Unable to fully recharge 12 volt system

Re: Unable to fully recharge 12 volt system

Technically, equalization is not really charging. It is intended for pushing current through the series cells when (for example) 5 of the cells are at 100% State of Charge and one cell is at 80% State of charge. High voltage gets current to flow through the low cells while "over charging" the high cells.

More or less, true equalzation is only needed with the specific gravity difference between high and low cells is ~0.015 to 0.030 or greater. You typically want around 5% or so maximum current during equalization--Batteries can get hot during this period (most energy is converted into heat and gases).

As you equalize, make sure the batteries do not get over ~115-120F, and check the specific gravity every 30-60 minutes... When the SG stops rising between readings, that is pretty much it.

If the batteries are getting sulfated, you might need to discharge the bank (down towards 50% state of charge) and again recharge it to "full" (specific gravity readings). It can sometimes take several weeks to get the batteries sort of back inline (sulfation is not "fixable"--At best you are causing it to sluff off to the bottom of the cells).

Also, monitor water usage in your battery bank... If you are refilling once every month or more often, you are probably over charging.

If you are never refilling, or every 6+ months, probably under charging. Nominally having to put some water back in every two months is good (there are some low maintenance batteries that use dramatically less water). Never let the plates get exposed to air--Will damage/ruin cell/battery.

-Bill

Re: Unable to fully recharge 12 volt system

OK--We have some good information here we can start with.

First, your 5.5 kWH per day is not a "small system"--It is pretty good sized. A small system (minimum cabin, no fridge) is probably on the order of 1 kWH per day.

A full off grid, very energy efficient home is around 3.3 kWH per day (fridge, well pump, lights, laptop computer, washing machine, efficient TV, etc.).

So--First the battery bank and genset/AC battery charger.

Chokosna Cabin wrote: »

Thanks for both replies, seeing my SC was around 1.17 I am going to start by equalizing over a long period. As for my system: the Batteries are Trojen L16 RE 2V with a 20 hour rating of 1100AH. My generator is a "Chang Chai" diesel supposedly able to generate 7K. It is on its way out and I am replacing with a Honda outfitted for propane. The inverter is doing the charging. It can transfer up to 160 amps DC, which should fulfill the 5-13% IF I am comprehending that correctly.

Your cells would like between 5% to 13% rate of charge--And with an AC battery charger, you can get up to 20-25% rate of charge.

Some of your tradeoffs... The batteries probably would do best around 10-13% rate of charge. 20-25% is OK, but you need to monitor bank temperature (so batteries do not overheat with high charge rates).

On generator side, a diesel genset usually wants 40-60% of rated minimum load to avoid "wet stacking", carbonizing, or cylinder glazing from low operating loads/temperatures.

And general gasoline/propane gensets should run around 50% or higher rated load for better fuel efficiency. Running these types of gensets at 25% load (or less) can cut your fuel efficiency by 1/2 or worse.

So, the batteries:

• 1,100 AH * 5% rate of charge = 55 amps minimum
• 1,100 AH * 10% rate of charge = 110 amps nominal
• 1,100 AH * 13% rate of charge = 143 amps maximum without temp monitoring
• 1,100 AH * 20% rate of charge = 220 amps a lot of current from AC charger
• 1,100 AH * 25% rate of charge = 275 amps rough never to exceed (flooded cell)

Since 120 Amps looks real nice--The SW2512 would need to draw around (worst case guess):

• 120 amps * 14.7 volts charging * 1/0.80 charger eff * 1/0.65 power factor = 3,392 VA
• 3,392 VA / 0.80 generator derating from name plate = 4,240 VA genset name plate

So, the diesel should be able to run at full current fur the SW charger--And if you get a 4 kWatt or larger propane (which is derated from gasoline) genset you should be OK.

We have had some folks suggest that a gasoline genset may be easier to start/run in far northern conditions (propane and diesel need series heating to get started and fuel pressure up/keep from gelling)--But I am in California where I cannot keep my freezer at 0F--So, take my suggestions with a grain of salt here.

You are probably at the maximum you would want to wire a 12 volt battery bank+inverter+chargers... If you go larger (or for your next battery bank), you may want to look at smaller AH cells and a 24 or 48 volt battery bank to keep DC currents (and voltage drops) reasonable. And, yea, that will kill you as you are looking at new/different battery bank, AC inverter, etc.

The solar panels are a 12 volt set, I don't have the documentation near by, but believe they are made by kyocera. They haven't come into play recently due to very little sunlight. (in the last 3 days I recorded 9 ah) according to the controller they have produced up to 23 amps. S by my understanding the C40 controller shouldn't be an issue, since the panels are out of play? I set the Trace inverter for 10 hour equalize.

