Mixed battery form in seperate banks

Re: Mixed battery form in seperate banks

By the way, how are you monitoring your battery bank... Are you using a hydrometer (with temperature correction--if needed)--assuming flooded cell. Do you have some form of battery monitor?

I really like a Battery Monitor... They are not perfect--but they do a very good job of giving you the equivalent of a fuel gauge for your gas tank... You can do your generator management by looking at the gauge. Something along the lines of:

• Hit 75% state of charge--start genset next morning if no sun in forecast.
• Hit 50% state of charge--start genset
• Turn off genset when state of charge >80-90% (really when charging starts to taper off--probably below 50% of max charging current--saves genset fuel/runtime costs)

And review your generator/battery charger sizing and usage... L16H battery around 420 AH at 6 volts... You have 6 strings x 4 per string for 24 volts @ 2,520 AH total.

For solar panels--we start with a rule of thumb of 5% to 13% of 20 Hour battery bank capacity. Below 5%, it is difficult to get the batteries properly recharged (without using a genset). Above 13% -- becomes a waste of solar panels--And is the "average" maximum recommended charging current for many flooded cell batteries (can overheat with more current).

You have 18x175 watts panels--your maximum charging current roughly is:

• 18x175 watts * 1/29 volts charging * 0.77 overall efficiency derating = 84 amps average peak

Relative to your battery bank:

• 84 amps / 2,520 AH bank = 0.033 = 3% rate of charge

You could easily double or triple the amount of solar panels for your current bank size... You have about the maximum battery bank that your current solar system could support anyway... A larger bank is really not warranted right now (based on current solar array)--assuming no stupid math/post reading errors :roll:.

Double checking battery bank size using our 3 day no sun, 50% maximum discharge level (for longer life). Assume 6kWh per day, 85% inverter efficiency, 24 volt bank:

• 6,000 Watts * 1/24 volts * 1/0.85 * 3 days * 1/0.50 = 1,765 AH at 24 volts

So--using our battery sizing rule of thumb--your bank is plenty large enough.

Now, lets look at your genset sizing... For a generator based battery charger--they should be around 5% to 30%--So, for your bank:

• 2,520 AH * 0.05 = 126 amps minimum useful @ 29 volts
• 2,520 AH * 0.13 = 328 amps recommended maximum useful @ 29 volts
• 2,520 AH * 0.30 = 756 amps maximum useful @ 29 volts

So, for fuel efficient loads on your gensets--your battery chargers ratings should be somewhere between:

• 126 amps * 29 volts * 1/0.80 eff batt charger = 4,600 watts
• 328 amps * 29 volts * 1/0.80 eff batt charger = 11,890 watts
• 756 amps * 29 volts * 1/0.80 eff batt charger =27,400 watts

You have a 20 HP / 12 kW diesel with a 6kW transformer (for 120 VAC). Since you should run your diesel at 50-75% rated load--the minimum battery charger load ideally for your genset would be:

• 12 kW * 50% = 6kW minimum battery charger load
• 6,000 Watt * 80% charger eff * 1/29 volts charging = 166 amp minimum charger at 24 volts

So--if you can run your genset most of the time pumping > 166 amps (approximate)--you should be minimizing runtime and fuel usage per charging cycle.

You could use a smaller battery charger--but the smaller you go, the more fuel you use and longer runtime to recharge your battery bank.

Of course, you can use the small Honda with an appropriately sized charge controller (400 watts - 1,600 watt load)--for reasonably fuel efficient recharging--but it will take a lot of hours to move the bank's state of charge an appreciable amount. For maximum power output from the eu2000i--look for a Power Factor Corrected power supply (PFC allows you to more efficiently use a smaller genset--It is the difference between VA (volt*amps) vs Watt ratings).

-Bill

Re: Mixed battery form in seperate banks

audredger,

Or stick around and let us know how things work out with the larger AC charger, more panels, and if you decide to try a Battery Monitor.

If things work out--you may be able to cut your fuel use and runtime to a 1/2 to 1/4 of what you are doing now! (crossing fingers)

By the way, are you running both the Xantex SW and the Quickcharge at the same time on your diesel set?

And then, you can be one of the folks that answer the questions for the next person such as:

Here is the rub: We will often get 4-5 days in a row (Winter) with out significant sun. Trying to limit the batteries to only 20% discharge, I only have 1.75 days of backup! I need more storage!

:cool:;):D

Bill