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

 

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.

 

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

 

What is your desired cut-in and cut-out voltage?

 

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.

 

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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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.

 

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.

 

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.

 

Actually 10.5 volts I was being conservative...actual cutoff voltage (under load) depends on the load current.
Go to the following site, for useful technical info:

http://www.panasonic.com/industrial/...A_Overview.pdf

 

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.

 

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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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

 

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?

 

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.