Problems with output amps

[Simonbr]

I have a Midnite classic 150 with 4x 350w panels, two pairs series then paralleled. I can confirm the output is at 20a 77.6v range so I’m pretty sure there isn’t a problem with the connection. My problem is the output to my battery isn’t getting my configure 84a, it’s bouncing all over the place. It does reach 71.5 once in a while but then goes back down. Today the sun is out and there are no clouds at all. Any thoughts on why the output amps are all over the place?

[Vic]

Hi Simonbr,

In full sun at solar noon, with the PVs at right angles to the sun, and no shade, you should expect as much as 1050 Watts from your four PVs.

What is your battery voltage?

If you have a 12 v battery, you could see Classic output currents in the 80 A range, under ideal conditions.

As you know, the Classic defaults to about 84 A Maximum, as a current Limit setting, if there is sufficient input power from PVs.

Vic

[boB]

Thanks Vic.

I am not sure what the battery voltage is either.

Is that 20 amps to the battery and 77 volts input from the PV ?  If so, then we would  need the voltage at the battery to help determine what is going on.

77V and 71V is about right for a "48V nominal"  PV array at times.  Lower PV input voltage if it is hot out.

boB

[Simonbr]

Thanks for the reply. I am on a 12v system. I thought It would handle more then just 1050w and over panelling would help keep it at a more consistent max output amperage for charging. I have a total of 1600w so I am not sure why the amps where jumping all over the place.

[Simonbr]

Thanks Vic.

I am not sure what the battery voltage is either.

Is that 20 amps to the battery and 77 volts input from the PV ?  If so, then we would  need the voltage at the battery to help determine what is going on.

77V and 71V is about right for a "48V nominal"  PV array at times.  Lower PV input voltage if it is hot out.

boB

I’m using 12 volts, the 20 amps is what I measure coming from the pv and the 77 range was the open circuit voltage.

[Vic]

Simon,

PV module watt Vmp and Imp ratings are at Standard Test Conditions (STC).  This is with 1,000 watts of illumination per square meter, and at a solar cell temperature of 25 degrees C (77F).  When in the sun, the IR radiation from the sun (and losses in the cells), raises the cell temperature, this reduces the cell voltage, and, therefore the power that the cells/PV module can produce.  The common derating value is nominally 77% of the STC power rating, at solar noon, with PVs at right angles to the sun, etc.

A certain amount of over-PVing on Classics is fine, within limits.

So, you said that you have 1600 watts of input into the Classic.  Four of the 350 watt PVs, should yield an STC power of 1400 watts, nominal.  So, do you have additional PVs, accounting for that additional 200 watts?

What are the Vmp, and Imp ratings of the 350s? What is the string configuration to the other 200 watts (of assumed PVs), and what are the Vmp and Imp of those/that PV/s?

Thanks for the added info, Vic

[Simonbr]

Thanks for explaining all this info. I only have a total of 4 panels. 2 in series paralleled to the other 2 in series

[Simonbr]

Second image

[Vic]

Hi Simon,

Thanks for the info.

Two strings of two of those 350s should be fine on your Classic, for a 12 V system.

I had guessed that you might have some additional PVs, which might not have been too compatible with the 350s, but this is not the case.

You might want to re-torque all of the cable connections on the PV side of the Classic, and on the battery side of the Classic.  It is common for copper-compression connections to relax, after the initial torquing of these screw type connections.  This can result in poor connections, especially when high currents are flowing in these cables.  You should probably check all battery cable connections, and re-troque, as well.

Good Luck, Vic

Am thinking that there might be a bit of a loose connection somewhere.

[boB]

I'm not sure what the problem is ?

20A at 77V should equate to around  100+ amps at the output to the 12V battery, LESS Classic efficiency, which should still put you up around the maximum output current/power at 12V.

What is your output current to the battery and the battery voltage ?

Or, power ?

Are you seeing current limiting from the Classic ?  You very well may especially on edge of cloud events which can take the irradiance even higher than nameplate rating.

But you will rarely get nameplate rating in normal hot weather. Usually a bit less.  Sometimes 20% less.

boB

[Simonbr]

Ok I think I get it now, so you can safely say that you only get 80% of what your pv can push on a nice day because of the heat, so for my 4x 350 watts panels that would be 20% of 1400w, 1120w. Using the formula a=p/e I can figure out what amperage I have while charging, so the closer I get to my bulk set point the amps will be lower. In my case I have it set at 14.4v so I would see an output of 77.7a once bulk is complete.

