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

In summary: That's a really good point. I've heard of some people running their full-sized EV's at 24V (like 20 12V batteries in series, I think), because there's a lot more 24V industrial electric vehicle stuff out there than 120V (or 144V or 156V or 300V or 300+V, for that matter...) stuff. Lower voltage = higher current, but the current (and voltage) ratings of the motor and controller should be the most important thing for you. And for crawling around at low speed, you shouldn't need that much power...In summary, the conversation discussed the use of DC systems for powering a motor and the comparison of
  • #1
tyquestions
5
0
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
 
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  • #2
tyquestions said:
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.
 
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  • #3
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
 
  • #4
tyquestions said:
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.
 

1. What is the relationship between voltage, amperage, and wattage for DC motors at low RPMs?

The relationship between voltage, amperage, and wattage for DC motors at low RPMs is known as Ohm's Law. It states that the current (amperage) flowing through a conductor is directly proportional to the voltage and inversely proportional to the resistance. This means that as voltage increases, current also increases, and as resistance decreases, current increases. Wattage, which is the measure of power, is calculated by multiplying voltage by amperage.

2. How does voltage affect the speed of a DC motor at low RPMs?

Voltage is one of the key factors that affect the speed of a DC motor at low RPMs. In general, a higher voltage will result in a faster spinning motor. This is because a higher voltage will create a stronger magnetic field, allowing the motor to overcome more resistance and spin at a higher speed.

3. Why is amperage important for DC motors at low RPMs?

Amperage is important for DC motors at low RPMs because it determines the amount of current flowing through the motor. This current produces the torque that is needed to spin the motor. At low RPMs, the motor may require a higher amperage to overcome the resistance and start spinning. However, as the motor reaches higher RPMs, the amperage may decrease as the motor becomes more efficient.

4. How does wattage affect the performance of a DC motor at low RPMs?

Wattage is a measure of power, which is the rate at which energy is transferred. In the case of DC motors at low RPMs, wattage can affect the performance by determining how much power is available to spin the motor. A higher wattage motor will be able to overcome more resistance and spin at a faster speed, while a lower wattage motor may struggle to start and maintain a consistent speed.

5. Can voltage, amperage, and wattage be adjusted for DC motors at low RPMs?

Yes, voltage, amperage, and wattage can be adjusted for DC motors at low RPMs. This can be done by using a power supply with variable settings, such as a bench power supply, or by using different batteries with varying voltages. It is important to note that adjusting these factors can affect the performance and lifespan of the motor, so it is recommended to consult the manufacturer's guidelines before making any changes.

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