Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 02:42pm 20 Sep 2008
Copy link to clipboard
Print this post
Well I had sorted through the battery lot that I was given and found that I had 13 good ones. It was one of those blustery mornings and so I had the bright idea of "lets see what she'll do mister" type of thing going on in my head.
I had also pondered what to do with the excess power that the chainsaw blade mill seemed to be producing. I had read some of Daveb's posts on water heating... so I got the bright idea that I would use it as a dump load, and/or use the mill to heat up hot water.
The obvious conclusion was that in order to have reliable water heating, I would use the batteries to heat the water while the mill was charging. This would allow me to use say 5kwh to heat up some water, and if the mill was in reasonable wind, it would carry the load some of the time, and top up the batteries after the heating was done.... thats the plan.
So I dutifully fired up the mill, and proceeded to charge the batteries a 72v configuration from the 48v windings of the mill... It seemed to be putting in a fairly steady 10 or so amps, and so while it was doing that I hatched a plan to test the water heating idea.... funny how we think sometimes.
Armed with a plastic 1 gallon (4.5 litres) icecream bucket and a 4 ohm load, I wandered back to the battery bank and proceeded to fill the icecream bucket with cold water, and with the aid of two microwave transformer primaries, freshly stolen from two unsuspecting transformers, I put them in series, and threw them into the bucket of water. (The transformer primaries come out complete from the transformers with 6mm spade connectors, and were about 2 ohms each) I spaced them a few inches apart, and hooked them up to the batteries in series with an amp meter.
The 72v bank was now at about 80v, I hooked up the resistor (coils) to see what would happen.
I had forgotten that they were actually wire coils and was thinking only in terms of resistance...
You'd be surprised how fast they move together when you dump 80v@20A into two coils in a bucket....they were now tightly stuck to one another in the center of the bucket... I wiped the water from my surprised face ... they had moved through the water very fast and smashed into each other erupting the water everywhere.... and I mused...oh well, no harm done... just frightened the hell out of me.
We were now putting about 1600 watts into the water. I shifted the mill input to the coil (resister/heater) side of the meter. That way I could see how much the mill was putting in versus the batteries. ie no mill power, the meter reads 20A, as the mill gets some wind the amps contributed by the battery drop, and the meter moves towards zero.
A gust of wind came along and the meter dropped to zero, which meant the mill was carrying the full load, it then pushed the meter well below zero, with the meter hard on the stops, this means running the heater and charging the batteries.
It was at about this time I had the bright idea of dropping the batteries from the circuit, and see if the mill could do a reasonable job of driving the 4 ohm load by itself.
I repositioned the meter wiring to reflect this change, and the mill was putting out a nice steady 15amps or so.
By this time, the water was starting to get quite hot, and the wind a little stronger and it moved between 15 and 20 amps... all was going swimmingly.
Suddenly a larger gust came along, and the amps went up to about 25, and I got a little concerned, but it subsided as quickly as it got up.... then it happened, a bigger stronger more lasting gust came along that just seemed to increase and keep increasing, the amp meter went hard over the 30A mark, until it was rammed up against the end of the meter, A quick look at the volts said 145,-150 the amps were well over 35A, and things were getting a bit interesting.
This lasted for an eternity (probably a minute or two really)... I dashed around the corner to see how the mill was coping... it was running perfectly, no vibration at all, no sign of trouble.... except the blades were just a blur.
I raced back to the batteries, to find steam all over the place, and hot water bubbling over the side... 5kw into an icecream bucket is not all it's cracked up to be.
At last the wind eased up, and I quickly re-attatched the batteries, which calmed the mill further, then shorted the 3 ph and the mill stopped nearly instantly.... it was over.
Luckily Zubbly's blade balancing method worked,... but the yaw didn't. Daveb was right about the furling part into resistors. It didn't look like furling. ( and the yaw bearing on the temporary tower was very very stiff)
So it was just over 5kw into a resistive load in I would say a 30 odd mile per hour wind on a 3.5 meter pole.
The weather bureau says 50kmh winds with gusts to 63kph... I think it was a bit stronger over this side of the island.
And that was the morning that was.
............oztulesEdited by oztules 2009-10-31Village idiot...or... just another hack out of his depth
Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510
Posted: 04:18pm 20 Sep 2008
Copy link to clipboard
Print this post
So... just another day at the office for you, I understand.
