Bulk and float on 6v golf cart batteries

[WU9B]

I have just connected four 50 watt panels (approximately 18V - 3 Amp) to a Xantrex C40 Charge Controller and in turn to two 6V 220AH golf cart batteries in series (Interstate batteries made by Johnson Controls). The batteries gave me 12.6V when I brought them home from the store and after being on the charge controller all day they are at 12.6V still which sounds OK to this newbie. I have had little opportunity to put any kind of a load on the batteries yet as they are brand new.

My question however is about the proper Bulk and Float voltage settings on the charge controller. The manual suggests 14.6V Bulk and 13.4V Float for Deep-Cycle - Liquid Electrolyte Lead batteries.

The charge controller manual states that the LED will stay on without blinking if the batteries are fully charged and the LED blink slowly indicating that the batteries are not fully charged. I am guessing that behavior is based on my Bulk and Float settings as suggested. Ny charge controller suggests to me that the batteries are not fully charged yet they are sitting at 12.6V.

I am looking for a reality check. Are my settings correct? Don't want to damage my new batteries and hopefully I can have them for a several years of service.

We newbies appreciate the advice of those in the know and thanks in advance for any feedback.

[Sunking]

Greetings this is Kilo Foxtrot 5 Lima Joliet Whiskey... I can straighten you out and help.

Ok for voltage settings on a solar system Set Bulk = Absorb = 14.8 volts, and float for 13.2 volts for a GC2 battery.The reason Bulk and absorb are set to equal is there is not enough Sun Hours in a day to cycle through both modes. Bulk is a constant current mode, and Absord is a constant Voltage mode with current taper. When you set Bulk and Absord to equal values forces the controller to stay in constant current mode until it reach 14.8 volts or 100% fully charged. In otherwords it gets there much faster in about half the time. A full Bulk Absorb can take up to 12 hours, and there are no such thing as a 12 Sun Hour day, 4 is average.

Float mode is just a constant voltage charge to overcome the self discharge rate of batteries and holds them at 100%.

However you will not measure 14.8 or 13.2 volts on a fully charged battery at night. The only time you will ever see it is during daylight when there is an active charge going to the batteries. At night batteries on solar are not being charged. What I am driving at here is what is called State Of Charge or SOC for short. SOC is a voltage measurement of a battery that has no charge or discharge current. In other words disconnected just sitting there with an open circuit that has been rested for a few hours to bleed off surface charges. A 12 volt battery that is 100% charged will measure 12.6 volts. That is what you are seeing at night.

Here is a reference you need to know and understand. Various voltages and SOC for 12 volt batteries.

100% = 12.6 volts
75% = 12.4 volts
50% = 12.2 Never ever allow the battery to go below 50%
25% = 12.0 volts. Major unrepairable damage and loss of capacity.
0% = 11.9 volts = Toast throw battery away it is done because you destroyed it.

Now with that said you cannot determine the true SOC of the battery while it is either charging or discharging because of the batteries internal resistance. Only after it has been rested for a few hours.

Finally SOC is not real accurate. The only way to accurately determine a battery SOC is with a temperature corrected specific gravity.

73's to you.

[Mike90250]

.....
25% = 12.0 volts. Major unrepairable damage and loss of capacity.
0% = 11.9 volts = Toast throw battery away it is done because you destroyed it.....

Well, it might last you a week while you shop for replacements.. And you usually get the core refund for all the lead.

[Sunking]

Well, it might last you a week while you shop for replacements.. And you usually get the core refund for all the lead.

Yeah I know but more dramatic and gets the point across my way.

The real point is the static SOC voltages are pretty meaningless on a active system. You and I both now we can take a brand new battery that is 100% charged up in great condition, connect a load to it and it will drop to 10 volts instantly. If an untrained eye were to witness that would conclude the battery is bad when it is not. When the real reason is you put more load on the battery that it can handle. You know these guys who use a marine 12 volt battery with a 1000 watt inverter using a microwave oven.

[WU9B]

Sunking,

Thanks so much for the explanation. I am using 14.8V for the Bulk a setting now. No where in the Trace/Xantrex owners manual is the word "absorb" used, however. I have the float setting at 13.2 V per your recommendation and all appears to be in fine order. The charge controller is showing that the batteries are fully charged so I will go ahead and hook up all of my accessories as well and see how it all goes. This has been a great learning experience.

