Bulk charge current

[Riley5781]

ok, dumb question I know but I want to double check my understanding is correct.

My solar power system is using S-555 6 volt batteries wired in series for a 48 volt system.
the spec on these batteries for C20 rate is 428Ah.

I read that the Bulk charge current should be 10% to 20% of the C20 rate.
So does that mean that the Bulk charge current should be 42.8A to 84A?

My inverter generator can only bulk charge at about 38amps.... is that an going to create a problem with suffation?

I have about 3KW of panels and I reach full charge in a few hours no problem during the sunny days and I think it's charging about 40Amps as well when on solar.
I've been checking my specific gravity and it's been looking pretty good but just wondering if these low Bulk rates will be a problem.

[Sunking]

For a generator you want to charge at maximum charge rate to minimize fuel burn and charge time. You can size the solar to charge at C/10 but for the generator you want to charge at C/5 or as close as you can.

I read that the Bulk charge current should be 10% to 20% of the C20 rate.
So does that mean that the Bulk charge current should be 42.8A to 84A?

Correct. It can be expressed as a percentage as you used, or a fraction which is more common. C/10 = 10%, and C/5 = 20%. Take note the minimum rate is C/10 which means the minimum size panel wattage at 48 volts = 2100 watts.

Where C = the battery AH capacity, and the number is Hours.

Amp Hours = Amps x Hours
Hours = Amp Hours / Amps
Amps = Amp Hours / Hours

Simple 5th grade math. The generator is used for 2 things and a must have item.

1.To cover your butt during cloudy spells or else you go dark.
2. To equalize batteries as it can take up to 24 hours on a generator.

To EQ start the enerator a few hours before sunrise to do the Bulk and most of the Absorb phase, then let solar try to finish or restart the generator near sunset to finish. DO NOT PUT OFF EQ or else you will significantly shorten battery life. Additionally use your hydrometer to set your controller voltage. Near the end of the day, check specific Gravity. If low raise the charge voltage.

[Riley5781]

Thanks Sunking.
I can only squeeze about 3.2KW out of my older Onan but I'm attached to it.. so will live with it for now.

What's a good rule of thumb for EQ? Should I not worry about running EQ periods for 4 or 5 hours or more (seems long compared to defaults ect) ?

Keep running EQ until all the batteries are at/near max?

I guess that's why such a long EQ period is needed.

[Sunking]

Thanks Sunking.
I can only squeeze about 3.2KW out of my older Onan but I'm attached to it.. so will live with it for now.

What's a good rule of thumb for EQ? Should I not worry about running EQ periods for 4 or 5 hours or more (seems long compared to defaults ect) ?

Keep running EQ until all the batteries are at/near max?

I guess that's why such a long EQ period is needed.

EQ and charging batteries are not timed events. You EQ batteries until the SG stops rising for a period of 1 hours. Only EQ when required, Like I said EQ can take up to 24 hours after the batteries have been fully charge. Read the Rolls manual please.

[Riley5781]

Ok, got it. Thanks.
Some how I missed the point to continue EQ until SG stops rising.

[Sunking]

Ok, got it. Thanks.
Some how I missed the point to continue EQ until SG stops rising.

There you go, that is the trick. Solar is not really capable of an EQ charge, thus one reason why a generator is a must. Try starting the genny a few hours before sunrise to do get a full charge and jump start on EQ. Once you have good sun use solar for as long as needed and if not done in late afternoon start genny back up and finish. DO NOT STOP until they are EQ'ed or you just wasted your time, fuel, and undue stress on the batteries.


Like I said DO NOT EQ until your hydrometer says it is needed. Be sure you know the difference between undercharged and unbalanced. With most solar users, you never reach full charge and thus need the generator every few days to just get back to 100%. Chronic undercharging is the number 1 killer of Pb batteries. Anything less than 100% is undercharged.

Find the cell that always seem to have the highest and lowest SG. When they differ more than .0030 it is time to EQ.

[Riley5781]

Sounds good and that's exactly what I did today.
Now when I come back to the cabin, I need to make sure I am getting to 100% after the daily charge.
Right now I have the Bulk and Absorb set at 60.0V as per manual and was planning to continue to increase the absorb time until I get to 100% on a good day.
That being said, do you suggest I goi higher on Bulk & Absorb voltage? (above the 60V in the manual?).

