Classic 150 Calibrating Battery & PV Voltage

[gkerlin]

Theres a section in the manual about doing this.

I'm confused why this would be necessary for starters.   Especially the PV voltage.

I have 1120w of panels wired to come down to the controller at about 35.4 vmp  Comes down in two strings 15.7 imp each.   (4 #10 conductors) and the positive leads combined after the disconnect circuit breakers.   I have both negative leads combined at the PV neg input of the controller.  Voltage drop on the PV leads is about 1% at imp.

I have #2 Welding wire making a 15' run to the batteries so I do have a slight voltage drop there - higher as the current increases.   Is it suggested that I take a reading at the Batteries 15' away, then a reading at the Battery connections on the Classic and make an adjustment to the classic?   Reading the manual literally it says to take the reading at the terminals on the classic.

Since there is no remote battery voltage sense wire I thought this might be the purpose.

If if is - when to take the readings??   At the normal current flow value that is generally expected?  (i.e. I wouldn't want to do it at max power)

[Resthome]

Theres a section in the manual about doing this.

I'm confused why this would be necessary for starters.   Especially the PV voltage.



I have #2 Welding wire making a 15' run to the batteries so I do have a slight voltage drop there - higher as the current increases.   Is it suggested that I take a reading at the Batteries 15' away, then a reading at the Battery connections on the Classic and make an adjustment to the classic?   Reading the manual literally it says to take the reading at the terminals on the classic.

Since there is no remote battery voltage sense wire I thought this might be the purpose.

If if is - when to take the readings??   At the normal current flow value that is generally expected?  (i.e. I wouldn't want to do it at max power)

Assuming you have the MNGP with the LCD display. If you have a Classic Lite forget this. You want to measure the voltages at the Classic terminals and adjusts the TWEAKS settings so that the voltage displayed on the MNGP readout agree with the Voltmeter readings. You need to use an accurate voltmeter for these adjustments such as a Fluke voltmeter. The readings should be taken while the Classic is Resting or the Mode is OFF.

[zoneblue]

> I used #2 welding cable from controller to the batteries. This was a trade off. I normally like to keep voltage drops below 1.5% but because of the larger size of this array, it would require just too large a wire. At full output my loss will be about 2.75%

The 2% rule doesnt apply there. You want to get the voltage drop under 0.1V to keep setpoint accuracy.
Eg here: 1 foot 4awg, 70A= Voltage drop: 0.035V, Voltage drop percentage: 0.13%

>Reading the manual literally it says to take the reading at the terminals on the classic.

Yeah, this isnt to compensate for cable drop. (varys with current obviously). Try to use big enough wire to get rid of the drop. Generally we all put the CC right at the disconnect, hence voltage drop is not an issue.