# 7.2 chest freezer conversion problems

sichan86
Registered Users Posts:

**4**✭
Howdi all. I converted a chest freezer to a fridge with a Johnson controls relay. I have it plugged into a micro solar pure sine wave 1000w/2000w peak inverter. My problem is when the motor for the fridge kicks on the inverter beeps as if the voltage is too low or some other problem I can't define. After a 10 second beep, the motor continues to operate. I am running two 6v 210ah golf cart batteries as 12v. I find that running this way for a 24 hour period drains the batteries down to 40% or so. I might have accidentally let the batteries get below 40% 3 days ago before I hooked up the fridge. Have I ruined my batteries? Is the inverter too small? I'm stumped and frustrated. Any help appreciated!

## Comments

4,478✭✭✭✭✭It could also be that it beeps in the surge range from 1000w to 2000w to warn you to reduce load to below surge range. If you have a multimeter you could watch voltage at the 12v inverter terminals to figure out which it is.

Pulling batteries down below 40% SOC regularly will shorten their life some. Leaving them at a low SOC for long will kill them, quickly if they're warm, more slowly if cool.

Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer

Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter

244✭✭✭What size wires did you use and how long are they on the dc side?

Got any power info on the chest-freezer. Amps, volts, watts or kwh used etc?

30,520adminThe battery bank is also very small. The amount of load 2x 6 volt @ 210 AH batteries (12 volts @ 210 AH with batteries in series) would be:

- 12 volts * 210 AH * 0.85 AC inverter eff * 1/20 hour discharge = 107 Watt load (for example) 5 hours per night, 2 nights with 50% maximum discharge (for longer battery life)
- 12 volts * 210 AH * 0.85 AC inverter eff * 1/8 hour discharge =268 Watt load maximum for ~4 hours of load (and 50% max discharge
- 12 volts * 210 AH * 0.85 AC inverter eff * 1/5 hour discharge =428 Watt max continuous load for minutes to ~1 hour or so
- 12 volts * 210 AH * 0.85 AC inverter eff * 1/2.5 hour discharge =857 Watt max surge (seconds--Motor starting)

Maximum inverter for that size battery bank would be around ~428 Watts (with 857 Watt surge).If you wanted to run the refrigerator for 2 days of "no sun", 50% max discharge, on a 24 volt battery bank with a 1,200+ Watt AC inverter, the system would look something like (this would be a full time off grid system sizing):

- 120 Watt load * 0.50 duty cycle for freezer * 48 hours of run time * 1/0.85 AC inverter eff * 1/24 volt battery bank * 1/0.5 max discharge = 282 AH @ 24 volt battery bank

4x 6 volt * 210 AH battery bank would be 24 volts @ 210 AH -- Still a bit small for this size system. 8x 6 volt @ 210 AH batteries in 4x series by 2x parallel strings would be 24 volts @ 420 AH battery bankTo charge an 8x battery bank, you would need solar panels rated for:

- 420 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 791 Watt array minimum (weekend/seasonal cabin/emergency backup)

- 420 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,582 Watt array nominal (full time off grid)

- 420 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 2,056 Watt array "cost effective" maximum

And then we need to size the system to the amount of load and average amount of sun per day. Say you are in Los Angeles California:http://www.solarelectricityhandbook.com/solar-irradiance.html

## Los Angeles

Measured in kWh/m2/day onto a solar panel set at a 56° angle from vertical:Average Solar Insolation figures

(For best year-round performance)

- 120 Watts * 0.50 freezer compressor duty cycle * 24 hours per day = 1,440 Watt*Hours per day (guessing)
- 1,440 WH per day * 1/0.52 off grid system eff * 1/4.41 December average hours of sun = 628 Watt array minimum

Lots of guesses, but the recommended array for 8x golf cart batteries, guessing at your load and location would be 791 Watt array minimum and a 1,582 Watt array would be really nice (plus you could run other loads during the day time).You should use a Kill-a-Watt type power meter to measure your AC loads--This would give us a better idea of your load(s).

Also--where you will install the system and how you want to use it will help us to better design your system.

