Newbie with question for Sunking

[flockhart]

Recently upgraded a small solar system in our hunt camp, installed 2#95watt 5.5amp panels, 30amp MPPT charge controller and 2#L16 420ah 6volt batteries, wired to 12volt. Have panels hooked in series to give 24v to controller aprx. 60ft of 6 gauge cable from panels to charge controller. My question is after reading other post do I have enough panels to properly charge batteries, we only use cabin for a few weekends in summer and winter, and a week in late fall for hunt. Only running lights and a radio but considering small fridge. Lights are all CFL main light is total of 35w for aprx 6hours a day in winter, others are 13w for maybe a couple of hours a day. Everything is 120v from inverter, we do have a small gas genny for emergencies and to run power tools if needed, am thinking of possibly running genny to initially cool fridge down so I dont draw batteries too low. Any advise would be appreciated. Thanks Steve

[Sunking]

Hey Steve I will try to help out.

I would not recommend you attempt putting the refrigerator onto your solar system as you rpanel wattage is just not up to it to get the batteries recharged fast enough. But there might be a work around which I will get to in a minute.

Your panel wattage is very low compared to the battery bank size you have. L-16's are a rather tall battery that are suject to stratification which means the heavier acid tends to gravitate to the bottom of the jar leaving the lighter water on top. To prevent that from happening requires enough charge current to make the electrolyte to bubble and roll to stir things up. The amount of current to do that sufficiently is up around C/12 to C/10 where C = the Amp Hour Rating of the battery at the 20 hour rate. For L-16's 20 hour rate is 420 AH so 420/10 = 42 amps. So you have a 195 watt panel and at 12 volts the most current they could ever produce is 195 watts / 12 volts = 16.25 amps. Not only that but your charge controller is not up to the task either at 30 amps max.

But there is a work around as I elluded too earlier, but dpends on what size generator you have. If your generator is rated at least say 1500 watts or higher (which is a extremely small unit). More likely I suspect it is up around 5000 watts which is good. Buy a 40 to 60 amp 12 volt AC powered battery charger to run on the generator.

So when you arrive at the cabin, the batteries should already be fully charged up. Turn on the fridge let it run several hours then run the generator for an hour to recharge and strir up the batteries. Then the day you intend to leave, start up the generator to fully charge the batteries because your panels will not be able to keep, and give the batteries a godd stirring up before you leave.

The only other work around is considerable more expensive by purchasing 500 watts more panel wattage and replacing your 30 amp CC with a 60 amp charge controller. That would run you around $1500 vs say $400 for a good 12 volt 50 Amp AC powered charger to run off the generator.

Hope that helps.

SK

Edit note: For a charger you can use a DC power supply made for Amatuer radio equipment. Look around on Ebay and on QRZ forum for Astron 12 volt power supplies with adjustable voltage output and current limit. You can pick them up used for around $100 to $200. They are what we call boat anchor power supplies which mean they are heavy and very rugged and last forever. Good Astron models to look for are:

Vs-70 = Variable output
VS-70M variable with metering

You can crank the output up to 15 volts, and adjust current limit all on the from panel. Even th eRS series can be adjusted but from the inside using the potentiometers on the circuit boards.

[Mike90250]

Let me add just 2 more points to Sunkings comments.

Power Factor http://en.wikipedia.org/wiki/Power_factor

Depending on the individual power supply/battery charger that you get, you may need to read the labels and determine the Power Factor of the device. This will affect what size generator is needed.


Fridge Starting Surge Starting a compressor motor takes 5-10x the running power, so whatever inverter you plan on using, it needs to be able to start the fridge. If the nifty Morningstar Suresine 300 had a bit more peak surge capacity, it would be able to start fridges - but sadly, it can't start most of them. So you have to go up one more size to get the motor starting capacity, with the higher idle losses.

An "auto throttle", "inverter generator", like the honda EU2000 series, is a great way to get the max power out of a tank of fuel.

