Battery systems for stationary applications

I have 16 GC2 size 6V flooded lead acid batteries (48V system). Can get them here very cheap. Over priced Li Ion batteries are waste of money when weight and space are not an issue. I have never depleted my batteries below 50% and most of the time, not below 80%. Will have to watch it though, with my Solterra charging.

Rarely get smoke here on the coast, so not a factor. Interior of BC gets it sometimes in the summer. Unlike winter (more rain and clouds), summers here get a lot of sunshine. The only time I have used a generator in the past is for some power tools and my log splitter, because of my past undersized inverter. But with my new inverter (4000W peak, 2000 continuous) that is no longer necessary.

And remember this is a cabin, so we don't live there. Although in summer it gets a lot of use with family and friends. It's a great location. I have a floatplane, so fly up most of the time, but sometimes have to take a car, and of course others have to drive. But 1/2 hour flight sure beats a 2 hour drive, incl last part over a very rough FSR. The lake is near sea level at 33 ft.

 

Semantics.

Home user, connected to grid who consumes less power in a year than their array produces equates to a reduction of supply from the power line. This is the bookkeeping behind net metering.

https://news.energysage.com/how-solar-helps-the-grid/

 

That's very true. We know several people at the lake, incl one of our neighbours who went through a couple sets of L16s in 5 years because they severely mistreated them. They would run them dead periodically, and also overcharge them. Their systems had older charge controllers (but expensive) that were professionally installed (also very expensive). They were told to periodically boil the batteries (equalizations). However they did it too long and at high current. I looked at their batteries, and they were bulging at the sides, totally ruined.

My controller is cheap, but works great. It does a 1 hour auto equalization once every 30 days, at higher voltage but very low current.

I don't expect to have to replace my GC2s for a long time yet. And they are way, way cheaper than equivalent capacity L16s. There is a local battery guy here that picks up surplus stale inventory from stores and distributors (they write them off after a certain time) and sells them as used. But each one is tested and only sold if they meet the new battery spec. The price is about 1/4 of a new one.

 

The default is 30 days, and from reading the forums, that is pretty normal. Some go 2 hours, but mine is only 1 hour. What is most important is very low current (amps/watts) at the higher voltage. I have been doing that for several years with this charge controller, and batteries are all still good. And yes, need to keep an eye on water levels.

The neighbours were old (finally sold their cabin last year) and had a hard time comprehending how to look after the batteries. I gave up trying to help them. The equalization process was not automated with their controller. And their solar guy was no help with his instructions and advice. I think he probably figured if they wreck their batteries, well, more business for him. They did have a back-up generator, and had to use it a lot.

 

Not sure what you mean by cycling on a daily basis (what %). We or someone is usually using the cabin about twice a week for a day or two each time. In summer it is used almost continually by someone. In winter we go up there maybe once a month. Most of the time the batteries don't go below 90% (as per first thing in the morning). Often not below 95%. Occasionally, we might have darker clouds for a few days (white clouds still charge up). and it could drop to 70, but not very often. If we used it in winter, would be a different matter.

Every time we go up our batteries are sitting at 55.4V (float charge for 48V system), before we turn on the inverter. The controller does keep history, so I should check when and how often the batteries were equalized.

So based on that type of usage and cycling, what do you recommend? The setting are easy enough to change, so could have different intervals depending on time of year and usage.

 

Yes, have a temp sensor on the batteries, well just between two of them. Can't do it on all 16 of them. 55.4V is the equivalent of 13.8V which is a normal float charge for 12v batteries.
Below is from the manual for FLA:
Constant voltage Floating voltage
14.6V 13.8V


a) Constant Current Charging_CC(Bulk Charging)
In this stage, the battery voltage has not yet reached constant voltage (Constant or Boost Voltage), the controller operates in constant current mode, delivering its maximum current to the batteries (MPPT Charging).
b) Constant Voltage Charging_CV( Constant and Boost Charging)
When the battery voltage reaches the constant voltage set point, the controller will start to operate in constant voltage charging mode, this process the charging current will drop gradually. The constant charge voltage will increase 0.2V on the basis of constant voltage at 1st of each month, charge time is 60 mins. ( The data of boost charge voltage can be set via PC software and APP)
c) Floating Charging_CF
After the constant voltage stage, the controller will reduce charging current to maintaining the battery voltage on the Floating Voltage set point. Charging the battery with a smaller current and voltage on Floating Voltage stage, while maintaining full battery storage capacity.
In Floating charging stage, loads are able to obtain almost all power from solar panel.
If loads exceed the power, the controller will no longer be able to maintain battery
voltage in Floating charging stage. If the battery voltage remains below the Recharge
Voltage, the system will leave Floating charging stage and return to Bulk charging
stage.

 

The charge numbers are from my charge controller manual. And I do know that some battery specs say 13.5 for a float charge. When I see my charger voltage, when there is zero load, it sits at 13.8 (12v mode), but when I shut off the PV panels it immediately drops to 13.6 or lower, and holds at 13.2.

At home in the past, I have charged up some 6Vs and here is what I found. I have 2 chargers. One had a float charge of 13.8 while the other was 13.5 (6Vs were in series for charging). The 13.8 one would fully charge the battery to 6.36v (after surface charge removed) and hold there. The 13.5 would finish early and the holding charge was only 6.30 or 6.31. So at least for these batteries (Interstate), they liked the higher float charge one better.

While I could lower my float charge setting slightly, not sure if that is necessary. I do want a fully charged battery. And have not seen any excessive water boiled off. I add a bit of water about every 2 years.

Here is an excerpt from a deep cycle battery charging guide. They say that 13.8 is OK, although an upper limit. I could change mine to 13.7 or 13.6, but not sure if that is necessary as have been doing it this way for years, and batteries are still good. And I don't want undercharged batteries.
https://deepcyclebatterystore.com/the-battery-blog/how-to-charge-12-volt-6-volt-batteries/
Sustained charging, where the batteries are “floated” at a constant charge (as in the RV converter or with an automatic portable charger) should not be done at more than 13.8 volts (and 13.65 makes batteries last longer).

Here is another table from a charger manual, that my local solar store sells. It's specs are pretty well identical to mine, also with 13.8v for FLA. And I think pretty well all the charge controllers I have seen are this way.

 

What does your charger manual specify for a float charge? And what do you see on your display panel when in float mode?

 

That's about what mine shows when there is a load, ie inverter is turned on and usage is happening in the cabin and with Starlink. When everything is off, but PVs on, it show 55.4. Be interesting to see what yours show when all load is turned off (ie inverter off) and PVs still on, but with a full battery.

 

Can you not shut down your grid tie-in and shut off your inverter leaving only the PVs on charging the battery?