[Overlander23]

It's quite simple. You can't get something for nothing. In this case, you're essentially wondering whether 900 watts can power a car 55mph. One horsepower is roughly equivalent to 750 watts, so can 1.2 hp (900/750) propel a full-sized vehicle 55 mph. Errr, no. And that's assuming 100% efficiency between the generator and the wheels.

In the end, volts, amps, it doesn't matter. Watts is power. You can use volts and amps to derive watts; amps * volts = watts... If you heard that someone can power a vehicle down the road on just 0.8 amps, and let's assume 15 hp for something like a Civic @ 55 mph:

15hp * 750 = 11250 watts

watts = amps * volts, so: 11250 watts / 0.8 amps = 14062 volts

14062 volts, not very realistic. But something more realistic would be:

11250 watts / 80 amps = 140.6 volts. So in this case, 140 volts is needed to power a Civic at 55 mph (15 hp), while pulling 80 amps. Much more in-line with a conventional EV conversion.

The relationship is simple. Look at it another way. What about a 36 volt system? That's 11250 watts / 36 volts = 312 amps. A lot of amps, but it can be done if the batteries can handle it.

A 300 volt system? 11250 watts / 300 volts = 37.5 amps.

So there you go, the higher the voltage, the less amps are needed to create an amount of power. The lower the voltage, the more amps you need to create the same amount of power.

At 55 mph aero drag is a big concern. Some vehicles will consume more than 15 hp maintaining it, while more aerodynamic, lighter vehicles will consume less. But 1.2 hp? Nope... Very light, aero-sheathed, recumbent bicycle maybe...

Let's look at your second posting.

Open Guy is claiming 100 amps out of a 5 hp generator. That's 5 hp * 750 = 3750 watts. 3750 watts / 100 amps = 37.50 volts. There's your "36v" system. But it's still only 5 hp.

You researched a 2300 watt generator @ 120v. That's 2300 / 120 = 19.17 amps. Sounds like almost 20 amps (which is what its rating was). But it's only 2300 watts / 750 = 3 hp.

Most consumer generators are 120v, because they're designed for household appliance use. A 100 amp generator @ 120v would be producing, 100 amps * 120 volts = 12000 watts. That's a big generator. And 12000 watts is, 16hp. So yes, a 100 amp, 120 volt generator could probably get most of the way to powering continuously @ 55 mph. And I'll bet that generator will be using a 16+ horsepower engine. Probably closer to 20hp due to efficiency losses. See how much fuel that burns in an hour.

Keep in mind that 15 hp is generally what you will need to maintain 55 hp. To get there requires either a bit more, or a lot of patience.

 

[Overlander23]

Amps x Volts = Watts... It's all there.

Watts and HP are the same thing, more or less, just different units (750 watts per HP) of power. Power is the motivating force.

100 volts x 100 amps = 10000 watts = 13.3333 hp

10 volts x 1000 amps = 10000 watts = 13.3333 hp

1000 volts x 10 amps = 10000 watts = 13.3333 hp

Get it?

Solve for 1 hp; 750 watts...

750 watts = 100 volts x 7.5 amps

750 watts = 10 volts x 75 amps

750 watts = 1 volts x 750 amps

Random one; 750 watts = 34 volts x 22.05 amps : 750/34 = 22.05 : 750/22.05 = 34... take your pick.

Each of those voltage/amperage combination produce the same amount of power.

Put it this way. It's impossible to have a situation where 750 watts of power is created from 12 volts and 100 amps, because 100 amps x 12 volts = 1200 watts.

Generally higher voltage (and therefore lower amperage) setups are more efficient than lower voltage (and therefore higher amperage) setups.

Doesn't matter if an electric motor or an ICE is providing it as far as power/constant speed is concerned. Power is power. A watt (over time) is what gets you down the road regardless of how it is generated. Acceleration is where you'll see a difference in characteristics between a motor and an engine.

 

[Overlander23]

A watt is an instantaneous measure of power. A joule is a unit of energy, or the amount of power produced over time.

One watt delivered for one second equals one joule. Or 1 Watt-s = 1 Joule. Going further, you can see that by adding time you can get watts per hour (watt-hrs) as a unit of energy. One Watt-hr = 3600 joules (since there are 3600 seconds in an hour).

Take a 100W lightbulb. It takes 100W to illuminate it. Apply that amount of power for an hour and the lightbulb consumes 100W-hrs of energy, or 360,000 joules.

Notice that this is how you derive the energy capacity of a battery pack. A battery pack made up of 10 cells, each at 1.5v and 100 amp-hours of capacity yields a battery pack that is capable of storing 1500 watt-hrs of energy (10 x 1.5 x 100 = 1500 watt-hrs). That's equivalent to 5,400,000 joules of energy (1500 watt/hrs x 3600 = 5400000 joules).

