🆘 Relay specifically tripping inverter!!! 🆘 - Page 1
Forum section: electronics / general

author: bigjoncoop
author_rank: Regular Contributor
timestamp: July 24, 2023, 07:33:24 pm
content: I have spent over a week on this problem, pulling my hair out and finally narrowed it down to the relay itself....ISSUE: trying to power a small air conditioner unit from inverter, but when using the factory relay that kicks on the compressor, it trips the inverter protection! IF I BYPASS THE RELAY AND HARD WIRE THE COMPRESSOR, THE INVERTER HAS NO PROBLEM RUNNING IT. (specific relay datasheet below)Main Question: is there a simple solution to mitigate the spike of the relays contacts closing? Or should I remove the relay and try to use a mosfet instead?(from searching online I found a couple possible solutions. Using either a Metal-oxide Varistor (Vos) or a TVS Diode. Your thoughts, would these work?)More Info: the air conditioner main board has a time delay to engage the compressor. Originally every time the compressor kicked on it was tripping my inverter. So I went down a week's long rabbit hole trying to implement a couple different soft starter methods. I've tried using NTC inrush current limiters, as well as making a resistive inrush current limiter with a on time delay circuit and I had some varying success...So I then decided to just completely bypass control board and to my surprise with no inrush current limiting whatsoever, the inverter has no problem powering the air conditioner with the fans and compressor kicking on at the same time.So I now narrowed it down to the relay for the compressor is what is tripping the inverter! It would be ideal to be able to still use the factory main board in the air conditioner since it provides all the float switch sensors and the delay for the compressor etc.. If I can't figure out the relay problem I'm just going to hardwire the whole damn thing but I'd rather notAny ideas on how to avoid this? Is there a way to smooth the spike of the relay contacts or should I maybe try to remove the relay and install a mosfet instead?

author: edpalmer42
author_rank: Super Contributor
timestamp: July 24, 2023, 09:03:49 pm
content: A MOV or TVS Diode is unlikely to solve your problem or if it does solve your problem, it's solving the wrong problem!How old is the air conditioner?Since bypassing the relay works, your inverter is able to tolerate the inrush current from the compressor. The relay's purpose isn't to limit inrush current, but to control when the compressor operates. Isn't it the main control to turn the compressor on and off in response to the thermostat? If you bypass it, aren't you disabling all temperature control?My first thought is that the relay is either old and near failure or just cheaply built. When the (perhaps burnt) contacts close, the arcs generated at the contacts send noise back into the inverter that shuts it down. If you have a beefy powerline filter, maybe in a power bar, you could wire it between the air conditioner and the inverter and see if that helps. Note that the filters in power bars are typically low end and might not be adequate. And their 15 amp rating is marginal when considering the inrush current from an air conditioner. A proper test would involve a standalone filter module rated for at least 20A.Ultimately, I think the proper solution is to replace the relay - perhaps with a higher power unit.Ed

author: bigjoncoop
author_rank: Regular Contributor
timestamp: July 24, 2023, 11:12:31 pm
content: Hey @edpalmer42Thanks for your reply.The air conditioner is brand new. It's an LG portable air conditioner. I've only run it a few times for a couple minutes here and there trying to get this all to work.I mentioned I could just bypass the relay and hardwire it because having temperature control / thermostat is not necessary for my application. But like I said I would rather not do that since I would loose the built-in safeties and controls.So you think the culprit might be the relay itself though huh? That would be easy enough to diagnose. I will give that a shot this evening when I get home and report back. That would be very convenient if that's the problem 😜! Fingers crossed!* also I was thinking that another easy solution could be to just use the current relay to trigger either a mosfet or SSR... I have a spare solid state relay that's rated high enough for a compressor.

author: Someone
author_rank: Super Contributor
timestamp: July 24, 2023, 11:18:42 pm
content: When you bypass and "hard wire" I assume that is while the inverter is off/isolated, if so then when you turn it on the inverter is likely "soft starting". A relay turning on/off will cause a hard transient load, compressors are notorious for tripping inverters or stalling generators as they can demand a huge startup current. Oversize the source inverter/generator or get a compressor with its own inverter drive circuit that soft starts.

