Different slant on the refrigerator question

[Rocinante33]

Hi all,

I hope that it is OK to start a new thread on the subject of refrigerators + inverters as the questions that I have a re not really addressed on the existing forums that I have found, including the excellent thread in August. My questions are more about inverters and less about fridges

I put a dorm fridge in and hooked it to a West Marine 1000w inverter back in the summer. West has four different 1000w inverters on the shelf ranging from $60.00-$400.00. I bought the middle priced 1000w (model # 1582 479 1000) for about $140.00 and plugged in my Home Depot Magic Chef dorm fridge which is rated to draw .8 amps and it worked. I have a 2x4 solar panel that generates 120 volts. The boat has little other in the way of power hogs (2 bilge pumps, water pressure pump, navigation electronics, couple of radios, and a bunch of LED lights). I have 3 deep cell batts with ~90 amp hour storage.

In the summer in south Florida that panel would generate sufficient power to run the fridge 24 hrs per day whether I started it up or not. Occasionally, around 5 am the alarm would switch on and I would just cut off the inverter and turn it back on when the sun came up.

When I returned at Christmas, the inverter had changed its behavior. There are three running conditions when you start the thing up;

All of these colors relate to the LED in the power button which has the only condition light;

blue light=all ok.
yellow light=low voltage flashing, inverter works
red light=inverter shuts down with warning signal indicating loss of (or insufficient) power

If I try to start the inverter with engine shut off, it goes immediately to red and fails to start.

If I try to start with engine running it fails in the fashion above. But if I unplug the fridge, start inverter and replug, it sounds alarm, but starts. I then unplug again, and when I replug in the fridge, the inverter starts and runs normally.

If I run the engine, the fridge runs indefinitely. If I shut off the engine, I will get only about an hour before the inverter goes to red. This happens whether I run the engine for 5 minutes or I motor for 5 hours. The owners manual is telling me that power has dropped, but my screen is telling me that I still have 11.9-12.2 volts

Since I had bought the protection plan, I took the inverter back to West and they gave me a new one. Worryingly, the price on the remaining units had been cut 50%. When I plugged that one in I get the exact same results as above.

My Lowrance has a built in multimeter that shows the DC current and it shows 13v with engine running, and between 11.8 and 12.5 (mostly 11.9-12) with the engine shut off regardless of how long it is shut off. By morning it is usually still reading 12.2-12.4 so I think that I have adequate storage.

Have tried for two days to call the Black and Decker # on the inverter for customer service and after waiting for several minutes, calls are auto dropped. Had hoped to talk to a tech there, but does not look like that is going to happen.

Thanks in advance, any thoughts most appreciated!

Cheers

[StuM]

Your battery bank is too small, you've been killing them with the way you are using them (too high an Amp draw from the inverter all the time).

I presume you mean that your solar panel is 120 Watts, not Volts ( you may like to read here: http://www.cruisersforum.com/forums/...ml#post1933764). You have probably not been bringing the batteries back to full charge, so that has helped in killing them.

The 11.9-12V battery voltage also says that they are dying. That means that the batteries are down to less than 25% SOC! They should NEVER be allowed to get that low!

There is almost certainly nothing wrong with your inverter or fridge. It's your under-spec'd battery/solar setup that is the problem. You need new batteries and a better energy source - either a lot more solar, or a small genset (or an engine alternator) that you can use to get a quick bulk charge first thing in the morning.

[tkeithlu]

StuM speaks with great wisdom. I'd like to add that refrigerators and inverters don't like each other very much because the start-up spike when the refrigerator compressor kicks in is a whopper, and can cause the inverter to flip out when there is still plenty of battery left to do the job of running, but not starting. Once they flip out, they don't flip back. You can take some steps to minimize the problem (really big battery to inverter cables, a capacitor on the DC side), but don't think that the running watts listed for the refrigerator is what you need from the inverter.

[hellosailor]

As stu said, you've murdered your batteries. Apologize to the inverter, and start battery shopping. Even if you have real deep-cycle batteries, that means they can provide the rated power about 50 times, and that's all. They can provide 50% of that power more like 800 times, and 1/3 of the rated power maybe 2000 times. So you really never want to pull more than 1/3 of the rated capacity out of them.

Your fridge and inverter together are pulling more than 100 amps at 12 volts, more like 110-120amps. So in 24 hours, they would pull something like 2700 amp hours IF the fridge really took that much power on a continuous basis. It may only pull full power1/4-1/2 of the time, as it cycles on and off.

