Fridge time-on measurement
- Thread starter Mark Maulden
- Start date
Not without some custom or specialized electronic equipment. I would like to make the same measurement, but I'm too lazy to put together the equipment needed.
By knowing how many ampere-hours (about 35) are delivered and the typical current (about 5 amps) I have concluded that my 3.5 cubic foot Isotherm runs for about 7 hours a day. That is in Richmond CA where it does not get above 70 degF much.
That is from my solar charge controller. I have been thinking about investing in one of these:
powerwerx.com
That is from my solar charge controller. I have been thinking about investing in one of these:
Powerwerx Watt Meter, DC Inline Power Analyzer, 45A Continuous, 12 Gauge, Bare Wire Ends
Measuring capacity up to 60V and 100A. 12 gauge bare wire leads. Bright green backlit LCD display. Measures 8 electrical parameters: Amps, Volts, Watts, Amp-hours, Watt-hours, Peak Amps, Minimum Volts (Sag), Peak Watts. No configuration, works automatically!
powerwerx.com
Take 30 minutes of your day. Measure the cycle time on and off during this time. Multiple this by 48 and you will have the time it runs in 24 hours. You then need to determine how many Amp hours it uses when running to determine total refer Amp hours in a day.
My refer runs approximately 50 percent of a 24 hours and uses 5 Amp hours when running. My total amp for 24 hours is 60. My house battery bank is 460 amp hours. I'm good for 3 days (72 hours) on the hook before my refer and all other 12 volt usage draws my house bank down close to 230 (50%) amp hours remaining before I run the engine to charge.
Good luck
My refer runs approximately 50 percent of a 24 hours and uses 5 Amp hours when running. My total amp for 24 hours is 60. My house battery bank is 460 amp hours. I'm good for 3 days (72 hours) on the hook before my refer and all other 12 volt usage draws my house bank down close to 230 (50%) amp hours remaining before I run the engine to charge.
Good luck
Wouldn't the ambient temperature have an effect on how much the refrigerator might run during the half-hour period? If you timed the half-hour at 07h00 on a rainy, cloudy day it might be different than timing it at 14h30 on a 100º scorcher.
Assuming what you really want to know is the draw over a specific period rather than simply on/off intervals.
If so, simply isolate the compressor circuit and connect an amp-hr (wattmeter) to it to observe the cumulative draw.
If so, simply isolate the compressor circuit and connect an amp-hr (wattmeter) to it to observe the cumulative draw.
Mark, do you have an ammeter in your panel? Turn off everything else for 1/2 or an hour and do as Steve suggested. Or do the same if you have a battery monitor, like a Link or a Victron.
My A/B fridge uses 5 amps when it runs, loaded and cold it runs maybe half the time (or less), so 60 ah per day. I've seen this on my Link 2000. I often crosscheck my loads when at anchor: I've listed all the loads on a spreadsheet (blank, just for entering amps & ah consumed from the Link) and keep track of ah used for the first day I'm on the hook or at a park dock or mooring. It is very consistent.
What fridge do you have?
My A/B fridge uses 5 amps when it runs, loaded and cold it runs maybe half the time (or less), so 60 ah per day. I've seen this on my Link 2000. I often crosscheck my loads when at anchor: I've listed all the loads on a spreadsheet (blank, just for entering amps & ah consumed from the Link) and keep track of ah used for the first day I'm on the hook or at a park dock or mooring. It is very consistent.
What fridge do you have?
You can get a Hobbs meter for about $13 on Amazon, but that doesn't solve the problem; you don't want to measure power-on time, you want to measure the time that the cooling system is energized, i.e., when the thermostat calls for cooling.
It might be easier to measure the time it's not cooling, since this could involve just wiring the Hobbs meter across the thermostat; when it closes, i.e., calls for cooling, the meter stops.
It might be easier to measure the time it's not cooling, since this could involve just wiring the Hobbs meter across the thermostat; when it closes, i.e., calls for cooling, the meter stops.
Stop watch. Just sit in the boat and hit go when it comes on and stop when it goes off. Do this for 30 minutes to an hour and then project it out over a 24 hours. This will be an estimate because it will vary somewhat over the day as the outside temp changes but it should be pretty close. Of course, if you are on the boat out on the hook and cooking, etc, you will be opening the fridge which will make it run more as well so consider that.
I know it's early in the morning, the coffee hasn't kicked in yet, and the parrot's demanding attention, but do you want to explain the difference between these two statements:
Somehow I know I'm going to regret asking this
.
Are these not the same thing ?
Somehow I know I'm going to regret asking this
.
On my Isotherm fridge with an Isec controller, Im not sure how useful the time on and off would be, curious how the OP would use this information?
On my system, when the fridge first turns on, the current can be much different than the current just before the fridge turns back off. I believe the controller also may run the compressor harder (higher current) when it senses higher battery voltage. Ie, the current varies a lot.
As someone mentioned, the fridge used energy is very dependent on ambient temperature. Energy transfer through and insulator is dependent on the temperature difference accross the insulator and how effective the insulator is (ie, R value). If the fridge inside temp is set to 40 F and the ambient is 50F, that is 10 degrees difference. But at an ambient of 90F, the difference is 50F. Ie, going from an ambient of 50F to 90F results in five times the energy transfer through the insulation. Add in the efficiency loss of the cooling system and the energy required to cool at 90 vs 50F could be considerably higher than 5X.
