There are many permutations of Ohms law -

In your example: E = I * r this is the solution for volts, not power.

Watts = volts * amps
P = E * I

960 = 120 * 8
960 = 12 * 80

What else can I say?

 

I should carify further:

In my example I used a typical small electric motor which consumes 8 amps at 120 volts, this device consumes 960 watts of power.

To have a 12 volt device cosume the same amount of power, the amperage would have to increase by a factor of 10.
therefore 80 amps at 12 volts will also = 960 watts.

 

OOPS! my bad. I realized before your last post that operational power for the device is 960 watts no matter what.

Yelrihseam

 

Thats cool, I enjoy the pratical application of things I learned in school :-)

 

Two things,

Ryan50hrl, you have your pullys reversed. you would have to have the 30inch pully on the crank and the 2inch on the supercharger. Otherwise the the supercharger would spin SLOWER that the crank.

GR8diesel, turbos are very efficient. Turbos require no engine power, and only restrict the exhaust a little bit. (which is easily overcome by the increase in HP and torque) Turbos compress the the incoming air, providing boost. The exhaust side spins faster and faster (which inturn spins the compressor faster and faster) because of the rapidly expanding compression ignited fuel/ air mixture. (more air out, turbo spins faster, forces more air in, even more air out, turbospins even faster, forces even more air in, etc....) I know that you have to keep adding fuel to keep this cycle going. This is the way a turbo works, no engine power is tranfered to the turbo, only byproducts of combustion. (heat, pressure and volume of exhaust gases) Turbo lag means that the volume and pressure of the exhaust is less than what is nessary to create boost. Otherwords, you have to reach a certain volume of exhaust (by way of increased load on the engine (more fuel) or RPM (pumping faster).

If you watch drag racing ( bracket style), The turbo cars must use a trans break to accomplish two things, bring rpms up to stall speed( for the TC) and load the engine to create maximum boost from the turbos. For a performance car, the least amount of turbo lag, the better. Also belt driven turbos are not as efficient, but they are linear system (more rpms = more boost). An exhaust turbo is dynamic, they can make boost at almost anywhere in the rpm range.

For a truck, an exhaust turbo is the way to go.

There are very little centrifigual forces on the fan blades in a turbo. The fan and compressor blades are make of thin lightwieght materials. I have seen some that are ceramic and only 1/64 of an inch thick. The blades on a turbo are very delicate. Very very small particles of dust and debris can crack and or destroy the fan blades. The blades on the compressor side extend into the housing to compress the incoming air, you only see a small portion of the blade from the outside. the exhaust fan is small, for a reason. Try blowing (with your mouth) into a big box fan, you may be able to turn the blades one rotation. Do the same thing to a small desk fan. You will more that likly get it going pretty good. The smaller fan will turn more quicly because you can provide enough voulme and pressure. Same with turbo, Volume gives the fan power and the pressure turns it faster. Any of you with turbo diesel dumptruck, try this, put the truck in nuetral, rev the engine to 2200 rpms. Do you hear the turbo? if you, should be just barely. Now set the parking brake, put it in gear and rev to 1000 rpm. Otherwords, put a load on the engine with out moving anywhere. You should hear the turbo screaming. You may want to open the hood when you do this, since alot of the newer trucks have alot of sound deadening material in the cab and hood.

This clearly demonstrates the relationship between volume and pressure. You would have about the same amount of pressure at 2200 rpm unloaded as you do at 1000 rpm, but the difference in volume is HUGE. So the turbo spins with more power, creating boost.

Enough of TURBO 101,

any questions?

I worked as a hot test engine speciallist for Caterpillar for 2 1/2 years testing 14.6L 3406 inline 6 cyl. turbocharged diesels. Some up to 600 HP. I received alot of training on the subject of turbos.

I am now a Mainframe computer programmer for the same company.

