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Old 03-19-2015, 02:29 PM   #1
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Go Power Solar and Interstate GC2 batteries charging issue

Hoping the pros here can help me. I just bought two Interstate 6v golf cart batteries to put in my FR Stealth Toyhauler. They will be wired in series obviously.

I have a Go Solar PMW Digital Solar Controller that has four charging stages. The charge specs for flooded batteries are 14.4v absorption/bulk; float 13.7v and equalization 14.8v. The absorption/bulk charge of 14.4 is applied one hour each morning and the equalization charge of 14.8v is applied for two hours every 28 days. I cannot change these settings.

The Interstate GC2 charging specs are bulk at 14.4v; absorption at 15.5v; float at 13.2v; equalization at 15.6v.

I called Interstate and they told me that these GC2 batteries need the high absorption and equalization charges to prolong their life.

Not sure whether I should look into another solar charge controller or just live with what I have. The convenience of letting the solar charger maintain the batteries when in storage is great. These batteries are too damn heavy to bring home with me.

I wish I could program the voltages on my controller but manufacturer says it's impossible.

Thanks.
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Old 03-19-2015, 08:39 PM   #2
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Short answer is yes, get rid of the CC.

Long answer is the voltages are too low. Absorption/bulk time is way too short. Bulk time varies with battery discharge and available sunlight. Get a programmable MPPT and you'll realize about a 20% increase in available power output and your batteries will appreciate it too.
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Old 03-19-2015, 08:45 PM   #3
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Oh, there are some CC's out there that have a remote programmer too.
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Old 03-19-2015, 08:52 PM   #4
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Quote:
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Short answer is yes, get rid of the CC.

Long answer is the voltages are too low. Absorption/bulk time is way too short. Bulk time varies with battery discharge and available sunlight. Get a programmable MPPT and you'll realize about a 20% increase in available power output and your batteries will appreciate it too.
I'm clueless on these controllers. What do you mean by CC? (edit: I assume you mean charge controller).

Is it as simple as replacing the controller and I can keep my panel and the rest of my system? If so, what do you recommend that will allow me to program the bulk, absorption, float and equalization settings?
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Old 03-19-2015, 09:02 PM   #5
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I do believe what RP means by cc is the charge controler.
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Old 03-19-2015, 09:06 PM   #6
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I guess I should also mention I have a built in 4000w Onan generator. When boondocking I could run that daily but I'll have to figure out if the inverter/charger that came with the trailer puts out any more charging volts than the solar system.
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Old 03-19-2015, 09:20 PM   #7
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Sorry, CC = Charge Controller.

Yes, you'll be able to use your existing panels. You'll need to know a bit about them. The size in watts, Voc (voltage open circuit) and Imp (current maximum power) If you don't know these, don't fret, just look up that info from your existing CC. Whatever CC you pick, it has to be able to withstand those specific values. Higher is better. To high of an Voc or too much Imp and the CC will burn up.

There plenty of MPPT controllers out there that will work. I use a Blue Sky 2412iX with a IPn Pro Remote. I can set all charging parameters and it is a power meter / battery status meter as well. Again, there are other really good CCs out there too.
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Old 03-19-2015, 09:36 PM   #8
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I guess I should also mention I have a built in 4000w Onan generator. When boondocking I could run that daily but I'll have to figure out if the inverter/charger that came with the trailer puts out any more charging volts than the solar system.
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Old 03-19-2015, 09:49 PM   #9
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Sorry, CC = Charge Controller.

Yes, you'll be able to use your existing panels. You'll need to know a bit about them. The size in watts, Voc (voltage open circuit) and Imp (current maximum power) If you don't know these, don't fret, just look up that info from your existing CC. Whatever CC you pick, it has to be able to withstand those specific values. Higher is better. To high of an Voc or too much Imp and the CC will burn up.

There plenty of MPPT controllers out there that will work. I use a Blue Sky 2412iX with a IPn Pro Remote. I can set all charging parameters and it is a power meter / battery status meter as well. Again, there are other really good CCs out there too.
Thanks for the info. I need to educate myself. Time to start reading. What is confusing me the most is the fact that a lot of MPPT controllers come preset with the same charging voltages as my PWM controller. There are also lots of debates on whether it's a good idea to use an absorption charge at 15.5v. I'm certainly not seeing any stand alone chargers that are programmable.
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Old 03-20-2015, 06:43 AM   #10
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Your CC should bulk charge (max current in that the battery will accept) until the absorption voltage is reached on the batteries. Then the CC should switch to absorption mode where the voltage is held constant (at the absorption voltage) until the current going into the battery drops to a pre-set level (I have mine set to .2amp/100 AHr as determined by a hydrometer reading) Once that level is reached the battery is considered charged and the CC goes
into float mode.

