Understanding Voltage, Amperage, and Wattage for DC Motors at Low RPMs

[tyquestions]

Hello All-

COuld someone please give me a primer on DC as it pertains to voltage, amperage and wattage. Specifically, if I have a motor that i need to run at very low RPM (50 -150), how does the motor compare across a 12v system vs. a 24, 48 or even 60v system. Do 60v systems run more efficiently than 12v systems? Pound for pound (or mass for mass) will a 60v battery of roughly equal size as a 12v battery run a motor longer ?
Let me paint the broad picture-
my project is to build a frame that will weigh 2000lbs gross, (frame and cargo), and have it crawl at 1.5-3mph. I have found wheel/hub motors that by spec sheet can do the job(enough nm or ft/lbs of torque), but they come in a w-i-d-e variety of voltage platforms, again 12v-60v. Needing to run this cargo platform continuously for approx. 90 minutes at a constant speed,(between 1.5-3mph), which is a better voltage platform to run on 12,24,36,48,60v?
If amp draw is constant across voltage platforms, which would run the motor longer?

I guess to sum up - Why would i want to use a higher voltage platform?

Any help or direction would be hugley appreciated .

by the way here's a great energy conversion link i found @ www.1728.com/energy[/URL]

Thanks to all,
tyler

 

[berkeman]

Hello All-

COuld someone please give me a primer on DC as it pertains to voltage, amperage and wattage. Specifically, if I have a motor that i need to run at very low RPM (50 -150), how does the motor compare across a 12v system vs. a 24, 48 or even 60v system. Do 60v systems run more efficiently than 12v systems? Pound for pound (or mass for mass) will a 60v battery of roughly equal size as a 12v battery run a motor longer ?
Let me paint the broad picture-
my project is to build a frame that will weigh 2000lbs gross, (frame and cargo), and have it crawl at 1.5-3mph. I have found wheel/hub motors that by spec sheet can do the job(enough nm or ft/lbs of torque), but they come in a w-i-d-e variety of voltage platforms, again 12v-60v. Needing to run this cargo platform continuously for approx. 90 minutes at a constant speed,(between 1.5-3mph), which is a better voltage platform to run on 12,24,36,48,60v?
If amp draw is constant across voltage platforms, which would run the motor longer?

I guess to sum up - Why would i want to use a higher voltage platform?

Any help or direction would be hugley appreciated .

by the way here's a great energy conversion link i found @ www.1728.com/energy[/URL]

Thanks to all,
tyler[/QUOTE]

Welcome to the PF. The link appears to be missing something... 1728.com does appear to have lots of calculators (and no obvious ads, so I'll you linking to it), but the URL you posted does not get to the page you intended.

On your questions, I think it mostly comes down to what power source you have available. Where are you going to be getting your power? Where will your frame be crawling around at? Do you intend to battery power it? Or is DC power coming from something else (like a vehicle's electric system)?

In general, the higher voltage systems will be a bit more efficient, because Power = Voltage * Current, or P = V * I, so the higher the voltage, the lower the current required, so there are less losses in the wiring and motor coils.

 

[tyquestions]

Thanks berkeman-
It's www.1728.com/energy.htm, forgot the .htm part.

The crawler will be self powered with an on board battery. I'm assuming if an electric forklift or pallet jack can run all day, then I should be able to get 90 minutes with some sort of industrial, off-the-shelf battery supply. As far as surface goes smooth pavement or concrete will be what it is running on. thanks for the input on the higher voltage being more efficient, similar to 110 vs 220 in the AC world i guess.

If the efficiencies are only minimal, would i be better served using a lower voltage platform, either 12v or 24v, that would have more readily accessible parts and accessories?
thanks
tyler

 

[berkeman]

Thanks berkeman-
It's www.1728.com/energy.htm, forgot the .htm part.

The crawler will be self powered with an on board battery. I'm assuming if an electric forklift or pallet jack can run all day, then I should be able to get 90 minutes with some sort of industrial, off-the-shelf battery supply. As far as surface goes smooth pavement or concrete will be what it is running on. thanks for the input on the higher voltage being more efficient, similar to 110 vs 220 in the AC world i guess.

If the efficiencies are only minimal, would i be better served using a lower voltage platform, either 12v or 24v, that would have more readily accessible parts and accessories?
thanks
tyler

Absolutely. The efficiency differences should be small, so yes, pick a system voltage that gives you a good range of parts to choose from.