Max Charging Current of typical GC2 battery

[brulaz]

Say the GC2 battery bank has been drawn down to 25-50%, what will be the max current they will initially accept?

For sure it's greater than the ~24A max my solar charger has reported as that was limited by the solar panel outputs.

[brulaz]

BFL13 wrote:

...
Meanwhile--yes, on solar it is not always possible to get to full each day. You can go days and days with an incomplete recharge, and get sulfated. Later on, when the sun shines and you can get to full, it does not mean you are out of the woods.
...

Yes equalization is important after a couple of weeks of partial charge. One of the reasons I've been avoiding AGM, as they seem more difficult to recondition afterwards. Not sure how long these batts will last like this, but we're only snow birds, not full-timers, and they may well get stolen before they die anyway (like happened last winter in storage).

And Berries? About the only thing I miss about the Wet coast are the Salmon berries and fish. Certainly don't miss the fires further inland where it's not wet.

We've had a wet year here in Central-North Ontario, but it's great for the berries, and no forest fires, thank gawd. Not so good for my solar charging though.

[MEXICOWANDERER]

North Pacific coast. Where there is fog the berries grow. Blueberries like it a little warmer. Raspberries are the most delicate. Now I have to go to Costco when I go north and buy an assortment for my toast.

[MrWizard]

i love black berries and rasberries

[MEXICOWANDERER]

Ooooo I could take that one and go a looooong way - but I'll be nice.

[mike-s]

MEXICOWANDERER wrote:
I went to Hornby Island in August BFL. Thick Pendleton Shirt all day, jacket in the morning, Flowing water was fit for penguins. What size wet suit did you use at "The Lake"?

Skipping your meds isn't good.

[MEXICOWANDERER]

Constant voltage charging at 14.8 volts is the highest rate I would recommend. And you'd better believe there is a significant difference between 14.4 and 14.8 voltage set points in relationship to overall charge time. Yes, between 1.260 and 1.280 charge acceptance is much lower. but then a Delta T (differential amperage) needs to be clearly stated between the four tenths volts spread. It is anything but insignificant.

But then the issue will refocus on feasibility of obtaining a device that can support fill voltage in constant voltage mode throughout the procedure.

Again the entire subject of constant voltage charging is irrelevant if the device is not subject to a long term off-grid heavily cycled use.

I went to Hornby Island in August BFL. Thick Pendleton Shirt all day, jacket in the morning, Flowing water was fit for penguins. What size wet suit did you use at "The Lake"?

Yer gonna get Eee-clip-sed soon. That otter drop yer banana boat tropical clime another 2c. You can watch an Al Gore, movie to help ease the shivers.

Actually I am quite envious of the Blue, black, rasp, and huckleberries in your neck of the woods.

[BFL13]

OldSmokey wrote:
I'll give you a pro tip here and it's for Trojan T105's
but is applicable to other GC2's if used with care..

it's all about max heat capacity, for a T105 the best figure I would use is 0.05 watts per Ah. a T105 has an internal resistance of 0.003 Ohms . so that's 0.001 Ohms per 2 volt cell.

The max thermal charge limit is square root of (.05 x 225Ah) / .001 = 106 amps. yes.. you can charge a T105 at this rate..
this is approx c/2

I wouldn't advise you do this often, but it can be done.

Somebody a few years back posted that he was talking to a Trojan tech support guy about all this, and he said the Trojans could accept any amount of amps at first.

The whole thing is based on the simple fact that the acceptance rate at any SOC depends on the voltage. If you are at a lower SOC then at any same voltage the batt will accept more amps than at a higher SOC. (which is why amps taper in the Absorption Stage). For the same SOC, jack up the voltage, and it will accept more amps.

If you hit the batt with a huge amps rate, the voltage will spike and amps will immediately taper to what the battery will accept.

You can see in my ugly graph above how that works where there is a diminishing returns in going to higher amps for how long it takes to do a 50-90. Even if the battery will accept way more amps, you might only save 10 minutes of generator time going to a 70 vs a 55, so why pay way more for a way higher amp charger and then need a way higher wattage generator to run that higher amp charger, just to save 10 minutes of gen time? OTOH there is a big diff in time between 55 and 35 amps on 220AH.

(You double the times for doubling the AH at the same amps, BUT you do not halve the charging time on the same AH by doubling the charging amps.)

