Figuring Energy Consumption

[redhead]

I have a 110 volt 5 amp refrigeration system. I'd like to run it through my large inverter and 6 golf cart battery bank. The batteries are set up series parallel to give me three large 12 volt batteries (220 amp hours per 12V battery)

How do I figure out how long it's going to run before I have to charge batteries?

[a64pilot]

It gets complex.
First a 5 amp 120 V system is roughly 50 amps at battery voltage, so now you know how many amps it pulls when it's on.
Then You need to know it's duty cycle, if it's 50% well then of course that cuts your use in half.
Then factor in both the efficiency of the inverter, often around 90% and how much the inverter draws just being on.

However duty cycle I have found is wildly variable, throw in a case of beer and a 20 lb watermelon, and my fridge runs continuously for 24 hours.

I also question the power consumption as 5 amps at 120 V is 600W, and that would be one monstrous fridge.

You have 660 AH of batteries, likely really only 600 AH as most things are not as good as they claim to be.
So you have 300 AH usabe, so if you really do pull that much power, you can run that fridge for less than 6 hours of running time.
One reason is if you hit batteries that hard, they don't come close to giving rated power, you have to drain them over a 20 hour period to get that, then there is the inverter efficiency and it's power it uses just being on.


I can't imagine a fridge drawing 600 W though.
A dorm fridge might draw 60, but I'd suspect more

[Stu Jackson]

http://www.cruisersforum.com/forums/...ge-180007.html

[waeshael]

Originally Posted by redhead

I have a 110 volt 5 amp refrigeration system. I'd like to run it through my large inverter and 6 golf cart battery bank. The batteries are set up series parallel to give me three large 12 volt batteries (220 amp hours per 12V battery)

How do I figure out how long it's going to run before I have to charge batteries?

Answer:
First you can only take out each day what you can put back in with the solar panels, or engine charger. And you need to generate 20% more input A_hrs than you use. It doesn't matter how big the battery bank is, the limit is the charging system
Your fridge would take 50 Amps at 12 volts, and a good fridge will run on 3 Amps (mine does) SO there is no way to run that fridge at sea. In any case the solar panels have to run the fridge not the batteries. In other words during the day the panels must be able to run the fridge and still charge the batteries, so that at night only a small amount of battery power is used up. On my boat from 4PM to 6AM the battery runs the fridge which stays closed all night and so runs less time. It uses about 25 A-Hrs during the night. So next day the sun has to put in 30 A-hrs to recharge the batteries, 35 A-hrs to run the fridge and about 40 A-Hrs for other electronics (autopilot, Nav lights, radio etc. So each day I would need about 100 A-Hrs going back into the systems. I have 8 siemens 55 watt panels sitting in the clear and can generate 24 amps at noon, for a total of just over 125 A-hrs a day. Now all I need in the battery bank is about twice that, to enable me to keep them fully charged. SO 250 A-Hrs would be good for battery capacity. That's if the batteries stayed in new condition, but they deteriorate and when the charge held gets down to 50% they need to be replaced, so I would start with 440 A-hrs in battery capacity which is 4 golf cart batteries.

Measure the A-Hrs on the controller and keep a log for a week or so to see what the worst case is for charging.
Then install a fridge that can run on less A-Hrs than you can provide. Inverters are lossy, so a 12 volt fridge is best. One that is very efficient like an Engel. Here's my old unit file:///Users/charlesmiller/Public/waeshael.com/Refrigeration.html

Newer smaller units are even more efficient.

Of course you have to also run instruments, radio autopilot and so on. Find out what they take in Amperes using a clamp on ampere meter or read each devices consumption from the charge controller. Log the current, the number of hours it uses that amount of current, and calculate the A-Hrs a day it needs. Total it all up, and start figuring out how to reduce it by installing more efficient lights, fans, and so on.

Hope this is helpful

Waeshael E.E. O.N.C. O.S.V

[redhead]

Thanks A64. The fridge is a 110V commercial refrigeration condenser built in 1981 by a bunch of drunk merchant marines who were imagining storing all those cases of beer. We have 3 built in, front opening boxes - each about the size of a dorm fridge. Freezer (supposedly) on top with cold air seeping (supposedly) into two cold boxes below.

