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Old 24-04-2017, 11:26   #1
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Solar amps in, consumption amps out, check my math please?

Hello all,
First off THANK YOU to all who have posted here. I have learned a LOT!!!

We're planning a month long (3 to 4 weeks), cruise through the San Juan Islands in July on a 26 ft sailboat. We have two new Group 27 starter/marine/"deep cycle" batteries and dedicating one exclusively to start our engine, leaving the second battery for house use.

I'm upgrading/refitting a lot (New #25 Mantus, 40' 5/16" G4 chain, 10' Achilles dinghy with 6hp O/B, water tanks etc) and had planned on purchasing a 200watt system, but funds are being depleted fast! I already have several smaller panels (and controllers for them), and I'm considering using them for this trip and moving up to the larger solar system later.

I've compiled my solar input and power consumption figures (I personally think the stereo/CD estimates are low, but feel confident that I'm in the ball park?) Hourly use estimates are high... (In general, I've tried to calculate consumption rates higher (We don't need to use our autopilot being so close to our destinations.), and solar power input low just to play it on the safe side.)

I don't have a 110 battery charger and we really want to spend as much time as possible on the hook or on mooring buoys. When we first purchased our boat, we did a "shake down" period of 3 weeks up at the lake to test out living space and power consumption. At that time, we only had about 2.5 amps of solar and had no problems. (Wished I had checked the batteries after the trip, but I didn't. I do have a digital volt meter and will check batteries daily.

I'm hoping for input from other members here regarding my math and estimates (Not interested in advice to install more panels... Our budget is tight!) Maybe ideas like running the GPS, Depth and stereo on both batteries while motoring?

Am I "in the ballpark"?





My numbers:

SAN JUAN TRIP POWER MANAGEMENT:
Mercury Bigfoot 9.9 produces 6 amps/hour (3A "extra" usable?) Estimate 3 hours motoring per day: O/B produces 9A “extra” for use of GPS. VHF, Stereo & depth while motoring?

Using solar only at house batteries.

House Power Consumption:
VHF: .5A, receiving x 6 hours = 3A, 6A, transmitting on 25 watt
LED lights: .2A (Anchor light x 10 hours = 2A) We use AAA LED lights for interior (These are not connected to out house bank! Using Alkaline AA cells which (tested), run "forever".) (We will NOT be sailing/motoring at night!)
Garmin 640: .6A x 6 hours = 3.6A
Hawkeye depth finder: .2A x 6 hours = 1.2A
Knot meter: (Self powered…): .0A
Wind meter (Self powered…): .0A
Autopilot: 1.0A x6hrs = 6A
CD/Stereo: 1.5A x 6hrs = 9A

Total daily (average), power use: 24.8 Amp Hours
(Does NOT include phone or laptop charging!)


Solar panels: (13 watts (1A), per sq./ft.)
2ea 30 watt: 3.8A
Flexible: 20 watts: 1.6A
Glass: 13 watts: 1A
Large/rigid: 15 watts: 1.25A
Total hourly: 7.65A

Total Solar Daily @ 7.65A:
X 1hs: 7.65A
x 2hrs: 15.3A
x 2.5hrs: 19.1A
x 3hrs: 22.8A
(I've used a low number of daylight/solar charging hours as a way to provide a lower estimate of power (Amps), in.)


Group 27 12V “Deep cycle” 90AH x 50% = 45AH (usable)
@ 24.8A daily consumption:
Without solar: 1.8 days
@ 1hrs solar: 2.6 days
@ 2hrs solar: 4.7 days
@ 2.5hrs solar: 5.8 days
@ 3hrs solar: 22.5 days

I feel faily confident in my numbers (days capable of cruising without 110 charging), except the last (days capable without 110 charging), figure. I've used a calculator for everything so I'm pretty sure it's not my math, but I just don't see how the "days on the hook" jump from 5.8 to 22 days with only an extra half hour of solar input.

Thanks!

Richard
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Old 24-04-2017, 11:38   #2
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Re: Solar amps in, consumption amps out, check my math please?

It looks correct, I see no glaring errors.
You however have 23 to put in and 25 coming out, and I believe that batteries are not 100% efficient, I mean by that if say you take 10 out, you need to put more than 10 back in.
Units intentionally left out.
Does your outboard have a charging circuit? Any way you can borrow a small Honda type of generator?
I'd want another source of charging available myself.
Best laid plans of mice and men you know
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Old 24-04-2017, 11:53   #3
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Re: Solar amps in, consumption amps out, check my math please?

