Electric power primer

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Pontiacguy1
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Re: Electric power primer

Post by Pontiacguy1 » Thu Sep 17, 2020 3:40 pm

That's why you have to SIZE your motors and controllers so that you get the power delivery that you need. Just like the full size locomotives: you gear it for your top speed, and then make sure that you have powerful enough motors to pull the load you require. Passenger trains were typically geared for a top speed of 100-110 MPH, while freight trains often had a 70 MPH top speed. Some switchers might have been geared for a 40 MPH top speed.

Just figure up the power that you will require to move your load, realizing that you can't lay down more power than the available traction, unless you use sand or something to enhance your traction.

Just shooting from the hip here: A small 7 1/2" gauge locomotive like the above-mentioned critter might be fine with approximately 350 watts powering each axle. A 650 lbs locomotive might need 500-600 watts per axle depending on the number of axles and weight on each axle. On your grand scale locomotive, you might need more than that.

Look at Tom Artzberger's 2 1/2" scale narrow gauge center cab electric to get an idea of what ballpark you should be in: http://www.tacllc.biz/geprod.html Here is a calculation page that he has on his site too: http://www.tacllc.biz/pledeslcalc.htm
His locomotive uses 8 motors (2 per axle), a 24 volt drive system, a 200 amp controller, and weighs about 1000 lbs. With it being 200 amps total output, that means each motor is consuming approximately 25 Amps. At 24 volts, that means he's got 500-600 watt motors, 8 of them. If you built your system using similar sized components, it would be pretty powerful.

On thing you have going for you: You're running 12" gauge, which means you can use physically larger/longer motors and they still fit between your wheels.

I hope this helps you out. I'm not an EE, just had to go through something similar trying to figure out how to power a small critter, so I know that it helps out just knowing what has worked on other applications so you know if you're in the ballpark or not.

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dnevil
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Re: Electric power primer

Post by dnevil » Sun Sep 20, 2020 1:57 pm

Daris Nevil
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http://www.ibls.org

Glenn Brooks
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Re: Electric power primer

Post by Glenn Brooks » Thu Oct 15, 2020 12:35 pm

As an update, Here is a tractive effort calculator method for live steam equipment, written for the Golden Gate Live Steamers. Pretty simple to follow and well written. It makes several key assumptions relevant to miniature train scale and gauge that relate to determining proper tractive effort for our size equipment.

https://www.goldengatels.org/library/To ... Effort.pdf

Using these formulas, I was able to calculate that my center cab electric would need two 7.5kw small forklift motors, one per each truck, to pull an 8,000# consist - up a 2% grade and around 35’ radius curve. Pretty radical capacity! Flat track, (under 1% grade), wider curves >50’ Radius 15Kw (20hp) Power would theoretically pull in excess of 10,000# - 5 loaded cars, 40adult passengers!
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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skid-roe
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Re: Electric power primer

Post by skid-roe » Fri Oct 23, 2020 4:31 pm

I used Daris A Nevil's article "Building and Powering AAR A Trucks" in the IBLS website to repower a pair of old Koster's trucks.
The major difference was that I utilized 4-350 watt 24VDC gear motors.

http://ibls.org/mediawiki/index.php?tit ... R_A_Trucks

https://www.ebay.com/itm/24V-350W-Elect ... 1016Z3-US/

The biggest job was modifying #35 chain sprockets to fit the motors
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SteveM
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Re: Electric power primer

Post by SteveM » Sun Oct 25, 2020 10:27 pm

Glenn Brooks wrote:
Thu Sep 17, 2020 1:30 pm
So, what do people do for gearing to start up and pull a heavy train? For example, an extreme example perhaps, pulling a 20,000# train with several loaded cars, or maybe a ballast car with two yards of gravel? Seems like one would need a very low gear ratio to deliver high tractive effort at slow speeds, then somehow, shift to a higher gear, once momentum is built up?
What about having an extra motor with a separate switch to kick in when you need it?

Kind of like a turbo boost.

You might want to somehow limit it from kicking in when you are at higher speeds. You're not looking to set speed records, just get off the line a bit quicker or have some oomph to climb a hill.

You'd have to completely disconnect it when it's not in use so that it presents the least amount of drag. Maybe have a sprocket that freewheels in one direction, so that you could gear it low for starting torque and when it runs out of RPM, the sprocket freewheels so to not overdrive the motor.

