Solar amps in, consumption amps out, check my math please?

[Jarel Design]

Great birthday surprise!!!!

I received a $3,000 payment this morning for a client project that I TOTALLY forgot about! WOO HOO!!!

So, I can go back to my original plan to purchase two 100 watt solar panels and all the goodies that go with it! Also: A Pro-mariner, dual bank, 8 amp charger!

I totally revised my calculations keeping my original high power consumption as well as my low numbers to ultimately figure out how many days we can stay on the hook without using shore power.

I still feel my autopilot amp draw is too low, but we really won't need to use it. Just want to try it out, find out how much it draws and learn if it "plays nicely" with the boat (under sail and while motoring).

I added a 60% solar power-in to "guesstimate" power in on cloudy days etc.. (Rain or zero solar days is reflected as well with the 110v charger, used to make up the difference. If it's raining or we don't get enough solar, we can always cut down on power consumption and/or pull into a marina.

I know the pro-mariner charger won't produce what I've written but it's a good enough "guess" for me.

"Last thoughts"?


SAN JUAN TRIP POWER MANAGEMENT:
Mercury Bigfoot 9.9 produces 6 amps/hour. Estimate 3+ hours motoring per day to charge starter battery.


Using solar only at house batteries:
House Power Consumption: Max. Hours: Reduced


VHF: .5A, receiving x 6 hours = 3A, 6A 3A Hand-Held

LED lights: .2A (Anchor light x 10 hours = 2A) 2A 2A
Garmin 640: .6A x 6 hours = 3.6A 3.6A 3A
Hawkeye depth finder: .2A x 6 hours = 1.2A 1.2A 1A
Knot meter: (Self powered…): .0A 0A 0A
Wind meter (Self powered…): .0A 0A 0A
Autopilot: 1.0A x6hrs = 6A 6A 0A
CD/Stereo: 1.5A x 6hrs = 9A 9A _____7A
Total: 24.8A Total: 17A

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

Solar panels: (13 watts (1A), per sq./ft.)
2ea 100 watt (5.5A) each to charge house battery: 11.Amps
Maximum total hourly: 11.Amps


(Below, based on 24.8A daily consumption

Total Daily: @ 11.A (x 60%) (@ 100%) (@ 60%)

X 1hs: 11.0A 6.6A 3.8 Days 2.4 Days
x 2hrs: 22.0A 13.A 16.0 " 3.8 "
x 2.5hrs: 27.5A 16.5A Full + " 5.6 "
x 3hrs: 33.0A 19.8A Full + " 9.0 "

Group 27 12V “Deep cycle” 90AH x 50% = 45AH (usable)
@ 24.8hrs daily consumption:
Without solar: 1.8 days


Pro-mariner Pro-sport 8 Gen 3 Charger - 8 Amp - 2 Bank $107 Shipped (Amazon) 4 Amps per battery: x10 hours = 40 Amps (“Max.”) (Shore power every 3 to 9 days)

Use rigid solar panel (15 watts/1.2Amps), for charging AA batteries







To me, it looks like I have PLENTY of elbow room to adjust power consumption, stay on the hook longer and still have shore power as our back up. (Also purchasing two cheap, digital volt/amp meters. One will monitor amps in from solar to battery, and the other: amps out from battery to house. These units display actual numbers at the moment (revised once every second), and accumulative. ($15 each on Amazon!)



Laughing at myself here as I'm not certain my numbers are accurate... TOO MANY numbers in my head!!! Being able to purchase the two 110 watt panels leaves me feeling a LOT more comfortable just monitoring as we go and not worrying about it like I was before! LOL!


OK... Going out to the shop now to fabricate our new bow roller!









THANK YOU AGAIN to everyone!


Best,
Richard

[Tayana42]

That should be sufficient. [emoji6]Dayenu!

[Jarel Design]

Thanks!

This "Chinese fire drill" (of not having enough funds to set up our charging systems the way I wanted), REALLY helped me understand this aspect of our electrical system!!!

