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Old 28-05-2020, 18:34   #1
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fridge and power help.

help!!! dc power is not my forte...
recently my old dometic gas/elec died so i need to replace it..

i still work so adding solar or more batteries is not going to happen for a few years.
just trying to work with what i have and would prefer NOT to put another propane unit back in...

this is my setup. i am at a dock with 110 power and will be for a few more years. sailing is mostly day sails with the occasional over night at anchor.
i have two interstate deep cycle group 24 batteries, 12 volt, i believe 160 amp hours total for both house and start (yes i know but as i said this is
what i have and not ready to change things yet)..
i am looking at an isotherm cruise 130 elegance which power consumption (W/24) is 400..
no solar so the only charging is shore power or off engine when running (which is just in and out of marina)..

the question is, do i have enough battery to run this all day and still start my engine 10 or 12 hours later???
also do i have enough to spend the night and restart engine the next day, lets say 36 hours later???
the rest of my power consumption is minimal, a radio (sirus radio boom box), nav lights if needed, water pump for dishes, not much else.

thanks for the help.... Frank
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Old 29-05-2020, 03:06   #2
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Re: fridge and power help.

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Originally Posted by SunKing View Post
help!!! dc power is not my forte...
recently my old dometic gas/elec died so i need to replace it..

i still work so adding solar or more batteries is not going to happen for a few years.
just trying to work with what i have and would prefer NOT to put another propane unit back in...

this is my setup. i am at a dock with 110 power and will be for a few more years. sailing is mostly day sails with the occasional over night at anchor.
i have two interstate deep cycle group 24 batteries, 12 volt, i believe 160 amp hours total for both house and start (yes i know but as i said this is
what i have and not ready to change things yet)..
i am looking at an isotherm cruise 130 elegance which power consumption (W/24) is 400..
no solar so the only charging is shore power or off engine when running (which is just in and out of marina)..

the question is, do i have enough battery to run this all day and still start my engine 10 or 12 hours later???
also do i have enough to spend the night and restart engine the next day, lets say 36 hours later???
the rest of my power consumption is minimal, a radio (sirus radio boom box), nav lights if needed, water pump for dishes, not much else.

thanks for the help.... Frank

Yes. You’ll just barely squeak by with your given setup, but at least buy yourself a starting battery for the engine so you can separate the house and engine bank.

A starting battery costs nothing compared to your new refrigerator and will allow you to use those house batteries without feeling all the stress you’ll have wondering if you went too far to be able to start the engine.

It’s too easy to make a mistake (listening to a little extra music or leaving a couple hours later to go home due to weather) and have your engine unable to start. So pay your $80 for that safety.
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Old 29-05-2020, 05:22   #3
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Re: fridge and power help.

As far as fridge replacement, would just get a dorm sized land based fridge for now, then at your leisure possibly build in a dc fridge and your dc system.
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Old 29-05-2020, 05:24   #4
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Re: fridge and power help.

Like Chotu said, grab a starter battery and keep it as a separate bank. Then even if you run the house batteries dead with the fridge you can start the engine and get back to dock. Your food will keep for most of the day even if the batteries are dead, until you get back to dock.

I grabbed a cheap 200w solar "starter kit" off of Amazon last month. Even in the heat of key west my 60qt fridge only uses half the day, so the panel is on float for 5 hours a day. I'm running two 90ah batteries (for now) as a stop gap until I finish the complete rewire of the boat.


I just have the solar panels sitting on the deck, with the wires running through a vent into the engine room. It would be easy to set this up so you could take it down while out sailing, and set up in 10 minutes when you anchor. Especially if you went with a smaller size just to "top off" your batteries at anchor.
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Old 29-05-2020, 06:11   #5
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Re: fridge and power help.

SunKing, you've gotten good starting advice above, in particular that of separating out a starter battery so you are not at risk of not being able to start the engine coming home. Separating it at the minimum means charging it off the alternator and using shore power to charge the house batteries. Combining/separating the two sources for shore/alternator charging means a battery selector switch (the big round red ones) or a pair of jumper cables in the meantime.

Let me recommend Charlie Wing Boatowner's Illustrated Electrical Handbook.

https://www.amazon.com/Boatowners-Il...s%2C215&sr=8-5

He'll lead you through DC circuits, and on to such topics as AC circuits and corrosion control. Ultimately, knowing your boat keeps you safe and happily sailing.
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Old 29-05-2020, 07:55   #6
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Re: fridge and power help.

You know that you can get these units in dual voltage right? 110 Vac and 12/24Vdc.
That way it runs on shore when available and then switches automatically to dc when you unplug from the dock
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Old 29-05-2020, 10:17   #7
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Re: fridge and power help.

Quote:
Originally Posted by Chotu View Post
Yes. Youíll just barely squeak by with your given setup, but at least buy yourself a starting battery for the engine so you can separate the house and engine bank.

A starting battery costs nothing compared to your new refrigerator and will allow you to use those house batteries without feeling all the stress youíll have wondering if you went too far to be able to start the engine.

Itís too easy to make a mistake (listening to a little extra music or leaving a couple hours later to go home due to weather) and have your engine unable to start. So pay your $80 for that safety.
Ditto!
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Old 29-05-2020, 10:27   #8
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Re: fridge and power help.

Fridge/Freezer is usually 1,5 Amps/hr when cold and around 4Amps/hr cooling freezing down for 4-5 hrs. So if both required you need 20 + 28,5 = 48-50 Amps/Day
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Old 29-05-2020, 17:12   #9
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Re: fridge and power help.

for cheap quick and easy i'm with Bill O.
dorm fridge about $100. small inverter about $50.
run it from shore power when you're at dock. switch
to the inverter when you're away from the dock.


will give you time to really think about fitting out
the boat for the future while you're driniking a cold cerveza...
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Old 29-05-2020, 17:21   #10
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Re: fridge and power help.

I have two inverters but I would never ever run a 230V AC unit on board if I can avoid it. An AC Fridge? Why? looka at the Waeco units. They do not use much power, are super silent and efficient as hell.
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Old 29-05-2020, 17:49   #11
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Re: fridge and power help.

thanks for the input... i have already brought a small ac powered unit for temp use and will just shut it down for daysails while i decide on the plan of action. it will just be for cold drinks for now..

the fridge i am looking at is a 110/12 volt unit and will be on shore power most every night and only be on 12 volt during the day and already cold. also hopefully a few weekends at anchor too. it is for then i was asking if i had enough power to run it and still have plenty to start my engine.

it is in the plan to upgrade the batts and add a start batt isolated but that is/was for the future.
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Old 29-05-2020, 18:44   #12
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Re: fridge and power help.

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Originally Posted by moseriw View Post
I have two inverters but I would never ever run a 230V AC unit on board if I can avoid it. An AC Fridge? Why? looka at the Waeco units. They do not use much power, are super silent and efficient as hell.


Well, Iíll guess that a Waeco would set you back much more than the price of a secondhand bar fridge and small inverter.

Which, for the OP, is what I did while I was refitting my boat. I wanted a decent inverter for cruising, so I bought that first, then used it to run a $70 bar fridge for about a year.

Meanwhile, as part of the fitout I built a 230 litre chest spillover fridge/freezer which is now powered by an Ozefridge eutectic.

Sold the fridge on gumtree for $50, so I was $20 out of pocket for the year and I didnít need to stress about damaging the thing while I was doing the fitout.
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