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Old 12-03-2014, 02:52 PM   #1
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How long will ref. run on DC

I am planning a trip to Alaska this coming summer.

Some of the legs of this trip will be on The Alaska Marine Highway System (Ferry).

They will disconnect my propane tanks in order to put the vehicle on the ferry.

I am trying to plan on weather to have food in the ref or not.

I have two 90AH Batteries and the Ref current draw on DC is supposed to be 15A.

How long should I reasonably expect the camper/ref to be able to run on DC before the batteries are completely discharged?
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Old 12-03-2014, 03:03 PM   #2
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Forget using 12 V. Buy some ice or dry ice for the ferry trip. Keep fridge closed.
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Old 12-03-2014, 03:13 PM   #3
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You need to upgrade your batteries, You have 90 amp hours you can use and at that point the batteries will be suffering damage (True deep cycles would not, yet) so 90/15=6 Of course other draws present so make it 5, or since those are likely Marine/Deep cycle 4

Upgrading to a pair of GC-2 Golf car batteries in series (Taller than you existing ones) would give you 230 amp hours 115 usable, so that woudl add an hour or more to your run time.

Fridge can sit, door closed, for several hours, epically if you turn down furnace a few degrees. (6-8 is very reasonable)

Hope this helps.
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Old 12-03-2014, 03:20 PM   #4
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Tell us how long the ferry trip will be and we can make some recommendations. And ... what is the ambient temperature at that time of year on the ferry?
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Old 12-03-2014, 03:26 PM   #5
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Bhoffman,

First let's do some simple math:

2ea 90 AH batteries = 180 (sounds like a grp 27) as it is probably not a real deep cycle, discharging more than 50% of capacity may cause damage. Marine combined types are not real deep cycle.
So, lets say you have 90 AH available from a real 100% Charge. (more about that later)

They say that the DC heater draws 15 Amps.
That would give you 6 hours (6*15) hours. That assumes 100% Duty cycle. For most RV reefers, 100% duty cycle is Quartzsite in the summer.
It also does not allow for the Peukert loss, but I don't think that is going to matter.

Let's guess at a 60% duty cycle.... That gets you about 10 hours. Maybe 12 if the weather is cold and you are lucky. Unfortunately, as I remember, may legs of the AMW are longer than that.

Things going for you:
-The reefer will not get warm immediately. A lot of people drive five or six hours with 2-way units and the gas off.
-Loading the freezer with ice will keep that cold enough to stay frozen and everything else cool if the door stays closed.

Thing not in your favor:
The likelihood of your having the house bank at 100% when your vehicle is loaded is not good. From a 50% to a 100% charge takes 6~8 hours of charging.

Enjoy the excursion. Try to take too many pictures. Carry extra camera memory and spare batteries.

Matt
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Old 12-03-2014, 03:31 PM   #6
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And, you won't be able to get at the refrigerator to shut it off when the batteries reach 50%, so unless it is a short trip, it is likely that you will discharge them more, resulting in the early demise of the batteries. Better to leave it off & buy food at land stops and eat it all, or, as Joe suggested, some dry ice (which will freeze things - careful of liquids).
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Old 12-03-2014, 03:36 PM   #7
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Quote:
Originally Posted by Bhoffman View Post
I am planning a trip to Alaska this coming summer.

Some of the legs of this trip will be on The Alaska Marine Highway System (Ferry).

They will disconnect my propane tanks in order to put the vehicle on the ferry.

I am trying to plan on weather to have food in the ref or not.

I have two 90AH Batteries and the Ref current draw on DC is supposed to be 15A.

