Over Voltage Solar Array

In my relentless pursuit to maximize the solar charging capability of my EP500Pro’s I have found an interesting tidbit of information via experience and many tests.

The 150 volt maximum only occurs in certain conditions.

If your battery is needing a charge AND the solar input is connected before the voltage reaches 150v or more, the voltage will not exceed 150v and set off an alarm possibly harming the charge controllers because the power draw from the connection to the EP500Pro while under charge pulls off around 20v from the actual incoming current.

As an example:

Tested solar VOC (disconnected) will be 150v. While the voltage after connection to EP500Pro will be around 130v.

I use two 455W Split-Cell Mono PERC Solar Panel arrays 3 panels each in series which are rated at 49.35VOC each panel. Each 3 panel array is coming in just under the 150v max input requirement in almost all circumstances. On cold clear mornings there is the potential to cross over the 150v max if you have your array unplugged and don’t check it with a volt meter before making the connection with the aviation plug. If the array is putting out 150 volts or more you have to wait until the array is putting out less voltage and then make the connection. If you do this before the sun really hits the panels you can beat the overvoltage issue and get the chargers going, pulling the voltage down before it can hit the 150v limit. NOTE If your battery is fully charged before the conditions (temps and sky) drive the VOC down below 150 naturally, you will set off the alarm and possibly damage your Bluetti.

I have a hard time justifying the $600 x 2 cost (if you could actually purchase the PV VOLTAGE STEP DOWN MODULE(D300S) from Bluetti) it would take to deal with this little overvoltage situation I have with both EP500Pros and their twin 3 panel arrays, So this has become my solution until I find a better one.

Anyway, I hope this info helps someone who is fighting the same problem I am.

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Hi Mike.

I’m not 100% sure I understand your issue… But I’ve been documented the following issue with my AC500’s that they’ll get stuck receiving low voltage from my array until I reset the solar system using my PV shutdowns.

Here’s my issue:

Bluetti Engineering will be sending be test firmware that may resolve my issue. Does yours sound similar?


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Good morning @twister36 . The Bluetti EP500Pro’s have a max input voltage of 150v. My arrays produce just under that in normal conditions. However; in the winter time down here in Texas, when the temps go below the rating lab temp I think it’s 77*, the voltage can spike. Especially if the the panels remain cold and the sky is really clear. I am seeking a simple, cost effective method of capping the voltage output at 150v. Bluetti keeps a module on their accessories page ( PV VOLTAGE STEP DOWN MODULE(D300S) $600 normal price) but it is seldom in stock and as I have 2 EP500Pro’s powered by 4 arrays I would need two of those modules. Logically, the cost to lop off 5 or 10 volts over the 150 that potentially can happen a few days a year should not cost me $1200. I know there has to be a simple way, not as simple as unplugging the arrays from the Bluettis, but you get my drift.

Off the top of my head I would guess your issue is connected to the cutoff switch. No pun intended. Like the internal contact surfaces aren’t fully engaging every time you have a closed circuit. But, that is just a quick guess.

good luck and thanks for your reply!

i don’t understand why you are anywhere near 150V. according to the specs, the EP500Pro has 12-150V at 12A*2 limited to 1200W each. So you should be targeting 100V Vimp at 12A for 1200W. This should give you a VOC of 120V which even with freezing temps would only spike to 130V-140V. Or am i missing something?

At near peak sun on a warm, not hot, day here in Texas two arrays feeding one EP500Pro looks like this using 3 panels in each array.

I’m interested in feeding as much pv power as long as I can in each day.

Does this make sense to you?

The trouble is only if the batteries are fully charged because the draw on the VOC from the charging function takes 20-40 volts off the DC input voltage. And this is only a problem a few days a year but if I screw up and don’t check the VOC before plugging in the arrays or if it completes the charge it will spike and potentially do damage, or so I’m told to my mppt controllers.


It’s been a long time ago since I had my electronics education, but as far as I remember: With a 150V Zener-Diode parallel to the PV Input it should be possible to limit the voltage to 150V.
You only have to make sure that the diode is mounted the correct way because in the wrong direction it would limit it to 0.3-0.7V. So if you connect it parallel to the PV cables and the voltage drops from 1xxV to less then 1V then you have to reverse the mounting.

E.g. Amazon.com

That is an interesting item. I have a call into their Tech Department for tomorrow to verify the application. Thanks for the heads-up on it!


The important point is that the Solar Panels doesn‘t deliver to much power at 150V.
E.g. if the voltage is 155V. when it is cold and the Solar Panel would already deliver 1A when you limit it to 150V then you would need a Zener Diode which can take at least 150W (150Vx1A) and a good cooling. Especially if the battery is fully charged and the power station does not draw anymore power then the Zener Diode has to take the excessive power until the solra panel delivers less then 150V or the Powerstation kicks in.
Otherwise you will burn the Zener Diode.

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I was doing some reading on the Zener Diode, fascinating stuff really.

If you swap the pv array inputs to the AC500 (PV1 and PV2) does the low voltage show up on the other input? If so, it’s likely your PV cut-off switch or other connections. If not, and voltage drop is on the same MPPT controller input, it’s likely the AC500.

Hi @PowerMat,

Yes I’ve seen this happen on both PV1 and PV2 on both my Master and Slave units. Since this posting, I’ve confirmed with Bluetti Engineering that they are aware of this issue and issued me a beta firmware to test. This firmware did help a bit, but the issue still exists.

I will be automating my solar array to turn off for a moment every day at 10am to reset the PV array, until Bluetti has a fix.


Thanks for following up on the response @twister36 I’m wondering if it is becoming stuck at a specific current (like 7A) in your case each time. Maybe the voltage matching the single panel is just coincidental in your case. It looks like even the higher voltage PV input jumped slightly higher when you switched the disconnect.
I’m curious if this is impacting other models as well. I’ve seen some strange “steps” in the input current plot on full sun days (EP500P) and wondering if it is something similar to this. Perhaps the MPPT controller is having some trouble, so I’ll try that little trick and see if it works the same.
I’m curious in your situation, if you shut off only that low voltage array input and cycled it, would behave the same? Do both inputs need to be shutoff to exercise the workaround?
I’m also very interested in how you would automate the switching of the input with that much current, please do let us know how you did it. Ditto on the response from support for possible resolution.

My PV switch is per AC500. Meaning that both PV1 and PV2 go through a single PV shut-off switch. So I never tested just shutting down one PV port.

However, since my last post Bluetti has released DSP 4045.10 which completely resolves the issue. I posted on the FB AC500 group page a few days ago showing the difference since installing DSP 4045.10… massive improvement. I’m producing easily 60% more power do to the software correction.