author: Circlotron
author_rank: Super Contributor
timestamp: July 25, 2023, 12:10:49 am
content: Could be that contact bounce on your relay is sending very rude signals back to the inverter. I'd try a SSR in line with the relay and switch the relay on first / off last.

author: KaneTW
author_rank: Frequent Contributor
timestamp: July 25, 2023, 12:22:44 am
content: Quote from: Someone on July 24, 2023, 11:18:42 pmThis is my take as well. Bypassed relay -> inverter soft starts -> less inrush current on the load -> no trip.With a non-bypassed relay:1) relay switches close to 0V, lower inrush current, no trip2) relay switches closer to line voltage, higher inrush current, trip

author: edpalmer42
author_rank: Super Contributor
timestamp: July 25, 2023, 09:00:20 am
content: Someone made a good point about the inverter soft-starting.An easy test to seperate the idea of hard-starting through a flaky relay vs. soft-starting would be to bypass the relay with an ordinary light switch. Standard light switches are rated for 15A so that they can be used to switch an outlet on and off.If the inverter shuts down with the light switch in the circuit, it means that the compressor's starting surge is causing the shutdown. If not, then the relay is suspect.Ed

author: tom66
author_rank: Super Contributor
timestamp: July 25, 2023, 09:30:02 am
content: I think it is the inverter soft starting too but I'm curious as to why the precharge circuit tried by OP didn't work ... a bit odd.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 25, 2023, 01:28:14 pm
content: How old and what brand is the inverter? I recall Vector made some inverters with V/Hz ramp up in the 2000s but they were found to be infringing a patent. But they were legendary, would start motor loads that most cheap inverters of the time will not.Quote from: tom66 on July 25, 2023, 09:30:02 amThese won't lower frequency which is what's needed for soft starting induction motors. They are intended for universal motors and capacitive loads, which just need initial current limiting.

author: BrokenYugo
author_rank: Super Contributor
timestamp: July 26, 2023, 02:07:14 pm
content: Is the inverter well supplied? Heavy cables and battery up to the job? Sound like it's just a marginal combination.If by portable you mean the roll around type, keep in mind those are considerably less efficient than the window type, especially if it only has one hose (1 hose blowing out keeps room/building at neg pressure, constantly sucking in hot wet air from outside the room). That's why you don't see portables under 8000btu.At the high end it seems a lot of this stuff is starting to go to variable speed compressors that soft start themselves, that may be another option.

author: bigjoncoop
author_rank: Regular Contributor
timestamp: July 27, 2023, 02:52:52 am
content: @BrokenYugo @NiHaoMike @tom66 @edpalmer42 @KaneTW @Circlotron @SomeoneHey guys, thanks for all your replies!!!I have some more details and things that I've tried.So unfortunately I have tried a couple different relays and today I tried 2 different Solid State Relays and still they all trip the inverter when the compressor kicks on!I've also tried using a light switch as someone suggested to see if that helps and it made no difference. Soon as turn on the switch the inverted trips.I know someone asked if it was a portable or window unit, the unit I'm dealing with is a portable unit on wheels. As I mentioned it's brand new.I made a video yesterday if anyone would like to watch it quick. I tried to cover all the details. The video does not include me testing the solid state relays because I did not receive them until today from Amazon. I purchased two SSR's , one is controlled by DC and one is controlled by AC. But as I mentioned they also tripped the inverter.https://youtu.be/shoD-iH4Plo***So unless someone may have an idea besides purchasing a new AC unit or a larger inverter, I'm just going to have to bypass the main board and just hardwire both fans and the compressor.I'm thinking I'll install a contactor between the battery and the inverter and use relays connected to the float switches in order to cut the unit off, and most importantly wire up the high and low pressure switches...

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 27, 2023, 04:37:38 am
content: Quote from: BrokenYugo on July 26, 2023, 02:07:14 pmMod it to a 2 hose type, it will work a lot better.Quote from: bigjoncoop on July 27, 2023, 02:52:52 amHow about modding the inverter to have a remote enable input (or if it already has one, use it) and connect it to the compressor relay? Then power the control logic from DC.

