Inverter Battery Useage Questions

[Tator]

OC Diver- I'm curious if you have a pure sine wave inverter. We use a lot more power overnight-around 250ah or 500ah/day. Our battery bank is 1100ah. We run a 10cu.ft household fridge circa 2004 and a small chest freezer of the same age. I have discovered that on our modified wave 3k inverter that the timer on the defrost for the fridge appears to stay on-I can feel heat on the surfaces where the door seals meet the cabinet. I disabled the timer and the air circulation passages filled with frost in two days. No problem on shore power or genset.

At one time I was going to install a Magnum pure sine wave unit that I was told was a drop in for our Xantrex. Being based in a small town in SE Alaska with limited supplies available, I checked out the specs of the Magnum and discovered it really wasn't a drop in. Among other things it necessitated a different platform, had different size poles on the power connections, needed a 4/0 ground on the chassis and different clearances. I punted as there were more important projects on the list for our limited time in Alaska. If the boat was back here in Puget Sound it would be a done deal. Fridge continues to work, inverter is doing fine (except for the defrost timer) and we continue to have to run our genset for 4-5 hours/day when at anchor.

Tator

 

[O C Diver]

OC Diver- I'm curious if you have a pure sine wave inverter. We use a lot more power overnight-around 250ah or 500ah/day. Our battery bank is 1100ah. We run a 10cu.ft household fridge circa 2004 and a small chest freezer of the same age. I have discovered that on our modified wave 3k inverter that the timer on the defrost for the fridge appears to stay on-I can feel heat on the surfaces where the door seals meet the cabinet. I disabled the timer and the air circulation passages filled with frost in two days. No problem on shore power or genset.

At one time I was going to install a Magnum pure sine wave unit that I was told was a drop in for our Xantrex. Being based in a small town in SE Alaska with limited supplies available, I checked out the specs of the Magnum and discovered it really wasn't a drop in. Among other things it necessitated a different platform, had different size poles on the power connections, needed a 4/0 ground on the chassis and different clearances. I punted as there were more important projects on the list for our limited time in Alaska. If the boat was back here in Puget Sound it would be a done deal. Fridge continues to work, inverter is doing fine (except for the defrost timer) and we continue to have to run our genset for 4-5 hours/day when at anchor.

Tator

Mine is a pure sine wave Magnum. The boat came with a modified sine wave that had issues with a few electronic appliances and made the microwave sound terrible.

I don't know how the modified sine wave impacts power consumption. If I were you, I would get one of the power consumption meters that measure consumption over time.

https://www.google.com/search?q=pow...oECBIQAg&biw=360&bih=564#imgrc=PDfhB-K8-jvEtM

Do a test with both appliances for 2 or 3 days on shore power and then on the inverter to see how much the efficiency suffers on the modified sine wave. If the defrost cycle is running more frequently, that would certainly increase power consumption.

Ted

 

[DDW]

"Modified sine wave" inverters are usually more efficient than true sine wave, as they are operating strictly in switch mode. However the appliance they feed may be considerably less efficient when operating on the square wave they produce. The heating elements are resistive and wouldn't care - but the control circuits might well.

 

[syjos]

Compressors and motors seem to run hotter on modified since than pure.

 

[FF]

"I replaced a 7 cuft. Norcold refrigerator with a 10 cuft. FROST FREE Summit refrigerator. It is 50% larger, FROST FREE,"

The gov. annual KW estimate (depending on year) does nor include the KW used in heating insualtion to dry it out or heating the door seals to keep them working.

The very thin insulation that allows larger internal volume MUST be kept dry to function well .

"I can feel heat on the surfaces where the door seals meet the cabinet. I disabled the timer and the air circulation passages filled with frost in two days."


The heat is from resistance elements that gobble electric .

 

[O C Diver]

"I replaced a 7 cuft. Norcold refrigerator with a 10 cuft. FROST FREE Summit refrigerator. It is 50% larger, FROST FREE,"

The gov. annual KW estimate (depending on year) does nor include the KW used in heating insualtion to dry it out or heating the door seals to keep them working.

The very thin insulation that allows larger internal volume MUST be kept dry to function well .

"I can feel heat on the surfaces where the door seals meet the cabinet. I disabled the timer and the air circulation passages filled with frost in two days."


The heat is from resistance elements that gobble electric .

Linked below are the standards for Energy Star testing that clearly state that defrost cycle power consumption has to be included in the test.

The Summit unit I have operates in the Frost Free mode (I've never manually defrosted it) and consumes half the energy of the Norcold that requires defrosting. Spin it anyway you want, my SOC meter confirms the reduction in energy consumption.

The insulation of most high efficiency refrigerators isn't fiberglass, but instead an injected closed cell cellulose foam that doesn't absorb moisture.

Defrost cycle heating is accomplished with the heated refrigerant gas from the compressor, not resistance heating.

https://www.google.com/url?sa=t&sou...FjABegQIBRAJ&usg=AOvVaw3I0qpGPf_hIew9AK7dCYZr

Ted

 

[Tator]

An interesting and informative read concerning the Energy Star program. My fridge is 1000 miles away at this point, but I seem to remember that the from looking at the wiring diagram that at least some part of the defrost circuit involved resistive loads that were activated by a non-settable timer.

