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Old 12-30-2019, 08:26 AM   #1
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AGM charging with charger, alternator, and solar

My house bank of 8 x 6V AGM golf cart batteries (Deka 8AGC2) is 2 1/2 years old. We don't spend much time in marinas, and we don't run the gennie very often (60 - 90 minutes every 2 - 3 days to make water and bring the batteries up, but never to 100%). We have about 1,000 watts of solar and are in the Caribbean, so we typically get at least 8 hours of pretty good sun. (The last 5 days' log shows 200 - 220 Ah being sent to the batteries from solar panels, and our daily usage is somewhat less than that.)

We did just spend about 7 weeks in a marina connected to shore power, so the Magnum 3112 Inverter / Charger got a chance to very thoroughly charge the batteries, and keep them charged, for a good long time.

The Magnum has what seems to be the most accurate default settings for my batteries, their "AGM2" setting. (AGM1 is Lifeline, AGM2 is Deka, et al.) The Absorption voltage is 14.5 and the Float is 13.5. The solar controller is also set to 14.5 and 13.5. The Balmar's AGM defaults are 14.18 and 13.5, so I'm thinking I should modify it to also be 14.5 and 13.5, even though we don't move the boat very often, so the Balmar isn't charging the batteries very often.

FINALLY, the question: am I hurting the batteries by not bringing them up to 100% SOC at least 3-4 times each month? Or, asked another way, what should I be bringing the SOC up to when I run the gennie, and how often should I do that?
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Old 12-30-2019, 08:40 AM   #2
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The last 5 days' log shows 200 - 220 Ah being sent to the batteries from solar panels, and our daily usage is somewhat less than that.)
My question is, if your solar is typically putting in more AH than you are using, why isn't that bringing you up to 100% ? Is it only exceeding usage by a slight margin? How far short of 100% SOC are you ending up at?
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Old 12-30-2019, 08:52 AM   #3
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Generally speaking, AGMs like to be fully charged on a regular basis. I have read that best practice is 3 - 4 days when on anchor, but no less than weekly. You can probably read on line for your specific battery.
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Old 12-30-2019, 09:08 AM   #4
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I agree with the above. The longer a battery, AGM or FLA, sits at less than full charge the more sulfate precipitates out. Recharging fully every 2-3 days puts that sulfate back in solution. Leaving it longer not charged fully also lets it consolidate so it is harder to re-dissolve.

So in your situation I would run the genset more, preferably early in the morning when the batteries are at their lowest. Your Magnum charger should put in 75-100 Ahs after an hour of genset running. Then let the solar panels bring the batteries up to full charge during the day.

Also 200-220 Ahs in a full sun day in the Caribbean is low. Should be 300-400 Ahs. That implies that there is something wrong with your solar system or maybe it really is fully charging the batteries each day which limits the total amp hours. I assume that the solar controller never switches to float on a normal day, right? What is the amperage and voltage from the controller when the sun begins to go down?

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Old 12-30-2019, 10:20 AM   #5
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Originally Posted by caltexflanc View Post
My question is, if your solar is typically putting in more AH than you are using, why isn't that bringing you up to 100%?
That's a really good question!

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Originally Posted by caltexflanc View Post
Is it only exceeding usage by a slight margin? How far short of 100% SOC are you ending up at?
Right now (noon on a sunny day in Bequia), with the solar panels switched off, the draw is 12.2 amps. That's a Norcold over/under freezer/fridge (3.6 A), a Dometic portable freezer (3.0 A), and all the rest must be various chargers, which we keep plugged in all the time, some DC and some AC (through the Inverter). There are no lights or fans on anywhere on the boat right now. So maybe we're simply using more power than I thought: 12.2 x 24 = 292.8! And at night, we do run a couple small DC fans all night, and of course, there are some lights on for typically 3 - 5 hours.

Two nights ago, I ran the gennie until the SOC was 95%. Last evening, at the end of sunlight, the SOC was 86% after a normal 24 hour period.

Maybe I'm simply using more power than I used to. The Dometic portable freezer was added after our first year with the batteries, and maybe it's running almost all the time? I guess I need to do an energy audit so I really know what's happening.
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Old 12-30-2019, 10:42 AM   #6
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Yes you are probably using more energy than you think.


I also would take the SOC values with a grain of salt. They are usually derived by summing net amphours against battery capacity. If battery capacity is wrong for some reason (deterioration) then SOC is wrong.

Like I said in my PP check the actual current and voltage at the end of a charge cycle. If the current is small, ie 5 amps or so then you are near 100% charged. Then reset your SOC meter to 100%.

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Old 12-30-2019, 10:44 AM   #7
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Also 200-220 Ahs in a full sun day in the Caribbean is low. Should be 300-400 Ahs. That implies that there is something wrong with your solar system or maybe it really is fully charging the batteries each day which limits the total amp hours. I assume that the solar controller never switches to float on a normal day, right? What is the amperage and voltage from the controller when the sun begins to go down?

