Some things to keep in mind during an upgrade.

[Mattb4]

I just recently added another 2-200w solar panels to my auxiliary 30a MSB SCC. I call it an auxiliary since the main 1200w solar array feeds my 24vDC AIO, but it is maxed out for wattage, so I added an additional SCC to help feed the battery bank. At first it just had 390w worth of panels and things were sized at that setup. However by adding the additional panels I am now slightly beyond the SCC rating for panel wattage (740w ratting) not much of a issue and I assumed it would likely not reach the panels max output at any rate. Over paneled.

I was surprised the first day things were up and running to see instead of the 800w of the 4 panels (2 of which are actually rated 195w) I was pulling 846w in full sun! I had not thought that was possible but I forgot to allow that 30a output at higher battery voltage of 28v + for charging would be higher watts.

Things I did change before hand. The wire from the original 2 panels was 12 awg. I replaced this with 10 awg.

Things I did not change until seeing the results of panel output. I had a 25a breaker between SCC and battery. This I replaced today with a 40a breaker. My wires going from SCC to battery was one pair of 10awg. Charging at the max of 30a is a bit too much and so I added in another pair of 10awg. wires. Although 10awg should be good for 30a I do not like being at max for anything if I can avoid it.

One further thing I did not think of until this morning. Recommended charge rate to the batteries. My 3 -80ah 24vDC batteries have a 20a charge rate (thus 60a). I am now over that with the 2000w combined arrays if they are full out. (2000w/25vDC=80a). It probably won't hurt in the short run especially since there is the load the house has that reduces total charge rate, but I am ordering in another battery to more closely match the PV potential charge ability.

Upgrades to an existing system are not always just an add and go.

 

[chrisski]

One further thing I did not think of until this morning. Recommended charge rate to the batteries. My 3 -80ah 24vDC batteries have a 20a charge rate (thus 60a). I am now over that with the 2000w combined arrays if they are full out

Limiting charge with multiple SCCs is something I dealt with when I had lead batteties. Never had a good way to deal with that.

I had been fully charged early in the day prior to exceeding the limit, but I’d turn a high wattage appliance on in the afternoon, and when I shut it off, max charging would be exceeded since the sun was now high in the sky.

My SCCs can individually limit current, but not a total limit for all three.

I ended up wanting more power and went with lithium.

 

[Mattb4]

I noticed one interesting thing today. I had doubled up the 10awg wire going to the battery from the Makeskyblue SCC. There are two output terminals on the SCC that can handle this. Out of curiosity I did an amp check of the wires just a minute ago. With the SCC reading ~20a charge I expected the two wires to read around 10a each. However one reads 11.5a and the other reads 8.5a.

The wires are fairly close to same length so that should not be causing the amperage difference. However the wires while both 6mm square (10AWG) they are not the same type or manufactor. The old ones are tinned copper fine strand solar wires and the new ones are bare copper Temco brand solar wires. The bare copper wires have the higher amperage. I suppose I should only use identical wire and precise lengths if I needed exactly half and half amperage.