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MPPT controller question


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18 hours ago, reg said:

Trying to get my head around this. Is my thinking wrong here. 

First array is passing 2 amps to controller battery output terminals. 

Second array is passing 4 amps to controller ouput terminal. 

So actual current passed through connections to battery bank will only be 2 amps? 

I'm thinking of the scenario where solar panels of different currents are wired in series such as shown here 

Solar Panels in Series of Different Currents

http://www.alternative-energy-tutorials.com/energy-articles/connecting-solar-panels-together.html

 

If you run your engine, while connected to shore power with your battery charger turned on, and your solar is working, there are 3 lots of charging amps heading for the battery terminals. The batteries and the system seem to be able to sort this out, and we generally don’t even think about it.

 

A second solar controller is just another charging source added to the system so, perhaps, we need not concern ourselves :) 

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2 minutes ago, Richard10002 said:

If you run your engine, while connected to shore power with your battery charger turned on, and your solar is working, there are 3 lots of charging amps heading for the battery terminals. The batteries and the system seem to be able to sort this out, and we generally don’t even think about it.

 

A second solar controller is just another charging source added to the system so, perhaps, we need not concern ourselves :) 

 

That is because the control/regulation in all those sources basically monitors voltage and when the voltage reaches the particular unit's pre-set it starts to "pulse" the output to maintain a safe average voltage. If another charging source has a higher pre-set voltage then the lower one will shut down but that is fine because to get to that voltage the batteries would have to be well charged. As soon as they discharge or a load goes on the battery voltage will fall and the "turned off" unit will starts to charge again.

 

There is a valid concern when an alternator shuts down and puts on the charge warning lamp because that scares many boaters. This seems to be coming more common with the increase in large solar arrays.

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40 minutes ago, Richard10002 said:

If you run your engine, while connected to shore power with your battery charger turned on, and your solar is working, there are 3 lots of charging amps heading for the battery terminals. The batteries and the system seem to be able to sort this out, and we generally don’t even think about it.

 

A second solar controller is just another charging source added to the system so, perhaps, we need not concern ourselves :) 

However I understand Reg's thought process on this and wouldn't dismiss it by reasons of the comparison you've made.

 

The whole point in investing in solar and MPPT controllers is to have on-going charge to the batteries regulated to maximum efficiency while off grid. If running the engine for a few hours was to interfere with that efficiency and effectively cancel out the solar input or reduce it, it's no great shakes. Similarly if on shore power you don't care what the solar is doing because you've got a permanent charge there which isn't using the MPPT and which you've already decided is worth paying for (presumably for large or multiple power drawing appliances or for winter heat) irrelevant of your solar input. Chances are in that scenario you've bought the solar for times when you're away from shore power anyway.

 

I tend not to run my engine from dawn till dusk every day and all year, and I would be surprised if many boaters who use large solar arrays do unless they think life is the BCN. :D  But if we invest in MPPT and PV systems it would be nice to know that having a second PV system doesn't screw up the efficiency of the first, because they both WILL be working dawn till dusk every day all year to some degree,  whether we are aboard or not. And it's good to get our money's worth from the investment at least, even if (thankfully) the duelling-banjo controller action won't destroy the batteries.

 

I know it has been clarified that having two solar inputs isn't a very big issue on the efficiency of each system, but that there is some reduction in maximum potential input later in the charge cycle. I don't agree that your argument is a good justification to dismiss Reg's thought processes on it though, however reassuring you might think you sounded. Reg's argument makes sense to me when trying to get the most out of two solar arrays, and not swapping one or both for engine power or shore power (which are fairly constant, reliable and abundant, so not very comparable to a system that's a delicate balancing act between two MPPT Controllers reading each other's variable outputs).  

33 minutes ago, Tony Brooks said:

 

That is because the control/regulation in all those sources basically monitors voltage and when the voltage reaches the particular unit's pre-set it starts to "pulse" the output to maintain a safe average voltage. If another charging source has a higher pre-set voltage then the lower one will shut down but that is fine because to get to that voltage the batteries would have to be well charged. As soon as they discharge or a load goes on the battery voltage will fall and the "turned off" unit will starts to charge again.

 

There is a valid concern when an alternator shuts down and puts on the charge warning lamp because that scares many boaters. This seems to be coming more common with the increase in large solar arrays.

Very coherent explanation. Thanks, Tony. :)

Edited by BlueStringPudding
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1 minute ago, BlueStringPudding said:

Reg's argument makes sense to me when trying to get the most out of two solar arrays

Set the larger array to charge fractionally higher than the smaller array, by 0.1V.

 

It's probably best to set the smaller array to 0.1V less than your batteries want rather than increase the other.

 

When it gets that close to full, the larger array should keep going.

 

If your solar arrays are the same size it doesn't matter which one is shut down.

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Interesting. Thanks. This is assuming that the larger array which has a larger potential voltage drop because of distance from the batteries and are much older than the smaller array, really does constitute a "larger array" in terms of maximum output ?

 

Also, what if what you decide is the larger array becomes more shaded than the other array some days and not others. How does that work with presetting the 0.1v difference? Will the shaded array still be treated preferentially by the MPPT Controller or will the shade cause it to be ignored by the controller and the sunny array used instead?

Edited by BlueStringPudding
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