I'm on decaf today, someone correct me if my math has gone wrong.

There are plenty of threads online, plenty of web sites, couple of very good books, all of which can tell you how to do all the math. But the bottom line is, you murdered those batteries and you'll need a very much bigger set if you want the next ones to last longer. In any case, you need to run those numbers and find out just how big a battery bank you will need, factoring in whatever power the solar array puts out

[Sailmonkey]

.8 amps at 120 vac is more like 8.3 amps at 12 vdc.

However, your solar panel is insufficient to support loads like that, leading to murder of your batteries.

[Stu Jackson]

sailorchic34 has been using an inverter and dorm fridge successfully for many years and has written extensively about her setup. Do a search using her username to find them. Stu's right.

[Ivansgarage]

Here is one more option, I was a truck driver for years and used these
kind of refrigerators 12v, a inverter waists energy, I have had a truck frig run for days on three batteries 300ah and still start the truck.

TruckFridge Model: TF49 - Fits most KW, Pete - 63" sleeper, Freightliner Century, Columbia, Coronado, Cascadia, Mack and 2009 + International Pro Series Trucks

[Rocinante33]

Thanks for the replies,

My following questions/thoughts are designed to illustrate my thought process and not an argument. Since it is not working right, obviously there is a flaw. I would appreciate help highlighting the flaw in my analysis.

First off, the solar charger is 120 watts and not 120v. Thanks for the quick reference StuM

So my thought process went like this. The dorm fridge will consume a little over 2 amps/hr, which means about 48 Amp Hours per day. This is a little high as the thing cycles on and off, but this assumes constant operation.

The solar panel generates 5.5 amps/hr (@ 18 volts) and the sun shines on average in South Florida for 12 hours. Assuming all of the conversion to 12v is lost, that is 66 amps per day into the batts.

First, on a continuing power consumption basis (not power from storage)

Assume that I lose half of that for sun angle, cloudy, etc. I am still at 2.75 amps/h and not pulling nearly that amount, so why would it shut down on a bright sunny day? A 'murdered' battery should not make a difference at that point, right?

On the power storage issue;

I can see that putting in 66 amps/day and then assuming 50% loss is going to put consumption ahead of production. I can see that I will need to increase the capacity of the batts.

What rule of thumb ought I use? If my calculations start at 2.5 amps/hr and lets say for argument that I want the fridge on all night, then I will be using 60 amps per day.

If that is right, then how much solar power do I need to produce 60 amps in 12 hours of sunlight with shade, angles, clouds, etc. Is assuming 50% loss reasonable?

If so, then will 2 solar panels, which generate 66 amp hrs/day each (total 132) and then I lose half due to inefficiency, take me back to 66. That seems to be 10% over with some generous assumptions for loss.

Now on the question of storage, I clearly do not have enough. Thinking of a batt as a pail of water is probably not the right methodology, but it is the one I used.

How many amp/hrs should I plan to store in order to meet the storage needs for the above consumption and generation? If I use 60, and I never want that ot be more than a third, then 180 amp hrs of storage (round up to 200) be enough?

The only forum post regarding 'sailorchic' that I could find seems to indicate that she has 400 amp hrs of storage for what I have proposed above.

I do not want a genset, and I do have the alternator already.

I estimated 90 amp hrs of storage, but I have 125 on paper, was just assuming that as teh batts age, I lose capacity. You are, if I understand you correctly, clearly telling me that a reading sub 12 indicates dying (murdered) batts?

StuM, thanks again, but are you telling me that a reading of less than 12v on my screen multimeter tells me that the batts are dying per se? Guy I knew told me that until I read 10.5, things were fine. He was probably wrong, but one thing is clear, it reads 13v when alternator is on an 11.5-12 when off.

I appreciate the input here, thanks again

Cheers

[a64pilot]

If you have an automobile, measure the battery voltage before and after you start the car, you will see voltages like you should in your boat.
Your Solar is inadequate, to begin with figure 5 hours of Solar and then actually measure output, you will be disappointed, but you will understand

[a64pilot]

Send Sailor Chic a PM, she is doing it, so she can explain better than anyone

[Kelkara]

Originally Posted by Rocinante33

So my thought process went like this. The dorm fridge will consume a little over 2 amps/hr, which means about 48 Amp Hours per day. This is a little high as the thing cycles on and off, but this assumes constant operation.

