What the heck happened?

[Basketcase]

Hey there. I've come here for some advice on diagnosing and upgrading my off grid setup at my Island house. I have made a very good living from 12v electrical since 1998 so I am completely familiar with batteries, ohms law, amps etc etc. My system is one my father installed perhaps 20 years ago before I took over the house and is very rudimentary. It consists of 3 panels for a total size of approximately 3'x4' but I do not have wattage specs on them. The charge controller is a tiny white box perhaps 3"x2" with a 4 posts (+- to array, +- to batt) and a red light. There are two 12v deep cycle batteries (from 2011) in parallel and we run about 5 lights and a few phone chargers. Pretty basic setup. This house is opened in late may and closed usually early September although I kept it open late this year. The batteries are left connected to the array but loads are disconnected through the winter.

On to my issue. In june of this year I checked the levels and both batteries were slightly low so I filled with distilled water. Fast forward to this weekend. I only had about 1 hour of lights before I had dead batteries. I ran for 3 days once when we discovered that the roofer never reconnected the array so this was odd. The next night we had the same result which means there was some recovery during the day even though it was cloudy and my angle is 20 degrees off for October. I disconnected the batteries and had roughly 11 volts coming from the panel on a very cloudy day at 10am 20 degrees off. Normal?

So I bring the batteries home when I close up this year. I figure they served their life but me being me I decided to put them on my charger. One read full charge, the other had 2 volts. Open the tops, both batteries had no visible electrolyte! I admit I'm not the best at battery maintenance. I only do it once a year and I forgot last year but there was still visible electrolyte in June when I topped them off.

So my questions are...Where did the water go? Should I expect more than 11 volts under those circumstances? How can I improve things?

I have a theory about the water. The dead battery caused the charge controller to see low voltage and continuously charge, boiling off the water in short order. Possible?

I appreciate the help. I've been reading on here for days all about the off grid systems. Seems like most are way cooler than mine but mine was one of the first on the island 20 years ago so it was cool then!

[jflorey2]

On to my issue. In june of this year I checked the levels and both batteries were slightly low so I filled with distilled water. Fast forward to this weekend. I only had about 1 hour of lights before I had dead batteries. I ran for 3 days once when we discovered that the roofer never reconnected the array so this was odd. The next night we had the same result which means there was some recovery during the day even though it was cloudy and my angle is 20 degrees off for October. I disconnected the batteries and had roughly 11 volts coming from the panel on a very cloudy day at 10am 20 degrees off. Normal?

No. Open circuit voltage AT THE PANELS should be 16 to 20 volts. (Measure at the panels, not after the charge controller.)

So I bring the batteries home when I close up this year. I figure they served their life but me being me I decided to put them on my charger. One read full charge, the other had 2 volts. Open the tops, both batteries had no visible electrolyte! I admit I'm not the best at battery maintenance. I only do it once a year and I forgot last year but there was still visible electrolyte in June when I topped them off. So my questions are...Where did the water go?

It "boiled off" (really electrolyzed off) due to overcharging.

Should I expect more than 11 volts under those circumstances? How can I improve things?

Get new batteries. Connect them in series not parallel. (i.e. two 6V cells not two 12V cells.) Ensure they remain charged most of the time. Never discharge below about 50%. Set the correct absorption and float voltage. Make sure your batteries match your load, and make sure your charging source matches your batteries. Ensure you have a generator to periodically fully charge the batteries.

You got five years out of those batteries which is a lot more than I would have expected.

[Basketcase]

Thanks for the info. I too was surprised that these batteries lasted as long as they did and I've learned enough on here to know that my next set should be a pair of 6 volt cells in series. These batteries were put into service at the beginning of 2011 and failed right at the end of their 6th season so that really isn't bad for such a system I suppose. I do not, and most likely will not have a generator at this location. We are located on a small island in Rhode Island and everything comes to the island on a small boat and stays there forever. We also don't have a great place to store a generator. If it means we replace batteries sooner, then I think we have to live with that and accept it. $300 bucks every 5 or 6 years is acceptable.

