Fridge compressor too big or inverter or batteries too small?

softdown

A friend wanted solar for his recreational cabin.  He bought a new 24 volt Cotek PSW 1500 inverter from me after I did a lot of work on his trailer.

Then he got busy:
1000 watts of Renogy panels
4 T105 Trojan 6 volt batteries
Big old fridge made in the 90's
Cotek 1500 pure sine wave inverter

Plus he tied to the grid since that only costs $8000. He wants his solar set up to be capable of running the fridge and lights.

The inverter doesn't have the oomph to power through the compressor surge of the big, old 90's fridge. I suggested that a newer Energy Star fridge should be fine with the 1500 watt inverter. He liked that idea much better than spending well over $1000 for a larger, higher quality inverter.

The batteries are brand new and have 2/0 inter connects so I would guess the cables to inverter are appropriately sized. However...I consider it possible that four T105s *may not* provide optimal oomph for a significant compressor surge. There are 225 Ah/battery. These are 62 pound batteries according to Amazon...not even GC2 sized. Bit surprised by the 225 Ah rating.

Seems that fridges may have significant start up surge. My lights sometimes dim a little bit for a fraction of a second when my fridge kicks on. 

Also.....can this hurt the inverter? I think it may hurt the fridge compressor when there is inadequate power. I would guess that he got the old fridge for free though. It is a 90's fridge...at best. He seems comfortable with finding an Energy Star fridge.

706jim

Fully charged GC's should be able to start a fridge. Even though there are only four of them, they can develop a high surge current for several seconds. I would suspect the fridge in this case. As for damage to the inverter I can't say. Mine is one of the old style units with a transformer and is bullet proof compared to cheaper solid state inverters that I've seen fail.

softdown

Agreed about the batteries. I use to use one 125 pound 8D for short runs with a 15 amp saw. 

The fridge is the logical culprit in any normal scenario. Though I wouldn't completely rule out the inverter becoming damaged either intentionally or inadvertently. Could be a bad connection or small cables. Hard to really say without seeing it.

I'll bet things are fine with an Energy Star fridge. No brainer to use an Energy Star fridge with off grid solar unless batteries are literally free.


706jim said:

Fully charged GC's should be able to start a fridge. Even though there are only four of them, they can develop a high surge current for several seconds. I would suspect the fridge in this case. As for damage to the inverter I can't say. Mine is one of the old style units with a transformer and is bullet proof compared to cheaper solid state inverters that I've seen fail.

solarvic

Anyone think a hard start kit might start the refrigerator. They use them on compressors when the compressor won,t start.  I could not get my compressor to start and bought one and installed it.  It has a capacitor to store up enough energy to give it a boost to start and runs normal.  you can get them from ebay for about $15 or less.

softdown

solarvic said:

Anyone think a hard start kit might start the refrigerator. They use them on compressors when the compressor won,t start.  I could not get my compressor to start and bought one and installed it.  It has a capacitor to store up enough energy to give it a boost to start and runs normal.  you can get them from ebay for about $15 or less.

They *might* also be called soft start capacitors. Yes....the fridge could likely be induced to work. 

However...it is foolishness to use a fridge that is not close to being Energy Star rated. The wear and tear on the batteries alone would costs much more than a used Energy Star fridge. 

Colorado has a lot of federal employees and quasi-execs. It is very easy to find very good, used fridges for less than $200 at ...say... Habitat stores. 

BB.

Place a volt meter on the DC input to the AC inverter and see if you get a lot of sag when starting the fridge (or place an 800 Watt hair drier (or up to a 1,500 watt space heater) on your inverter and see what the voltage drop is.

-Bill

softdown

BB. said:

Place a volt meter on the DC input to the AC inverter and see if you get a lot of sag when starting the fridge (or place an 800 Watt hair drier (or up to a 1,500 watt space heater) on your inverter and see what the voltage drop is.

-Bill

Good idea I'm sure. A large voltage decrease be indicative of insufficient power being available? That seems logical to me. Possibly due to a bad connections or too small of inverter cables. 

I use an identical inverter for powering a large 14 cubic foot freezer. The fan turns on for a second when the freezer kicks on. No struggle at all...and the freezer is serviced by at least 125' of  #12awg wire. Might be closer to 150'. 

BB.

Long AC wiring from inverter to refrigerator/freezer load can actually be a help. The longer wiring+resistance reduces the high surge current. This is a version of "soft start".

Some folks have simply put a 100' (not heavy duty) extension cord on their refrigerators to fix "hard start" issues.

Obviously, too much resistance is not good either (motor will not start, more energy losses).

-Bill

mike95490

Using a long, thin gauge, AC extension cord, has been known to have enough resistance to aid (reduce) the starting surge, yet still pass enough power to properly run the compressor.
 (long cord on the AC side, not the low voltage DC wire runs)

softdown

BB. said:

Long AC wiring from inverter to refrigerator/freezer load can actually be a help. The longer wiring+resistance reduces the high surge current. This is a version of "soft start".

Some folks have simply put a 100' (not heavy duty) extension cord on their refrigerators to fix "hard start" issues.

Obviously, too much resistance is not good either (motor will not start, more energy losses).

-Bill

New large Energy Star freezer may have a start up surge....................and the rest disappeared. The Post Comment button has "issues" for me. I waited several minutes for it to decide to become functional.