I'd say the first flaw is here.

You said the fridge is 0.8A at 120V, as was pointed out your inverter will be running 8-10A at 12V.

Where has your "2 amps/hr" figure come from? If this is neither a number supplied by the manufacturer nor one that you measured yourself, then we can probably stop right here.

[nb. since you said "this assumes constant operation" it appears that your incorrect use of amp/hr (A) is different from some other people's incorrect use of amp/hr (Ah). and you mean that the fridge draws 2A while it is cycling on, and not that it will average 2Ah per hour accounting for the cycling - this is a situation where it does make a difference]

Is this your fridge?
Magic Chef 2.6 cu. ft. Mini Refrigerator in Stainless Look, ENERGYSTAR-HMBR265SE1 - The Home Depot
Then it clearly specifies that the estimated annual electricity use is 215kWh. Your 120W panel at 50% efficiency for 12 hrs per day for 365 days a year gives 262kWh - Assuming some ineficiencies in your system for the inverter, batteries etc, and the fact that the fridge installation will not be in the optimal environment as used by the manufacturer for their EnergyStar certification - you are certainly cutting it a bit fine even if you never have a cloudy day.

[StuM]

Originally Posted by Rocinante33

Thanks for the replies,

My following questions/thoughts are designed to illustrate my thought process and not an argument. Since it is not working right, obviously there is a flaw. I would appreciate help highlighting the flaw in my analysis.

First off, the solar charger is 120 watts and not 120v. Thanks for the quick reference StuM

But did you actually read and understand it? It seems from the rest of this post that you didn't.

So my thought process went like this. The dorm fridge will consume a little over 2 amps/hr, which means about 48 Amp Hours per day. This is a little high as the thing cycles on and off, but this assumes constant operation.

Again no such thing as Amp/hr. I presume you mean that it will average 2 Amps and therefore consume 2 Amp hrs per hour.

The important thing is those Amps are at 110 Volts. So those 48 Amp hours total 5280 Watt hours. (48 x 110) which is 440 Amp hours at 12 V ( 5280/12)

The solar panel generates 5.5 amps/hr (@ 18 volts) and the sun shines on average in South Florida for 12 hours. Assuming all of the conversion to 12v is lost, that is 66 amps per day into the batts.

Again, Amps, not Amps/hr and Amp hours per day, not Amps per day!

5.5 Amps @ 18V = 99 Watts. OK, that's slightly low for a nominal 120W panel when the sun is directly overhead on a clear day. But lets work with 100 W as a round figure.

Since the sun will rarely if ever be in that situation, you can expect less than 99 Watts all the time. When the sun is lower in the sky in the morning and afternoon, a lot less. A good rule of thumb is that you may get about 5 hours "full sun equivalent" out of your panels, so plan on 500 Watt hours per day. At 12 Volts, that is about 40 Amp hours per day.

First, on a continuing power consumption basis (not power from storage)

Assume that I lose half of that for sun angle, cloudy, etc. I am still at 2.75 amps/h and not pulling nearly that amount, so why would it shut down on a bright sunny day? A 'murdered' battery should not make a difference at that point, right?

You really need to understand the relationship between Watts, Amps and Volts. You can't compare Amps at 110V with Amps at 12 V.

It's easiest to think in Watts, because then the Voltage doesn't come into the equation.

Your panel will at most generate 100 Watts, and will average about 50 Watts during day light hours. In the early morning and late afternoon, it will be a lot less than 50 Watts.

If your fridge draws 2 Amps at 110 Volts, that 220 Watts.

So you've got a 220 Watt draw and are trying to drive it with a maximum of 100 Watts and an average of 50 Watts.

Obviously that deficit has to come from your batteries. So you are drawing between 100W and 220W from your batteries for the 12 hours that the sun is up and a full 220 W for the other 12 hours.

On the power storage issue;

I can see that putting in 66 amps/day and then assuming 50% loss is going to put consumption ahead of production. I can see that I will need to increase the capacity of the batts.

What rule of thumb ought I use? If my calculations start at 2.5 amps/hr and lets say for argument that I want the fridge on all night, then I will be using 60 amps per day.

(It's getting tedious, but - that's 2.5 Amps and 60 Amp hours per day!)

Remembers those Amps and Amp hours are at 110Volts, not 12 Volts!

OK, we've established above that with your current solar, you need batteries to be constantly providing between 100 and 200 Watts (that's 8 - 16 Amps) for your fridge. But if you increase the solar, the battery demand will go down.

