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Wind turbine battery controller

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vielle568

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Hello,

I've recently installed a wind turbine and got it running OK but it doesn't provide enough electricity for 100% use. I need to install a relay that will sense when the when batteries are low and switch the load (the house) to the national grid. It will re-connect later when the cells are recharged.

I can't figure out how to toggle the relay at the low voltage and disconnect at the higher battery voltage. Some kind of window comparator circuit that will latch the relay during the charge cycle and then release when the batteries have sufficient charge. I'm sure the answer isn't too complex but I can't seem to see it!

Any helpful suggestions gratefully received! Thank you.

Vielle568
 

MikeMl

Well-Known Member
Most Helpful Member
...I can't figure out how to toggle the relay at the low voltage and disconnect at the higher battery voltage. Some kind of window comparator circuit that will latch the relay during the charge cycle and then release when the batteries have sufficient charge. I'm sure the answer isn't too complex but I can't seem to see it! ...
Use a 555. Feed the Vcc pin with a 10V regulator. The trip points of the two comparitors will be 3.333V and 6.667V, respectively. Now make two voltage dividers off the sensed voltage input such that one produces said 3.333V when the sensed voltage is at your lower trip point, and the other divider so that it produces 6.667V when your sensed voltage is at your upper trip point. The 555 can drive a small relay, or buffer its output as needed.

I built a battery charger using this trick. The two voltage dividers utilize trim pots, so the upper and lower trip voltages are easily adjustable. I can post an LTSpice schematic if you want.
 

fernando_g

New Member
waaaaay back, there were several book outlining how to use the 555 in truly weird an amazing apps like this one.
 
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MikeMl

Well-Known Member
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What is your desired cut-in and cut-out voltage?
 
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vielle568

Member
Thanks Mike for your reply. I've actually been trying to get a 555 to do the job for several hours today but I still can't seem to get it right. The 555 is wired as a bistable so that it'll trigger and remain stable between the two states. The trouble now is that it needs to be grounded to toggle and my high/low comparators are putting out positive voltage when they activate; not a ground. I tried using an inverter but with no success. Maybe if the comparators control an analog switch that grounds the 555? It all seems to be getting too complex for a relatively simple task.

You asked about the battery charge voltage. Low is 240 volts and high is 260 volts (there are twenty 12 volt batteries connected in series). The input for the comparitors is stepped down from this and they trigger at around 10 to 12 volts. I've got the trim pots and the voltages all sorted out; I can't figure out how to switch the relay at the two different levels.

And yes, I too am trying to create some kind of a battery charger and I would appreciate taking a look at your circuit diagram.

Thanks for your help.
 

MikeMl

Well-Known Member
Most Helpful Member
Here you go. I used a LED as a temporary load. You can use a small relay. I would put a snubber diode around the relay coil. If you want it to be ON when the LED is OFF, you can return the other end of the relay to 12V instead of ground. Use a 12V relay with a coil resistance greater than about 100 Ω
 

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vielle568

Member
Hi Mike,
Thanks for supplying the circuit. I can replace the LED with a relay OK; I'll check it out today and let you know how I get on. I think that the main problem here is that I'm a mechanical engineer and not properly qualified in electronics. I do appreciate your help.
 

MikeMl

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Most Helpful Member
Note that I greatly simplified the circuit just to demonstrate the basic operation. You will have to provide a d.c. power source (wall wart?) of not less than 15V to feed the LM7812. I would put trimpots in the battery sensing voltage dividers so that you can tweak the trip points. I would pick R1 and R3 to be about 10K less than what I showed in the diagram and then put a 20K trim pot in series (center the trimpot at 10K), so that you can fine tune the trip either way...

I noticed that the 555 pin order (cw) as depicted in the schematic is as viewed from the bottom. Pin numbering as viewed from the top of a DIP is usually depicted running ccw.
 
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fernando_g

New Member
vielle568:
If you cut out @ 240 volt (or 12 volts per individual batteries), you are not using its full capacity, perhaps 70% of its total available amp-hours still remain. You need to cut out at a lower voltage, 10.5 volts per battery, to obtain all the available juice.

Don't go below that point though.
 

vielle568

Member
OK, Thanks for all the feedback. First of all I have added trimpots to regulate the two incoming voltages. The new circuit will be fitted into the existing system controller and I can easily tap +12 volts and get a ground from there. The schematic was a great help and I didn't get confused by the pinout.

