PV input power tracking occasionally fails

Hi, I am the original owner of the early release AC200, and use it every day. It mostly works very well for me, but once in a while, it will decide to stop charging from my solar panels (with external battery attached).

It seems like the programming for PV power tracking gets into a mode where it decides to just gradually reduce the PV input power it needs to keep itself charged up. It will reduce the power input to zero, and it simply allows itself to discharge completely if I do not catch it and unplug/replug the PV input wire connection.

The AC200 does not give any alarm or error mode, it just allows itself to discharge completely even though maximum PV input power is available to it.

Is there a firmware update to improve this operation of this? (it is a early unit)

DSP version 8001.04
ARM version 8002.03
BMS version 1102.02
HMI version 7000.09

Thank you for any assistance.

Can you explain a little more regarding what you mean by “external battery attached”?

I have a offgrid PV system with a number of panel strings that are paralleled with each other using a PV combiner box.

The PV system drives my DC loads, and one of the loads I have is to charge my AC200.

In addition to the DC loads is a battery system that takes the extra DC power from the PV system and stores it for use when the sun is not shining.

The PV-DC voltage I provide to the AC200 varies between approx 65V and infrequently up to about 100V, usually it provides approximately 80V to the AC200.

For example, I just looked and the AC200 currently reports 78.5V from PV, and the AC200 is fully charged (100%) with zero PV charging power used at the moment.

I observe the AC200 usually reporting around 700 W PV charging power (when not fully charged), or zero power(100% charged), except on those occasions when it acts a little odd or enters the failure mode I described previously, which might happen one or two times in a week, often it goes for many days with no problem, as the issue does not happen. It is pretty random. The exception to the randomness is that the problem typically only happens at the end of a day.

Is that the information you needed?

Any more questions?

It sounds like your combiner may be having incompatibility issues with the AC200 MPPT. It would be interesting to split off 700 or 800 watts of the solar panels and connect them directly to the AC200 and see if the function is now normal.

Do you get any error codes that are logged on the AC200?

“The AC200 does not give any alarm or error mode, it just allows itself to discharge completely even though maximum PV input power is available to it.”

Can you provide details of any known equipment compatibility issues with the AC200?

Can you share any details of what can make the mppt fail in this way?

How can it know what equipment is giving it the PV DC power?

It would be nice to update the AC200 so it does not fail in this embarrassing way.

Since it recovers fully, upon disconnecting the PV input for a short time, and then reconnecting it, the code seems to simply be a little naive.

You are making an assumption that the MPPT is failing when it may simply not be compatible with the solar panel system you are using. I have no compatibility issues to share other than having heard of several instances where another charge controller being in a system before the AC200 or other models for that matter will not allow proper charging.

I can’t help notice that the time you spent discussing an “embarrassing failure” could have been spent more productively on actually connecting 700 to 800 watts of your array directly to the AC200 as suggested. To determine if your personal set up is the issue or not would require some troubleshooting on your end by eliminating the items you have beyond the solar panels. The system is designed to be solar charged by connecting directly to solar panels. Try that and see what happens.

Two points in reply on this:

Point 1:

There is no reason to think that my combiner is having any compatibility issue with the “AC200 MPPT”.

It has safety features, but is operationally exactly like a light switch with an “on” position and an “off” position.

It is “on” 24 hours a day, and operates without fail or need for intervention on my part to use it.

The combiner box works fine, has never failed, and it is having zero issues, and it does not “know or care” if the AC200 is plugged in or not.

Point 2:

It would not be interesting (at all) to connect 700 or 800 watts of the solar panels directly to the AC200.

I have already done that, since the time I purchased it in 2020, as it is the way I initially used the AC200. To repeat this now would be a pointless waste of time.

Of course, what happens in that configuration is the sun goes down, the AC200 has no power to work from and so it discharges to zero before morning. Seeing this happen once again as you are insisting I do, would not be helpful in any way to solve this mystery.

I have put together a far more robust PV system with batteries, and I now enjoy the benefits of all this extra PV energy.

The AC200 is works very well for quite some time, almost always operating very well indeed with my current PV system (except for rarely, occasionally sometimes it fails, -thus the mystery).

To be more helpful you should try to address the specifics of the failure mode.