73, Steve WU9B

[Sunking]

Glad I could be of some help Steve. Just be aware not to drain the batteries more than 50%. Also get the batteries recharged back to full ASAP. Leaving LA batteries in a discharged state accelerates aging via sulfation.

[NEOH]

Greetings this is Kilo Foxtrot 5 Lima Joliet Whiskey... I can straighten you out and help.

Ok for voltage settings on a solar system Set Bulk = Absorb = 14.8 volts, and float for 13.2 volts for a GC2 battery.The reason Bulk and absorb are set to equal is there is not enough Sun Hours in a day to cycle through both modes. Bulk is a constant current mode, and Absord is a constant Voltage mode with current taper. When you set Bulk and Absord to equal values forces the controller to stay in constant current mode until it reach 14.8 volts or 100% fully charged. In otherwords it gets there much faster in about half the time. A full Bulk Absorb can take up to 12 hours, and there are no such thing as a 12 Sun Hour day, 4 is average.

Float mode is just a constant voltage charge to overcome the self discharge rate of batteries and holds them at 100%.

However you will not measure 14.8 or 13.2 volts on a fully charged battery at night. The only time you will ever see it is during daylight when there is an active charge going to the batteries. At night batteries on solar are not being charged. What I am driving at here is what is called State Of Charge or SOC for short. SOC is a voltage measurement of a battery that has no charge or discharge current. In other words disconnected just sitting there with an open circuit that has been rested for a few hours to bleed off surface charges. A 12 volt battery that is 100% charged will measure 12.6 volts. That is what you are seeing at night.

Here is a reference you need to know and understand. Various voltages and SOC for 12 volt batteries.

100% = 12.6 volts
75% = 12.4 volts
50% = 12.2 Never ever allow the battery to go below 50%
25% = 12.0 volts. Major unrepairable damage and loss of capacity.
0% = 11.9 volts = Toast throw battery away it is done because you destroyed it.

Now with that said you cannot determine the true SOC of the battery while it is either charging or discharging because of the batteries internal resistance. Only after it has been rested for a few hours.

Finally SOC is not real accurate. The only way to accurately determine a battery SOC is with a temperature corrected specific gravity.

73's to you.

So are these GC2 batteries really "Deep Cycle" type batteries or are they more like Marine "DC" Hybrid batteries?
If true DC batteries then can't they be discharged down to 20% charge remaining and not be damaged?
I do understand the concept of "the deeper the discharge state, therefore the fewer the total cycles",
but is there any Deep Cycle battery ( Rolls Surrette, etc ) that can be deeply discharged to 20% charge remaining
without incurring Major Unrepairable Damage?

[inetdog]

Any deep cycle battery can be discharged down to 20% SOC without suffering immediate noticeable damage. Battery banks for forklifts are one example of this kind of usage.
Rather than a sudden loss of capacity or mechanical damage, you will just have a reduction in the cycle life of the battery.

But this is only sustainable if you have a way to immediately recharge the battery to 80% SOC or more and regularly get back to 100% SOC.
Leaving the battery at a partial charge, especially when below 50%, for any length of time will lead to damaging "hard sulphate" formation on one plate.

If instead you did the same thing (very deep discharge) on an SLI (automotive) battery, you would soon be suffering from mechanical damage to the thin plates with their thin active chemical layer.

In addition to the mechanical differences, the lead alloy used in the construction of the plates will be different for different applications.

[NEOH]

Any deep cycle battery can be discharged down to 20% SOC without suffering immediate noticeable damage. Battery banks for forklifts are one example of this kind of usage.
Rather than a sudden loss of capacity or mechanical damage, you will just have a reduction in the cycle life of the battery.

But this is only sustainable if you have a way to immediately recharge the battery to 80% SOC or more and regularly get back to 100% SOC.
Leaving the battery at a partial charge, especially when below 50%, for any length of time will lead to damaging "hard sulphate" formation on one plate.

If instead you did the same thing (very deep discharge) on an SLI (automotive) battery, you would soon be suffering from mechanical damage to the thin plates with their thin active chemical layer.

In addition to the mechanical differences, the lead alloy used in the construction of the plates will be different for different applications.