Well the figures I suggested for starting and ending the charge cycle were purely arbitrary; just figures that seemed to me to be somewhere in the ballpark. The existing system controller is programmed to put out a loud beep when the batteries are low (around 225 volts); shortly after this the sine wave inverter cuts out because the voltage is too low and then the house plunges into darkness without any electricity. I never get to hear the warning signal because all the hardware is setup in an outbuilding and not in the house; hence this project to build the low voltage sensing relay to switch over to the national grid. Luckily these last few days have been windy and the batteries have been keeping up a good charge.

Maybe the low voltage setting could be down somewhere between 225v and 230v; I don't need the upper limit set at maximum (276v) or there'll be too long a delay before the 20 batteries are fully charged. The system seems to run OK on an average voltage of around 250v so I thought that once it's charged just above this level it could be let loose again.

Meanwhile, the circuit from the schematic was been soldered onto a PCB today and is now ready for connection to the system controller for a test! Here though it's nighttime and tomorrow I've got to be sociable with the family; the electronics will have to wait a day for their trial.

I'll get back soon and let you know how I get on.
 

vielle568

Member
Some progress but another problem.....

The battery charge circuit has been built using MikeMl's schematic (image attached). So far I haven't added the relay but just the indicator LED, and the output of the 555 goes high when I connect Vcc.

The Vcc is a 12 volt source that I am taking from the existing wind turbine controller; I am also using the ground from the same circuit. However, neither one of the two cables that come in from the battery bank are connected to ground and there's a large potential difference of over 100 volts between these cables and the turbine controller circuit ground. Measuring the difference across these two cables I can obtain the actual battery bank voltage, but how do I tap this value and use it as an input for the charge circuit I'm trying to install? Is it possible or do I need to find an alternative solution? Any suggestions greatfully received. Thank you
 

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MikeMl

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...
The Vcc is a 12 volt source that I am taking from the existing wind turbine controller; I am also using the ground from the same circuit. However, neither one of the two cables that come in from the battery bank are connected to ground and there's a large potential difference of over 100 volts between these cables and the turbine controller circuit ground. Measuring the difference across these two cables I can obtain the actual battery bank voltage, but how do I tap this value and use it as an input for the charge circuit I'm trying to install? Is it possible or do I need to find an alternative solution? Any suggestions greatfully received. Thank you
Couple of things. First, in my circuit, I assumed that the negative side of the LM7812 voltage regulator is tied to the 555's ground pin. It HAS to be for the circuit to work. Further, I assumed that negative terminal of the battery bank is also tied to the 555's ground pin. It HAS to be, since the 555's comparitors are looking for either 4.00V or 8.00V from the two voltage dividers, so the ground end of the dividers must be referenced to the same ground as the comparitors..

I also assumed that the 12V supply (LM7812) for the 555 is VERY WELL REGULATED, and is 12.00V ± a few mV. I assumed that you would be using a 120V A.C. powered transformer-isolated 15 to 20V D.C. Wall Wart to feed the LM7812. That way, you can connect the ground side of the Wall-Wart to any voltage you want, including the negative end of your battery bank.

If you choose to use your existing 12V supply, you will have to determine if it is ok to tie it to the negative end of your battery bank or not. You will also have to determine if it is sufficiently accurate and well-regulated enough to act as a reference against which the main battery voltage is compared.

How does the existing charge controller measure the battery voltage? It has to be referenced to one end of the battery bank or the other:confused:
 

vielle568

Member
The wind turbine controller is an elaborate piece of equipment. It monitors the batteries indicating overvoltage and undervoltage conditions, but it is not a charge controller. Its function is to control the turbine. It doesn't actually show the battery voltage on the display panel; it shows only the charge level coming from the generator. It receives signals from an anemometer and a dogvane and these are used to control a servomotor to keep the generator turned towards the wind.

Inside the turbine controller the PCB connected to the LCD display panel is wired to a power supply with +/- 12 volts, +5 volts and ground as outputs; this source was used for the 555 circuit; it seems pretty stable. The supply also has terminals marked L and N (AC) that give out a signal corresponding to the generator output, somewhere between 230-270 volts. This value goes up and down with the speed of the turbine. The voltage is measured across the two L N terminals and not via ground; it is the same voltage that appears across the battery bank terminals when the generator is turning. The difference between both L or N and ground is over 100 volts.

However, if for example the live (L) terminal is monitored against ground it too will go up and down as the turbine changes speed but will only be at about half the battery voltage. I tried to adjust the 555 circuit to work using this signal but the resistors in the voltage divider dropped the voltage far too low and I thought I'd better stop and ask advice!