You said:

“You are making an assumption that the MPPT is failing when it may simply not be compatible with the solar panel system you are using.”

my response on this:

Point 1:

I have observed a failure in the AC200 operation, and the MPPT is an obvious, logical culprit to point a finger at. This is why I posted this AC200 issue and asked about the firmware for it.

Point 2:

When you say that the AC200 MPPT “may simply not be compatible with the solar panel system” that I am using, I agree, this looks to be a perfectly correct description that the AC200 is failing in this way. -A strange and infrequent failure mode of the AC200’s MPPT operation. This is a failure, when it has operated well for many days, and then when nothing has changed on my PV system, the voltage is still there, and full power is available, and it just shuts itself down, as it does on occasion, it sets no errors in the system, it sounds no alarms, that is a failure that serves no useful purpose at all. It just silently allows it’s battery to be fully discharged. That truly is embarrassing and sad, and is something that likely can be corrected in firmware.

But thank you for acknowledging that the AC200 MPPT may not be compatible. Some more specifics to the compatibility would be helpful.

Also thank you for saying that you “heard” of several instances where another charge controller might be in a system that will not allow proper charging.

But I have no such charge controller installed, so that possibility can be eliminated for this case in my PV system.

Again, the mystery is exactly what signal (if any) caused the AC200 to shut down the PV input. It would be useful to identify that.

There must be some kind of specific “cause” event to produce this shutdown “effect”.

Question: did it happen in a circumstance where the PV input voltage remained high in the nominal range? and did it happen when full power is available to the PV input as well? If so, that is very similar to what I am occasionally observing.
There should be a specific cause, unless the firmware just occasionally “rolls the dice” so to speak and then shuts itself down when the wrong numbers come up.

With the simple panels-only setup that you keep calling for, if there is a flaw (a feature or a bug) in the firmware that can randomly shut down the charging from PV input on rare occasions, it might never present itself if the input gets reset every day as the sun goes down, and the PV input voltage drops to a low level when that happens.

If this is the case, then the firmware is ripe for an update to allow continuous operation without this MPPT failure, or, at least, allow the system to self-detect this failure mode, and to reset itself to restore charging of the AC200 battery.

Specifically, what kind of compatibility issue can cause the AC200 MPPT to shut down charging it’s battery?

What voltage /signal or such can make it do that?

-This is the troubleshooting that is needed.

Your grasp of electrical and solar issues troubleshooting is obviously superior to any feedback I could provide you. Since you are unwilling to remove the unique (combiner) piece of the equipment in the chain to see if different results present themselves. You seem dead set on assuming the AC200 is the compatibility issue without any willingness to isolate other items to perform basic troubleshooting. If the suggestions do not match up with your preconceived theory then they must be wrong to you. Good luck in the future with your issue.

Ricardo, I have the AC200P (upgraded version of you AC200?) and it performs well.

I think that I understand that your unit will randomly but repeatively scale back or completely stop charging when there is a PV voltage provided 24/7, and removing the PV voltage will “reset” the unit to again start full charging via PV. And that having only solar panels providing the PV voltage input essentially provides that “reset” once a day when the sun sets, so that most users won’t experience the issue you are observing.

As an obvious workaround for your setup, a timer switch/relay to turn-off the PV input for 1 minute once every 12 hours might mitigate. Wouldn’t it be nice to know if that were indeed necessary, and why? :slight_smile:

My AC200P will “turn on” (with the DC output turned on if it was on when I powered down the unit) when there is a voltage sensed on the PV input. This can create its own issue, ie, when I turn off the unit in my van, no loads, but then enough sun to turn the unit back on. Then several days of no sun will run the battery down because it turned itself on. This tells me that the processor performs some functions when sensing a PV input, ie, the reset you do to get yours charging again. For my purpose, when I turn the unit off, I also need to remove the PV input to keep it off.

I see that you “observe the AC200 usually reporting around 700W PV charging power” and your PV input is usually about 80V. Is that correct?

I observed that my AC200P would charge with near 300W using three 100W panels in series in full sun (about 60 volts) but had no increase when a fourth panel was added in series (about 80 volts). I was hoping optimize my PV charging using technical specifications about PV input voltage vs max current input and/or find the specifications on whether the AC200p intentionally scales back PV charging input when the battery is “almost full” vs “almost empty” that might explain what I observed.