If you are only going to use the hunt camp for weekends, consider just an ice box. It takes about 12 - 18 hours compressor run time to really chill down a fridge, and if you are only there for 48 hours, it's hardly worth it, a 10# block of ice will do as well, and pre-chill all items before they go in the fridge.

[flockhart]

Thanks

Thanks Gentlemen, I wish I had found you before buying the batteries, had never heard of stratification and did a lot of research before hand. I used numerous online calculators and the 400ah range seemed to work with all and acomplished everything I was thinking of. I had a choice to go with 4#T105's or 2#L16's and everything seemed to say less connections is better, hence the L16's. I'll probably go with more panels as my little genny probably wont handle the bigger charger. I do already have an old 70A charger but not sure if works properly, I'll take it to the cabin and try it with the genny, how would I check if it is working properly? Another question, is there a calculation you use to determine the wattage of panels needed to properly charge batteries, ie to avoid stratification? My charge controller is capable of up to 720w input at 24v by what I understand you saying that would be enough to do what you are saying. However by hooking panels up in series I would only be able to do 6@95w or 570w to stay under the 720w max unless I mix different wattage panel into the system, something you seem to be against, am I right?
Thanks again
Steve

[flockhart]

Just realized you have already answered the question of current needed to charge batteries, another thing I never saw in the calculators online. Thanks
Steve

[Sunking]

Thanks Gentlemen, I wish I had found you before buying the batteries, had never heard of stratification and did a lot of research before hand.

Steve it is mostly a problem for tall Flooded Lead Acid batteries where height is significantly larger than width and depth. In addition with FLA batteries you need at least a C/12 charge rate to disovle soft lead sulfate crystals. It is too late to tell you this now but for the type of application you are using being infrequent use and remote left unattended for long periods of time an AGM battery would have made a good fit for your application. AGM batteries do not have stratification issues, and have lower minimum charge rate requirements.

I used numerous online calculators and the 400ah range seemed to work with all and accomplished everything I was thinking of. I had a choice to go with 4#T105's or 2#L16's and everything seemed to say less connections is better, hence the L16's.

Given the choice between 4 of the T-105's or 2 L-16's you made the right choice for the right reasons of no parallel strings. However your application falls between the cracks of standard design practices.

Normally the battery capacity is selected based on daily watt hour use. For example if you use 1 Kwh per day you would size the batteries at 5 Kwh capacity. That still applies to your application well sort of if using FLA. Where you get off track is the infrequent use and the size of the panel wattage required. Panel wattage is determined by your location and DAILY EVERY DAY USE. They have to be capable of replacing the energy used every day for the shortest winter day months. When you calculate that way the charge current falls into place automatically and not something you have to worry about.

So if I were to reverse engineer your system with only knowing your battery capacity, and assume you live in an area where in winter you only receive 3 Sun Hours and using a MPPT charge controller. Daily usage would be [12 volts x 400 AH] / 5 days = 960 watt hours so let's say 1 Kwh close enough to keep it simple. So the panels need to generate 1500 watt hours in winter with a 3 Sun Hour day so panel wattage required = 1500 wh / 3 h = 500 watts. a 500 watt panel using a MPPT controller with a 12 volt battery will charge at 500 watts / 12 volts = 41.67 amps. Perfect right? The recommended charge rate for a FLA battery is between C/12 to C/8. 42 amps on a 400 AH battery = 400/42 = C/9.52 and that is right in the sweet spot.

I'll probably go with more panels as my little genny probably wont handle the bigger charger. I do already have an old 70A charger but not sure if works properly, I'll take it to the cabin and try it with the genny, how would I check if it is working properly? Another question, is there a calculation you use to determine the wattage of panels needed to properly charge batteries, ie to avoid stratification? My charge controller is capable of up to 720w input at 24v by what I understand you saying that would be enough to do what you are saying. However by hooking panels up in series I would only be able to do 6@95w or 570w to stay under the 720w max unless I mix different wattage panel into the system, something you seem to be against, am I right?

What size generator do you have? I can't imagine smaller than 1.5 Kva. As for panel wattage using 2 L-16's you can go as low as 460 watts and max of 700 watts assuming you are using a MPPT controller. If using PWM is where things get ugly and requires a minimum of 600 watts and max of 900 watts.

