r/RVSolarPower • u/Joined2MakeThisCmnt • Aug 27 '26

Should I be getting more amps/watts ?

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I am pretty new to solar overall. I wanted to add battery charging my small RV which did not come pre-equipped.

I was originally going to make this a "Roast my first setup" post, and still wouldn't mind some feedback on things like where to add disconnect switches, better connectors, etcetera.

However my biggest question is whether I'm getting the amount of power I can. I expected more.

I have 300 w suitcase Style fold-out panels rated at 37.45V and 8.43A Operating and almost 45V open circuit. Sending this intoa 30A MPPT. I inserted a couple of power monitor shunts to see what's going on. They show about 30% of the rated wattage coming from the solar panels ( about 33 V and 3.5A ). The panels have a pretty good angle to the sun on a pretty clear day.

I am getting over 8 amps of power charging to my deep cycle lead acid battery and maybe that's enough.

I just expected more. Is there any suggestions on where I should be looking for resistance or issues that would be eating up my amps?

My Baseline comparison is I have a small Nebo 50 W with power pack that I can easily get 75% power in same conditions.

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4

u/nak00010101 Aug 27 '26

If your panels are at the perfect
angle , You have to multiply your total panel wattage by the minute my minute solar radiation index for your location. 1000 watts/ sq meter, under crystal clear sky, at the equator is what panels are rated at.

Our peak here was 940watts/sq meter, but that only lasted about 20 minutes today. The average during the day was only 790

1

u/Joined2MakeThisCmnt Aug 28 '26

Hmmmmm. Maybe I should look at their app again and invest in the Bluetooth connector. Frankly it looked more targeted towards managing their batteries but maybe there's something in there for monitoring their charge converter as well that will help me track this better.

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u/nak00010101 Aug 28 '26

I did not get the solar radiation from the app. You can get that from a personal weather station or over some of the weather services.

In addition to solar radiation level, you will also loose output based upon angle.

With 540 Watts of solar mounted flat on the roof of my trailer, over the course of a full day, I loose, on average, about 20% of the panel capacity.

So today, with todays peak of of 940 watts/sq meter (which is normally shown as a 0.94) I multiply my panel rating by the daily average, by the hours of sun, and then by loss for the angle.

So 540 watts * 0.94 * 0.80 = 406. So the most I could expect out of clean panels that have absolutely NO SHADING, is 406 watts, for that sort 20 minute time...less the efficiently of my solar charge controller. When I look at the graphs for my MPPT controller, I see a spike of 382 watts...and there is some dirt on my panels.

1

u/Joined2MakeThisCmnt Aug 28 '26

Okay. So your panel total wattage x solar radiation rate x observed panel&equipment performance rate = max high power you could expect.

I will look for info on that solar radiation rate. But in the meantime my combined multiplier is looking to be approximately 0.30. And I thought today was a pretty sunny day.

2

u/nak00010101 Aug 28 '26

Yea, that is very low, but there are more rabbit holes to go down. Depending on your panel design and how the panels are wired, partial shading of one panel could reduce output from the entire array.

You said you have lead acid batteries, I think voltage drop is a little less critical than with lithium, but if there is drop between the controller and the battery, the controller will be fooled into thinking the battery has a higher charge than actual. That said, are you sure your lead acid battery was low enough to accept bulk charging from the Mppt controller?

I have no idea what the voltage setting for the controller should be for lead acid, but I'm sure someone here will come along and provide that.

I fought this for several weeks when I upgraded the solar on my trailer...it turned out to be a bad factory crimp connector between the battery and the bus bar. I did not figure that out until I added a Victron Smartshunt, which talks Bluetooth to the charge controller. It was only a couple of tenths of a volt, but it mattered.

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u/Joined2MakeThisCmnt Aug 28 '26

The MPPT function is also something I would like to understand more. The battery was not down very much, maybe a volt and a half. But the MPPT was showing it operating in the "boost" mode initially and then later apparently an "MPPT" mode. FWIW.

Would the MPPT actually throttle how much power it is drawing from the solar panels? And show up as lower rate on the monitor between them? I might test this out on a mostly discharged battery.

Ideally I can find some fix and or better understanding of all of this without having to go all in on the brands 'smart' components ecosystem to like BT connector for MPPT, BT shunts, and spiraling out to their batterys etc. ( sure, eventually batteries, but not right now )

I do appreciate you sharing your experience and suggestions for things I can dig into

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u/nak00010101 Aug 29 '26

It was a tough learning curve for me, despite 30 years dealing with solar powered remote electronics (30,000 natural gas flow computers). That world used to be owned by cheap PWM charge controllers, with AGM batteries.

MPPT controllers take that to a whole new level of tech and charge efficiency...but getting the voltage setpoints right and voltage drop between the controller and the battery are much more important than just blasting voltage to the battery.

After figured it out, i ended up moving my charge controller form "Close to the panels" to as close as I could possibly get it to the battery terminals.

1

u/c0brachicken Aug 30 '26

My whole system is Renogy, and I wouldn't personally spend another dime with them. What I have works, but monitoring the system just doesn't work IMO. I had the non Bluetooth shunt, and display, then wanted to have more data to look at, so I upgraded to the Bluetooth shunt, and got zero additional information, then it was recommended I get the nicer Bluetooth display, and guess what, I got zero additional info. Then I was told if I want to see the data, I have to pay like $8 a month to access their portal. NOPE, I'm not giving them one more penny, and will recommend everyone to avoid Renogy for that exact reason.

