Author Topic: Stupid things we (ok I ) do  (Read 14170 times)

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Offline oztules

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Stupid things we (ok I ) do
« on: February 20, 2012, 07:19:18 pm »
Stemming from an answer to Wolv regarding driving resistive loads:

Here is one experience I had with it. ;D

========================================================= from fieldlines some years back

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 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 side of the meter. That way I could see how much the mill was putting in versus the batteries. ie no mill power meter means  20A into the coils from the batteries, 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 soon 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 pouring out of the icecream bucket, and hot water bubbling over the side.


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.


So it was just (well)  over 5kw into a resistive load in I would say a 30 odd mile per hour wind on a 3 meter pole. Now it is over it seems good really, but I didn't care for it at the time. The stator was absorbing around 500-600 watts (.39ohms in star @35A) the load was copping about 5kw (4 ohms) so the stator could have done this all day. The blades worked well, and I walked away with the mill all in one piece.


And that's how silly I can be....


............oztules
Flinders Island...... Australia

Offline philb

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Re: Stupid things we (ok I ) do
« Reply #1 on: February 20, 2012, 07:39:08 pm »
If I don't make dumb, 'I should have known better' mistakes, I don't learn. :)

Offline birdhouse

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Re: Stupid things we (ok I ) do
« Reply #2 on: February 20, 2012, 07:57:34 pm »
geez, you could have at least used a five gallon bucket...   ;D

great story!

Offline niall

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Re: Stupid things we (ok I ) do
« Reply #3 on: February 20, 2012, 08:05:05 pm »
running away is my preferred option ...

and then maybe throw a few stones at it a bit later from a safe distance to shut it down ..... :P

great write up there indeed ... :)

Offline Wolvenar

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Re: Stupid things we (ok I ) do
« Reply #4 on: February 20, 2012, 09:12:44 pm »
I would still stick by my first assessment that the resistance was changing as the elements were not staying cooled enough.
Also it seems very likely there was not nearly enough load to handle the mill you were driving with.
It may be possible to handle this by adding additional load as voltage rises with a controller monitoring such things.
Then you can keep it out of stall until needed?

Unless I am missing something completely, as far as I understand batteries they just naturally increase resistance as input voltage rises ( but decreases as battery voltage does ( to a point).
Where as resistive loads like nichrome acts in reverse as heat builds
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Offline oztules

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Re: Stupid things we (ok I ) do
« Reply #5 on: February 20, 2012, 10:25:18 pm »
Hmmm how to put this.....

Ok, the figures of current and voltage tell us the resistance was still not too far from 4R, 150/35 =4 ish... so no I don't think so.

The coils must not get much over boiling point due to the massive energy needed to achieve state change from water to steam.
Without the water, then the temp would rise crazy, but you only need to quench red hot steel to see it drops to water temp very very quickly.

State of charge influences the battery impedance. dead flat... high impedance, mid charge, low impedance, fully charged high impedance to charge current, low impedance to load...

When flat, they lack ion carriers. When they convert lead oxide to lead sulphate, the h2so4 converts to h20. Pure water is a lousy conductor, so as the ions are very scarce at dead flat, we see batteries wont take much charge at all. As they do, they create more h2so4 (h3+ available to carry charge now.. hydronium ions from memory).. so the charge current comes up until there is enough carriers to make the reaction go well, and then we charge full bore.

When full, the active sites on the plates that can still accept the redox reaction are few and far between... we are charged now, and if we keep the voltage on the batts, they will finish off any left over sites (pbso4 to pbo and h2so4), but the rest of the current will dissociate the hydrogen from the oxygen. The current we see going into a full bank is really only that...... losing our water to h2 and o2. ... thats equalising, those cells still with active sites still charge and bubble, those full, just bubble.

(I think Chris knows lots more about this battery business  than me)...

Nichrome does as you say.


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

Flinders Island...... Australia

Offline Wolvenar

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Re: Stupid things we (ok I ) do
« Reply #6 on: February 20, 2012, 10:58:45 pm »
As far as batteries go, that is basically what I was getting at, I was just being more simple.
With the exception that they have a difference to a resistive load like nichrome.
Because is it not if you apply a higher voltage to them, given the same state of charge, the apparent resistance rises?.