Getting our "originally planned" 200 watt solar system AND a "proper" 110v marine charger has taken a major load off my shoulders. I also feel much better about using the 110v charger as our "back-up", while exploring towns and sleeping on board. (I never felt comfortable resorting to using a "car charger".)

Now working on my "To-do" priority list before heading out to the shop! (I have it revised down to three pages!)

LOL!

[Adelie]

You indicate 2each panels 30w, is that 30total or 30 each? It looks like 30w total. I'll assume that. All the panels together have 80w of nameplate capacity.

Rule of thumb is 25% of nameplate in watts is what you can expect in amp-hr/day. Cruising PNW in May-July days are long so lets bump that to 30% which works out to 24a-hr.

Outboard produces 6a so for every 1hr running time you produce 6a-hr. Since this is the PNW I could see averaging 3hr a day motoring which would be 18a-hr. To be conservative let's assume 6a-hr.

Total produced is going to be about 30a-hr/day.

I think you are underestimating autopilot use and power consumption. I would put it at 12a-hr/day which brings you total up to 30a-hr/d.

You look to be pretty in balance over the long term.

Figure 1hr motoring even on days you mostly sail.

Cloudy days when you sail a lot you will fall behind.

Cloudy days spent sitting at anchor you may break even.

Cloudy days motoring more than 1hr you will start catching back up.

Loads that happen at the same time as charging is going on will incur no inefficiency linked to power going thru the battery.

Are you incapable of hand starting your main outboard? If so I can understand the arguement for keeping a separate starting battery though I would not do so.

If you can start it by hand then combine both batteries into one bank. Because of the lower discharge rate each battery sees you will actually get more power out of them and charging will be more efficient too.

[Jarel Design]

Hi Adleie!
Thank you for so much info!!!

I "think" you may have been going by my first post? Please see today's post with totally revised numbers. I received a client check for a job I completed that I totally forgot was not paid (Great birthday gift!) =D

We went back to our original plans to use 2ea 100 watt panels!

Although our outboard can be started by hand, I turned 63 today (not a biggie though... usually starts right up, so taking your advice about hand starting is something I think I will try to do unless there's an emergency.), but our existing battery wiring has the starter and house batteries wired separately and in very different locations. I just don't have time to re-wire them before our upcoming trip (Still have battery selector switch though). After our trip, I'm planning to gut all the wiring and create a much better system still using a separate starting batter but using two T145s as our house bank.

I'm VERY curious about what you wrote: "Rule of thumb is 25% of nameplate in watts is what you can expect in amp-hr/day."

Does this mean you're saying that I can expect only 25%-30% of power from a panel? (Example: New 100 watt panels will yield only 25 to 30 watts?) Is this per hour or "daily"expectations due to variables during the 24 hr day? I've calculated 1hr to 3 hrs (Max. of "solar light"), and nothing more. Does this approach fit with your 25% to 30% solar amp yield? I've read a LOT on these forums and other websites and never heard of these kinds of numbers before... I would expect 50% to 60% output per hour taking into consideration: efficiency, wire/controller loss, angle of sun, shading etc..)

The testing I've done here with some of the smaller panels I have here at home using my testing equipment (I develop prototypes for a living), yielded a much higher percentage of hourly output power...

I'm not disputing you... One of the best things I've learned over time (Especially when I think I know what I'm talking about! LOL!), is to approach everything with an open mind that reflects the mind set of "I don't know anything"!

Would you mind defining; sharing more about this?

Thank you!
Richard

[Adelie]

On a boat you will have a variable amount of sunlight due to shading by sails, rig and clouds.

For flat mounted panels output will follow a sinusoidal curve as the angle of the sun changes thru the day.

Batteries tend to be rated in amp-hr for capacity with 12v assumed.

Panels are generally rated in watts which means you don't have to calculate area and efficiency both of which vary panel to panel.

