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offgrid View Drop Down
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    Posted: 28 Jun 2019 at 4:54pm
I know the founders of Morningstar very well and can’t speak more highly about them and their products. Great folks ( and I don’t get paid to say that😁).

I still doubt that your issue was caused by the reverse polarity fuse. That is a passive device which was simply closing a circuit to the WFCO which was shut off anyway. I still think something else was causing the problem. Time will tell if things are now stabilized for you. If the system starts cycling on you again then I’d bypass the LVD until you can sort out the underlying problem.

Good luck!
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JR View Drop Down
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Posts: 343 		Direct Link To This Post Posted: 28 Jun 2019 at 9:55am
Thank you for all the insightful information offgrid which has helped me a lot and to determine / resolve what I will call a cyclical negative feed back issue effecting the charge controller's performance.  Removing the 40a reverse polarity fuse on the circuit board has seemed to resolve the issue.  At least I haven't experienced the issue in the last 3 days and your right the Morningstar is a good piece of equipment and they have fantastic service techs, who are very helpful.  My thoughts are that the charge controller has always been doing its job and was just getting sketchy inputs from the WFCO circuit board via the reverse polarity circuit.  Time will let me know if I was wrong.

As to the amperage at the solar array, this is just curiosity on my part and if there was a simple meter (or something) that would be great but as I said I didn't think its possible.  I know there are ways of measuring the current if you disconnect the panels from the system but in reality it's just not that important.

Again thank you for all for the helpful insights.   
Jay

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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 28 Jun 2019 at 7:04am
Morningstar is a good company and makes excellent products. I haven’t heard any reason to think their controller isn’t charging correctly. Your reported issue was the opposite one, it sounded like the low voltage disconnect function was perhaps causing some problems with your loads cutting in and out.

I had the impression you wanted to do an independent confirmation of the charger operation. The way I suggested doing that doesnt rely on and any controller readings. If you’re comfortable then just use it’s internal data, that’s fine. Take a look at the controller output power. If your battery is at a relatively low voltage so the controller is in bulk mode, it’s noon-ish on a clear summer day, and you’re getting about 70-80 percent or more of your solar array power rating to your battery then you can call that good and just focus on troubleshooting what was causing the load cycling issue.
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JR View Drop Down
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Posts: 343 		Direct Link To This Post Posted: 27 Jun 2019 at 7:45pm
Offgrid in your 4:30 post you mention to measure the voltage and current on the solar side of the controller then measure the voltage and current on the battery side of the controller and multiply the voltage and current to convert the readings to wattage on the solar side and then the battery side of the controller.  I get that and then do the math and find out the controller's efficiency and that's understood but obtaining the voltage and current measurement on either side of the charge controller what would be the best way to get that accomplished.  Keeping in mind that I have a computer inter-face with the Morningstar and via that inter-face all that information is available on the readout but it's coming from the charge controller and if that is not working properly would those readings be accurate?

I guess this is just getting a little too far out, so that I can say, just look at all the power the solar array is receiving now and have a warm and fuzzy feeling all over.
Jay

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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 27 Jun 2019 at 3:37pm
To answer your other question about what the charge current is, the way an mppt controller works, it will adjust the voltage the solar array sees so that the array only produces the power that is required by the battery at the particular state of charge, so if it’s in bulk mode it should be maxing out what the solar array can produce but if it’s in absorption mode it will push the array voltage above the max power points so the array produces less power/current to the battery. IOW the controller can’t dump power from the solar array, instead it arranges for less power to be produced when less is needed by the battery.
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 27 Jun 2019 at 3:30pm
The Morningstar controller you have is an mppt controller and you are taking a nominal 24v solar array down to nominal 12v battery charging. The voltage is getting reduced and the current increased by the controller. So, the short circuit current measurement you get if you short out your solar array with no controller will be lower than what you will see when the controller is fully charging the battery.

If you want to assure yourself that your controller is doing its thing you could measure the voltage and current on in solar side of the controller, multiply those to get watts. And do the same on the battery side. If you divide the battery side watts by the solar side watts you should get the controller efficiency, which should be in the 90+percent range. If you do this on a clouldless sunny day with your solar array directly facing the sun and at a low battery State of charge (so the controller is in bulk mode) the watts you get on the solar side should be about 80% or so of the nominal solar array power rating. The 20% or so loss is because the solar modules are running hot, you will only get the nominal rating on a pretty cold day (like around freezing).

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podwerkz View Drop Down
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Posts: 966 		Direct Link To This Post Posted: 27 Jun 2019 at 2:43pm
You could wire a switch to disconnect the controller and short the panels thru an amp-meter when you want to check that...but most of just assume that the panel label will be approximately correct when you have full sun and the panel is not shaded, angled too much off-axis, or too hot.

A panel can actually over-produce if a few specific conditions are present, but usually they under-produce. 

Your controller should show actual amperage coming from the panels, which as you know will vary with loads and battery state of charge.
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JR View Drop Down
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Posts: 343 		Direct Link To This Post Posted: 26 Jun 2019 at 7:49pm
Thanks for the input but I am just a lazy one that just wanted to flick a button and see the amps available but I can get an idea through what voltage the array is putting out.  But thanks for the confirmation.
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Posts: 966 		Direct Link To This Post Posted: 26 Jun 2019 at 3:54pm
Originally posted by JR


Or is there a way to measure the available array amperage? 

 

Yes there is: Disconnect the panels from the controller and, using an amp meter or DMM with a high enough amp setting, and short the panel connectors thru the amp meter.

You can short a 100 watt panel and see about 5-6 amps in full sun. Two panels in parallel will double the amperage. Two panels in series will double the voltage but the amps will remain about the same.

Each solar panel should have an Isc rating, which is, essentially, 'amps, when short circuited'.
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Posts: 2629 		Direct Link To This Post Posted: 26 Jun 2019 at 3:29pm
Originally posted by JR

offgrid I think I know the answer to this question before I ask it but here goes, is there a way to know the available amperage available from the solar array at any given time?  My understanding is that the solar array amperage, that in my case is being measured by a trimetrics battery monitor or by the Prostar charge controller is just the current (amperage) that is being processed (used) not what is available at the time in the array. 

Is my thinking way off?  Or is there a way to measure the available array amperage?
It depends on the controller. Some are more comprehensive than others. We have some from Midnite Solar that give you so many metrics it's a challenge to keep up. The amps (or watts) that most display is what the batteries are absorbing at the moment. If the controller also displays array voltage, you can sort of infer what the panels are providing, but the voltage curves are not normally linear.

The solar array is inherently current-limiting; if you short the leads on a solar panel, it will just happily provide as many amps as it is capable of. If there's not a lot of sun, not too many amps. If the sun is full on, then it will be close to the maximum it can provide.
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