When to disconnect from dirty grid?

[BajaDave]

I live in Baja, Mexico. The grid here is essentially an island, and we are at the end of the transmission line. So we have dirty power with wide swings in voltages, one phase dropping out, brownouts, and occasional frequency fluctuations. People complain of fried boards on refrigerators, stoves, washers, etc.

I have a sol-ark 15k, 6.5kw of panels, and 42kw of batteries, no sell back. I really only need the grid if we have 2-3 cloudy days in a row. But, because I am connected to the grid, my house voltage/frequency is synchronized to whatever the grid is putting out.

I want to protect the electronics and appliances in my home while at the same time still using the grid for charging batteries when needed. After an hour of searching, I cannot find any specific guidelines for safe grid voltages and frequencies that will protect 95% of home electronics.

I tried setting the sol-ark grid params to something like 220<>250V, and 57.2<>62hz. But with these params the grid cuts out dozens of times per day - and if the batteries are being topped off at 9000w, can't be good to be continually ramping up/down. Not to mention the annoying notifications. I loosened up the params quite a bit, and the disconnects have stopped. But I have no idea if my home electronics are at risk.

Does anyone have a good source for safe voltage/frequency ranges for home appliances and electronics?

 

[hwy17]

I would guess that it has to be voltage cutouts not frequency, I think you're probably at least on a feeder off the western interconnection.

Voltage concern would be for inductive loads. For example, a pool pump would get hotter running for prolonged periods on 220v than 240v. But usually I think like 210 or something at the motor terminals is considered acceptable.

Frequent voltage problems are probably as local in origin as your service drop and transformer rather than a grid wide problem.

I am generally a naysayer about all grid concerns though. Brownouts are mostly a myth, sags and swells don't kill things, lightning and open neutrals do.

 

[timselectric]

Buy a Chargeverter.
Problem solved.

 

[BajaDave]

I would guess that it has to be voltage cutouts not frequency, I think you're probably at least on a feeder off the western interconnection.

Voltage concern would be for inductive loads. For example, a pool pump would get hotter running for prolonged periods on 220v than 240v. But usually I think like 210 or something at the motor terminals is considered acceptable.

Frequent voltage problems are probably as local in origin as your service drop and transformer rather than a grid wide problem.

I am generally a naysayer about all grid concerns though. Brownouts are mostly a myth, sags and swells don't kill things, lightning and open neutrals do.

Baja Sur does not connect to the Mexico grid, let alone the western US grid. There’s been talk of building an undersea cable across the sea of Cortez for the last 20 years, but no activity yet. All of our power is generated by two diesel plants and one propane plant in La Paz. Our town is at the end of the transmission line which runs in a big arc to the west, down to the south, and then back up the east. When a cloud hits the solar panels in Cabo, voltage sags across the whole grid. New interconnects are forbidden for this reason.

maybe this is just circumstantial evidence, but after some long brownouts, there will be complaints on Facebook about broken appliances and people looking for repairman. Some folks have spent money on a brown out detection device that cuts off their power when low-voltage is detected, but it can be annoying to have your power cut off a dozen times a day.

we lose power entirely maybe 50 to 60 times a year, for durations ranging from a couple of minutes to three or four days.

So your recommendation is to have a minimum voltage of 105/210. I’ve seen voltages peak at 132/265. at least as reported by Solar assistant. I don’t have any more granular monitoring capability for more transient surges. Any issues with that level on the high voltage side?

 

[RCinFLA]

Your biggest consideration is how often the SolArk disconnects from grid. Dropping off and on grid often can put a lot of stress on the pass-through relay contacts in the SolArk.

Grid voltage bumps, up or down in voltage, will likely be followed fairly well by SolArk and will not disconnect as long as grid voltage stays within the range of the high/low limits set up in SolArk. If the grid voltage changes abruptly it will cause surge loading on inverter and may trigger a disconnect due to excessive inverter load current.

On a small area grid, frequency slump is usually correlated to total load placed on the small grid area. As voltage slumps due to excessive loads, so will the frequency of the grid power supplying alternator. The SolArk phase lock tracking is relatively slow and if AC input changes at a rate greater than about 0.3 Hz per second it will cause an overload on inverter causing it to release from AC input.

