Time to replace defective and potentially dangerous absorption fridge

[oldmansax]

(07-09-2013 20:17)davidmbrady Wrote:  No one, and I mean no one has a door latch mechanism like my Dometic NDR1292. It's a thing of beauty as is it's built-in and cabinet grade door panels.
Okay, so let's get back to that Amish Cooling Unit thing. We need to get to one to Tom.

My Norcold DOES look good compared to the residential models. I just wish my carpentry skills were on par with the refrigerator!

I gonna get one of the Amish units myself. I would get one now & look it over except I just don't have time in the summer to fool with anything. I haven't had time to actually look at the advertisements closely either. I seem to remember there were several "Amish" models. Some better than others maybe? I am open to any information anyone has on various new or rebuilt models other than the standard replacements from Norcold.

TOM

[gondolaguy]

http://www.samsung.com/us/pdf/energyguid..._Guide.pdf

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(07-09-2013 22:33)gondolaguy Wrote:  http://www.samsung.com/us/pdf/energyguid..._Guide.pdf

I come up with 50 watts/hr to run this. Somebody check my math.

[davidbrady]

Corey,

I'll take a swing at it.

There's a chap on some forum I read somewhere who reports real world data for the RF197 of 12 amps at 120VAC for initial compressor start which ramps down to 1.3 then 1.0 after a minute or so. Then there's a 3.5 amp draw at 120VAC for the defrost cycle which runs for 15 minutes, but he didn't report how often it runs only that these high efficiency fridges need to stay on top of the defrost, so let's assume it runs every 6 hours.

That means the steady state AH (at 12V) draw is 23hrs * 1A * 10 = 230AH at 12V, but the compressor doesn't run continuously. Let's assume the compressor runs 50% of the time, so divide the steady state AH by 2 to get 230/2 = 115AH.

Next we have the defrost cycle. The defrost cycle runs for 15 minutes 4 times a day, so we have 1hr * 3.5A * 10 = 35AH.

Next we have the compressor startup current of 12A. Let's assume it quickly decays to 1A in around 2.5s and it does this once every 2 minutes. This means for every other minute there's a 2.5s period where the current draw averages 6A. That's 0.5 hours per day of compressor startup decay which gives us 0.5hrs * 6 * 10 = 30AH

Our grand total is steady state + defrost + compressor startup = 115 + 35 + 30 = 180AH consumed in a 24hr period.

There's a bunch of assumptions here including the duty cycle of the compressor which depends how often the doors are open, and the ambient temperature.

Our Lifelines have a capacity of 210AH * 6 = 1260AH, but we can only drain them down to 50% Depth of Discharge (DOD) so effective AH is 630.

To restore your batteries to full capacity you need to put back 180AH.

According to the Lifeline Technical Manual for AGM batteries. The recharge time to restore 180AH is (DOD*Battery Bank Capacity / Rated output of Charger) + 2 hours. In this case we have 180/1260 = 14.3% DOD, so our charge time is (0.143 * 1260 / 280) + 2 = 2 hours and 40 minutes.

The person who reported the real world numbers said he gets thru the night with a drain of around 75AH.

[pgchin]

Keep in mind that the usage figures are based on a premise of "clean coils" ". My bottom cooling refer at home, when the coils get full of dog hair at the end of the month, NEVER shuts down........ Maybe 15 minutes per hour it is off...........even if you do not have dogs, the dust bunnies build up in a bus is amazingly fast when you are in it months at a time gong to various places that have anywhere from grass to dusty rock roads, etc.
I do like the additional capacity, but I want to see more reported real world data on usage........I'm OTR too long every year to rely on just batteries and genny............. gennys get old, bearings burn out, fuel pumps break, radiators leak...........yadayadayada!

[gondolaguy]

(07-10-2013 00:58)davidmbrady Wrote:  Corey,

I'll take a swing at it.

There's a chap on some forum I read somewhere who reports real world data for the RF197 of 12 amps at 120VAC for initial compressor start which ramps down to 1.3 then 1.0 after a minute or so. Then there's a 3.5 amp draw at 120VAC for the defrost cycle which runs for 15 minutes, but he didn't report how often it runs only that these high efficiency fridges need to stay on top of the defrost, so let's assume it runs every 6 hours.

That means the steady state AH (at 12V) draw is 23hrs * 1A * 10 = 230AH at 12V, but the compressor doesn't run continuously. Let's assume the compressor runs 50% of the time, so divide the steady state AH by 2 to get 230/2 = 115AH.

Next we have the defrost cycle. The defrost cycle runs for 15 minutes 4 times a day, so we have 1hr * 3.5A * 10 = 35AH.