As far as elements in small amount of water, I was looking for if the elements were heating to fast causing bubbles around the elements, and hot spots.. If you had more water  creating larger water flows that would stay cooler, maybe this would not happen as quickly?
Also it does seem that if you had enough load it should keep it under control. If you short the alt, it does stop it, that is none the less resistance. Determining that load may be easy on paper, as we all know what looks good on paper, may not be true in real life. Teila and error might be the best way to get working numbers.
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Offline oztules

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Re: Stupid things we (ok I ) do
« Reply #7 on: February 21, 2012, 12:33:19 am »
W=E^2/R

Now my prop at 12 mph develops 350W, and the alt makes 48v oc so into the 4R load so that is 48x48/4 or 2304/4=576W
So at 12mph, 4R kills the prop.

At 24 mph the blades make about 3kw but the alt is only at 96v oc so 96x96/4=2304 watts. The prop now has more power then the load can take at designated TSR.

At 36mph the blades are making over 9000watts the gen should be at 144v oc so 144x144/4=5184watts

So we have gone from stall to way over power by 4000w. The prop will speed up until it is well off it's tsr,and power will fall... and the load will now match.

Can you see how far your resistance would need to change to make even a tiny bit of difference?

As the wind increases past a certain point we need to add load... and lots of it. squared function against a cubed function on a linear rpm.

That certain point here.......... would be about 20mph :the prop would do about 1600W.  Alt about 80vvoc  so 80x80/4=1600w

Any wind above 20 mph will give us too much TSR.... overspeed,  and any wind below that will probably pull it to a stop after a short time.

Does that make sense now.

For the battery.
If we raise E and say R rises, then I (current) must stay the same..... E=IR

But in a battery in mid charge, if we could raise E by even only 2v, Current  will go through the roof... so R must stay the same. ( in fact on a big bank we do not have enough power at our disposal to push it up 2 volts in one hit) .....If the resistance went up reasonably, we would have no trouble.
But that does not happen. Try and raise volts much, and current  takes off. not R.... until we are near full or empty... then all bets are off.



Did I explain it right this time :)


..................oztules
Flinders Island...... Australia

Offline Janne

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Re: Stupid things we (ok I ) do
« Reply #8 on: February 21, 2012, 06:14:08 am »
Heh that was a fun story to read.
I'm sure everyone has his / her own memorable moments like these. Of my own I think the furling failure on my 3.2m axial mill would be pretty high on the list. The winds were between 20-30m/s when it refused to furl and was pumping a bit under 3kW into my 12V battery bank... about 160 amps but the battery bank was at 18V at that moment :D, since the dummy load was not rated for that kind of amps. Ahh the smell of sulphuric acid..

Also pretty memorable was the first testing of the same 3.2m rotor, but poorly balanced on a 2m short test tower.. not having much clue what kind of power and speed it would be capable.. of course with high winds and a 45W bulb "surely providing enough load". I ran pretty fast when it started to sound like a helicopter jumping up and down at the same time.
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Offline oztules

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Re: Stupid things we (ok I ) do
« Reply #9 on: February 21, 2012, 03:02:18 pm »
Yes Janne... when your new to high lift props.... life's learning curve is very very steep.

My first set of 8 footer blades were carved from the boards from a transport pallet.... not flash, but followed the proper curves as best you can with 4"x1" free timber.

It was with the naive knowledge of a three your old with bright eyes, that I screwed the boards ( now blades) to a triangle, poked them on a stout screw driver, and walked from the shed into the big wide world........ I was 47yo.

The breeze wouldn't even get them to turn on the screw driver  shaft for a bit, then slowly it started to move.

I was fully in control, and completely nonchalant, as these seemingly harmless bits of wood started to turn in the breeze. A bit more breeze turned up, and they started to spin harmlessly up.... nothing. At this point I'm wondering how these things are going to power anything.... but we'll see if they can do any better.

Whilst thinking all these things and others like it, I'm oblivious to the fact that they have been slowly getting faster, and are now getting to the transition point where they are no longer drag driven but lift driven.

So I'm still daydreaming and disappointed at their performance...... and then there is that certain noise as they suddenly transform prom placid drag blades to fearsome roaring man killing weapons of doom.... they have taken off.

Now it must be doing over 400 rpm, making that unloaded prop roar, and I am rooted to the spot, with my fear ridden gaze transfixed to the propeller  that only minutes ago was just a toy, and now was trying to kill me with every tiny move I made to turn it out of the wind.

The good lady wife, who had been wily enough to watch from a distance ,heads for the door of the house ( ostensibly so some one will be left alive to call 000 or 911).

By now I appreciated just what lift does to a blade. I appreciated that gyroscopic forces could cut my head or toes of... dependent on which way I turned, and that my life could well come to a sticky end right here.

Turning out of the wind wasn't an option, the wind was building .... and I was in trouble.

