Can Classic 250 CC benefit me over FM60?

n1st
n1st Solar Expert Posts: 77 ✭✭✭✭
in Solar Beginners Corner #1
If my calculations are correct, I can use (limited by 10g wire run in place):

With FM80:
2 strings of 2 175w panels. Each string is 350, 5amps. The panel voc is 44.4 + winter temp correction, minus line loss, etc adds up to 110v. 3 panels would be 165v and too much.

With Classic 250:
2 strings of 5 175w panels. 5 panels add up to 267v. Each string is 875, 5amps. This is over 250, but there is the additional +48 (battery size) buffer of HyperVoc, and Vmpp is 35.8 so normal voltage will be around 220v.

The Classic config should provide me somewhere around 1750 watts / 220v / 8a into the the CC.

So my question is, with my 220ah battery bank, is there anything limiting the apparent benefits of the Classic in terms of battery charging, using loads while charging, etc.?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Can Classic 250 CC benefit me over FM60?

    It is my understanding that the Classic's HyperVoc function does not affect the operational parameters of the unit; it's only there to protect the controller in case of cold temps. In other words the Classic 250's Voc limit is still 250 Volts. More than that and it will shut down.

    So to work this one out we'll need to know the length of that 10 AWG wire run and the full specs on the panels. Just as a rough example, 100' of 10 AWG under 15 Amp load (three strings in parallel @ 5 Amps each) will suffer less than 3% Voltage drop. So you may be able to run three strings of three each: 9 panels total for 1575 Watts, which should be enough for your 220 Amp hours of battery. That would mean you could run the Classic 200.

    But the length of that wire run is critical.
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  • n1st
    n1st Solar Expert Posts: 77 ✭✭✭✭
    #3
    Re: Can Classic 250 CC benefit me over FM60?

    The round trip from solar panels to circuit panel is ~350'. I live in CT, so -10F is possible. Thanks.
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  • n1st
    n1st Solar Expert Posts: 77 ✭✭✭✭
    #4
    Re: Can Classic 250 CC benefit me over FM60?

    Please also comment on this alternative configuration...

    I have 2 systems, grid (SMA) and back up (FX Outback). The two systems are separate aside from an AC feed (and ground) from grid to the backup system so if grid fails, fridge (plugged into a backup circuit) continues to be powered. Even separate electric outlets.

    If the grid was down for a period of time, I'd have to do some manual rewiring of the panels so to feed a subset of them to the backup system per msg #1.

    I'm thinking it may be less $$ and manual work in the case of a multi-day grid outage, to route the output of the grid inverter to AC couple it to the backup inverter (FX). This would allow me to avoid buying any CC and make use of the full set of panels I have.

    To AC couple it, my understanding is that I simply disconnect the grid inverter AC connection from the main panel and route this line, to the AC output of the FX (and keep existing connections on the AC out of the FX). This would result in:

    Day time: panels feed grid inverter, grid inverter feeds AC to backup circuits and the inverter's charge circuits so batteries are charged if necessary.

    Night time: FX sees no AC on it's output or input, so draws from batteries and feeds backup AC circuits (also still supplies AC to grid inverter, but I think it will shut down because of no DC input.).

    Extended no sun: manually disconnect grid inverter from FX's AC out, and connect gen to FX's AC in.

    Is my understanding correct?
    Is there additional hardware I'd need, i.e. AC circuit breaker between grid inverter and FX's AC out?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Can Classic 250 CC benefit me over FM60?

    Let's answer the second question first: no.

    Lots of people try to back-feed off-grid inverters from grid-tie systems. They have varying degrees of success, but always the same headache level: major. The basic problem is that the GT system needs someplace to send all of its power to, and the OG system does not necessarily have the capacity to absorb that even with loads running and charging the battery. BTW, you have to feed the GT to the AC OUT, not the AC IN: without the AC signal from the OG inverter the GT inverter thinks the grid is down and won't generate anything.

    But you would have an even bigger problem: The Outback FX is a 120 VAC inverter. The SMA almost certainly puts out 240 VAC. This goes beyond major headache level.

    To answer the first question, the nine panel configuration I outlined would work with the Classic 200, but the wire run @ 175 feet one way means you'd need 8 AWG or better to keep the Voltage drop "reasonable" (under 3%).
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Can Classic 250 CC benefit me over FM60?

    There is also the $2,000 solution: the Xantrex XW MPPT-80 600. Designed to take very high Voltage arrays (up to 600 Volts) such as you might find with a standard GT inverter and charge typical OG battery banks like 48 VDC.
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  • n1st
    n1st Solar Expert Posts: 77 ✭✭✭✭
    #7
    Re: Can Classic 250 CC benefit me over FM60?

    Sounded too easy and good to be true. True it is 240v. I was thinking of just connecting 1 leg, but as you say, it may not be happy if it has no where to dump all the power it inverts.

    XW-MPPT 80-600 tip - excellent. Thank you!
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