# USA SD40 Current Draw Problems



## SteveS (Dec 27, 2007)

I have a 15-20 yr old USA SD40 and have never been satisfied with its pulling power (12 cars max on level track). Power is a 12-volt battery controlled by a LocoLinc KLR-106 receiver (6 amps max). After some recent testing I have come to the conclusion that the motors in the the trucks are drawing more current than the six amps the receiver/decoder can handle. Since this is the largest receiver that LL makes the solution will have to be found elsewhere.


Has anyone else solved this problem? Does anyone know of a more efficient replacement motor (more torque/less current)?


I am thinking of installing a second receiver with one driving each set of wheels and then MUing them as two locos in the same body. Has this worked for anyone else?


Any feedback is appreciated.






Steve Seidensticker


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## SD90WLMT (Feb 16, 2010)

Hi, I can share a couple thoughts about this issue... 

I have run My SD70 on up to and just exceeding 7.15 amps - yes on LL... no shut downs... 

secondly, I run a 18 volt battery pack, and have seen it running under loads up in the 14 volt ranges... 

I would consider you may not be feeding your SD40-2 enough food...! 

as the trucks/motors are the same as a SD70, unless they have been improved in the years you have had yours. I can easily pull 50 - 60 - 70 cars... 

go thru and recheck all parts again...do some real world testing - including how much effort it takes to pull the 12 cars, they could be a source of trouble also... 

My experience is based on a running loco - with on board meters, direct reading, under actual loads..... 

Dirk


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## K27_463 (Jan 2, 2008)

Your current draw is too high because your voltage supply is too low. Ohms law takes over in this case. For the amount of work you want to do, you need more V. Also most likely what are you using for a 12 volt source? Gel cel? if so, they have linear discharge and drop below 12 almost immediately. Other chemistry battery are not usually 12 volts.


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## Michael Glavin (Jan 2, 2009)

Steve,

Simple math will reveal and solve the problem, as Jonathan suggested Ohms Law is in-play.

Power = Watts; how you get there determines your needs.

Dirk suggested 7.15 Amps @ 18V works for him… 7.15A x 18V = 128.7 Watts

Your example; let’s say 7A @ 12V = 84 Watts

That said, what skews reality is the batteries ability to sustain rated voltage under load… So voltage depression is a factor that is realized as higher current draw, elevated temperatures and lower potential…

Simply stated your battery may not be able to provide 12V under load, so the numbers realized under load dictate the results. Add food as Dirk suggested. 
Michael


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## TonyWalsham (Jan 2, 2008)

Steve, I didn't see anything to the contrary in your post, so if your 12 volt Gel Cell is also 15 years old there is a good chance it is below its best anyway. Batteries do not last forever. I also agree that 12 volts is too low anyway. 
I would use at least 18 volts. In my case a I still prefer NiCd, although there are other chemistries that may appeal.


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## Bill Swindell (Jan 2, 2008)

Try this http://www.gardenrrsupply.com/battery-li-ion-14-8v-4400mah


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## SD90WLMT (Feb 16, 2010)

just food for thought, while I agree with the above math,.... 

My readings of 7.15 amps would be the highest readings, and these were not under battery voltage by design of 18 volts, but rather in the 14. something dropping down into the 12. ... something range, 

I also noted that while the loco was crawling it's way up grade, as I increased the throttle setting, the speed also slowed, voltages dropped, and heat build-up increased... 

one conclusion was the equipment responded to My increase in throttle setting, watching the voltage drop, but also that it had enough of the coal drag game,by slowing down... 

so using even 14.0 volts and 7.0 amps = 98 watts ( really in the max load range in my case, running on 2.5 % or better, dragging 70 intermodals & containers ) 

When I get back to My hobby bench ... ? ... needs a super cleaning job including better access ... I will be up grading to 24 volt systems... 

I run Lead acid, with out issue also... 

Dirk .... happy running!


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## SteveS (Dec 27, 2007)

Thanks everyone for the observations and advice. 

Re: Higher voltage source. I started the latest series of tests with a relatively new 16.8 volt NiMH battery set up. The loco was able to pull only a few cars. I measured the current flow and it showed that the LL receiver was cutting out at about 2 amps. This lead me to believe that the receiver was defective. I talked to Behren Reeves at LL and he told me that the protection circuit in the receiver was designed so that it would cut out at 6 amps at 12 volts. He recommended that I lower the voltage. 

I bought a new NiMH 14.4 volt battery set and installed it. It pulled a few more cars, but still not usable. When I put it on the bench and put a load on the wheels the receiver cut out at about 4 amps. 

I then made a 12 volt set up of 10 NiCD C-cells that were 5-7 years old but had never been used. They took a charge just fine and showed 13 volts when charged. 

It had the best pulling power (12 or so cars level). But as expected the top speed seemed to be lower but acceptable. When I checked the amps it showed 6+ amps just before cutout. 

I have not checked out the voltage under load, but will do that next. 

Also, my cars are not what you call "free wheeling." Because I do a lot of switching I have deliberately put a little drag in the wheels to keep them from rolling in the breeze or down very slight grades. OK, I guess they may be 2-3 times the drag of the best free wheeling cars. 

