# locomotive amperage draw



## domer94 (May 4, 2015)

can you guys please tell me the typical draw for
usa trains alco s4
aristo U25b
arist RS3
arist FA1 / FB1
LGB 2095
LGB white pass diesel

thanks


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## chuck n (Jan 2, 2008)

As a rule of thumb, I figure maximum of one amp per motor. If there is sound and smoke add another amp or so for good measure. At the end if you need precise numbers, you need to measure it yourself, because your track, curves, length of trains all have an effect. The numbers I suggested are a reasonable value. Your situation may be different.

Chuck

I have a USAT train that pulls 7 amps. The engines are F3A and B followed by 6 streamliners with lights. 4 amps for the engines and 0.5 amps per lighted car.

Looking at your list of engines, I'd recommend a 10 amp power supply at a minimum. If you buy something with less output and you need more later, why buy twice when you can buy once. More power may cost more at the beginning, but if you need more later, what was the saving?


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## Dan Pierce (Jan 2, 2008)

LGB smoke units only draw 1/10 (.1) of an amp. If you change to LEDS, only 20 ma per light max. LGB uses the same motor in the white pass and the 2095.

I have found USA motors draw the most current, LGB the least.


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## Greg Elmassian (Jan 3, 2008)

Also, the USAT smoke units draw a bit, depending on the model.

All I can say is measure them for yourself to be sure.

You also need to understand the difference between "typical" (which is really useless) and maximum or stall currents.

The decoder needs to be rated for stall, but this is still not a good enough definition.

Some decoders are rated at "continuous" and "stall for xx seconds"... some decoders just have a "max" rating. On top of that, some ratings are inaccurate.

It unfortunately takes experience (yours or someone you trust). If you don't have that, then the next best answer is bulletproof it... Don't try running a 2 amp decoder on a loco that draws 2 amps on average.

Greg


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## mgilger (Feb 22, 2008)

Here are some current measurements that I made several years ago when I was considering moving to battery power. All are based on the engine(s) pulling 8 cars. 

SW4 = 2.4 AMP
NW2 = 2.0 AMP
RS3 = 1.8 AMP
SD45 = 3.2 AMP
E8 = 2.6 AMP

Hope that helps.

Mark
*http://mmg-garden-rr.webs.com/*


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## Greg Elmassian (Jan 3, 2008)

No smoke but all lights on?


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## mgilger (Feb 22, 2008)

Yes, no smoke and head lights were on. 

After I converted to battery operation, using a trailing battery car I built up a test car using 2 Harbor Freight DVM's. The battery car was placed behind the test car so the voltage had to pass through the test car to get to the engine. One DVM measures the current, the other voltage. 

http://mmg-garden-rr.webs.com/apps/photos/photo?photoid=92838627

Mark
*http://mmg-garden-rr.webs.com/*


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## Greg Elmassian (Jan 3, 2008)

Excellent idea Mark, $10 for 2 digital meters, and I suppose they could be made smaller by removing parts from the cases. (have not looked at the LCD connections).

An idea that every modeler can afford.

Greg


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## mgilger (Feb 22, 2008)

The best thing about these meters is that they are free at Harbor Freight. So the price is right for sure. 

Mark
*http://mmg-garden-rr.webs.com/*


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## attaboy (Oct 26, 2016)

*Tractive Effort Tests .. with Amps*

I had this stashed in my LS reference "_library_" and although it's a little dated, might be helpful. I too gotta plan for amperage's and decoders .. kinda leaning towards the NCE wireless DCC. Thanks to the Author .. a huge effort indeed.

http://www.girr.org/girr/tips/tips4/tractive_effort_tests.html#results


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## Greg Elmassian (Jan 3, 2008)

Those measurements are golden, and George's measurements started the "enlightenment" about running vs stall and why early decoders were going bust.

Greg


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## JackM (Jul 29, 2008)

Here's an idea that might be helpful. Could one of you guys give us an illustration of where you put the probes when measuring current draw? Especially when using two meters. Picture worth a thousand, etc.

