Are 24V portable solar panels okay?

rainyescape · 06-11-2022, 08:12 PM

I have the ETI installed 190W panel on the roof (18V) with the Go Power controller, and single 100 Ah lithium battery. I also installed a smart shunt to monitor the battery, if that matters.

Harbor Freight currently has a deal on 100W panels (with fold up legs) for $100, but they are 24V:

https://go.harborfreight.com/coupons/2022/06/179905-57325/

Is it terrible/destructive/you’re-gonna-set-your-trailer-on-fire-bad if I use these? Or if I maybe buy a couple of them with a “solar connector” that I assume wires these together in parallel (which would then be in parallel with the rooftop panel).

Alternatively, I could get a similar 18V panel from HF for $190, but at that price I could get (just about) 2 of these 100 W panels. If I wanted 200W or 300W if portable power, is it worth getting a bunch of these cheaper panels?

I know that max peak power tracking will result in some inefficiencies. So I’m just curious what you all think about how “bad” it is to use 24V panels vs. paying more for an 18V panel (but is maybe more rugged?). Thanks!

alanmalk · 06-11-2022, 09:14 PM

Quote:

Originally Posted by rainyescape

...
I know that max peak power tracking will result in some inefficiencies. So I’m just curious what you all think about how “bad” it is to use 24V panels vs. paying more for an 18V panel (but is maybe more rugged?). Thanks!

There are no serious "bad" effects of using an 18 V panel in parallel with a 24 V panel, other than loosing a bit of the power that you might have obtained with a pair of MPPT controllers (at another expense and complexity). As far as ruggedness goes, that depends on the manufacturing quality, not the design voltage.

But that said, a 24 V panel is somewhat of a rarity. I'm wondering if it really isn't an 18 V panel with a slight exaggeration factor thrown in for marketing? (Somewhat like the portable drill industry has exaggerated the voltage of drill batteries. Bigger numbers sound better and come from using non-standard methods of measurement. But I digress...) Anyway, if you can count the actual number of cells in the panel and report back it might be informative. 36 cells is very common for 12 V battery charging uses (the Escape 190 Watt for example.)

rainyescape · 06-11-2022, 09:36 PM

Well that’s good to hear that it isn’t horrible. And thank you for doubting what the Harbor Freight website says: the specs in the manual for the $100 panel actually say 18V output, so I have no idea why the website specs say 24V.

The $100 panel has 36 cells, see first image below.

The second image has the $190 panel (orange corners, hinge in the middle), it’s not easy to see where the cells are.

And yes, I understand rugged has nothing to do with voltage, but it does influence the price and whether it’s worthwhile spending an extra $90. But now that I know that both are 18V, the bonus ruggedness features are less worthwhile!

Crazypill · 06-12-2022, 01:32 AM

Regular solar panels are already quite stout. I'd just get one 200w 18v panel. Make sure you check polarity because the zamp port is reversed. Your SAE-MC4 adapter should have a polarity reverser. I ended up with 2x 100w hqst panels and it's a pain to parallel wire them every time. Will repurpose those on a shed or something and just get a 200w single.

RBRV · 06-12-2022, 06:16 AM

I recently bought that folding one from Harbor Freight when it went on sale, was able to get it for about 140 bucks. I measured the voltage it produced in very bright light and it produced close to or right at 20v which is what the 160w panel on my escape produces also. I like the protability of the folding unit and that it comes in a padded carrying case.
Also, my trailer is second hand and I checked the polarity on my Zamp port that was evidently installed by ETI (because it was part of the build sheet) and the polarity was sae standard and not reversed.

rainyescape · 06-12-2022, 10:16 AM

For checking polarity in the Zamp plug, can I use a meter in DC Voltage mode at the port itself? I assume it’s as simple as lining up the solar panel’s cable connector in the right orientation to plug into the Zamp plug (but not plugging in yet), checking voltage across the panel’s connector, and then doing the same on the Zamp plug, using the same red/black meter wires in the same orientation between the two connectors. If they both read positive, then I don’t need a polarity reversing adapter.

