Awesome new MPPT controller with bluetooth control for $99

[titanpat57]

A question for the experts...can I run a 20 amp mppt controller with a 100 watt panel, is there some issue that could arise.

For some reason I'm not getting anything that I can tell into the controller from the panel located on the front of the trailer. The panel then goes to the controller on the inside rear of trailer (about 12' of good quality #12 from Mcmaster Carr....then it heads back up to batteries under the bed (about 7'- 8') with the same wire.

Thanks in advance.

 

[george_tlc]

^ no issue with 100W panel and a 20A controller.

Should be easy to fault find. Measure voltage out of panel. Measure voltage at other end of cable (to solar controller). Just locate where the voltage 'disappears'...

cheers,
george.

 

[titanpat57]

Thank you George!

 

[Overland Tailor]

For vehicle usage we use lugs to connect to 12awg (or thicker) that easily handle 23A. Standard connectors used in our applications are Anderson SB50 and there's no issue at all with 23A. Typical wiring is automotive with appropriate insulation. Not sure why you are fixated on 12awg anyway. Most of us are running 10AWG or 8AWG or thicker depending on current carrying and length of wiring. This kind of wiring has insulation that is well rated about 90C maximum. Though I doubt anyone would be running 20A+ and not size wiring appropriately.

NEC ratings are typically looking at wiring in conduits, home wiring etc. This is automotive where we aren't running solar wiring in large bundles and along the exhaust system or inside walls... Cables are typically just in a sleeve and with plenty of air around them.

Fuses/circuit breakers of course are a smart thing to use in any wiring, especially vehicle.

Anyhow, glad you're looking at absolute worst case scenarios. Panels (at least the kind we use) have diodes to protect against reverse voltage (primarly to prevent battery discharge back into the panels at night), so even if one panel had severe shorts it would make no difference to other panels that are connected in parallel - no appreciable current will flow into the damaged panel.

All pretty moot given the majority of us are using 100W or maybe 200W of panels. We aren't talking about a house system or tops of RV's covered in panels. We're also specifically talking about the mppt75/15 and having 300W or 400W of panels connected to it (lets have them parallel and nominal 20V VOC) will not cause issues with it since it will limit its maximum output to a nominal 15A. Of course connecting more panel capacity than the controller can output will just be a waste of capacity.

Solar panels aren't quite current sources, they have an 'interesting' VI curve and that's why an MPPT algorithm works well to extra maximum power as the panel output varies with temperature,clouds,shading etc.


cheers,
george.

George -

I'd at most have room for (3) 100W Renogy Panels on my Alu-Cab.. Using the 75/15 that I currently have, how much capacity waste would i have with that setup.. Just trying to understand this before making the decision to move from a 2 panel setup to a 3 panel setup...

Very much appreciated,

John

 

[george_tlc]

^ well, 75/15 has a 15A max output (their 'spec'), so I'd guess the most you could push into the battery is 15A before the controller limits output. Let's assume it's pushing out 13V at 15A, so that's 195W. With say 95% efficiency in the controller you would have say 195/0.95 = 205W at the input. That would be the maximum usable solar input when the cells are at their nominal peak - max sun and panels pointing at the sun etc.

Since I assume you plane to mount the panels on the top then they won't in general be pointing at the sun or producing max power. So, 300W is not totally overkill into the controller if taking into account some cloud cover/dirty panel/panel not optimally pointed at the sun etc.

Of course the other option is to move to a higher capacity victron controller... they have 100/20 and 100/30 etc too. Cost more of course.

cheers,
george.

 

[Semi Hex]

The newer Victron units have the dongle built in, which is nice to track what your setup is doing.

 

[Overland Tailor]

George,

Thanks for the time and math. I'll have the ability to point them somewhat as the alucab opens, but never the best scenario..

Just didn't want to waste time and money..

I'll probably start with the 2 panels and I agree with 3 I should move up to a larger controller..

Cheers and thank you again..

John

 

[e9999]

