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Forum Index : Electronics : Variable input voltage bat charger
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| Janne Senior Member  Joined: 20/06/2008 Location: FinlandPosts: 121 |
It's been a while, but a little update on this project. To remind any new readers, the system has a 5.2m diameter axial flux wind turbine, with rated voltage at 250V. It is used in conjunction with solar panels to charge a 24V battery bank. The heating resistors are an additional load, they are used if there is enough power available from the turbine. The whole contraption is controlled by a PLC. The psu we acquired worked quite ok, but there was one serious drawback. When the batteries were discharged almost flat, the psu drew too much current from the windmill, and it stalled it..(i think someone made a remark of this earlier in the thread, can't remember who) Which then caused the contactor to switch constantly on / off as the turbine speeded up and then slowed down again. The solution to the problem was to get a different version of the psu, in which the output voltage and current limit could be controlled by an analogue signal from 0 to 5V, instead of the trimpots in the original one. The retailer of the psu was nice, and we only had to pay the difference between the two psu models. So we upgraded the logic controller with an analogue output + input module. The analogue outputs were connected to control the current limit and maxium voltage of the psu. The new psu also gave feedback back to the logic controller, so the actual battery voltage and charging current could also be measured. I then wrote a function, which calculates the power available in any specific generator voltage (voltage was used to measure the speed of the turbine), and that power was then used to calculate the current limit of the psu. The actual measured values of charging power are then used and compared to the available power, to switch on and off the heating resistors. After fine tuning the function to calculate the available power, the system now works pretty well. The battery charger stays on (when coming down on voltage), to some 40V, when there are only a few mere watts awailable from the windmill. On some winds a heating load will be cycling on and off, but i guess there is not much to do to help it. It doesn't seem to be happening too often though, so the contactors should still last a decent while. On the to-do list is still a better battery charging algorithm, right now it is using a constant voltage to charge the batteries. Though the turbine is used only when the owner is staying at the remote cabin, and other times the solar controller maintains proper charging voltage on the battery bank. If at first you don't succeed, try again. My projects |
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Downwind Guru  Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Janne, Whats the big mill in your photos, is that yours?? Its a monster home build. Pete. Sometimes it just works |
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| Janne Senior Member Joined: 20/06/2008 Location: FinlandPosts: 121 |
Hi Pete, Yes it is. It was originally built by my late father with the 12m blade set.. It's been then downgraded to 8.8m diameter blade set, and at the same time the pitch control was discarded. It's currently not operational. The main problem was the generator, which blew apart after the rotor windings came loose. It was made from a wound rotor induction motor, hence the windings in the rotor. After that I've acquired another motor of the same type, but lately I've been thinking more and more of going to a PM generator, or even direct drive. The wound field generator has the advantage of easy control. Output can be effectively controlled by varying the field current(same thing as in a car alternator.).. But then again comes the extra trouble with the sliprings feeding the rotor. I guess it boils down to what I can get my hands on when I have the proper time to tackle the project :) If at first you don't succeed, try again. My projects |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Janne, I think the wound rotor with AVR control is a nice system..... if you have the variable pitch blades to limit overspeed. All bets are off with fixed pitch, unless you use the AVR to load the alternator with an mppt algorithm sort of thing.... else runaway. A machine that size would lend itself to asynchronous alternators direct grid driving would be my first instinct.... but being off grid cruels that angle. .............oztules Village idiot...or... just another hack out of his depth |
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Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi Janne, Could I please invite you to descibe the working function of the feathering unit of the "morkula"photo in the "windmill"forum blade angle thread.I along with others would be very interested and find it of assistance if you are able to go to the trouble of doing so.Thanks for your consideration!Few would attemp projects of such magnitude,congratulations. Kind regards Rastus see Rastus graduate advise generously |
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| leeyn Newbie  Joined: 21/03/2011 Location: Posts: 5 |
You could try it. Find say a, 30-50W 13.8V SMPSU charger and a spare car battery and give it a go. Buy RS GoldRunescape GoldRS Gold |
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