Not what the OP is looking for... but what I felt was important to measure was the amp hours used over a 24 hour period. I have a Linklite battery monitor that I believe is accurate even for signals up into the Khz range. Ie, it does a good job measuring and integrating current even if its changing fairly rapidly.
My battery monitor is in the typical spot of measuring the current into/out of the battery ground. Any loads or charging sources will influence what the monitor reads. So what I did is to start with a full battery, note the time and then remove all charging (put a sleeping bag over the solar panel) and loads except the fridge. I then came back exactly 24 hours later and noted the battery monitor amp hours.
I also did this measurement at two different ambient temperatures (couple months apart) and did see very large differences in the amp hours used.
On my system, when the fridge first turns on, the current can be much different than the current just before the fridge turns back off. I believe the controller also may run the compressor harder (higher current) when it senses higher battery voltage. Ie, the current varies a lot.
As someone mentioned, the fridge used energy is very dependent on ambient temperature. Energy transfer through and insulator is dependent on the temperature difference accross the insulator and how effective the insulator is (ie, R value). If the fridge inside temp is set to 40 F and the ambient is 50F, that is 10 degrees difference. But at an ambient of 90F, the difference is 50F. Ie, going from an ambient of 50F to 90F results in five times the energy transfer through the insulation. Add in the efficiency loss of the cooling system and the energy required to cool at 90 vs 50F could be considerably higher than 5X.
Not what the OP is looking for... but what I felt was important to measure was the amp hours used over a 24 hour period. I have a Linklite battery monitor that I believe is accurate even for signals up into the Khz range. Ie, it does a good job measuring and integrating current even if its changing fairly rapidly.
My battery monitor is in the typical spot of measuring the current into/out of the battery ground. Any loads or charging sources will influence what the monitor reads. So what I did is to start with a full battery, note the time and then remove all charging (put a sleeping bag over the solar panel) and loads except the fridge. I then came back exactly 24 hours later and noted the battery monitor amp hours.
I also did this measurement at two different ambient temperatures (couple months apart) and did see very large differences in the amp hours used.
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We can only presume @Mark Maulden does not have a battery monitor and is looking for a ballpark measurement of time on for the compressor at an estimated amperage draw.
Probably the kind of sailor that goes out and enjoys sailing rather than being obsessed with electrical minutia.
Probably the kind of sailor that goes out and enjoys sailing rather than being obsessed with electrical minutia.
No, they are not the same thing. The refrigerator power is always on, from when you energize the entire system with the circuit breaker. That, however, is not the time that the cooling system is running, i.e., the time the compressor is energized by a call for cooling by the thermostat. It's only the latter that is interesting, and what I presume the OP is interested in. So, you want to know the time thermostat contacts are closed.I know it's early in the morning, the coffee hasn't kicked in yet, and the parrot's demanding attention, but do you want to explain the difference between these two statements:
Are these not the same thing ?
Somehow I know I'm going to regret asking this
If you connect a Hobbs meter to the 'fridge circuit breaker you won't get this.
This gets cheaper all the time.
You can now measure you refrigerator's TIME ON during the day for only $3.41 CAN.
At that low price, better get several because the meter isn't going to last for very long
!
You can now measure you refrigerator's TIME ON during the day for only $3.41 CAN.
At that low price, better get several because the meter isn't going to last for very long
!
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I knew it, I knew it, I knew itSomehow I know I'm going to regret asking this
!Even though you probably just made a slip of the fingers on the keyboard, there is no way you are going to admit you could have possibly made a mistake. And only a registered
nut job would ever suggest placing the meter across the initial power supply to the fridge. Certainly no one here ever suggested that.And if I may be so bold as to paraphrase @justsomeguy :
I couldn't have said it better.
@jviss , thanks for all the laughs you give me with your idiosyncrasy of NEVER, EVER, under ANY circumstances admitting you're wrong
. Keep up the good work.
You know Ralph, it's not necessary, polite, or consistent with this forum to atack someone personally. It's too bad you find it necessary.I knew it, I knew it, I knew it
Even though you probably just made a slip of the fingers on the keyboard, there is no way you are going to admit you could have possibly made a mistake. And only a registered
And if I may be so bold as to paraphrase @justsomeguy :
I couldn't have said it better.
@jviss , thanks for all the laughs you give me with your idiosyncrasy of NEVER, EVER, under ANY circumstances admitting you're wrong
I stand by what I said. There's no straightforward way to use a Hobbs meter to measure compressor on-time, unless, of course, you connect it across the thermostat and the thermostat wires have enough open circuit voltage to run the meter.
Hobbs meters aren't activated by current, butt by voltage. So, yes, it's crawing current or it isn't, but how, exactly, does that activate a Hobbs meter?
The above will actually indicate the time the compressor is not on - so two meters, one for raw power, the other for thermostat not closed, and do the math.
If you are lucky and the thermostat is grounding a wire to activate the compressor, a single meter connected on one side to +12V and the other to the "top" thermostat wire would do it.
If you are lucky and the thermostat is grounding a wire to activate the compressor, a single meter connected on one side to +12V and the other to the "top" thermostat wire would do it.