120V on the PV line?? Discussion of Will's video

[EastTexCowboy]

Even Will admits that there wasn't any consistancy between all the units he tested. It looks like you scored a good one.

Good to have more checks posted! ?

True. But the inconsistency makes it more scary than if they were all doing the same thing. On the other hand, I can't see that I would have ever messed around inside with the AC input live. I had to intentionally leave it on this time just to test it. I don't really mind working stuff hot when I need to but not reaching around up in those tight little places.

 

[Vigo]

I dont know if my Growatt SPF5000ES's did this from day one or not, but they definitely do something like it now. I have not put a meter to it but the thing that clued me in to it was that occasionally i'd see ~80v dc from solar in total darkness. Turn off the PV breakers and it goes away. I made the mental leap that ~80vdc was perhaps half-wave rectified 120vac after passing through panel diodes, minus some voltage drop from said diodes, so figured it might be connected to my using an autotransformer since the growatts themselves don't make 120v. But that correlation might be totally coincidental. It doesn't seem to hurt anything so i never finished diagnosing it and never was shocked by it.

On the other hand, i WAS shocked by AC on my battery circuit! I used an incandescent lamp to ground to see what the 'ampacity' of the issue was, and it turned out to be tiny, then measured by meter to be ~10ma. Not tiny to my nervous system but not something i needed to 'fix' other than the shock hazard, so i just grounded the battery circuit and carried on and its been leaking 10ma continuously ever since, as far as i know. I can't remember if i checked the voltage or frequency of that and what it was. I have no grid connection either way but i assume if i had one, then measuring frequency would tell you whether it originated from your inverter (60hz) or from full-wave-rectified mains (120hz) on your DC bus which happened to still contain excessive ripple. But that's just where my brain goes, possibly also a made up or irrelevant correlation.

 

[OffGridForGood]

Well since you guys brought this up, I had to check.
My set up: twin MPP 6048's, incoming utility available 120/240, PV arrary frames (only) grounded (per manual)
I can confirm zero Volts-AC on the MPP terminals, between 0.2 and 2.6 VDC while battery is connected, Zero when battery is offline, even with AC-IN online. Switching PV main-disconnects makes no difference - complete darkness at the time.
Not enough voltage to cause any harm it would seem.
I tried to light up a 1.5VDC pen-light-bulb and couldn't get more than a dim glow.
After watching the Video, I feel a bit better about purchasing new rather than used PV panels.
So, do we start a spreadsheet to list inverter models and which show AC or DC voltage on the MPP terminals, and to what order of magnitude?

 

[timselectric]

I think that people are measuring this incorrectly.
You should be measuring from + to ground and - to ground, to check for this AC voltage.

 

[EastTexCowboy]

I think that people are measuring this incorrectly.
You should be measuring from + to ground and - to ground, to check for this AC voltage.

That's how I measured mine. Positive on PV to ground and negative on PV to ground.

 

[EastTexCowboy]

Well since you guys brought this up, I had to check.
My set up: twin MPP 6048's, incoming utility available 120/240, PV arrary frames (only) grounded (per manual)
I can confirm zero Volts-AC on the MPP terminals, between 0.2 and 2.6 VDC while battery is connected, Zero when battery is offline, even with AC-IN online. Switching PV main-disconnects makes no difference - complete darkness at the time.
Not enough voltage to cause any harm it would seem.
I tried to light up a 1.5VDC pen-light-bulb and couldn't get more than a dim glow.
After watching the Video, I feel a bit better about purchasing new rather than used PV panels.
So, do we start a spreadsheet to list inverter models and which show AC or DC voltage on the MPP terminals, and to what order of magnitude?

That's good that you don't have the issue. As for the spreadsheet, according to Will in the video he was getting reports of different voltages from the same models from different people so I don't know how much value it would be.

 

[timselectric]

That's how I measured mine. Positive on PV to ground and negative on PV to ground.

