Inverter high voltage shut down

kansas · January 2015

The inverter in my little off-grid system (Morningstar 300 SureSine) shut down today for the first time, and was off for something less than 1.5 hours. I suspect that it reached its high voltage disconnect setting of 15.5 volts, even though, as I understand it, the Morningstar ProStar 30 charge controller shouldn't allow that voltage. The ProStar 30 has three voltage setpoints for flooded batteries: Regulation voltage 14.4 volts; float 13.7; equalization 14.9/15.1.

I checked my Trimetric meter just a few minutes before the disconnect and it was registering 15.4 volts. I thought at the time that was a high reading, and it occurred to me that the CC might be in equalization mode, which is preprogrammed, meaning I can't really tell when it happens or is going to happen. I have had the same experience several other times with the Trimetric showing voltage above 15.1 before 100% SOC (as high as 15.3), or above 13.7 (as high as 13.9) during "float," ie at 100% SOC.

The only load on the inverter when it shut down was a 12 watt bulb. After I returned from lunch the inverter was back in operation and the Trimetric showed 13.9 volts.

The inverter and charge controller are located within 18" of each other under the cabin where the temperature today was 48 fahrenheit. The batteries are also down there, about 3 feet from the CC and inverter. The shutdown was during full sun at noon. Outdoor temperature was around 18, low last night 7. I didn't attempt to confirm the 15.4 reading with my multimeter - I was hungry and went to have lunch first. When I returned the inverter was back on and the Trimetric was reading 13.9. I have compared the Trimetric reading with my multimeter reading in the past and they were within 0.1 volts.

The CC setpoints are referenced at 25 C, voltage accuracy at 0.5%

Any explanation other than a high voltage disconnect? Any cause other than excess voltage from the CC?

Thanks.

westbranch · January 2015

Re: Inverter high voltage shut down

Does that unit have temp compensation? Is it on? Is there a temp sensor?

kansas · January 2015

Re: Inverter high voltage shut down

The CC is temperature compensated. The manual indicates as follows: "Temperature Compensation: Four control setpoints (25°C reference) are compensated for temperature (PWM regulation, float, equalization, high voltage disconnect). The charging is compensated by –5 mV/°C /cell (–30mV/°C for a 12V battery). Compensation is limited to minus 30°C."

waynefromnscanada · January 2015

Re: Inverter high voltage shut down

Your overnight temperature was 7, I assume that's 7F, not 7C.
To maintain proper battery charging, all good and decent charge controllers will vary the charging voltage according to battery temperature if the remote battery temperature sensor is used, and if it's not used, the charge controller uses the best guess of battery temperature using a sensor built into the charge controller. This is not as accurate but it's the next best thing to an actual remote sensor located on the battery. It's normal for the charge controller to boost charge voltage when batteries are cold. Normal and necessary for proper battery charging. Only garbage charge controllers don't increase charge voltage when it's cold, and the batteries suffer as a result.
From what you just told us, I'm 99.999% certain that your inverter did indeed shut down due to over-voltage. Welcome to off grid solar in Winter. How can you avoid it? One way is to locate the battery bank in a heated location and use a remote battery temp sensor. Actually that's the best solution other than purchasing a different inverter designed to still operate at 16.5 volts, although you will be hard pressed to find a better inverter for it's power output than the Morningstar.

kansas · January 2015

Re: Inverter high voltage shut down

I'm afraid the batteries are located in the most consistently "warm" place there is, since the cabin itself is not heated at all when we are away and gets well below 48 F. I can live with anything I have to live with, or at least I have so far. If this is what happens with off grid solar in Winter, I'll accept that and be glad some part of my setup isn't wrongly designed, poorly installed, or malfunctioning.

Thanks for our comments.

waynefromnscanada · January 2015

Re: Inverter high voltage shut down

kansas wrote: »

I'm afraid the batteries are located in the most consistently "warm" place there is, since the cabin itself is not heated at all when we are away and gets well below 48 F. I can live with anything I have to live with, or at least I have so far. If this is what happens with off grid solar in Winter, I'll accept that and be glad some part of my setup isn't wrongly designed, poorly installed, or malfunctioning. Thanks for our comments.