If wired in series, the battery pack will be a 15v pack with 100 amp-hrs of storage.

If wired in parallel the battery pack will be a 1.5v pack with 1000 amp-hrs of storage.

Notice, though, that both packs contain the same amount of energy, 1500 watt-hrs.

Typically, you'll read about the amount of energy required to power an average EV quoted in watt-hours per mile. It can range from about 100 to 600 watt-hrs/mile depending on the weight, aerodynamic efficiency, and average speed. Using this info, and the aforementioned 1500 W-hr battery pack, you can see that a car with an average efficiency of, say, 250 watt-hrs can travel 6 miles before depleting its energy reserves.

 

[Overlander23]

so, how does one convert the 300kj needed to push a 1 ton car just over 55mph into watts needed then? by seconds?

As mentioned previously, 1 watt-s = 1 joule. Also previously stated, a watt is instantaneous work. Add the time factor and it becomes an amount of energy.

300,000 joules = 300,000 watt-s, or 5000 watt-minutes, or 83 watt-hours.

If you were to provide 83 watts of power over the period of an hour, you'd be using the energy equivalent of 300,000 joules.

If you used a more useful period, say the acceleration time of a car going from 0-55 mph over 10 seconds, you'd have 50,000 watts over 10 seconds. That's 50,000 watts delivered for 10 seconds equaling the energy of 300,000 joules... ~65hp for 10 seconds. Reasonable for a 2000lb car.

It's all there. People haven't given you the specific answer to your numerical problem, but they've given you the tools to figure it out.

The best problem solvers are those that can be artists and understand the numerical reasons why. The artistry is good for problem solving. The math makes the problem-solving practical. Thankfully, humans aren't either-or. It's not like you give up artistry the more math you know, and vice-versa.

 

[Overlander23]

Using "engineering" units, convert mph to fps, multiplying by 22/15: 55 mph = 80 . Divide weight (in pounds) by 32.174 to get mass in slugs. Substitute these values in formula above; you should get 215.9 × 10³ (10,000???!!!) ft lb. (215900???? formula calls for 215.9 x 1 to get 292.72 result!) Finally, convert to J, multiplying this by 1.356 J/ft lb. I get 292.72 kJ.

I mean no offense by this, but you seem to have a serious problem with units. It's either self-imposed, because you make assumptions, or you're not careful with your reading/comprehension.

Let's look at what you found... 215.9 x 10³. First off, 10³ = 1000, not 10,000. So you end up with 215,900. Then the equation says, multiply by 1.356 J/ft to get Joules (note: not kilojoules). The result is 292760.4 joules, which is close to the stated 292.72 kJ. The cubing was fine.

See Major's post for the rest. But you're probably not reading this anyway...

trying to get the math down but that darn apples & oranges crap as well as bogus info even within a formula is holding me back. i have this INCORRECT kinetic energy formula to start with,

Using "engineering" units, convert mph to fps, multiplying by 22/15: 55 mph = 80 . Divide weight (in pounds) by 32.174 to get mass in slugs. Substitute these values in formula above; you should get 215.9 × 10³ (10,000???!!!) ft lb. (215900???? formula calls for 215.9 x 1 to get 292.72 result!) Finally, convert to J, multiplying this by 1.356 J/ft lb. I get 292.72 kJ.

that's OK though, the 10 CUBED can just be ignored and just multiply 215.9 by 1.356 to get the proper 292.72 instead of 292720.
215.9 x 1.356 = 292.7604kj actually. they didn't even multiply their own numbers correctly DESPITE the erroneous cubing.

 

[Overlander23]

I find this all terribly amusing. Terribly... amusing...

I'm pretty sure I don't have to worry about the OP reading this and taking offense either, since not only have several people given the answers to his questions from a theoretical standpoint... and from a literal standpoint.

Duncan seems to be the only person he reads.

Maybe I'm in his "ignore" list and he's just not getting the posts. In which case, I suppose this post is just as pointless.

Why else would someone post

"if no one pointed it out yet, 10 cubed is 1,000 and not 10k as 10 to the first is 10."

at 1:37 pm PST when at 10:16am PST I wrote,

"Let's look at what you found... 215.9 x 10³. First off, 10³ = 1000, not 10,000."

It's also hard to point out the difference between a Joule and Kilojoule when the answer makes the OP feel stupid. But how much simpler can the explanation get? It was not my intention to make you feel stupid. It was my intention to point out that 1000 joules = 1kJ... and countless other relationships.

OP... ARE YOU READING THIS?!?!