Panel/CC for AGM batteries

woozy

Hi, I'm new here, and mostly clueless.

I have 8 UPG 121000, 12V/100ah batteries (long story They are 3 years old, not well cared for, but I've charged them carefully and all seem ok.

I'd like to maintain these batteries and eventually use them in a small solar set-up.

What kind of panel/charge controller minimums do I need to try to keep these batteries healthy? I will definitely wire them correctly.

Cariboocoot

Re: Panel/CC for AGM batteries

Welcome to the forum.

Merely maintaining batteries doesn't require a lot of power: 1 or 2 % of the Amp hour rating would do. For that you're looking at <30 Watts per battery (check the actual Imp rating of the panel).

You will have a problem with current sharing if all 8 batteries are connected in parallel. You could wire them as two parallel strings of 4 in series but then you'd need a 48 Volt charge set-up.

woozy

Re: Panel/CC for AGM batteries

I've been looking at the SmartGauge wiring diagrams, so I *sort of* get this, but I really, really, don't want to do a 48V system on my first attempt. Is there any other way?

Cariboocoot

Re: Panel/CC for AGM batteries

Divide them up into manageable portions, but that means separate panels & controllers per on 12 Volt.
You could do 4 parallel on 24 Volt.

But before you buy anything, figure out where you want to go with it. Best to buy stuff once, not twice.

BB.

Re: Panel/CC for AGM batteries

You can parallel them (following the Smartgauge web page)--Ideally, each battery string (or battery) should have a fuse/breaker per connection to the + bus common point.

These Blue Sea fuse assemblies are pretty nice (small) for connecting to your battery terminal/bus point (there are one and two fuse versions):

Attachment not found.

I also highly suggest getting an inexpensive DC Current Clamp meter... (like this one from Sears). You can measure the charging/load current in each parallel battery string and find problems before they become bad and ruin one or more batteries (check once a month or so).

Since you already have the eight x 100 AH @ 12 volt batteries--The suggested solar array size that would support 5% to 13% rule of thumb for an actively used system:

• 14.2 volts charging * 800 AH battery bank * 1/0.77 panel+charger deratings * 0.05 rate of charge = 738 Watt array minimum
• 14.2 volts charging * 800 AH battery bank * 1/0.77 panel+charger deratings * 0.10 rate of charge = 1,475 Watt array nominal
• 14.2 volts charging * 800 AH battery bank * 1/0.77 panel+charger deratings * 0.13 rate of charge = 1,918 Watt array "cost effective maximum"

These are just basic rules of thumb to get you in the area (for costing/performance expectations). Say you plan on using the system fairly heavily and choose 10% rate of charge... The numbers would look like:

• 1,475 Watt array * 0.52 system eff * 4 hours of sun (typical avg in US) = 3,068 Watt*Hours per day (AC power out of inverter)
• 1,475 Watt array * 0.77 panel+charger derating * 1/14.2 volts charging = 80 amp minimum recommended MPPT type charge controller

A Midnite Classic 96 amp or Outback FM80 MPPT controller would be in the class of charge controllers to look at.

AGM batteries can supply very high current (30 minute rate or higher is common for UPS applications)... For a typical 12 volt system--I like to recommend 100 amps nominal max continuous current or ~1,200 watt maximum AC inverter for sanity (size of copper wiring, voltage drop, etc.). That would work well with a C/8 discharge rate (which is the max continuous if you substituted to 800 AH of flooded cell batteries).

If you can split your loads into smaller loads (electronics, cell chargers, TV, computer, lighting), the MorningStar 12 VDC 300 watt (600 watt for 10 minute) TSW inverter is a real killer--It has options for power saving/system control that you don't see on small/less expensive inverters, especially in 12 volt models. You could always get a larger 1,200 watt less expensive inverter (TSW or MSW) to power tools/etc. when needed.

For your battery bank, I would highly suggest a Battery Monitor (Victron is another good brand)--since you cannot measure specific gravity with AGM/Sealed cells.

If you do not want/need this large of solar array--You could cut it by about 1/2--Going any lower, you should also reduce the number of parallel batteries too (a huge battery bank needs a large array to properly recharge--AGMs can run with a bit smaller array, but if you will be using a fair amount of power, do not scrimp on too small of solar array--It can cause batteries to sulfate/age prematurely.

-Bill

woozy

Re: Panel/CC for AGM batteries

Wow, I am "over-batteried"!

I'd like to have lighting, laptop, mini-printer (not often), an antenna booster, and an led monitor in my 12x16 TuffShed barn.

I already have the barn WELL insulated, a propane genny outside in an enclosure, propane heater, a small wood stove, some thinlights, led lights, and a few propane lights. I have a solar oven, propane stove burners, and some other items that reduce electric usage.