Then you have checked it correctly.
But I would check while the SCC is running.

 

[EastTexCowboy]

Then you have checked it correctly.
But I would check while the SCC is running.

Nag, nag, nag.

Okay, I'll head out there and check it now <sigh>

 

[Vigo]

But.. (looks out window) the sun is no longer up in Texas.. whatre you gonna run the scc with?! ?

 

[EastTexCowboy]

Then you have checked it correctly.
But I would check while the SCC is running.

Well, well, well. You do have a nasty habit of being right on a very frequent basis. ? I'm getting 102v AC on both the positive and negative PV input ports that don't have PV cables connected. Same on both inverters. WTH?

 

[OffGridForGood]

Then you have checked it correctly.
But I would check while the SCC is running.

I will have to wait for some sunshine!
To confirm my earlier post, on the 6048's MPP pos to EG in volts AC -zero, ditto MPP neg to EG -zero.
in DC volts, from MPP pos to EG a few milli-volts and from MPP neg to EG 60mVDC to 2.6VDC (there are four neg MPP terminals and each is different potential to EG).
These measurements were done while the inverter is running from the batteries, utility available but not charging. Sun is down so no incoming PV.
I will measure again when the SCC is running on incoming PV to see if that changes things.

 

[EastTexCowboy]

I will have to wait for some sunshine!
To confirm my earlier post, on the 6048's MPP pos to EG in volts AC -zero, ditto MPP neg to EG -zero.
in DC volts, from MPP pos to EG a few milli-volts and from MPP neg to EG 60mVDC to 2.6VDC (there are four neg MPP terminals and each is different potential to EG).
These measurements were done while the inverter is running from the batteries, utility available but not charging. Sun is down so no incoming PV.
I will measure again when the SCC is running on incoming PV to see if that changes things.

@timselectric said test it while it's running. It's running. It's not getting solar input but it's running. I plan on checking it again tomorrow when it's running but also getting PV input, but it's weird that I'm getting 102v on it now.

 

[SignatureSolarJames]

Can we all just get along and use isolators?

 

[EastTexCowboy]

Can we all just get along and use isolators?

I didn't think we weren't getting along. Actually I thought we were doing a pretty good job of collaborating. If I came across otherwise it wasn't intended. For me at least this doesn't present a major safety issue because I'm not going to be poking around in there with any kind of power connected. But I think there's a lot of concern about why we're seeing this.

 

[timselectric]

I'm not concerned. I didn't expect it at first. So it introduced itself to me a couple of times last year.
But, I managed to not fall off the roof.
And we are good friends, now. lol

 

[SpongeboB Sinewave]

This is not all that surprising to me since the inverter and PV MPPT sections are not galvanically isolated in most of these AIO units. Just have to be extra careful.

Ungrounded PV systems ground-fault have required both positive and negative lines to be disconnected for a while now (pretty sure). But the GF current required for it to trip is still higher than the lethal current to ground I believe.

The battery side to AC/PV sides are usually isolated though which is good. Just reduces the efficiency a bit.

Unfortunately, the old single 1/2 amp fuse or breaker tying the negative to ground won't work for that. BUT as it turns out, that old John Wiles GF disconnect method is not safe either because it can cause lethal PV voltages from negative to ground when tripped.

There's always a compromise somewhere.

boB

 

[Will Prowse]

I finally got around to testing mine this afternoon after I did some re-cabling and cleanup. I have zero voltage on the PV connections on either inverter. Here's the scenario of my test -

Battery and battery breaker turned off
Solar input turned off at disconnect
No load
AC input turned on - 120v on AC input on both inverters

Testing all the PV input I had zero voltage on any of them. I tested both AC and DC voltage, although the situation in question was only AC.

These are two MPP LV6548 configured for split phase 240.

I do have the grounding screw removed on the primary inverter but I can't see where that would matter, and I do have everything grounded back to the earth ground on the main panel only.