Setup SolArk so it holds onto grid as long as possible, but releases if grid changes voltage/frequency to appliance damaging levels. This is to minimize the amount of disconnect/reconnect the SolArk pass-through relay is subjected to. The grid rate of change is out of your control and the min/max setting on SolArk will not make a difference when rate of change is too great. SolArk will release based on inverter overcurrent when there is an abrupt grid voltage/freq change.

I would start with setting SolArk limits on AC input voltage between 205vac to 260 vac (half this if talking about 120vac unit) and frequency between 55 Hz to 65 Hz. You can tighten these ranges if you don't get disconnects too often.

 

[BajaDave]

Buy a Chargeverter.
Problem solved.

Have not heard of these. interesting solution, I could remove all grid input and let my inverter create a nice clean supply to my house. set the chargeverter to a charging voltage roughly corresponding to maintaining a 30% state of charge. However, I see no way to manage remotely in the units I could find. we travel in the summer during the hurricane months, but when I see a hurricane approaching I change the minimum state of charge to 100%. This ensures the batteries are topped off during an extended power outage with associated cloudy skies and the food in my freezer and fridge doesn’t go bad, the sump pumps keep working, etc.

 

[hwy17]

Any issues with that level on the high voltage side?

I would be less concerned about high voltage +10% but I wonder if you could actually be getting split second transients even higher and that's what's killing electronics.

Certainly all a good reason to consider going 100% double conversion Charger > Batter > Inverter > Loads. But it does get complicated to do that.

 

[timselectric]

Two Chargeverters.
Controlled by wifi switches.

 

[BajaDave]

Your biggest consideration is how often the SolArk disconnects from grid. Dropping off and on grid often can put a lot of stress on the pass-through relay contacts in the SolArk.

Grid voltage bumps, up or down in voltage, will likely be followed fairly well by SolArk and will not disconnect as long as grid voltage stays within the range of the high/low limits set up in SolArk. If the grid voltage changes abruptly it will cause surge loading on inverter and may trigger a disconnect due to excessive inverter load current.

On a small area grid, frequency slump is usually correlated to total load placed on the small grid area. As voltage slumps due to excessive loads, so will the frequency of the grid power supplying alternator. The SolArk phase lock tracking is relatively slow and if AC input changes at a rate greater than about 0.3 Hz per second it will cause an overload on inverter causing it to release from AC input.

Setup SolArk so it holds onto grid as long as possible, but releases if grid changes voltage/frequency to appliance damaging levels. This is to minimize the amount of disconnect/reconnect the SolArk pass-through relay is subjected to. The grid rate of change is out of your control and the min/max setting on SolArk will not make a difference when rate of change is too great. SolArk will release based on inverter overcurrent when there is an abrupt grid voltage/freq change.

I would start with setting SolArk limits on AC input voltage between 205vac to 260 vac (half this if talking about 120vac unit) and frequency between 55 Hz to 65 Hz. You can tighten these ranges if you don't get disconnects too often.

thanks, very helpful. What disconnect rate would you consider acceptable? Number of times per day/week?

 

[RCinFLA]

thanks, very helpful. What disconnect rate would you consider acceptable? Number of times per day/week?

I would say four or five a week but depends on how much current is going through AC input when it disconnects from grid.

Although the 15k pass-through relays are rated for 200 amp continuous current they are only rated for about 55 amps make and break current to make their life rating.

When grid totally drops it usually goes to near zero volts causing inverter to be momentarily overloaded as it tries to power the collapsed grid, up to inverter surge current protection limit at which point it disconnects pass-through relay.

When you have brown-outs the amount of surge current on inverter varies depending on grid rate of change. You want to try and avoid a lot of pass-through relay openings under high current as much as possible to avoid contact arcing wear.

Too much arcing of pass-through relay contacts can weld their contacts together.

 

[dougbert]

Buy a Chargeverter.
Problem solved.

I switched to this mode.

ignore the charger in the Sol-Ark and strictly just use the inverter to run your loads all the time -

I use the grid to power the Chargeverter to charge the batteries AND to run loads when needed. Due to snow here, I have NOT seen the sun for 3 days and my panels have over a foot of snow on them (I am sick at the moment so cannot clear them), so the grid is powering the chargeverter. The grid breaker to the inverter has been off for months now - so I view myself as off grid in that respect.

I have 2 chargeverters that I can power from a generator if needed at the same time, and to me the grid is simply a 2nd generator

 

[BajaDave]

I would say four or five a week but depends on how much current is going through AC input when it disconnects from grid.