Steve

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NP317
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Re: Electric power primer

Post by NP317 » Mon Oct 26, 2020 12:08 am

Follow prototype locomotive operation:
Connect the motors so they can be switched from parallel to series in various combinations.
Electric gears.
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John Hasler
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Re: Electric power primer

Post by John Hasler » Mon Oct 26, 2020 8:26 am

Also follow the prototype by using series wound motors.

Glenn Brooks
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Re: Electric power prime

Post by Glenn Brooks » Tue Jan 12, 2021 1:25 am

Well, over this crazy winter break, finally settled on using two DC series wound, 48 volt traction motors to power my Center cab yard goat. (One motor per truck with 6:1 two stage chain and gear reduction). I found the motors and their controllers for a $100 bucks from a local EV member (electrical vehicle conversion enthusiast), who used something similar to replace his gas engine in his SUV.

So, planning to move ahead with installing one traction motor (and it’s controller) dedicated to each truck. The motors are 6.9”diameter 48 volt forklift traction motors. The controllers are the older style, Curtis 1205 manual controllers with a max rating of 350 amps. So nothing fancy, but plenty of power to do the job.

Also, I re-ran the numbers for tractive effort, train resistance, and torque requirements, and confirmed they would perform to the general operating requirements folks suggested earlier in the thread. The numbers came out to roughly: 1550# locomotive weight on drivers, 340 # tractive effort; 5 cars, 30 passengers, 10 MPH, 2% grade, 10,000# train weight, 300# train resistance.

Turns out, one motor would be sufficient for torque and tractive effort. However, I want to go with two motors, one on each truck, to better distribute tractive effort to all four axles.

So, now trying to understand how to actually design and build the actual high voltage circuit to run the motors. I could really use some help with the Three big questions that come to mind with all this:

1)how to best set up the motors and controllers? Apparently there are two approaches - design a master/ subordinate circuit, such that one controller (and motor) acts as the master controller, thereby controlling the second controller and motor, or; connect both motors and controllers in parallel to a single speed control (pot)? I do want both motor speeds to be controlled with one throttle device. (Both motors are identical size and models.) not sure what the pros and cons are of these approaches....

2) The second big question is what is the correct design to achieve forward-reverse operation with two single pole contactors and a three way switch, using two traction motors??

Finally,
3) wondering what my total current draw might be when both motors operate synchronously with each other? (To estimate size of the electrical components and battery pack etc.)

For example, the Curtis 1205 controllers are rated at 350 peak amps. If both motors require peak current at some point, should I be looking to install 750 (1000) amp fuses and switch’s etc?

Any advice on this would be much appreciated!

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

John Hasler
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Re: Electric power primer

Post by John Hasler » Tue Jan 12, 2021 9:22 am

There is a schematic in the manual (http://www.fsip.biz/Documents/1204_05.pdf).

You probably cannot use a single pot for two of those controllers. Check with Curtis.

Each motor requires four sets of contacts for reversing. The schematic in fig. 6 in the manual is good.

Maximum total current will be 700 A. You might want to consider using a double pole main switch and one fuse per motor.

The fuse(s) must be located near the battery and rated to interrupt its short circuit current.

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BigDumbDinosaur
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Re: Electric power prime

Post by BigDumbDinosaur » Tue Jan 12, 2021 4:36 pm

Glenn Brooks wrote:
Tue Jan 12, 2021 1:25 am
Turns out, one motor would be sufficient for torque and tractive effort. However, I want to go with two motors, one on each truck, to better distribute tractive effort to all four axles.
Also, such an arrangement reduces the temperature rise in each motor. Overheated and burned-out traction motors are a constant threat in anything that uses DC for traction power. Have you given any thought to cooling your motors?
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NP317
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Re: Electric power prime

Post by NP317 » Wed Jan 13, 2021 11:50 am

BigDumbDinosaur wrote:
Tue Jan 12, 2021 4:36 pm
[snip]
Have you given any thought to cooling your motors?
Glenn lives in NW Washington State where tracks are often under water...
:lol:
RussN

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BigDumbDinosaur
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Re: Electric power prime

Post by BigDumbDinosaur » Wed Jan 13, 2021 8:43 pm

NP317 wrote:
Wed Jan 13, 2021 11:50 am
BigDumbDinosaur wrote:
Tue Jan 12, 2021 4:36 pm
[snip]
Have you given any thought to cooling your motors?
Glenn lives in NW Washington State where tracks are often under water...
:lol:
RussN
Ah-ha! Water-cooled traction motors! Why didn't I think of that?
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