Chew on that a while and see what you think.

Hope that helps.

[Sunking]

Hind Site Comments

Steve using Hind Site based on what info you have provided of using 1 Kwh per day, 2 days per week infrequent use here are what would have been my 2 recommendations for you.

Option 1

• Solar Panel wattage = 30 to 50 watts.
• Charge Controller = MorningStar Sun Saver PWM 6 amp.
• Battery = 12 volt 250 AH AGM.
• Small 1000 watt LPG generator made to generate 12 volt DC only at 50 amp alternator. Gasoline could be used but would require fresh gasoline. Heck it could even be home brewed with a small Briggs & Stratton Lawn mower engine and a car alternator.
• Inverter if needed based on connected load?

Here is how it would have worked. The solar panels would be used as a float charger to keep the batteries at 100% while you are away and ready for your arrival. So lets say you arrive Friday afternoon the system is ready to go. Use it Friday and most of Saturday. Then a few hours before lights out on Saturday run the generator a couple of hours to fully recharge the batteries. A couple of hours before departure on Sunday run the genny again to recharge. Throw the genny in the truck and go home. The system will be fully ready when you return.

Option 2. Security
For such a small system you do not even need the solar stuff, or leave any of it at the cabin to be stolen

• Battery = same AGM battery
• Genny = same generator
• Inverter = same if even needed.
• AC Powered Battery charger = Float type battery maintainer of about 5 to 10 amps.

Pretty self explanatory. Keep it all at home safe and secure. While at home connect battery to AC powered charger. When you go take genny, battery, and inverter with you and use it as above except no Sunday run time. Just throw the battery and genny in the truck and go home.

Me thinks you wished you had thought about that before huh?

I even like Mike's idea of scrapping the fridge and use a cooler with a block of ice. You would not need a generator or any solar. Just a much smaller battery and battery charger to recharge at home.

[flockhart]

Thanks again, I really dont know what the genny is, its what I call a one man genny. Nice, small and light, I'm going up to the cabin tomorrow so I'll check. We dont need to worry about things being stolen, on 400 acres of private land accessible only through my buddy's land at the end of the road, he lives on the road, his mother lives on the road and a good friend lives adjacent to the trail. A couple of years ago two people walked in to go hunting and the phones began ringing, I just so happened to be at the cabin and sent them packing on the way out, my buddy's wife was at the end of the trail waiting for them coming out and gave them an awful tongue lashing. They have never been back! Gotta love rural nieghbours.
The trail in is terrible and we dont want to have to lug anything in or out, I appreciate your answers and knowledge and if the genny will run the charger I'll go that way, otherwise I buy more panels to bring it up to the 500 watt range. Either way it'll be at least $1000 new genny and possibly new charger or panels, I know it's really not practical butwould rather go with more of the quiet solar panels than a noisy genset. There is nothing better than sitting at the cabin at night lit up with no sounds but the noise from the bush.
Thanks again
Steve

a pic off the cabin
206973_1009486553352_1110612885_30038550_1828_n.jpg

[Sunking]

Good luck to you Steve. Now you know your options and can make an informed choice. Hope I was of some help.

SK

[flockhart]

Thanks for all of the information as I said will try the charger but am leaning toward more panels, checked the website of company i got my panels from and they have 140watt units @18.3 v the 95's I have are 18.34v so by what you and Mike have said on other posts I can add 2 of these and reach that majic number you recomended. My only other question is that since the cabin sits Idle for extended periods should I have some sort of load on the system? Just to make sure that the batteries get a good charge to avoid stratification.
Once again thanks for the info
Steve

[Sunking]

My only other question is that since the cabin sits Idle for extended periods should I have some sort of load on the system?

No not required.

[flockhart]

Thanks again, dont you ever sleep? I think I'm done with my questions at least for now
Thanks for everything it's greatly appreciated nice to ask someone whose main objective is not selling me product.
Hope you dont mind if I ask further questions in the future
Steve