Although the 15k pass-through relays are rated for 200 amp continuous current they are only rated for about 55 amps make and break current to make their life rating.

When grid totally drops it usually goes to near zero volts causing inverter to be momentarily overloaded as it tries to power the collapsed grid, up to inverter surge current protection limit at which point it disconnects pass-through relay.

When you have brown-outs the amount of surge current on inverter varies depending on grid rate of change. You want to try and avoid a lot of pass-through relay openings under high current as much as possible to avoid contact arcing wear.

Too much arcing of pass-through relay contacts can weld their contacts together.

Understood. 95% of the time, only 20w is coming from the grid. But that 5% is when I'm running 9000 watts/180A to top off the batteries. I think I could reduce my battery charge rate to 55A and accept a longer top off period. But when a hurricane is approaching and power is uncertain, bump it back up to 180A manually. And then post hurricane, when I'm desperate for power after no grid and many cloudy days, I'd like to charge at 180A, but the grid is really flaky post hurricane. So leave at 55A.

 

[dougbert]

Have not heard of these. interesting solution, I could remove all grid input and let my inverter create a nice clean supply to my house. set the chargeverter to a charging voltage roughly corresponding to maintaining a 30% state of charge. However, I see no way to manage remotely in the units I could find. we travel in the summer during the hurricane months, but when I see a hurricane approaching I change the minimum state of charge to 100%. This ensures the batteries are topped off during an extended power outage with associated cloudy skies and the food in my freezer and fridge doesn’t go bad, the sump pumps keep working, etc.

YES

I have a set of Solid State Relays, one per leg, that are controlled by my inverter's DRY CONTACTOR. The dry contactor (AUX port) have enough power to turn on and off a 12v bosch automotive relay. that then powers the SSRs, the SSRs feed the grid's 2 legs power to the CV

An alternative to SSR is this relay , TWTADE/JQX-62F-2Z Coil Voltage AC 220V 80A DPDT

I can set for ENABLE power to the chargeverters by LOW BATTERY level or by TIME OF DAY. I can also manual ENABLE or DISABLE via the internet access to the inverter

link to my documentation that I am adding to on this, been sick so not yet finished

currently my battery is at my FLOAT voltage and runs the house loads in effect as needed, if I lose the grid i have a big UPS running
SOOO much simpler than time slicing the inverter/charge unit with software complexities.

note: this allows only enable/disable ability remotely. voltage and current level setting is performed ON the CV manually

@timselectric gives the one possible solution of using 2 CVs each with a different remote ENABLE/DISABLE switch/AUX port. One CV set for your 30% SoC, the second set for 100% SoC. then set one or the other or both to be on, remotely as needed

throwing hardware at the problem via the inexpensive CV gives options AND saves wear and tear on your vital and expensive inverter. Use it as an inverter only and reduce your stress

 

[Skypower]

Two Chargeverters.
Controlled by wifi switches.

Id put some whole house surge protectors ahead of the Chargeverters.

 

[dougbert]

Id put some whole house surge protectors ahead of the Chargeverters.

great idea

I got several spread in my system

Table of Contents and Schematics link to my system schematics, etc

 

[timselectric]

Id put some whole house surge protectors ahead of the Chargeverters.

It wouldn't hurt.
But, they seem to be pretty robust. And are quite happy with any voltage in the operating range.

 

[zanydroid]

Id put some whole house surge protectors ahead of the Chargeverters.

I kind of think the chargeverters will take one for the team, if there’s a surge. They are probably internally isolated too, so the surge will have to blast through a layer of transistors as well as a layer of transformer

 

[dougbert]

I kind of think the chargeverters will take one for the team, if there’s a surge. They are probably internally isolated too, so the surge will have to blast through a layer of transistors as well as a layer of transformer

one thing about CVs, is at $400 a pop, you can have one or 2 or more spares in you parts bin

I love this solution in this video

 

[RCinFLA]

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.

 

[DIYrich]

UL1741SA is a good starting point:

https://sunspec.org/wp-content/uploads/2015/06/SunSpecUL1741SARule21ImplemenationGuideD6.pdf

In your situation, go off grid with the inverter. Use the Chargeverter to top up the batteries each night from 6pm to midnight. Then the need to charge up before a hurricane is minimal (mostly charged already). Or, get a smart switch so you can turn on the CV's remotely. You can also use the gen start signal to have the inverter turn on the CV's.