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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 11:28pm 09 Apr 2009
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Matt,
You may well have close to right already, remember there is a finite amount of current required to keep the battery up at float. When the dump gets released as the battery drops (loses plate charge), the input pulse will drag the plates back up to 13.8 (or whatever... if cycling the little battery, perhaps 14.4)
or:
It should be straight forward to make the load big enough to pull the input to below the battery threshold. ..Make R bigger EDIT:(I mean less ohms so I guess I mean smaller R. bigger resistor bank watt wise), or use ohms law to size the load.
The battery impedance is dynamic, (which is why we don't say resistance.... even though the measured impedance is expressed in ohms) so measuring it is difficult except in an instant by instant process..... It gets worse really. The internal resistance of a charged battery is very low... so looks to the load as a low resistance/impedance driver. If we try and charge the same battery in the same charge state (full), it presents to the charger a high impedance (takes very little charge... and to the charger looks like a high resistance and so little current flows.... so it all depends which end of it your on as to the impedance of the battery.
It is all back to front when discharged... ie high impedance as a driver and not capable of high current any more, but the charger sees it as a near short initially, and a low impedance to push high current into..... that why we can't allocate a static resistance value to it like say a load resistor.
If you size the load to drop the voltage below battery... say 10v if you turned it on full time to test, then if any current flows to the battery when it pulses it, it is because it needed it to maintain float voltage..... providing you are sampling quickly. Op amps do it in real time, and are preferable to dinosaurs like me.
In closing, if your dump keeps the batt voltage at float, any current flowing is maintenance current... and a good thing.
..........oztulesEdited by oztules 2009-04-11Village idiot...or... just another hack out of his depth
So getting the dump load to the right size for the windmill/generator is important in making sure that the voltage over it will drop below the float voltage of the battery.
I've got a bunch of 50W 15R resistors so I can play around with that.
GeWatPE, I posted in the windmills because I thought it was the most appropriate for the topic at the time. Is there a way of moving the thread now to electronics?
Cheers,
Matthew
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 10:12am 10 Apr 2009
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Sorry Matt,
I had to edit the last post. Where I said bigger R, I was thinking smaller resistance, but bigger resistor, or more of the same in parallel.
This is what we in the business call.... stuffing it up
It appears you knew what I was getting at anyway....
...........oztulesVillage idiot...or... just another hack out of his depth
Oztules,
I was just reading http://www.thebackshed.com/Windmill/articles/ChainsawBlades3 .asp, and I saw you wrote "putting 19A@70v into the batteries" - which is kind of what I was worried about when I started this thread. Isn't 70v into your batteries enough to damage them? Or is it OK for short periods?
Cheers, Matthew
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 10:05pm 11 Apr 2009
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Yes Matt,
Purely evil, and not something I would allow into a decent battery bank.... but these were very old >7years, and I was just testing the mill, and didn't care what the batteries said.
It was also for very short bursts, which probably did more desulfication good than bad. This was bare bones testing. You would never use a windmill without a dump load or similar in place..... only a dill would do that.......
Did I mention mine has no dump load?
............oztules
Village idiot...or... just another hack out of his depth
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 11:16pm 11 Apr 2009
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I have some data from a windmill at a good wind location. This windmill, 2.5kW rating, Skystream3.7 has produced 20kWhr in a 12 hour period.
This is graphed data for a 1hour period. the mill produced up to 4.5kW at times. This is connected to a 48V RE battery bank, so approx 90A was put back at times to the battery [650Ah] through the Outback inverter/charger.
This is not a homegrown system but I offer it as an example.
With grid connection and a good wind site, this could subsidise holidays pretty well.
Gordon.
PS edit: the brown trace is the power produced.
Edited by GWatPE 2009-04-13become more energy aware
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 11:53pm 11 Apr 2009
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Yikes!!!!
.......oztulesVillage idiot...or... just another hack out of his depth
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 03:37am 12 Apr 2009
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You can imagine the difficulties with diversion loading this beast. The 4.5kW peaks create some problems with the physical sizing of the heater. A significant part of a wall is required for the radiator bank. I have been told that the room gets quite warm in a storm.
I have had a bit to do with this installation. I am looking at a revised 240V, AC coupled proportional loading system, modelled on the setup I use on my own battery bank, that gives programmed boost, equalization, absorbtion and float voltage settings. This will be an ideal use for some 600V 20A mosfets, that will be arriving shortly. The battery maintenance aspect is difficult to incorporate in AC coupled systems at these power levels.
Gordon, any chance you could email me the data used to produce this graph? Over a week period if possible?
That would be much appreciated!
matt at mattvenn dot net
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 11:30pm 12 Apr 2009
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Hi matt,
Gee, only a week. I can't see how someone else's data really would be of any use, considering your application. A weeks data from this mill would be approx 10MB file as raw data, and of no use without the application that knows how to display it in a graph. I had to do quite a bit of data manipulating [merging of files and date/time stamp calculating] to get this graph from raw data. the data is recorded at about 3sec intervals for 30 parameters, and the limits of Excel are pretty soon reached.
I offered the graph as an example, for interest only.
I guess this is a no.
I was asking because I couldn't really see the graph because it seems low resolution on my screen.
It might not be entirely relevant to this project... but I'm interested in other projects and you seem to have a lot of data!
Which reminds me, have any of you checked out this crazy website?! http://bwired.nl/ Now THAT is a lot of data!
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 11:06pm 16 Apr 2009
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The graph is just a screen capture .jpg. I do have a lot of data, relevant to wind sites I have access to. I offer advice to other real people, and not just those in cyberspace. I have limited internet bandwidth so I refuse to support sites like U-tube etc with MB downloads needed. Maybe with a fibreoptic connection, MB/s downloads, but this is a way off for me yet.
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.
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