Trace SW4024s AC2 input good light is blinking green but they are drawing power

[technovelist]

Hi all,

I have two Trace SW4024 units stacked to produce 240V as well as 120V. Everything has been working fine until today.
However, I just ran a load test, obviously with the grid input disconnected, and found that the "AC2 Good" light continued blinking on both inverters even after they were taking power from the generator. Of course that light is supposed to blink until synchronization and then go solid green but it stayed in blink mode.

I looked in the manual and it says that blinking means that the inverters aren't synchronized with the generator, but clearly they are because they are drawing power from it; "AC input amps" and "AC load amps" look correct and the grid is disconnected so I know the generators are providing the power.

I'd be more worried if only one inverter was doing this but I would still like to know if it is a known issue and what might occur next.

Has anyone run into this?

Thanks.

 

[Steve777]

Just a guess. I have a single SW4024. The green blinking light on a grid or genny source means the inverter is trying to "sync" with that source. If it never stops blinking then that source is not of sufficient "quality" as far as the inverter is concerned. It can still draw power from that source without sync'ing with it as I recall.

I have seen this before when grid voltage was quite low (<100v) after the power co did some repairs on a downed line. On a generator I would think that frequency variation might be the most likely problem.

 

[RCinFLA]

Blinkiing green means inverter see AC voltage input but is not sync'd with AC phase of source.


If it sync's to grid then it is likely the generator out of freq range or unstable governor causing too much wobble in freq/phase for inverter to grab a hold of.

You can temporarily put generator on AC1 port to see if you get sync.

 

[littleharbor2]

When the light is blinking the inverters are still drawing power from the batteries. When it "qualifies" the ac2 input then, and only then, it will draw power from the genny. You can clearly hear the generator load up once this happens. Also, keep in mind, once the genny takes over it has to cover your loads before your batteries will receive charging power. This will usually require your charging amps setting in the inverter to be set lower than you'd like if your loads are substantial. Of course this is limited by the genny's output. A large generator will usually cover all loads without issue and have plenty available reserve for battery charging. Smaller generator's, not so much.

 

[technovelist]

Thanks for all the input.

I should clarify that I'm 99% certain that the inverters were actually drawing power from the generator rather than inverting, for several reasons:
1. I heard the generator load up.
2. The yellow "inverting" light went off on both inverters when that occurred.
3. The load includes my heat pump, which runs the batteries down to the cutoff voltage in 5 minutes. However, the battery voltage was stable.
4. When I went back on grid power, the inverters didn't go on bulk charge, which they do when the batteries have been in use for even a couple of minutes.

BTW, I have no idea how to put the generator on the AC1 port. How would I do that without opening up the inverters?

My next plan is to try the other generator.
If that doesn't work, then I'll turn the inverter output off and back on and try the load test again.
If that doesn't work, then I'll reboot the inverters (turn their DC and AC off and back on).
Any other suggestions?
Thanks!

 

[littleharbor2]

Huh? Do you have a clamp meter? I'm curious what kind of current is being drawn from the generator.

 

[technovelist]

I don't have an AC clamp meter. According to the inverters they were drawing about 23 amps at 120V from the generator.

 

[littleharbor2]

I don't have an AC clamp meter. According to the inverters they were drawing about 23 amps at 120V from the generator.

They must be just passing it along to your loads and not charging your battery. This is strange though. I would swear my SW 4024 has to qualify the source ac power before it accepts it and then I hear the generator load up. Huh?

 

[technovelist]

They must be just passing it along to your loads and not charging your battery. This is strange though. I would swear my SW 4024 has to qualify the source ac power before it accepts it and then I hear the generator load up. Huh?

Yes, that's the way it always worked before yesterday. Let's see if it happens the next time, which should be later today.

 

[RCinFLA]

You can see all the numbers in 'Meters' menu 4. You have to have AC input sync and pass-through relay closed to see Input AC amps.

 

[technovelist]

Yes, AC input amps were about 15 on each inverter.
BTW, the behavior is back to normal on both inverters currently.
I guess this will remain a mystery...

 

[Steve777]

If you have a meter which will show AC frequency might be helpful to put that on the generator output next time this happens (if it does). If nothing else it will give a hint if the gen freq is stable or bouncing around.

 

[RCinFLA]

If you have a meter which will show AC frequency might be helpful to put that on the generator output next time this happens (if it does). If nothing else it will give a hint if the gen freq is stable or bouncing around.

A DVM freq function will not show wobble, only average frequency. Their sample gate is too long to detect variance.

Easiest way is to listen to generator. Should be smooth and steady sound with no wha-wha sound pitch variance.

 

[technovelist]

The generator is running at 58-59 Hz according to inverter meters, and the sound is pretty steady when under a significant load.

BTW, this type of generator is supposed to be able to put out 6700 watts on propane but if I try to draw more than about 36 amps at 120 (4.3 KW), it drops down to 57 Hz and the inverters stop drawing power from it. I think that may be because it's too far from the propane tank; at least the propane technicians told me that could be a probem.

 

[Firstrapid]

Consider the propane derating factor along with about 2% per 1k feet in elevationa ove sea level.