Generator questions..any Tech guy's around.?

[skyline1]

Hi Gus

An AVR is a D.C. Regulator of sorts as it controls the field of the alternator and hence it's voltage output.

I was involved with testing some motors for the Canadian Navy which required a locked rotor test for 30 Seconds at full voltage We had to hire a 2MVA containerised genset to do it. The AVR on it couldn't cope with sudden high loads like this so we had a manual one, me ! I though I had met my maker when they put the load on, the noise and vibration inside there was incredible and it nearly stalled the genset. 16 cylinders 2 Turbos and heaven only knows how many litres (about 20 I think maybe more).

Regards Mark

 

[charlesfitton]

..still not sure why you don't go to a single terminal, self regulating alternator... apparently it doesn't even matter which way it turns..

 

[mu38&Bg#]

Most MPPT solar regulator will not boost voltage. This is because a solar panel making low voltage will also make very little current. The panel is most efficient at 17-19V on a 12V system so the MPPT need only buck mode operation.

Alternators are not very efficient. There is also the need for greater efficiency loss( gears or belts) to get the alternator to a speed at which it makes power. If it's necessary to speed the generator up use gears or light timing belt.

I would use a brushless DC motor wound to generate the appropriate voltage. Assuming the steam engine has a governor, the generated voltage, after rectification, would peak at the battery float voltage. As the system load increases and battery voltage drops, the governor would increase the steam engine torque output to supply current. This of course depends on how sensitive the governor could be. At 400 RPM this would have to be a large diameter short stack motor with a large number of poles.

Another option, I think, is to generate ~110VAC connected to a ac/dc power supply set to the battery float voltage. In general power supplies will operate over a fairly wide range of power input /frequency and are already regulated on the output. Possibly some form of current control ( even as simple as a resistor) would be needed if the system was connected to a battery with a very low voltage to prevent the power supply's over current protection from tripping. Efficiency is quite good. This would be a plug and play solution after the appropriate single phase generator motor was sourced or rewound. Getting ~60Hz from 400RPM would require 18 poles.

There will be losses no matter what generator system you choose. There are many ways to skin this cat, and if efficiency is the goal it can get complicated. Efficiency is important because the more efficient the generator is it's compounded by the steam systems efficiency. So a small change in generator efficiency can result in a large change in the amount of energy required in wood to feed the boiler.

BTW, what is the scenario where steam is the only form of power generation?

 

[jpeter]

Someone used the word dynamo. From what I remember, back in the day converting dc voltage from low to high was quite an involved project. High voltage was needed too because electron tubes needed high voltages for plate voltage. One solution was to use a thing called a vibrator which, simply discribed, worked like a buzzer to make and break a low voltage circuit at a prescribed frequency, determined by the mechanics of the thing. That stop and start flow of current was used as a quasi AC which could then be transformed in the normal way, transformer, to high voltage and then recitified to DC for high voltage DC applications. When more current was needed a different approach was used. A motor was attached to a high voltage DC generator to create high voltage. These units were generally packaged in a tube like configuration with the motor on one end and the generator on the other on a common arbor. These were referred to as dynamos.
To my knowledge DC generators that used commutators and brushes to commute the voltage to DC were always called generators.
Interestingly, most dictionaries refer to any dc generator as a dynamo. So go figure.

Bottom line is, I think maintaining adaquate control of the output voltage generated by a permanent magnet dc generator turned by a steam engine is going to require some type of complex electronic switching regulator, dc to dc or mppt, etc., or a really good governor on the engine. Without such you're going to not light lights, burn out lights, boil out batteries or drain batteries back into the generator. (The governor idea might not be a bad one.)

I may be wrong but I love this discussion.

 

[charlesfitton]

So somehow this:

"I would use a brushless DC motor wound to generate the appropriate voltage. Assuming the steam engine has a governor, the generated voltage, after rectification, would peak at the battery float voltage. As the system load increases and battery voltage drops, the governor would increase the steam engine torque output to supply current. This of course depends on how sensitive the governor could be. At 400 RPM this would have to be a large diameter short stack motor with a large number of poles.

Another option, I think, is to generate ~110VAC connected to a ac/dc power supply set to the battery float voltage. In general power supplies will operate over a fairly wide range of power input /frequency and are already regulated on the output. Possibly some form of current control ( even as simple as a resistor) would be needed if the system was connected to a battery with a very low voltage to prevent the power supply's over current protection from tripping. Efficiency is quite good. This would be a plug and play solution after the appropriate single phase generator motor was sourced or rewound. Getting ~60Hz from 400RPM would require 18 poles."

is somehow simpler than a couple of pulleys and a self regulating device that is intended to charge batteries (which, when all is said and done, is what the gent wants to do...)

 

[mu38&Bg#]

is somehow simpler than a couple of pulleys and a self regulating device that is intended to charge batteries (which, when all is said and done, is what the gent wants to do...)

If you have any concern about the efficiency of the system, it matters. For simplicity sake do whatever you feel works.

