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Old 27-03-2016, 20:01   #1
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Solar ... Wattage ... Voltage and boat size

I am considering 160 total wattage for a 29' Bristol, with all LED lights, no air conditioning, well-insulated FrigoBoat fridge and rarely need for anything more than "personal"-type fans.

My Tv is 7" and draws 1.5 amps, my laptop draws 2 amps, and my larger laptop draws 3.5 amps(for cad use only). My notepad uses 1/2 amp if I remember right

I have no need for electronics, other than the laptop or the notepad, although I do have a depth meter.

I'm curious to hear what other boaters have for wattage, needs, and if they think they can get by with less or need more.

I'm also curious about the balancing of batteries to wattage and power needs.

After all if I only need 5 amps a day, isn't there a point where more batteries actually become more problematic, since not enough juice is being used/replaced?
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Old 27-03-2016, 20:30   #2
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Re: Solar ... Wattage ... Voltage and boat size

OK so let's see what you really are using you say your stuff draws 5 amps so now you need to know how many hours you will be running the items and you also need the ah draw of the frigoboat refer .
I would estimate from your rough numbers you are using about 60 ah per day and 160 watts of solar would give you about 50 ah so I would recommend going up to a minimum of 200 watts of solar and at least 200 ah in your battery bank personally I would recommend 400 ah house bank.
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Old 27-03-2016, 21:29   #3
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Re: Solar ... Wattage ... Voltage and boat size

These laptop consumption numbers seem low, if the laptop's batteries are depleted, and if the laptop is doing some more intensive task, like streaming video.

My laptop consumes 2.1 to 2.4 amps typing this with one window open to on this forum, 3.5 amps streaming video, 4.5 amps spinning a DVD, and upto 7.8 amps maximum when turned on and recharging the laptop's depleted 9 cell battery, and upto 4 amps turned off charging the laptop's depleted battery.

How little solar you can get away with depends on how much you actually consume, and knowing how much the frigoboat fridge actually uses, and how much the other loads will actually draw and consume as you use them.

Other charging sources and how often they are applied to depleted batteries plays a huge part in the necessary wattage/capacity ratio.

Also if AGMS are employed, and deeply cycled to the 50% range, a low and slow solar only regimen will tickle them to a premature death, even if the solar can hold them at the proper absorption voltage until amps taper to 0.05% of capacity.

My Northstar AGM requires a high amp recharge every 4 to 5 deep cycles, when each discharge cycle is followed only with a low and slow 100% solar recharge, or voltage under load tanks. After 5 low and slow recharges to 100%, time at absorption voltage to reach a true 100% afterwards takes progressively longer, which eventually requires other charging sources, as the day is simply not long enough.
So the High amp initial recharge when the battery is most depleted saves me from this walk down in performance/capacity, and I consider it necessary.

So more solar is mo better, but still might not be enough to keep a battery happy in deep cycle back to back usage, even if absorption voltage is held for long enough each recharge. The initial charge rate plays a part to some degree, depending on the specific battery.

My solar to capacity ratio is 198 watts to 90AH of AGM, and without the alternator or other charging sources to high amp recharge, and/or hold absorption voltage for long enough, the battery would not be happy, perhaps at the recyclers by now, instead of still impressing me cycle after cycle.

So more than 2 solar watts to 1AH of capacity, in my usage of 35 to 45AH each night, every night, is by itself, not enough for my AGM battery. The high amp recharge requirement is not met, but I'd rather have a battery which likes and occasionally requires high amp recharging, rather than one that gets miffed at currents high enough to quickly attain absorption voltage.

I can install a similar tool to the following link inline on any single device and measure its actual consumption over time, with ~ 90% accuracy in the 0.5 to 30 amp range: : WindyNation AccuMax Watt Volt Ammeter Power Meter Analyzer Wind Solar RC : Patio, Lawn & Garden

Mine is actually a lesser versions of this same product that came with 12 awg aluminum leads. I removed the 12 awg aluminum from circuit board and replaced with 8awg and 45 amp powerpoles.

NOt terribly accurate under 0.5 amps and might not even read loads under 0.2a, though I had one version capable of reading 0.02amps accurately.

So I say to find out how much AH you actually require, unless premature battery replacement is not much of a concern.

Some people are keen on a lot of battery capacity and just enough solar to replenish what might be used overnight on average, but I have had 345AH of capacity cycled 45 to 60Ah each night, not last as long as my current 90AH cycled much deeper, that same 45 to 60AH each night. So I recommend one's solar system, at solar noon, can at least approach, and better yet, meet or exceed the battery manufacturer's recommended rate. Trojan recommends 10 to 13%. This is more than 2 solar watts to 1Ah of capacity most of the year.

Lifeline AGM recommends 20% minimum when deeply discharged
Odyssey AGM recommends 40% minimum.

Totally unrealistic solar wattage to battery capacity ratios to meet these battery manufacturer recommendations. Other high amp charging sources must be utilized every so often or these will much more quickly walk down in capacity.

My 198 watts of solar can achieve around 13 amps at solar noon on June 21, into a 90AH AGM battery, and this battery, on solar only, without a high amp charging source employed every 4 to 5 deep cycles, would likely have been recycled and considered a waste of money at this point.
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