What's the plan after the positive results of this experiment ? Expand on it and build a proper water heater (real heating coils and mounted fixed, no plastic bucket, plenty of water (more than 4.5 L)), adjust the furling mechanism to furl at the proper power/windspeed ?
BTW, was that the windmill with the chainsaw blades with knots in it ? If so, they do seem to keep up it ok despite these weak spots.
Anyway, looks as if there's some potential for this application with this particular generator.
My day has been just as boring, standing on top of a 5m ladder in windy conditions with a paintbrush in one hand and clinging to the ladder for dear life with the other hand. Just *don't* look down... Yes, time seems to pass much slower doing stuff like that... Relativity... Einstein was right!
philb Regular Member Joined: 05/07/2008 Location: United StatesPosts: 96
Posted: 05:00pm 20 Sep 2008
Copy link to clipboard
Print this post
A video would be nice. Just kidding!
I did something similar a while back, only without the water. The wire became a runaway heater and I couldn't wait to get it unplugged. Afterwards, I couldn't stop laughing at myself. No harm done, this time, but close, I thought.
My mill seemed to act weird when hooked up to a resistive load vs batteries. It took more wind to get it spinning. But it was less subject to quick change in rpms with wind gusts. I suspect it was in stall because of the increased noise. The furling mechanism seemed to be frozen. Most of the symptoms make sence now except the furling. Lots still to learn.
Thanks for posting your mistakes as well as you successes. Sorry, cancel out "mistakes" and insert "fun learning experience".
Time for coffee now. I'll have to heat the water on the stove.
philb
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 11:05pm 20 Sep 2008
Copy link to clipboard
Print this post
Dinges,
I have been coming up with plans on how to use this mill to best effect for some time so far.
I always envisiged this machine to somwhow mitigate some of the power bill from the grid.
It has undergone several iterations in plan. At one stage I was going to buy a grid connect inverter, and use a battery bank to stabilise the voltage, then I was going to use batteries to store maybe 10kwh, and then drive it into the grid with an induction motor for a few hours a day, and then perhaps use the batteries and an inverter and disconnect part of the house to run solely off that.
It has become clear that I have no idea what I will do with this mountain of power I seem to have now.
The best bang for your buck would appear to be water heating, as the mill is certainly attaining better outputs in kw terms with resistive loads. In that same wind into a 48v batt bank, I would only have seen 1.5 or more kw, and the stator would have seen the same... ouch
If I had run it into a 72v bank, this would come out to over 2kw and then some.
If I can give the mill the chance to stay on tsr, we find 5kw or more.
I have decided MPPT is a waste of resources, as one big enough to let this mill get the best output would be very big and expensive... if it could be done at all... and it appears not to be.
So Flux (as is usually the case) is correct again, boost converter for battery charging. If I use a 72v bank with a booster then I can probably get very handy KWH per day out, but what to do with it arises again.
We seem to get through 6kwh/day of hot water. I have a second electric hot water unit (almost new) and if I can get a suitable 48v or 72v element working, I think this will be the best use of the power with the least electronics.
The dump load can be the induction motor driven from a 4kw dc motor to drive the grid. In some experiments conducted to this end, I have driven 4kw back into the grid, and watched the meter spin rapidly backwards. In this way perhaps I can get the biggest bang for buck, with no losses to heat the water, but plenty of losses for grid drive.... but better than heating hot air for nothing.
If the grid goes down, then a staged shutdown of the mill via triacs shorting the 3ph to stall it.
So on a windy day we may get hot water and maybe 4kwh into the grid, and a calmer day perhaps just the hot water.
The blades are the knotty ones. I used a hole saw to cut out the knots, and machined press fit wood to fit into the holes with wood glue. Seemed the strongest way out.
What I saw the blades doing yesterday, makes me feel that the system worked. Ronb is safe.
Have fun up the ladder
.........oztules
Note these plans are subject to change.... about every day or so.Village idiot...or... just another hack out of his depth
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 11:16pm 20 Sep 2008
Copy link to clipboard
Print this post
Philb,
The furling doesn't work properly in this instance because the mill doesn't present such a dead load as it does when it is stalling with battery charging. It runs more freely, and more of the wind pressure is used for rotational torque and less for pushing backwards torque around the pole. So it does not exhibit the same torque at the yaw head, as at the same rpms as it would have with the batteries.