There is also this concept which does away with the need for steam altogether.

http://en.wikipedia.org/wiki/Thermoelectric_generator
http://tegpower.com/products.html

Greg

 

[skyline1]

I think Greg's solution would work but I agree about it being a little complicated and whilst 110VAC is not considered a dangerous voltage it could give you a bit of a shock if you touched it especially if it was single ended not centre tapped to earth as is the common practice, granted you would have to touch both poles at the same time if it was fully floating, and as power supplies tend to have about an 85% efficiency or lower at the extremes of their voltage range nothing much would be gained here as the efficiency of the MTTP regulators Martin mentioned is similar. This idea would reduce I squared R losses, which is why mains power is transmitted this way, but as we are talking about smallish currents anyway I don't think the gains would be that great.

He is right about the number of poles I'm talking about European here but at 50Hz synchronous speed for a 2 pole A.C motor is 3000 R.P.M. so for 375 R.P.M. ( 3000 / 8 ) you would need 2 * 8 = 16 poles A 110V 16 pole permag alternator. would be a pretty complex expensive machine and probably hard to find.

As Martin already has a usable D.C. generator his best bet is probably to stick with it and accept that it's not going to be wonderfully efficient. I have found that in small scale frictional and thermodynamic losses tend to be much more of a problem that electrical ones anyway.

Regards Mark

 

[metaltrades01]

..still not sure why you don't go to a single terminal, self regulating alternator... apparently it doesn't even matter which way it turns..

An alternator need to be turn at about 2000rpm + to start to develop a current, so it would have to be geared up via a chain or belt etc, which introduces loss's that I can't afford.

 

[metaltrades01]

I thought i'd already posted these test result from a few days ago...

On the advice of a previous post on this thread, I have just load tested the generator on a small lathe that is fitted with a digital rpm indicator.

At 460 rpm it produces about 13 volts, which is what I was after. I had a small 12v car driving light as the load and it drew 4.6 amps.

I increased the load to 2 driving lights and the the overload tripped on the small lathe that I was using at about 240 rpm.

I held the shaft in the chuck and held the generator by hand, considering the load with one light, I'm confident that the engine will be able to turn the generator at full load.

I'll fit a coupling to the generator and bolting it down to test it on a steam engine, and see what the max output is at around 13.5 volts .

 

[gus]

Hi Gus

An AVR is a D.C. Regulator of sorts as it controls the field of the alternator and hence it's voltage output.

I was involved with testing some motors for the Canadian Navy which required a locked rotor test for 30 Seconds at full voltage We had to hire a 2MVA containerised genset to do it. The AVR on it couldn't cope with sudden high loads like this so we had a manual one, me ! I though I had met my maker when they put the load on, the noise and vibration inside there was incredible and it nearly stalled the genset. 16 cylinders 2 Turbos and heaven only knows how many litres (about 20 I think maybe more).

Regards Mark

Hi Mark,
Were you testing an alternator or synchronous motor? Sounds scary.Am glad ,I was never involved with locked rotor testing.

The biggest Synchronous motors I started up in 1975,were two EM 1500hp motors coupled to Ingersoll-Rand Centacs Centrifugal Compressors. MG(motor generators) were used to provide D.C. for the exciter rings. Starters were reactor type which made lots of noise on starting.We had the HT starter supplier/builder to help us with startup. Auto Trans starter is practically noisless except for the humming.The reactor trans starter had 100 cats screaming away on starting.

During startup,the shipyard engineers quietly disappeared leaving us alone.

 

[skyline1]

Hi Gus

They were 50KW synchronous motors for starting up the gas turbines on Naval frigates so they had a very high spec on them. In use they have a very high starting load so they need to be able to withstand being stalled for a couple of seconds. With the rotor locked there is very little back E.M.F. so the supply "sees" a near dead short. hence the huge genset. For this reason locked rotor tests are usually done at much reduced supply voltage and the results extrapolated.But not so in this case. It certainly tested the motors and also the genset, and me !. According to my colleagues it made the ground shake and the set emitted a huge cloud of black smoke every time we did it.

We used reactor starters on some rotary frequency converters we made at the same company they were so noisy that they were mounted in soundproofed enclosures. After having had two of them catch fire on test it was discovered that the manufacturers had got one winding out of phase. That made them even noisier and prone to overheating and bursting into flames.

Very strange machines they were used to power the I.T. gear in a big datacentre for a bank. and the output frequency was 440Hz (Middle A on a piano) deliberately designed that way so they could check the speed with an old fashioned tuning fork.

Working on the test bed at that place could be pretty "Interesting", minor fires and flashes and bangs were a regular occurrence. We even caused the complete evacuation of the factory once. It was an "authorised admittance only" area for obvious reasons, but even people with a legitimate reason to be there had a sudden desire to be absent if we had a "big 'un" on test. Half a ton of armature has a lot of inertial energy at 1000 R.P.M. and doesn't like being brought to an instant stop. It complains very spectacularly and dangerously !

Regards Mark