[littleharbor]

Which manual are you referring to? Your voltage settings should be what your battery Mfg. recommends.

[Sunking]

Now when I come back to the cabin, I need to make sure I am getting to 100% after the daily charge.


Right now I have the Bulk and Absorb set at 60.0V as per manual and was planning to continue to increase the absorb time until I get to 100% on a good day.
That being said, do you suggest I goi higher on Bulk & Absorb voltage? (above the 60V in the manual?).

Hold the bus. Cabin suggest part time use. If it was daily use then YES raise the voltage. Part Time no. Real simple the batteries will saturate in the time you are not there and fully charge before you return.

[Riley5781]

Well the wife is there 7 days a week.... and using the system... I am just a weekend husband and take care of her and the batteries only on the weekend.

LittleHarbor & regarding manual - yes the battery manual.

When I am there this Friday, I will check the SG after a good sunny day and if not at 100%, I will raise the voltage slightly.
The battery manual states 60V for bulk and absorb so I'm a little nervous to go above that......

then when my wife leaves later this month, I need to remember to turn it back down.....

[Sunking]

When I am there this Friday, I will check the SG after a good sunny day and if not at 100%, I will raise the voltage slightly.
The battery manual states 60V for bulk and absorb so I'm a little nervous to go above that.......

I Understand being nervous, perfectly acceptable. But here is the deal, the book assumes you are using commercial AC power and Charger with unlimited time and power. You have neither luxury with with solar. Pb batteries are a chemical process and lead is dense. It takes time for the chemical reaction to reach the deepest parts of the lead from the surface. Even a commercial 3-stage charger is not finished when it switches to float. It can only measure the surface charge. The differences is with a AC charger even when it switches to float, the battery is still charging and after 4 to 6 hours the batteries fully saturate to deep inside the lead plates and grids. Solar cannot do that effectively and is compounded by undersized panel wattage. So with Solar turn up the voltages to speed things up as much as possible with the very limited amount of time and power you have available.

Just keep in mind that turning up the voltage may not work for the simple fact if you are using more than the system can replace. It can really show up in winter months. Just do not go above 2.6 vpc. If 2.6 does not get you to 100%, back off to 60 volts and get a generator to fully charge every few days.

Does that help?

Well the wife is there 7 days a week.... and using the system... I am just a weekend husband and take care of her only on the weekend.

I did that with my first wife decades ago when I had to work on the road a lot and in the Guard . I thought that was working out OK till I found out she had sex every night rather I was there or not. Being 20/30 something sure is fun, but we are awful dumb and ignorant during those years.

[Riley5781]

Thanks for the advice Sunking (both kinds ).
This time of the year, I have a lot of time to charge... the system is kicking into Float at like 1:00pm and I have another 3 hours of full sun.
So perhaps I should leave Bulk and Absorb at 60V and just try lengthing the time of Absorb?
then later in the summer and fall start to push up the voltage...

[Sunking]

Thanks for the advice Sunking (both kinds )..
So perhaps I should leave Bulk and Absorb at 60V and just try lengthing the time of Absorb?
then later in the summer and fall start to push up the voltage...

Good place to start and better than doing nothing. Like making a million dollars, you gotta do something different and start somewhere because siting on your but gets you no where except on welfare voting for democrats to keep the checks rolling in.

[Matrix]

Sunking, why is 2.6vpc the limit? I have a 2500 watt array and regularly use 2.625 to reach fully soaked max rise SG. I could also turn the absorb volts down and set absorb to 10 hours so the system stays in absorb all day and use lower absorb volts. What is the trade off?

[Riley5781]

Sunking, why is 2.6vpc the limit? I have a 2500 watt array and regularly use 2.625 to reach fully soaked max rise SG. I could also turn the absorb volts down and set absorb to 10 hours so the system stays in absorb all day and use lower absorb volts. What is the trade off?

I don't know much and a newbie but 2.625 is very close to what my battery manufacturer states as the EQ voltage. Seems to me that's like doing a EQ everyday. Wouldn't that be really hard on the battery?