Most equipment lists amps drawn rather than wattage since you need amps to correctly size your wiring. 12v is assumed so you can calc wattage if you want to.

Since everything else is in amps or amp-hr converting panel output to similar units is the way to go.

The rule of thumb is not a measure of efficiency, it combines several steps into 1. It converts watts to amps assuming 12v and it averages all output thru the day to get a length of time at full output. My guess is the 25% is good in or near tropical regions where day length is more consistent thru the year.

So the rule of thumb takes you from watts of panel output to amp-hr which is the units you want when discussing battery charging and discharge and daily loads.

[Jarel Design]

Thank you!

[Adelie]

Starting battery.

In the past the reason to have a starting battery separate from the house bank was to still be able to start the engine even if you'd run the house battery down too far. This was before solar panel became widely available so the engine was likely the only charging source and was for engines too big to hand start.

These conditions don't apply to your case. You have solar panels and you can hand start.

Don't skimp on using to electric start you don't need to. The draw on a starter for your car is on the order of 200a or less for 1-2sec. You aren't even using 1a-hr to start your car.

The starter on your outboard probably draws around 36a. You would need to crank for 100s (almost 2min) to use 1a-hr.

What I would do in your case was make sure you can hand start the motor once per week and use the starter the rest of the time. If you can't hand start then figure out what happened to the motor, assuming the problem isn't you.

So you don't need to reserve a battery for starting and can put both in the house bank. The advantage is that by doubling the size of the bank you more than double the capacity. Battery capacity is dependent on discharge rate, discharge slower and you can get more out of the battery. With the same load but 2 batteries you are effectively discharging each battery at half the rate you would be discharging one battery in a 1-battery bank.

[Adelie]

The marine batteries you have are a compromise between starting amps which favors thin plates and cycle life which favors thicker plates.

You don't need cranking capacity for an outboard so true deep cycle would be the best use of money over time.

You indicated T-145 batteries. These are 6v batteries which you only want if you are going to get 4 or more of them.

With and even number of batteries you can wire them in series and parallel to get the 12v most marine equipment works on.

If you have only 2 6v batteries to get 12v and one cell in one battery goes bad you only get 10v or so and trying to recharge the battery runs the risk of starting a fire if the bad cell overheats enough.

If instead you get 2 12v batteries with about the same dimensions you should get about the same capacity but if one cell in one battery goes bad you disconnect that battery which still leaves you with 12v to run everything but half the capacity which means you limp along for several days or weeks until you get replacements. But at least you have something for time being and no risk of fire.

I'm going to get 2 T-1275s for this reason rather T145s.

[Jarel Design]

Thank you SO much!!!!
I had no idea what my O/B starter draws (I thought it was MUCH more than what you shared (makes sense though!), and from what you've shared, I'm now thinking the following:

Start O/B on both batteries, keep on both batteries. This will almost double my "house draw" capacity... Charging amps from O/B will reach both batteries?

Also, starter battery is much more convenient to hook up solar to. If I keep battery selector to both, can I assume that solar current going into starter battery will also reach house battery via 1/2/both battery switch? If I'm correct on both above, I'll benefit from O/B charging both batteries and solar charging both batteries. When on shore power, 110v charger is a 2-bank charger with 2 pairs of leads.

Very familiar with 6v batteries (connected in series for 12v power supply). The Group 27 we now have are what we have and will not change for this trip. ($$$ and battery box rebuild to facilitate). I'm not totally certain as to what house batteries we will "eventually" have (and with what's on my plate to get this boat ready for this trip, I just don't have time to even think about it. (I've printed what you've shared and placed it in our "Boat Electrical" file.. Future re-fit includes galley rebuild and installation of re-fridge/freezer unit, upping our power consumption... but that's for next year. LOL! (We have LOTS of printed (and digital), files created from over a year of serious research covering all sorts of boat topics and details.

Again, thank you for sharing your well detailed info!
Richard