Tare load/Standby load on the inverters - Choosing a DC vs AC refrigerator?

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electrichi01 asked Aug 21, '21

Tare load/Standby load on the inverters - Choosing a DC vs AC refrigerator?

Hello

As we all evaluate the features and benefits of using an inverter to run loads, balancing using a dc appliance, like a refrigerator is important in a boat, rv, or off grid application.

Seems like on the multi-plus 3k inverter datasheet it consumes 20 watts in standby mode? Is this correct?

So to keep the inverter on, it's 20 watts x 24 hours = 480 wh's of consumption on the battery.

As it relates to my first question, if you have the choice to use an ac refrigerator as the inverter will be on most of the day to run other loads, does it make sense to purchase a dc refrigerator?

When evaluating the cost of a 3.0-4.0 cu ft off-the-shelf ac refrigerator around the USA from the big box stores, they cost around $200. A comparable dc refrigerator costs $800+. The ac unit consumes about 1 kWh per day or so.

Does it make sense to purchase the less expensive ac refrigerator and get more storage (LiPo) to compensate for the difference in consumption?

Thanks,

Keith

MPPT Controllers PowerPlus

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shaneyake answered · Aug 21, 2021 at 07:04 PM

The inverters do use that +-20w standy.

I would say if you already have the inverter running 24/7 then I would get regular fridge and bigger batteries.

However the DC fridges from Snowmaster, National Luna, Waco tend to have a lot more insulation than a regular fridge and also tend to use a lot less energy. 82L Snowmaster in 30C ambient temps could run the whole day off 400wh. I would also get a chest fridge if you can as they don't lose as much cooling when opened. If it is stand up fridge I think they will be a lot closer in energy usage DC vs AC fridges.

By LiPo I really hope you mean LifePo4/LFP. LiPo batteries like the type found in RC cars, are not great for long term use and tend to catch fire when on charge for long periods of time.

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electrichi01 commented · Aug 22, 2021 at 05:40 AM

Yes that seems to be the approach on the 24/7 but I understand the engineering that goes into the dc versions like efficiency and insulation.

I also considered when an ac unity fails, that you can get a replacement relatively easy. For their dc cousins, this could take time to track down a new one or repair the one that is broken.

Correct, LifePo4!

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bradleypaton answered · Aug 21, 2021 at 10:43 PM

One thing to consider is being able to run the load on the generator if the inverter fails.

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electrichi01 commented · Aug 22, 2021 at 05:41 AM

For my application, I do have a second alternator, so combined with solar, and a shore power plug, three options present themselves. The generator is another option.

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klim8skeptic answered · Aug 22, 2021 at 03:31 AM

I looked at this extensively a couple of years ago, and came to the conclusion that for myself I was better off getting an ac 2 door fridge/freezer over a dc f/f.

Purchase price- a decent ac f/f is 1/4 the cost of an equivalent capacity decent dc f/f. The cost savings can be used to increase the capacity of the battery/solar array/inverter.

Energy efficiency- ac f/f can have good efficiency when proper evaluation is used. You have to compare same volume ac and dc f/f's and their power consumption. A dc f/f that uses 55Ah/day (12v) uses the same energy as an ac f/f that is rated at 265kwh a year.

Model range and features- there is a much wider # of ac powered f/f to choose from, compared to dc models. ac f/f can have more useful features, ever seen a frost free dc f/f? Inverter drive f/f?

Volume matters- I managed to get an ac f/f that holds 2.5 times the food as my equivalent dc powered f/f, while using less power overall. That means I only have to shop (move) once a month, rather than every 2 weeks. Fuel_costs_money.

Positive points for dc powered f/f..

Dc f/f will have better tie down points, and door locks.

Dc f/f will be rated for mobile use. Ac f/f might not have warranty if used in a mobile setup.

After 2 1/4 years how did my ac powered f/f perform?

Energy efficiency- the f/f did actually better than its 265kwh/year figures. The power meter that records the inverters total output power reads 547kwh for the 27 month period. That figure includes all ac powered cooking (kettle/toaster/hotplate/skillet/air fryer/clothes washer/power tools etc). My average yearly ac power consumption is approx 243kwh!

Cooling performance- At temperatures of 45c (113f) my ice cream was solid. At temps over 40c the compressor might not actually cycle, drawing a constant 65w ac. The compressor seems to have 3 power levels/speeds (??), adapting power use between 15c - 35c.

Some further thoughts..

Energy that falls out of the sky is free!- You just need to harvest (panels) and store (battery) it.

LPG/propane is expensive. I am onto my third 20lb bottle, and only use gas when it is cold, or energy levels are low (or bad prolonged weather is predicted).

Gasoline/petrol is expensive- generators are noisy/require maintenance. I have used maybe liters in the 27 months.

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electrichi01 commented · Aug 22, 2021 at 05:46 AM

Seems like we've reviewed the current environment and you have 2 1/4 years of history to come to a similar conclusion.

Running the math, as you have, factoring in all of these things, it makes mean lean towards ac as well. I stopped in Home Depot recently and asked the staff if we could plug in a 3.2 cu ft unit they had and it was difficult to hear the compressor kick on. Relatively quiet considering my preconceived notions about how noisy I thought it was going to be.

And hopefully, over time, the cost of storage keeps falling or the density goes up as well as a reduction in weight (AGM's are almost 3X of lithium today).

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Answer 1 · 2021-08-22T05:47:44Z

electrichi01 answered · Aug 22, 2021 at 05:47 AM

Thanks, everyone for the responses.

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