solar system catastrophe and rebuild

[Mike90250]

i suspect your charge controller is not a true MPPT controller. You typed MPP, which is close enough for a sales scam/pitch, but it won't downconvert your 41V to 30V for charging. Measure your Amps in from the solar, vs the Amps out from the controller to the batteries, (without any loads on)

> 6 flex panels, 160w each, 22.8 voc, 8.6 amps per panel.
> Wired 3 groups of 2 in series parallel for a desired total of 41v and ~25amps.

4 panels wires 2S2P would produce a mess. 22.8Voc is not a usable power measurement, We need the Vmp voltage, which I will guess is about 18V
160W @ 8.6A = 18.6Vmp
With panels , voltage is easily achieved, and as sun gets stronger, the amps increase. in real life, you can expect to harvest only about 80% of the panel nameplate rating.
160 x 4 = 640w / 80% = 512watts @ 37.2V = 14 amps. A true MPPT controller will increase those amps a bit, as it matches the charging voltage of the batteries around 30V

[Jayson]

Thanks for all of this input Bala and Mike.

I will test individual panels for short circuit current today. I need a little more instruction on this. Initially I tested each panel in moderate sun, and I was achieving the ~80% output getting 21v and 5.6 amps (around 120w). I will post panel specs shortly <vmp, voc, imp and so on).

As far as the controller, let's get those details clear. Yes, this is a true mppt charging system. MPP Solar is the brand.

[Jayson]

Specifications:
Main Color:black
Item Size: 118/54/0.2cm
Package Size:120/59/3cm
Maximum Power: 160W
Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 18.6V
Open-Circuit Voltage (Voc): 22.8V
Optimum Operating Current (Imp): 8.6A
Short-Circuit Current (Isc): 9.47A

[Jayson]

You guys are helping already! Got a nice hazy sun and getting the best numbers so far, although still not ideal. Maybe a panel or 2 was damaged in the accident....

Currently showing 150w pv input, with 33v, 5a. I suspect this is the mppt converting some of the voltage to higher amps.

Mike, would there be a better way to wire the array e.g. one group in parallel or ?

I think if I could get the expected 500w, it would supply my loads and keep me charged up.

Bala, unfortunately the clamp meter I bought was ac only. Luckily I do enough residential ac so it's not a complete loss...but yes I need a DC version. Recommendation?

[Mike90250]

You are at an awkward voltage with only 2 panels in series. That is barely enough voltage to activate a MPPT controller. But if the controller is actually working properly (which you cannot tell without a DC amp meter) it's as good as you can expect

[Jayson]

Thanks Mike for trying to help. I'm a bit confused about this being an awkward voltage, as I thought my initial (6 panels, 3 groups of 2 in series) was ideal. The voltage has not changed since losing 2 panels from the array (41v) Here is exactly what I have now:

2 groups of 2 panels wired in series, connected together in parallel. The array produces 41 volts with varying amperage. I was expecting ~ 12 amps at peak performance.

The controller shows 30 to 41 volts with varying amperage.

Best so far is 168w at 32v , ~6 amps.

Also, I do have the hall effect sensor which measures DC up to 100 amps. I can relocate this to any part of the circuit I need a reading, just a pain with the closed loop sensor. It is working properly currently connected to the incoming pv +.

[Mike90250]

(Vmp): 18.6V = nearly ideal voltage for a PWM controller to charge a 12v battery

with a 24v battery, 37.2v is only slightly higher than the charging voltage (31V, only 6 volts to play with) When the battery is low, at 25V, then there is more spread for the MPPT function to work, but it relies on the difference from the solar PV voltage from the current battery voltage, and so it converts some of the extra volts, to amps. As that difference lessens, there is less "overhead" for the MPPT to function, and it eventually reverts to PWM charging. If it's a warm day, the panel voltage decreases from heat, so there is even less advantage to MPPT.

