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Old 08-06-2018, 02:10 PM   #21
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Originally Posted by k9medic View Post
Currently I “burn” about 0.7kw per hour A/C running my freezer,
Fridge, ice maker and one air conditioner set at 80 degrees for humidity control.

How do you know that? IF it is from a monthly power bill then it is accurate, but who knows how much of that is the air conditioner.


But if you are looking to run the fridge and freezer for weeks whiie you are away, you need a different set. A well insulated and designed 12V 6 cu ft fridge and separate freezer compartment should only take 75 amp hours daily with no one there to open and close it. That can be covered with 300-400 watts of solar panels. The cost of the panels and solar controller will be about the same as your 3,000 watt inverter. Unfortunately efficient 12V fridge/freezers are expensive, about $1,500.



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Old 08-06-2018, 03:08 PM   #22
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I’ve calculated the loads from this sales ad -https://m.grainger.com/mobile/product/MARVEL-Refrigerator-1LBF5 and thrnnised this site to conver AC to DC - https://www.batterystuff.com/kb/tool...-inverter.html

This comes out to 64amps. I’m assuming thst is per hour while running?
I have a 3.1 cubic foot two door Haier that in ambient temps of 80 degrees uses 60Ah per day as measured by my Kill-a-Watt meter. Recently I posted a series on my website which may offer insight.

Article here:
Powering the Refrigerator article on janice142

In a nutshell you need more solar AND more batteries.
Also please don't forget as your boat heats up more power will be required to keep the refrigerator cool. I have two fans blowing at the back of my reefer. One is pointed towards the compressor and the second pulls hot air out of the compartment.

Adding: The fans are only turned on when the starboard side of Seaweed is facing the sun.

The Kill-a-Watt meter is a great tool. Don't take it as gospel however when it is giving you figures inside an air conditioned boat.

Good luck.
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Old 08-06-2018, 03:35 PM   #23
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My power readings are from my meter and comparison photos between two times over an unoccupied period of 96 hours.



Ill check out the blog. It sounds as if the easiest way would be to just replace my appliances with 12v and boost my batteries.
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Old 08-06-2018, 03:49 PM   #24
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Sorry if I missed it, but are you leaving your boat on the hook for days or where shore power is available?

If the latter then should no issue with a good marine charger.
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Old 08-06-2018, 04:16 PM   #25
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Sorry if I missed it, but are you leaving your boat on the hook for days or where shore power is available?

If the latter then should no issue with a good marine charger.
At a marina in the Bahamas with metered electric. .65 cents per kw though. If I use .8/hr that’s about $375 in electricity per month just to sit there maintains a cold fridge and freezer.

Dockage is already expensive and I’m planning on flying back and forth monthly so saving at least $300 a month is important.
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Old 08-06-2018, 04:39 PM   #26
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Originally Posted by k9medic View Post
At a marina in the Bahamas with metered electric. .65 cents per kw though. If I use .8/hr that’s about $375 in electricity per month just to sit there maintains a cold fridge and freezer.

Dockage is already expensive and I’m planning on flying back and forth monthly so saving at least $300 a month is important.

Hmm... at $375 per month, you could recoup the cost of additional solar and battery capacity pretty quickly.


The other option would be to simply not keep food frozen while you are gone. Use the freezer when you are on the boat and the rest of the time just have the fridge running. That would cut your power load by over half. I'd look at swapping out that 100W panel for a really good (and expensive) high capacity panel or two. I use a single panel rated at 365W. In the summer here it is able to keep up with a 12v fridge/freezer as well as 12v freezer/cooler in the cockpit. The days are long but it gets shaded quite a bit from the arch and radar etc...
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Old 08-06-2018, 04:41 PM   #27
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Another consideration is marinas in the Bahamas have electrical outages more regularly than what you may be accustomed to. Inverter could drain batteries to LBCO point typically set way to low rather quickly with your assumed usage and battery capacity.....
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Old 08-06-2018, 04:48 PM   #28
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Lots of good advice on here. You need a lot more solar AND a lot more battery bank to confidently do what you want to do.