OK, I've just been out to check up on the wiring. It's as I said. The red/black wires from the battery bank come in and connect to the terminals in the controller; they then pass to some large black box and then on over the power supply input. I checked with a meter and there's no resistance on either cable so the circuit must be OK. The generator's turning this evening; across LN the voltage was running at 250v; L to ground 110v; N to ground 118v. The batteries are not tied to ground and are being charged directly from the generator.

Is there still any possibility of adding the 555 to regulate the charge?
 
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MikeMl

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Most Helpful Member
...
Is there still any possibility of adding the 555 to regulate the charge?
Sure, just give up on the idea of using the 12V supply inside the charge controller!

Build a separate a.c. powered 12V supply to power the 555 voltage detector. Since it is transformer-isolated, you can tie it to the battery bank's negative and positive terminal without regard as to what is happening inside the charge controller. The 555 voltage detector's output is a relay, so that is isolated, too.
 

fernando_g

New Member
How tall is your tower? At least 15 meters my guess.
Also, did you make the turbine yourself or did you purchase it?
 

vielle568

Member
Hi Fernando,

The mast is just under 12 metres tall. Here in Europe there's a limit of 12 metres on the height of the mast. If it's over 12m you need to get planning permission from the local authorities and also permission from the regional authorities because the generator will create "an impact on the environment". If the thing is under 12m you can avoid all this administration.

The generator is 3KW and drives a series of 20 batteries of 200AH. There's a controller that monitors the charge, the wind speed and direction. The wind speed and direction signals are used to control a servomotor in the generator and keep it pointing towards the wind. The circuit will also sense when the windspeed is too high and turn the generator through 90° thus acting as a kind of brake.

There are solar panels to augment the wind turbine output but as yet these haven't been installed (I need to repair the roof on the barn!) The system was purchased from a company called Kingship in China: turbine, mast, blades, batteries, controller, inverter, solar panels, and delivery $10,500

I live in France and I had to pay customs on the import. I have since put the system together myself. A large foundation was dug out for the mast (18 metres cube), a battery box, underground cables, a crane to hoist up the mast, etc. There were several initial problems getting the thing running because the blades weren't properly balanced, and then one had a leak and picked up water causing a further imbalance. Now it seems to work OK and the batteries supply enough power to run the house for four or five days from full charge when there's no wind. The noise is negligible, around 50-55dB.
 

tcmtech

Banned
Most Helpful Member
This is a circuit I came up with some time ago. Its great for doing just what you are trying to do. It gives you a high set/low reset window.
I use it on my grid tie inverters to tell them when to connect and disconect based on input voltages.
The opto isolator can be used to trigger stuff or just be ommited if you just want to run the relay in its place.
its not so fussy about its power source voltage either. All you would need to do is put the right resistor voltage divider together for the voltage referance input.
 

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vielle568

Member
Hello Again,

Still not much luck I'm afraid. I followed your suggestion Mike and I connected the circuit to a 12v transformer instead of using the wind turbine controller power supply. I then connected the negative side of the battery bank to the ground of the 555 circuit. However, when I connected the positive side of the battery bank to the circuit there was a large spark and quite a bit of smoke. It looks like the voltage division resistors have got cooked, probably not surprising since they were connected directly between the two battery bank terminals.

Thanks too for your circuit tcmtech, it was something like my original idea of a window comparitor driving a SCR, but after what's just happened this afternoon I have a feeling the same problem will occur again in your design. The battery input consists of 20 batteries (200Ah) connected in series that will be shorted across the two trim pots in your schematic. Yes, the voltage will be there alright, but there are far too many amps for my liking and I see the thing exploding again. I'm certain both of these circuits would work fine, but how do I tap off a voltage reading to regulate the chip without all that power getting in the way?

As I mentioned in an earlier reply, neither of the battery bank cables are tied to the wind turbine controller ground; there's about 100 volts difference. However, I have tried putting a pair of voltage dividing resistors between ground and the terminal marked 'L'. When I first tried this the 100v dropped to almost zero; I don't know why, but the system continued to function, nothing got hot or started to smoke. The right resistors will have to be selected to obtain a 4v or 8v output but it might be possible to get the circuit working like this. I'm just guessing of course, I'm really out of my depth so if someone's got some sound advice I'd be glad to hear it!

Thanks everyone for your consideration and helpful ideas.
 
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