SP200 Solar Panel slow charge

Hi. I’ve tried charging my new AC200P with the SP200 Solar Panel I got with it. I am only getting about a 5% charge improvement per day and we have had no clouds in the sky over the last couple of days.

Does this seem low to you?

You need a minimum of 2 SP200’s to charge the AC200P and in the settings the DC input needs to be set to PV instead of car.


Thanks will 2 double the input or more? You were right on that it wasn’t set to PV. I will try it again tomorrow.

Yes, two in series will double the voltage which is what you need to get above the 35 volt minimum that the AC200P requires. Typically I get from 140-160 watts input per panel so 2 will give you around 300 watts, 3 would get you 450 watts etc.

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Hey friend,

Only one SP200 is not enough. Because the OCV of AC200P is 35-150v. At least two SP200 can get the minimum OCV. We suggest you use 3 panels to charge because there will be conversion loss, 2 panels may not have good effect.


Thanks guys… ya, I switched it to PV and am getting no charge today. I’ll get another panel or two when I can save up the money.

I’m using 4-100W solar panels in series to charge my AC200P. I’ve noticed that with 3 panels, I get close to 300W charging (expected) but with 4 panels I still get only 300W charging. I tested on a full sunny day by covering each panel with the cardboard shipping box, all panels work. Covering 2 panels reduced charging to 200W (as expected). Removing one panel at a time from the string maintained 300W charging (as expected). My expectation was near 400W charging with the 4 panels. The solar panels are Renogy 100W, Voc 24.3v, Vmp 20.4V, Imp 4.91A, Isc 5.21A. Thanks!

If you have 4x100w panels in series and you cover 1 of them, you will get close to 0w not 300w, as the covered panel will produce almost no current and pull down the current of the entire string to 0. Also, it is very rare (like almost never) for a 100w panel to produce 100w, you will need tropical sun and arctic temp. You may realistically see 90% max on a great sunny and cool day. Are you sure you hooked them up in series?

Your described behaviour of lossing 100w at a time when shaded seems to suggest you connected them in parallel. If you did that, then adding the 4th panel won’t add wattage as you will exceed the max current. Though I am surprised parallel work at all given it is below the min input voltage requirement.

Your panels voltage between 20-24v, so 4x in series are still within spec for the AC200 which takes 35-150v. If you get 300w with 3 panels (which is rare), then you should get 400w with 4.

Try hooking them up starting with 2 in series to see what you get, then try the other two. Then move to 3 and 4.

Hi Snowstorm,

Thank you for the quick response.

The panels are definitely connected in series as the only wiring used is +/- wiring from the panels, there are no parallel connectors and the open circuit output voltage measures accordingly. My data was taken on two consecutive days in late June with clear skies and intense late morning sun in Seattle, 47 degrees north, so the azmith of the sun was approximately 24 degrees (about the same as at the equator in June?) and cool morning temps, although not arctic. I did the testing late enough that the charge rate was high but early enough before the batteries were fully charged.

I did start with 3 panels because when I ordered 4, one was back-ordered. With the 3 panels, the AC200P showed close to (but less than) 300W, maybe in the 270W range which agrees with your realistic expectation. The only power (watts) measurement I used was the AC200P display. I was very happy to see that charge rate; it was almost 3X the 12v cigarette lighter plug I was using before adding solar. When I added the 4th panel, I expected an increase of about 30%, but there was not. Wondering if the new panel was a dud, I removed one of the previous panels, and with a 3-panel string (including the new panel), the AC200P still showed close to (but below) 300W of charging.

I then put all 4 panels back into the serial string, and used the solar panel shipping box to cover each panel, one at a time. The AC200P continued to show close to (but below) 300W in each case, all consistent, and not dropping significantly (if at all), never to near zero.

After reading additional post, I wonder if my AC200P was too fully charged and throttling back the charge rate. Some post suggest to do these kind of tests with a near depleted battery, and mine was around 80% or above, as a refrigerator was the only load overnight from a fully charged battery.

I was also wondering if the AC200P has a “sweet spot” solar voltage input to maximize the charge rate.


Interesting. I would have expected wattage to drop to near 0 if you totally cover 1 panel of a 4 panel series, not to 3/4 of the wattage. If you have a voltmeter, try measuring the open circuit voltage of the 3s and 4s configuration to see if it is what you expect.

The fact that your battery is 80% full may slow down max charge rate, but even at 400w, it is still only C/5 so I won’t really expect it to be that limited just yet at that level till it is like >95% full.

I believe the reason that shading a panel didn’t block the current is that they have bypass diodes. Bypass Diodes | PVEducation

Yes, I checked the Voc for each individual panel prior to mounting and again after they were connected in series, everything checked out. The Voc is 24.3V, Vmp is 20.4V, so the 4 in series will be between 80-100 volts, max current is Isc 5.21A, well below the 12A max input for solar charging. But I saw no increase with the 4th panel. I can try again; I don’t need max sunlight to check that.

Even while parked (camped) under heavy forest or heavy overcast skies, it almost always shows some charging during daylight. I think 30W or so is the lowest I’ve seen. I just read this article that the voltage stays fairly constant, but the current suffers in low light. PV Panel output voltage - shadow effect? - Victron Energy

So maybe I should configure a string of 2 sets of 2 panels in parallel? The voltage would be around 40, meeting AC200P’s minimum voltage of 35V, but the current would be doubled. That would better match the Bluetti PV350 solar panel which has a Vmp of 37.5V (just above the 35V min). If two of those in series is meant to achieve 700W of charging, the AC200P might be optimized for voltages close to 70V and fade off at higher voltages? This article describes how a “standard controller” (vs an “MPPT controller”) will work with high voltage panels, but you will lose power because it reduces the voltage to the controller’s input voltage. Solar Charge Controller Basics | Northern Arizona Wind & Sun

I’m very satisfied with the AC200P, but think the technical documentation is lacking. Lots of guessing on the specs.

You can try a 2s2p configuration and see what happens, though I wonder if that will exceed the max current resulting in some wasted power.

I though bypass diode will help when a part of a panel is shaded, but I didn’t know it will work when the entire panel is shaded.