You have to do a proper analysis of the whole picture to decide on your best bet for a set up for how you (not some other guy) camps.

Meanwhile--yes, on solar it is not always possible to get to full each day. You can go days and days with an incomplete recharge, and get sulfated. Later on, when the sun shines and you can get to full, it does not mean you are out of the woods.

You still need to desulfate from all that time earlier on. You can avoid a lot of that if the weather forecast is any good, by doing a bit of gen charging in the morning so there is time for the solar to catch up that same day and get it done.

Above, I described winter camping, but here in August on solar it is way different. Gottaluvit! Who cares about batteries? It is all about corn on the cob, BBQ steaks, and picking blackberries for dessert (after a swim up at the lake of course) 🙂

[OldSmokey]

I'll give you a pro tip here and it's for Trojan T105's
but is applicable to other GC2's if used with care..

it's all about max heat capacity, for a T105 the best figure I would use is 0.05 watts per Ah. a T105 has an internal resistance of 0.003 Ohms . so that's 0.001 Ohms per 2 volt cell.

The max thermal charge limit is square root of (.05 x 225Ah) / .001 = 106 amps. yes.. you can charge a T105 at this rate..
this is approx c/2

I wouldn't advise you do this often, but it can be done.

[MrWizard]

i posted this last night in my AGM battery thread
take note these are Surplus server batteries removed from routine service
they are going on month 14 of daily use & recharge, they are at 400+ cycles

just a quick note

70 minutes after stopping all charging
down 15 ampHr aka 3AH per battery
load 10amps , 2amp per battery
battery SOC 97.7%
battery voltage 13.00v

fully charging batteries everyday of use, makes a significant difference
in batteries maintaining voltage

now at 4:45 am this morning (restless night)
4 amp load
91.0% SOC
12.87v

i routinely see over C 10% charge starting and see 1/2% when done charging
yes i'm using more gas than i used too, i need the genny for A/C anyways
winter time will see some reduction in generator hours
this set of batteries has never seen 50% SOC from my use
it does see full recharge almost every single day

i'm not a weekend camper, we are full time
many of you will never see 400 cycles on your batteries, before you replace them or the RV

getting 5years by going weekend camping twice a month is ONLY 120 cycles
that should be an easy life for ANY battery, but many die with only 2yrs of use

Battery Mantra "charge charge charge"

[brulaz]

MEXICOWANDERER wrote:

...
What DOES hurt batteries sir, is to constantly undercharge them for weeks or months at the stretch. They will sulfate, and few people want to learn how to never mind actually equalize a battery. That ends up killing a battery.
...

Sadly this is what we often do with only solar and no generator.

So far only 2 weeks of under-charging max though, with a 32V equalization afterwards. Truck charging as we travel between boondocking sites should help.

[BFL13]

The usual 10% charging rate recommendations are for longer battery life as measured in number of cycles.

Meanwhile an RVer has to meet camping situations and get it done.

My requirement is to do 50-90s in two hours or a few minutes more (generator hours as set by the campground) if I cheat, and that 40% recharge has to be enough AHs to get me by till the next recharge.

I know I use about 70AH a day in summer plus at least another 70 in winter, so to get by in winter using 140AH where that is 40%, that means I need a bank with 350AH or more. So that is four batteries at 440AH (but that is at 25C and this is winter at 5C, so knock 10-15% off that 440 and you get say 380AH and your 50-90 is now about 152AH, which is enough to get by.

OK so how to replace 152AH in two hours? See ugly graph where the 70amps did it on a 220AH bank. This is a 380AH bank so 380/220 x 70 = 121 amps.

I need a generator that can run a charger doing at least 121 amps and a 121 amp charger. Turns out my 3000w Honda can handle 130amps worth of non-PF corrected chargers before popping a breaker. My collection of Vector chargers could do 130a.

Since then I have gone over to PowerMax adjustable converters, and their 100 amper is PF corrected. The Honda can run it and a PM3-55 amper without popping its breaker for a total of 155 amps initial charge. I crank the voltage to 15.2v at 5C which is the same as 14.8v at 25C. (Good luck with your 14.4v converter 😞 )

Target has been met and then some. Which is good because the furnace can use over 100AH a night and it is dark longer and so forth, so it can be 200AH a day --BTDT several times.

