Need a push in the right direction

[fauxf0x]

Through the engineering department at my school, I could essentially inherit a PMA. The model is a 190STK2M 500RPM and the datasheet is provided below:
http://www.alxion.com/e_produit/83.pdf

The initial design problems I see are the high rated RPM and the voltage/current output which is high voltage and low current. From my understanding, for charging batteries, you would want a low voltage (14.5-13.3 V) and a relatively large current (or at least larger than the rated 2.8 A). I would like to be able to charge two Marine batteries since I can also get them for cheap through school connections. Just looking for ideas about how/if using this PMA would be possible. My initial thoughts are that a transmission could fix the RPM requirement which also takes advantage of the only advantage of this PMA and that is the low required input torque. I am also wondering if a voltage regulator or transformers would be necessary, I was thinking of using a transformer to step down the voltage to around 20-30 V and then regulating it to the 14.5 V. From reading information on this site, it seems I would not need to do the second regulation but just clamp the voltage to the batteries that would bring it to it's charging level. Also I was wondering what kind of charging current I should be aiming for. Rectifying seems to be a pretty routine design, do you guys have any recommendations on a full-wave bridge rectifier or if another rectifier is better? I was looking at the Toshiba 30L6P45. Then finally, what kind of charge controller would be easy to implement. Three stage controllers do seem to be the best way to go, but how much added complexity is there.

TOSHIBA 30LP645 datasheet: http://doc.chipfind.ru/toshiba/30l6p45.htm

I plan on doing much more research before actually embarking on this project, but just would like a consultation of feasibility before I start this.

Thank you for your time and knowledge.

[Rover]

In my opinion,  I think the RPM is too low for the rated voltage if trying to charge 12v bats. 244V at 500 rpm,  or ~2 volts/rpm is quite high.

At ~ 14 - 16v , I think it will stall out , roughly 8-10 rpm.

I think the power produced would be negligible at that speed, seems like a decent alternator, but not for this purpose perhaps without a coil rewire of some kind. Since they also make a 1500 rpm version of the same model, you might get lucky and be able to change the coil arrangement.

Just my thoughts
 

 

[WindriderNM]

The batteries will clamp the voltage. I have an alternater that puts out 90V AC 3 phase running free in 15 mph winds. When I connect to the rectifier and batteries  the voltsge drops to about 14V DC.

[ghurd]

I agree with what they said.
Not much hope to use that one.

"Voltage at no load" is what the guys here call 'open voltage'.
357V at 500 RPM points to useless for charging 12V batteries.

G-

[fauxf0x]

Thanks for the replies guys, what about a 24 V battery bank? Just trying to problem solve and be resourceful here. With wind testing around here, it seems the wind speeds would be low so the PMA would actually be working at half speed or 250RPM and approximately 100 V, does that change anything?

[oztules]

" Just trying to problem solve and be resourceful here"
I would have to agree with what has been said above....., but the air down here must be different...... and I'm a bit odd.

 If you want to make a project of it, I would grab some old microwave transformers, and rewind them and test again. Your pole count is quite low, but this just means more steel to cope with the lower frequencies than I play with over here. here we have a 30 pole unit that sees 400 plus volts at those rpm open circuit. A decent transformer WILL solve your dilemma, but only cheaply if you do it yourself and wind your own on free cores (eg. from microwaves.)

This board has a blind spot where transformers are involved (mostly from those who have never actually tried it), but the best turbine I have seen long term is still the AWP, with HV windings and transformers. It will solve your matching problems, and goes a long way to pushing your reactance limiting way up the watt scale.


Here is the unit that transforms the AWP down to battery voltage


The down side is you will need to have a system to cut the transformer in when the frequency you want it to cut in at turns up..... and this is where the folks seem to baulk

Here is the controller that takes care of that, but it needn't be as complex as this one either.



All problems are solvable, it just depends on what you can bring to the table in the way of skills.

If you have poor wind then direct drive Dan/Hugh types are by far the best solution, but if you gave good wind, then all kinds of things become  viable. ... even wound field units.

So you have options, but with less wind there are less useful alternatives, if your blessed with good wind........ darn near anything will work



.............oztules

edit if your curious, then more stuff on that unit is here  http://www.otherpower.com/images/scimages/5171/awp_1.html and a few more I can't find.

[Flux]

I don't follow the data. I presume you are looking at the small unit with the red curve. it claims about 240 something volts and 2.8A at 500 rpm yet the claim is a similar voltage at 11 or so amps at 1500rpm.