Good start. If you can monitor state of charge of your batts you can adjust your usage early.
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Old 24-04-2017, 11:54   #4
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Re: Solar amps in, consumption amps out, check my math please?

Taking a portable radio / ghetto blaster would tip the charging and discharging ratio in your favour. Or don't have 6 hours of music each day, seems a lot.

What happens when it rains or is foggy, we have the same problem and resort to burning dino juice to charge the batteries.

Rent a small genny would be good.

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Old 24-04-2017, 12:06   #5
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Re: Solar amps in, consumption amps out, check my math please?

Thank you so much for your quick reply!

LOL! (yes... best laid plans of mice and men!) LOL!

Our outboard is an electric start and does have a charging circuit.

No, I don't have access to a Honda generator (on our wish list).

I agree about efficiencies etc... I calculated fewer charging hours as a way to lower solar charging expectations. The 6 hour 'average" use time for most of our electrical consumers is pretty high. Most of the islands/destinations are pretty close to each other. One of the largest consumers is the autopilot. We certainly don't need to use it at all... Mostly just wanted to test it out while we are on the water.

I'm thinking our biggest consumer will be our stereo, but 6 hours is a LOT of music for us... We'd much rather listen to our surroundings while at anchor, or hiking.

I do have a good quality auto battery charger that automatically drops charging from 10A to 2A and less, that I'm "considering" using if we check into a marina as our "alternate" charging source.

I started with these figures and then decided not to worry by going with the larger 200 watt system. Now that $$$ reality has checked in, I just wanted to learn if I was out in left field for this trip.

Thank you!
Richard
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Old 24-04-2017, 12:16   #6
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Re: Solar amps in, consumption amps out, check my math please?

Wow! More replies!
Thank you!!!

Renting a generator for a month would probably add up to buying the 200 watt solar system (although I haven't checked).



We have a handheld VHF (in addition to our base unit), and it can use AA cells. As posted, we don't need to use our autopilot. Stereo hours is more than we will use. All of these can be cut back dramatically which will help reduce our power consumption. My power consumption estimates were intentionally high to tip the scales of my calculations "against" us...

Daily monitoring is my plan and helps us decide what and what not to use on a daily basis.

As for rain, fog etc... nothing I can do about that except cut back on power use or pull into a marina if batteries are getting low, but using our 110 volt automobile battery charger is not something I want to do. If we NEED it, maybe...

Totally welcoming more input!
Thanks again!
Richard
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Old 24-04-2017, 13:14   #7
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Re: Solar amps in, consumption amps out, check my math please?

The charging circuit on your outboard may be big enough to get you by in the event of rainy days etc. It may serve well as your safety net
I'd find out how big, some I think even may have alternators?
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Old 24-04-2017, 13:55   #8
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Re: Solar amps in, consumption amps out, check my math please?

Did I miss a mention about refrigeration? What are you doing about perishables? Cooler? canned food only? What about phone charging?
Cutting your music in half plus amps from your outboard gives you more leeway.
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Old 24-04-2017, 13:57   #9
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Re: Solar amps in, consumption amps out, check my math please?

Thanks!
I'm not "counting" on the O/B as a power supply. (My numbers aren't' tested first hand. Only going by factory specs: 6A output ...and not knowing how many amps the starter will draw.) This O/B also has a hand pull starter (tried it and it's not too bad: reliable/newer engine), and we'll be carrying our 6hp dinghy O/B on an adjustable mount mounted on our stern (Just got it in the mail a few minutes ago!), so we can keep it out of the water, make it easier to transfer to our dinghy AND use it as an emergency powered propulsion component when lowered. 1 to 2 pull starts.

"IF" the O/B provides enough to power the GPS, depth, VHF and maybe the stereo (2.8A total), while motoring, it would be great! (I'm "hoping" that if the O/B produces 6amps and I use 2.8A of that for these items, the remainder will go back into the starter battery while motoring. Those listed items would then be transferred to our house batteries. (GPS and depth would be shut down. Keeping the O/B 12v output as a power source will be in the back of my mind, but I'm only working with solar numbers in my calculations as I'm trying to side on the error of not enough solar and too much power consumption just to be "safe".

If I'm "close" with my numbers, I'm hoping I can adjust daily consumption by monitoring the batteries each day, keeping a log and adjusting our usage as needed with possible days of no solar... That's why I'm figuring my final numbers as "days" with limited number of solar amps input. (The number of days we can get by without solar.)

I think it looks to me as if bringing our car charger as a final back up may be in order.

I've read LOTS of threads advising AGAINST using an automobile charger on a boat, but as a temporary/limited back up, any thoughts (Safety etc)?
I'm looking at the Pro-Mariner 20 Amp dual bank charger for permanent installation, but for now, I just want a temporary "fix"/backup for this trip.

