# 2 fridges and a chest with solar



## Greasyrick (10 mo ago)

Hello everyone, new here, after browsing around this forum, I see there is a wealth of knowledgeable members, and would like to take the opportunity to ask about something I can’t get a straight answer about no matter how many people I ask.
I have a new refrigerator, side by side, it’s 5 amp and 120v, guess that makes it a 600 watts, also a 15 yer old one in the garage, (it’s also a side by side) that im guessing it’s a bit higher on the wattage, since it’s older, (can’t find the decal with the specs on it), and a chest cooler (in the garage also).
Im going with 1800 watts for all 3 to be safe, (since chest coolers are about half the consumption of a fridge)
I wanted to ask if 3 12 volt 200ah lifePo4 batteries with a 3000 pure sine wave inverter would be enough to get them running, and the main doubt I have is, how many 12 volt 100 watts solar panels are needed to keep the batteries from going empty in a 24 hour period, I do have a gen set setup outside the house and some fuel stored but, I always have the, (what if) question in the back of the head.
Anyways, I appreciate any imput I can get from you guys.


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## Back Pack Hack (Sep 15, 2016)

It's hard to 'run numbers' like this. A lot depends on start-up current. Not only are you starting the compressor motor from a dead stop, you're doing so against the pressure of the refrigerants. So it takes a LOT of current just to get it up to speed. And under normal use, each unit will cycle on like this 30-40 times per day in order to maintain temperature. 

So I seriously doubt you'll be able to get by with 600ah. What we'd need is some actual test results of what each unit actually uses, not SWAGs.


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## paraquack (Mar 1, 2013)

I agree with Back Pack Hack. While you might be able to get the smallest (amperage) frigde up and running. I really doubt you could them both up at the same time. You really need to find the sticker for the older one. Refrigerators usually need 3-4 times the inverter's ampacity to start. But the only way you'll know, is to try. Just make sure the fuses in the inverter haven't be increased, or you may burn something out.


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## Crash5291 (Sep 18, 2019)

I'd recommend working at a higher voltage like 48v and using better Panels then the typical 12v stuff. 
Higher voltage lowers the currents. 
3000W @12v = 250Amp 
3000W @48v = 62.5Amp 
That's a large difference in acceptable wire to move that current for a 4' lead from the battery to the inverter @250A is a 2ga wire(3.35% droop), but at 62.5A thats a 14ga wire (3.24% Droop) less droop is better and i would still aim for 1/0Ga wires 48v/62.5A is 0.06V drop or 0.12%, 1/0Ga on 12v/250A is 0.24V drop but 2% of the total. 

That also has an effect between the panels and the charge controller, 25' at 600W/12v is 50A load on 2Ga with a 4.2% loss leaving you down 1/2 a volt between the panels and charger. where as 600W/48V is a 12.5A load on a 14Ga wire for the same loss 4.05%, or much better at 10Ga wire with 1.55% loss. 

You will also have issues with finding controllers at a decent price for that massive amperage at 12v. Where as a 48V MPPT that will do 600W input is easy and lower cost 


You also need to be thinking longer term then 24hours. being that its a critical load and uptime is a must i'd say you're looking to 3 days bare minimum, personally i'd go double that where i am. 

As for working 12V accessories directly from the 48V bank, you can get buck converters that will do as needed.

There is so much more to it then that though, A 600 watt panel array may work in the south but will need to be larger in the north to do the same job. 

Upside chest freezers are pretty efficient for power use when used (opened) where as stand up fridges are horrid when opened. 

Cheers


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## Greasyrick (10 mo ago)

So would it be safe to have 5 batteries (1000ah total), and 26 100 watt solar panels?


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## Greasyrick (10 mo ago)

Crash5291 said:


> I'd recommend working at a higher voltage like 48v and using better Panels then the typical 12v stuff.
> Higher voltage lowers the currents.
> 3000W @12v = 250Amp
> 3000W @48v = 62.5Amp
> ...


Sorry, I posted that answer about the 5 batteries and 26 panels before I saw your answer.


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## Back Pack Hack (Sep 15, 2016)

It's hard to get 48v with 5 batteries. You'll need either 4... or better yet, 8.


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## Crash5291 (Sep 18, 2019)

You need to pin down your load requirements before you can really sort the rest of the system out. Something like a "killawatt meter" will be helpful in that regard to an extent, ideally you'd want to take that measurement over a few days at a time when your devices would be using the higher end of their needs like mid summer. Some have a function to hold the peak draw for startup but I'm unsure what units and of the quality, upside is that close will likely suffice in peak draw. 

You can then use that info for each one to put together your sheet of needs. With the daily KWH needs and the peak starting load you can size the Inverter and support system. 

Some things to keep in mind, while it might be tempting to use an inverter for each device the idle draw from that would waste more power (requiring more batttery/solar) then a single unit.


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## KellyDude (11 mo ago)

A great resource for solar questions is https://diysolarforum.com/


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## Back Pack Hack (Sep 15, 2016)

Just remember... when working with solar numbers, it's all theory. Equipment ratings tend to be laced with a healthy dose of Madison Avenue. Compound each component's little white lies, and when all is said and done you've got far less capacity than you think you do. A good rule of thumb is to cut the final capacity in half. Meaning, you'll need to double your calculated capacity in order get the actual capacity you need. Doing so will also compensate for the inevitable aging of the batteries.


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## Greasyrick (10 mo ago)

Crash5291 said:


> I'd recommend working at a higher voltage like 48v and using better Panels then the typical 12v stuff.
> Higher voltage lowers the currents.
> 3000W @12v = 250Amp
> 3000W @48v = 62.5Amp
> ...


So, can I achieve this with 4 200ah batteries hooked to get


Greasyrick said:


> Sorry, I posted that answer about the 5 batteries and 26 panels before I saw your answer.


What 48 volt DC to 120 AC volt inverter with at least 3500 watts do you recommend? I don`t want to wire it to the house panel or a generator, I just want to plug the 3 units to it with extension cords. Don`t see too many choices out there. And do you think 4 200ah lifePo4 plus batteries connected in series will be enough?, (providing the 3 units Don`t pull more that 3000 watts at start up, Which I doubt it), plus correct me if I`m wrong, wiring the batteries in series will keep my Amps Hour at 200 correct? And is that good or bad vs having them in parallel? I don`t know if it will be enough, I`m not sure.
I`m not too good at this, pardon my ignorance.


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## Back Pack Hack (Sep 15, 2016)

Just off-the-cuff, 800ah won't run it very long. If you get a couple very cloudy days, you'll have dead batteries.

Extension cords? If they're any distance from your system, pony up for 12- or 10-guage cords.

Four 12v/200ah batteries wired in series will create 48v/200ah. In theory, that will supply 20a at 120v for.... 3 hours. Take that in half for real-life situations, you're down to an hour and a half. 

True, your 3 units won't be pulling 20 amps constantly. But each one turning on will drain a lot of power from those batteries just to get the compressor running. It's those start-up spikes that will kill your batteries faster than them just running at 3 or 4 amps.


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## Greasyrick (10 mo ago)

Back Pack Hack said:


> Just off-the-cuff, 800ah won't run it very long. If you get a couple very cloudy days, you'll have dead batteries.
> 
> Extension cords? If they're any distance from your system, pony up for 12- or 10-guage cords.
> 
> ...


I’m having an Issue locating a MPPT charger controller that has a LifePo4 battery selection in its battery selection menu, I only find Lithium-ion battery option in almost all of them, is it ok to charge LifePo4 batteries in Lithium-ion battery mode? I don’t want to harm the batteries or the charger controller,


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