These Snow Days are the Days I love My Car......

[madvlad]

Ironically enough Electric Motors are my specialty!!

The nitty gritty is in fact air density which effects ambient temperature, the thinner the air the less the cooling capacity, electric motors MUST have a set amount of cool air blowing over them to push the heat dissipating on the cooling fins of the body. The hotter a motor gets the less performance it has, the solution is oversize and de-rate to account for the power loss. The principal per EASA is a 3% de-rate per 1,000ft after 3,300ft ASL (above sea level).

Those little RC cars dont have much power in them for you to even notice that 3% loss per 1000FT even if you have a 1hp operating at 6,000ft with a 9% loss you would have roughly .93HP not nearly enough to visually notice. The other thing you have to factor is you live in Colorado and in Parker along where I live we are already above 3300ft ASL you already have losses that you are accustom to and dont even know it. The motors i deal with range from 100HP to 500,000HP so the de-rate and loss is very significant.

I actually just had two 450HP motors at Cripple Creek gold mine in Victor Colorado overheat and fail three weeks ago because the original engineer did not account for altitude, the demand on the machine they were running was 450HP but because they only gave them a motor capable of 450HP at the 10,000 ft ASL they were at (21% de-rate) the motor was actually only operating at 355HP thus the demand was forcing the motor to work harder to keep up, the motor will do what is asked of it so it works harder, hotter until something either goes boom or burns up.

Result I sold them two 600HP motors operating at 474HP @ 10000ft ASL. Good day for me bad day for them

[Kim-n-Dean]

Indeed it would and correct but keep in mind these motors get hot fast, there is low voltage but high current flowing through them and the harder the motor works the higher the current. On an RC car every time you stop you have to start again and starting or ramp up is the peak of the torque curve demanding higher current.

It's pretty amazing the current these little suckers are capable of! My 6400 mAh LiPo batteries, brushless 2400Kv motor and ESC can pull over 160 amps.

[Grim2.0]

It's pretty amazing the current these little suckers are capable of! My 6400 mAh LiPo batteries, brushless 2400Kv motor and ESC can pull over 160 amps.

160Amp @ 2400Kv is pretty impressive, and will tickle if you touch it as well, I imagine there are quite a few capacitors in there, and this is all DC power we work with a ton of AC power but we also sell Variable frequency drives so the AC from the utility comes in, is converted to Dc through IGBT's then back to AC to the Motor.

The Lower the voltage the higher the current draw, always makes me laugh when someone brags about voltage being high IE 100,000 volts but its only drawing 1.2 Amps enough to sting but not put you down.

Then i have a 230V motor that can pull 7,250 amps that will not only kill you but will cook, and blow your ass up.


SCIENCE!!!

[Kim-n-Dean]

The Lower the voltage the higher the current draw, always makes me laugh when someone brags about voltage being high IE 100,000 volts but its only drawing 1.2 Amps enough to sting but not put you down.

What makes me laugh is when I hear someone say they are going to swap out all their 110V equipment for more expensive 220V because they think their power bill will go down. I hear it all the time for grow room lights. A 1,000W light still pulls 1,000 watts regardless of input voltage. Since the power company charges by watt/hour, your bill remains the same! Dropping amperage on the line doesn't help your bill.

[Grim2.0]

What makes me laugh is when I her someone say they are going to swap out all their 110V equipment for more expensive 220V because they think their power bill will go down. I hear it all the time for grow room lights. A 1,000W light still pulls 1,000 watts regardless of input voltage. Since the power company charges by watt/hour, your bill remains the same! Dropping amperage on the line doesn't help your bill.

so lets increase the voltage input when the demand never changes?? makes sense to me.....

The other question is where are they going to pull the 220V and what phase? unless your house was built in a friggin industrial park where they have a third leg it wont do you any good. Every neighborhood is equipped with 110V Single phase power nobody has 3 phase access.

We had a guy who was retrofitting his own lathe, he "acquired" a three phase 230/460V 7.5HP 3600RPM motor, some motors have up to 12 leads but if its single wired for one voltage either 230 or 460 WYE or Delta there are only 3 leads. His had 3 leads wired for 460V, naturally when you dont know what you are doing three leads clearly would mean 2 power 1 ground right??? So thats what he did, he took 3 power leads put two in the power supply and 1 on the ground....motor go boom black smoke and bad smell.

