refrigerator and battery drain

[bkw]

this might not be the correct forum for this question but here goes.
assuming your batteries are in good shape how long can you run the refer before having to start and charge batteries.
bob

[PBzeer]

The main problem with your question isn't where you put it, but that there are too many variables to consider, in order to give you a good answer. The size of the battery bank, the draw of the frig, as well as other systems running at the same time, are two important factors. Without those, it's hard to say.

The simpliest solution would be to monitor the batteries and chart your usage. If you don't have a battery monitor, it would be a worthwhile addition.

Regards,

[hellosailor]

Well, you CAN run the reefer till it stops and the batteries are dead, then you start from another means.

In practice, most batteries give much longer life if you only discharge them and cycle them to the 50% discharge point, which is roughly 12.1 volts for wet acid batteries. You'll need to run some numbers and/or use a multimeter to see how long you can run your own particular reefer before reaching that point for your own battery setup.

[camaraderie]

First thing you need to know is how much YOUR fridge draws for current in amps. Average unit draws between 4-6 amps. Then you need to know the amp hour capacity of your house battery. (You want to have a starting battery separate from the house!) Then divide that amount in half. If you have a 4D battery with 150AH capacity...you have 75 Amp hours to work with. If your fridge in this case drew 5 amps...you would be able to run it for 15 hours absent any other electrical needs. Note that fridges don't run full time and most boaters DO run other stuff so a more practical solution is to wire in a LINK10 which monitors your usage over time and adjust.

[sailingdog]

That's kind of like asking how far a car will go on a full tank of gas without knowing what engine is in it or how large the gas tank is, or how the driver will be driving it, and what the route they're taking is. It depends.

If you have a huge battery bank and a tiny refrigerator...might go a few days... If you have a huge refrigerator and a small battery bank, might only be a couple of hours.

You need to do an electrical budget survey of your boat, and your typical electrical usage. This will give you a rough idea of how many amp-hours your are going to use over the course of a day. Then you have to look at what the capacity of your battery bank is.

Running your battery bank down more than 50% is a very good way to shorten its lifespan...so take whatever the amp-hour capacity of your battery bank is and divide it by two or three, and then divide that by the amp-hours of your average daily usage, and that will tell you how many days, on average, you can go before having to recharge your batteries.

For example... your daily amp-hour usage is 100 amp-hours. Your battery bank consists of four (4) T105 golf cart batteries, for a total of 420 amp-hours. That means you can go roughly two days before recharging your batteries.

However, this also assumes that you have sufficient charging capabilities to properly charge up your batteries in a reasonable amount of time. 80% of your charging takes 20% of the time and the remaining 20% of the charge takes about 80% of your time. Many people skip the last 20% but this will also lead to fairly shortened battery life.

[SmartCaptain]

Some real-world data points:

My O'Day 25 had a small icebox (about 2.5 cubic feet), rather poorly insulated, with a small Isotherm refregeration system. The unit drew about 4 amps when running and ran about 1/3 of the time in hot summer weather. Energy used was about 8 hours x 4 amps = 32 amp hours.

My Island Packet 38 has a large icebox (14 cubic feet) with medium to poor insulation. My Adler-Barbor cold machine uses 6.5 amps when running and runs about 2/3 of the time when the outside weather is 80 degrees +/-. Energy used is 18 hours x 6.5 amps or about 117 amp hours. Clearly, I need better insulation. :-)

How about some other data points?


Jeff

www.smartcaptain.com

[camaraderie]

Jeff...More data points....Two big separate cold plate boxes..one freeze, one fridge with front opening door (lets the cold air out!). Both well insulated.
Seafrost DC compressor draws 40 AMPS...(no typo!!) but only runs a few times a day for about 1/2 hour at a time as it freezes the cold plates solid in about a half hour. Averages 150 AH/day in 80+ degree weather.

[btrayfors]

Jeff,

More data points. My boat has a 16 cubic foot top-loading refer with small freezer compartment on one end, medium to poor insulated like yours. No holding plates.

The 20-year old air-cooled Adler-Barber draws over 6 amps, and runs 75-80% of the time in 80-deg ambient temp. Same draw as yours...over 100AH per 24-hour period.

Bill

[ebs001]

My air cooled alder-Barbar also draws 6 amps and runs about 75% of the time in 80-deg weather. I am looking into adding more insulation on the inside of the icebox. I have found a material that has a 30R value per inch and am going to investigate its suitability and cost for my application at the Annapolis boat show. For some reason boat mabufacturers do not think refers need insulation and I have no idea why.

[hellosailor]

ebs-
"For some reason boat mabufacturers do not think refers need insulation and I have no idea why." Easy. Because if their ice box is six inches smaller than the next brand, or their $200,000 boat costs $100 more than the next brand, the average buyer is going to buy that other cheaper boat with the bigger ice box and they lose the whole $200,000 sale.

"Mass market" manufacturers can't spend money on intangibles or invisibles, the mass market won't support it.