Achieving full charge with solar system

4 Golf Cart batteries will have an AH rating of anywhere from 420 to 480 AH. A 20 A charger will take a long time to recharge from 50%

Here is a paragraph shamelessly copied from the Trojan web site:

"A properly sized charger takes into account battery capacity and the time interval between charges. In applications where cycling is infrequent, such as weekend RV users, or infrequent or seasonal trolling motor usage, a charger with an output current rating between 10 and 13% of the battery's rated 20-hour capacity will suffice. In applications where battery recharge must be accomplished within 8 to 10 hours, a three stage, automatic charger, rated at 20% of the battery capacity, may be required."

(Highlight is mine)

According to the above you should be charging with at least a 45 Amp charger.

My Xantrex Prosine 2.0 (2 KW pure sinewave inverter with a 100A charger) is set to charge at to 96 Amps (20% of AH rating).

My 420 AH of solar (charges at a max of just over 20A) needs a boost every 4 or 5 days so that is when I run the Xantrex charger either overnight or a at least few hours in the morning before the sun gets over the hill. This allows the solar to get the batteries up to or very near 100%. I was seriously undercharging my previous set of group 24 batteries by not getting the Xantrex on often enough.

(Response to an often asked question: I run on solar when possible to reduce electricity costs which are very high in Mexico.)

If any of the real experts (from whom I have learned a lot I think) wish to contradict or correct me I'm always ready to learn!)

What are you considering 100% full?

Do you think that charging to the point that not one amp will go into the battery means that it is full? It will never really do that.

With 4 golf cart batteries, you could be charging at 14.4 volts at 10 amps, and just boiling away water from batteries that are completely full.

I never really liked charging by golf cart batteries to more than 13.8 volts. After reaching that voltage and amperage below 15 amps, the battery is very close to full, and just boiling a lot of water. When my 70 amp charger is charging at 45 + amps, the battery gets warm. I know that is not 'good' for them. Usually I would restrict amperage to less than 50% of my 70 amp capacity, both to keep the cooling fan off, and keep the battery cooler.

I have a E-Meter, and it carefully measures the amperage going out of the battery, and gives a reading like -120 AH when I have been running the TV a lot at night. Then I would run the generator for about 1/2 hour at breakfast, and shut it off. My 400 watt solar system could finish the charge by 5 pm.

Normally my e-meter reads about -10 amps say at 3 pm, and might read +10 to +15 amps when it is finished charging. This means that more than 15 amps went back into the battery bank, more than came out. This makes up for the in-efficiencies of the battery chemicals.

This place had some 140 watt panels for $229 each a few weeks ago. SunElec.com

Have fun camping!

Fred.

MEXICOWANDERER wrote:
"Smart" anything is like allowing the government to think for you. I've got plans to place the "smart" out of circuit from 90% SOC upwards and hammer the batteries direct from the panels -time limited by utilizing a spring wound timer-

Is there a difference between spring wound and electronic timers?

"Smart" anything is like allowing the government to think for you. I've got plans to place the "smart" out of circuit from 90% SOC upwards and hammer the batteries direct from the panels -time limited by utilizing a spring wound timer-

Sometimes I have a "conservative day" allowing the batteries their complete fill by starting out at dawn with 80%+ state of charge then manipulating manual controls to afford a top charge. A lot of homes down here have manually controlled panels to allow batteries to fill completely, after the smart controller goes on strike.

Do not ever try to pass the charging from a charger or converter through a solar controller!!! (The controller works by shorting the solar panel, which is fine, but your charger or converter won't like being shorted! )

Getting to a true full is just a matter of time and amps to the battery at a high enough voltage to create "gassing" ( mid-14s)

Solar can do it but often runs out of daytime too soon. The charger can do it on shore power but on generator now it runs out of time too. the last 10% of the recharge takes hours and hours.

If you get the math right for your situation, you can run the charger first to get the batts up quicker than the solar can early in the day and then let the solar finish the recharge taking all the rest of the daytime. Problem is you also are camping, so that means getting the batts full before say 6pm when you start using the 12v to make supper and then watch a movie say.

moved from Technology corner

Are you charging at 14.8 volts?
I assume so, default output of the charger
How many hours in absorption?
Can’t tell, no display.
If you get down to 2 or 3 amps they are as full as they are going to get.
I have used the Xantrex and a cheesey Canadian Tire automatic charger, both showing “full”.
The MPPT external meter shows up to 90% and then falls back to 60 – 70% within an hour of disconnecting the charger.
I also have a 500amp shunt and digital meter, shows same voltages.
Are you verifying 100% with a quality hydrometer?
Going to get a hydrometer after work!

Are you charging at 14.8 volts? How many hours in absorption?
If you get down to 2 or 3 amps they are as full as they are going to get.
Are you verifying 100% with a quality hydrometer?

Getting to a full 100% charge is harder to do than most folks think... The only real way to know is to do the HYDROMETER test on the battery fluids.

This is what PROGRESSIVE Dynamics states in their operating manual on how long it takes to charge a battery using the DC VOLTAGEs listed below: "Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.

14.4-VOLTS(Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.

13.6-VOLTS(Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.

13.2-VOLTS(Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge." This is based on having 17-20AMPS DC current available for each battery in your battery bank...

NOTE That Progressive Dynamics doesn't even list using DC Charge Voltages around the 12.0VC range as this would take alot more than 100 hours to achieve a 90% or 100% charge state.

Your typical 120WATT SOLAR panels only produce 5-6AMPS DC current so you will expect it will be many hours of being charged to reach 100% charge state. The typical HIGH SUN DAY is probably only 7-8 hours of high sun...

Battery Science states that a single deep cycle battery will want to use between 17-20AMPS of DC current when hit with 14.4VDC. Since the typical solar panel only produces 5-6AMPS you can see that a very long time will be needed for a single battery to reach the 100% charge state.

Just some of my thoughts here... I am just now considering getting into some solar panels for my off-road POPUP trailer battery setup. I can achieve the 90% charge state is a three to four hour generator run time using my PD9260C converter/charger being run by my generator when camping off the power grid. It would take around 12-14 hours of generator run time to achieve the 100% charge state for my battery bank.

I most often am not allowed to run my generator that long due to generator run time restrictions where I usually camp so the solar panels will really help me out here if I am staying for a long period of time at the camping location.

Roy Ken