The only specs in the manual is PV input must be between 35-150v and max current input is 12A. So it’s obvious it needs at least 60v to reach 700W, but no curves, tables, or other detailed descriptions. I’ve been looking for instances (on blogs and youtube reviews) of PV charging reaching 700W, and you are the first example that I’ve found. And it’s at 80v, right?

The product performs well. But technical specifications and support could be improved!

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Hi johnmiller,
You are correct about the operation and occasional need to unplug the PV to restore operation of my AC200.

Yes, it seems that there is no real support folks who can chime in, who know how their product works, and the company many simply have no interest in updates to improve the product.

You are also correct about the workaround idea. I have had that kind of Idea myself. I thought about putting together a circuit to monitor and detect when the AC200 goes brain-dead and stops charging, and in that case, automatically do what I have had to do manually to keep it from shutting down overnight. A simple timer can work too, but with it cycling every night (just in case) would mean lots of wear on a relay or such, and that could become a reliability concern as well. I still may do it, but doing that should really not be necessary for a product like this.

For your “it turns itself on” issue, It sounds like a simple solution to your issue would be an on/off switch on that PV input line. It could be added externally in the cable, or to be slick would be to open it up and find room for an internal on/off for the PV input inside the AC200. In operation it would be much easier to deal with since you are intentionally turning the unit off anyway.

Also, yes, it typically operates at close to 80V day and night, sometimes a little lower. I checked it again right now, ( I have to keep checking daily each evening to be sure it is still operating) I currently see the AC200 reporting 80.5V and the battery is at 100%, so it is good for another day.

I cooked some popcorn an hour or so ago, and saw it use a little over 700W to top the battery back up.

When i first started using it with different panel setups, I think I had around 60V with one method, and later had in the 90V+ range. It worked the same either way. Clouds, etc made the voltage vary back then of course.

I have not observed my unit using less PV power when it is near full. I just checked again and now it is topping off its battery with just over 700W from PV, and it shows 99% charged. Your unit may have newer, different cells and a different charge profile from what mine has.

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The expected life of even the cheapest electro-mechanical relays are in the range of 100k cycles for the contacts, and usually millions of cycles for the mechanical portion. So the relays in your AC200 should last for decades. The reliability of solid state relays are much higher than electro-mechanical.

Do you know whether periodically unplugging the PV input prevents the charging issue, verses the “brain dead” issue needing to occur before resetting works?

If periodically disconnecting the PV input does prevent the brain dead issue, an inexpensive proof-of-concept and possible solution could be to use one of those lamp-timers, 7-day programmable for $11 from Amazon.

Plug a small USB charger into it and use the 5vdc output to control a solid state power relay. Most of us have phone chargers laying around.

$6 for a 2-pack USB cable.

The 5vdc output would control the solid state power relay to turn-off your PV voltage for a minute once or twice a week, which should simulate unplugging the PV power.

$17 for a 100A SS relay.

Also needs a heatsink.

700W at 80v is less than 10A, so you could probably get by with the 25A relay and put the $7 savings toward the heat-sink. I like to design using components with specs of at least double the needed capacity, which the 25A relay meets.

The SS relay control turns on with a dc voltage of 3-32vdc and and draws a max of 25mA. A small iPhone USB charger is rated at 5vdc @ 1A and should work reliably providing a regulated voltage output. Cheap chargers can have ripple and noise on the output, so avoid those. Here’s a link to lab test of different chargers.

The timer has two outputs, so you could run 2 USB chargers in parallel (with diodes to isolate them from each other) for added redundancy. The relay is designed to switch a DC voltage of 5-240vdc up to the rated current.

Free returns on both the timer and relay reduces the risk of your investment to try-and-see if it works.

If periodic PV input disconnect does not prevent the “brain dead” situation, that will make a work-around more complex.

Your issue reminds me of a situation I saw years ago with a communications system using Windows XP operating system. We had required monthly periodic maintenance to reboot the system. A maintenance technician took an extended vacation, the monthly PM was missed, and the whole system locked-up. The questions were along the lines of “why did the technician go on vacation?” instead of “why does an operating system designed to run business servers crash?”

I’m glad to know that you hit 700W PV charging and I will try some different configurations with my panels. I’m in Seattle so will wait for long sunny days before messing with it. My case with the PV input turning the unit back on is described in the manual, I just missed it.

