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alco_diesel:
Hello,

I am a long time satisfied user of RailPro and am considering moving to Dead Rail. My question concerns the minimum voltage for the LM3-S module. I’m thinking of using a 3.7volt battery and a step up to 11.1volts. Is 11.1 volts enough for the LM3-S to operate?

Thanks,

Jeff

Alan:

--- Quote ---Is 11.1 volts enough for the LM3-S to operate?
--- End quote ---

Yes barely, but you will continually get low voltage warnings on the HC. An LM seems to shut down somewhere around 10V.

Make sure that 3.7V battery has a high mAh rating. You will be pulling a lot of amps from it using the step-up arrangement.

alco_diesel:
Thanks Alan,

I think I’ll investigate putting batteries in series to get a higher voltage. 

Jeff

KPack:
Use this voltage converter: https://www.litchfieldstation.com/product/pololu-12v-step-up-voltage-regulator-u3v12f12-2/

I use a cheap 3.7V 700mah battery with this converter and LM-2S.  There are no low voltage warnings for me and I can run for hours.

I need to do a follow up video, but here's the original one I made a while back:
 

-Kevin

Alan:

--- Quote ---... and I can run for hours
--- End quote ---

The math says about 1-1/2 hours light load continuous running equivalent to mains power. 700mah @ 3.7v = 2.59 watts minus buck efficiency = 2.33 watts. 100mA @ 14.8V = 1.48 watts. 2.33 / 1.48 = 1.57 hours.
About 30 minutes of heavy load continuous running equivalent to mains power. 700mah @ 3.7v = 2.59 watts minus buck efficiency = 2.33 watts. 300mA @ 14.8V = 4.44 watts. 2.33 / 4.44 = 0.52 hours.

Lots of start and stop would likely eat away from those numbers since an LM initially pulses full current (1.5A typical HO) into the motor to get the armature spinning. Battery will see a few brief 6.6A peaks each time the motor is started from zero RPM. Use of sound will also detract from run time. Audio amplifiers are power hungry.

Of course the loco will continue to operate after these time frames as the battery fades away, just not at equivalent performance to a mains supplied loco.

Typical LiPo batteries have a 500 cycle charge lifetime (at best) with a significant performance falloff after the first hundred or so cycles. If you run the loco a lot keep a replacement battery handy.

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