Setting charge voltage

[cabinfevor]

Hello all, this is my first post to the site so I guess I'm a newbie. I've read a lot of good posts here but haven't found one that addresses this question. At least not yet. I'm getting ready to jump into the solar charging world because I'm tired of dumping gas into my generator.

I've got a off grid camp in Maine that's more like a small house. I powering it with a 4k watt Xantrex inverter charger. My battery banks are 1000 amp  and 850 amp 24vdc. I use a 425amp continuous duty marine battery selector switch for picking either bank or both plus I have a 250amp breaker that I can disconnect the inverter.

I' find myself running the gen everyday to keep the batteries above 60% charge. I've got all florescent lighting but the monitor heaters and well pump take their toll in power consumption.

My goal is to install a solar panel or two that will charge the banks when I'm not using the camp but I was told by some one with a similar set up that I would need to be careful of charge voltage when not using the camp for extended periods, He stated the normal charge voltage(28. would bake the batteries when they are not being cycled.

1. Is this true? Do I need to change the charge voltage setting when I'm not at camp?

I've already purchased a Xantrex C40 charge controller but I have not yet purchased any panels due to the high cost. I was planning to buy a used one off ebay.

2. Any suggestions as to whether I should buy two 12 volt panels and wire in series or one 24 volt panel. I don't think I'll need a huge array as the system will have a few weeks to recharge between being used. Some times longer. Thanks for any advice.

[AbyssUnderground]

28.8v is a bulk charge voltage, you need around 26-27v to float it while you are away. My charge controller floats at the voltage I set it at so for me there is no danger. You will need a charge controller similar to that to make sure you do not boil them away.

[Sparky01]

Yes I believe that you are on the right track. I have the C-60 version of your controller and you do have a bulk and float adjustments. There are trim pot knobs on the inside of the controller that do have a few voltage marks on them. Use the voltages given by AbyssUnderground, You may need to use a multimeter to get it right. Where is your camp in Maine? I live in Unity, Maine myself. Oh yes as far as the panels go either way is fine allthough you may find 12V panels a little easier to find.

Good luck

[cabinfevor]

Thanks for the reply.

I'm in Milo. I guess I'd opt to set the charge voltage to the low side 26-27 given by AbyssUnderground. I also need to get a new book for the charge controller as the one that it came with got lent out and never came back. I was hoping the charge controller would work like the charger on the inverter, where as it would pound high charge voltage and current and taper off the current as the batrery voltage got closer to full charge, then drop the voltage to a float level. I guess the solar charger does not work that way. I'll prabaly apt for a new 24vlt seeing how people are paying almost new prices for used 12 vlt panels on ebay. One 24 vlt will be easyer to install. I hope? Any suggestion on manufactures that are better than others?

Thanks and be well.

[Brian H]

Hiya cabin,

 There are other more imminently qualified people here to answer your question, but I've been monkey-ing around a with a small solar system for a couple months now, so I can relate to your question. I've been reading and reading and reading, and I still feel like I've only scratched the surface. A good starting point is here:

http://www.uuhome.de/william.darden/index.htm

 I have a Xantrex c12 controller, and so far I really like it! The only thing that is lacking is good documentation for all the settings that are possible. The first thing I would do in your shoes, is find out as much as I can about the batteries that you have. The type of battery, as well as it's condition dictates the optimum charge controller settings, as well as  the life expectancy of the batteries. For example, a flooded lead-acid battery has a self-discharge rate of about 1% per day, but a AGM battery is only 1% per month. This is a huge factor in how much wattage you need to look for in your solar panels. A solar array that doesn't even keep up with your self-discharge rate is better than no solar array, but even better if you can keep your batteries floating, as well as having enough excess power to perform an equalizing charge once a month or so.

 The more you study, the more you will benefit from your system, and the more money you will save in the long run, that's what I've learned so far. And I've still got a lot to learn!

 Good luck, and have fun with it!

BrianH

[SamoaPower]

Actually, the C40 DOES work that way. Set the bulk to 14.4 and the float to 13.2 (depends on battery type).

[Spdlmt150]

I have four 75w matrix panels running through a morningstar charge controller. Everything is autonomous. Bulk & float voltages are maintained by the charge controller, as well as automatic equalizations. I've had things running for four years now, and haven't had to touch a thing (aside from cleaning the panels occasionally & adding water to the batteries)

Most charge controllers will manage the voltage to keep from damaging the batteries. So long as they are not wired directly to the batteries, everything should be ok.

I'm assuming the 1000 & 850 are AH ratings on the batteries? My four panels are running into 440AH of batteries, and take a couple days to charge completely with no load. If you have that much battery, a couple panels won't provide much. The C40 will prevent overcharging (if you get enough output to worry about it) Once the charge controller is set up, it shouldn't make a difference if you are there running loads, or away & charging constantly.

[cabinfevor]

Thanks for the reply and the great battery link you sent. I've learned a lot already. I knew that one of my banks I built out of AGM batteries. They were used but not that old 2-3yrs. They are Dynasty Batteries (20 of them 100Ah each wired pairs for 24vlts. The second bank I built from 10 batteries that came out of an industial diesel gen plant. They are huge (170 lb each) Vented but no removable caps, Flooded acid batteries. Again these weere two years old. It's been over a year since I put all of this together so I dont remeber the brand of the second bank. I do remeber doing the math and that bank had 850 ah at the 20 ah rating.

I plan on putting a 175 watt panel on one of the banks and seeing how things work out. If I can afford it in the long run I'll add another to the second bank.

thanks again for your response.

[mukunthko]

why dont you try mppt (maximum power point tracking) charge controllers. From what I'm told they convert any input voltage to the charging voltage that your battery needs at that particular moment in time using some complicated algorithms in ICs. I've seem them on ebay.