In respect to the open circuit voltage. I did read both before and after the charge controller but I left the controller connected even though I knew I should have disconnected it. Would that have caused a low voltage reading? Do I understand correctly that a panel in poor sun conditions should still produce it's full voltage? To me this says that the available amperage is what suffers in these conditions? This seems counter intuitive to me, but I'm here to learn and I admittedly have very little PV experience. When I return in spring I will bring my good fluke with me and measure the voltage and amperage on a nice sunny day so I can see if this array is enough for two batteries. I also figured a better charge controller cant hurt. Especially since they are so inexpensive. Since I plan to replace batteries and controller anyway, it may not be relevant but do we think that a bad battery caused the overcharging condition or did a bad charge controller cause overcharging which led to the bad battery? I assume this is pretty hard to speculate.

Thanks for the info so far. Much appreciated.

[Basketcase]

So I have decided on some 6v FLA golf cart batteries that I can buy locally for a good price. I also want to replace the charge controller. What would be nice would be one with a display that shows charging rate, battery condition etc. (if that exists) Can someone recommend one for me? There are so many of them, and so many brands and I feel that just asking for a recommendation is the easiest way to go. I have a small array with just two 6v batteries (230ah total) Unfortunately I do not know the wattage of my array. I know it has 4 "panels" and it is also at least 15 years old. Thanks for the help.

[sensij]

Thanks for the info. I too was surprised that these batteries lasted as long as they did and I've learned enough on here to know that my next set should be a pair of 6 volt cells in series. These batteries were put into service at the beginning of 2011 and failed right at the end of their 6th season so that really isn't bad for such a system I suppose. I do not, and most likely will not have a generator at this location. We are located on a small island in Rhode Island and everything comes to the island on a small boat and stays there forever. We also don't have a great place to store a generator. If it means we replace batteries sooner, then I think we have to live with that and accept it. $300 bucks every 5 or 6 years is acceptable.

In respect to the open circuit voltage. I did read both before and after the charge controller but I left the controller connected even though I knew I should have disconnected it. Would that have caused a low voltage reading? Do I understand correctly that a panel in poor sun conditions should still produce it's full voltage? To me this says that the available amperage is what suffers in these conditions? This seems counter intuitive to me, but I'm here to learn and I admittedly have very little PV experience.

Thanks for the info so far. Much appreciated.

Yes, the current will vary based on the sunlight, voltage only really varies with temperature. Your reading of 11 V is consistent with a small load on the panels, or the panels were still hooked up to the battery.

Small island... Block Island? I live in San Diego now, but have great memories of summers in RI.

I think something like the Tracer 30 A charge controller would be a good one for you. You can get a PWM controller for about $100 less, though, if you are just interested in replacing what you had.

[Basketcase]

Yes, the current will vary based on the sunlight, voltage only really varies with temperature. Your reading of 11 V is consistent with a small load on the panels, or the panels were still hooked up to the battery.

Small island... Block Island? I live in San Diego now, but have great memories of summers in RI.

I think something like the Tracer 30 A charge controller would be a good one for you. You can get a PWM controller for about $100 less, though, if you are just interested in replacing what you had.

Thanks for the info. Our island is Hog island. Much smaller than block island and we do not have power there. It is a wonderful place. I see the controller is an MPPT controller. I was wondering if it was worth the extra money for an MPPT in my case. I was thinking since my array is small and old, every last bit of efficiency I can get is a good thing. 125 bucks is till pretty inexpensive. Looking at what I have, it is in line with a 20 dollar cheapo. If it's worth the money for the MPPT, I'm all for it.

[sensij]

I don't know if it is worth the money for you. It would be better to have an MPPT if you ever decide to replace your panels, because 20 V panels can cost much less per watt than 12 V panels, but would need an MPPT to be compatible in a battery application. It should definitely get you more power out of your existing panels, but so would just putting another panel in parallel with what you have, into a PWM controller, for probably the same money or less.

