area.

My 3.8 AH batteries run my Mallet 2 to 3 hours continuous, depending on the grades. Longer if "operating" cause you spend lots of time sitting. Since my $25 charger charges them in a little over 2 hours, 2 packs can keep me going all day. However, I'm thinking about turning the smoke unit on, drawing another half-amp.
 

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Hi Tom.

The RCS acceleration rates are time based.
It takes the same amount of time to get to maximum voltage output no matter what the battery voltage is.

The higher battery voltage, the faster the rate of acceleration will seem to be.
Conversely, the lower the voltage, the slower the acceleration rate will seem to be.

With RCS, if you want to have a faster take off at a lower battery voltage, just set the acceleration rate to a faster setting.

I can't tell you if other brands of R/C use the same method.
 

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Discussion Starter #8
O.K. fellows you have convinced me that I do not need 26 v - 5amps of power, since I am not proficient with electricity, etc., my next question is, if I use 2 , 7.2 v, 2600 mah battery packs connected in a series, will this setup give me a total of 14.4 v at 5200 mah power output and will this be enough for loco power and how much run time will I achieve ?
 

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Nope. It will give you 14.4v at 2600MAh.

I get 9.6v 3800 MAh NIMH packs from all-battery.com and put 2 in series to get 19.2, which is a little higher than actually needed, but this 19.2v 3.8Ah battery costs only $32. The charger is $26.
 
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