# Would a high voltage low current generator be more efficient?

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#### Njguy

##### Member
Generators have to deal with counter torque. The more electrical load placed on the generator, the greater the counter torque. Since the counter torque is a function of load current, if one designed a generator to be low current/high voltage, and in conjunction used a transformer to then convert to higher current/lower voltage on the other end, would this reduce counter torque? Or would there be something I'm completely missing..?

#### MikeMl

##### Well-Known Member
All other things being equal, isn't the counter-torque proportional to the power that the generator delivers?

#### ronsimpson

##### Well-Known Member
Since the counter torque is a function of load current,
1) there is no free lunch. Power translates to power.

2) one way to look at counter torque:
12V 1A = x torque.
24V 0.5A = x torque.
48V 0.25A = x
120V 0.1A = x

So it is really "power" not current. It is just easy to measure current.
If you have a 12V generator, at 0A you have 0 counter torque and at 1A you have some amount of torque. So commonly you only have a current meter.
If you pulled the wire out of the generator and put back twice as much smaller wore, (2x more turns) you get 2x the voltage but 1/2 the current at the same torque.

#### Njguy

##### Member
2) one way to look at counter torque:
12V 1A = x torque.
24V 0.5A = x torque.
48V 0.25A = x
120V 0.1A = x
I agree that there is no free lunch, but the field strength in a solenoid is not a function of power, it's a function of current no? Assuming the solenoids had the same number of loops, a 12V 1A solenoid would produce a more powerful counter field than a 120V 0.1A solenoid...I think.

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#### alec_t

##### Well-Known Member
A 120V solenoid would have a lot more turns (loops). The magnetising force depends on turns times Amps, so the greater number of turns compensates for the lower current (other things being equal).

#### Njguy

##### Member
A 120V solenoid would have a lot more turns (loops). The magnetising force depends on turns times Amps, so the greater number of turns compensates for the lower current (other things being equal).

I figured that the primary coil of the transformer would act as a resistor and reduce current. That way it would reduce the counter torque which would increase the generators rpm thus increasing voltage.

#### kubeek

##### Well-Known Member
First of all, torque times RPM is equal to power (times some arbitrary constant). If you´d have a low current high voltage generator, then yes the torque would be lower, but the RPM would be higher to get the higher voltage, and you gain nothing.
Or in other terms, low or high voltage does not matter, as the efficiency of the generator is basically the same. There is no power inherently lost by using low or high voltage, and unless you exactly quantify the losses, the two are exactly the same.

#### ronsimpson

##### Well-Known Member
I figured that the primary coil of the transformer would act as a resistor and reduce current.
What transformer?
While a transformer dose have some resistance, that is not it primary function. The resistance is small.

The example of a solenoid is good. Amp * Turns.
Low turns, high current, low voltage OR High turns, low current, high voltage
Either way it takes work to do something.

#### ClydeCrashKop

##### Well-Known Member
Just a few thoughts on this matter.
If a 1/2 HP 3450 RPM motor is gear reduced 2:1, do you get the same output power as a 1 HP 1725 RPM motor?
The 1/2 HP motor is certainly smaller and cheaper.
Why is it practical to run a generator at that obnoxious 3600 RPM instead of 1800 RPM?
The cheap ones all run at 3600 RPM.

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#### Les Jones

##### Well-Known Member
No. The power is always the same except for the loss in the gearing. The 2: 1 gearing will double the torque and half the speed. On the generator question I am assuming that you are assuming that the engine speed is the same as the generator speed. (No gearing.) You would need a larger engine to drive the same POWER generator at 1800 RPM than 3600 rpm because you would need twice the torque. Also the 3600 rpm generator will be chaeper and lighter.
Les.

#### ronsimpson

##### Well-Known Member
The 1/2 HP
You can only get 370 watts out of 0.5 HP. Back to no free lunch.

If a 2:1 gear helped then why not a 10:1 gear? 100:1 or 1,000:1?
1 hp(I) = 745.699872 W
1hp = 740W if there is no loss in the system.

#### ClydeCrashKop

##### Well-Known Member
If a 2:1 gear helped then why not a 10:1 gear? 100:1 or 1,000:1?
Right! Like hydraulics, with enough gear reduction you can move mountains. It would just take a while.

Say you have a machine that has & needs a 1 HP 1725 RPM motor.
Wouldn't that machine work just as well with a 1/2 HP 3450 RPM motor that is gear reduced 2:1 ?
Wouldn't it be half the speed & twice the horse power?

Sorry, I didn't mean to hijack. I was just planting seeds to think about the original generator topic.

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#### kubeek

##### Well-Known Member
Say you have a machine that has & needs a 1 HP 1725 RPM motor. Wouldn't that machine work just as well with a 1/2 HP 3450 RPM motor that is gear reduced 2:1?
Wouldn't it be half the speed & twice the horse power?
No, you´d need twice the speed and half the torque, but the power needs to remain the same.

#### schmitt trigger

##### Well-Known Member
Just a few thoughts on this matter.

Why is it practical to run a generator at that obnoxious 3600 RPM instead of 1800 RPM?
The cheap ones all run at 3600 RPM.
An electrical generator's speed is always designed to match the prime mover's most efficient speed. (1)
3600 RPM is an efficient speed for small displacement gasoline engines. That means a two pole generator for 60 Hz.

Note (1): The exception to the rule are gas turbines. To be thermally efficient, they must have rotational speeds which are several times higher than the fastest generator design. Down-gearing is a must.

#### mranderson

##### New Member
Well is interesting your question cause if you diminish the torque you could harvest electricity from less speed air stream for instance to charge a battery, may be in more time. So your question has more than one edge answer. In that respect your question could have a answer. Yes you probably generate more energy along the time not in time.

#### dr pepper

##### Well-Known Member
If you could make the generator safe & reliable a high voltage may be more efficient, if you were planning on transmitting the power a longer distance, as then you wouldnt need a step up transformer.
You dont see these often for the first 2 reasons.

##### Well-Known Member
If you could make the generator safe & reliable a high voltage may be more efficient, if you were planning on transmitting the power a longer distance, as then you wouldnt need a step up transformer.
You dont see these often for the first 2 reasons.
Actually hydro-electric power stations like Niagra Falls have generators producing 13 KV. A little higher than my 240 VAC home generator.

Ron

#### dr pepper

##### Well-Known Member
I was thinking in the order of 500kv.
13kv is still high enough to make a mess of a person.

##### Well-Known Member
I was thinking in the order of 500kv.
13kv is still high enough to make a mess of a person.
They raise it after they make it for transmission. The generators are really cool, I saw them when I took a tour many, many years ago. Another really cool hydro-electric plant is Hoover Dam that think amazes me and they give tours also.

Ron

#### Beau Schwabe

##### Active Member
The "KEY" is to match the impedance of your power source (wind, turbine, etc) with your primary power conditioning or the "front end" of the system.

The analogy I like to give is like riding a bicycle .... sure you can get from point A to point B in the wrong gear, but it's so much more efficient if you change gears to better match the impedance of the power source (YOU in the case of riding a bike for this analogy)

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