Thing is though, if the batteries get cold inside your cabin and the voltage goes high enough to shut down the inverter when you're not there - - - unless you have need of running a load while you're away - - who cares. But when you're there, you'd have heat on, the batteries would warm up, the voltage would stay within range of your inverter, and all would be well with your AC electrical supply while you're there. It would require though, having the remote temperature sensor attached to the battery.
And as long as they're properly charged, cold temps will only lengthen their lives.
Temp of my batteries right now? minus 2C. Two days ago they were at minus 6C. That's 28F and 21F. As shown on the remote display from my Morningstar controller. They live in an unheated out building / shed and when I was running the Morningstar inverters, which I truly loved and still do, I regularly ran into the exact problems you are having. Unfortunately I couldn't move the batteries inside where they would stay warm, and since my loads grew I needed bigger inverters anyway, I got inverters that would handle up to 16.5V and have had no more problems.

kansas · January 2015

Re: Inverter high voltage shut down

I'm pretty much in the same boat as you. The cabin is small and really has no room for my batteries in the heated area. It will be interesting to see how this high voltage problem plays out. The disconnect today lasted something less than 1.5 hours. I don't know for sure because I left for lunch just after it happened and the inverter was back on when I returned. The SOC that morning was at 80% and the sun was up on a clear day by 7:30 or so. I'm assuming the +15.5 volts (the disconnect level) occurred at the peak of the bulk charging and tapered off as the SOC increased. This is the first winter for my setup so I don't know how cold the cellar will get. Of course, I also can't predict how much sun there will be relative to the SOC, so who knows when or for how long the batteries will call for something in excess of 15.5 volts and the weather will allow the CC to deliver it. The cellar is insulated and mostly below grade, so its temperature is slow to change so the cold batteries and high charging voltage is likely to persist.

As I understand it, when it is very cold the solar panels will produce their maximum voltage. Is the +15.5 voltage a result of optimal panel output, or, as I suspect, is more voltage than that routinely available but never called for by the CC except when the batteries get cold? My panels are rated at 22.1 Voc I guess I can check this with my voltage meter on the solar side of the CC.

My batteries are in a battery box that I built to isolate and vent any hydrogen gas generated during charging. With a little rewiring I could further enclose and insulate the batteries and perhaps maintain a somewhat higher temperature for a longer period. I suspect the difference would be slight, however. Yesterday was the first time there was a disconnect, or at least the first time we noticed it. As I said, I had seen the voltage around 15.3 before, but not higher. The cellar was a steady 50 degrees until the last few days. Perhaps the cellar temperature will hang in there at 48F and the disconnect problem will occur, when it does, for a fairly short period on days with enough PV input. Am I right to think that as the cellar/batteries get colder, the disconnect periods will get longer, other things being equal?

Thanks again - Bill

waynefromnscanada · January 2015

Re: Inverter high voltage shut down

kansas wrote: »

I'm assuming the +15.5 volts (the disconnect level) occurred at the peak of the bulk charging and tapered off as the SOC increased.

As I understand it, when it is very cold the solar panels will produce their maximum voltage. Is the +15.5 voltage a result of optimal panel output, or, as I suspect, is more voltage than that routinely available but never called for by the CC except when the batteries get cold? My panels are rated at 22.1 Voc
My batteries are in a battery box that I built to isolate and vent any hydrogen gas generated during charging. With a little rewiring I could further enclose and insulate the batteries and perhaps maintain a somewhat higher temperature for a longer period. I suspect the difference would be slight, however. The cellar was a steady 50 degrees until the last few days. Perhaps the cellar temperature will hang in there at 48F and the disconnect problem will occur, when it does, for a fairly short period on days with enough PV input. Am I right to think that as the cellar/batteries get colder, the disconnect periods will get longer, other things being equal?

Thanks again - Bill

Hi again Bill,
It's the Charge Controller (CC) that decides what voltage it will charge at, assuming the panels are capable of producing that required voltage. When the sun comes up the CC will use every bit of energy available to it (from the panels) in an attempt to get the battery voltage up to the required voltage for proper charging. Early in the charge cycle the batteries will suck up so much power that the voltage cannot yet reach that ideal point. This is called the BULK stage. Eventually the battery bank will get to the point where the voltage will come up to the set point, and the CC will then start to regulate the voltage at that point. This is referred to as the Absorb stage. After holding the voltage at that point for a set time, or until the delivered amperage drops below a certain point while maintaining that voltage, it is assumed the batteries are fully charged. At this point the CC reduces the voltage to the FLOAT level and holds it at that voltage as long as possible. The next day the process starts all over again. I'm surprised the Absorb voltage is going that high when the batteries are still hanging around 48F. Is there a remote battery temperature sensor attached to one of the batteries? Wondering if the wind turbine is driving the voltage high when the CC is cutting back? Does the Turbine have a CC and if so, do it's settings agree with the Prostar 30, or is it connected directly to the batteries? I know the only time my voltage gets high enough to shut down a Morningstar inverter is when they're below the freezing point. Have you checked the SG to see if your batteries are being overcharged? One of my biggest problems was the MX-60 controller I used to use. It was relatively slow to do it's sweep, and while doing that sweep, it ignored totally the battery voltage, so if the sun was shining and the batteries near fully charged, the frigging thing would drive the battery voltage sky high until after the sweep was completed, and by that time the inverter had shut down. It was a pain in the donkey in that respect, otherwise it was an awesome CC. The Midnight Classic totally eliminated that problem. But your Prostar 30 is a PWM controller, not a MPPT type, so that is not something that can happen in your case. Your controller doesn't do sweeps. I'm wondering more about the settings of your controller, are the batteries being overcharged, and is the turbine driving the voltage higher than the controller is set to do. Just seems to me the voltage is too high for batteries at 48F.
Hope I'm not confusing you with my rambling thoughts - - - -