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2023, 04:46:03 am
content: Quote from: bigjoncoop on July 24, 2023, 07:33:24 pmThis should work if you set it up right and an NTC (or multiples) seems like the easiest solution to me. How much current does your AC draw when running, immediately after startup? And what is the maximum output of your inverter? (Model and datasheet would be nice too....)

author: AVGresponding
author_rank: Super Contributor
timestamp: July 27, 2023, 05:36:28 am
content: Quote from: BrokenYugo on July 26, 2023, 02:07:14 pmShould be reasonably easy to check this, with a DMM looking at the DCV at the inverter supply terminals. If the DCV drops by anywhere near to 20%, there's a good chance the inverter would shut off.

author: bigjoncoop
author_rank: Regular Contributor
timestamp: July 27, 2023, 09:39:24 am
content: Quote from: bdunham7 on July 27, 2023, 04:46:03 amI've tried using Ametherm SL32 NTC thermistors. I've tried 1 and 2 in series with each other. I've tried this on the factory setup just connected to the compressor after the relay. Also when using a different relay and when tring both SSR's... Makes no difference.Inverter Specs:WZRELB 1500w / 3000w burstSEE ATTACHED IMAGEQuote from: BrokenYugo on July 26, 2023, 02:07:14 pmYes the inverter is VERY well supplied. (Building custom lithium batteries is my specialty 😁) It consists of Qty 256- ANR26650M1B cells in a 4s64p Configuration. Each cell is capable of 50A continuous output! So the battery is 12v almost 2.5kWh and capable of pushing 3,200 amps continuously. I currently only have it setup with fuses to push a maximum of 800amps. I also bypassed the BMS so that wasn't a limiting factor.

author: bigjoncoop
author_rank: Regular Contributor
timestamp: July 27, 2023, 10:28:02 am
content: !!! A QUICK RECAP TO CONSOLIDATE ALL THE INFO !!!Situation:Trying to run a new 8000btu portable air-conditioner off of a inverter.Main Issue:If the compressor is connected to the factory on-board relay, the inverter goes into protection when the compressor engages.If the relay is bypassed and the compressor is wired directly to the mains input, the inverter has no issue at all and compressor run perfectly fine every time...The battery is way OVERKILL and is supplying plenty of power to the inverterThings that I've tried:Used a different relayTried using 2 different Solid State Relays (1 controlled by DC & one controlled by AC.Tried using a 10ohm 25a Ametherm SL32 NTC inrush current limiting thermistor also 2 in series with all above mentioned methods. So after each of those solutions failed, I then connected the NTC's to each one and made no difference.Tried using a resistive in rush current limiter consisting of 2- 6ohm 50w power resistors in series for 12ohm connected to a "On Time Delay"Also tried using a normal 120v light switch to turn on compressor in order to see if that would still cause the inverter to trip... Still tripped inverter.I am open to any ideas and I appreciate any help.ThanksI also posted a short video the other day before trying a couple recent solutions. If u would like some more details...https://youtu.be/shoD-iH4Plo

author: tom66
author_rank: Super Contributor
timestamp: July 27, 2023, 10:43:10 am
content: I don't think 12 ohms is enough resistance for inrush limiting. Depending on if the inverter is true sine or not, it will be outputting peak voltage of around 170V to create 120V rms. That is a peak current of 14.1A with a dead short load, or 2400W momentary load. Can you try with something closer to 47 ohms? The challenge you will have is having enough resistance to not trip the inverter but enough to get the compressor started. It may be the only option is to buy a different inverter.I am quite sceptical of brand names you cannot pronounce (may just be a pop-up-and-run kind of Amazon company), and question whether the inverter is capable of its rated power outputs.