David
Hmmm.... maybe that's my problem. Right now - noon, and it's been sunny all morning - my solar summary shows that it's in Bulk mode, which, if I understand correctly, is a fixed amperage, not a fixed voltage. I have 55 volts coming into the solar controller, but only 12.9 going out, at 33 amps.

I also have only about 400 - 420 watts coming in from the panels right now, but the maximum from them at some other time today was 925. I wonder if my radar is really blocking that much of one panel? There are four panels, wired as two pairs. I believe that shade on one panel of a pair reduces the output of the entire pair, correct? Maybe I need to control each panel separately, to reduce the shade loss?

Seems like I need to educate myself on solar panels and controllers.
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Old 12-30-2019, 11:06 AM   #8
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Quote:
Originally Posted by BrianSmith View Post

The Magnum has what seems to be the most accurate default settings for my batteries, their "AGM2" setting. (AGM1 is Lifeline, AGM2 is Deka, et al.) The Absorption voltage is 14.5 and the Float is 13.5. The solar controller is also set to 14.5 and 13.5. The Balmar's AGM defaults are 14.18 and 13.5, so I'm thinking I should modify it to also be 14.5 and 13.5, even though we don't move the boat very often, so the Balmar isn't charging the batteries very often.


Balmar's AGM setting seems to be for Lifeline. You could choose the Balmar setting for OPS (Optima Spiral-wound AGM's) which has voltages 14.6, 14.4, and 13.4.

I have run Deka AGM's with this setup for ~20 years. One set lasted 11 summers.

I do also have batt temp and alt temp monitoring connected to the Balmar.
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Old 12-30-2019, 11:32 AM   #9
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Balmar's AGM setting seems to be for Lifeline. You could choose the Balmar setting for OPS (Optima Spiral-wound AGM's) which has voltages 14.6, 14.4, and 13.4.

I have run Deka AGM's with this setup for ~20 years. One set lasted 11 summers.

I do also have batt temp and alt temp monitoring connected to the Balmar.
Richard, I didn't even look at that column in the Balmar manual - thanks for pointing that out! I'll make that switch. (I also have battery and alternator temperature monitors connected to the Balmar 614.)
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Old 12-30-2019, 12:10 PM   #10
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12.9 V at 33 amps. Firstly that voltage looks low unless the batteries were really discharged.

12.9*33= 426 watts plus a little for the controller's inefficiency, so maybe 440 watts from the panels which is half of rated. Also 55 volts from four 24V nominal (presumably) panels wired series/parallel looks low as well. The MPP voltage (the voltage where the total power produced is maximum and therefore producing the rated wattage) should be about 34V for each panel or 68V for two wired in series.

I would first run the batteries down to 50% just before noon, then power up the panels and see what you get. With well discharged batteries they are acting like a big wattage sink and should be demanding all that the panels can put out. If you still get those kinds of numbers (440 watts or half of rated power) at noon with full sun then something is off.


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Old 12-30-2019, 12:41 PM   #11
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Set the battery parameters to the manufacturer's spec for your batteries. It can be considerably different than the canned settings. I'm with David, run the genset in the morning to get the bulk charge done, then have the solar float the batteries during the peak sunlight time. If you're not reaching 100%, then your solar isn't keeping up. An audit should tell the tale.



If you have a shading condition, it may help to change the panels to parallel configuration, adding diodes to the connections to minimize the effect of the shading. You can lose a significant portion of the output if the panels are series connected and they are shaded part of the day. With series wiring, shading drops the output of the entire array if one panel is shaded, with parallel, only the output of the shaded panel is affected. So there might be some advantage in looking into the wiring.
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Old 12-30-2019, 01:46 PM   #12
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If Brian is using Magnum's BMK to estimate SOC, then it is very accurate. If he doesn't I highly recommend getting one. It also gives you an accurate view of power consumption among other things.