So far my AC200P has operated reliably as advertised. I use it in my van to run a fridge, galley pump, and Airtronic furnace/heater, all 12vdc from the 25A output. My biggest concern is running it down camping under trees and cloudy skies which could spoil food in the fridge.

I contacted technical support about the 90% Battery Discharge Depth auto shutdown, I wanted to know if the unit shuts down when the LCD shows 10% of battery, or if the LCD would run down to 0% while keeping 10% of battery reserve to prevent damage to the battery. The response was a confusing non-answer, telling me that I could run it to 0% but doing so would damage the battery. (???) So I put in a switch that allows me to run the fridge off the vehicle battery when the Bluetti is so low it might not make it through the night.

It sounds like you may have run your AC200 down to “dead”. Do you have insight to how the auto-shutdown works, if it preserves 10% of battery to prevent damage?

I think you are correct in that the company won’t provide updates to products in the field, but they seem to improve products with new generations. My AC200P doesn’t look field serviceable at all. I expect when the batteries are dead, the entire unit will be done.

“Do you know whether periodically unplugging the PV input prevents the charging issue, verses the “brain dead” issue needing to occur before resetting works?”

I do not know, but I have no interest, and that approach seems to be counter-productive. The unit can run for many days while sitting connected to PV and operating my loads without issue. When you do have to unplug the PV connection and then re-connect it you get a big strong spark, so it is not at all desirable to do that as a matter of routine.

Yeah, your parts list illustrates why I am not keen to cobble together an assembly of timers, connections and parts onto the clean elegant AC200. I currently have no interest in such a fiddly mess nor time to spend in that kind of project. Perhaps I will do something later.

“It sounds like you may have run your AC200 down to “dead”. Do you have insight to how the auto-shutdown works, if it preserves 10% of battery to prevent damage?”

I did not run it down to dead.
It ran itself down.
It ran itself down to an indicated zero battery charge. I still had a provided full power available to the AC200 on it’s PV input, and it just stopped charging itself for no good reason.

I sure hope that the low voltage battery protection feature is still working when it allows itself to run down completely. Next time it happens I can have a look at the battery information screen details, instead of just getting angry that it did this.

At the time when it does this (at least two times so far) the AC200 has no energy for output, and it does not let the user re-activate the AC output, even when it has resumed charging at full power (~700W) on PV, plus is charging from the AC input wall adapter at the same time. It refused to resume AC output until the battery has charged up to some percentage level. I don’t know what level it was, but probably it was about 5% or so.

I hope to keep using the AC200 for many additional years, and having the MPPT update would make it a perfect device for me, instead of it having that significant reliability issue.

Right now, if I plan to be away from having to baby-sit the AC200 every evening, I can unplug my refrigerator from it, moving that to AC power until I get back. My other loads are small enough that the AC200 could make it overnight even if it decided to fail again while I am away. If I go on vacation then the AC200 would need to be shut down completely and that is quite a shame.

I understand your frustration and agree that your AC200 should operate continuously with 80vdc provide to the PV input. But it doesn’t. Many products, both consumer and industrial, have bugs and do not work perfectly as advertised.

Understanding the details of the symptoms of failure are indeed productive. They are productive to assist Bluetti to determine if the symptoms are inherent to the product (which an update might fix), or if you have a defective product that can be repaired or replaced.

If Bluetti remains silent, understanding these details can help you to figure out a work-around so that your AC200 will still provide the service you need from it despite its shortcomings. These details are also productive so others on this forum can suggest ideas or mitigations that you haven’t thought of.

Your AC200 isn’t providing the clean elegant solution as advertised, and that’s a bummer. My understanding of your need is to have a maintenance free system. For now, it seems the pros of cobbling together a work-around does not outweigh the cons of your daily-check and disconnecting/reconnecting the PV input when required, which is a valid choice.

Your concern about the “big strong spark” when reconnecting the PV might be mitigated by adding a toggle switch in-line to the PV feed. This will move the arcing (and concerns of damage) from the PV connector to the toggle switch. But the pro vs con decision is yours to make.

The AC200 is clearly advertised as NOT being an Uninterruptible Power Supply (UPS), so that’s why it has to charge the battery up a bit before it will resume AC output. That is by design and not a shortcoming or defect.

