Inverter/controller Voltage discrepancies

Murphyslaww

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Dec 27, 2021
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Howdy,

I have an off-grid shed/studio system with 4x300 watt panels wired to a combiner box to an epever Tracer8420AN, and two powerqueen 200ah LIFEP04 12v batteries wired in parallel. The Voltage showing on the controller and that on the Inverter (RoarBatt 2000w) differ by about .5 to .7 volts at any given time for battery reading. I think this is affecting settings on the Epever for float settings, and I'm thinking that the Epever is not fully charging the batteries. When the Inverter is reading 13.0, the Epever is reading around 13.5 to 13.6.

If I disconnect the PV and Epever from the battery, it matches what the Inverter is reading. This leads me to believe I have the settings for float and boost charge too low on the Epever, and 13.6 set on the Epever may only be charging the batteries to 13.0. I've been moving those settings up, cautiously, as the array may only be charging to maybe 30-40% of capacity, and that bears out when the Mini-split attached to it runs down the battery in an hour or two when it seems like, mathematically, it should run all day with fully charged 13.5v batteries at 5000kw capacity and the PV putting out at least 400watts, and the Mini-split only using around 600-700 watts.

Any other places to look?
 

Ellcon123

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Every cable and connection will have a voltage drop due to resistance. The higher the charge or discharge current then the higher the voltage drop. SCC will have a voltage, battery will be lower, and inverter will be lower again. You need to tailor your settings to suit.
 

Murphyslaww

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I'm generally charging at around 40A. I've googled all the settings, and think I may have something that is working at the moment. I turned everything off other than the inverter, which showed about 20watts on the LCD. It charged up to about 13.89V, on the controller, where I had the Float voltage set to, which shows to be 13.5V on the inverter, which is what PowerQueen docs say should be 100% charge, and we've been getting about 500-600 watts today, out of the 1200 watts of panels. They are mounted two to each side on an angled shed roof. I guess I had thought we'd get more than that out of 1200 watts of panels in semi-direct sunlight.

I have this coming today, to hopefully tell me more about what is going/coming out of the Batteries.



IMG_4050 (2).JPG

I generally only see about 27-30V coming from the panels in the controller coming from the combiner box. Does that sound right for Southeast Texas? When I originally tested the used panels, they all showed 42-44V, by themselves, and are rated at, I think 45-46V.
 
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Ellcon123

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If that is the voltage into the SCC then it is low. Even in poor sunlight there should be nominal 40V onto the SCC.
 

Murphyslaww

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If that is the voltage into the SCC then it is low. Even in poor sunlight there should be nominal 40V onto the SCC.
Yeah, I pulled one of the panels out of the combiner box, and it was at 39v, so it appears that something is not right with the combiner box. In the morning, it seems to get up as high as 34v, at start, and then goes down as the watts produced go up. That seems counter-intuitive. Thinking I am going to take the combiner box out of the picture and see what changes. I'm now leaning towards operator error, as the box is in fairly direct sunlight, and performance may be going down as the temps go up ?
 

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12VoltInstalls

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seems to get up as high as 34v, at start, and then goes down as the watts produced go up. That seems counter-intuitive.
While that seems weird on one hand, on the other hand the load is sucking up the voltage. Watts is the product of volts times amps; if watts are going up so are amps.

I’m not sure you’re looking at related ‘screens’ for PV. You may be looking at PV volts and charging watts instead of PV volts and PV watts?

I look at the other the readouts occasionally but really all I care about is battery volts and amps to the battery bank, only looking at PV watts from curiosity during cloudy or partial sun/high clouds aka hazy conditions.
 

12VoltInstalls

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Oh- if you shut off inverter and DC loads with full batteries, the SCC readout should be just a titch above battery voltage measured with a vom at the batteries. They may never agree due to cabling/resistance in the circuit. I don’t worry about it: once you have it running healthy I just monitor for variance from the norm; as long as they stay no-load consistently “different” voltages by 0.1V or whatever is normal I don’t get concerned about it.
 

Murphyslaww

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Bu then there is this: The Controller is seeing 500-600 watts from the panels, but it appears the meter things there is 800 to 1000 watts going into the batteries. I'm guessing there is some kind of calibration I need to do with the meter, as there is no way this thing is at 174 Ah at only 11.94 V. I'm really trying to troubleshoot whether or not I'm actually getting 400Ah out of these powerqueen batteries, because it appears that I am not.

IMG_6588.JPG
 

pollenface

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I have 1200 watts of panels in near full sunlight, only producing 500-600 watts though, that seems a bit low.

What is the size of your panels?

Sometimes panels are marketed as being of a higher output than they are capable of producing in real world conditions. I recommend you work on a 200w/m2 rule of thumb.

In doing this I've realised that my cheap ebay sought 250w panels are only about 150w which is why I never get more than 432w out of three of them :)
 

Ellcon123

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Yes, bought a handful of 18V panels on ebay and lucky to get 2/3 of rated power. Now have 2nd hand 200W panels from an actual house system and they give rated power at the right angles. You really need a clamp DC meter so you can check all components. Don't trust readings until you've checked them.
 

Murphyslaww

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Not denying any of the aforementioned, These are used, 300 watt commercial PhonoSolar, from a school district install that had to replace their roof, and took all of them off. They are at a pretty shallow angle. They produce 42-44v when not attached to the system. If I'm understanding right, it seems that the controller is probably cutting off 33% of the total charge, because it's an 80amp controller, and could be producing 120amps.

I'm going to get a 3000 watt, 24v inverter and series the 200Ah batteries(12v in parallel now) so that the max amps are down to 63A, which should get all the production then ? Hopefully, the 3000 watt will have enough headroom to keep the fan off most of the time. I'm assuming that going up to 24v might lower overall temps on the equipment as well ? The 12v, 2000w inverter runs up to around 1000watts with the mini-split running, mid-day, so it's over it's 40% setting for the fan to come on. It's an Art studio, so I'd like it to be peaceful and without noise as much as possible for the S/O to work.

Until then, I have a RF controller, that is turning the Mini-split on at the right time, and off at the right time, so that the batteries are fully charged by the time the sun goes down. It's insulated enough that it holds the temp at under 80 inside from 7pm with the AC not running. That RF controller is really nice, and cheap. It shows the temp throughout the day inside the shed, and told me when I should turn it on, and off. Then you set a routine to shut off or turn on at a certain time(or a certain Temp)

Slowly, but surely, figuring this all out. Learning here in the U.S. so that I know what to do when we move to Panama, entirely off-grid in future years. Our house has a new, enphase, grid tie system. I think 5.4 kw.



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