When to disconnect from dirty grid?

[zanydroid]

I saw one or two threads where people ran into issues with AIOs that had non-cooperative chargers (not sure if SCC or AC charger) when put in parallel with CV. What is the best practice for verifying compatibility or defending against weird interactions?

 

[timselectric]

I saw one or two threads where people ran into issues with AIOs that had non-cooperative chargers (not sure if SCC or AC charger) when put in parallel with CV. What is the best practice for verifying compatibility or defending against weird interactions?

Never heard of that one.
Not sure what compatibility is needed.
Do you know what issues they claimed to be having?

 

[zanydroid]

Never heard of that one.
Not sure what compatibility is needed.
Do you know what issues they claimed to be having?

I think a Growatt flipped out when it wasn't the exclusive charger attached to the battery.

My theorycrafting was that it didn't have reverse polarity protection. I think inverters designed to work with other chargers on the same DC bus should tend to be find. For instance, Battery/Inverter always has to work with a MPPT, and stackable AIOs probably are more inclined to be correct since they can have multiple AC chargers and MPPTs (assuming the protections are always active).

 

[timselectric]

I think a Growatt flipped out when it wasn't the exclusive charger attached to the battery.

My theorycrafting was that it didn't have reverse polarity protection. I think inverters designed to work with other chargers on the same DC bus should tend to be find. For instance, Battery/Inverter always has to work with a MPPT, and stackable AIOs probably are more inclined to be correct since they can have multiple AC chargers and MPPTs (assuming the protections are always active).

It doesn't make any sense to me.
The Chargeverter is just a voltage source. No different than a battery.
I don't see how it would be a problem. Unless the inverter wasn't designed for the voltage it's putting out. 57v is it's highest setting. Which should be fine for any 48v system.
I can definitely see it being a problem for a lower voltage system. (36v, or 24v)

 

[zanydroid]

It doesn't make any sense to me.
The Chargeverter is just a voltage source. No different than a battery.
I don't see how it would be a problem. Unless the inverter wasn't designed for the voltage it's putting out. 57v is it's highest setting. Which should be fine for any 48v system.
I can definitely see it being a problem for a lower voltage system. (36v, or 24v)

The AIO can sense the battery voltage before turning on its charger, and the battery voltage can never exceed the charger if it does this. So there is no need for reverse polarity protection if the AIO charger is guaranteed to only ever connected to a battery.

Now suppose the CV turns on and picks a voltage higher than the AIO charger, and the charger has no reverse polarity protection. That sounds bad.

 

[timselectric]

The AIO can sense the battery voltage before turning on its charger, and the battery voltage can never exceed the charger if it does this. So there is no need for reverse polarity protection if the AIO charger is guaranteed to only ever connected to a battery.

The polarity is never reversed unless it's connected incorrectly.

Now suppose the CV turns on and picks a voltage higher than the AIO charger,

The AIO charger just sits idle. Because it sees the connected source (assumed battery) as full.

Mine operates this way, without any problem.
Daily, this time of year.

 

[zanydroid]

The polarity is never reversed unless it's connected incorrectly.

What if AIO charger turns on at 50V.

And then CV turns on, senses 50V, and turns on at 51V? That is reversed relative to the AIO expecting 50V or less.

There might be a safe way to set the charging thresholds to avoid this. If there is only AC charging then that can be fully disabled in favor of CV. However if there is MPPT charging I'm not sure what you're supposed to do.

Perhaps the answer is that the MPPT and AC chargers can both be on at the same time, and since they may operate independently they have anti-reverse protection already.

 

[timselectric]

What if AIO charger turns on at 50V.

And then CV turns on, senses 50V, and turns on at 51V? That is reversed relative to the AIO expecting 50V or less.

Why would 51v be a problem for a 48v AIO?
It should be good for up to 60v.
I don't see how there would be a problem.

 

[zanydroid]

Why would 51v be a problem for a 48v AIO?
It should be good for up to 60v.
I don't see how there would be a problem.

OK, I'll try to find an explanation at circuit level.

But another way I see your response is, it also claims that we can assume all DC power supplies can have their outputs tied together. I know for sure that one way to have redundant DC power supply is to set it up with blocking reversing diodes in front of each one.