Genset in the morning (or evening as the case may be) I agree with. We had a much more electricity intensive boat, to be sure, so typically did both. All electric galley with full size appliances, laundry, dishwasher, a variety of things like beverage coolers, ice maker etc. So we'd gang up on using as many of those at a time a run the genset for an hour or two and in the course of that got the banks fully charged. We lived full time on moorings much of the year, and anchored out most of the time when not.
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Old 12-31-2019, 08:18 AM   #13
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Well, I think I have some kind of issue with the solar panels / wiring / controller. When I got up this morning, the SOC (from the Magnum BMK) was 66%, the batteries at 12.2V. I started the gennie and the Magnum charger kicked in, taking the SOC to 88% and the voltage to 12.9% after about 70 minutes of running. The charge mode had changed from Bulk to Absorption somewhere around the 50 minute mark. So far, so good.
I shut off the gennie and look at the solar controller - it's still in Bulk mode, outputting only 12.9V. Right now, it's showing:
56.5 VDC in
6 ADC in (amps)
12.8 VDC out
25 ADC out
320 watts in
When I turn off the breaker for Pair 1 (there are two pairs of panels), the wattage in drops to about 40.
When I turn Pair 1 on and Pair 2 off, the wattage is about 300.
Pair 1 is the forward two panels, wired in series. Pair 2 is the aft two panels, wired in series. Both pairs' output is then wired in parallel to the charge controller.
The wattage output makes a little sense, as the radar dome is currently shading the aft pair, but not the forward pair. The wiring diagram is attached. I'll also look this afternoon, when the shading should be on the forward pair, but not at all on the aft pair.
However, I don't think the radar dome could possibly be shading more than about 25% of any one panel - that shouldn't drop the wattage all the way to 40, should it? (Yes, it's fully sunny right now.)

Obviously, I have more to investigate.
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Wiring of the panels together.jpg  
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Old 12-31-2019, 09:04 AM   #14
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I think that shading is your problem. I have found that 10% shading of a panel will drop its output dramatically. And if another panel is wired in series with that one, both drop dramatically. That is why your aft panels are only putting out 40 watts.

Your only solutions are to move your panels so they can't be shaded or rewire all four panels in parallel. With all in parallel if one is shaded the other three will continue to put out fully.

You need to check your controller's specs for the maximum allowable input current. Wiring them in parallel will double the current but halve the voltage.

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Old 12-31-2019, 09:27 AM   #15
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Yor charge controller. Is going in absorption at 12.9 volts, that seems very low. I do not know what the specs on your batteries are but for the Trojans they 14.8 volts for absorption
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Old 12-31-2019, 09:38 AM   #16
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I think that shading is your problem. I have found that 10% shading of a panel will drop its output dramatically. And if another panel is wired in series with that one, both drop dramatically. That is why your aft panels are only putting out 40 watts.

Your only solutions are to move your panels so they can't be shaded or rewire all four panels in parallel. With all in parallel if one is shaded the other three will continue to put out fully.

You need to check your controller's specs for the maximum allowable input current. Wiring them in parallel will double the current but halve the voltage.

David
The panels (Kycera KU260-6MCA) have these specs:
Max watts: 260
Vmp ("loaded voltage"): 31
Imp ("loaded amperage"): 8.39
Voc ("max voltage"): 38.3
Isc ("short circuit amps"): 9.09

The FlexMax80 controller can accept up to 80 amps and 1,000 watts, so it would appear that the amps from all four in parallel would be fine (4 x 9.09 is way less than 80), but the total wattage of the four panels (4 x 260) would be a little more than the controller is designed for. (But how often will the panels output their full capacity? The controller's stored data says it has never seen more than 947 from the panels.)

The more I dive into this, the more confused I become. It seems like we decided to wire the panels into two pairs for some good reason, but at this point, I sure don't remember what it was.
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Old 12-31-2019, 09:53 AM   #17
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You're only seeing 12.9 volts because the batteries are still charging. The voltage across the batteries rises as they become more fully charged.

Even a small amount of shading causes a huge drop in output.

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Old 12-31-2019, 11:09 AM   #18
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You're only seeing 12.9 volts because the batteries are still charging. The voltage across the batteries rises as they become more fully charged.

Even a small amount of shading causes a huge drop in output.

Ken
Yes, I know the batteries are still charging, and the voltage is still rising. But very, very slowly, and the solar controller is still in Bulk mode. Since the gennie / Magnum charger completed its Bulk mode, and the voltages for Absorption mode are set to the same levels on the Magnum and the solar controller, I would think that the solar controller would go into Absorption mode, too.

Maybe the logic of the two chargers is simply too different for them to work the way I expect them to work.

RE: shading - I did some testing, and man, it's horrible! Just putting my hand on one panel causes the total output to drop by almost 100 watts. I'm probably going to have to rewire them so they're all independent of each other, as there's no way for me to eliminate the shade completely.
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Old 12-31-2019, 11:47 AM   #19
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Brian:


I doubt if you will ever see more than 1,000 watts from those panels unless you cruise in the tropics where the sun can be exactly overhead.


The other specs look fine for all parallel operation. You should easily pick up about 150 watts even with one shaded if you do this.


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Old 12-31-2019, 02:04 PM   #20
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Brian:

I doubt if you will ever see more than 1,000 watts from those panels unless you cruise in the tropics where the sun can be exactly overhead.

The other specs look fine for all parallel operation. You should easily pick up about 150 watts even with one shaded if you do this.

David
Well, we are in the Grenadines now, at about 12.5 degrees North, so we get a lot of near-direct overhead sun. But I agree - 1,000 watts seems unlikely. I think I'll try the parallel setup, and see if that helps.

Thanks.
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