Is it possible to connect it in different ways or are there various voltage versions. If you look at the 240 something volt option at 11A at 1500 rpm then this starts to look as though it might be useful for 24v with a suitable prop.

I don't understand the data and i have no idea of your intended prop size and more worryingly I have doubts about your local wind speed from your last comment.

Without knowing very much more about this alternator, your proposed ideas and the available wind then it's not possible to give useful comment.

I also see that it emphasises the sine wave nature of the load so they certainly have no intention that is is for rectifier applications so yet another unknown.

Flux

[Flux]

Another thing about the data is that nowhere do I see if this is single phase or 3 phase. i am sure the bit you linked to is only a bit of the data from that manufacturer so the rest may be available.

If this is single phase than personally I wouldn't bother but it could still work.

Oztules makes some perfectly valid points but there is not enough details of the alternator or what you intend to do to help much.

I will make one comment about using transformers in general, the main benefit comes if you have to transmit the power a considerable distance and the cable losses become excessive at low voltage. If you want to do it on the cheap with home made transformers or you have a cheap source of commercial ones then it becomes quite attractive especially for high frequency alternators.

For normal cable runs and going out and buying everything new then it can be very expensive and probably never cost effective.

You don't always have to disconnect the transformer at start up but it makes for cheaper transformers if you do. The transformers can have less turns and more magnetising current if you disconnect at start up, but with suitable transformers the things follow volts/cycle and the magnetising current at start up may not be enough to warrent the trouble of disconnecting. For low frequency alternators the transformers become big and costly for even low power and you may need to compromise and run with high magnetising current, in which case you will have to start on no load ( no transformer).

The switching is really simple and you can do it with a 2917 tacho chip and a relay in the star point of a 3 phase transformer.

Flux

[DanG]

Links for people curious to see more...

Application Notes STK permanent magnet frameless alternators:
http://www.alxion.com/e_produit/110.pdf

STK Alternators General Description:
http://www.alxion.com/e_produit/94.pdf

The 350V open circuit voltage would be fun to design around.

Machining weatherproof bearing supports would be even funner.

[Tight Yorky]

Hi fauxf0x,

Thought I could assist in explaining some of your parameters on the alternator data sheet.

The power cable line describes 4 x 1.5 mm2. This is a star connected alternator. The three phases and a common.
The voltage rating 244V is from phase to phase. ie 244V x 2.8A x root 3 = 1183 W (shown as 1118 W).

Data sheet indicates 6 pole pairs. At a speed of 500 rpm will produce 3000 sine wave peaks per minute. That is 50 Hz (per second).

The open loop voltage of 357V gives an indication of the voltage throughout the speed range as this tends to be linear ie 357V at 500rpm, 178.5V at 250rpm, etc.

Operating point at max rating...244V at 2.8A. This shows a voltage drop of 357-244=113V across the internal impedance of the alternator phase. Part of this volt drop is due to the copper resistance and part due to the inductance(reactance). Total impedance is 113V / 2.8 A = 40.36 Ohms.
The inductance is stated as 83.8mH so the reactance at 500rpm is 2 x pi x Fr x L = 26.33 Ohms. Note the Frequency is 50 Hz.
So the phase resistance at max rating is 40.36 - 26.33 = 14 Ohms approx.

Quite a few numbers shown above, but this allows the alternator to be used at different speeds. The primary limit is the 2.8A maximum phase current. Exceeding this for any extended period will burn the windings irrespective of voltage.
The load voltage for a particular speed can be estimated from the open loop voltage (for that speed) minus the load current times the impedance. Assume the resistance part of the impedance stays constant, 14 Ohms. The reactance part will change with the speed as shown above.

The alternator appears to be designed to operate at mains voltage of about 230V/240V 50Hz. I can not see you being able to use a transformer to get down to 12V or 24V. The problem is the varying frequency from a turbine. Maybe the route to go down is a switch mode supply. Note that the rectified alternator output to DC will be quite a dangerous voltage. Perhaps use some old laptop power supplies to create a 12/24V DC bus for charging batteries. These tend to be variable input voltage but may need a low voltage cut off relay.
Note there is nothing to stop the alternator to be designed to be used at a lower speed to limit the output voltage but this will limit the power output.

Hope the above assists and is not confusing.

Regards.
Clive

[scoraigwind]

This seems to me to be a good candidate for transformers.  Line voltage is about 360 V at 50 Hz (left hand column version), so it can be used with standard (220V50Hz) transformers connected star.  When frequency is lower the volts will also be lower so that works out.

