# 14 volts vrs 18 volts



## John J (Dec 29, 2007)

I have a search going on E bay looking for 18 volt Milwaukee Ni-Mh batteries.

I have noticed that I am getting a a lot of 14 volts in my search.

Has the cordless drill industry gone to 14 volt batteries?

Do you think the 4 volts more makes that much difference?

What difference does 4 volts make ?

JJ


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## Homo Habilis (Jul 29, 2011)

How about trying the following Google search term - 

replacement 18 volt Milwaukee Ni-Mh site:ebay.com​
Give me bunches of 18 volt results. Whether or not they aren't already sold or are what you are looking for is a separate issue.


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## toddalin (Jan 4, 2008)

John J said:


> I have a search going on E bay looking for 18 volt Milwaukee Ni-Mh batteries.
> 
> I have noticed that I am getting a a lot of 14 volts in my search.
> 
> ...


 
Big difference, especially in that range.

I typically run at ~16 volts. I think 14 volts is too slow for a USA diesel passenger liner running though open county. Then when the battery starts going flat...


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## Greg Elmassian (Jan 3, 2008)

No, the cordless drill companies have gone higher voltages... I have a set of tools that have 36 volt Li-ion batteries.

JJ, motors are nonlinear in their response to voltage, most of the speed is in the last few volts.

Example: running DCC on my layout, but still voltage to the motor is PWM just like your Revo. E8 would only go 65 scale miles per hour with 20.3 volts on the rails... but kick it to 23.9 and I got 92 smph... those last few volts mean a lot to the rpm.

Greg


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## Trains (Jan 2, 2008)

John,

Depends on what you are going to run, 14 volts work good in my USA GP's buy barely run my
LGB engines. LGB like 18 volt or more.

Don


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## Bill Swindell (Jan 2, 2008)

I have put batteries in a lot of LGB engines. They run just fine. If your LGB engine needs 18 volts, the motor may need help. The only engines that like more voltage are the Aristo and Accucraft engines. Aristo run OK on 14 volts but if I change batteries in my SD-45, I will probably go for 18 volts. If you are running AirWire receivers, thy are much happier with 14 volts. That minimizes radio interference and reduces heat output from the receiver.


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## toddalin (Jan 4, 2008)

If we assume that the top speed of an engine is directly proportional to the power-to-weight ratio, and we assume that the engine does not change resistance/impedience with voltage (and we run track power or your batteries weigh the same for 14 and 18 volts), the 18 volts would provide ~65% more top speed (i.e., (1-(18^2/14^2)) x 100% = 65% ). That's pretty substantial.


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## Trains (Jan 2, 2008)

Bill,

I have four LGB engines, with very little run time on them and they all run better on 18 volts.
They will run on 14 but very slow. They have all the LGB boards in them.

Don


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## Greg Elmassian (Jan 3, 2008)

Both assumptions are not true for electric motors in model trains.

The rpm vs. the voltage is nonlinear. I gave a real life example on a real G scale train.

I understand how you might assume that a motor was linear, although you did use the word impedence, which is nonlinear in almost every device that exhibits it, (that is why it is used instead of resistance pretty much) but what's the rationale for top speed proportional to power to weight ratio? The motor does not care about the weight except when it affects load or resistance. On flat track this is pretty minimal.

Greg



toddalin said:


> If we assume that the top speed of an engine is directly proportional to the power-to-weight ratio, and we assume that the engine does not change resistance/impedience with voltage (and we run track power or your batteries weigh the same for 14 and 18 volts), the 18 volts would provide ~65% more top speed (i.e., (1-(18^2/14^2)) x 100% = 65% ). That's pretty substantial.


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## toddalin (Jan 4, 2008)

Greg Elmassian said:


> Both assumptions are not true for electric motors in model trains.
> 
> The rpm vs. the voltage is nonlinear. I gave a real life example on a real G scale train.
> 
> ...


 
But your own accounting of voltage and speed bears this out so well. 

65 mph x (23.9^2/20.3^2) = 90.1 mph


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## Randy Stone (Jan 2, 2008)

So, since we are on the subject of voltage, can we get a list of what voltages the manufacturers designed their locos to be powered with?

Yes, many will run on 14.8 volts, but if they are designed to run on 18 or 24 volts, I would think they would run better overall at the designed voltage. I hear people say, (Ah, the loco goes too fast on 18 volts). Isn't that why you have a speed controller.

Plus, add a smoke unit and sound card and you're dropping the amount of voltage the motor has left to operate on. Correct?


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## toddalin (Jan 4, 2008)

Randy Stone said:


> Yes, many will run on 14.8 volts, but if they are designed to run on 18 or 24 volts, I would think they would run better overall at the designed voltage. I hear people say, (Ah, the loco goes too fast on 18 volts). Isn't that why you have a speed controller.
> 
> Plus, add a smoke unit and sound card and you're dropping the amount of voltage the motor has left to operate on. Correct?


As I pointed out, and Greg quantified for us, the higher the voltage, the less you need to incur more speed. If speed is based on a linear relationship to the difference in the square of the voltage, the difference between 16 and 18 volts is ~26%. So if someone complains 18 volts is too fast, no big deal to cut it back a bit with a speed controller.

As long as the power supply can supply the needed current (amps), the voltage should not "sag" with the inclusion of the smoke and sound units. What you loose is run time because you need to supply these additional amps while the motor is running. In the real world there would probably be at least a bit of sag with a slight reduction in speed.


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