New system install and could use some feedback

[CouleeJas]

I really could use some constructive criticism with my newly installed system. I should have asked these questions before initial set-up I realize, but better late than never I guess. Unfortunately, I am one of those people who suffer from analysis paralysis - so for a lot of projects I need to dive right in and fix it up later - I know that is not ideal, but I have found this is only way I get started sometimes...

48 Volt system. Charge controller is Midnite Solar Kid with battery temp sensor . Inverter is Exeltech XP600. Solar Panels are Solar World SW255 (nameplate Voc 38.7 and 9.05A) - 3 of them in series.


Batteries are 6-year old Interstate DCM0075U (12v 75AH AGM) in 2 strings - so total of 150AH @ 48V. Batteries are from some backup system - before installation their resting voltage was 12.7-12.8, so I think they still have some life in them. I could use some guidance on what absorb and float setting to put into Kid. The spec sheet for the batteries says "Float 13.5-13.8. Cycle 14.4-15.0". Currently I have them set for Absorb 57.6V (120 minutes) and Float 54.0V. I don't believe these batteries should be equalized, so I set that at 57.6V as well.

My loads on this system are minimal - running/charging a couple of laptops, charging phones, charging some cordless tools, running a few fans, and chest freezer to fridge conversion. I am expecting daily loads to run about 600-750 watt-hours - I don't have permanent wiring yet - running off extension cord and plan to hook Kill-a-watt up for a few days to measure total loads.

Wiring is as follows:

• Panels to Kid CC - 50' of 10awg PV wire going through 15A MNEPV Breaker on + wire (breaker in BigBabyBox)
• CC to pos and neg bus bar in Big Baby Box - 10awg wire with positive going through 30A MNEPV Breaker.
• Batteries connected in series with 4AWG wire and each string connected to pos/neg bus bars with 6' of 8awg wire. 30A MRBF fuses between positive string and 8awg wire.
• Inverter connected to pos/neg bus bars with pos wire going through 30A MNEPV breaker - 8 AWG wire for this.

I have attached rudimentary wiring diagram - hopefully it makes sense.

Currently, panels are not grounded - they are on temp mount practically on the ground. Inverter, Kid, and Neg batteries are currently grounded. I have current ground set up with 8 AWG copper to 8' ground rod in moist area right outside shed.

Questions:

• Big Red Flags?
• How are my CC settings so I get max life out of batteries?
• Sizing of panels to batteries to loads balanced?
• Are my wiring sizes correct?

PV Wiring diagram.jpg

[Mike90250]

Are there any numbers/instructions on the batteries for charge voltages for Standby / Cyclic usage ?

Looked it up for you - https://www.sumppumpsdirect.com/manu...M0075_Spec.pdf

I get 14.5 - 14.9V for charging. I'd start with the 14.5 and chart the amps every hour, to see when it drops below 1A You may not have enough solar hours to get full charge in 1 day.

and 6 years on a AGM with a 1 year warranty is good.

[CouleeJas]

Mike - thanks for looking things over. I am attaching spec sheet for these batteries. It looks like it lists Float 13.5-13.8. Cycle 14.4-15.0. Currently I have the Kid set to Absorb 57.6V (120 minutes) and Float 54.0V. Sounds like you think I should raise absorb to 58.0?

So when you say chart the amps, you are saying I should look at charge controller and note for how many hours it is pushing less than 1 amp? How many hours should I be looking for?

I am confused in how to get feedback about whether I am sending enough or too much to my batteries...

Thanks for any guidance

[Mike90250]

> Absorb 57.6V (120 minutes) and Float 54.0V. Sounds like you think I should raise absorb to 58.0

NO I did no say that

AGM batteries can be easily destroyed by overcharge. You have to slowly sneak up on your charging regime so that you are neither under or over charging. You need to track the amps in and out of the battery and/or measure End Amps to tell when the battery is finally full. Solar does not have enough hours in the day, (unless you are very lightly cycling your batteries), to complete a full re-charge cycle. Some folks say, don't bother with daily 100% full, some say as long as you are > 85% full. I don't use AGM , so I'm not the best advisor for them. They have lots of quirks, like going negative resistance at end of life and lighting on fire.

That's why I suggest learning on a set of golf cart batteries, and after things are dialed in, when they die of old age, replace them with something fancy.

https://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

[CouleeJas]

Sorry for mis-interpreting when you said you would start at 14.5v - I thought this would translate to 58v for 48v system.. I am a total beginner. I can see why you advise folks to start with golf cart batteries, but the batteries I have are what I have, so I want to make the best of them.

How do I " track the amps in and out of the battery and/or measure End Amps to tell when the battery is finally full"? What type of equipment do I need or does the Kid do this?

[Mike90250]

> Cycle 14.4-15.0
That difference of 14.4 and your misread it as 14.5, turns into nearly half a volt for a 48V bank. Details matter. A lot

There are several totalizing ampmeters, you need one with a Shunt, that can measure the amps. Bogart, Trimetric & Xantrex LinkPRO can do it.

Midnight Solar makes the WhizBang Jr, which I know works with the Classic charge controllers. I don't know if it works with the Kid

[Tecnodave]

Mike90250,

The WhizbangJr does work with the Kid controller

[neweclipse]

Whizbang Jr., for Midnite gear, does a real good job for both as a battery gauge and controller of end-amps...look no further.