JackM


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## attaboy (Oct 26, 2016)

*Watt Meter and Power Analyzer*

Hey JackM,

Perhaps consider a simpler solution amigo. Just get a "power analyzer" which combines *Both* meters into one very compact device. These are commonly used for monitoring battery condition in RC aircraft and multi-rotors. I have a couple different flavors of these here, but you would want a version _Without_ an external current shunt .. keep it simple.

Now, the "_Watts Up_" brand name was the original which has been dutifully copied by other Chinese manufacturers .. as is normal, but it's 3-4 times the money for basically the same functions. Your application is certainly less critical than flying time 

And for you guys running on battery power, they're cheap enough to put one in each Loco, starting at about ten bucks a pop, or alternatively affix one to each battery pack .. quiescent current is nominal and shouldn't affect what the charger sees (depending on your balancing circuitry). No, they're not _Uni-T_ or _Fluke_ in accuracy, but certainly adequate for Locomotive amperage 

https://www.amazon.com/s/ref=nb_sb_...&field-keywords=Watt+Meter+and+Power+Analyzer

Now, for you guys/gals that get more into the nitty-gritty of electronics, you might consider getting a dedicated precision power supply, which also shows both amps and volts simultaneously. I have this one in the lab .. works well for me and has good reviews .. https://www.amazon.com/gp/product/B00LBOICL8 and can be set for either constant voltage or constant current, if that is useful for you.

Hope this is helpful .. or use the freebie (coupon) HF DVM's method .. series and parallel .. like the olden days. Cheers!

Jon in the woods
mendorailhistory.org


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## Ted Doskaris (Oct 7, 2008)

*Example Track Power Setup*




JackM said:


> Here's an idea that might be helpful. Could one of you guys give us an illustration of where you put the probes when measuring current draw? Especially when using two meters. Picture worth a thousand, etc.
> 
> JackM


Jack,

If you use track power, then this is an example how I configured my track power setup with an early model Revolution Base Station with volt meter and amp meter.

Aristo Revo Base Station Example Block Diagram
(Note both Amp & Volt meter are at the input of the Revo Receiver,etc., so it will indicate some current draw in addition to what ever loco is on the track, but I found this to be very minimal. The voltmeter indicates only the power supply voltage so I could check on its output and adjust the voltage as needed.










The Aristo Revo Base Station example here is setup in discrete components
(Later Revo Receiver models were factory packaged in a plastic housing)










-Ted


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## JackM (Jul 29, 2008)

Well, I can see I'll be getting one of those Power Analyzers. And, Ted, thanks for the schematic. It's been a good twenty years since I last laid my hands on a 3906, and I probably still have the parts to build your demo, except mine would look like all the parts got chewed up by the muffin fan. (Shame nobody builds HeathKits anymore.)

JackM


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## Dan Pierce (Jan 2, 2008)

There are kits available for many projects.
You do it electronics have kits, as does MPJA.com


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## attaboy (Oct 26, 2016)

It has occurred to me, after the above photo joggled some brain cells, that the power analyzer solution I suggested above would Not work with a DCC track power system, as DCC is actually a kind of alternating square wave. In that case, you could always just plug your AC into a _P3 Kill A Watt_ and get a rough idea I guess. Divide the watts being consumed by your track voltage to get amps .. maybe 85% accurate. Just remember to subtract your static/phantom watts (loco stationery) from your loco under load watts,

I echo the Heath Kit sentiments. Actually, I(we) used a special Heath Kit for teaching 1st year Electronics which embraced both vacuum tube and solid state technologies on the same chassis, going through many different circuit designs. This was in '63-'64, when a CK722 still cost a princely sum. Another kit maker was _PACO_. I received a _PACO_ VTVM Kit for my 13th Christmas. Another one was of course _EICO_, and even both Lafayette and Allied Electronics sold various kits back then. Nowadays, you can simply buy a copy of _"Eagle"_ and simulate just about anything you want, but nothing can substitute for the good ole _hands on_. jmho .. Cheers!


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## Dan Pierce (Jan 2, 2008)

You can always measure the current fronm the DC supply used on DCC systems.
Subtract the no load current from the current drawn by the loco.

Or get a scope with a current probe and measure it real time.


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