# New to this power thing - have a question



## FiatFan (Feb 12, 2013)

I've been running a Bachman Big Hauler 4-6-0 using the original power supply which was designed, I'm sure, for indoor use. I have about 140 feet of code 332 brass (all joints are soldered) outdoors and have purchased a USA Trains dual motor GP7. USA Trains indicated I need to provide 2.5 amps for the motors. 

I plan on using this controller

http://www.ebay.com/itm/New-PWM-DC-...416?pt=LH_DefaultDomain_0&hash=item416e91b280

along with a 13v 3 amp transformer http://www.radioshack.com/product/i...702&filterName=Type&filterValue=Transformers# and a bridge rectifier. My plan is to use 16 gauge speaker wire to hook this up. Total length of the wire will be about 35 feet from the transformer to the controller to the track. The reason for the length is so that we can have the speed control on the table next to us as we sit on the patio. I don't plan on using the 24 volt tap because the grandkids and great-grandkids can be slightly more aggressive at the throttle than I am.

For an overall view you can see the layout here. http://www.youtube.com/user/MrFiatfan?feature=watch

No other trains will be run with this nor will there be any lighting or other circuits. This will only be to run this train. Train length will be about 6-8 cars.

All this is a roundabout way of asking: am I headed in the right direction for providing power to the train?


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## Greg Elmassian (Jan 3, 2008)

I'd say the pwm controller looks ok, not a terribly complex circuit and does not look like any protection. Not really wild about the thick blobs of solder underneath, probably trying to handle more current, would be better to have bigger copper traces than try to do it with solder. 

You need a filter capacitor along with the bridge rectifier. 3 amps may be marginal, and remember that the transformer output voltage will sag when presented with a lot of load. It should be fine however on the Bachmann alone, but in my opinion you should get something more robust for the USAT loco. Plan on 5 amps, the loco may draw over 2 amps easily. 

I would also get higher voltage, you are really close to 12 volts, the minimum allowed for the throttle... look for something like 18 to 24 volts. For the kids, maybe it might work but better to get like 16v... you could always set up a resistor in series with the speed control to limit top speed. 

At 2-3 amps, there will be noticeable voltage drop if you are running the USAT loco with a sizeable load, but I think you would be ok. What about kicking up to 14 gauge wire? 

Those are my suggestions. 

Greg


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## FiatFan (Feb 12, 2013)

Thanks, Greg. One ting - there is a fuse on the circuit board. That's one reason I chose this particular board. Many of these PWM boards don't have a fuse. 

Thanks again. 

Tom


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## Greg Elmassian (Jan 3, 2008)

Yes, fuse the input to the unit and the output from it. 

I looked at the picture again, where is the fuse? I can identify every component and don't see anything that looks like a fuse. 

or on the parts layout:











Greg


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## FiatFan (Feb 12, 2013)

Looks like I made a mistake. I thought the indicated area was a fuse. Guess I'll have to figure something out for that. Thanks for catching my error. 










Tom


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## FiatFan (Feb 12, 2013)

Also looks like I have to read the section on how to post images. 

Tom


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## FiatFan (Feb 12, 2013)

Let's try this. 










Tom


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## TheRoundHouseRnR (Jul 15, 2012)

All that simple is , is a Diode, prolly to protect the circuit from an accidental reverse of polartiy. Not a fuse. 
The Roundhouse RnR


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## Greg Elmassian (Jan 3, 2008)

Yep, and a high current one, as opposed to the smaller signal diode "closer" in the picture.

If you study the underside carefully, it appears that the diode is across the motor leads, probably to kill BEMF from the motor. The cathode connects to the motor - lead, and the anode connects to the positive input, which is also connected to the motor plus.

So the only effect would be to stop any "reverse" (Back or B) "voltage" (ElectroMotive Force or EMF)...


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## FiatFan (Feb 12, 2013)

So what kind/size/type of fuse should I use and where in the circuit should I put it? 

Tom


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## TheRoundHouseRnR (Jul 15, 2012)

You are suppose to protect any circuit powering any type of motor with a diode. Wether it be a coil in a relay or any type of coil for that matter. It protects from reverse voltage as greg stated. You would use a fuse adjusted according to how much you plan to draw currunt wise. So if your trains would draw around 4 amps, then go with a 5 amp automotive fuse. You wire it in series with one of the leads going to the track. So one lead from the controler to the fuse. Then the other side of the fuse to the track. 

If you go larger , lets say 10 amp. If your train derails. The current will have to reach 10 amps to blow the fuse. Which basically equals more sparks! 

