My 200W, MMPT system could not recover "full charge" in bad conditions.

**rickst29** · 08-23-2015, 11:25 PM

And so, maybe it's time to add a 3rd panel.

My 2619 (finally given a name: "The Rogue", in honer of its now-discontinued MPPT Controller) was unable to recover from a tough night during the following charging day (today). The day was pretty severely compromised by smoky conditions from the fires burning in CA. (We were in CA, along the Eastern Sierra).

The #1 factor in compromised Solar Charging was the smoke. The #2 factor was: the length of effective charging day in August, has probably declined to about 7 hours under the best of conditions (maybe 30% less than the "length" of effective Solar time available in late June and early July.)

But the real killer was my power usage. Overnight, my usual loads were perhaps roughly doubled by running an air cleaner continuously, at about 40 watts.

As usual, I ran the CPAP continuously (without humidifier; maybe another 30W - but only 15W average over the "discharge" day, because I sleep barely half the length of the non-charging portion of the mid-August days. The Compressor Fridge ran at an average of about 30% cycle time from the end of the previous charging and travel day for about the first half of the night - that's another 30 watts for half the night, followed by maybe 5 watts average until the charging day began. (I'll SWAG an average of 20 watts continuous). And "phantom loads", my home-built external fridge fan (continuous) plus evening lights, probably averaged another 5W over the night.

To summarize: my "typical loading" is up around 40W through a night which starts warm, but the continuous air cleaner usage DOUBLED that figure. 80W/12V is a bit less than 7 Amps, and run in "discharge mode" for about 14 hours consumed about 90 Amp Hours. That's basically 1/2 of my battery bank, and my mid-AM reading (12.2V) agreed with that figure (as a rough estimate, without getting into finicky details).

The unpleasant surprise, though, was failure to charge on the road - with Solar active, AND the TV connected via Bargeman. Driving through smoky sun for the "prime" early afternoon hours, the battery got home at only 12.8V, far less than I had hoped for. I plugged it into the wall, and the Converter jumped into action, and fired up it's fan. I would not have managed a second day under such conditions, with the air cleaner running. Bummer!

(Update 9/23/2015: I have designed a solution for failure to charge from the TV, http://www.trailmanorowners.com/foru...ad.php?t=16761).

**rickst29** · 08-23-2015, 11:30 PM

... because it was all pretty obvious (with just a cursory look).

Redtail Cruiser · 08-24-2015, 07:15 AM

Sounds like you should maybe start bringing a small generator with you.

BrucePerens · 08-24-2015, 09:03 AM

Most MPPT controllers, including my Morningstar MPPT 60, are "buck" converters. That means they can reduce the voltage coming in from the panel to charge the battery (increasing the current), but they can't increase the voltage. So, if the voltage coming in from your panels is less than 16 Volts, your battery won't charge. And the optimum under-load voltage of your panels is probably only 18 volts. So, a single panel or a group of panels in parallel would need close to full sun to work.

The solution for this is to connect your panels in series, if they aren't already so. That way, there will be a higher voltage, and even dim conditions will yield enough voltage to get you some charge. Look up the maximum open-circuit voltage, multiply by the number of your panels, and make sure you do not exceed the maximum voltage specified for your controller. At an open-circuit voltage of 21.5V, my Morningstar MPPT 60 which is specified for 150V will support up to 7 panels. Of course you could also have several strings of 7 in series which are themselves connected in parallel to make up the maximum current rating of the controller.

You will get the same wattage in series that you would in parallel, except that it will work better in dim conditions. MPPT controllers use the voltage from your panel to charge a capacitor, and then they charge the battery from the capacitor. This allows them to deliver more current, and less voltage, than their input.

The MPPT 60 is way over-specified for any amount of panels I could get on a Trailmanor. But it will run reliably, and I like that it has Ethernet.

Be careful about safety! 150 VDC is about as dangerous as 115 AC.