John, the Victron specs for the (bluetooth) 75/15 state that in "12V" mode, the incoming power is limited to 220W by the controller. So, yes, on a bright summer day around noon pointed straight at the sun you might have potentially close to 300W available with 3 panels and some would be wasted. Not so much the rest of the year or in other orientations. The basic question is really "How much energy (not so much the power if you have a battery as a buffer) do I need" and go from there to figure out how many panels you would need and what controller to accommodate them. Practically speaking, though, an actual 220W is already quite a bit and would support a lot of hardware. For context, my not so efficient Edgestar fridge uses -averaged out over time- something like 20W with ambience around 70F or about 500 Whr a day. Say it would be 50W average instead in a hot truck or 1,250Wh over 24hrs, well you could run that fridge then with a true 220W available over 6hrs during the day, but that likely won't be possible with a "220W" panel. The problem when looking at these things is that many people forget that a "100W" nominal panel does NOT produce 100W most of the daytime (and of course produces zilch at night), and especially so if left in a fixed position. The average over the entire daytime will be much less than that, let alone averaged over 24hrs. So if I had "220W" nominal of panels it may be able to generate about that 1,250Whr (say 220W*12hrs/2) in the summer but probably not too much more. And likely significantly less than that the rest of the year. (All that at moderate latitudes.) 300W nominal, however, will give you some safety margin, even with the 75/15, because you'll be able to produce 220W more hours during the day. Of course if you are not talking about a 50W device running 24/7 like a fridge, than a smaller panel will likely be just fine.

There are online calculators out there that will allow you to figure out fairly accurately how much energy you can expect to generate at just about any location in the US for a given panel, orientation, local weather etc.

 

[Overland Tailor]

Thanks e~

Appreciate the time you took in posting the information. I'm going to be just fine with 2 panels and plan to just stay there unless I need the added capacity. I'll just be running a National Luna 60L, some lighting and portable ham radio... I also swap from the house to the primary to keep it charged up as well during the day.

Again, Thank you -

 

[e9999]

that's probably the best way to go if you have an unclear situation, run it and see if it's enough. Too many variables. The Victron will tell you how much you produced, and I would suggest an inexpensive (about $20?) little energy meter that you'd connect to the fridge to see how much it uses.

 

[george_tlc]

^ if you wire the fridge as the 'load' output of the victron then it will tell you how much the load used...

cheers,
george.

 

[e9999]

I found that a little energy meter is useful for a number of things, so well worth the money IMO. Although the accuracy of the inexpensive ones is not that great. And yes, the load can be up to the full 15A for the 75/15 IIRC which should be plenty for the usual fridges. One advantage I think is that you can set the cut off voltage for the load to avoid overdrawing on your battery if there is no cutoff built in the fridge itself or if it's too low. I don't remember that the software will tell you the cumulative energy use for the load, though, but I'll take your word for it.

 

[Cruiserdrew]

^ if you wire the fridge as the 'load' output of the victron then it will tell you how much the load used...

cheers,
george.

This is a pretty fun way to look at the load of the fridge.

I have found that 160 - 180 watt panels supply enough power in almost all circumstances and will supply plenty of camping power. And I run 2 fridges.

So 2 x100watts sounds like will do a good job for you and you can wait to add a 3rd based on experience

 

[Overland Tailor]

This is a pretty fun way to look at the load of the fridge.

I have found that 160 - 180 watt panels supply enough power in almost all circumstances and will supply plenty of camping power. And I run 2 fridges.

So 2 x100watts sounds like will do a good job for you and you can wait to add a 3rd based on experience

Thanks Drew -

Always good to see some real world assessments.

I have been a big fan of my Foldable Renogy 100W panel, as I can maximize the input by adjusting angle and moving it around for the sun..

I'm just trying to eliminate some interior gear / slim down a bit, so I'm thinking 2 panels mounted on the RTT should help with some of the inefficiency of solid mounting and bad angles.

Having said that, when I get out west the portable setup is very nice so you can park in the shade and still get some juice! There is just not 1 solution for every situation.

Cheers -

John

 

[e9999]

yup, makes a big difference if you can keep the truck in the shade both for comfort and also to help the fridge. Unfortunately, not too much shade in most desert places I've gone to. And better not forget the long extension cord...

 

[Overland Tailor]

Just got my 2 Renogy panels up and I ready like the setup.. First sunny day in almost a week here in the Southeast..

 

[Overland Tailor]

Went back and changed out the smaller Anderson for Sb50 connectors. Much more robust now..

 

[iptman]

I read through the manual and didn't see if the 75/15 will shut itself off if no panel is connected. I want to wire it in to my aux battery but will only have the panels connected on trips. I'd rather not have to connect in a switch for the controller to not draw down the aux battery if the truck sits for a couple weeks.

 

[george_tlc]

The mppt unit will draw about 22mA in 'standby' since it is powered from the battery - as per my previous test/post in this thread.

So, amp.hour draw is 0.022 x 24 hours x 7 days x #of weeks...

cheers,
george.

 

[Josie'sLandCruiser]

Hi all,

For those of you with "hard mounts" of the Victron MPPT, do you have it wired to the primary vehicle battery or the "house" battery?
Is it connected to the battery even when the solar panel is not deployed?

Thanks,

Alan