If that is right, then how much solar power do I need to produce 60 amps in 12 hours of sunlight with shade, angles, clouds, etc. Is assuming 50% loss reasonable?

Is that 60 Amps (Actually Amp hours) in addition to what you are currently supplying with your existing solar?

Let's go back to basics (and ignore all the other factors such a Peukert, inverter losses, other house loads etc which further increase your requirements). As a theoretical minimum:

You need enough solar to provide about 5000 Watt hours to keep up your 2+ Amps @ 110 V for 24 hours.

Half of those Watt hours are needed at night, so you need to store and then supply 2500 Watt hours.

From the above discussion, based on 5 hours "full sun equivalent", you need 1000W of solar panels to generate your 5000Wh of total energy.

Those 2500 Watt hours overnight is about 100 Amp hours or an average draw of about 8 Amps.

That suggests that about 300 Ah of battery would be a good start, assuming that all of your other house loads are fairly minimal.

...
StuM, thanks again, but are you telling me that a reading of less than 12v on my screen multimeter tells me that the batts are dying per se? Guy I knew told me that until I read 10.5, things were fine. He was probably wrong, but one thing is clear, it reads 13v when alternator is on an 11.5-12 when off.

I appreciate the input here, thanks again

Cheers

Guy you know knows very little. A lead acid at 10.5 Volts is absolutely dead. When the alternator is on, you are reading the alternator output, not the battery voltage. Once a battery gets down to 12V it is well below a 50% "state of charge". Keeping batteries at those levels will destroy them very quickly. If you can't get them back up to around 12.5/12.6 and have them hold that voltage, then they are indeed "stuffed".

[PaulMarion]

Well done Stu, lots of work there! The other thing I noticed was "the meter reads 13v when alternator is on an 11.5-12 when off." The alternator output, should read 13.9 - 14.2 Volts if working correctly! With the batteries in an obvious poor state, they could be preventing proper alternator output via resistance, or a problem could exist with the alternator as well. A good way to check if either or both batteries are u/s is to disconnect one and start engine, whilst watching voltage output,then do same with the other. If both are showing the same low voltages whilst running the engine, you'd need to get a known good (or new) battery and connect it by itself to see if the alternator or batteries are causing the low output. Of course there could be poor wiring/ earthing problems in there as well. Obviously if the batteries are dropping back to 11.5 - 12Volts even after a 15 minute engine run, there must be either a big load happening, alternator problem or the battery's are U/S! If they are lead acid and are able to be hydrometer tested, that's the first step, if not, as above, then as Stu and others have suggested when you sort batteries out.

[StuM]

Originally Posted by PaulMarion

The alternator output, should read 13.9 - 14.2 Volts if working correctly!

Not if there is a high load such as the fridge and stuffed batteries - they will pull the voltage down. Or if he is running the engine at insufficient revs when charging (there have been more than a few people who thought that they could charge their batteries with an engine at idle )

[AndreBruijntjes]

Hallo guys, don't know about your maths qualities on the other side of the ocean but here in Europe the consumption of the refridgerator is a factor 10 lower.
This means that production and consumption, taking only the refridgerator into account, are nearly balanced.
The refridgerator draws approximately 600Wh per day and the solar panel produces approximately 500Wh per day meaning our sailor is approximately 100Wh per day short.
Using a 12V system he has to supply 9Ah per day from his batteries. A 90Ah lead acid batterie will need to be recharged fully every 3 days. Either by running the motor with a smart regulator or charging on shore power with a smart charger.
Personally I think 90Ah is far to small for a boat using a refridgerator and I would Always advice an AGM batteries. In this case I would go for at least 2 deap cycle AGM batteries of 90-100Ah parallel having at least 50% of 180-200Ah=90-100Ah for disposal for consumption.
If there is enough room on board and Rocinante installs a second solar panel of the same size he will never have to drain his batteries and the solarpanels wil maintain his batteries in a perfect state. This on the condition that his solar charging is driven by a proper regulator.
If there is not enough room for a second solar panel Rocinante has to make a few hour trip every week charging his batteries by his Alternator, here again on the condition that the Aternator is driven by a smart(3 step) regulator.
Not clear from the posts, but I assume Roccinante has a set up where he uses a dedicated battery for starting his motor? If this is the case be sure to have a separator which copensates the voltage drop, if not consider installing a second battery and a separator.