-Bill

4✭4,478✭✭✭✭✭Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer

Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter

30,520adminAnd be careful about Amp and Amp*Hours. Power (Watts) and Energy (Watt*Hours or kWatt*Hours) are "fully" defined units. I.e., that is "all we need to know" when doing the electrical math.

Amps is a "partially defined unit"--We also need to know at what voltage...

- Power = Volts * Amps = Watts (a rate like miles per hour)

- Energy = Volts * Amps * Hours = Watt*Hours (like total miles driven)

So--A very efficient freezer to refrigerator conversion may use ~230 Watt*Hours per day- 230 WH * 365 days = 83,950 WH per year = 84 kWH per year (1kWH = 1,000 WH)

A typical (pretty good) refrigerator or freezer may use around 1,000 to 2,000 WH per day. Or 365 to 730 kWH per year.- 224,000 WH (per year) * 1/365 days per year = 614 Watt*Hours per day
- 614 WH per day / 120 VAC = 5.1 AH @ 120 VAC per day
- 614 WH per day * 1/0.85 AC inverter eff * 1/12 VDC battery bank = 60.2 AH @ 12 VDC per day

So--The AH at 12 VDC are roughly 10x that at 120 VAC...Assuming your freezer draws ~120 Watts when running, and you are seeing 5 minutes of runtime per 60 minutes, the estimated AC energy usage per day would be:

- 120 Watts * 24 hours per day * 5 minutes run * 1/60 minutes duty cycle = 240 WH per day

Which is what it should be running (note that fridge and freezers run longer at 90F than at 70F room temperature).Now--You can see that running your fridge takes a 120 Watts, and starting it draws >~600 Watts (typically starting load for induction motors is something like >5x running power/current).

Your battery bank is really too small to support a 600 Watt starting load--At 12 volts for a flooded cell battery bank (using our rule of thumb of 400 AH per 1,000 Watts of starting load) need around 266 AH minimum.

Realistically, the suggestion is a 1,200 Watt minimum AC inverter (supports ~2,400 Watts starting surge) and a:

- 2,400 Watt surge * 400 AH (at 12 volts) * 1/1,000 Watt surge load = 960 AH @ 12 volts battery bank

If the refrigerator is your only load--You can probably get away with 2x 6 volt @ 200 AH * 2x series string or 4x batteries at 12 volts @ 400 AH battery bank.The killer with refrigerators/freezers and standard induction motors is the starting surge--That drives your minimum AC inverter and Battery bank sizing. Typically, I would suggest that adding a fridge/freezer to an off grid power system takes it from a a small to a medium size system--And that means a 24 volt battery bank+inverter (for reliable operation)--24 volts * 200 AH (4x 6 volt @ 200 AH batteries).

And a solar array to support that size battery bank.

-Bill

4✭> [email protected][email protected]

Oops. I didn't realize I had to do the conversion through 12v. I thought that was redundant because I was going through the inverter. Still seems like I'm using way more than it should though. Any suggestions for this little system? Do you see any wasteful problems? More batteries? Larger cables like you said? Thanks

1,518✭✭✭✭2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

4✭> Sounds like you're undercharging and at a low state of charge your start up surge is pulling your battery voltage low enough to set off the low battery alarm in the inverter. When your batteries are already low and you put a heavy load on them the voltage will drop briefly while the inverter is trying to put out high enough amperage to start the compressor in the fridge/freezer. Once you correct the charging problem you should be good to go. A 24 volt system would help but unless you can reliably replace the daily power draw you will continue to have this problem.

When you say under charge, is that because I am not topping them off? The battery charger I have says that I am getting them to almost 90% which may not be completely accurate but it also says atleast 12.6v with the multimeter. I'm still confused why this "efficient" method of refrigerator is still pulling so many total amps throughout the day. I guess I'm not getting it

4,478✭✭✭✭✭Read Bill's post through a few more times. Lots of good info but may take a few reads.

Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer

Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter

5,183✭✭✭✭KID #51B 4s 140W to 24V 900Ah C&D AGM

CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM

Cotek ST1500W 24V Inverter,OmniCharge 3024,

2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,

Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep

West Chilcotin, BC, Canada

194✭✭✭thom