battery choice

[pianotuna]

Hi,

I am in analysis paralysis.

I will be purchasing AGM jars.

Here are my two choices:

AGM L-16 Surrette 400 amp-hour six volt with 0.145 plates cost $520 plus tax and shipping Four are needed.

AGM group 27 but group 31 plates 120 amp-hours twelve volt with 0.118 plates cost $230 each plus tax and shipping. I have room for seven.

Charging sources are:

magnum inverter charger @ 125 amps max
progressive dynamics 40 amp
alternator
256 watts of solar with a blue sky 3024di controller.

Which would you choose?

Why?

[MEXICOWANDERER]

I can charge a flooded battery at 14.1 volts or 14.8. I can float it at 13.1 or 13.6, I can charge an AGM at 14.0 volts or 14.7.

The CHEMISTRY of various AGM batteries is identical. They all use pure lead positive plates with a bit of silver and perhaps calcium in the positive plates. Many high dollar AGM batteries have less AIR GAP SEPARATION within the cells, meaning impedance is lower, meaning higher CCA and higher charge AMPERAGE acceptance.

But wild claims of YOU GOTTA DO THIS and YOU GOTTA do that voltage-wise, are marketing ploys. In essence, B. S.

If it makes you feel better jumping through hoops, do it. If you spend money or tear your hair out trying to meet hairball sales pitches then being free and 21, go for it. The prime directive of sales pitches is AVOID APPEARING LIKE WE ARE A "ME TOO" COMPANY.

Senor PianoTuna, Rolls took a more conservative approach than did Concorde in regards to temperature/capacity derate. Sure, you and take whatever specs Rolls provides to the bank. I was not challenging your data but I should have asked the source of your fact in a different manner. Please excuse me.

Do Rolls and Surrette manufacture their own absorbed glass mat batteries?

[full_mosey]

EsoxLucius wrote:
I also think it unwise to make blanket statements regarding AGM charging. My AGM batteries require 14.7 V (77 degrees F) for bulk charging, suggesting the manufacturers specifications should be followed and AGM batteries can differ by manufacturer.

You're confusing bulk with absorption. Bulk is a fake stage where your charger is too weak to raise battery Volts to your 14.7V charging spec. That is when absorption begins. Fewer charger Amps result in longer bulk times.

Using temp comp charging, you could hook your battery to Hoover Dam's current so long as you maintain 14.7V. Bulk might take a nanosecond, after which 99% of the charging would be done during absorption.

IMHO and YMMV. 🙂
John

[EsoxLucius]

I also think it unwise to make blanket statements regarding AGM charging. My AGM batteries require 14.7 V (77 degrees F) for bulk charging, suggesting the manufacturers specifications should be followed and AGM batteries can differ by manufacturer.

[pianotuna]

Hi Mex,

The derating came from Surrette. I kinda sorta trust them.

[MEXICOWANDERER]

For required charging of absorbed glass mat, apply 14.4 volts corrected for temperature. Whatever the current ends up at is the correct amount. The current requirement suggests ("suggests"" has a specific meaning) that some minimum level of laminar plate/electrolyte stimulation is needed. When I get a chance I'll try and use some bamboo splinters and get an answer.

The 1.300 specific gravity used in mat electrolyte indicates the battery can withstand -60C temperature when fully charged. PT are you sure about the figure you expressed above regarding temperature de-rating? Is it for FLA or for 1.300 AGM?

[EsoxLucius]

Surrettes do not have a ten year warranty on mobile applications, it is five years. Ten year warranty applies to fixed applications.

[full_mosey]

PT;

If the worst case is when the bank would be at 65% capacity then 65% of 800Ah is 520Ah. Four 120Ah 12Vs inside at room temperature would provide 480AH.

This configuration gives you a 25% charge ratio with the Magnum alone. A smaller bank gives a shorter charge time which also saves fuel. Add 60A solar and you can bulk charge in the AM with the Magnum and then shut down the genny.

Life brings changes. I still buy green bananas, but I am not in the market for a 10yr battery bank.

HTH;
John

[jrnymn7]

If trying to minimize charge times, and if doing various dod cycles, the charger would have to be sized for the deepest discharges. So a 50% dod on a 400Ah bank would require 200a of charging. But if you never go below say 70%soc on a 400Ah bank, a 120a charger would suffice, and amps would taper from the beginning (instant Vabs charging).

As I've pointed out, a 1a/-1Ah charge rate is quite normal for abs/cv charging. The bank will take care of itself, charging amps wise. As soc rises, and battery acceptance drops, charging amps will naturally follow the banks lead. But to deliver less amps than the bank can accept, at any given moment, only serves to prolong charge times.

Of course, there is a limit as to how far to push things, and battery temps should indicate if the charge rate is too high.

[Ductape]

Unless I misread the Lifeline technical manual, high current charging is recommended when DOD exceeds 50%. Is that not correct?

IOW is it needed if doing 70-90 for instance.

[pianotuna]

Hi Land,

Thanks for the links.

[landyacht318]

I think lots of AGMs are tickled to death with low bulk current. If one is not gong to take advantage of their ability to accept huge currents, well there goes one of their major benefits.

I have a Northstar AGM group27 at 91 AH. It responds well to 40 amps from my MeanWell power supply. It does not really seem to like 200 watts of low and slow solar. Voltages under load after a solar only recharge sag noticeably in comparison to a MW 40 amp blast, and the rather impressive ability to crank my engine extremely swiftly fades with each solar only low and slow

Now, I never discharge it unless I can plug in the meanwell or have a good enough highway drive so the alternator can quench the thirsty devil.

I personally would not get AGMS for a solar only recharge application.

This guy knows his feces:
http://forums.sbo.sailboatowners.com/showthread.php?t=124973

[pianotuna]

hi John,

I'll be keeping my two bank configuration--so the Magnum will offer 125 amps @ 12 volts (nominal) into 400 amp-hours. I expect to not use 200 amp-hours very often.

I do know my flooded banks tied together last fall would draw 125 amps from the Magnum when it was being powered by the Yamaha sIEB 3000, while powering a pair of 1/2 size oil filled heaters.

full_mosey wrote:
275A of solar plus Magnum's 125A will get you up to 25% charge ratio.

HTH;
John

[pianotuna]

Hi,

I snowbird--but not in my RV. Therefore the RV has to endure -40 and 120 days of being in storage.

Heating from -40 to 0 C (32f) would consume a lot of energy.

jrnymn7 wrote:
PT, can't you put Lithium batts in a heated cabinet? That's my plan, eventually... replace the vent grill with an insulated panel, in winter, and heat either electrically or hydronically.

[full_mosey]

275A of solar plus Magnum's 125A will get you up to 25% charge ratio.

HTH;
John

[jrnymn7]

PT, can't you put Lithium batts in a heated cabinet? That's my plan, eventually... replace the vent grill with an insulated panel, in winter, and heat either electrically or hydronically.