kansas · January 2015

Re: Inverter high voltage shut down

Thanks for following up. First the easy answer: my "wind turbine" is actually a water pumping windmill that is entirely mechanical. The 702 Aermotor is a part of the landscape in Kansas. Mine lifts water about 100 ft from the standing level in the well, into a tank that I use to irrigate my garden and for summer fun. It is furled and shutdown for the winter.

I'm beginning to understand the charging process pretty well. You say that during bulk charging the CC will send all available energy to the batteries until they reach the absorption set point. What confuses me is that the Prostar 30 has a high voltage disconnect (solar) of 15.2 volts at 25C, (the HVD is one of the temperature compensated values). I take this to mean that in an ideal world where the batteries and CC are both at 25C, the ProStar could not allow more than 15.2 volts to the battery during any part of the charging process. Is that right?

Isn't the solar input to the CC from the PV panels substantially more than 15.2 volts on a sunny day?

As I understand it, since the CC and batteries are now both at 48F, the CC HVD (solar) will be higher than 15.2, and will continue to increase as the temperature declines. The formula for how much the voltage will change relative to a change in temperature is as follows:

"Temperature Compensation: Four control setpoints (25°C reference) are compensated for temperature (PWM regulation, float, equalization, high voltage disconnect). The charging is compensated by –5 mV/°C /cell (–30mV/°C for a 12V battery). Compensation is limited to minus 30°C."

If I were smart enough, I could probably use this information to determine what the setpoints should be when the batteries and CC are at 48F.

The specific gravity readings for my batteries the last time I checked were all between 1.25 and 1.265. The manufacturer indicates a full charge should be 1.27, minimum. My system became operational on September 1, 2014 and has gone through very few - 2 or 3 - cycles were the state of charge reached 80% or less. The lowest, again according to the Trimetric, was 69%. Because the batteries are "new," haven't been worked hard, and the plates still "forming" I take these specific gravity readings to indicate a full charge.

The inverter seems to have stayed on all day today. If there was a disconnect it was fleeting and unobserved. There was a slight overcast and the absorption voltage was at 14.8 (uncompensated value is 14.4 volts) pretty much all day. I would have followed the charging voltages more closely, but I was splitting firewood.

I'm going to start another thread and see if BB or someone out there can make the calculations to determine what the temperature compensated setpoints for my system should be.

Thanks again.

BB. · January 2015

Re: Inverter high voltage shut down

kansas wrote: »

I'm beginning to understand the charging process pretty well. You say that during bulk charging the CC will send all available energy to the batteries until they reach the absorption set point. What confuses me is that the Prostar 30 has a high voltage disconnect (solar) of 15.2 volts at 25C, (the HVD is one of the temperature compensated values). I take this to mean that in an ideal world where the batteries and CC are both at 25C, the ProStar could not allow more than 15.2 volts to the battery during any part of the charging process. Is that right?

In general, the ProStar should not allow the battery voltage to exceed the programmed set point... However, it is not always true.

Obviously, there can be a failed charge controller. And there is the detail understanding that it is really the battery bank that "regulates" the voltage of the DC voltage bus.

Basically, a PWM controller is an "on/off" regulator. ON, the solar array is connected 100% to the battery bank. Off, the charge controller "turns off" the solar array.

The PWM controller is cycling on/off 10's to 1,000's of times per second (I don't know the exact frequency). One the battery has reached the "set point" voltage, the controller starts changing the "on time" during the cycle. Say it is a 1 second cycle. 1 second on, 0 second off is 100% power. 0.5 seconds on and 0.5 seconds off is 50%. 0.1 second on and 0.9 seconds off is 10%... Etc. (usually at a higher frequency).

