Went out of power in 4 hrs.

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elvatoli
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Went out of power in 4 hrs.

Post by elvatoli »

we went sailing on Sunday and after 4 hours of sailing the power alarm from the inverter started to sound
We have two group 27 Interstate marine batteries (8 mo old), connected together (fully charged), and an inverter (2000w)/ charger.
We run 1 small fan, a small fridge, the CD stereo, a depht sounder/speed (standard horizon)
So I started the engine, and it turned on with no problems, so there were enouh power left in my 2 battery bank combined.
Do I need a third battery ?, or better charge reserve batteries ?

Thank you
Hector
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bartmac
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Re: Went out of power in 4 hrs.

Post by bartmac »

You need to carefully add all power used and for how long and then set up a system.But most certainly the fridge is the one item which will suck the most juice.Unless you run your engine regularly or have another charging system what you have described is wholly inadequate except for very minor usage ie radio/stereo,instruments but certainly not a 2000W inverter.....the amperage draw will suck those batteries dry and leave you without starting power not to mention what it will do to your life span of the batteries.Unless you are prepared to spend a fair bit of money forget about the fridge
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Russ
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Re: Went out of power in 4 hrs.

Post by Russ »

My bet is the AC fridge is pulling a LOT of juice. A 200 watt fridge is not much at 110v but on the other side of the inverter is probably closing in on 20 amps!

That's why many of us use real 12v compressor coolers. See this thread.

--Russ
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Re: Went out of power in 4 hrs.

Post by mikelinmon »

me to on the refridg causing the battery to go out. My one and last refr exper. was a motor that left me stranded with only an onshore storm wind. Pull anchor and sail out of danger. i now use the old 8lb block of ice, it will last all weekend.
Mike
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rwmiller56
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Re: Went out of power in 4 hrs.

Post by rwmiller56 »

RussMT wrote:My bet is the AC fridge is pulling a LOT of juice. A 200 watt fridge is not much at 110v but on the other side of the inverter is probably closing in on 20 amps!

That's why many of us use real 12v compressor coolers. See this thread.

--Russ
I agree with Russ. AC fridges are not optimized for power consumption. The 12V marine fridges are.

BTW, a good rule of thumb to determine DC current draw from the batteries when using an inverter is to divide the AC power consumption of the appliance by 10.
So, the 200W fridge will draw about 20 Amps from the batteries. This takes into account the typical efficiency of most inverters (85%).
This agrees with Russ's estimate.

Just total up all your DC loads, in amp-hours, for one whole day of use. The goal should be to not draw the batteries down by more than 50%. This will leave you with ample starting power for the engine. If you will be on the hook all night, you will need to replace that amount of power by running the engine, or by some other means. If you are heading back to a marina with shore power, then it is a moot point!

- Roger
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Re: Went out of power in 4 hrs.

Post by Highlander »

I try to keep a plastic bottle or two of frozen water in my 12volt cooler then when I disconnect from the 110hydro at my slip the the cooler will stay cold while sailing when powering I can plug into 12v

J
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Re: Went out of power in 4 hrs.

Post by Catigale »

C fridges are not optimized for power consumption. The 12V marine fridges are.
Is this really true? (Im not a fridge expert) Power losses in electronic stuff are usually resistive, and low voltage DC means higher currents which means more loss...

Last time I bought a fridge, I recall there was quite a bit of cost-of-ownership marketing on it, so I do think they pay attention to electrical efficiency...
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Don T
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Re: Went out of power in 4 hrs.

Post by Don T »

Hello,
I just looked at a small fridge in my office. It pulls 1.5 amps at 115V. That's 133 watts which figures 156 Watts (133/.85) netting a 15.6 amp draw. Depending on the batteries you have (I am assuming they are not Trojans), maybe 100 amp/hrs you can use until 50% SOC. At continuous draw that's 6.5 hours. At 25% duty cycle you will get 24 hours, BUT not really. Inverters alarm when Battery voltage drops to 11V (average but is adjustable). So the alarm goes off early because it checks while under load. Sulfated batteries will drop more voltage under the same load.

