Design help

Discussion about the MX60 Charge Controller

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solarchick
Forum Junior Member
Posts: 4
Joined: Thu Sep 05, 2019 9:31 am
My RE system: FX3624
8 Trojan L-16s
MX60
Bergey XL-1

Design help

Post by solarchick »

I hate this question, just so ya know, but want input before I yell. I designed a system for an off grid newby last year and rather than use my design they independently ordered components, made mistakes, and now want me to finish their system using what they already have. What they have is...

VFXR3524 (good!)
FX80 (sure!)
2 kilovolt lifepo batts (nothing wrong there)
3-420w modules (48.88voc, 40vmp) (um..)
300' to the only available field.

Options I can see include
-1 more module for 2 strings of 2 which is not enough input for them really
-3 more smaller modules and replace all of the quick connects to make 3 strings of unmatched modules but decent enough voltage
-2 more same size modules for 2 decent strings and one undersized string ( I think option one is better than this)

It'll be stupid expensive to try to use single module strings without losing everything in voltage, I'm trying to give them the best solution given their poor choices to begin with while being sure to NOT spend their money making more poor choices. My inclination is to tell them to buy 6 new modules so I can size strings well, but to do that I'll likely have to offer to buy their current panels and I don't want to.
thanks for input
raysun
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My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Design help

Post by raysun »

There's nothing wrong with 2 PV panels in series here. Its more than enough to drive the charge controller and charge the battery to 60V if specs call for it.

Another panel would clearly need needed to make a 2X2 array.

That being said, a 4 panel array is unlikely to be enough to charge the battery and service loads, power-wise. They would be much better served with a 4X2 array @ 3360W.

I'd stay away from purposely mismatched arrays, too many resultant compromises. If there's a bunch of odd panels laying around and the owner insists on using them, thats one thing. But to specify it from new parts - thats just bad design.
fcwlp
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Posts: 791
Joined: Wed Jan 22, 2020 9:40 am
My RE system: GS8048A, FM80 w/3,600W PV Fixed, FM80 w/2,700W on Zomeworks tracker, Mate3, 24 Trojan 2V L16 1100AH @ C20, Grid-Tied with Kohler 14RESA LPG Generator and MEP-803 Diesel if needed.

I install and maintain grid-tied and off-grid systems in my area and consult on solar system design/operation.
Location: 80 miles NE of Phoenix at 5500'

Re: Design help

Post by fcwlp »

raysun wrote: Sun Apr 18, 2021 1:06 pm Its more than enough to drive the charge controller and charge the battery to 60V if specs call for it.
@raysun, unfortunately it is a 24V inverter.
solarchick wrote: Sun Apr 18, 2021 12:31 pm I hate this question, just so ya know, but want input before I yell.
My proposal to them would be, give me your FM80 (time to upgrade your MX60) and buy a FM100 and two more 420W panels. This will give a nominal 2,100 watts. Wire the five in series, which will minimize the voltage drop over 300' wire run. At six panels in series the FM100 Voc limit will likely be exceeded on cold days.

Second option, after getting their FM80, would be to buy five more 420W panels and wire them in two strings of four panels.

My guess is they also undersized the wire running to the panels. For Option 1 with ~10A of current, to keep V drop below 3% requires 8 AWG wire. For Option 2 with ~20A of current will require 6 AWG.
raysun
Forum Emperor
Posts: 4578
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A, (2) FM80, MATE3s, FlexNetDC
SimpliPhi 48-3.8 (6 @ 48v)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Design help

Post by raysun »

Oops! I misread the inverter model. It does limit the amount of array power by half.
solarchick
Forum Junior Member
Posts: 4
Joined: Thu Sep 05, 2019 9:31 am
My RE system: FX3624
8 Trojan L-16s
MX60
Bergey XL-1

Re: Design help

Post by solarchick »

Hey both of ya, thanks for input!

I hadn't even thought about upgrading my 60 to their 80; I like the way you think!!

The only fortunate thing is that they rigged up the modules haphazardly in a temp fashion, so this upgrade will place the panels on real racking, run the final homerun DC line with a combiner, and if they go for the FM100 they'll be able to add mods later as well. Brilliant. I was looking at having to tell them they'd need a minimum of #2cu or 2/0aluminum which was just hurting my soul.

Considering all the mods I have sitting around my place, upgrading myself to an 80 will be, like, a new life!!

best
fcwlp
Forum Czar
Posts: 791
Joined: Wed Jan 22, 2020 9:40 am
My RE system: GS8048A, FM80 w/3,600W PV Fixed, FM80 w/2,700W on Zomeworks tracker, Mate3, 24 Trojan 2V L16 1100AH @ C20, Grid-Tied with Kohler 14RESA LPG Generator and MEP-803 Diesel if needed.

I install and maintain grid-tied and off-grid systems in my area and consult on solar system design/operation.
Location: 80 miles NE of Phoenix at 5500'

Re: Design help

Post by fcwlp »

Southwire has some good phone apps for sizing wire, conduit fill, etc.
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