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Old 08-06-2018, 05:40 PM   #29
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Are you sure that's the model fridge you have/are getting?
That's an explosion-proof fridge for hazardous locations:
https://www.agamarvel.com/scientific...tion/haz-6ear/

Also, the amperage quoted from your Grainger link will not be the amps it pulls most of the time, but the ultimate maximum it would ever pull in the worst case scenario, probably with some safety factor. In other words, this number is not what you're looking for when sizing your battery bank.
'Auto cycle defrost eliminates the need to manually defrost the refrigerator'

It is the defrost timer that turns on a small heater, that is where they get the advertised 3 amps number. Normal running this is likely around 1 amp. so the figuring out this battery requirement ought to consider it.

I also went with a 3000 watt MSW inverter, been happy enough with it. I am not using the MSW all that much, it is only for if the gen wont run and we are out away from shore power, or want peace and quiet.

One day I forgot to turn on shore power, or the grandkids had turned off the switch after coming back to slip. 3 days later, the inverter had flattened the house batteries, even with the battery charger on. My shore power, I put in a separate relay, so when I plug in to the shore dock plug, the battery charger will come on regardless if the relay for the AC system of the whole boat is set to off. But my house batteries were also 6 yr old starter batteries and they had self destructed with shorted cells. I replaced them with Duracell 'deep cycle technology' 12v batteries from Sam's club.


My auto defrost 10 cu foot fridge draws 0.9 to 1.1 amps with the compressor, and maybe 5 to 6 amps when defrosting cycle is on. I have an AC digital amp meter on both ac lines. Easy to see volts and amps real time.
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Old 08-06-2018, 05:46 PM   #30
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I would rely on mains, bank as a fallback for outages, shut down the heavy consumers as much as possible while away, go more "voluntary simplicity" provision for each trip out.

Next choice capital investment, really go as efficient as possible on appliances, beef up the solar and put in good monitor logging consider it an experiment, constant quality improvement until everything is reliable, ROI payback from the $300 / mo savings.
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Old 08-06-2018, 07:17 PM   #31
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We stayed in the Bahamas at the same marina from July 6th through July 21st.

Our total electric bill was $723.91 plus $86.87 for the VAT. We used a total of 1113kw according to my math. That comes out to about 3.3kw per hour with everything on (3 A/C's hot water heater, etc...)

Skimping on the food in the freezer is not an option. We plan on packing the freezer with as much as possible and then bring over what we need when we fly over.

I did make an arrangement for one of the local guys that I know to check on the boat for me while I'm gone but I still need to solve for the electricity issue.

As dhays said, I can recoup a lot of electricity cost over the 5 months that the boat will be there that way.

I just looked into 6 volt deep cycle golf cart batteries. I could drop two of them in there and get 500aH and since they don't have to start anything, I could probably draw them down to around 30% which is 350 aH.

If I drop two 100 watt solar panels on the top of my hard top then I could possibly see 150 watts an hour. So let's say a total of 750 watts on a 5 hour day sunny day.

Is this math coming out better?
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Old 08-06-2018, 07:49 PM   #32
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Are your 66ah batteries 6v? It takes two 66ah 6v batteries in series to get 66ah at 12v. Double check your math.
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Old 08-06-2018, 07:51 PM   #33
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I don't think this is going to work. Imo, there are too many failure points for unattended success. If it were me, I would want an inverter/ battery charger that would keep the batteries charged and switch to inverter if shore power went out. Then do a few months and see what you really consume in electric (shore power).

One of the calculations that's been missed is how much solar you will really need if you get the rare 2 cloudy days in a row.