I'm not complaining, but it's a little strange that everyone else is getting a range of AC voltage on the PV inputs and I'm not. Maybe y'all can figure it out. I'm thinking it's time for a Shiner Bock myself.

Can you connect the battery again and turn on the inverter? Why did you disconnect the battery? I do not understand the point of your test. Connect the battery, and turn on the inverter. Or charge from grid and tell us what your results are.

 

[Will Prowse]

"Never heard anyone mention this issue" - forum members have described getting a shock from unconnected PV input.

@Will Prowse Disconnecting battery and grid inputs alone isn't enough. Need to also wait a while for charge on PV input capacitors to drain away. So check voltage of those too before starting work. Most of my SMA inverters, it says wait 15 minutes or so. I'm impatient, of course. When I see the LCD display go blank it is ready. At that point, the 400V has drained to about 30V.

The Sunny Boy 5000US I'm presently using says,

"1. Switch off all AC and DC breakers or switch-disconnectors. Ensure they cannot reconnect
accidentally.
2. Wait at least 5 minutes until the residual voltage has been drained."

MC connectors on inverter makes it easy to just connect PV+ and PV-, not think about ground. Need a separate ground wire from PV frames back to inverter. That will protect against shock from damaged or leaky module (some old Trina modules developed leakage), also protects against AC leakage current through PV panel capacitance.

When conduit is used for PV runs it is easier to include ground, and terminals may remind you.

I find mention of grounding PV panel frames in Sunny Boy 10000TL-US-12:

View attachment 135565

And the current SB5.0-1SP-US-41: "• Only ground the mounting frames of the PV modules."
And the earlier 5000US:

"PV Grounding
The grounding conductor in the framework of the PV array must be connected to the PV grounding
conductor and the DC grounding conductor (see section 4.2 ”Locating Internal Component Parts”
(page 20)). The cross-section of the grounding conductor corresponds to the cross-section of the
largest conductor in the DC system."

Good to know. Thank you for posting this. Did not see that in the other manuals.

 

[Hedges]

There have been a few posts of prior incidents:

Growatt 5000es AC voltage detected on PV input!

Hi. I have two growatt 5000es hybrid inverters connected in parallel. All connections are correct as per instructions: For each inverter: AC input: 230v L and N and ground Ac output: 230 v L and N and ground So ground of input and output are connected to same ground wire. PV input: 300V...

diysolarforum.com

Dc mini breaker confusion

The thing you should have done was check polarity on PV side prior to closing switch. If inverter side is concealed, then after confirming zero volts on that side see if you can verify connections (desired polarity at breaker) with ohm meter. You can connect PV panels and wires in series...

diysolarforum.com

AC voltage from lvx 6048 to a wire not connected to anything? 83V

I'm assuming I have a short somewhere but I'm also a little stumped. My solar arrays are 400ft from the house. I ran 5 wires through plastic conduit, 2 hot, 2 neutral and 1 ground. I'm getting 120 AC voltage on every wire even though they're not connected to the LVX 6048. I get voltage from L1...

diysolarforum.com

Safety tips for all-in-one inverters

Hi All, Are there any safety methods that you know for the longer life of all-in-one inverters? For example, one method I heard was, "Don't cut the battery power while the inverter is powering the loads". Likewise are there any other small tips that you know? Thank you.

diysolarforum.com

The "Meg" Build

Alright, im doing testing. Here's what I've found so far. The negative from my 48v battery is grounded to RV chassis. Im assuming this is happening through the 48v to 12v converter, because the output of the 12v side is grounded to a common ground screw on the frame. The inverters do have...

diysolarforum.com

This forum format works for conversations, but difficult to look up topics.
Think we can get ChatGPT to index it and provide natural language query?
Searchable VAERS database?

 

[Rednecktek]

Think we can get ChatGPT to index it and provide natural language query?

Do you want the AI apocolypse!?!? Teaching them how to power themselves on renewable energy is how you get the AI apocolypse!!

?