Three energy sources

[Tim McMurran]

Have a interesting issue.

Our place is off grid, solar, wind and a 25kw Stamford head on a lister HR3.

Ideally what I want the lister to do is run our larger applicances like the stove and dryer as well as kick in when battery voltage drops to ensure things stay in peak condition while not burning more fuel than needed.

What would be the best for a 48 volt battery bank controller/solar and wind as well as how can I have the lister auto start when the voltage drops below (x) volts?

Off the shelf or other ideas would be welcomed.


Thanks

Tim

[Brian McGowan]

I have found in general a lack of any kind of coherent overall system management.
I personally think this is the charge controller's responsibility since they are intimately in charge of the battery but the charge controller manufacturers don't seem to want to do anything but charge batteries and happily choke the panels down to save the batteries instead of arranging to divert that power to other uses in an attempt to make best use of all the power that can be harvested.

That being said, I have decided to explore Arduino and other microcontrollers to do everything else that the charge controller does not do and to keep the system harvesting as much power as possible and send it to the most useful places.

There are people out there that are using alternators hooked to various engines to keep their batteries charged and run devices, controlling them with the Arduino and even including auto start features. I post a link below to get you started on your search. There is a link right at the top of this page to another page also with this person's previous work. This controls things like auto start/stop based on battery voltage, alternator field control and throttle control based on alternator temperature. You probably don't need those last two things since you are running an AC generator.

http://smartdcgenerator.blogspot.com/

Anyway, I am looking into Arduinos for dump load and low voltage disconnect control and for control of the new inverter I just purchased. I want to turn the inverter on when battery voltage reaches 16.5 and off when it gets to 15. Currently my charge controller has a single relay to be used for either dump load or low voltage disconnect and in dump load mode the relay turns on when the battery reaches a given voltage and off at some period of time after it falls below that same voltage which causes it to cycle on and off all the time.

One advantage of using the Arduino will be having one device reading the voltage and making decisions about what to do with the power. I think I will have 8 outputs. If I use 1 for the inverter control I will have 3 for low voltage disconnect and the remaining 4 will be for dump load control

The low voltage disconnects is one place where I hope to make a significant improvement. I currently have hardware low voltage disconnects and the nanosecond voltage falls below a setpoint I have no control over it trips off. If the inverter is on and the fridge kicks in that momentary spike is enough to trip it off and it will not come on until the fridge kicks off and battery voltage rises back up again.

Anyway, that is why I want some kind of programmable control over all of this stuff and it seems like that is what you are looking for also.

Brian

[Rob Beckers]

How-die Brian!

My guess is that charge controller makers see it as an inverter function to do something useful with excess PV. Such as a sell-back engine in the inverter that diverts excess power to the grid. This is based on Voltage, so you should be able to do something with an Arduino along those lines (run a PWM type setup to make hot water for example, the Arduino will even do PWM for you).

More knowledge of available solar PV and current coming from the charge controller could help elevate this to a much finer-grained control; a solar cell and current sensor could do that for you.

I've been itching to do some Arduino projects myself, but just never seem to find the time. So, let's live vicariously through you! :cool: Let us know how it goes.

-RoB-

[Brian McGowan]

I still think it has to be the charge controller's responsibility. That is the device that knows the status of the battery and how much power it is able to create from the panels also attached to it. It knows how much it needs to send to the batteries and how much is left over to dissipate to other places. And no matter how you cut it, if another device is making these decisions it has to sense the battery voltage on it's own and there will always be a difference of opinion between these two devices. If the charge controller thinks the battery voltage is 16 volts for example and the device dumping the power thinks it's 15.9 volts and wants to start at 16V then the charge controller could start choking down the panels before the dump starts working and you would lose generating potential.

Another thing I am surprised is lacking in charge controllers is remote battery voltage sense. All controllers sense voltage within their box before shoving a pile of current down the wires to the batteries and therefore cannot gauge the loss due to wire resistance when current is being drawn through it. When you are talking about such low voltages a couple of tenths of a volt can make a difference. Most of the good bench supplies I have used in my careers have had separate remote sensing wires to make sure voltage was correct at the load no matter how much current was being drawn through the supply wires.

Anyway since none of the above exists in this world I am forced to do this with other devices. The arduino will have to be that device. I will keep you posted as to how I make out and will post programs and circuits I develop here if that is OK. I have 4 current sensors in my system as it is so I should have no problems monitoring what is going on.

Brian

[Rob Beckers]

It's not really surprising that charge controllers don't have sensing wires: It adds more complexity, when many already have trouble wiring up a charge controller (you'd be surprised, we sell a lot of charge controllers...). I can already see a whole heck of a lot of people confusing the sense wires with the charge wires, and burning the place down!:eek:

It also makes zero difference in charging a battery. Think about it: The only time you see high currents and therefore inaccurate Voltage measurements is when the batteries are not yet near "full". They need the charge at that point, so whether the Voltage is a tenth higher or lower doesn't make too much difference. As the current tapers when the batteries reach "full" the Voltage measurement gets more and more accurate. Maybe not idea, but certainly good enough for charging.

Heck, lots of people don't use remote temperature sensors to charge, which causes much larger errors in what the charge Voltage should be.

-RoB-