 

in DC (AC is not appropriate for this conversation), power is voltage * current. I was generous in my calculation, assuming no resistance, and perfectly efficient motors. 1 Volt * 1 amp = 1 Watt. 746 Watts = 1 Horsepower. In AC, you have to consider the "power triangle", with apparent power, power factors, phasor currents and voltages, impedences, yada yada yada.

where'd you guys go to school? This is some seriously good stuff here! Civil & Environmental Engineer at The Citadel here, I'm a Geotechnical Engineer nowadays. TK

 

fishin1976
I in no way intended to infer that turbos are inefficient, in fact they are quite efficient and that is why the are so popular. However, there is a fundamental difference in the way a turbo charger and a supercharger operate and that was all I was attempting to illustrate. Evidently I have failed in the attempt and I apologize.


TorqueKing,
I started with electronics in the 3rd grade. My education in the same ended with my high school education. I wish that I could have pursued it further but fate had other plans for me.

 

It's me who should appoligize,

I'm sorry for seeming like I was chewing you out,

It wasn't meant that way.

After rereading your post, I agree with you that turbos are not as efficient as superchargers(blowers). But there is the difference of drive style. Roots style blowers use engine power to overcome friction of the belts, gears and internal parts. They do this very well, but are linear in nature(more rpm=more boost).
and have to be large in size( heavier and most won't fit under your hood) to accomplish this at low speeds(rpm's) because of the high volume of air it has to move with every rotation. Turbos move less air per rotation, but do it very, very fast.

This has been fun, havn't talked turbo's for along time.

GR8diesel, I hope your not mad or hurt.

Hard enough making friends, let alone making enemies.

later,

 

Fishin1976,

No not hurt at all, I very much enjoy these discussions as it helps to get the grey matter exercised. I use this forum to help others to help break up the time while I look for new employment.

I always thought superchargers looked 'cool', but I didn't want to accept all the tradeoffs to have 'em. Turbo lets me get a little boost from the exhaust, it is a simple design, and I'm impartial to the sound of a turbine.


Take care,
Bill

 

I always thought a nice belt driven supercharger with a clutch would be nice. Use a "backwards" waste gate to allow the engine to see normal atmoshere most of the time until you fliped the "GO switch". Clutch engages, Boost comes up, overcomes the backwards waste gate, supplies boost to carb or EFI, and VAROOM!!! Something like an unlimited nitrous supply!

Kind of like the "Mad Max" setup

 

Centrifugal SC's are very similar to turbo's, except they are belt driven instead of exhaust driven.

JJ

 

Wow, I learned a ton off of this thread. I don't remember if this was brought up or not, but how about taking a furnace blower and putting small pully on it and run it off the engine? And would blocking it off do any good or would it just blow the sides off itself?? Sorry if this was already mentioned......

 

Whoa, superchargers are no where near as efficient as turbochargers. Why, because turbochargers don't take engine power to turn, plus they always make boost. I know how they work. I am curious as to how my idea wouldn't work. Even if it only provided a couple pounds of boost it would be cool.

 

WHOA! Actually turbochargers DO take engine horsepower to run. Otherwise we would have them turning generators for perpetual motion machines. The restriction the turbo places on the exhaust system robs some horsepower by placing some back pressure on the exhaust. There ain't no such thing as a free lunch here guys.

An exhaust driven turbocharger gets it's energy from restricting the exhaust which reduces engine HP available at the crankshaft.

A belt driven supercharger whether positive displacement or not derives the HP to drive it from the crankshaft.

p.s. -Forget the furnace blower. Not enough RPMs, CFMs, or pressure with a draft inducer blower. They might work for a 1 pound boost on a 3HP Briggs... The big squirrel cage main blower would have enough CFMs tho, just not enough of anything else.

 

Torque1st, do you know (or anyone) that makes a system for superchargers that enables you to turn them on and off? Cause all it would take is either a magnetic clutch setup (farm machicery uses this type of cutch and it is a very very adaptble system) or a mini version of a clutch like whats in a manual tranny. spmeone tell me if this has been done cause i'm looking for a science project.

Oh and the thing bout turbos and their efficienciey. Turbos per pound (actuall weight) per psi of boost make more power and are more effiecient due to the fact that they use the "wasted power" (as in the heat) of the engine then belt driven supercharges of any kind. Now turbos cause less of a parasitic drain on the motor (because of the increased in back pressure but this loss is less then that of a supercharger) and because of a turbo's design you so not have to run mufflers on a turbo equiped vehicle and still be legal (i looooove that turbo wine)