Motor voltages and currents

Rhinochugger

Rhinochugger

Retired Oik
27 Oct 2009
26,690
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North West Norfolk
OK, then that is as I asked, the same size about 5 x 11 mm, so indeed the common size for a 10 mfd, npo electrolytic.

I agree with Phil, keep the voltage near the original. Some of the advice above implies you can lower the voltage with settings, but all of this equipement is PWM, pulse width modulated, which means you control speed and "voltage" by varying pulses of FULL VOLTAGE, as these circuits are just an on off switch with varying "on" times.

The point here is that using a much higher voltage and then narrowing the pulses on time way down is not the same as longer pulses at lower voltage, you can get heating and other unwanted effects when there is a gross increase in voltage.

Greg
I can remember when, what we now refer to as PWM, was just called a transistorised controller in the model railway world - mind you, that was a few eons ago, and I soldered up a fairly inexpensive controller kit; the speed control on small locos was fantastic. Sadly, it's been stored on a board in the garden shed and the low temperatures and humidity have killed it off. In its day, it was better than the Gaugemaster controllers >:)
 
Greg Elmassian

Greg Elmassian

Registered
8 Mar 2014
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San Diego
www.elmassian.com
Actually many of old the transistorized controllers were just that, just a transistor controlling the output, and some were "chopping" the parts of the AC sine wave, not many were PWM.

There was a lot of experimentation, and the older motors heated more from "pulse power" so there were things like a constant narrow pulse for starting, and a rising "background" of pure DC.

What brought it into focus was the availability of low cost high current FET transistors, and inexpensive PWM circuitry. Now almost everything is pure PWM.

Greg
 
M

MickyF

Registered
24 Aug 2019
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Essex
Back to the original question:

If you are using the original motor, then feed it with around the 7.2V that the six-cell Ni-Cad battery pack would give it.

Personally, I would continue to use said Ni-Cad pack, until it died. Then replace with either a six-cell, 7.2V NiMH pack, OR a 2S Lithium pack.

The motor-shield you are considering, should be adequate for this particular loco, or other similar single-motor models. - Especially the likes of the smaller LGB offerings, the Buhler motor's are very good.
Well... time has moved on and the Arduino transmitters are done using RF-Nano that have the 2.4Ghz built in - very clever. Definately using 7.2v for the motors and now decided Mosfets would be better for motor drivers coupled to the Nano so have got some cheap as chips IRF520 boards (about £1 each on Amazon).
 
M

Michael

Registered
26 Jan 2010
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36
Well... time has moved on and the Arduino transmitters are done using RF-Nano that have the 2.4Ghz built in - very clever. Definately using 7.2v for the motors and now decided Mosfets would be better for motor drivers coupled to the Nano so have got some cheap as chips IRF520 boards (about £1 each on Amazon).
Using a MOSFET is a great way to drive a loco, especially low voltage ones, because you lose very little voltage. Virtually all the battery voltage is applied to the motor. You will however need a relay (fitted after the MOSFET to control direction) if you want it to go in reverse.

My first ESP, bought from Tony Walsham 10 years ago, contained a transitor (not sure what type) and a relay and worked very well. When I started to make my own ESPs, I first used an L296 motor drive. This turned out to be a bad choice as it lost over 2 volts and subsequently got very hot, reduced top loco speed and reduced battery life. I quickly reverted to a MOSFET and relay.

Modern motor drives are better than the L296 (lower on voltage) and I use them in my smaller locos (Pololu Max 14870). However for my larger locos I still use a MOSFET and relay.

Michael
 
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PhilP

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
25,007
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Tamworth, Staffs.
Using a MOSFET is a great way to drive a loco, especially low voltage ones, because you lose very little voltage. Virtually all the battery voltage is applied to the motor. You will however need a relay if you want it to go in reverse.
Unless you can find a H-bridge driver.. Then the relay is a transistor, to switch which FET you are using. :nerd:
 
M

Michael

Registered
26 Jan 2010
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Unless you can find a H-bridge driver.. Then the relay is a transistor, to switch which FET you are using. :nerd:
Thanks. I've editted my post to hopefully make it clearer, i'm hopeless at explaining things:). The PWM signal is applied to the MOSFET. The output goes through a dpdt relay to the motor. The relay is driven separately to control the direction.