Another crazy guess I’ll offer is that your feed into the PV input has something going on that triggers the AC200 PV input to disconnect (protecting itself, or just going into an undefined state, ie, “brain dead”), and then requires the reset. This could be some switching along with capacitance and inductance of cabling and other components that might trigger the PV voltage to go above the 150vdc. Or just static electricity. In my field of business we install surge protectors on cables over about 20’ to deal with all types of “weird” problems caused by transient voltage spikes. This is an example of why the configuration of the 80vdc source going into your AC200 PV input matters.

I wish you luck in figuring out something that works to your satisfaction.

Trying to understand your system. What all equipment are your PV panels connected to? You mentioned a combiner, so that normally will simply be connecting multiple solar arrays together to get a single output. From there what is connected? From what I read you have batteries being charged, DC devices being powered, and the AC200, so three devices taking the solar input and providing different DC outputs?

Hi, a combiner box allows multiple strings to be connected in parallel.
From there it is connected to DC bus bars, from there to DC circuit breakers, from there to loads, including the AC200. The battery is also operating as connected to the bus bars.

The AC200 has a feature called MPPT that is supposed to function in it’s job to track the “Maximum Power Point” in charging its battery. It mostly does this very well, except, on occasions it does not.

Occasionally, it fails, in that it decides to not use the maximum power it can, that is available, in fact it decides to use zero power, for an extended period of time, allowing its battery to be depleted, and dropping all AC loads it is powering.

When it happens, this failure is the MPPT, transitioning to become a zero power feature.

BTW, it has been going on two weeks since the AC200 has failed.

Nothing has changed in my system, all has been operating perfectly all this time.


Consider your PV panels a constant current source. Your AC200 MPPT controller changes/lowers its input impedance to find the Max Power Point, MPP, of 700W. When its input impedance changes, so does the input voltage.

By contrast, the output of any upstream controller to charge a battery, and the battery itself, is a constant voltage source. When your DC bus batteries are fully charged and capable of supplying greater than 700W, that’s probably when you see things as stable. When your DC bus batteries discharge or other DC loads kick in to the point where the batteries with PV panels can’t supply 700W to your AC200 while maintaining voltage, that’s probably when things go wonky.

Your AC200 MPPT doesn’t “decide” to stop working. It’s being driven to an “undefined state” where its logic ceases to work until removing the DC input allows the logic to reset.

Your issue might be inherent to the AC200 MPPT when stable DC voltage is present for extended periods of time, a bug in the AC200 as you contend.

But it could be that the AC200 MPPT is lowering its input impedance to the point that your DC bus detects it as a short circuit, creating a race condition, sometimes resulting in your AC200 MPPT entering an “undefined” logical state. This would explain the 35v swings you’ve observed on the input voltage.

Doesn’t your combiner box output DC via a controller to charge of DC bus batteries? If so, that means your AC200 MPPT input is in series with another battery charge controller, right? Or do you connect the combiner PV output direct to the DC bus batteries and other DC loads without a controller?

The moderator’s comments earlier were: “heard of several instances where another charge controller being in a system before the AC200 or other models for that matter will not allow proper charging.” That makes sense. An MPPT lowering its input impedance to a level that drives a constant voltage source (upstream controller or battery) below its spec will cause that source to protect itself by shutting down. The MPPT senses zero current, so increases its input impedance, the upstream voltage source turns back on, and so on, ie, a race condition.

In your earlier comments, you said the voltage into your AC200 varies approximately from 65-100v, but is usually around 80v; 78.5v at the moment you wrote the comment. Is your battery DC bus 72v? (nominal about 80v?) Was that voltage you observed being measured from your DC bus, or was it indicated by your AC200 panel?

I would expect your DC bus voltage to be stable. If your AC200 is displaying a 35v swing of input while charging, that might be an indication of crazy things on the DC input, and/or an indication of your AC200 MPPT fighting with an upstream controller/battery system that can’t deliver 700W while maintaining a constant voltage.

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The real issue is that solar panels can only be connected to a single device (the charge controller). Any other devices connected will interfere with the MPPT controller logic and cause the problems you are seeing.

Hi Ricardo,

Sorry for your problem.
I’ll help you to follow up this issue. May I know your email address? And have you contacted with our customers service for your problem?