RailPro and Dead Rail

[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]

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

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]

... and I can run for hours

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.

[KPack]

That's good info Alan.  When I run, I typically will only run for an hour and a half or so, and it's not continuous.  I have run the locomotive over several of these sessions without charging it.  Granted, I don't run this locomotive much because I usually forget to put it on the trickle charger and I'm assuming after sitting for a month the battery will have drained some. 

Interestingly I haven't noticed much of a difference when the battery charge gets low.  Normally it just runs like normal until it's out of power and then it suddenly shuts off completely.  Of course, this may be the battery low on charge and not completely drained.  I have no way of measuring remaining charge in the battery.

Also, would those numbers change much if instead of 14.8V you are measuring 12V?  The step up regulator I use is 12V.

[Alan]

Also, would those numbers change much if instead of 14.8V you are measuring 12V?  The step up regulator I use is 12V.

The 14.8V is the mains reference. So yes, if you change the reference to 12V then the battery unit would appear measurement-wise to perform slightly better.

I would think running on a layout that really taxes the loco is where the battery idea gets sketchy - steep grades, long helix, long trains, etc. An HO loco under heavy load is going to drain the battery pretty fast. My Atlas 4 axle locos pull roughly 100mA @ 15V when dragging a 16 car train (all metal wheels) on flat track at normal main speeds hence why I used 100mA as reference.

Interestingly I haven't noticed much of a difference when the battery charge gets low.  Normally it just runs like normal until it's out of power and then it suddenly shuts off completely.

The LM PWM magic in action. Your loco used in a conventional DC manner would make it obvious the battery is fading away.


Reminds me of a funny battery story. Recently I was working a project that required driving #12 x 4" screws into southern yellow pine. I was using a Bosch 3/8" electric drill for which I had to string 300' of cable to get to power. My buddy questioned why I wasn't using a battery (cordless) drill and started shooting his mouth off about how his DeWalt driver would run those screws all day long. I said bring it over, let's see it. The cordless drove about 30 screws and it was done. Time to swap batteries. I then (with great pleasure) showed him the box of 1000 screws and informed him I was on the second box. I didn't hear anything more from him about using battery tools.

[TwinStar]

Reminds me of a funny battery story. Recently I was working a project that required driving #12 x 4" screws into southern yellow pine. I was using a Bosch 3/8" electric drill for which I had to string 300' of cable to get to power. My buddy questioned why I wasn't using a battery (cordless) drill and started shooting his mouth off about how his DeWalt driver would run those screws all day long. I said bring it over, let's see it. The cordless drove about 30 screws and it was done. Time to swap batteries. I then (with great pleasure) showed him the box of 1000 screws and informed him I was on the second box. I didn't hear anything more from him about using battery tools.

When I was in corporate aviation I had access to battery shops that would rebuild my Dewalt/Milwaukee batteries for half the cost of Home Depot/Lowe's replacements. But you are correct, a cordless anything is like a printer. It's cheap until you have to start replacing batteries/ink. I have several cordless tools that have specific jobs but nothing beats 115V being run across the shop/yard.