Solar wind troubles

[stojke]

Hi guys, pardon the fancy topic name, but I could really use your help!
It involves an solar / wind turbine power generation process in order to charge accumulators and store power for later usage.

There is a friend of mine who has an solar / wind turbine setup at his cottage, which is completely off the grid, and he would like to use these two alternate power sources in order to power on his devices, such as lights, fridge, tv, etc. The setup consists of three solar panels, a wind turbine and four accumulators. Solar panels are wired in parallel and are rated 12V 100W. They are also attached in parallel to an Wind turbine rated 12V (400~600)W which supplies power continuously (and not via impulses as I am told) and routed onto the four 12V 120A Excess Solar Gel accumulators (AGM VRLA). Charging of accumulators was done by an dedicated charge controller that died. Charging is currently done very roughly, which is connect the accumulators to bare wires and disconnect them after a few hours ( ). We have tried to fix the existing charge controller but , just look at it  >

.  Besides the bad controller it seems that also one of the accumulators has also died and is being sent back for service (or replacement).

Due to all of this I have suggested that we build an charge controller instead of investing into a new one as it would serve as an great learning experience for both of us. I also work at an computer service and have a lot of spare parts from power supplies that we could use.

Can anybody suggest an schematic or project we could use, and if possible confirm that the wiring done with all the components is correct? Thank you.

[Simon]

that looks like a circuit that probably just has a comparator that controls a relay, so your putting 12V solar panels straight into a 12V battery ? no wonder one battery is damaged. "12V" solar panels can easily hit 17V. at 15V your batteries will be boiling away liquid.

[stojke]

Yes, measured voltage from the panels is usually 17V, but from what I understand the battery died before the controller died.

[Simon]

Due to all of this I have suggested that we build an charge controller instead of investing into a new one as it would serve as an great learning experience for both of us. I also work at an computer service and have a lot of spare parts from power supplies that we could use.

Can anybody suggest an schematic or project we could use, and if possible confirm that the wiring done with all the components is correct? Thank you.

Err, who made the original controller. Looks like that was home made.

[stojke]

It was made by an small local firm that produces and sells such devices.

[Seekonk]

I live off grid 5 months a year.  I have a very small PV system that runs a fridge, heats water, and charges batteries.  I started a "project" to build a control system at almost no cost using E waste.  My system has been up and running many years and have never found anyone interested in this project.  If you can find any old small UPS, you can build a controller.    Three panels (36V) in series is ideal for this system.  It operates  the panels at power point of about 50V.  Small electronic wall warts provide power for micro and high side FET drivers.  System runs on a UNO or NANO using simple code.  My whole system costs about $10 and is overall far more efficient in use of energy than other more expensive systems.  Your panels probably waste half of their potential power the way they are hooked up.

[Ian.M]

There is no particular problem feeding multiple low power charging sources into a flooded cell Lead acid accumulator bank of sufficient capacity without a smart regulator as long as you have an over-voltage cutout, the battery bank is NOT maintenance free, and electrolyte levels are checked regularly and topped up as needed.   One approach is to dump power into a large load once the battery voltage reaches 14V.  The load has to be able to handle the full output of the charging system continuously so will probably need to be fan or water cooled.  You will need to use a beefy MOSFET to switch the load as it will cut in and out very frequently and a relay or contactor that isn't built for regulator duty wont stand up to that sort of abuse.

Another approach is to disconnect the charging source, and reconnect it once the battery terminal voltage has dropped sufficiently.  You can use the same 14V cut-out voltage, but the correct cut-in voltage is dependent on the load on the battery bank, so done right, it needs a shunt for a current sense circuit to offset the lower comparator threshold.  Also, it is generally not a good idea to disconnect the load from a wind generator as that tends to result in many types over-speeding, so depending on the model, it may need shorting to brake it or it may need switching to a brake resistor, or a solenoid to activate a mechanical brake or feathering mechanism.

