# Running USA SD-70 on batteries



## Terry Jackson (Jan 4, 2008)

I am running my new SD-70 on 2 7.2 volt batteries which gives it 14.4 volts. It runs ok, but was wondering if another 7.2 volt battery added to it making it 21.6 volts would make it run for a longer time and faster if needed. The batteries are charging a 3 volt battery that runs the Pheonix sound unit and also lights. No smoke unit also using the Aristo mini onboard unit. Do I need more voltage available if needed or is 14.4 volts good enough?


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## eheading (Jan 5, 2008)

If you add another 7.2 volt battery to your SD70, it will definitely go faster, but not longer. Adding it in series increases the maximum voltage but not the amp-hours/running time. Greg and others have discussed this fairly extensively on another thread.

Ed


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## TonyWalsham (Jan 2, 2008)

All this is assuming the 27 MHz TE Mini on board can actually handle the current draw of an SD-70mac hauling a train.


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## NTCGRR (Jan 2, 2008)

My Macs are the fastest runners gear wise and I still use 18 volts. 14 has always been to slow for me.


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## Paul Burch (Jan 2, 2008)

Terry,
What is the mah rating of your batteries? Also,if you add a third battery,at full charge they will be over 24 volts.


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## Terry Jackson (Jan 4, 2008)

Radio shack brand batteries for RC cars. 7.2 v at 3300 mah Paul.


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## eheading (Jan 5, 2008)

I sort of use 2 hours as an absolute minimum for runtime on my engines. My USAT GP38 needs 4000mah to give me 2 hours of run time. I believe the SD-70 has twice as many motors, so I would think it would draw at least somewhat more current than my GP38. If so, I would think your 3300 mah would be marginal, at least for me.

Ed


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## Greg Elmassian (Jan 3, 2008)

I have to agree with Ed, you are too light on your amp hours. Also, I agree with Marty, the 14.4 is a bit low for mainline modern freight. 

I'd use different battery packs, which is probably what you do not want to hear. 

18v at 4000 mah minimum, and I'd consider the Aristo 21v packs if you were not running the TE. 

Which Aristo TE are you using? Since you said "mini" that limits it to about 3 products. Is it the new Revolution TE? If so, you may encounter problems above 18v and high current. 

So, please, more info. 

Regards, Greg


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## eheading (Jan 5, 2008)

Greg, I believe the Revolution TE is rated for24 volts max. I run mine with the Aristo li-ion batteries which are above that when they first come off the charger, and so far with about 5-6 months of pretty heavy usage, I haven't had any problems yet.

Ed


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## Terry Jackson (Jan 4, 2008)

I am using the older 27 mhz mini on board unit.


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## Greg Elmassian (Jan 3, 2008)

So Terry, your unit looks like this?









Good for about 2.5 to 3 amps. If you run heavy loads on your loco, you could exceed the capacity of the unit.

Ed, I'm aware of the specifications on the Revo TE, but it is not rated 5 amps AT 24 volts (i.e. BOTH at the same time), each of those is a maximum. You will find a post from Lewis on the Aristo site about not running full amps at full volts, recommending a person with overheating problems to run at 18v rather than 21.


I'm pretty sure that the 5 amps is at 12 volts, and derated at higher voltages. This is based on the experiences related on the Aristo site, and my own personal experience.

This is very similar to the AirWire receivers where they are listed as 10 amps, but they are 10 amps at 12 volts, and much less at higher voltages.

The bottom line is being able to dissipate the heat generated, and watts is a function of current AND voltage. BOTH are in play at all times.


Anyway, I wanted to explain my statement, and you can get all the proof you need on the Aristo site. Sorry for the slight derail fellas...

Regards, Greg


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## Treeman (Jan 6, 2008)

Terry, will you be able to make it to Marty's. I will bring a good selection of batteries, and a charger that will work at different voltages and battery chemistry. Hope you like that loco, and sound system.


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## TonyWalsham (Jan 2, 2008)

Greg. 
It would surely be nice if the manufacturers made the Va (or watts) rating *CRYSTAL* clear, instead of just saying AMPS.


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## Terry Jackson (Jan 4, 2008)

Greg that is what I have less the capacitor and resistor. And Mike I am bringing it to Marty's I am sure we can fix it up when we arrive. We will be there Thursday afternoon.


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## Greg Elmassian (Jan 3, 2008)

Great, now we know the hardware. I have been unable to find published specifications for this unit, since it was obsoleted long ago. 

George Schreyer gave those approximate current capabilities. Under very heavy loads, the SD70 can exceed that. I would monitor your current a few times to be sure you are in good shape. 

Also, when installing, if you can get some airflow across the metal plate, it would help, a small fan, and ensuring that there is some venting inside the SD70. 

Regards, Greg


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