It was some minutes later that I recovered my composure as I had shuffled back sideways to the shelter of the shed, breaking off the wind.... I felt 97 years old.

I have done a lot of things in my time, but never had I been confronted with decapitation, or serious slashing.... by my own hand, and in my control with such surprise...... My life was on the end of a screwdriver with a roaring 8 foot slashing machine.... and it was my next move.

By gad I learnt a lot right there right then.



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

An adumbrate version of fear with a prop ;D
Flinders Island...... Australia

Offline Wolvenar

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Re: Stupid things we (ok I ) do
« Reply #10 on: February 21, 2012, 03:34:53 pm »
Ok I have to admit it, I did almost exactly this same thing.

I had a smaller 6' 2 blade plus it was mounted well on a small generator and the head unit that was to go on the tower.

I was probably being a bigger idiot though.
I DID understand the gyroscopic forces from previous much smaller yard ordainment size windmills, and the likeliness of the spin up being rather fast..
Only I did it anyway, in over 25mph winds..

I was walking to put this thing on the tower when I got the hair brained idea to let the blade loose
That this was likely over 500 rpm in mere moments when I let er rip.

Thankfully I did have so much of the machinery there and the entire device was just heavy enough to aid in control but not to heavy to be unmanageable. I was able to move it to the point I could slow it to a stop , then grab the blade just as it seemed about to reverse.

Yup, never doing that one again, I learned something..

Or did I..

About a year later I had a 2 blade 8 footer up for a test
Maybe some remember the surprising output alternator I made from ceramic magnets scrounged from many microwaves
That was the bad boy that actually got me.

I had put this thing up with intention to see what it would do in real life and not just the bench.
I found out really fast that my magnet backplate was not up to meet the the forces involved.
Magnets were hitting the stator ripping it up pretty quick when I forgot to tie it down for the night.
I went out to try to rope the blade, and could not pull it off from the ground.. So,, with the fear of god I climb the tower and tried again.
Yup got it.. but it immediately got me too as repayment. When the rope caught the blade it turned right into me clipping my shoulder.
I was lucky to kept my head ( in all manor of speaking) and got away with only a really nice bruise and about 3 weeks of pain.

Yeah, now that the wife will learn the real truth of how I got that. I'll see if she still lets me keep playing with this stuff.  :-\





Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline niall

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Re: Stupid things we (ok I ) do
« Reply #11 on: February 21, 2012, 04:19:52 pm »
not long after putting up a small mast for the machine ..i had to re adjust the cables in the turnbuckles after things "bedded in".....i had the winch still there , so i decided to let the whole thing down  ...(test run kind,of)

before disconnecting the extension piece on the main winch stay i got into a bit of a muddle with the shackles ....did i loosen this one or that one ...where is the big one and (most important ) why is the dog looking at me like that ?

so i was really standing there holding the main stay in one hand with the mill (luckly very slightly of vertical) for an instant ...... a good day to have no wind .... ???
 

Offline Wolvenar

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Re: Stupid things we (ok I ) do
« Reply #12 on: February 21, 2012, 04:45:22 pm »
Sounds like a touch of ADHD there lol
I can relate.
Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline tomw

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Re: Stupid things we (ok I ) do
« Reply #13 on: February 21, 2012, 05:12:53 pm »
In another life...

I went into a 35 MPH curve at about 90 MPH on a 1976 Heritage softail. Proved a couple finer points of physics. You cannot slow down much at that speed with a few seconds of warning. Muddy fields can be almost as hard as concrete.  And the fact that I think I can operate a motorcycle MUCH better than I actually can!

Once the bike kicked out from under me (bailed out) I imitated a bean field luge run for a couple hundred feet feet first.  Beat the hell out of me but mostly damaged pride and trashed leathers. No clue how I avoided the barbed wire fence  on the way into the field but I think I went over it.

I didn't quit riding motorcycles until after a drunk guy in a van changed lanes and actually ran right  over me. I didn't get up and walk away from that one and it was my last motorcycle ride on the street. It still hurts daily.  :o.

I did the thing with a 2 meter 3 blade prop holding the "test pole mount" in my hands with the turbine screaming and trying to yaw. Luckily the wires were hanging off the alternator so I just puinched them together with my left hand and it slowed enough to get it out of the wind against the gyro forces.

Tom
Do NOT mistake me for any kind of "expert".

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Offline m12ax7

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Re: Stupid things we (ok I ) do
« Reply #14 on: February 21, 2012, 05:12:57 pm »
The most stupid thing "I ALMOST DID"  was to post about the most stupid thing I did do!