EB70 Solar Input (over?) Voltage with folding 200W panel

First post here from a solar/powerstation newbie.

I purchased one of these “Massimo” 200W folding/portable panels because the listed VOC and amperage were high but in range for the EB70, and well, Costco (on sale and easy to return).

Specs are listed as VOC 22.4V and “working voltage” as 24V and 8.3Amp max working current. I thought the voltage listing was a little weird since how could the “working” voltage be higher than the VOC, but thought maybe they just got those two mixed up on the costco site.

Anyway, I just received the panel (same specs on the box) put it out in the daylight (cloudy) and I got a 30.4V with a digital meter with “cold” panels. 30 minutes later that dropped to 29.4.

Are those voltages too high (I’m thinking yes)? I don’t have any way to measure the voltage under load without connecting it to the EB70 and I’m hesitant to do that in case the EB70 doesn’t have built in over-voltage protection (by the way, does it?).


I have found the EB70 to trip the overload limit at around 29.5 volts. so your panels are right at that limit. If it were me, I would try the panel and see if charging initializes and the voltage will drop. I have had success with another mfg. running with panels that were overvoltage by covering the panel with a towel but still leave about 20% exposed. Then I plug in the panel and let charging begin. After charging stabilizes, I remove the towel and the wattage increases which then lowers the voltage to be within the range. I have not however tried doing this with a Bluetti product. I have two Aiper 160 watt panels that are in high 20’s on voltage and the other vendors product had a max input voltage of 25. You may find it much easier to lower your voltage slightly with the Bluetti than I did.


So there’s a “tripping” mechanism? I won’t let the smoke out? That’s reassuring and gives me the feeling that I can experiment a bit. This is a portable panel. I’ll be setting it/taking it down each day (or multiple times a day), so it’d be fairly trivial to keep and eye on it/baby it – again, assuming there’s shut down protection built in.

Thank you very much!

edit: what about adding a resistor of some sort (maybe a pigtail that I created to connect between the panel and EB70) to bring down the voltage a volt or so? I guess the issue there is that once there’s a load on the panels and the voltage drops below the “allowed” range, the resistor , the resistor would continue to take that volt or so, dropping the working voltage and ultimately, power output.

There is a tripping mechanism but do not know the limit before damage will occur. I have read several occurrences with another mfg. that some customers had connected higher voltage than allowed (50 to 100%) that damaged the unit and they no longer charged. I personally have gone over voltage (less than 25%) on all my units without damage when using a variable voltage power supply for charging.

In your case, you are very close to the upper limit and all may work fine with no issues. I suppose you could put a resistor in line if needed and I have also heard of people running extra length of MC4 extension cable (at 14 to 16 ga for a single or double panel set up) to act as a resistor due to the extended length.

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Oh actually that’s kind of a brilliant idea. I’m going to be using this with a 25-50’ extension cable most of the time. I was going to use 12ga to minimize the voltage drop, but (duh) 14ga may be a better choice as I want some drop. I’ll make up a cable and give it a try. The nice thing about “cable-as-resistor” is there’s no component that could fail and accidentally feed the EB70 with too much voltage; if the cable fails then there’s no voltage at all.

I make several 25’ cables and then I can snap multiple sets together depending on the desired length. My use is strictly portable though an no benefit from doing this on a fixed solar install.

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Yep, fully portable here. Great idea with the 2x 25’ vs. a single 50. Thanks!

OK, the weather finally (at least temporarily) cleared up and I was able to do some testing. I still haven’t made the long extension cables, but I think that’ll be the ticket. For now, I used the XT60 to 8mm (7909) that came with the panel built in. There’s also MC4 connectors on that pigtail that I can use with the MC4-to-7909 that came with the EB70 (more on that later). There’s also a straight DC 5.5 to 5.5 with included 7909 adapter that I tried. So plenty of connection options.