With no load the loco consumes about half an amp. With sound on it takes about one amp. My goal is to get the locomotive to spin its wheels before the the receiver cuts the current.


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## Greg Elmassian (Jan 3, 2008)

Really sounds like you have tried various combinations. If you must stay with the locolinc, you need to try heat sinks and fan cooling. 

Greg


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## Paul Burch (Jan 2, 2008)

Another two cents. I strip out all the USA circuit boards and start over. I think that the USA electronics and lighting are partly the culprit for high current draw. I use 14.4 and 14.8 batteries. My 4 axle locos are fused at 4 amps and 6 axle at 5 with no problems. I have about two dozen locos all done the same way.


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## SD90WLMT (Feb 16, 2010)

I should add that I also removed the USA boards - in favor of direct to motor wiring from the LL decoder.. 

I no longer use the LL, as the ranges kept decreasing in use fullness, finally getting to about 10-12 feet to start a loco, and NEEDing to be as close as 2 FEET to stop the darn thing... not safe in My mind... or fun any longer... 
Might as well have just been a remote control unit on a 4 foot cable.... not... 

Dirk - DMS Ry.


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## Curmudgeon (Jan 11, 2008)

While the lighting boards and lights do draw a lot of power, they are not (or should not be) in the motor power circuit. I've done these things for years and years....what was the first GP9....1995? 
3 amp throttle won't cut it, never, ever had any issues with a 6 amp. 
While ohm's law does have validity, one wonders with the load....unless you are applying full power to the motors at a high voltage....whether slot trains might be in your future. 
We control our trains with varying voltage. Having a whole lot of overhead voltage you'll never use has not been a good idea. 
BTDT. 
For example: 
USA F-3's. Set of three, A B A, hauling....shoot...9 or 10 of their streamline cars. 
Customer said it takes three engines to move the train with track power. 
Hogwash. 
I did one loco, radio/battery, 16.8V, and it hauled it all. Dummied the other two engines, and he's still happy, 6 years later. 
TOC


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## Greg Elmassian (Jan 3, 2008)

F3's don't have a lot of pulling power, often because of "split axles" and power just not transmitted... also not much weight in them. 

The USAT streamliners have carbon brushes for power pickup, can add drag IF not in good shape. 

But yes, the motors have a very high stall current, some ESC's just cannot keep up. 

Greg


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## Curmudgeon (Jan 11, 2008)

Posted By Greg Elmassian on 30 Aug 2013 05:23 PM 
F3's don't have a lot of pulling power, often because of "split axles" and power just not transmitted... also not much weight in them. 

The USAT streamliners have carbon brushes for power pickup, can add drag IF not in good shape. 

But yes, the motors have a very high stall current, some ESC's just cannot keep up. 

Greg 
I should have added....all carbon wheel bushes removed fully.....batteries in baggage car....half (as in every other) bulb removed in cars....those things can light up yards 4 blocks away.....and one loco hauls them all.
F3 power trucks same as...GP9, GP3X, basically any 4 wheel power truck except the 20 tonner and NW.


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## Ted Doskaris (Oct 7, 2008)

Posted By SteveS on 12 Aug 2013 11:09 PM 
SNIP My goal is to get the locomotive to spin its wheels before the the receiver cuts the current.
SNIP


Steve,

Does your SD 40 still have working traction tires? If so, spinning these wheels will put a profound load on the motors with excessive current draw.

-Ted


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## chuck n (Jan 2, 2008)

I'm a bit confused. When I first read this post a couple of weeks ago I thought that 6 amps for a USAt SD40 was very high. Now that I am home, I have a chance to measure mine. I use track power with a Bridgewerks 10 power supply. It has an amp meter made of of red LEDs. I have never noticed significant numbers of LEDs lighting up. I just ran my engine with 12 USAt 3 bay hoppers and a USAt lighted baywindow caboose. The LEDs indicate % of full power. They indicated at 20 volts about 25% or 2.5 amps. To check that I brought out a Simpson Amp meter. It also indicated between 2 and 3 amps. There was no significant increase going up my short 3-4% grade. I would have to say that there is something in your electronics that is significantly adding to the load and if it is the engine, you might have a bad motor.

Taking the caboose off the track did not significantly reduce the current draw.


Chuck

P.S. At 14v the draw was closer to 2 amps.

As an aside, I just measured my USAt SD70 Mac. With the same train it runs at 2-3 amps, but it takes 5 amps to get it moving.


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## Curmudgeon (Jan 11, 2008)

Ah. yes, short range with 75MC...who would have thought... 

But: 

On the SD-40, have you checked to see if all six axles are turning? 
Shipping damage, dropped, crash...sometimes even opening it up and putting it back together....amiss....can do all sorts of things. 

Look specifically at the end axles...the steerable ones. They have a slip[ yoke and u-joints. Any opening, remove the chrome plate, bottom cover, the unit flops over, shaft disconnects, and you're dragging a wheelset...high draw.... 
Drop, hard crash, shipping...the ears get broken off, and the same thing happens. 
Mark all the wheels with a felt marker at the bottom, run it a ways, see if they've all turned..get down low and watch. 
First thing I'd look at....just to eliminate. 

Next is motors. 

TOC


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