DC marine fridges use a thermal mass plate internally to improve efficiency and reduce duty cycle and therefore use less power. It helps to use pre-frozen / cooled food so the fridge does not have to cycle a lot to cool the contents which can increase the duty cycle to at least 50% on the ac unit. That will shorten time to 50% SOC by half (12 hours)

Inductive loads require a pure sine wave inverter. If you are using a modified wave inverter the loads are much higher and a lot more power is dissipated as heat.

I hope that is clear enough.
bartmac
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Re: Went out of power in 4 hrs.

Post by bartmac »

Its also a case of be prepared......freeze everything you can...bottles of water which can later be drunk,milk..... BUT NOT THE BEER.....get the fridge cold on mains prior to departure
And maybe you can't have all the comforts of home but that makes it an adventure
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Re: Went out of power in 4 hrs.

Post by Hardcrab »

Not to mention that inverters have an "overhead" current sucking on batteries before any AC load gets applied.
I could be wrong, but a 2000 watter is around the 8-10 DC amps range, as I recall.
Add that to your known AC loads and weep.

Overkill in inverter wattage is not always a good thing.
One popular strategy is to size an inverters expected load at 50 to 80 percent of inverter rating.
Or in other words, a 50 to 80 watt AC load calls for a 100 watt inverter, a much better choice than that same 50 to 80 watt load on a 2000 watter.
vizwhiz
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Re: Went out of power in 4 hrs.

Post by vizwhiz »

Don T wrote:Inductive loads require a pure sine wave inverter. If you are using a modified wave inverter the loads are much higher and a lot more power is dissipated as heat.
Man, I got goose-bumps reading this techno-explanation! Who'd have ever thought sailing could be so cool! :D
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Re: Went out of power in 4 hrs.

Post by Catigale »

To really get to the bottom of the efficiency question you would have to measure voltage, current,and duty cycle over a day and add up the numbers. The disconnect I have is I thought that Peltiers (Viva la France!!!) were about 10% Carnot efficient, but compressors are ROM 40%...maybe Ive got that wrong.
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Re: Went out of power in 4 hrs.

Post by Hamin' X »

The refrigeration units that use the Danfoss type of compressor, use about 1/3 of the energy of a similar sized home unit and run directly on 12v.

~Rich
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Russ
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Re: Went out of power in 4 hrs.

Post by Russ »

Another factor is home fridges have front opening doors. Open the door and most of the cold air rushes out. Not a big deal when you have 110v to cool it back down. Running on 110v from 12v inversion it costs more.

Big inverters should be used for short duty cycles only IMO.


--Russ
bartmac
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Re: Went out of power in 4 hrs.

Post by bartmac »

Re- the front opening fridges and the air rushing out....my thoughts were the same however the actual math of the volume of air and the amount of BTU's.....well my knowledge is not good enough but it was explained to me to relatively insignificant.We live in an area where there are a lot of alternate people and with no mains power and for the most were using gas (LPG /Propane) to run thier refrigeration ie absorbtion? rather than compression.The advent of more efficient inverters,solar panels etc has seen most switch to 12 & 24 Vdc fridges.
Hopefully as we are looking to set up both a 26X and a motorhome capable of long/medium term independence from mains....using small front opening second hand fridges I buy from the big boat people upgrading thier "ginpalaces & floating footpaths" inconjuction with a Waeco 35 litre top opening fridge/freezer capable of subzero operation (loaded at home brought down in temp using mains filled with a combo of foodstuffs capable of freezing and bottles of ice)The bottles of ice are later used for drinking or if still ice transfered into the fridge to help minimise temp.
Having just purchased a programable solar controller and inconjuction with 200 watt panels which is capable of charging multiple battery banks...the thought was to install a 3rd battery set up to take the excess 12 v which could be used for extra "luxury" refrigeration when available ie freeze water...ice cubes,beer or just water bottles.We would end up with the 2 start batteries charged,3 AGM "house"batteries charged and a smaller bank useable when there's enough 12 v ie sun
The portable waeco fridge is also doing double duty in the tow vehicle/motorhome going to and from launch sites and is able to run of the abundant 12 v made by the alternator of our tow/motorhome
Last edited by bartmac on Wed Oct 06, 2010 9:56 am, edited 1 time in total.
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