However you have AGM VRLA batteries which *CANNOT* be safely charged without a smart regulator or close manual supervision, as there is no way of replacing electrolyte lost to gassing. Once fully charged they need to be held at the manufacturer's recommended, temperature adjusted float voltage, ad have very little tolerance for error.  You are taking on a major project, involving switching and monitoring currents in the 75-100A range, and a significant software component to handle tracking the charge and discharge history to determine when to switch from bulk charge mode to float mode, and how often to initiate an equalisation cycle.   You'll only save money against a leading brand smart battery management system with MPPT if you don't allow for the cost of your development time and you get it right first time.  If the delays to complete it cause more batteries to fail due to the crude manual charging, or the algorithm is faulty and significantly shortens the battery life, it could cost you far more.

Unfortunately, it is probably uneconomic to convert to a higher battery bank voltage, due to existing 12V loads and the wind generator.

[Simon]

It was made by an small local firm that produces and sells such devices.

I say they are not too sure of what they are doing

[stojke]

However you have AGM VRLA batteries which *CANNOT* be safely charged without a smart regulator or close manual supervision, as there is no way of replacing electrolyte lost to gassing. Once fully charged they need to be held at the manufacturer's recommended, temperature adjusted float voltage, ad have very little tolerance for error.  You are taking on a major project, involving switching and monitoring currents in the 75-100A range, and a significant software component to handle tracking the charge and discharge history to determine when to switch from bulk charge mode to float mode, and how often to initiate an equalisation cycle.   You'll only save money against a leading brand smart battery management system with MPPT if you don't allow for the cost of your development time and you get it right first time.  If the delays to complete it cause more batteries to fail due to the crude manual charging, or the algorithm is faulty and significantly shortens the battery life, it could cost you far more.

How will we learn unless we take advantage of the situation and understand the risks
It's easy to invest into an complete project once every other option has failed.

I have seen projects that use an Arduino Nano and custom code to control and monitor the charge process. I am guessing that these are good ideas to try since I can modify the circuitry for my (friends) devices and their specification and leave the rest the same (arduino circuitry and stuff).

I live off grid 5 months a year.  I have a very small PV system that runs a fridge, heats water, and charges batteries.  I started a "project" to build a control system at almost no cost using E waste.  My system has been up and running many years and have never found anyone interested in this project.  If you can find any old small UPS, you can build a controller.    Three panels (36V) in series is ideal for this system.  It operates  the panels at power point of about 50V.  Small electronic wall warts provide power for micro and high side FET drivers.  System runs on a UNO or NANO using simple code.  My whole system costs about $10 and is overall far more efficient in use of energy than other more expensive systems.  Your panels probably waste half of their potential power the way they are hooked up.

Is there a place where I can see information on your project? I have around 15 Power Supplies and many already salvaged ones. Some are higher end Delta, Enermax, FSP, etc.

I say they are not too sure of what they are doing

 

[Ian.M]

How will we learn unless we take advantage of the situation and understand the risks
It's easy to invest into an complete project once every other option has failed.

You learn this stuff by building a smart charge controller for flooded cell batteries with removable caps (because they are far more tolerant of abuse).  After getting that going and running it for enough months to build up some statistics, you fully test the batteries and determine if it has maintained them well.  If it has, you can tweak the setpoints and algorithm for AGM batteries, and run the flooded cell batteries as if they were AGM batteries.  That will undercharge them slightly, but not harmfully.  If it continues to test OK, you then try it on AGM batteries, testing their performance on a regular basis.

The only shortcut is if you can find an OSHW project that does what you need and that has enough users to build up a knowledgeable community.  If one already has a proven design and firmware implementation, one is starting with the equivalent of an off-the-shelf controller in kit form, and will only need to do basic testing before putting it into service.

Doing a project like this for a friend and getting it wrong is likely to lead to a choice between being seriously out of pocket or breaking a friendship.   If it was for your own use, I might be a little more optimistic.