I also have the wiz bang shunt and have configure in the hidden menu to only allow 84a to the battery, not in the normal limits option on the classic. I did this because I have a dc fridge and an inverter running and didn’t want more then 84a going into the battery but knew that I might be stealing 10ish amps for the fridge and inverter. Last year this was fine because I only had 2x 6v 420aH batteries that only required 42a max amps. So the MPPT would push out closer to the 52a. This year I doubled the battery bank so I have 4x 6v series/paralleled to double to 12v 840aH. I can assume that my current setup doesn’t reach the top end of my 82a + 10ish amp.

So a couple questions with all this,

1. Does the wiz bang current limiting work the way I think? I don’t have anything connected after the shunt, the fridge and inverter are all connected before.

2. Would adding 2 more 350w panels, one to each series, be worth it? This would give me 2100w (1680w at 20% loss) with an opportunity of 116.6a, if the classic would handle it. Another option is I have an epever 40a MPPT I can use for the other 2 panels, allowing me the full 40a with the full 77.7a from the classic and just allowing the whiz bang to limit the end amps to the battery. This would allow me above the 96a classic threshold when needing the full 84a battery charging + current usage like fridge and inverter demands.

[Vic]

   ...   2. Would adding 2 more 350w panels, one to each series, be worth it? This would give me 2100w (1680w at 20% loss) with an opportunity of 116.6a, if the classic would handle it. Another option is I have an epever 40a MPPT I can use for the other 2 panels, allowing me the full 40a with the full 77.7a from the classic and just allowing the whiz bang to limit the end amps to the battery. This would allow me above the 96a classic threshold when needing the full 84a battery charging + current usage like fridge and inverter demands.

Little time right now,  but, you do NOT want to go to strings of three PVs, especially on a 12V system.
Strings of three of the 350W PVs, will raise the string Voc, into a rough territory,  and even the operating string Vmp will add extra heating on any MPPT Charge Controller (CC), especially on a 12 V system.  The greater the voltage difference between the battery voltage, and the string voltage, the less efficient is the CC,  resulting in more heat, and some other details,  like current and voltage Jitter, etc.

The operating Voc will vary, depending on cold WX temperatures for your location  ...

More later, others will fill in, more detail.   Good questions, though,   Vic

[boB]

Not sure what you mean about the fridge and other things being wired on the WB Jr. ?

One side of the WB Jr. should ONLY be connected to the battery negative terminal.  Nothing else.  Then on the other end of the WB Jr, all of the other negatives are connected.

The Classic will not put out more than 90 some amps before it self limits and can limit to a lower value if it gets too hot.

Also, at the end of Bulk charging, the Classic's output current and power will go DOWN because the batteries do not accept  more current when the Classic is keeping the voltage regulated at the Absorb voltage.

And the other things that Vic said.   Thank you Vic !

boB

[Simonbr]

Sorry i might of not explained it well. I am trying to push 84a to the batteries, I know the classic 150 can only do 96a max. I configured the Wizbang to limit the end amps to 84, so if my fridge and inverter are not running (they are connected on the opposite side of the shunt going to the battery) it will limit to 84a. If the fridge and inverter are running, they will get as much current the CC has up to 96a of course.

i do know the current goes down for the absorption stage, i as just using setpoint for my reference in the math.

Would it be a better idea to do one of the following;

1. Add 2 more serried panels paralleled the the other 2 series, bringing up my current to 30a and keeping the Voc 77v?
2. Adding the new 2 350w panels on the Epever 40a MPPT and connecting the negative before the Whizbang shunt (to have the shunt keep limiting the battery charge current)

[Simonbr]

   ...   2. Would adding 2 more 350w panels, one to each series, be worth it? This would give me 2100w (1680w at 20% loss) with an opportunity of 116.6a, if the classic would handle it. Another option is I have an epever 40a MPPT I can use for the other 2 panels, allowing me the full 40a with the full 77.7a from the classic and just allowing the whiz bang to limit the end amps to the battery. This would allow me above the 96a classic threshold when needing the full 84a battery charging + current usage like fridge and inverter demands.

Little time right now,  but, you do NOT want to go to strings of three PVs, especially on a 12V system.
Strings of three of the 350W PVs, will raise the string Voc, into a rough territory,  and even the operating string Vmp will add extra heating on any MPPT Charge Controller (CC), especially on a 12 V system.  The greater the voltage difference between the battery voltage, and the string voltage, the less efficient is the CC,  resulting in more heat, and some other details,  like current and voltage Jitter, etc.

The operating Voc will vary, depending on cold WX temperatures for your location  ...

More later, others will fill in, more detail.   Good questions, though,   Vic

Would it be a better idea to add the extra 2 panels as another paralleled series to my existing 2 strings? This would bring up my current to 30A, im not sure what the maximum the Midnite can handle.  Another option is add the other 2 on my space 40a CC. What do you think?