54.6ACvolts, how to determine amps in dual rotor

[indicjames]

finally the open voltage reading looks good,
http://www.youtube.com/watch?v=Cy_WkU0alio

it is new #18g of 250turns per coil/2 coils per phase and three phase star connected,
N42 , 8 magnets per rotor, air gap is 2mm between stator and rotor
140 to 200 RPM

the open voltage shows me 55Acvolts, but when we try charging(recitified it using 3510 rectifiers) the battery (100Ah Sealed Lead Acid), it takes pretty long to charge from 11.5volts to 12.6(almost two days),

as soon we try rectifieing it using MBC3510 rectifiers it show 13DCv (ACV x 1.73 = DCvoltage is this correct?),

we are trying an analogue ammeter to find out the amps it is producing, but as soon as we connect the ammeter, the generator part comes to a stand still.

we would love to finish this generator part, then move on to Vawt design (mostly sandia lab's design help, thanks ron.)

[TomW]

Ohms law works for either sources or loads.

E=I*R (Volts equals Amps times Resistance [ohms])

If you know the resistance of the coil you can determine possible amps at any voltage.

Charts exist online to determine the resistance of a length and gage  of wire.

Without special tools / equipment you cannot likely measure a coils, resistance directly.

Tom

[indicjames]

thanks tom

with the help of DMM when i tried its ohms by connecting one end to another end of coils in a phase, it was showing me 2 ohms . but when the rotors were moving, it was not going beyond 1. tried it with 20k ohms, still it shows 1.

what kind of special tools we might use it here?

[JW]

what kind of special tools we might use it here?

An RMS corrected/true AC voltmeter, would help.

Here's the best link I could find at the moment. Remember impeadance, is corrected for AC, and resistance is corrected with DC.

http://www.bcae1.com/voltages.htm

Im certian Flux could chime in the the .707 correction factor (for RMS). Thats if he's watching this thread...

JW

[indicjames]

Oops

http://www.home.agilent.com/agilent/product.jspx?nid=-536902435.0.00&lc=eng&cc=IN

is pretty X-pensive

adding the multimeter info.

i am using http://www.amazon.com/8-Function-19-Range-Analog-Multimeter-YX360-TRE-B/dp/B000P7F666 and another local made DMM,

[ghurd]

we are trying an analogue ammeter to find out the amps it is producing, but as soon as we connect the ammeter, the generator part comes to a stand still.

it was showing me 2 ohms . but when the rotors were moving, it was not going beyond 1. tried it with 20k ohms, still it shows 1.

Sounds like not using the meter correctly.

G-

[Perry S]

Not to parrot Ghurd but I think you should first figure out why your DMM won't measure the current. Don't get too caught up in special expensive equipment to measure what your dmm is capable of. Place it in series between your rectifiers and your battery. Make sure your leads are plugged in correctly. If hooking a meter in series causes your gen to lock up your just not using correctly. Hope this helps.

Perry

[JW]

The limit on most DMM's is ten amps, so that's a meager 120watts, most are producing way over 500 watts, so a carbon-pile is what is used around here, when measuring current to a battery bank that has 25% state of charge. Oh ya the carbon-pile has a "shunt"..

JW

[indicjames]

sorry for being so dumb here..

what is "carbon-pile is what is used around here".

[electronbaby]

A "Carbon-Pile" is whats used in old battery testers. It has the ability to be able to dump large amounts of current, while using a shunt to accurately measure that current.

[tanner0441]

Hi

Another thing on DMMs is the leads are normally not capable of handling the current of the highest range. Test meters need flexible leads, and flexible and high current don't sit well together.

I know welding cables do flexible and high current but they won't fit the meter....

Try and borrow a DC Clip on and remove some of the variables.

Brian

[Flux]

Not sure what you are doing, 250 turns per coil seems a lot. No idea of your magnets or stator thickness but your 50 plus volts ac may be correct.  If you rectify this the open circuit dc volts should be near 70v dc.

If you connect the battery to the rectifier you will measure the battery volts and I suspect that is where you get the 13v. With so many turns I have a feeling that you will have a lot of resistance  and it will be more than the 1or 2 ohms that you claim to measure.

I suspect the current into a 12v battery is quite low if it takes that long to charge but it ought to be something higher than this with such an excess of volts over battery volts.

When you try to measure current and you can't turn it you may be measuring the short circuit current if you have the meter in the wrong place.

I wasted my time watching a picture of a multimeter on Utube, if it had shown the rest of the set up I might have had a better idea of what you have and what you are trying to do.

If you post full details of the alternator with magnet size, disc size, real air gap which is the distance between magnet rotors then I may be able to run some figures but at present I have little to go on.

I wouldn't worry about expensive rms meters, you have no idea of the waveform so the true rms figure is useless, the cheap average reading thing will be plenty good enough.

Flux

[JW]

Flux is correct to mention harmonics.

 Unless your using 9 coils to 12 mags per rotor, 24 mags with dual rotors (still 9 coils). Or 3 coils to 4 magnets per rotor, a completed magnetic circuit would use dual rotors 4 mags apiece with only 3 coils.

basically you can use peak to peak AC voltage, if your machine is not actually 3 phase, for example single phase. It could save you some money to build the thing, and measure dc output from the bridge rectifier directly(your going to have to guestimate power in watts, that the bridge can handle, under full load, as far a power-factor is concerned). Or you could compensate for heat loss in the winding and measure with no load before rectification, with an expensive true rms meter, but it wont make much of a difference if your dual rotor air core machine is not true 3 phase. 24 magnets(dual rotor) to 9 coils(stator) wired in delta 3phase.

