If I go over XW60 150v specs...

machineman

Currently I have 4 panels of evergreen ES-A-205w 12v(820watts) going 80ft (8ga cable) to my Xantrex XW60 150volt mppt charge controller. I calculated % voltage drop. I want to add 2 more panels making all 6 in series through my 80ft 8 gauge cable. Using the Xantrex sizing tables if I run 6 panels in series I will be hitting the max voltage (150v) when temps get <20degF. I don't want to upgrade the 80ft 8ga run to handle the amps if run in parallel. My winter temps will probbaly only get <20degF a few times a year. So what happens when the volts exceed charge controller max 150v for that few days a year? Damage or just loss? Seems like I can do this since I wont be hitting the mppt input 150v max 99% of the year.

Sizing table
http://www.se-renbu.com/support/xwsizing/Default_SE.aspx

solarix

Re: If I go over XW60 150v specs...

Yep, the 150v ceiling. Don't flirt with blowing up your CC. Haven't seen any tolerance on this spec, but all the CC makers seem pretty firm on it. My advice is to do strings of just 3. Its only 2 strings in parallel for your situation so you don't need a combiner and your 8ga wire should handle the 12 amps or so both strings will generate. Plus, the CC will be more efficient running at lower voltages. Haven't seen any efficiency curves on the XW60, but the lower the ratio of in / out - the more efficient they run.

machineman

Re: If I go over XW60 150v specs...

If I do 2 strings of 3 it will be ~24amps (54Vmax) which has to much Voltage drop on 80ft of 8ga.

Cariboocoot

Re: If I go over XW60 150v specs...

Do not exceed 150 Volts on input. The controller will shut down and may not restart due to the "fault" condition (has to be reset). So an unattended system will just turn off. Do it too often and it won't turn back on again. I'm not sure of the tolerance of the Xantrax unit, but it would be risking death with an OB.

Voc (what matters for this issue; not Vmp) on the Evergreen 205 is 22.7 Volts. Six would get you 136.2, or 126 under typical temp conditions (25C). But as you know cold causes super-conducting and increases the output Voltage. This could be 20%-30%. Worst case: 29.5 Volts per panel.

I don't think you could go over 5 in series on that controller. And at 24 Amps (two strings in parallel) you're at the current limit for 8 AWG - although the low temps would help there (when they're low).

dsp3930

Re: If I go over XW60 150v specs...

The XW SCC works best at < 120 Vdc.
At 120 - 140 Vdc it reduces output to prevent voltage spikes.
It may shut down as low as 140 Vdc.
(All per the manual)

You can buy an "Apollo Low Voltage Low Temperature Bypass".
It is supposed to be able to drop one panel out of a string at low temperatures.


David

mike95490

Re: If I go over XW60 150v specs...

I believe the overvoltage danger is at dawn, as the panels are icy cold, and "wake up" but have so little power, the charge controller can't function yet, and that's the high voltage that cooks them, whn running, I think the panels heat up, and the voltage drops.
I don't know if a 100W 140V zener diode could solve the problem.

machineman

Re: If I go over XW60 150v specs...

OK, so my first question has been answered.. Don't go near or over the CC 150V limit. If I consider the panels thermal Voc coeff and the record lowest temperature, I calculate no issue running 5 panels in seires becuase the max will be <130V.

Solutions to run 6 panels:
1. That "Apollo Low Voltage Low Temperature Bypass" looks like a really neat solution to run an additional panel in series but the max current is 8amps and my panels Isc is 11.93A. So unless there's a higher current model, this won't work.

2. I haven't found a reliable voltage drop calculator but if I stay with 80ft of 8-2ga Array to CC, and parallel 2 strings of 3 panels, that doubles my current to 24A and lowers my Voc voltage (on a hot day) to <70V. That puts me close to 5% voltage drop which isn't acceptable either. If I upgrade to a 80ft length of 6-2 ga wire the drop will be right around 3%.

The best solution would be to run 2 strings of 5 panels (10 total) which would boost my voltage up enough to keep the drop % while keeping the 8ga cable. However I can't afford 6 more panels.

niel

Re: If I go over XW60 150v specs...

machineman,
have you seen the voltage drop calculator in the facts and info area? see my signature for a copy and paste link.

dsp3930

Re: If I go over XW60 150v specs...

The best solutuon is just to buy larger wire.
You can buy five hundred foot spools of 6awg for less than two bills.

David