I wasn't thinking on something so big.

Edit: Could I keep 4 of the batteries on trickle charge? I have a BatteryMinder.

Now I'm thinking about doing this instead of storing the batteries

BB.

Re: Panel/CC for AGM batteries

That size battery bank and 1,500 watts of panels--That is a nice sized system for a full off grid (albeit very efficient and somebody watching energy usage) home with refrigerator/lighting/well pump/washer/laptop/etc...

If you have AC power of some sort (extension cord, generator, or just grid power), you can get a Kill-a-Watt type meter and start measuring you daily loads. It is really amazing how much power we use/waste.

3.3 kWH per day/100 kWH per month is only a $10-$20 per month power bill--Vs buying all of that off grid hardware to supply the same (panels are much cheaper, the rest of system costs are probably going up now with the price of copper/lead/labor/inflation).

-Bill

westbranch

Re: Panel/CC for AGM batteries

found this, note the charging details at the bottom of the page...
http://www.batteryconcepts.net/yuasa/ub121000.html

woozy

Re: Panel/CC for AGM batteries

Now my head is really spinning. This forum is amazing.

I've stayed out here in the boonies several times for 2-3 weeks with just occasional generator use. I guess I waste like most when I'm in town, but out here it's easy; usage, virtually 0. I charge my tablet in the truck while I'm driving. I have a Kill-a-Watt, but nothing to hook it to.

I have no grid power but it sounds like I could use the generator to charge these batteries and have enough electricity to suit me. That's crazy...

The bad news: Summer is out, I'm in Texas. I'd love to move out here and get outa town and off-grid, but the heat is brutal here in the summer, and I know AC is the deal-killer.

Loved the link on the batteries.

BB.

Re: Panel/CC for AGM batteries

You can setup a system to run the batteries/inverters at night and recharge the battery bank during the day (basically a hybrid generator system).

Because fuel efficiency is rather low when charging the last 15% or so battery capacity--You would probably be best if you have a minimum solar array (5%, or possibly 2% array) to finish charging and float the battery bank for now...

Or, drop back to only a couple batteries for cycling--You can use a much smaller array to keep the bank happy then.

A 12 volt ~220 AH battery bank (a pair of 6 volt 220 AH golf cart batteries), or a pair of your AGMs at this time may be enough--But without knowing/measuring your loads--It is hard to know.

The battery bank, we generally design for 1-3 days of "no sun" with 50% reserve capacity (for long battery life). Call it two days and 50% max discharge--That is 25% discharge per day. For two golf cart batteries (or two of your 100 AH batteries):

12.5 volts * 200 AH * 0.25 discharge = 625 Watt*Hours of load
200 AH * 0.25 discharge = 50 AH @ 12.5 volts

And reduce all of my suggested numbers for an 800 AH battery bank to 200 AH instead or 1/4 the solar array/etc...

We can suggest a battery charger/generator/etc. combination--But it will probably just be more confusing than helpful until we know more about your loads...

Amps*Hours per day/Watts*Hours per day, 12 vdc/120 vdc, etc...

And, with the modern mini-split A/C systems--In a well insulated/smaller home, there are folks here that are running off grid A/C. Obviously, a good sized solar pv system is needed to run A/C, but, for example, the Sanyo inverter mini-split system could run on as low as 300 watts of 120 VAC power (no surge, low cooling)--To bad the Sanyo's are no longer available. But others may work too.

-Bill

vtmaps

Re: Panel/CC for AGM batteries

Welcome to the forum Woozy,
You have been gently warned about having too many batteries in parallel.
Please read this: http://forum.solar-electric.com/showthread.php?14674

One thing not mentioned is that AGM batteries have extremely low internal resistance. All the reasons for NOT paralleling batteries are exacerbated by that low resistance. One AGM manufacturer (I forget which) explicitly warns against having more than 2 parallel batteries.

If you do go with parallel batteries, be sure to put a fuse on EACH battery.

woozy wrote:

I really, really, don't want to do a 48V system on my first attempt. Is there any other way?

What's wrong with getting it right on the first attempt?

--vtMaps

woozy

Re: Panel/CC for AGM batteries

vtmaps wrote: »

Welcome to the forum Woozy,
You have been gently warned about having too many batteries in parallel.
Please read this: http://forum.solar-electric.com/showthread.php?14674


--vtMaps

I wasn't planning on ignoring the warning, but since my need is so low, I was going to take the suggestion to separate them and keep a float charge on the extras.

I read the great thread you posted the link for. I have even a greater chance for a shorted string since these batteries are not new.