OR, less aggressively, all DC smart chargers can have their outputs tied together. (The distinction here is that the charger may have additional safety measures over a PSU)

I'm fishing for a circuit level explanation of why that is safe.

 

[zanydroid]

OK, I'll try to find an explanation at circuit level.

Both of the links below from this post are useful.

Note: I'm sure CV is fine in >95% of cases when used with the AIOs on the market (presumably mostly used with EG4's old school quality tier), given the average IQ / sophistication level of a EG4 customer. I just want to understand why it's safe.

Two identical DC power supplies in parallel for redundancy?

I'm trying to design a power backup system for my saltwater aquarium. In short, the system will be powered by a 12VDC power supply while the mains power is on. On power failure, the system will

electronics.stackexchange.com

No, it is generally not safe to parallel two power supplies (even of the same model) unless they explicitly support such a mode of operation. Some power supply chips (such as the LTM4625) are designed to be placed in parallel on the same circuit board. If configured correctly bench power supplies can be connected in parallel for load-sharing.

 

[timselectric]

Both of the links below from this post are useful.

Note: I'm sure CV is fine in >95% of cases when used with the AIOs on the market (presumably mostly used with EG4's old school quality tier), given the average IQ / sophistication level of a EG4 customer. I just want to understand why it's safe.

Two identical DC power supplies in parallel for redundancy?

I'm trying to design a power backup system for my saltwater aquarium. In short, the system will be powered by a 12VDC power supply while the mains power is on. On power failure, the system will

electronics.stackexchange.com

No, it is generally not safe to parallel two power supplies (even of the same model) unless they explicitly support such a mode of operation. Some power supply chips (such as the LTM4625) are designed to be placed in parallel on the same circuit board. If configured correctly bench power supplies can be connected in parallel for load-sharing.

I can see where a lower quality power supply might have issues with seeing a higher voltage than its setting. (It shouldn't, but cheap stuff usually cuts corners)
But multiple SCC's have no problem with being in parallel.
And an AIO has a bidirectional DC connection. So it wouldn't have any problem with seeing a higher voltage than its charging setting.
And the chargeverter has no problem sitting idle, when the connected source voltage is higher than its setting.
So, I don't see any issue that could happen.

If you can find a thread where someone had issues. I would like to see if I can figure out what happened.

 

[BajaDave]

Two Chargeverters.
Controlled by wifi switches.

The current through pass-through relay is not just what you are drawing from grid when grid collapses or a bad glitch occurs. When running sync'd up to AC input, the inverter is running in parallel connection with AC input.

For a moment, up to half an AC cycle, the inverter will try to power the collapsed grid so back feed current will momentarily spike to inverter surge current limit before it opens the pass-through relay. The relay contacts will be opening its contacts under the peak surge current limit of inverter, not what you were drawing from grid before grid glitch occurred. You may see a short period flicker glitch in your AC output from inverter as its pass-through relay releases. You may see it on LED lights but most appliances will ride through the short glitch with no resets to appliances.

Worse case surge is when you are unlucky and the grid happens to suddenly collapse precisely when the AC input sinewave is at its peak of sinewave voltage. The inverter will also be at its sinewave peak producing the greatest instantaneous surge current from the inverter pushing back at collapsed grid, until pass-through relay disconnects.

thanks for the explanation. That explains the periodic momentary flickering in my LED lights when there are no inductive loads locally to trigger them. after making the adjustment earlier today, no further disconnects, so fingers crossed.

 

[BajaDave]

I think I figured out a solution - treat the grid like a generator. Move the grid line in wires to Gen line in, which I believe can handle dirty power. Turn off TOU. Set gen charge batt % to something like 35% and gen charge amps to 180. This way, the grid is offline most of the time, and only comes online in the rare case where multiple cloudy days drain the batteries down. When the grid does start charging the batteries, it will charge them to 100%. Yes, the dirty grid might disconnect during the charge cycle a few times, but this might happen only 20 times a year instead of 10 times a night. I can control it via powerview remotely during hurricane season, and my house AC is no longer synced to dirty grid voltage and hertz.