Supplementing my batteries without spoiling my harvest

[Ninety-9 SE-L]

So, quick breakdown. I have a 16' trailer that I use as a mobile workshop. I found that I can fit 6 160W PV panels on top yielding me about 960W.

The 12V panels will be in series pairs for 24V, 3 pairs to produce about 40A total, decided on an EPEVER 4215BN 40A charge controller, didn't oversize since I can't physically fit more panels, anyhow. Power will be going to 2 100Ah batteries in series for 24V. Batteries will output to a 24V/1500W Pure Sine inverter to run a dehumidifier @ ~600W. Hopefully everyone is OK with this math, I could always double my battery bank, later.

I'm hoping that the 600W dehumidifier runs intermittently, but I'm OK if it cuts out a few hours a day. I'm already aware that 960W IN for 6-8 hours isn't going to provide 24hours of 600W OUT, but it will certainly reduce my electricity bill.

I'm looking to purchase a Noco GX2440 40A, 24V battery charger to supplement my harvest and keep my batteries from running too low and cutting out the inverter. Some reviewers have been happy with this unit on their off-grid setup.

My question is: When and how should I have the GX2440 kick in? I would like if it could only kick on within a certain battery voltage range. I don't want to go below cut-out, but I also don't want to go above the point where I spoil my harvest. It would be a shame if the sun comes up, but the batteries are already fully charged from the grid.

I the 4215BN has a DC/load output, which can support a contactor relay. I'm just not sure if it can be programmed to operate within a certain window.

Any advice?

[littleharbor]

Without actual panel specs. I am still thinking that your amperage will be more like 20 something amps @ 24 volts nominal. When series wiring, the voltage adds and current remains so whatever your amperage is, times 3 is what to expect.

[SunEagle]

Without actual panel specs. I am still thinking that your amperage will be more like 20 something amps @ 24 volts nominal. When series wiring, the voltage adds and current remains so whatever your amperage is, times 3 is what to expect.

It is possible that the EPEVER CC is a true MPPT unit that with 6 x160watt panels the OP could generate close to 40amps for a 24V battery system. Which may actually be too much for a 24V 100Ah system.

[Ampster]

............

My question is: When and how should I have the GX2440 kick in? I would like if it could only kick on within a certain battery voltage range.

I used a combination of a programmable timer and a programmable voltage relay on the AC side of a charger to do what you want to accomplish.

[Ninety-9 SE-L]

Thanks. Do you have any recommendations?

I found this one: http://www.intervolt.com/product/voltage-sensing-relays But it seems like it's not easy to find in the US.

[Ampster]

Here is one that is popular among the EV conversion crowd.

https://www.lightobject.com/Electronics/Digital-Panel-Meter/Volt-Meter/Programmable-4-Digit-Red-LED-ACDC-Volt-Meter-with-Dual-Control-Good-for-HHO-System

[Ninety-9 SE-L]

I wrote to intervolt. The one they offer looks great and will do exactly what I want it to do. Unfortunately, there won't be any new production until February, so that's not an option, for now.

Instead, I decided on a transfer switch that will automatically shift the load to grid if the batteries run under a certain setpoint: https://www.amazon.com/gp/product/B07F12RDZ2

[Ninety-9 SE-L]

It is possible that the EPEVER CC is a true MPPT unit that with 6 x160watt panels the OP could generate close to 40amps for a 24V battery system. Which may actually be too much for a 24V 100Ah system.

How can I be sure if 40A is too much charging load?

[SunEagle]

How can I be sure if 40A is too much charging load?

The range of charging amps for most batteries is between 1/12th and 1/8th the Ah rating of your battery system. With a 100Ah battery that calculates out to 8 to 12 amps. 40amps would calculate to a 2.5 charge rate which is way too fast and can burn up your battery.

[Ninety-9 SE-L]

Hmm, these are the batteries I'm using. I see someone is doing 20A. I might have to put a second bank in parallel, I guess. I don't have all my panels up, so I'm good for now, still piecing everything together. This is my main plan:

[Mike90250]

In many cases (but not always) the gradual charging of the batteries from dawn to noon, insures they rarely see too many charging amps, their voltage rises as the solar increases and all pretty much self-regulates. The problem happens on a cloudy/ foggy morning, and the the haze burns off at 11:30AM Boom High amps into the low batteries. If you are able to switch off some of the PV strings in the combiner box, that can help prevent that big surge. All that requires manual baby sitting of the system . High end charge controllers have a max amps limit that can be programmed into the controller, so you can throttle you 80A controller to 32A, and not fry your batteries. My Morningstar and Classic both have that feature.

[Ninety-9 SE-L]

As of right now, I only have 4 of the 6 panels purchased and installed. I just hooked up the PVs to the combiner box (Damn MC4 cables SUCK to crimp), so the charging side is complete.

Today is the first day I will charge my batteries, I don't expect I'm going to pull very many amps, the trailer is in a bad spot to get a lot of sunlight. Trees on both sides and the sun is pretty low because of winter.

Here's the setup, so far.

[Ninety-9 SE-L]

In many cases (but not always) the gradual charging of the batteries from dawn to noon, insures they rarely see too many charging amps, their voltage rises as the solar increases and all pretty much self-regulates. The problem happens on a cloudy/ foggy morning, and the the haze burns off at 11:30AM Boom High amps into the low batteries. If you are able to switch off some of the PV strings in the combiner box, that can help prevent that big surge. All that requires manual baby sitting of the system . High end charge controllers have a max amps limit that can be programmed into the controller, so you can throttle you 80A controller to 32A, and not fry your batteries. My Morningstar and Classic both have that feature.

For the record, I was always under the impression that batteries only take what they need, for example, a 150A alternator isn't going to throw 150 Amps of charging power onto a car's battery, the battery simply draws out the current that it needs. What will kill the battery is keeping the voltage too high when it has reached float capacity.

[littleharbor]

[QUOTE=Ninety-9 SE-L;n408828]As of right now, I only have 4 of the 6 panels purchased and installed. I just hooked up the PVs to the combiner box (Damn MC4 cables SUCK to crimp), so the charging side is complete.




Are you trying to crimp the MC-4 contacts onto the PV wire without a proper crimper? The MC-4 crimper makes this task pretty much a no-brainer. Seeing how the MC-4 die folds both tabs inti the wire and compresses the whole thing together I wouldn't recommend doing it any other way. Pretty much asking for problems.

[Ninety-9 SE-L]

[QUOTE=littleharbor;n408834]

Are you trying to crimp the MC-4 contacts onto the PV wire without a proper crimper? The MC-4 crimper makes this task pretty much a no-brainer. Seeing how the MC-4 die folds both tabs inti the wire and compresses the whole thing together I wouldn't recommend doing it any other way. Pretty much asking for problems.

I used my Astro Pneumatic crimper:
81AXeexeasL._SL1500_.jpg

I went with the Open Barrel 4-6 that was recommended on a website I found. The crimp came out beautiful. The problem was all the IP68 crap and getting the connector put together. I think the problem was the Renogy MC4 cables I used had REALLY thick insulation. It was a pain to slide the blue compression sleeve up the wire and screw it tight. By the 2nd or 3rd connector, I came up with a system where I shaved some of the insulation off the cable so the compression sleeve would slide on.

user45970_pic12079_1519236580.jpg