Thank you again!
Richard

Whew! "Watt" a juggling act!
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Old 24-04-2017, 14:10   #10
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Re: Solar amps in, consumption amps out, check my math please?

Hi Lizzard...

LOL! refrigeration is an item we will be installing but that also includes 400 watts of solar... in the future.

We'll have two coolers (one is part of the original design under our V-Berth and is well insulated. That one will be for longer term storage, the other, used as a "working" cooler (frequent use).

Both my wife and I teach self-sustainability and she also teaches canning (We just had 3+ year old Gumbo for dinner last night... Yummm... Like it was just cooked!) We have chickens too and those eggs can last for a month without refrigeration (unlike store-bought eggs). We're bringing a lot of those canned foods (Mostly meats: Goat, Deer, Elk etc...), with us. We'll also be crabbing and purchasing perishables (creamer for coffee, veggies etc), as we go. We BOTH have a long history of blue water cruising so food storage is something we're both familiar and comfortable with.

We'll have cell phones and laptops with us (3 extra batteries for the laptops and hoping to charge while plugged in at a free wi-fi cafe or while in a marina with 110 power. We do have a shore power system with breaker. But honestly, besides non-wifi guides and charts (not to be used with GPS while moving), we'd be using cell phones only to hail harbormasters, Customs etc... We don't want to be doing any "work" while we're out! LOL! Not expecting any phone charging to take up too much power-wise.

Again, Thank you to everyone here... So much to consider and there are times where considerations haven't been considered by us!

Best,
Richard

Between client prototype development, re-fitting our boat and getting all our ducks in a row... I wonder if a month out there will be enough to recover, let alone "re-charge" our batteries (pun intended.) LOL!
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Old 24-04-2017, 14:23   #11
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Re: Solar amps in, consumption amps out, check my math please?

Youv're forgotten the video cameras, then there is the drone to charge up plus the video editing suite.....

Enjoy the trip
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Old 24-04-2017, 14:38   #12
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Re: Solar amps in, consumption amps out, check my math please?

Pete:

Honestly laughed my head off OUT LOUD!

You're right! I DID forget the video cameras (Although we do have three extra batteries for each!) LOL!

(Still laughing!)

Fortunately, we don't have a drone (Yet! LOL!). Editing will take place at home, but we will be be downloading SD cards (carrying extras of those too), to laptops though! Maybe we can save downloading for when we're at a cafe and "plugged in".

Still laughing my head off! I TOTALLY forgot about those batteries!

I also didn't mention watching DVDs on our laptops! LOL!

This is why I decided to start this thread.... What else did I "forget"!

Thank you for that one!

And thank you for the laugh! (I needed it just now... Parts aren't fitting on a little robotic creature I'm creating for a toy company and I have to ship this week!)

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Old 24-04-2017, 14:38   #13
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Re: Solar amps in, consumption amps out, check my math please?

Still laughing...
Should I check my watch battery? LOL!
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Old 25-04-2017, 09:54   #14
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Re: Solar amps in, consumption amps out, check my math please?

1a pilot seems really low
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Old 25-04-2017, 10:27   #15
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Re: Solar amps in, consumption amps out, check my math please?

I've revised everything!

I lowered power consumption a LOT (LOWER hours for everything and eliminating autopilot to just testing it out one day. Also increasing our solar amperage input.)

Found some 30 watt flex panels for cheap and local. Connecting three of these to the larger one that I already have will produce 6 amps (maximum).

Also going ahead and buying the 110v Pro-mariner (8 amp/2-bank), charger.

We'll be using one of our smaller, rail mounted solar panels (separately), to charge phones, video camera batteries and AA nicads that we use on a lot of our items. (I have a really good R/C 12 volt charger that will monitor and control battery charging.)

With a few visits to marinas with power, I know we will not have any problems. (We spoke and in reality can't imagine not spending some exploring time in Friday Harbor, Sidney etc... So we can hook up and charge via dock power.)

Autopilot power consumption? (I agree! I got this is information from the instructions/specs. I just want to test it out since we've never used it before... We really don't need to "use" it...) This trip will allow me to connect my metering equipment to test everything in the "real world" and document each device and power consumption so I can make plans for our final power system knowing for certain what each device uses.

This is going to cost more than I wanted, but cheaper than the larger solar array I "wanted". (In the end, there's enough to concentrate on without worrying about our power status! LOL!) (I will keep checking battery status daily though.)

Thanks again to everyone! (REALLY! You've been a great help!)

Best,
Richard
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