In looking at various reviews of the more inexpensive electric meters it appears
that they probably won't work with a modified sine wave. I guess I can clamp on my Fluke and get some idea of the draws without a time component.

Tator

 

[O C Diver]

In looking at various reviews of the more inexpensive electric meters it appears
that they probably won't work with a modified sine wave. I guess I can clamp on my Fluke and get some idea of the draws without a time component.

Tator

Maybe a simpler approach would be to measure the boats consumption over a week with the shore power pedestal killowatt consumption meter. Divide that number by 7 for a daily consumption rate. Then turn off the shore power for a day and see what KW consumption is from your battery bank. 500 AH for a day (which you mentioned earlier) would equate to 6 KW. My guess is that your shore power consumption for those 2 appliances isn't half that number.

Ted

 

[OldDan1943]

Realize the Energy Star program is for residential appliances only.

 

[Tator]

Not a bad idea except I would have to subtract any hot water use and battery charger use from the dock figures as they are on my non-inverter circuit.

Tator

 

[O C Diver]

Realize the Energy Star program is for residential appliances only.

Yes, of course. And for an RV refrigerator company to replicate the test to show their units consumption following the test standards would cost how much?

Below is a link to a manufacturer's unit with a high efficiency compressor and substantial insulation. Near the bottom of the page are daily energy consumption numbers for 70 and 90 degrees. Pretty simple to do the testing and include the actual power consumption numbers.

https://sundanzer.com/product/dcrf290-10-2-cu-ft-refrigeratorwith-top-freezer/

Ted

 

[OldDan1943]

Yes, of course. And for an RV refrigerator company to replicate the test to show their units consumption following the test standards would cost how much?

Below is a link to a manufacturer's unit with a high efficiency compressor and substantial insulation. Near the bottom of the page are daily energy consumption numbers for 70 and 90 degrees. Pretty simple to do the testing and include the actual power consumption numbers.

https://sundanzer.com/product/dcrf290-10-2-cu-ft-refrigeratorwith-top-freezer/

Ted

Good looking box.... they admit/brag about the power consumption at the back of the box temp which is good. Alas, I do not have the physical space to install the box.
I figure with my 2 proposed fans, one at the compressor level to stir up the air and a fan in one of the two exit holes venting to the inside of the boat., I should knock down the ambient ‘back of the box’ temp to almost room temp. Normally the back of the box runs about 90F. IF I can knock that temp by 10F that is the best I can hope for. That’s all the perfume I can possible put on the pig.

 

[FF]

After reading the energy star lit , I believe "defrosting" as they use the term is for the evaporator in the box , not the frost on/in insulation or door seals.

The units schematic should show how its wired.

I still do not understand how the 2A per hour 2 x 24 = 48 AMPS of inverter simply thinking about operating is made up.

 

[O C Diver]

I still do not understand how the 2A per hour 2 x 24 = 48 AMPS of inverter simply thinking about operating is made up.

48 AH x 12 VDC = .6 KW
.6 KW + .8 KW (from the refrigerator) = 1.4 KW

A Norcold drawing 10 amps at 12 VDC with a 75% duty cycle draws 2.1 KW.

The Norcold draws more than twice the amps of the Summit. Now if you choose a 500 watt inverter with a .5 amp stand by consumption (.15 KW), the refrigerator and inverter consume less than 1 KW. I leave my inverter on regardless of which refrigerator I was using. So the reduction in refrigerator electricity went from 2.1 KW to .8 KW.

Ted

 

[twistedtree]

"I replaced a 7 cuft. Norcold refrigerator with a 10 cuft. FROST FREE Summit refrigerator. It is 50% larger, FROST FREE,"

The gov. annual KW estimate (depending on year) does nor include the KW used in heating insualtion to dry it out or heating the door seals to keep them working.

The very thin insulation that allows larger internal volume MUST be kept dry to function well .

"I can feel heat on the surfaces where the door seals meet the cabinet. I disabled the timer and the air circulation passages filled with frost in two days."


The heat is from resistance elements that gobble electric .

I disagree about the Energy Star power consumption figures. I have found them to be quite accurate and reflect normal, actual use.

If you to their web site they have extensive lists of products. I’m not sure how far back they go, but you might be able to find numbers for older appliances and compare to new. And not all new are low power consumption, so it pays to compare.

And Re defrost specifically, yet it definitely increases power consumption, but the energy star numbers will give you a way to compare how different manufacturers do it. Constant heating of one part of the unit while cooling other parts sounds pretty bad from a power perspective, and should be revealed in the consumption numbers

 

[twistedtree]

Yes, of course. And for an RV refrigerator company to replicate the test to show their units consumption following the test standards would cost how much?



Below is a link to a manufacturer's unit with a high efficiency compressor and substantial insulation. Near the bottom of the page are daily energy consumption numbers for 70 and 90 degrees. Pretty simple to do the testing and include the actual power consumption numbers.



https://sundanzer.com/product/dcrf290-10-2-cu-ft-refrigeratorwith-top-freezer/



Ted

Agreed. It’s a trivial job.