He cant for the life understand why it blew up he was certain it was wired correctly, i tell him its a 3 phase motor and you dont have 3 phase at your house you need to buy a single phase cap start motor.

It sounds like you know your electricity and wiring so imagine what happens when you take three power wires that all connect at some point and grounding one while power is flowing through??

[Kim-n-Dean]

The other question is where are they going to pull the 220V and what phase?

For lights, just put in a breaker that grabs both legs in your breaker panel. That's what I did for my hot tube and CNC mill. I was going to go three phase on the mill, but learned phase converters aren't worth a shit, so regular ol' residential 220.

It sounds like you know your electricity and wiring so imagine what happens when you take three power wires that all connect at some point and grounding one while power is flowing through??

What's that smell?!?!? My brother finished his basement and did his own wiring, which he knows nothing about. I asked him how does he know if it's right or not. He said he just kept connecting wires until the breakers stopped popping. I gave him a "live" demonstration of how a system can be wired where the breaker never pops, even while the circuit is throwing sparks and melting wires. He shut down his panel and called an electrician.

[Penadam]

You're wrong, and here's the numbers. Now first, I'll say in general. There are electronically controlled, ambient pressure adjusting wastegates. They are extremely rare in automotive applications, used mainly for aircraft. In fact I've never heard of one being used in an automotive application. There are also ambient pressure supercharger bleed-off valves, that basically spin the supercharger faster than needed all the time, and bleed off excess boost. Again extremely rare, and never been in an OEM application as far as I'm aware. This is for 99% of automotive applications, including the Subarus, BMW's, and my Fiero.

Sea level = 14.69psi
Colorado Springs = 11.7 (That is the cells that my piggyback is at with ign on, engine off).

Anyways, we lose about 3psi ambient pressure due to altitude. For an N/A car, this is a 20.4% loss in air pressure, which would equate to a 20.4% loss in power (Assuming same ignition timing maps, which is likely).

Back in high school, I had a friend who moved here from Texas, on the coast, who had a modded GTP. Via his data-logging software, he saw dead on 15psi. Added to the 14.69, he had 29.69psia. However here in Colorado, due to how a supercharger works, he only saw 12psi. Combined with the lower atmospheric pressure, he only got 23.7psia. He saw a 20.2% drop in psia, equating to a rough 20.2% drop in power, near identical to the N/A numbers.

Boost is pressure above ambient. Superchargers will show less boost as altitude increases. This is because they are set to run at a certain speed, which means a certain airflow. So on the inlet side of the supercharger, they are down 3psi ambient. Because there is less air going into the blower (3psi less), there's less coming out (3 psi less). So you've got a 3psi loss in boost pressure, mixed with a 3psi loss in ambient pressure, about a 6psi loss in total air pressure, which gets us our roughly 20% loss in power.

However, things are different for a turbocharger, since boost (Pressure above ambient), is kept equal at your peak power. So for me, it was 14psi. Added to the 14.69, at sea level, I'd have 28.69psia. Up here, that drops to 11.7 + 14 = 25.7psia. A 10.4% loss in power, roughly half that of the N/A and SC cars, exactly what we'd expect.

Superchargers suffer just as much power loss at altitude as N/A cars, with turbo cars being about half of those.

Two clarifications:

1) You're referring to positive displacement superchargers (roots and screw are typical), which have a fixed compression ratio. Centrifugal supercharges are more like belt driven turbos and can have wastegates, though it would be wasteful to size them as such (you'd be wasting engine output, instead of exhaust energy).

2) You can mitigate a lot of the power loss of a supercharge at altitude by changing the pulley size, causing it to spin faster for a given engine speed. You'll end up with absolute (atmospheric+boost) intake pressure closer to what you'd have at sea level.

[Aaron]

1) My first paragraph I mentioned that exception, where they essentially use a waste gate to bleed off excess pressure. This can be done on any type of blower, but is generally geared more toward the centrifugal since the primary goal isn't to combat altitude, it's to combat the linear boost increase with rpm. By itself, a centrifugal blower is hurt just as much at altitude as a roots and screw, and N/A cars. Waste gating superchargers is still really rare too.

2) You're right about that, and the same can be done with a turbocharger (Even easier actually). But it can be dangerous as your intake charge temps will be higher, and you are still limited at 91 octane.