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Old 03-21-2015, 08:15 PM   #21
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Yes, use the specific gravity. If it is into the 100% range, you're golden. Remember to give the battery a few hours rest before measuring the specific gravity. I used the manufacturer specs to set up the CC, but specific gravity readings to tweak the settings.
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Old 03-22-2015, 12:33 AM   #22
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RPAspey I read up on your CC and many other CCs. I have yet to see a CC that allows the bulk charging and absorption charging to have different voltage values. That is where I am confused. Interstate calls for a bulk charge at 14.4v and absorption at 15.3 (or 15.5v for the 12v battery).

So if I get a different CC and crank up the absorption to 15.3v the bulk charge will be 15.3v as well. Is this acceptable even though Interstate specifies a 14.4v bulk charge?

Common sense tells me the bulk charge can match absorption as the battery is easily eating up the voltage in bulk charge mode.

If this is the case there are a lot of very affordable PWM and MPPT CCs that allow the absorption and equalization voltage to be customized.

It seems as though Interstate has set charge specifications that no charger can meet.
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Old 03-22-2015, 12:57 AM   #23
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The bulk mode voltage can't be fixed as the CC is trying to increase the battery current which raises the voltage. In other words, when discharged, the battery voltage is low, say 12.2 v. The CC can only charge at a certain current based on voltage (12.2v) and internal battery (depending on battery makeup) resistance and available light to the CC. So, the CC will try to put as much current into the battery that it can, until he battery reaches the absorption voltage. At that point the CC will not let the voltage increase, but will allow amps to charge the battery until full.

Voltage doesn't charge a battery, current does. But voltage is needed to push amps (current) into the battery. Voltage is used by the CC to determine the state of charge, thus what it (the CC) should be doing
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Old 03-22-2015, 08:07 AM   #24
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Battery charge graph.

Battery charging graph from another member, Herk. Oh, I made an error, a CC may have a setting for bulk voltage and absorption, if so, the CC will push as much current as it can until the battery reaches the bulk voltage setting then back down to the absorption voltage allowing the battery to top off.

I'm going to look for another chart to show that.
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Old 03-22-2015, 09:18 AM   #25
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Here's the other battery chart. Again, credit to Herk. This one gives a good graphic of the relationship between charge voltage and current.
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Old 03-22-2015, 11:02 AM   #26
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Very good info here. I am enjoying learning about this. We own a piece of property in Montana which is very remote and will never be on the grid. If i ever get a garage on it I am hoping to build my own solar system.

Now that I understand that during bulk charge voltage is increasing based upon the charge state of the battery and continues to increase until it reaches the absorption voltage. It makes absolutely no sense that interstate gives a bulk charge setting of 14.4v, right? Trojan doesn't give a bulk charge setting for their T-105 GC2 batteries (btw Trojan absorption setting is 14.8v).

I have read the manuals of several high dollar MPPT CCs and haven't seen one where the bulk and absorption settings can be different. My Go Power CC specs lump bulk and absorption voltage as one in the same and I believe most CCs are the same.

I store my trailer outside close to my house. I have ordered a good hydrometer. I'm going to give my current solar CC a go and see if by chance it keeps them fully charged.

I will report back.

RPAspey what absorption setting are you using and what batteries? Thanks for all the education.
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Old 03-27-2015, 07:44 PM   #27
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I received my EZRED hydrometer today and my batteries are right where they should be. 1.285 SG. This hydrometer is supposed to have built in temp compensation. Not sure if it's a marketing ploy or it really compensates for different temps.

To get consistent readings I need to put the tube on top of the plates and make sure it is completely full of fluid. Making a fist with the ball is the easiest way. If I don't put it on top of the plates I'll get inconsistent readings often over 1300 SG. They are still holding some surface charge (13.07v) but I don't think that has any effect on SG readings.

These batteries have been overcharged at 10a for two hours with my old auto charger and put through one cycle of my CTEK 4.3a charger.

Tomorrow I'll put them on my trailer and let the solar take over. I'll report back with my SQ readings periodically after I get them cycled a few times.
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Old 03-28-2015, 04:07 PM   #28
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Mounted the batteries today.

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