How long should I reasonably expect the camper/ref to be able to run on DC before the batteries are completely discharged?
Don't think filling up with ice/dry ice will work. I want to be filled up with food (Food is expensive in Alaska, actually everything is expensive). Or just empty the ref. and stock up when I get in port.
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Old 12-03-2014, 03:43 PM   #8
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Originally Posted by wa8yxm View Post
You need to upgrade your batteries, You have 90 amp hours you can use and at that point the batteries will be suffering damage (True deep cycles would not, yet) so 90/15=6 Of course other draws present so make it 5, or since those are likely Marine/Deep cycle 4

Upgrading to a pair of GC-2 Golf car batteries in series (Taller than you existing ones) would give you 230 amp hours 115 usable, so that woudl add an hour or more to your run time.

Fridge can sit, door closed, for several hours, epically if you turn down furnace a few degrees. (6-8 is very reasonable)

Hope this helps.
I have 180 AH (Two 90 AH Batteries).

CG-2 Batteries are 6V, I have a 12V system. I could hook up two in series (If they fit). But I'll look into it.
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Old 12-03-2014, 03:46 PM   #9
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Quote:
Originally Posted by Bhoffman View Post
How long should I reasonably expect the camper/ref to be able to run on DC before the batteries are completely discharged?
Quote:
Originally Posted by yorgor View Post
Forget using 12 V. Buy some ice or dry ice for the ferry trip. Keep fridge closed.
Bhoffman
If you have an "LP, 120VAC and 12VDC refrigerator" and you operate it on 12VDC you will have no problems.
If, however. if it is an "LP and 120VAC" refrigerator and you intend to operate it on 120VAC power from your inverter, I would recommend using "ice" or "dry ice"... (as suggested by yorgor).
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Old 12-03-2014, 03:51 PM   #10
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Tell us how long the ferry trip will be and we can make some recommendations. And ... what is the ambient temperature at that time of year on the ferry?
Haines to Juneau 4.5 hrs.
Juneau to Sitka 6.75 hrs.
Sitka to Petersburg 9.25 hrs
Petersburg to Wrangell 3.25 hrs.
Wrangel to Ketchikan 6.0 hrs.
Ketchikan to POW Is. 3.0 hrs.
POW Is. to Ketchikan 3.0 hrs.
Ketchikan to Prince Rupert 7.0 hrs.


The weather should be in the 60s or 70s
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Old 12-03-2014, 03:56 PM   #11
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Bhoffman
If you have an "LP, 120VAC and 12VDC refrigerator" and you operate it on 12VDC you will have no problems.
If, however. if it is an "LP and 120VAC" refrigerator and you intend to operate it on 120VAC power from your inverter, I would recommend using "ice" or "dry ice"... (as suggested by yorgor).
Mel
'96 Safari, 134k miles
There won't be any 110 VAC or LP available. The unit will be in the hold of a ferry (LP disconnected).
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Old 12-03-2014, 04:00 PM   #12
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Well, what I can do is turn the fridge up all the way to 9 the night before while on AC power.


Turn the fridge completely off when putting the truck on the ferry


Whenever the 1st "pet visit" period is, go down into the hold/vehicle area and turn the fridge on (DC).


At the next "pet visit" period, check the battery level and turn the fridge off if necessary.


And so on, alternately.
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Old 12-03-2014, 04:14 PM   #13
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Get a bunch of the sealed ice packs, and freeze them. Then put them into frig as they will help keep it cold, but not turn to water that could leak. I agree once the frig is cold, it will stay that way for a good length of time if kept closed. The ice packs will work great for up to 10 hours in that already cold frig to maintain the cold.
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Old 12-03-2014, 04:35 PM   #14
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Don't think filling up with ice/dry ice will work. I want to be filled up with food (Food is expensive in Alaska, actually everything is expensive). Or just empty the ref. and stock up when I get in port.
Bhoffman
You don't "fill up" with either ice or dry ice... you use some to keep the inside of the fridge and freezer cold enough so that the food doesn't spoil while the propane is shut off... (rather than "taking a chance" with battery power and/or your batteries).

Quote:
Originally Posted by Bhoffman View Post
There won't be any 110 VAC or LP available. The unit will be in the hold of a ferry (LP disconnected).
I got that from reading your post #1 on this How long will ref. run on DC topic.
Mel
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