Now I am confused ...
You said, "... Any deep cycle battery can be discharged down to 20% SOC without suffering immediate noticeable damage ..."
Sunking stated, "... 25% = 12.0 volts. Major unrepairable damage and loss of capacity ..."

When I read those two statements, I see two very conflicting opinions.
Let's discuss these two statements, as they pertain to the OP's GC2 type battery ( ie a Deep Cycle battery ) and not an SLI type battery.
And yes let's assume proper recharging under all conditions.

If the Plate Thickness inside the GC2 batteries is approx 0.070", then they are more like a Marine Hybrid battery than a true Deep Cycle battery
If the Plate Thickness inside the GC2 batteries is approx 0.110", then they are more like a true Deep Cycle battery.

Here is the "Cycles vs DOD" chart for Trojan T105RE Deep Cycle Battery:
http://www.trojanbattery.com/pdf/dat...ata_Sheets.pdf

CASE 1:
20% DOD = 4,000 cycles
40% DOD = 2,000 cycles

CASE 2:
30% DOD = 2,750 cycle
60% DOD = 1,375 cycle

CASE 3:
40% DOD = 2,000 cycles
80% DOD = 1,000 cycles

SUMMARY:
20% x 4,000 = 800
30% x 2,750 = 825
40% x 2,000 = 800
60% x 1,375 = 825
80% x 1,000 = 800

In each case, I doubled the DOD and the chart showed exactly half the number of cycles <- Exactly what we should expect.
Trojan claims, regardless of DOD, the Total AH's (capacity) from their battery over its lifetime is not very dependent upon DOD ( 20% to 80% ).
Per Trojan, the Total AH's (capacity) obtainable from a T105RE is 180,000AH ( = 225AH x 800 ) regardless of DOD ( 20% to 80% ).

So, in the real world, are the "Cycles vs DOD" of an Interstate GC2 battery significantly different (worse) than the Trojan T105RE Data Sheet?

Or maybe, their chart is 100% pure theoretical and not based on any real world DOD cycles of their battery.

[PNjunction]

Warning - don't get too hung up on bench-racing specifications. Those are LAB results. Real world, especially with unknown operator maintenance skills is another.

So are these GC2 batteries really "Deep Cycle" type batteries or are they more like Marine "DC" Hybrid batteries?
If true DC batteries then can't they be discharged down to 20% charge remaining and not be damaged?
I do understand the concept of "the deeper the discharge state, therefore the fewer the total cycles",
but is there any Deep Cycle battery ( Rolls Surrette, etc ) that can be deeply discharged to 20% charge remaining
without incurring Major Unrepairable Damage?

Yes, the Trojan's ARE "true" deep cycle.

The damage we are talking about is that by taking it down to 20% SOC (aka 80% DOD on the flip side), is that when recovered, there is a heavier toll taken on recovery - don't expect full capacity restoration.

In the REAL WORLD, most of your gear is going to trip far earlier than that due to the voltage drop being excessive. Or at least with anyone wise enough to utilize an LVD that trips far ealier than the dead-man cutoffs of an inverter.

What differentiates the Trojan T105RE from others is that it is also designed to withstand moderate PSOC operations by incorporating carbon in the active material, improved grid structure, and an enhanced separator. Whether it incorporates pure-rubber (which is good!) in the separator is an unknown to me, but that is what I suspect. This isn't just marketing BS, but real enhancements to to life and longevity compared to a standard flooded lead-calcium. Note too that this isn't a ticket to treat them as maintenance free either.

In the end, NONE of the bench-racing statistics are meaningful unless the charging environment, or owner maintenance skills are taken into account.

In the end, WU9B may get excellent life out of his interstates with proper maintenance, whereas the duffer with the Trojans, despite their advances, could kill them within months.

WU9B hint - if your needs are the typical DC connections running shack gear, Powerwerx makes some simple adjustable LVD's. I use the ITS-12 model for both lead acid AND LiFePo4 but other models may suit your needs better.

Don't bench race specs....

[NEOH]

In the end, NONE of the bench-racing statistics are meaningful unless the charging environment, or owner maintenance skills are taken into account.

The BCI should require Battery Manufactures to state exactly how they Charged / Discharged their batteries under test, as a detailed footnote below every "Cycles vs DOD" chart.