So you can see that the battery is "averaging" the incoming current and out going current (loads) to keep the voltage inside the ~12 to 15 volt range.

Some of the ProStars have a "Telecom Jumper" setting. It changes from 100's to 1,000's of cycles per second to something like 1 cycle per second. This is used to reduce audio frequency buzzing in solar+battery power telecom equipment. Your ProStar probably does not have the Telecom Jumper cut (telecom mode on)... But is it possible. Note that this can cause the battery voltage to swing farther during the charging cycle (slower cycle).

For MPPT charge controllers, as Wayne says--They "sweep" the array (pull from zero to maximum current from the array) and calculate Pmp=Vmp*Imp ... And use that Vmp number for the next X minutes. During the sweeps, it is possible for a large array and a nearly full charged battery to "over voltage" during the sweep.

In any case, if you have a "bad charge controller", they can lose control of battery voltage/regulation.

Isn't the solar input to the CC from the PV panels substantially more than 15.2 volts on a sunny day?

It depends... For a PWM controller, when ever the controller is "ON", the array voltage will be very near battery bank voltage. When the controller is off, the array is at Voc (voltage open circuit). What voltage you will measure with a meter is a combination of battery state of charge (low SOC, controller is "on" all the time; when full the controller is "off" most of the time). And even the meter itself (analog meters will "average" the pulse train, digital meters may average, jump around, or even "alias" the pulse train (i.e., read all high peaks, or read all low peaks if the meter samples are "in sync" with the pulse train).

As I understand it, since the CC and batteries are now both at 48F, the CC HVD (solar) will be higher than 15.2, and will continue to increase as the temperature declines. The formula for how much the voltage will change relative to a change in temperature is as follows:

"Temperature Compensation: Four control setpoints (25°C reference) are compensated for temperature (PWM regulation, float, equalization, high voltage disconnect). The charging is compensated by –5 mV/°C /cell (–30mV/°C for a 12V battery). Compensation is limited to minus 30°C."

If I were smart enough, I could probably use this information to determine what the setpoints should be when the batteries and CC are at 48F.

I posted in your other thread.

The specific gravity readings for my batteries the last time I checked were all between 1.25 and 1.265. The manufacturer indicates a full charge should be 1.27, minimum. My system became operational on September 1, 2014 and has gone through very few - 2 or 3 - cycles were the state of charge reached 80% or less. The lowest, again according to the Trimetric, was 69%. Because the batteries are "new," haven't been worked hard, and the plates still "forming" I take these specific gravity readings to indicate a full charge.

You really only need to bring the batteries >~90% state of charge once or twice a week (roughly). You do not need to try to get to 100% every day--That can be hard on the batteries too (sort of like over equalizing, gassing erodes the plates, Oxygen forming on the positive plate causes corrosion, etc.).

-Bill

jonr · January 2015

Re: Inverter high voltage shut down

I suppose you could switch in a diode on the inverter input to drop the voltage that it sees if you really want power during that period.

gww1 · January 2015

Re: Inverter high voltage shut down

I do notice that my outback inverter goes quite a bit higher then the charging set points when charging from the grid. It looks to be more of a speed issue and how fast it reacts to voltage. It seems to give a burst and build voltage, then drop a bit and lose voltage. The charge controllers do a much better job of holding close to set points although when first reaching absorb voltage the two ccs will fight with each other and cut back voltage and solar production for many cycles till they finally get leveled out. It is like they are learning what is needed till finally getting it right. they don't over voltage like the inverter though.
gww

Vic · January 2015

Re: Inverter high voltage shut down

Kansas,

As you know, batteries have thermal mass. The larger the batteries, the greater this mass. The batteries will do a fairly good job of averaging the temperature over a fairly long time period.

How is it that you know the battery temperature at any time? Are you using an electrolyte thermometer of some kind?

Should have looked, but does the Prostar-30 have a remote temperature sensor option that attaches to the battery? If so, are you using it? Perhaps this temp sensor MIGHT be built into the CC. If this is the case, then the temperature excursions could be much wider due to very low thermal mass ... have read all of the posts in this Thread, but have forgotten some of the details ... But that still does not answer why the Absorb voltage limit is not acting to limit the voltage.

The Morningstar TS series of CCs have very strange and unpredictable behaviors (to me), often to poorly defined operation in the manual, EDIT, BUT, you have Prostar 30, which may well behave differently than the TS series ...

