Challenge Time! - Page 1
Forum section: electronics / beginners

author: Kennylxix
author_rank: Regular Contributor
timestamp: May 03, 2023, 11:17:15 pm
content: So here's the situation. I have a camper. That camper has a 55 amp converter that supplies 12 volt power from 120 volts shore power and charges my 400 amp hour lithium iron phosphate battery Bank. I recently got a larger generator to to replace the undersized generator I had for boondocking. When connected to this 4,500 watt generator having the converter on causes my air conditioner compressor to make a ringing hissing sort of sound. This does not happen when connected to regular shore power or strangely enough on my old 2500 w generator from the same brand.I contacted the generator company and they sent me a new inverter board for the generator. This did not fix the problem.It is not voltage sag because the smaller generator sags more under this load and doesn't have the problem. I can also run the microwave at the same time as the air conditioner on the 4500 watt generator and it does not cause the problem even though the microwave is more of a load.Frequency is right at 60 Hz the entire time other than a very slight fluctuation when load increases or decreases. This is verified with an oscilloscope and a bryman 867 meter.I tried a different brand of converter and it does the same thing.Looking at the oscilloscope waveform it is flat topping pretty dramatically when the converter is on but it does that on shore power as well and the noise isn't there.Getting a different generator might fix the problem but it might not and I'm not really in a position to buy yet another generator.I'm attaching a link to a video for exactly what's happening. This is me switching the 55 amp converter on and off.Questions are1) what could this be?2) other than replacing the generator what can I try to do about it?3) is whatever this sound is actually causing harm and can I just ignore it?I've asked in camper groups electronics groups on Facebook air conditioning groups and have not gotten any information beyond what I already know.Help is greatly appreciated!https://drive.google.com/file/d/1fsoHn04KBU5iVOQ0wzKR1nrUcSogAe9Q/view?usp=drivesdk

author: Jwillis
author_rank: Super Contributor
timestamp: May 04, 2023, 04:34:17 am
content: Sure sounds like the converter is injecting noise into the electrical system.. This can sometimes happen with some PWM converters.Which converter is it?Oh sorry I missed the part with the second converter.What does the converter wave look like with the generator. Can you post a picture?

author: MrAl
author_rank: Super Contributor
timestamp: May 04, 2023, 05:20:48 am
content: Quote from: Kennylxix on May 03, 2023, 11:17:15 pmHi,Could it be the natural noise of the AC unit? You may be hearing the natural sound for the first time due to the fact that you never had a power source that could supply the full power well enough. The others sounded like they sag more so maybe the AC was not working at full capacity until you got the better supply going.What you could do it is try looking at the current waveform with all three power sources. The current sometimes reveals things that the voltage can not because the current is due to both the voltage and the impedance. See if they look similar or one is greater than the other. This could just be a natural phenomenon for the AC.It could also be that the increased power combined with the flat topping is causing the noise, which is hard to say if it is harmful to the AC unit or not.How expensive was the AC unit if it does happen to blow out. Hopefully not that expensive.

author: Jwillis
author_rank: Super Contributor
timestamp: May 04, 2023, 12:54:03 pm
content: There is also one thing that you could consider. Since your running on a larger generator you might consider earth grounding. Earth grounding can significantly reduce generator noise. It has also been been considered as a safety issue as well but we won't get into that unless you want to. You might think this as counter intuitive being a "portable" generator but it is indeed recommended to earth ground portable generators.

author: Kennylxix
author_rank: Regular Contributor
timestamp: May 04, 2023, 01:16:41 pm
content: This is what the voltage waveform looks like when the converter is on. For my research the rectification in the power supply causes higher loads at the top and bottom of the waveform which causes this flat topping. The weird thing is it looks exactly like this on shore power and on the other generator but they don't make the noise.

author: Kennylxix
author_rank: Regular Contributor
timestamp: May 04, 2023, 01:17:59 pm
content: Quote from: MrAl on May 04, 2023, 05:20:48 amI suppose that's possible but I would think that the 30 amp shore power would provide more power than the generator and the smaller generator actually is in overload when running these two loads dropping the voltage significantly and it doesn't make the sound so I don't think that's it.Unfortunately I'm not able to take a current wave form because I don't have any current sensing probes for my oscilloscope.

author: Kennylxix
author_rank: Regular Contributor
timestamp: May 04, 2023, 01:18:57 pm
content: Quote from: Jwillis on May 04, 2023, 12:54:03 pmI haven't tried earthing the generator. I have tried bonding the neutral to the ground but the whole thing is still floating. I will try that today and see what happens.

author: Kennylxix
author_rank: Regular Contributor
timestamp: May 04, 2023, 01:19:45 pm
content: I was thinking about trying to add a power line filter to the converter to see if that would help but not sure if that would be beneficial or not. What do you think?

author: Kennylxix
author_rank: Regular Contributor
timestamp: May 04, 2023, 01:21:21 pm
content: Quote from: MrAl on May 04, 2023, 05:20:48 amThe air conditioner is about $1,300 and has a $200 soft start installed in it.

author: MrAl
author_rank: Super Contributor
timestamp: May 05, 2023, 04:41:21 am
content: Quote from: Kennylxix on May 04, 2023, 01:17:59 pmHi,Didn't you say the others would sag?You can get an idea what the current wave looks like with a small series resistor.For 10 amps you can use a 20 watt, 0.1 Ohm resistor.For 20 amps, 0.025 Ohms, 20 watts.You'll get a lot of noise but you can still compare.Don't run too long like that the resistor will get hot.Place the scope probe across the resistor to see the current being careful to watch out for grounding issues.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 06, 2023, 08:28:37 pm
content: I'd say, start with throwing that fnirsi thing in the garbage and buy a decent scope. Best I know, the fnirsi thing is not even capable of showing single shot signals, and it does a lot of averaging and other weird things to generate a "beautiful" signal. Any spikes, noise, and other nasty stuf that could have been made by your inverter is probably filtered out by the fnirsi thing. fnirsi just makes garbage and not even worth having as a beginner.I've seen a few reviews of the fnirsi thing, and when you for example switch a function generator from 1MHz to 100kHz, then you see the signal on the fnirsi slowly transitioning to the 100kHz signal. For some reason, the reviewers completely disregard this, but the fact is that this clearly shows there is a lot of averaging and filtering happening. It takes over half a second before the signal is stable again, so it may be averaging hundreds of waveforms.Maybe you can re-use it as an STM32 (compatible) uC board with TFT screen of something, but it's not a scope.

author: themadhippy
author_rank: Super Contributor
timestamp: May 06, 2023, 08:54:57 pm
content: maybe the inverter board on the genny is kicking out some noise thats making the motor windings sing