Practice tells you , you should have one going from the control to the power source also. Most people will wire the fuse to the postive terminals. 

The Roundhouse RnR


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## FiatFan (Feb 12, 2013)

Thank you. That will really help me out. Now I know what to look for. 

Thanks again. 

Tom


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## FiatFan (Feb 12, 2013)

Would this be an adequate fuse or should I use something a little smaller, like 3 amp? 

http://www.grainger.com/Grainger/CARLING-TECHNOLOGIES-Thermal-Circuit-Breaker-4VA71?Pid=search 

Tom


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## Greg Elmassian (Jan 3, 2008)

On additional suggestion: 

1. you need a fuse on the line side of the transformer... it should be sized according to max current draw. I won't size it since I have recommended a larger transformer. 

2. you can put a fuse on the output of the throttle, which should be sized to the greatest load you will draw from the throttle. 

3. I recommend a fuse in each loco, usually a "poly switch" which is a self resetting thermal "breaker". 

In general you don't want to limit your throttle if it will control different loads, but choosing a 10 amp fuse for the throttle output won't protect a 1 amp loco very well. But putting a 1 amp fuse on the throttle won't work when running a 3 amp loco. 

This suggestion covers more possible problems, but of course it takes more work. 

Greg


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## Totalwrecker (Feb 26, 2009)

I think fuses are faster than breakers.


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## Greg Elmassian (Jan 3, 2008)

That is true, but my recommendation is based on the fact that adding a fuse inside a loco means that you need to disassemble it to change the fuse, and very few people will do this or get frustrated. 

An alternative is to make the fuse externally accessible, which is also a pain. 

In a beginner's forum my recommendations keep in mind ease of implementation and minimization of frustration. 

Regards, Greg


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## Totalwrecker (Feb 26, 2009)

funny, I deleted a longer message for that one.... 'cause your better answer had showed up. 

I was repeating what I learned here. 
On my 4-4-0 I made a fuse holder under the tender 'cause I'm a simpler kind o' guy. 

PEACE 
John


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## Greg Elmassian (Jan 3, 2008)

Yes, it can be done. 

Not to argue but often this will require re-wiring of all power pickups to a single point in the tender, and then back. This can be a royal pain but clearly possible. 

To further reveal more thought and techniques: protecting locos can and should go further, so that you can also protect against a short through the wheel pickups on a typical switch derailment, which can require many more "fuses", therefore another reason for my recommendation of polyswitches. 

I did not want to derail the thread into this topic, but there's usually more reasons for my recommendations than I present, but now I am reticent to present them since I clearly have upset people by being a "know it all". 

This will finish my posts on this topic, the OP may email me for any further information.

Greg


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## FiatFan (Feb 12, 2013)

Thanks, everyone for the discussion. I think I know what I need to do now. 

Tom


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## Dan Pierce (Jan 2, 2008)

All, poly switch and poly fuse are much the same, google either one. poly fuse comes up right away with digi-key and Newark parts.


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## Greg Elmassian (Jan 3, 2008)

Right, the search function WILL find it, but go to Digikey and look what it finds... Polyswitch.... likewise littlefuse does not use that name. 

Why "correct" me to further propagate the wrong name? This is like Aristo and PWC when it should be PWM.... People are out there searching for what PWC means.... when it's just wrong.. Aristo only term for PWM which the rest of the world uses. 

There's a reason I am specific, so people will have the highest chance of success... not relying on someone else's mistake that the suppliers have been forced to accommodate in their search engines. 

(yeah yeah, greg just has to be right) 

Greg


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## TonyWalsham (Jan 2, 2008)

Yes Greg has to be right.......and rightly so. 
It is always better to name things correctly. Very rarely, if ever, does Greg get it wrong with technical data.


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## Greg Elmassian (Jan 3, 2008)

Not to just keep grating, but Aristo always called them polyfuses... and I searched the manufacturers and got no hits... when I did finally go to some suppliers, I found the "right" name. After that, using the right name I was able to find a superior version of them for less money, and much better suited to our locos... with the wrong name I could not find the alternate suppliers, since they were making the same product and used the "right" name. 

A whole lot of words, I know, but there's a reason I'm really specific, many people have a **** of a time navigating the Internet and large sites of commercial suppliers... and rightly so since they are model railroaders first, and computer people second. 

I only try to emphasize this on the beginners forum, where, well, most people are beginners. I try to avoid frustration by giving the best answer and lowest chance of problems. I really do think this out. 

Greg


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## Pjhinde (Mar 11, 2013)

Man I love the youtube video, that was way too cool! I guess I need to get one of those helmet cams. 

Pj


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