FWIW, Good Luck, Vic

kansas · January 2015

Re: Inverter high voltage shut down

[QUOTE=BB.;209527

You really only need to bring the batteries >~90% state of charge once or twice a week (roughly). You do not need to try to get to 100% every day--That can be hard on the batteries too (sort of like over equalizing, gassing erodes the plates, Oxygen forming on the positive plate causes corrosion, etc.).

-Bill[/QUOTE]

Thanks for the input, Bill. I'm beginning to believe I understand at least some of what's going on in my system.

You mention the disadvantage of bringing the batteries back to 100% everyday. The only way I can control that with an automated CC, that I can see, is to maintain a daily load sufficient to maintain a SOC ~90%, or to switch the CC off for that purpose. Do you recommend that? I'm keeping a careful watch on the battery fluid levels (and, as you can probably tell, everything else).

The average daily cycle at the cabin is probably from 90% SOC in the morning to 100% by days end, assuming it is at least partly sunny. During sunny weather, which we have a lot of in Kansas, the system can go from 80% SOC to 100% in one day. On many days now, and on by far the most days 6 months from now, when my daughter moves back to Pennsylvania, the system will just float. After the daughter leaves, should I make an effort to draw down the SOC, to say 60 or 70%, to give the batteries a workout once in awhile?

Bill

kansas · January 2015

Re: Inverter high voltage shut down

Vic, thanks for your reply.

I'm equating the absorption voltage with what Morningstar calls the PWM regulation voltage, which has a 14.4 volt setpoint at 25C. This is one of the temperature compensated setpoints that is automatically adjusted by the ProStar. It appears to be accurately compensated since it is reading 14.8 volts on my Trimetric meter. See BB's response to my other post concerning the calculation of temperature compensated setpoints.

As far as battery temperature goes, the CC and battery bank are in the same space, where the daily temperature variance is not great. The location is a cellar that is almost fully below grade. It is ~70F in the summer and has now reached ~48F, but the transition has been gradual. Do you think the fact that the temperature compensation calculation performed by BB coincided with my actual voltage readings confirms that the ambient temperature in the cellar is also the battery temperature?

I am giving some thought to further insulating the battery bank to perhaps eliminate the inverter shutdown issue next winter. If I do, I'll definitely add a remote temperature probe.

Vic · January 2015

Re: Inverter high voltage shut down

kansas,

Did remember that your batteries were in a root cellar, but had also thought that you mentioned that during times where the residence was not occupied, that the temperatures at the battery location might be lower in the Winter, than when the structure was occupied, or similar.

My picture was that this cellar might have the batteries is a different environment than the CC ...

I agree with BB Bill's calcs of the compensation -- had reached the same conclusion, but was too lazy to post, there. It was just the thought that the CC might have a different idea of what is the real battery temperature.

As stated earlier, the Suresine is a very great little inverter, and like many 12 V, and even some 24 V inverters, is simply has a too-narrow range of DC operating voltages.

FWIW. Good Luck, Vic

kansas · February 2015

Re: Inverter high voltage shut down

One other issue. After my inverter disconnects in cold weather because the CC's temperature compensated voltage exceeds the inverters HVD (15.5 volts), the inverter is designed to stay off until the voltage drops to 14.5 volts (its HVReconnect). That can take awhile. To solve this problem, i.e. the inverter is still off but the present voltage (15.1) is now less than the HVD (15.5volts). I went outside and briefly covered one of the PV panels. Voltage dropped below 14.5, inverter came back on, removed the temporary panel cover, voltage went back to up to 15.1, inverter stayed on. Figured it out all by myself !

waynefromnscanada · February 2015

Re: Inverter high voltage shut down

kansas wrote: »

One other issue. After my inverter disconnects in cold weather because the CC's temperature compensated voltage exceeds the inverters HVD (15.5 volts), the inverter is designed to stay off until the voltage drops to 14.5 volts (its HVReconnect). That can take awhile. To solve this problem, i.e. the inverter is still off but the present voltage (15.1) is now less than the HVD (15.5volts). I went outside and briefly covered one of the PV panels. Voltage dropped below 14.5, inverter came back on, removed the temporary panel cover, voltage went back to up to 15.1, inverter stayed on. Figured it out all by myself !

You can also reset the inverter by switching off the dc input breaker, switch or fuse for about 30 seconds, then restart the inverter and as long as the input voltage is below 15.5, it will keep running. Been there done that with 2 of those inverters.

Inverter high voltage shut down

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