If I were buying a PWM controller, I would look for three stage charging. It is a little pricier that some of the generic controllers, but this is probably what I would go with, still less than half the cost of mppt:

https://www.amazon.com/VS3024A-Regul.../dp/B01N49BEE4

temp sensor extra, they also sell a communications cable if you want remote access and can figure out the protocol

https://www.amazon.com/Temperature-V.../dp/B01N9QNQSH

I'd suggest going with a 30 A controller even if your panels can't generate that much yet, because your 230 Ah battery would really want to see 20-30 A of charge current if you can provide it.

[Basketcase]

Given the age of the panels, I'm sure an upgrade will happen at some point. I added to cart the MPPT one you mentioned but I did the one with the remote panel since my system is located in the loft. Now I can monitor it from downstairs. I'm a little OCD and it would drive me nuts if the panels were mismatched so adding one to an old array probably wont happen. Especially with the cost of new panels. I'd just do them all. One benefit that I have is that the depth of discharge will remain very low here. We run lights for a few hours at night (all LED, and maybe 4, 6 watt bulbs at a time) and cell phone chargers. The occasional laptop charger or cordless drill charger too but very rarely. We only use the house in summer (late may to late sept). I think I'll just order that first controller you suggested. Seems like it leaves me room to grow. Thanks again for the input!

[Basketcase]

So now that I have an MPPT controller, and I can use high voltage panels, I have a question. I was looking at specs for a 340 watt, 8.99 amp 37.8 VDC panel. What I'm gathering is that I could run this panel with this controller and the controller will put out the proper charge voltage. Does this mean that at 12 volts, I am getting 340/12= 28.33 amps @12vdc of charging from that panel with this controller? (theoretically, assuming no loss etc)

[sensij]

So now that I have an MPPT controller, and I can use high voltage panels, I have a question. I was looking at specs for a 340 watt, 8.99 amp 37.8 VDC panel. What I'm gathering is that I could run this panel with this controller and the controller will put out the proper charge voltage. Does this mean that at 12 volts, I am getting 340/12= 28.33 amps @12vdc of charging from that panel with this controller? (theoretically, assuming no loss etc)

Yes, correct.

[Basketcase]

Y'all are great. Thanks for the help. Even if I don't ever go as far as I hope to with this, I enjoy learning about it from people that know. Say I want to do two 340 watt panels. Max voltage for my controller is 100v. So would I run 2 of these in series? I'd get 75.6 volts and 8.99 amps, or would I run them in parallel and stay at 37.8 volts but go to 17.98 amps? I realize that either scenario would now make it necessary to run a 24v battery to keep my charge current below 30 amps. If I then decide to run more than 2 panels, I'll be over my max charge current, because I believe this charge controller only goes up to 24v battery voltage, but I think it would simply restrict the charge current if the panels produced more than the controller / batteries could handle. In this scenario, I would have higher charge capabilities in less than ideal conditions but the controller would be restricting amperage when the panels were at full power, yes? Am I understanding all of this correctly?

[littleharbor]

Max input voltage is based on Voc at the lowest expected temperature. Your Voc is probably in the 46+ volt range with those high power panels. Factor in cold temps and you will easily go over 100 volts, open circuit. You should parallel wire the two panels.

[Basketcase]

Makes sense. When they go to 46 volts, what is happening to the amperage? What I'm getting at, is would I be able to go to 3 panels? This would put me in the range of voltage I need, and, going by the specs on the panels, keep me at just under 27 amps of input current. Is what I think about over sizing the panels to get a wider time range of max charge current by having the controller limit current at times of max output correct?

I'll admit I'm surprised that the companies dont list their voltage at its maximum. Or do they? Is that specification typically a known value?

[sensij]

The Voc and the temperature coefficient are listed on the data sheet. You'll need to calculate for the coldest temp in your location. In some parts of the country, you could put two of those panels in series, in other parts, it gets too cold and would exceed the voltage limit.

[littleharbor]

There is no amperage flowing at open circuit. This high Voc is what your controller sees first thing on a cold morning. Regardless if amperage is flowing or not this is too high a voltage for your controller. If your controller has a max wattage rating for your intended battery bank voltage us its recommendations. Basically @ 12 volts you are limited to half the watts you can use at 24 volts as the amperage will be doubled. Your controller is amp rated at OUTPUT current, not input current. When the input voltage is stepped down the amperage is stepped up.