Basically I was able to leave the panel partially folded and out a towel on one section and that brought the VOC down to the mid 20s. Once I plugged it in and it had a load (the voltage dropped into the teens), I opened the panel one section at a time. I maxed out at 170W on a mixed-cloud PNW day. Not too bad. I’m still annoyed a bit that I have to babysit this panel until it starts up (mostly because it doesn’t match spec), but also it’s not a huge deal since I’m only using it for camping and will be setting it up from scratch every time I use it.

I’ll report back when I make up the extension cables.

(Edited to clarify 7909/8mm)

My next question is about the MC4 connectors. All the connectors that came with this panel work to charge the EB70 EXCEPT when I use the MC4 pigtail from solar panel connected to the Bluetti-provided MC4-to-7909 pigtail).

As I mentioned above, the panel-provide connectors start with an XT60 on the panel side then split into short wires with three different connector ends (DC5.5, DC7909, and MC4).

  • The DC 5.5 end (with panel-provided) 7909 adapter plugs in the EB70 directly and charges (center positive).

  • The DC7909 end plugs into the EB70 and charges fine (center positive).

  • However, when I plug the panel’s MC4 end into the Bluetti, charging stops because polarity is reversed (center negative) – again, these are all coming from one XT60 connector off the panel.

My thinking is that either the panel’s MC4 connectors are wired wrong backward, or the EB70/Bluetti MC4 are wired backward. So how do I know which one is wrong (or is one even wrong? It seems like the “standard” isn’t really a standard.

My Bluetti-provided MC4-7909 pigtail shows continuity from the center (+) pin of the 7909 to the “male” metal connector inside the MC4 plastic “female” housing (which is marked with a “-”). Is this factory correct?

Swapping the connector sides on that cable would fix my issue, but so would cutting/swapping the connectors on the panel side. (For the record, the panel side connectors show same setup as EB70 connectors (positive off the panel goes to the positive male connector, which also lives in a “female” plastic body but isn’t marked with polarity.

I was hoping I could find a “gender changer” but those don’t seem to exist in the MC4 format. I know I can also “fix” this when I make up my extension cables, but before I’d do that, I’d at least like to ensure at least the Bluetti MC4-7909 is how it’s supposed be from the factory.


If it were me, I would make an XT60 to MC4 cable to connect to your panel and then to your MC4 to 7907 bluetti cable. There is no firm standard but the Bluetti polarity is correct for the vast majority of panels. You may simply have a 7909 to XT60 cable that is designed to be attached to the panels with the MC4 (which is the most common) end instead of the XT60 end like it is now. In any case, if you make an XT60 to MC4 cable with the correct MC4 polarity, it will be the most common “Std” and will work with most units.

FYI…170 watts is outstanding and is the most wattage you will ever see regardless of panel(s). I would also try connecting the panel without the towel trick…it may just be close enough that it will work without it.

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Thanks. Sounds like XT60 to MC4 is the ticket! I’ll make up a longer one of those and probably an extension as well. You’re right, I can probably just hook this up without the towel trick (though I may keep it partially folded). I’m a bit paranoid about letting the smoke out of my EB70 :wink:

I have a couple of 160 watt panels (don’t remember the brand at the moment) that also have the XT60 ouput port on the panel. My panel voltage was also in the too high range and that is where I experimented with the towel to be able to use the panels on my Ecoflow RIvers which have a maximum voltage limit of 25.

I also made an XT60 to MC4 to have compatiblity with all my stuff. Has worked well so far.

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By the way, I tried it without the towel. It would start charging until I got it the VOC to 29.2V. Basically if I fold in one of the panels (which fully obscures two of the panels), that will do it. Then once it starts charging, I can open it up. Again, I still need to try it with the 12ga extension cable to see what kind of drop that gets me (and if that’s enough to start charging).

If you recall, I was going to try using 14 or 16ga extension, but the problem there is that I’d end up with the voltage drop (and lower input) all the time. I’d rather take the extra step of partially unfolding it, starting charging, then opening it, so as to get the full boost from the panel during the entire charging session.