For the size system you have right now, the C40 and whatever solar panels you have right now--Is really too small to properly recharge the present battery bank without lots of generator run time. 5% is the minimum current we would recommend for charging a cycling battery bank. In summer with long summer sun, you might squeak by with less--But still not a great idea.

On my end I went through the work sheet and I am a relatively low user. 2 appliances, a freezer and a Toyo heater, the estimated use with "safety factor" was about 5500 watts per day. In general the usage meter on the Trace inverter is at 1 or 2 amps, with 3 or 4 being the high when the heater kicks on then it backs off.

5.5 kWatt is a fair amount of power--You can choose to run it all from solar, or break it into two pieces... One part from solar/battery bank (night, quiet time, low power system) and fire up the genset when you need more power. Or size the battery system to supply all needed power (more expensive, less generator run time/fuel costs).

Just to see what a "balanced" system might look like (choose 48 volt battery bus for this large of system):

• 5,500 Watt*Hours per day * 1/0.85 invtr eff * 2 days of no-sun * 1/0.50 max batt discharge = 539 AH @ 48 volts

That is about 2x larger battery bank as you have now (or 1,078 AH at 24 volt battery bank).

Using PV Watts for Gulkana Alaska (guessing), fixed array, tilted to 62 degrees from horizontal:

Month    Solar Radiation (kWh/m 2/day)
1      1.22     
2      2.84     
3      4.69     
4      5.76     
5      4.92     
6      4.96     
7      5.03     
8      4.61     
9      3.64     
10      2.55     
11      1.34     
12      0.81     
Year      3.53      

Toss the bottom four months, and we are looking at 2.84 hours of sun in February:

• 5,500 Watt*Hours per day * 1/0.52 end to end efficiency * 1/2.88 hours of sun = 3,673 Watt Array for "break even" February

And for a 539 AH @ 48 volt battery bank, the array needed would be:

• 539 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 2,065 watt array minimum
• 539 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 4,130 watt array nominal
• 539 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 5,369 watt array "cost effective maximum"

So, a suggested array would range from 3,673 to 5,369 watts, wiht ~4,130 Watt array being a healthy nominal size.

Water usage hasn't been an issue, the system has only been up a couple months. All terminals are cool and cables are tight. All I have at this point is the refractometer and hydrometer, will look into a meter when I have a chance, closest store (of any sort) is almost 200 miles.

I believe that Refractometers need calibration (you have some 1.265 s.g. electrolyte?). Both should be rinsed well with distilled water between uses. Hydrometers can build up a sticky residue inside if not rinsed out between uses.

I am wondering, in hindsight, if I would have been better off with 2 or 4 6v batteries with a lower capacity, therefore easier to charge? But, I have to live with what I have.

Look at my numbers and calculations... There is no right or wrong answer. Energy usage is a highly personal set of choices. But once you make those choices, building a "balanced" system to support those choices is critical to long term system success (and owner sanity).

For example, I did not look at your winter vs summer loads--If you have less loads in winter (no refrigerator/freezer or need engine block heaters in summer) vs summer (for example), it could change the system design requirements.

Do the paper designs first. You can figure out the pluses and minuses for each--And the associated costs.

Big battery systems are expensive. And if there is an Oops (something left on when you leave your home for a week) and kills the battery bank--You just have a 1/2 ton of scrap lead.

Just checked the SG, it has gone from 1.17 to 1.225, so some improvement.

Great news. Ideally, you want to charge the batteries until the s.g. stops rising. At that point, log the temperature corrected specific gravity for each cell. That will be your "new" 100% SOC.

Your thoughts/questions?

-Bill

Re: Unable to fully recharge 12 volt system

I don't know about the propane conversion, bu the the Honda EM4000SX was a very reliable/rugged 4kW genset and worked well in very cold winters with a 70 watt bulb in an outside small generator shed.

Choosing a good generator

Also the Champion gensets seem to run pretty well too (Costco down here sells one of them in the warehouse):

http://www.championpowerequipment.com/products/heavy-duty/

Personally, I am a big believer in getting a genset no bigger than the minimum needed to run your loads (plus a safety factor).

If you get a genset that is 2-4x larger than you need (for day to day), you can draw 2-4x more fuel per kWH.

In many cases, getting s second larger (cheaper?) genset to run shop tools and as a backup to the backup genset is not a bad idea either.

Regarding hydro--If you can do it--It will be a pretty near solution for you. Given that hydro runs 24x7 (when you have water), the actual peak power does not need to be too much. For a 3.3 kWH per day system:

• 3,300 WH per day * 1/0.80 batt eff * 1/0.85 inverter eff * 1/24 hours per day = 202 watt average Hydro output

Good Luck!
-Bill