Author Topic: 🆘 Relay specifically tripping inverter!!! 🆘  (Read 2445 times)

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Offline tom66

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Re: 🆘 Relay specifically tripping inverter!!! 🆘
« Reply #25 on: July 27, 2023, 08:01:14 pm »
So I think at this point since I've spent so much time and aggravation on this, I'm just going to bypass the main board and just direct wire the entire thing.

I'll use a normally closed contactor between the battery and the inverter and wire the float switches to the contacts on the contractor in order to cut the power if the condensation tank is full. I'll also make sure to power up the high and low side pressure switches.

I know I could also control the contact with the thermostat, but temperature control is not needed for my application. I just need this thing to keep running until I turn it off.

Trust me I completely understand the the best thing to do is purchase a larger inverter but it s not in the budget rite now...

Bad idea, the contactor will burn pretty quickly switching a huge inrush load such as that inverter.  It will have a lot of bulk capacitance and you are switching it on and off frequently.  You would need to add your own inrush limiting, but that could interfere with the startup of the inverter if it was not designed for it in the first place.  Also, the hard switching could create ringing at the input to the inverter, which could damage it if it does not have a good TVS protection (unlikely for a cheap unit intended to be connected once to a battery and rarely disconnected.)

Far better to just buy a better inverter.  If the inverter manufacturer makes such claims as not being able to start unless it is rated to 3-7x (that seems like nonsense as they have claimed 3kW peak load) then what else have they lied about?  Your 8000BTU air conditioner is about 2.34kW cooling or around a 650W motor assuming COP=3.5.   I would send it back, get a refund, and buy another, a better one... otherwise you will be posting back on here next month asking how to repair an inverter that has blown up.

Remember the adage, buy cheap, buy twice.

Side note:  thermostat is important for A/C as otherwise the coil frosts up and efficiency drops off really quickly.  Good A/Cs have ice sensors, or at least cycle timers to allow the coil to defrost.
« Last Edit: July 27, 2023, 08:05:25 pm by tom66 »
 

Online Gregg

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Re: 🆘 Relay specifically tripping inverter!!! 🆘
« Reply #26 on: July 27, 2023, 08:10:18 pm »
You can also look at the refrigeration compressor itself. 
Small inexpensive compressor systems start the compressor at full head pressure whereas large commercial units run the compressor during shutdown to pressurize an accumulator with solenoid valves such that the compressor is ready to restart under minimal head pressure or even a vacuum. 
A very simple solution would be to install a bypass solenoid valve (rated for the refrigerant) between the suction and pressure side of the compressor and make a time delay to open it during startup so that there is very little pressure differential when starting. 
Of course you would need the tools and knowhow to install this properly, but it would alleviate the problem and probably extend the life of the compressor.
 

Online Ian.M

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Re: 🆘 Relay specifically tripping inverter!!! 🆘
« Reply #27 on: July 27, 2023, 10:27:01 pm »
Why not figure out how to power the A/C control board independently of the compressor, (either direct from 12V via some sort of DC-DC module, or via a cheap low power inverter), and hack the 1500W inverter's remote so the signal to the control board relay coil triggers a button push to turn the big inverter on and off with a slight delay turning it on so the relay is already closed.  Leave the relay in circuit so all the aircon limit trips still work even if the inverter remote becomes unreliable.

However I still reckon the above would put undue stress on the inverter so you'd better start saving to replace it by one rated for refrigeration loads.
« Last Edit: July 27, 2023, 11:52:07 pm by Ian.M »
 

Online bdunham7

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Re: 🆘 Relay specifically tripping inverter!!! 🆘
« Reply #28 on: July 27, 2023, 11:34:13 pm »
Solving an issue like this without some measurement is pretty hit and miss, more miss than hit in this case.  I dragged out a dehumidifier, which for our purposes is pretty much the same thing as the OP's air conditioner.  I took a screenshot of the startup and while the iniitial surge was >4X the running current, the surge only lasted about 8-10 cycles.  The compressor starts up pretty quickly.  This unit seems to use a zero-crossing switch to control the compressor, as the clean startup here is consistent, not just a random stroke of luck.  If it didn't have that, there would likely be an even larger inrush spike at times.  In order to really analyze the issue and come up with the proper fix, the OP would have to take some similar measurments to see if it is a very short inrush or a multi-cycle surge that is the problem.  However, my guess would be that the OP's AC unit draws about 8A normal running and if it were proportional to mine, the startup surge would be 32A or 3840VA but probably a 0.7 or so power factor.  Likely the inverter just can't hack it when presented with that much of a load when it is already on. 
« Last Edit: July 27, 2023, 11:36:19 pm by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Online NiHaoMike

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Re: 🆘 Relay specifically tripping inverter!!! 🆘
« Reply #29 on: July 28, 2023, 03:57:08 am »
If it does a V/Hz ramp up, the inrush would be basically nonexistent.
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Online BrianHG

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Re: 🆘 Relay specifically tripping inverter!!! 🆘
« Reply #30 on: July 30, 2023, 03:31:23 am »
@bigjoncoop, have you followed the path and measured the current along the Frame/Earth Ground.  The inverter may be tripping because of a built in safety mechanism monitoring the frame ground pin.  IE: Power everything up at once and the inverter sees a synced noise or bounce load throughout the system.  Have the AC partially powered up and the FG may be charging a cap somewhere & when the AC's relay is switched on, regardless of the quality of that switch, or the phase timing, that cap is discharged through the FG would make your inverter's safety fault detection function instantly trip.  IE: Your inverter may have a high speed electronic FG ground fault protection.

No series resistor or magic switch time will fix this unless you cut the FG pin.  (Not recommended for safety reasons)

Are there any motor AC caps with a wiring to the FG instead of the AC's Main COM/HOT line.  This would do it.
« Last Edit: July 30, 2023, 03:59:48 am by BrianHG »
 


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