Whats wrong with this system??

[Raul]

No I haven't , the only test I know is the resistor load test and a battery at80% life left probably will pass that as ok. For all I know they may be dead ish but I can still have good use out of them . 2P4S . I do notice a loss capacity at -25 degC but they spring up as it warms up.

[msalari]

An update: Thanks for all the advice/feedback.
Was up at the cabin last weekend and replaced the batteries with 2 new batteries and the appliances ran fine for the weekend. No complaining from the inverter for 2.5 days. Also installed 2 new panels for a total of 345W @ 24V, (2 batts were 100Ahr ea)
Now the problem is that I only had a 20A MMPT controller and at peak periods I will get up to around ~24A so added a quick disconnect for the 3rd panel, waiting for a new 30A controller to come in the mail.

Question: I would assume that any decent controller would have dark current protection (ie. diode etc) built in, correct? To be safe, I used to have a 8A diode in the line but of course this wouldn't work with the 3 panels now. So I removed my diode completely and I'm trusting that the controller protects against night drainage. Safe assumption?

thanks again

[msalari]

Hey Sunking - I tested the 2 questionable batteries on a clean bench test. They were 105Ahr batteries. Ran a 102 Watt load for 16.75 Hrs. Shut down the experiment so I did not drain them to 0. Voltage reading (taken a couple hours after shutdown) was 11.83 volts. I think this shows that they are still in "decent" shape - at least maybe for backup purposes. Let me know your thoughts.

Also, to anyone who can answer - I feel silly but I can't wrap my head around it: I have max'd my charge controller (30A MPPT controller, and now I have 3x8A panels). So if I ever wanted to expand the system, how do I do this ? Introducing a new charge controller, to me this means having a completely separate isolated system and that means I also have to double-up on inverters - I must be missing something because surely I don't have to run two inverters to my cabin's main AC. I am in no rush to expand my current , but just curious - what am I missing? thx

[SunEagle]

Unfortunately if you increase your battery or solar pv system you may have to increase your CC amperage. Unless the CC's are matched and can communicate with each other it is not wise to have 2 of them charging the same battery bank. They may fight each other.

Since that 30amp CC will only handle those 3 x 8A panels, if you get more you will have to go with a larger CC at 45amp or 60amp.

You have fallen into the trap of not sizing your system to handle your daily watt hour loads and now have to replace hardware as you increase the system size.

[sensij]

Two cc's charging the same battery bank usually works fine.

[SunEagle]

Two cc's charging the same battery bank usually works fine.

Won't they fight each other?

[sensij]

How will they fight? They both read the battery voltage, so as long as they are set the same, they should transition from bulk to absorb to float at about the same time.

[SunEagle]

How will they fight? They both read the battery voltage, so as long as they are set the same, they should transition from bulk to absorb to float at about the same time.

OK. I stand corrected. I was under the impression that unless the 2 charging points had communication with each other then one might stop charging based on the voltage it measured from the other CC. That could cause the 2 CC to keep switching on and off because of misleading voltage measurements.

[msalari]

OK thanks guys, this doesn't seem too complicated then. But point taken SunEagle, an ultra large CC from the start would have solved all.

[inetdog]

The only potentially serious problem is if the sum of the two CC bulk currents is more than the safe bulk current of the battery. (C/6 or C/8 for FLA.)
You cannot let each CC max out its own panels and still reduce the current based on what the other is contributing.
If your panel total is small enough this is not a problem.

[msalari]

Ok the problem is back (or perhaps a new one). My buddy just arrived at the cabin to find the batteries sitting at 11.5v! So the inverter was beeping again. This is after 2 weeks of charging. These are New batteries, and additional panels doing the work. The only difference this time is that i removed my 10A shotky diode (because 10A won't be enough any more and because I was trusting my CC that it prevents reverse leaking). Do you guys put diodes in your system? WTF?

[sensij]

You also changed out the panels, if I understand correctly. Are you sure the new panels were wired in correctly? What is the actual configuration of your system right now?

[msalari]

I added two additional panels, per advice here. Total 345W.
But until i install the 30A CC, I cant really run more than 2 panels right now. So at this moment I have 200AHr batteries, 230W 24v panels (putting out 16A max). Will be 345W putting out 24A in a couple weeks.
But I've never showed up there to find batteries not fully charged. (Inverter is always shut off when I leave)
Only thing i can think of is the diode! - wouldnt it have to be a pretty crappy CC to allow leaking?