[Jayson]

That helps so much and kind of what I figured was going on, but my knowledge of how the mppt algorithm works is very novice. Also other factors as you mentioned (heat, battery level, loads) can muddle my interpretation of the readings and what the system is doing. This is compounded by the different stages of auto charging modes...

I do get a steady 41 volts from the array into the controller so maybe a good 10v of play.

My float voltage is set at 27.1. I'm at 27.0 now and it seems to decrease charging effort as I near the float setting.

So what I'm wondering now as I prepare for individual panel testing is about the pv readout on the controller. Will it typically show the actual wattage being produced or some equation of what the mppt is using?
Also if I have the amp meter on the incoming pv +, is this the best location to meter incoming pv amps?

Thanks very much for your time.

[Mike90250]

Never trust the controllers, many items with built in metering, skew the data in their favor. That's why using a clamp on DC amp meter is so important

[Bala]

Bala, unfortunately the clamp meter I bought was ac only. Luckily I do enough residential ac so it's not a complete loss...but yes I need a DC version. Recommendation?

AC/DC Clamp meters are now available from most large hardware, auto parts, or electronics shops. Mine is 40A and 400A DC and was about $100Aud 2 years ago.

I would say its A accuracy is + - 1A but it is fine for Stand alone solar and Auto work.

Just make sure it actually has DC A. Looking at ones on Walmart website many dont seem to have DC amps.

[Jayson]

Thanks Bala, trying to hunt one down now. This bayite ampmeter is pretty accurate and easy to use, but it's a closed loop as opposed to a clamp...so disconnecting and all that is a pain but I currently have it hooked up on the pv positive from the array, prior to the breaker and mppt. Is this the best location?

[Bala]

Thanks Bala, trying to hunt one down now. This bayite ampmeter is pretty accurate and easy to use, but it's a closed loop as opposed to a clamp...so disconnecting and all that is a pain but I currently have it hooked up on the pv positive from the array, prior to the breaker and mppt. Is this the best location?

My reasoning for testing individual panels was because you said your system has never really performed well.

Testing for A where you are will tell what A you are getting but I dont think it will help determine why it is low.

It looks like Mike is all over what is likely your problem but by testing panel short circuit current individually and in their configuration you can rule them in or out then move on in fault finding.

My theory of fault finding anything is to start at the start and work through.

If your panels do test good and all your connections are correct and good quality then you are looking at the controller for current delivery and the batteries for accepting that current.

[Jayson]

Pretty full charge today at 27.0. I will test each panel individually tomorrow. Do I just perform the test at best sun or how can I test the short circuit current reliably? Do I need to connect a load or something?

Give thanks for your time!

[Bala]

Pretty full charge today at 27.0. I will test each panel individually tomorrow. Do I just perform the test at best sun or how can I test the short circuit current reliably? Do I need to connect a load or something?

Give thanks for your time!

Short circuit current is as the name suggests. If you are using the multimeter with probes when set on amps + lead from panel to + lead on meter and - to -..

If using a clamp meter just join the panel leads together then measure, you may be able to do this with your bayite?

NOTE: Do not connect or disconnect the leads unless the panel is covered or arcing will occur.

The highest sun/ noon will give you your best reading, if practical you could take readings at 10am and 3pm so you know what to expect from them at that sun angle.

This is form the Battleborn site: Two BB10012 batteries mounted in series to form a nominally 24V system should be charged using a bulk and absorption voltage of 28.8V, and a float voltage of 27.2V

[Jayson]

Excellent. I used the same Battleborn resource to verify settings. 28.8 is my bulk/absorb setting and I went with 27.1 just to be safe as they said anything under 27.2 is good and the "float” mode is kinda arbitrary for lifepo4.

I will cover the panels with a moving blanket, disconnect and test all panels. If I'm getting this, all panels should test the same, not necessarily at the short circuit current.
I will use the multimeter just as I did upon receiving and testing the panels.

What happens if the panels are disconnected "under load" and arcing occurs? Will the panels become damaged or suffer permanently in some way?

Very much appreciate your direct and thorough help. Knowledge breeds confidence