Sizing advice, 100/20 or 100/30?

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shawn-wright asked Aug 28, '20

Sizing advice, 100/20 or 100/30?

I have two 170W panels in parallel, with Voc=22.5 and Isc=9.4, which I believe will work with the 100/20 in my 12V system, but I am concerned with the rating of 20A charge current (and 290W power in 12V mode). Assuming a charge voltage range of 13.8-14.6 for FLA batteries, this means the maximum output will be a bit less than the panel output of 340W. I am upgrading to MPPT from an older PWM unit mainly to get more efficiency on cloudy days, so the maximum power loss of 50W on sunny days probably doesn't matter that much. But is this a greater chance of problems with running the controller at maximum charge output? My current controller will indicate >18A current (panel current I assume) in full summer sun when batteries are less than full. My battery bank is two pairs of 6V 110Ah FLA "GC2" type.

This is on a boat, and I don't have space for additional panels, so upgrading is not a concern. If I go with a larger boat and solar system, I would probably get a second controller for redundancy, so I'm thinking that getting a 100/20 now, then adding a second one makes more sense than a 100/30 now. Also, I don't need the output connectors on the 100/20.

Thanks

MPPT Controllers

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wkirby answered · Aug 28, 2020 at 04:44 PM

The 100/20 will be fine. It will limit it's self to 20A and just keep going. I ran a 150/35 with quite a bit more PV than it could handle which meant that it ran at full blast for hours either side of mid day. I did not encounter any problems and it's got 3MWh through it.
Your PV array power is not that much over the capability of the charger as your figures show so you'll only really see full power in peak sunshine on a cool day.

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shawn-wright commented · Aug 29, 2020 at 04:27 PM

Thanks, I think I will go this route then. Another option suggested by the dealer is two 75/15 units, one per panel, which are the same price as one 100/30. But I don't feel like adding additional wiring to separate the panels, so the 100/20 should do fine.

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Modifications Space

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Answer 1 · 2020-09-01T01:10:53Z

shawn-wright answered · Sep 01, 2020 at 01:10 AM

Picked up my 100/20 today, and installed it to replace the cheap PWM unit I had. I was disappointed to find that the wire terminals are quite small, and not as deep as the old unit I took out. It took several attempts to get a solid connection with the 10ga wire that would remain secure with a "tug" test. I can try tinning the wire, or use ferrules, but this wasn't necessary with the old unit. A bit surprised given the old unit was $30 vs the Victron at $235.

On the positive side, I am pleased with the bluetooth interface so far, which allowed me to re-locate the unit to a more discrete location, where I can quickly check the LEDs for status, or monitor with the app when needed.

I'm a bit puzzled that there isn't a preset for FLA batteries, only Gel, but I will post a separate question on this.

Thanks

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Matthias Lange - DE ♦ commented · Sep 01, 2020 at 05:25 AM

Victron can't create a preset for every battery type. Look into the datasheet of your battery and create your own preset.

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Answer 2 · 2020-09-02T17:49:07Z

russ-tanner answered · Sep 02, 2020 at 05:49 PM

You may consider running those panels in series. This will double the volts to 45 volts, the amps stays the same as one panel. The 100/20 converts those extra volts to amps very efficiently and you are well within volt/amp constraints.

I have two Renogy 100 watt mono's in parallel on top of our Rv. My first controller was a Renogy Adventurer Li 30A PWM. It wouldn't really start charging until 9 am or so. (Alaska, the sun is lower on the horizon) And with clouds, it wasn't keeping up.

I replaced the controller with a 75/15 and ran the panels in series. Voc is 21.6 v x 2 = 43.2 v. On a cloudy day, upon the "crack of dawn" the 75/15 would turn on. I was impressed.

PV voltage must be +5 volts over Bat V to turn on. While in bright sunlight, I doubt you could tell the difference between the two, but on cloudy shady days the mppt really shines. By running in series my PV is much higher earlier in the day.

As for the wire, try tinning the ends.

Strip off a good inch by using a sharp utility knife, make a cut all around. While pulling off the insulator, twist slowly, so when you pop off the rubber, it's already twisted tight. Try not to touch the copper. It wouldn't hurt to wash your hands.

Using a mini torch get it hot and touch a bit of electrical solder. Easy on that, not too much or you will have a fat end. Trim the excess off with a good set of snippers.

Now you'll have a nice tight end. If it's a little out of round, the solder is malleable and you can round it with some pliers.

When tightening the lugs, "worm" the lugs in. Tighten snug (NOT too TIGHT!!!), loosen, tighten, back and forth several times until it bottoms out.

You will have a superior connection.

Practice on a scrap piece.

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