For low speed cut-out I just use a relay powered by a separate rectifier.  I find that this has enough hysteresis and you just need a trimmer potentiometer to adjust the operating point.

I find that toroidal transformers can be got custom made a t low cost, but better still to use secondhand ones if you can find a good ratio.

I would for example look for a nominal voltage of 18 volts (this line voltage between the wires will be about 70% of the DC output from the rectiifier which would be 24VDC ).  Suppose that you aim for cut in at 250 rpm then open circuit is about 180 volts.  A transformer ratio around 10:1 would be good.  180V to 18Vac to 24Vdc  That's assuming you use the left hand column in the table - I am not sure which winding you have.  This is a bit of a tangle of numbers and the transformers don't help.

Maximum output would probably be limited by inductance rather than considerations of overload.  Hopefully you would still get 500 watts at 500 rpm with a seven or eight foot diameter machine?  Worth doing a bench test before designing the blades.

[Flux]

Clive
Thanks for explaining the data.

I agree with Hugh that this would need transformers to be useful at 24v. Star connected 220v primaries would be fine for the alternator voltage.

Clive -  Transformers are fine for variable frequency, if you choose a point that is correct for frequency and voltage it will work over the speed range.

The point has to be chosen to keep the magnetising current low so for 50hz you need a nominal voltage rating of a 50Hz transformer at this point. A 60hz transformer would work with lower magnetising current.

Over the speed range the volts/cycle stay constant. A 2220v 50hz transformer will support 110v at 25hz etc. the power handling is inversely proportional to frequency but that is no issue for wind power as the available power drops quicker than that .

I see no reason why this couldn't be made to work well with the correct size blades.

Flux

[scoraigwind]

Using transformers also allows you to change tappings and do some kind of MPPT stuff or at least overcome some of the reactive impedance limitations of the stator.  We did that with the high voltage AWP but I was not aware that the controller ever got satisfactorily perfected.  It's good to see that Oztules is happy with his AWP.  I have an AWP with transformers and I change the tappings manually sometimes but I never got a controller for it even though I contributed to the design.  It always seemed to me tricky to know how to get out of stall at low windspeeds.  YOu need to be able to access the actual windspeed as well as the rpm.

Another thing to play with when you have transformers is putting capacitors in parallel.  That can reduce the rpm a bit over a range when working with machines that have laminated cores.  However nowadays I prefer to work with axial flux alternators that do not have a steel core and the problems are different.

[SparWeb]

FauxFox,

You're getting great advice about the hook-up and speed matching issues so I can't add much there.

You did have other questions, and I don't think anyone has brought them up.

The rectifiers, batteries, charge controllers and what's often called the "balance of the system" is something that you can design and fit together when you know the purpose and needs of the system.  If you set out to make a back-up power system for your house, that's one thing, if you want to try the grid-tie revenue thing, then that's different.  Either one you can do with the turbine you build (in most cases).

Option 1

In battery power systems you should have at a minimum a shut-off switch, a voltage regulator, and over-current protection fuses or breakers, apart from the batteries of course.  Naturally there is also a load of some sort, meaning the way the energy is used so let's say it's an inverter to run AC loads.  No matter what size or what voltage of battery you arrange for, or the size of the loads you need to power, or the size of the energy source (within some limits) you're going to be juggling these main pieces to a wind-turbine system.

For example, small bridge rectifiers like the kind you get at Radio Shack do not last long in wind-turbine use, in my experience.  Even ones rated 30-40 Amps I've been able to melt down with ~20 due to, among other things, not heat-sinking it well.  Now I have an old 3-phase rectifier rated at 100 Amps.  It is very easy to hook up and has lots of surface area to mate with the heat sink.

Option 2

You don't need any of them if you are going to feed a grid-tie inverter.  Within limits, it can take the wild 3-phase AC and make it into useful AC to sell back.

Option 3

You have an unusual source for your "do-it-yourself" project.  It doesn't exactly suit the usual purpose, so there may be an unusual purpose you can put it to.  All that stuff about batteries and so on is just one way to make practical use of a WT.  How about high-voltage uses such as heating, or something really fancy like pumping water to a cistern at the cottage (instead of running a gasoline pump)?  I've no experience with either to add than just the ideas themselves.

Option 4

Sell it to the electric car people and pocket the cash!   

[hvirtane]

oztules wrote:

"the best turbine I have seen long term is still the AWP, with HV windings and transformers."

Where can we find more information on AWP turbines?

- hv