New fixed solar systems systems are required by the electrical code to have DC GFCIs for safety. I've not yet seen an outdoor-mountable one, and thus they can't be positioned close to the panels and aren't as helpful for an RV as they could be.

**rickst29** · 08-24-2015, 09:58 AM

Hi, Bruce! (BTW, I'm posting from Mageia-5, and did some some minor fixes and enhancements for kde, gnome, and qt in the past.) My 2x100W panels are in Series, and I've still got headroom for another 55V (open circuit voltage) before hitting the 100 volt MPPT limit. Anything less than a "48 Volt" panel can be added, although a high-power panel array will be power limited to 300W total system power at the MPPT under good conditions. But under good conditions, it would be switching into PWM mode after just a few hours anyway, because the batteries would quickly become nearly full.

Tim, I have an SUV (not a pickup), and so the slightly stinky gas-powered device would need to be inside the SUV. And we're already pretty loaded down with dog crate, down-the-road air cleaner (moved into the after reaching our destination on this trip), and "paraphernalia". And the the gas can would also take up some space, even though I've got a really good one which doesn't make smells. And finally, the generator would cost more than another panel.

I think that the "sweet spot" (for cloudy or smoky conditions, or partial shade) is right around 325-350 watts of max rated power. I have a slight issue with raising the panel-weighted shell, and another 17 lbs of glass/aluminum panel wouldn't help that issue. So I just pulled the trigger on a "135 watt flexible panel" from Ebay. It will actually run slightly less, because the current will only match the current on the existing glass/aluminum panels: 5.29A Amps (rated max). Under good conditions, the "excess" gets thrown away by the MPPT (operating as a PWM controller). But my shortfall under bad conditions - smoke or clouds - should now be resolved.

Padgett · 08-24-2015, 10:22 AM

A good generator inverter has a gas cap that seals when not in use. Suspect all you need is one of the smaller ones like a Honda EU1000i or Westpro WH1000i. DO NOT get one of the 800W two-strokes, they are very loud. Ones I mentioned are the quietest.

For my 2720, everything (two GC2s, solar controller, disconnect panel, and 2500W generator (I need AC) fit in the vented rear storage compartment. I have never noticed any gas odor.

(picture is with battery cover removed).

**rickst29** · 08-24-2015, 10:25 AM

And you know what they say around here: "It's a dry heat, not so bad".

Padgett · 08-24-2015, 10:43 AM

Yeah, swamp coolers work well there.

scrubjaysnest · 08-25-2015, 10:19 AM

We have run in to the same marginal charge conditions also. With the loss of the 120 watt that has made things worse. In our partial shade conditions series panels would make things even worse. In town for a chore day so won't be able to keep the two portables moving with sun. The Trimetric was showing 89% soc when we left the CG. Our usage is less then Ricks and I agree the sweet spot is around 300 to 350 watts; 400 watts may give better performance for the mppt CC's.
When we get home hope to be able to repair the 120 watt panel.
Move CG's tomorrow and will have more sun for the panels but the weather guessers are calling for rain this weekend.

LoveToCamp · 08-25-2015, 08:42 PM

Okay, electricians. Now you have me thinking, which when it comes to electricity, means I just get puzzled.

I have a 30 amp PWM solar controller that came with the TM. Max solar voltage is 28v (max array current 30 amps).

Each panel (I have one mounted, and have one in the box, ready to mount this weekend, each polycrystalline 100w) is "open current voltage" of 21.6v, map power volts (vpm) of 17.4v, and max power current (imp) of 5.75 amps. Now, I don't know how all of that relates, but that is what the specs say for the panels.

It was mentioned that you may wire in series to increase charging performance, but you have larger MPPT controllers. I believe, from the above specs, that I should not wire mine in series, but must wire in parallel. Is that correct? I don't want to fry my system, but I also want the fasted recharge I can get. I usually have good sun, but will occasionally have overcast or periodic shadowing.

Thanks for any education you may choose to give me.