So it gets to put out heaps more rotational power. If you reconnect the batts while in this state, it quickly pushes the prop backwards and furling begins very quickly.
Looking at it from a non-physics view, the batteries seem to be a short on the mill, and the blades a short on the wind. With resistance, the load looks like a load, rather than a short, and the blades look to be a transducer rather than a blockage to air flow.
If the stator had no resistance, you could not charge batteries at all, as the instant you achieved cut in, you would create full stall. It is only the internal resistance of the stator that allows the blades to speed up after cut-in. .... but as with all things wind it is a balancing act of resistance to get some reasonable air matching, and resistance low enough to not burn the stator.
.........oztulesVillage idiot...or... just another hack out of his depth
Robb Senior Member Joined: 01/08/2007 Location: AustraliaPosts: 221
Posted: 06:03am 21 Sep 2008
Copy link to clipboard
Print this post
Could you have a bet each way chargeing batts and heating water in series?
That thing sounds lethal . Hope it never throws a blade at you or the house.
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 07:46am 21 Sep 2008
Copy link to clipboard
Print this post
Robb,
That is the preferred system I think, but I have no use for charged batteries other than heating the water, so heater in parallel is useful in this instance. If I get to build a 48v inverter then I may do it differently.
It is pretty awe inspiring going at 5kw at ground level with 4m spinning in front of you.
.........oztulesVillage idiot...or... just another hack out of his depth
philb Regular Member Joined: 05/07/2008 Location: United StatesPosts: 96
Posted: 04:05pm 21 Sep 2008
Copy link to clipboard
Print this post
[Quote]The furling doesn't work properly in this instance because the mill doesn't present such a dead load...[/quote]
Thanks for the explaination. That makes more sense now.
I'm still not sure about your last statement about no stator resistance. In a battery or resistive system, the closer the stator resistance approaches zero, the lower the heat (I^2*R). Therefore, more power would available for use in the remainder of the system.
Provided that nothing else in the system has changed, this would mean higher rpms on the blades. The furling system and the prop diameter may have to be addressed. Am I getting it?
philb
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 10:37pm 21 Sep 2008
Copy link to clipboard
Print this post
Philb
It's like all things to do with wind, it is matching the load properly.
In the real world, if we build an alternator with very low resistance, it will not work very well at all or may never get out of stall.... unless you place resistance in the line.
The reason we have to do it is that the blades generate power from a combination of torque and rpm. If we give them a dead load (very low resistance) right after cut in, then with more wind, the torque will try to rise a little, but the rpm cant. If W=ExE/R and R=0, then any attempt to push up E will result in infinate power increase. (ExE/0=very big number).
So even if the blades tried to raise the rpm to get just 1 volt extra, we will see 1x1/0=inf.
Now this is assuming the batteries behave as a 0R load, which is not true, but mostly they are close enough to 0 for us to assume that for our purposes.
You can appreciate that the blades won't tolerate that, and so will stall at cutin and go no further.
Looking at it from another way, the power we put into the batts is a function of the (EMF in the coils- cutin voltage) squared and divided by the stator resistance.
If R=0 then the EMF will be at the Batt voltage (no resistance so no voltage differential) So if we normally say that power out is (coil emf - battVolts) squared / resistance of coils. this time emf-batt=0, r=0 so 0x0/0=0.
So we need resistance somewhere to help the rpm rise and so generate more voltage, it can only happen if we have some resistance somewhere, and blades to match the torque curve of the prop with that resistance.
Ideally, we wind the stator to give the least possible resistance... so we don't burn it up, but if we do a super job of that, and don't have big enough blades to drive it, it will sit in stall until resistance is introduced somewhere else or a mppt is placed in line.
Does that make sense now?
.........oztulesEdited by oztules 2008-09-23Village idiot...or... just another hack out of his depth
philb Regular Member Joined: 05/07/2008 Location: United StatesPosts: 96
Posted: 11:48am 22 Sep 2008
Copy link to clipboard
Print this post
Yes Oztules. Thank you! This subject is proving difficult to master.philb
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Print this post
Just kidding!
Afterwards, I couldn't stop laughing at myself. No harm done, this time, but close, I thought.
. Hope it never throws a blade at you or the house.
