Originally Posted by Robi.1014
Some sketchy math will help:
Power (watts) is the product of current (i) (in amps) times voltage (e). I never forget this because I like "Pie" (P=IE).
So the wattage consumed by your running refer is 4.3 times 120, or 516 watts....if we use these values literally. But, of course, your inverter is creating the "120 volts" from a 12 volt source....which means that 43 amps are needed from the 12VDC source. If we assume that the surge current needed at refer start-up is 5 times that of 4.3 amps, then at the 120v level, we need 21.5 amps (ever so briefly) to get the motor/compressor started from a dead stop). To get 21.5 amps at 120 volts is to need 215 amps from the 12 volt source. (again: ever so briefly).
I don't see any red flags here. Just be aware and a continuous draw from batteries of 43 amps is quite a large draw. So running your motor will be necessary.
Good morning Robi.
Thanks for the math calculations. We did the math estimates based on the same criteria as you did and according to that it seems to it should work.
now 2 questions:
1) Where the criteria of what some people say that the compressor needs 5 to 10 times more for the start-up comes from?
2) if we need 215 amps to start the compressor that is huge! I don't think that any regular alternator on a 1ton truck has that power capacity. I also got the info about the power inverter :
750 Watt Continuous Power / 1500 Watt Peak
Powers up to 6.8 Amps
Two GFCI 110/120 Volt AC receptacle
Maxx SST (Soft Start Technology) - gradually & safely ramps up output voltage
Automatic reset if inverter shuts down
Maximum Continuous Power: 750 Watts
Surge Capacity: 1500 Watts
No Load Current Draw: 0.4 Amps
Maximum Efficiency: Approx. 90%
Input Voltage Range: 10.5 - 15.5 VDC
Output Voltage Range: 110VAC 60HZ
Under Voltage Shutdown: 10.0 Volts
Thermal Shutdown: Auto Reset
Wave Form: Filtered Modified Sine Wave
Internal Fuse: 35 Amp
Dimensions: 10.7"L x 6.25 "W x 1.75 "H
So if it only power up to 6.8 amps I can't do it. But then is the question of: Why we were able to run the big RR with that power inverter?
Does it make a big difference that the RR was running already and that the Compact Refrigerator is completely dead?(it has not been running for the last couple of weeks) and the very first start-up takes a lot more than when it is cold already?
As we said before we are new on this and we need help.
Thanks for the help