Next we have the compressor startup current of 12A. Let's assume it quickly decays to 1A in around 2.5s and it does this once every 2 minutes. This means for every other minute there's a 2.5s period where the current draw averages 6A. That's 0.5 hours per day of compressor startup decay which gives us 0.5hrs * 6 * 10 = 30AH

Our grand total is steady state + defrost + compressor startup = 115 + 35 + 30 = 180AH consumed in a 24hr period.

There's a bunch of assumptions here including the duty cycle of the compressor which depends how often the doors are open, and the ambient temperature.

Our Lifelines have a capacity of 210AH * 6 = 1260AH, but we can only drain them down to 50% Depth of Discharge (DOD) so effective AH is 630.

To restore your batteries to full capacity you need to put back 180AH.

According to the Lifeline Technical Manual for AGM batteries. The recharge time to restore 180AH is (DOD*Battery Bank Capacity / Rated output of Charger) + 2 hours. In this case we have 180/1260 = 14.3% DOD, so our charge time is (0.143 * 1260 / 280) + 2 = 2 hours and 40 minutes.

The person who reported the real world numbers said he gets thru the night with a drain of around 75AH.

So probably fair to say, with new batteries, you'd easily get 4 boondock days before needing a recharge? That works fine for me.

Wonder how the dual compressor technology helps/hurts the equation?

[davidbrady]

Hi Corey,

It really sips power. It's approximately equivalent to leaving a 90W light bulb turned on 24 by 7! Our LXi's are very well equipped to handle this refrigerator. I don't know anything about their dual compressor technology. Maybe others can fill us in here.

It's interesting how long the battery bank takes to restore itself to 100 SOC. It's the Absorption stage. The Bulk stage only takes the batteries to 80% then Absorption kicks in. The trouble is, the refrigerator didn't deplete the charge to below 80%, so almost all the charge time is in Absorption which is slow. Absorption is constant voltage; Bulk is constant current. Bulk can force in 280A (our LXi charger capacity) for as long as the battery voltage stays below 14.3V. Absorption maintains a constant 14.3 by reducing charging current appropriately. I suppose you don't have to bring them to 100 SOC. you could run from 65% to 80% which would do almost all of the charging in the Bulk stage. This would reduce your genny runtime considerably.

[gondolaguy]

I'm thinking it's going to be a good time to add some solar capacity, it would be pretty cool if the reefer could get all it's needs from Mr Yellowball

[tcandt]

(07-10-2013 10:53)gondolaguy Wrote:  I'm thinking it's going to be a good time to add some solar capacity, it would be pretty cool if the reefer could get all it's needs from Mr Yellowball

We had a tech talk at Quartzsite a few years ago from a show vendor who had a pliable sheet solar panel he was selling. After all the hype and some excitement from Bird Owners, he was walked through a coach to see what electric demands our coaches had. He left saying our roofs were not big enough to get sufficient solar power to do much good for our demands.

Solar is only additive to our coaches and I do not believe the benefits of the hard panels are sufficient to sacrifice the weight and space on the roof. On the other hand, I recently installed solar electric on my house roof with great results in reducing my monthly bill. It helps to be in Southern Cal.

[gondolaguy]

(07-10-2013 12:04)tcandt Wrote:  

(07-10-2013 10:53)gondolaguy Wrote:  I'm thinking it's going to be a good time to add some solar capacity, it would be pretty cool if the reefer could get all it's needs from Mr Yellowball

We had a tech talk at Quartzsite a few years ago from a show vendor who had a pliable sheet solar panel he was selling. After all the hype and some excitement from Bird Owners, he was walked through a coach to see what electric demands our coaches had. He left saying our roofs were not big enough to get sufficient solar power to do much good for our demands.

Solar is only additive to our coaches and I do not believe the benefits of the hard panels are sufficient to sacrifice the weight and space on the roof. On the other hand, I recently installed solar electric on my house roof with great results in reducing my monthly bill. It helps to be in Southern Cal.

I agree that solar is not the 100% solution, especially in western NC this year!!! ughh!! On the other hand, it can be a very valid "extender" whatever is gained, just adds to the time available for boondock as well as keeps batteries topped off. If the Samsung 197, due its low power needs, can be covered by, say, 120 Watts of solar in an average location, the fridge has a net zero drain on the system. In fact, it would use less electrical power than a gas absorption fridge (fans, controls, lights) without the solar addition. That brings up a great question, what does the Dometic under fire (LRIM1200 or equivalent) draw for power to operate on gas?

[davidbrady]

I wouldn't bother with solar Corey - we don't run our generators enough as it is. Just run the genny!

Let's see, my Dometic doesn't have fans, and the 12W inside light only comes on when the door's open. The 12V controller board draws milliamps tops. With our LXi battery bank capacities, these Dometics and Norcolds can probably run the LP tank dry before we need to start the genny!