As for debates, well I think the manufacturers would know best. BTW, my controller is set to limit the output voltage to 15.2 (?) volts as my inverter doesn't like higher voltage and thus shuts down on safety.
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Old 03-20-2015, 07:16 AM   #11
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Morningstar MPPT charge controls work great for me.
We live off grid most of the winter on two golfcart batteries and 260 watts on roof
Good Luck
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Old 03-20-2015, 11:22 AM   #12
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Thanks for the responses guys. I'm also going to look into the new Trojan T-105 AGM batteries. My charger has the right voltages for them. They are just twice as much but won't need a new charger. 6 dozen one way, half dozen the other.
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Old 03-20-2015, 12:35 PM   #13
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You're welcome. One has to do what makes sense. Trojans are good batteries.
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Old 03-20-2015, 01:47 PM   #14
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I spoke with one of the charging pros at Interstate batteries who seemed like the golf cart battery charging guru. He told me not to buy a new charger and get a good hydrometer. He wasn't that concerned about my absorption voltage not getting up to 15.3v as only very expensive chargers can be set to do that. His main concern was that my built in solar will only equalize at 14.8v. He was also not really concerned that my float voltage is 13.7v instead of 13.2v. Said I would just need to check the water levels more often.

I have an old 10 amp auto charger with a manual setting. I'm pretty sure I can manually equalize the batteries with this when needed. Anyone tried this?

FYI I was looking at the Xantrex C35 PWM controller as an affordable controller that can be adjusted. Looked great except their is no independent adjustment for the absorption charge, just bulk and float. Absorption stays at the same voltage you set the bulk rate to.

Well at the very least I am learning what all this stuff means.

The Interstate rep did stress that I won't see full capacity from these batteries until they get cycled a bunch of times.
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Old 03-20-2015, 08:55 PM   #15
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After lots of research I have decided to let my Go Power Solar charger handle the everyday charging of my batteries. I will carry out periodic charge cycles and equalization using a Cytek 4.3 multi-charger. It will let me do bulk and absorption charging at either 14.4v or 14.7v using a cold weather setting. It also has a desulphate/rejuvenate setting that charges at 15.8v.

I also bought a good hydrometer and will check the cells from time to time. If I'm having problems I'll looks into the MPPT controllers.

Thanks again for all the advice.
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Old 03-21-2015, 04:03 AM   #16
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You're welcome. Happy camping too.
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Old 03-21-2015, 05:43 AM   #17
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I also saw where Interstate is publishing those charge rates for the GC2's, but I have to say... it is HIGHLY irregular. I can't imagine their battery chemistries are so completely different than everyone else on the market (especially considering that almost all brands of lower end true deep cycles are produced by the same manufacturer).

So basically what they are asking for is a lower voltage when you are pushing the most amps (bulk) and a higher voltage (saturation) when you are pushing diminishing amps. How does that even make sense?. I can see it if they are taking the approach that the higher amp input is easier to push when the battery more easily absorbs those amps.. while resistance increases as the charge rate increases... thereby requiring a high voltage to push them, but that would also create a great deal of excess heat. In other words.. creating more off gassing.

It seems counter productive to extending battery life.

The "norm" throughout the industry seems to be pushing as many amps as possible, as quickly as possible, during the bulk charge (hardly any heat build up since the amps are so easily accepts). Then decreasing the rate of charge during absorption so you don't "cook" your batteries with excess heat generation.

If you take a look around, almost ALL "default" charge rate settings on just about any "smart charger" follow this same charging profile. Interstate is the only company I am aware of that publishes this charge profile. Personally, I would NEVER cook my batteries at 15.5 (equalization rate) during absorption.

Might be I'll be proven wrong over time, but I just can't fathom using an equalization rate of charge for an absorption rate (which your batteries will be in the majority of the time) and expect any kind of length of life out of them.

Looking at their chemistry a bit.. if I owned Interstate GC2's I would run my charge cycles at 14.8-15 bulk, 14.2-14.4 saturation, 13.2 float, and equalize at 15.5 for 4 hours when needed.
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Old 03-21-2015, 07:19 AM   #18
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Yarome I don't know enough about batteries and charging to have an opinion about pushing 15.5v during absorption on a GC2 but I do know Trojan calls for 14.8v during absorption on their GC2 batteries.

Your are correct that no brand of smart charger puts out 15.5v during absorption. The only way to do this is to spend many hundreds of dollars on a MPPT charger. The Xantrex PWM chargers will let you program bulk and float, but not absorption. On Xantrex absorption will be whatever you set bulk to.

Yesterday I hooked up my old Diehard auto charger to my fully charged Interstate batteries (they are hooked in series). I gave them a one hour manual charge at 10 amps. They didn't get warm at all but I could smell the off gassing in the garage. Highest my volt meter went was 15.37v during this charge.

What I don't understand is why Interstate says they won't get fully charged unless you do the absorption at 15.5v. Won't my solar charger get them fully charged doing absorption at 14.4v but just take longer?
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Old 03-21-2015, 07:49 AM   #19
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the higher voltage is due to higher internal resistance. The only way to push that last bit of capacity into the battery is to increase the voltage to overcome that resistance.
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Old 03-21-2015, 01:46 PM   #20
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the higher voltage is due to higher internal resistance. The only way to push that last bit of capacity into the battery is to increase the voltage to overcome that resistance.
So how do I determine whether a 14.4v absorption charge is fully charging my batteries? Specs for 100% SOC is 6.48v or specific gravity per cell of 1.285

If I meet or exceed these numbers am I fully charged?
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