We are planning to tear it all out but the boat dollars just don't stretch that far this year.

Thanks again.

[redhead]

Originally Posted by redhead

Thanks A64. The fridge is a 110V commercial refrigeration condenser built in 1981 by a bunch of drunk merchant marines who were imagining storing all those cases of beer. We have 3 built in, front opening boxes - each about the size of a dorm fridge. Freezer (supposedly) on top with cold air seeping (supposedly) into two cold boxes below.

We are planning to tear it all out but the boat dollars just don't stretch that far this year.

Thanks again.

Thank you all. Your responses led us to measure the condenser draw, which the label said was 5 amps and right now it's only drawing 1.3 which is good news. Back to the calculations. Here's what we're dealing with.

[a64pilot]

You likely have a thermostatically controlled expansion valve.
It will vary the load on the compressor based on heat load in the box. Mine for example with warm cold plates will draw 15 amps at 13 VDC, but later as temps stabilize at or near set point, it only draws less than 5 amps. Add a case of beer or other large items to cool down and power will increase for awhile until time gets cooled again

You can live with that 13 amp draw, especially if it's not 100% duty cycle, but your likely going to need a Honda or other generator to recharge the bank every day, or probably more than 1 Kw of Solar.
1 KW of panels is good for a little over 300 AH on a good day

[djmarchand]

You need to know the running current draw, which you now report is 1.3 amps. You also need to know how many hours it runs in a 24 hour period.

Then convert that to daily watt hours by multiplying 120 times 1.3 times hours and divide by 12 and .9 (inverter efficiency). That is how many DC amp hours it takes to run the fridge for 24 hours.

Then divide that number into 330 AHs (the usable amount from 6 parallel/series GC batteries) to get how many days it will run without recharging.

David

[a64pilot]

If they are working well, I think Id spend some money feeding them, you can spend a tremendous amount of money replacing them and may not save as much energy as you think.
My opinion is energy savings is primarily in insulation, not in fancy controls and exotic installations.
If you decide to tear them out anyway, consider something like Engels or another good cooler type of fridge / freezer to replace them, that gives you redundancy , and as they are independant, you can run as many or as few as you need, and if they go bad, just go to the box store and buy a new one. They can also be either a fridge or a freezer so you could run all as fridges or all as freezers etc. As the cruise progresses, you turn one off as it gets empty so you have a variable sized freezer or fridge as you chose.

Even though you rbank is rated at 660 AH, Id do my calculations on it being only 600, that way you can be safe about not going below 50% capacity.
50% is not a cliff, but it's a good, safe number

If I were starting over, I think it's what I would do.

[sailorboy1]

My 12v dc frig draws less than 5 amps 90% of the time and less at night once I stop getting into it and go bed

But the big issue to me of this 120v AC system off he inverter is the power the inverter draws when in standby. My inverter draws 4 amps if you just run it on.

[a64pilot]

Wow, my MS 2812 which is a 2800 W continuous, 3500 surge I think, draws 20 Watts if memory serves, a little less than 2 amps.
However it’s enough so that over a 24 hour period, it adds up, up to about 40 AH, doing nothing, I bought the smallest pure sine I could find to run the TV etc. to get away from the standby power or whatever it’s called.

I stand corrected, it’s less than 8 Watts, searching, but 30W in standby no load, so 2.4 amps

[sailorboy1]

Yes I have. liittle 400w unit for the tv and laptop charging. You get that idea from anyone?

Btw I also have a USB multi port strip at the salon table off the house batteries. Uses nothing when not in use.

[a64pilot]

Likely this guy?
http://www.pbase.com/mainecruising/i...r_inefficiency
Although I question what kind of TV he is using for a 19”to draw so much, my 32” draws much less
Initially I ran a TV I got from Best Buy that ran off of 12V native and I didn’t need to use an inverter, except when we watch the Satellite, the Sat receiver has to have 120 VAC and that means an inverter, it draws almost nothing for power, but has to have an inverter.
The disk drive that is the recorder had a wall wort that I threw away and it runs off of 12 VDC as does the Blue Ray as it converted to 12V via a wort too.
My savings are a lot more than Maine Sail saw, I assume this is in part due to my main Inverter is larger and the one I got for the TV much smaller.
I’m using this guy
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1