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Old 08-06-2018, 08:34 PM   #34
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I don't think this is going to work. Imo, there are too many failure points for unattended success. If it were me, I would want an inverter/ battery charger that would keep the batteries charged and switch to inverter if shore power went out. Then do a few months and see what you really consume in electric (shore power).

One of the calculations that's been missed is how much solar you will really need if you get the rare 2 cloudy days in a row.

Ted


This. Go for minimizing shore power use. If it never comes on, you won’t spend anything. Strongly suggest a dc fridge. Also might want to go with agm batteries so you can charge faster when available. Size your battery bank not just for capacity, but to maximize the fastest charge rate when power is available, typically that’s around 25% of the bank ah capacity. Going from memory, others feel free to correct me. A smaller battery bank has a lower acceptance rate than a large bank. You also want to maximize the percent of time in a “bulk” charging mode. The last 20% of the battery charge will take more time than the initial charge for little added charge. Downside here is most batteries don’t particularly like going long distances between full charges. Gone for weeks will likely shorten battery life.

You are asking a lot. Might be worth it considering the relative value of replacing the food n the freezer, before t this kind of hardware is not going to come cheap. A plane ticket for the cooler might well be a cheaper option.
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Old 08-07-2018, 07:11 AM   #35
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From a battery perspective I have 4 AGM batteries that are 66aH a piece.
Those are pretty small. What BCI group? 12V batteries in parallel? That'd be 264 Ah for that bank when new, 132 usable at 50% DoD.


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I just looked into 6 volt deep cycle golf cart batteries. I could drop two of them in there and get 500aH and since they don't have to start anything, I could probably draw them down to around 30% which is 350 aH.
Most 6V GCs give approx 220 Ah each, so 220 Ah in series at 12V. Two pairs would be 440 Ah, etc.

The taller L16s in series would be about 300 Ah per pair...

Just because they're "deep cycle" doesn't mean manufacturers will recommend routinely drawing down below about 50% DoD.

Except for Firefly Carbon Foam AGMs, more $$$ each.

FWIW, our fridge/freezer units are AC/DC, so we don't lose anything to the inversion process when we run them on the batteries. Replacing perfectly good AC-only units would seem like getting into more serious money, though...

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Old 08-07-2018, 07:59 AM   #36
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Originally Posted by k9medic View Post
I just looked into 6 volt deep cycle golf cart batteries. I could drop two of them in there and get 500aH and since they don't have to start anything, I could probably draw them down to around 30% which is 350 aH.

Is this math coming out better?
Two 6-volt golf cart batteries would likely give you 220-250Ah, not 500. You need both of them in series to get 12V. Ah doesn't add together unless in parallel (you could have 500Ah at 6V).
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Old 08-07-2018, 08:47 AM   #37
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Old 08-07-2018, 03:50 PM   #38
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Well I dropped $20 on a kill a watt device today. The numbers will identify everything else I guess.

I got a hell of a deal on dockage for 5 months in the Abaco’s but an additional $300-400 a month for electricity would kill it.

I know I could turn the fridge and freezer on when I arrive but that would almost negate the “food savings” I plan on having.

In the end it’s only money I guess...
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Old 08-07-2018, 03:53 PM   #39
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Yes, in re-reading from the beginning, the whole system is designed for shore power, which is always cheaper than solar / DC.

If you want to go mostly-solar you need to put in much more efficient appliances and spend prolly at least $5K on supply and monitoring infrastructure.

Starting with consulting a pro who takes you walking through the boat, noting what can be salvaged and what needs replacing.

Big project, lots of owner time and energy.

In the meantime just pay for shore power.
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Old 08-07-2018, 08:44 PM   #40
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If you want to go mostly-solar you need to put in much more efficient appliances and spend prolly at least $5K on supply and monitoring infrastructure.

Starting with consulting a pro who takes you walking through the boat, noting what can be salvaged and what needs replacing.

Big project, lots of owner time and energy.

In the meantime just pay for shore power.


Great advice.
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