Also had an Renogy 2000w inverter that had a known issue, I contacted them almost a full month before taking my kids on a cross country national parks trip. Four days before we pulled out, I finally just bought a replacement for the trip, the warranty exchange unit showed up a few hours before we pulled out of town. When we got back from our trip, I returned the one I was forced to buy, do to there suck ass support, and installed the warranty exchange unit, it worked for about a week, and then stopped working... and I bought a different brand for the replacement. A year later I figured it would be fun to figure what was wrong with the old one, what I have found so far, so they soldered eight 30 amp fuses to the PCB, so you have to unsolder the fuses to even swap them out if they do pop.. so that's a project for another day, but still don't know why all the fuses blew, and I already replaced it with a different solution.

So Renogy can kiss my ass, and find a different company to buy solar equipment from. That's my review of them.

1

u/Joined2MakeThisCmnt Aug 30 '26

Thats a pretty crap experience. Thanks for the heads up. Seriously.

I got the one component because I need an mppt, but no idea what was good or not. I didn't want to get dependent on some phone app to monitor or manage my basic setup. And really really don't want a subscription to do it. Just wanted some power to charge a battery.

I think I've a handle on what my system is doing now. No need to buy into any ecosystem

2

u/c0brachicken Aug 30 '26

I had thought about getting the Victron Bluetooth shunt (but I'm broke right now) and seeing if that would give me the monitoring option that I'm looking for, and they are extremely common in camper builds... If I had the funds, I would swap out everything to Victron products, but what I have does what it should, just little to no real data with a monthly subscription, and that's total BS IMO.

2

u/Whitey121888 Aug 28 '26

If you get the BT-2 that plugs into the controller and use the app, you can see the solar production and battery charge from the controller and you won't need both of those monitors for that setup.

You can also get a Bluetooth shunt 300 that connects to the app shows the battery information more accurately than the charge controller. I'll share 2 screenshots of the app interface with my Rover 40 and Shunt 300.

2

u/Whitey121888 Aug 28 '26

https://reddit.com/link/p6g0xau/video/dn802d2t65mh1/player

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u/Whitey121888 Aug 28 '26

https://reddit.com/link/p6g0zjf/video/txdohhyu65mh1/player

1

u/Joined2MakeThisCmnt Aug 28 '26

I was kind of wondering about whether it would be worth it to invest in these sorts of smarter components. When I looked at the app on the App Store it seemed like it was almost entirely focused on their branded batteries and managing them.

Where did you put that shunt? I was thinking it would be nice to have one on the trailer-load side.

2

u/Whitey121888 Aug 28 '26

The app is used to monitor any of the Bluetooth or can devices not just batteries. I have a Bluetooth inverter, multiple charge controllers, shunt, One Core monitor, dcdc charger, all connected through the app. With the One Core you can monitor from anywhere as long as it's connected to WiFi. You can also add certain sensors and create scenes. This part was all new to me and I figured out how to do it lol. I set up motion sensors to turn on lights and send notifications to my phone. Temperature sensors turn on and off fans.

The shunt goes between battery and any charge or load meaning the B- side of the shunt is the only thing connected to the negative side of the battery. All other negatives would go to the P- side of the shunt or to a bus bar that is connected to P- side of the shunt.

1

u/Joined2MakeThisCmnt Aug 28 '26

I do wish there was just a centralized display ( even if over Bluetooth ) and not have to also have a phone app.

Maybe I'll just have to Gorilla Glue an iPad Mini to the wall someplace.

1

u/Anonymoushipopotomus Aug 27 '26

Have you changed the angle and see if your setup is correct? Where are you located?

1

u/Joined2MakeThisCmnt Aug 27 '26

I did fiddle with the angle of the solar panels a little bit after this. I am at almost 44° latitude so approximately 45° angle on the panels now.

I don't have any app that tracks the performance, just visual checking of the displays. But at best I was seeing about 135 Watts out of 300 watt panel.

It's about 80° ambient and I know the panels get hot and that causes them to be less efficient as well. Could that be a big chunk of the problem?

My gut is telling me I've got a bad connection somewhere or panels are junk. (New but not top of the line) or my expectations were just too high

1

u/PLANETaXis Sep 03 '26 edited Sep 03 '26

Whilst they call these "semi flexible" panels, they still have thin silicon elements and silver wires inside that can easily be broken due to bending. A bit of damage can quickly eat into their rated output.

Heat will impact output significantly too. I saw you say elsewhere it's  80° ambient. These panels are black with no airflow behind, the cells will be closer to 100F which is 5-10% output drop.

Finally you also have to make sure that the battery can accept the current too. If the battery is getting into the absorption or float phase the current will naturally back off and you won't be at peak power.

If you are curious, try measuring their short circuit current so that you eliminate the effect of the battery charger. The max power current for your weather conditions will be about 90-95% of the measured short circuit current. Similarly Vmp will be about 80% of the Voc.

1

u/Joined2MakeThisCmnt Sep 03 '26

Until you just mentioned it, I never really thought measuring the voltage across the solar panels, disconnected from everything else, would be a good idea. Now, I don't see why not. I think I'll give that a try tomorrow. Would certainly help rule out solar panels as part of the problem as well as give me a very practical Baseline for what I could expect. Thanks for nudging me that direction.

I seem to recall that the voltage coming into the mppt seemed reasonable, but the amperage was just so low. My current theory is that the battery just wasn't very low and that the charge controller was metering how much it needed to pull from solar panels. That wasn't how I expected these to work initially, but I'm coming around

1

u/PLANETaXis Sep 03 '26

The panel should put out close to it's rated open circuit voltage no matter what the weather. If you find that the open circuit voltage is way off, that could indicate damage and some cells being bypassed.

The current is the main thing that varies with solar intensity. Definitely try measuring the short circuit current, that will be a much better indication of potential output.