JW

[indicjames]

_{"If you post full details of the alternator with magnet size, disc size, real air gap which is the distance between magnet rotors then I may be able to run some figures but at present I have little to go on."}

Magnet size is 2" x 1" x .5" N42, Disc size is 10", the gap between top rotor and the stator is 2mm, bottom rotor to stator is 2.2mm, (tried to organise this so thin), height of the stator is 20mm

8 magnets per disc,  dual rotor,

disc is 3mm thick

sorry for wasting your time flux, i was trying to build 48V setup, but has ended up with 56+, la

[Flux]

Your alternator should work at the speed you quoted, I think it will be too fast for a savonious but that is not the present issue.

The total air gap is wider than i would have chosen but that is no bad thing with thin rotor discs. I sort of agree with your voltage figures and I would expect a winding resistance approaching 5 ohms.

I would expect this machine to give something like 7A into a 12v battery at 200rpm so I can only imagine you have problems with your connections and measurements. I am not sure how you are driving this but when you connect it to a 12v battery it should be very hard to turn, unless you have a powerful means of driving it it will slow down to the cut in speed for 12v.

Try these simple tests and report back.

Open circuit it should turn easily, short a pair of leads together and it will be impossible to turn it above a crawl by hand and it will shudder and turn in lumps. Short the other lead to the previous two and it will be even harder to turn and it will not be lumpy.

If it passes these tests then with your measured open circuit volts it is ok.  Connect the rectifier with no load on the dc side and your 50v should go up to about 70vdc. if not suspect the rectifier or your connections.

if you get the 70v then short the rectifier dc side and it should again be near impossible to turn just as it was when shorted with no rectifier. If it turns easy or is lumpy then again it has a rectifier or connection problem.

If you get this far then connect the rectifier dc to a 12v battery and turn it by hand. it will now turn easily at low speed but at something over 80 rpm it will become hard and smooth to turn and if you can get your ammeter connected correctly you should be able to crank several amps into the battery.

Report back and we can take it from there.

Flux

[indicjames]

_{"to a 12v battery it should be very hard to turn, unless you have a powerful means of driving it it will slow down to the cut in speed for 12v."}



Yes you are right , here when we connect to a 12V battery , the speed comes down to 120 to 140 RPM,

on Open Circuit it will be pretty fast touching the 200RPM

when i connect one phase to another using crocodile clip it will come to a standstill, even with hand i couldnt rotate it.

in my previous msg i missed out the rectifier specifications 1 KBCP3510, and 1 MBC3510, i could never be able to see 70Vdc per phase or in three phase's together, has been utilised here. regular house hold connecting wire's (i guess it can handle 5amps?) have connected on AC part and + will be connected to battery, the opposite plug of + will be connected to the negative point on battery.

[Flux]

I think you have answered your main question. If you can't maintain the alternator speed you can't expect to get current out of it. you are converting mechanical energy to electrical energy. What is happening is that the electrical energy is just dropping to the level that your drive source can supply.

Loading at 48v will probably get you more amps as the load will be better matched.

I don't know why you can't get 70v dc open circuit if you are connecting as a 3 phase full wave bridge. unless you can give your connection drawing I can't help on that one, it works if you connect it right and the meters are working properly.

I suspect the alternator is fine. As I said previously whether you can get anything from a savonious is a different question.

Flux

[indicjames]

_{Loading at 48v will probably get you more amps as the load will be better matched.}

do i need to load 48V battery bank or?

^{I don't know why you can't get 70v dc open circuit if you are connecting as a 3 phase full wave bridge. unless you can give your connection drawing I can't help on that one, it works if you connect it right and the meters are working properly.}

could it be rectifier connected wrongly,?

[Flux]

No the rectifier connection is fine. The reason you can't get 70v dc open circuit is that it is NOT open circuit. You show it linked to the battery and the battery will determine the voltage. It will clamp the mill voltage to something in the 12 to 14v range. This is normal and is rather fortunate as otherwise we should need voltage regulators to run loads from the battery when charging.

If you take the rectifier lead off one of the battery terminals and measure the volts from the rectifier when the ac volts is 50 ac then you will see the 70v but no need to try, you have it connected correctly and everything is working fine. if you can put in sufficient mechanical power it will all work.

Try it at 48v the match will be better and you will turn it easier, there is no need to load the 48v battery until it is fully charged, it will clamp the volts just as the 12v one does.

Flux

[indicjames]

sorry for the long delay,

now i got an anologue DC ammeter and placed it in between the battery and rectifier Rectifier (+) -> Ammeter (+) ->ammeter second terminal -> battery (+), and i couldnt see any amp rising?

also
Try it at 48v the match will be better and you will turn it easier, there is no need to load the 48v battery until it is fully charged, it will clamp the volts just as the 12v one does.

i didnt get this one flux,

[Flux]

Can you explain how you are driving this thing.

I still suspect you are driving it from a source with no available power and the speed is just sitting down at the cut in speed.

Fit a nice crank handle on the alternator and turn it by hand and i am sure you will see the amps rise.

Flux

[indicjames]

"driving it from a source"

i am using a hand drill flux, let me try as you suggested the crank handle stuff., will try this and let you know