So how to get by really? Going to need more battery bank and cheat some on the two hours even at that 155 amps. But no problem--nobody else is nearby in the park and the rangers are all hiding inside where it is warm, and don't care about your generator, so you can do it! 🙂

Just to complete the math on that-- 200AH is 40% so 100% is 500AH needed where that is maybe 85% in the cold from a rated bank of 588AH so you need say four T-1275s at 150 each, or six T-105s at 225 x 3 = 675.

So that all works until you get AGMs rated at 100AH each and it says do not recharge at more than 27 amps per battery!!!! Oops, now what?

600AH minimum needed so that is six of those 100AH AGMs and six x 27 is 162 amps. Saved! 155 is my max with the Honda and the two chargers. But it will take a bit longer than the two hours to complete the 50-90, more like an extra half hour. So cheat! Do it when the rangers are out there with their chain saws going and they won't notice your Honda at all. 🙂

Also keep the AGMs inside your rig where it is nice and warm and gain 10-15% in AH capacity (but do not overcharge them so badly that they vent!--ie, do not go over that 27a per 100AH limit in the spec--unless your AGMs specify they can do more like some can)

So just get it done and if the batteries only last six years doing that instead of twelve by following the 10% charging rate recommended, too bad. You want to go camping or not?

[wa8yxm]

Different manufacturers give diffrent max charge rates but for the GC-2 with a 110 Amp Hour capacity (C/20 rate) Xantrex recommends 33 amps max or 30% C-20

Lifeline on the other hand.. Suggests more than that for their AGM batteries.. ONLY LIFELINE.. and for GEL types. (not recommended I"d be surprised if you could find one) 20%

[MEXICOWANDERER]

Note that manufacturers recommend "limiting the charge current. Trojan says 3-5% of C20 (so about 11A for a 12V pair of GC2). US Battery says 10% of C20, Rolls and Crown say 10-20%"

Fifteen years ago my cardiologist wanted me running a half mile, doing a half hour of calisthenics daily and eating a near vegan diet. Near the same age as me.

Next month I turn 71 - he's dead.

I've gone over this a hundred times. Engineers have demands put upon them by management to make their product look as good as possible. Even if it means having the customer acting stupid to gain 3% in lifespan.

Trojan has changed their GC charging formula three times in the last seven years. Same battery, same plates, same paste, same electrolyte density. Global warming? Lost the Gulf Stream?, Magnetic Pole Shift? Earth rotating backwards? No, merely a new generation of engineers.

I have voltage saturated charging flooded batteries for over forty years, and that's how I life cycled tested over a thousand samples.

The key is to reduce charging voltage drastically if electrolyte temperature reaches 45c and cease charging altogether at 50c. This is damned hard to reach unless outside air temperature is extremely high to begin with.

What DOES hurt batteries sir, is to constantly undercharge them for weeks or months at the stretch. They will sulfate, and few people want to learn how to never mind actually equalize a battery. That ends up killing a battery. Like my cardiologist who was a kind, amiable, misinformed boob. Last week I had a hospital stay full radionucleide, sonogram stress test performed. That cardiologist reported "You have the heart muscle health of a 40-year old". But awful nerve impulse control. To prevent total A/V block they stuffed a dual node pacemaker in me.

Of course, for some these facts will enter one eyeball go onto a four lane highway and fall out an ear. I do not offer spuriously contrived advice. Many cyclable batteries survived hundreds of 5% amp hour total, constant discharge until 0.0 volts was reached whereupon full vAbs 14.8 volts was applied for a pre calculated number of minutes whereupon resumption of discharge was re-initiated. A very rude, a most relevant way to separate battery manufacturing quality levels. I tested engine starting batteries the same way. Southern California Edison loved me. Rank & File staff engineering wogs hated and feared me. I reveled in it.

So forgive me if I seem abrupt. Old antagonisms die hard. I dislike BS rote from professionals. I can appreciate an engineer's desire for his pride and joy to reside in battery heaven with 22 virgins and endless bowls of dates and goat stew - but life does not work that way. Generator run time rears it's ugly head. And my Rolls bank is nearing the quarter century mark.

[red31]

Trojan, up to 20%, when queried no limit but temp and $
http://www.trojanbattery.com/Tech-Support/FAQ/Charging.aspx
"What size charger should I buy?
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.

Example: A good charging rate for a battery with a 20-hr capacity of 225 amp-hr is about 22 to 29 amps. You can of course go slightly higher or lower depending on what is available on the market."