The reason I’m asking all this is we are out on a trip right now, and I fried the controller-less Jackery panels because I didn’t check polarity. I didn’t even think this was possible. The panels have a little USB plug outlet that started smoking, and they stopped producing power. So the Harbor Freight ones are attractive because there are stores nearby on our itinerary with panels in stock, and we are learning that our single 100 Ah lithium battery is not enough. I’ll also be picking up a better multimeter!

cpaharley2008 · 06-12-2022, 10:20 AM

Owning and using your Escape is certainly a learning experience......

rainyescape · 06-12-2022, 10:24 AM

That’s for sure. I’m super annoyed at myself because they were working fine back home, but I wasn’t getting good power out of them when I had some extension cables included here in our campsite. So I thought maybe I messed up the polarity somehow, and immediately saw about 35 A getting discharged from my battery when I included the polarity reverser. I’m hoping I just fried the USB plug adapter and they still work!

Did my plan for measuring polarity of the Zamp plug sound okay? I’m trying to make it fool proof, without worrying about getting wire colors to connector genders correct.

tdf-texas · 06-12-2022, 10:40 AM

Quote:

Originally Posted by rainyescape

That’s for sure. I’m super annoyed at myself because they were working fine back home, but I wasn’t getting good power out of them when I had some extension cables included here in our campsite. So I thought maybe I messed up the polarity somehow, and immediately saw about 35 A getting discharged from my battery when I included the polarity reverser. I’m hoping I just fried the USB plug adapter and they still work!

Did my plan for measuring polarity of the Zamp plug sound okay? I’m trying to make it fool proof, without worrying about getting wire colors to connector genders correct.

Below is a pic with the polarities for a SAE port. Male pin is negative - female socket is positive. If you have a Zamp solar panel, the polarity is reversed. As far as I have found, all other solar panels use the SAE standard polarity.

rainyescape · 06-12-2022, 10:43 AM

Quote:

Originally Posted by tdf-texas

Below is a pic with the polarities for a SAE port. Male pin is negative - female socket is positive.

If I want to be certain that ETI wired them like this, can I use a meter directly on the port when there is sunlight on my rooftop panel?

tdf-texas · 06-12-2022, 10:49 AM

Quote:

Originally Posted by rainyescape

If I want to be certain that ETI wired them like this, can I use a meter directly on the port when there is sunlight on my rooftop panel?

That's the way I would do it.

You could check the polarity of the portable solar panel(s) the same way but remembering that the male pin would be positive and the female socket would be negative.

If you want to test your portable panel to see if it was damaged by the reverse voltage, the video below does a good explanation of how to do it.

https://www.youtube.com/watch?v=eh6hzMb69gY

RBRV · 06-12-2022, 12:39 PM

Quote:

Originally Posted by rainyescape

If I want to be certain that ETI wired them like this, can I use a meter directly on the port when there is sunlight on my rooftop panel?

Yse simply connect your meter to the zamp port , red to red and black to black. Is voltage is negative then it it is reversed.

Perry Butler · 06-12-2022, 12:44 PM

I bought a Zamp port. Rather than deal with reversers, I wrapped the red wire with black electrician's tape and the black wire with red electrician's tape and then wired it to a separate Victron 100/20 solar controller. I don't have to worry that I'll forget the reverser and don't have to worry about my portable panel being a mismatch with my GoPower panel. You'll get the most power from your solar if you spend a few pennies more.

A year or so later I replaced that GoPower PWM controller for a Victron 100/30 controller, and last year added 300 watts to the roof of our 5.0. I just had to make sure the VMP of each 100 watt panel matched as close to the 170 watt GoPower panel on the roof. Instead of 470 watts on the roof we technically have 463.7 watts (for the anal). With that wattage we can live with the 6.3 lost watts from the minimal mismatch. I've seen over 435 watts a couple of times when I was fooling around. But the most watts I really see are around 350 or less, because the controller goes out of bulk mode, into absorption mode by 11 am at the latest (most days 9:30 or earlier). You can't have enough watts!

Food for thought,

Perry

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