author: Ian.M
author_rank: Super Contributor
timestamp: July 27, 2023, 12:39:39 pm
content: The test with the manual switch proves that the inverter simply doesn't have enough safe overload capacity to handle the motor's starting surge. Why does it work when you hard-wire the compressor and startup the inverter? Well, the inverter has probably got relaxed overload detection during inverter startup, and also it may well start outputting AC before its internal DC bus reaches 170V so reducing the compressor's inrush current. Repeatedly starting it with the compressor direct connected may damage (blow) the inverter.You can get soft start kits for refrigeration & AC compressors, which specifically limit the starting current surge. You'd need to fit one internally to the AC, between its controller relay and the compressor. The more effective ones aren't cheap and there is no guarantee they'll reduce the current enough for your inverter to be happy.

author: Psi
author_rank: Super Contributor
timestamp: July 27, 2023, 12:50:23 pm
content: As a quick test you could try wiring 3 of those mechanical relays you have in chain so one triggers the next one etc. to add a few ms delay. They would need to have 2 sets of contacts though, not sure if your relays do?But you have them shorting out series resistors. So it starts with like a 80R + 40R + 10R in series and ends up directly connected.80R+40R+10RFirst relay shorts 80R40R+10RSecond relay shorts 40R10RFinal relay shorts 10RNow its direct connectedIts not a system i would leave in place, but just as a test to see if it works.

author: mendip_discovery
author_rank: Super Contributor
timestamp: July 27, 2023, 01:07:44 pm
content: Measure the voltage at the battery. Could you be hitting a low voltage issue with the battery supply just enough for the inverter to go into shut down. The number of times I have had cars do this is annoyingly high.

author: Psi
author_rank: Super Contributor
timestamp: July 27, 2023, 01:18:12 pm
content: Quote from: mendip_discovery on July 27, 2023, 01:07:44 pmGood use for a supercap across your battery.

author: Ian.M
author_rank: Super Contributor
timestamp: July 27, 2023, 01:22:50 pm
content: The place to initially check if the inverter's input voltage is dipping is right at its screw terminals, not at the battery, as its far more likely to be a high resistance connection somewhere than a bad battery. If you find a significant voltage dip, re-check working back towards the battery to locate the problem.

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2023, 02:00:59 pm
content: Quote from: bigjoncoop on July 27, 2023, 10:28:02 amFirst, ease up on the formatting!I think we need to know the specifics on the AC unit. What model, etc? Is there a data plate that has information like LRA, voltage, etc? Post a photo if there is. Then you need to have a way of measuring some things--what equipment might you have? Current clamp, DMM, oscilloscope, ?Two 6R resistors in series gives you a current of 10A and that tripped the inverter? That doesn't make sense.

author: Gregg
author_rank: Super Contributor
timestamp: July 27, 2023, 06:31:34 pm
content: From the Amazon listing for the inverter in question:QuoteIt appears that the manufacturer is well aware of the device's limitations for high inductive loads and recommends sizing their inverters 10x the rated capacity for refrigeration systems.While I applaud your efforts to put lipstick on the pig, the best solution is to replace the inverter with something that will reliably function as necessary.

author: bigjoncoop
author_rank: Regular Contributor
timestamp: July 27, 2023, 07:28:20 pm
content: I am aware of the manufacturers note about inductive loads.But it obvious that the inverter is capable of starting and running this air conditioner, as long as the compressor starts immediately upon power up...@Ian.M I think hit the head on the nail with his last comment...Quote from: Ian.M on July 27, 2023, 12:39:39 pmSo 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...

author: tom66
author_rank: Super Contributor
timestamp: July 27, 2023, 08:01:14 pm
content: Quote from: bigjoncoop on July 27, 2023, 07:28:20 pmBad 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.

author: Gregg
author_rank: Super Contributor
timestamp: July 27, 2023, 08:10:18 pm
content: 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.

author: Ian.M
author_rank: Super Contributor
timestamp: July 27, 2023, 10:27:01 pm
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: July 27, 2023, 11:34:13 pm
content: 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.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 28, 2023, 03:57:08 am
content: If it does a V/Hz ramp up, the inrush would be basically nonexistent.

author: BrianHG
author_rank: Super Contributor
timestamp: July 30, 2023, 03:31:23 am
content: @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.