MPPT Controllers

Not yet, Don, and thanks for the info.. I'll check out the Victron Controller... makes sense keeping it in the family, re: the new meter, and I'm willing to spend a little more for quality and efficiency. I think a 60A controller should be adequate for my anticipated needs

Don't know how many watt-hours I'll be consuming, but I'll work on this value, and go from there...

I'd likely use different equipment today than I did in 2014.

I choose to install a battery monitor first so that I could get a reasonable accurate values of my energy usage. It met that goal: turn a light on/off and note the amp difference. Without AC note the daily battery usage, etc.

I was under no dillusion about my panels and any warranty. Bought them on a trip 400 miles away (advanced planning), made in China and rebranded by Solar Blvd, a popular LA dealer, no longer in business. Checked the Voc and Imp and departed with the panels in the basement.

While not a factor for many I wanted maximum shade tolerance. My 60 cell panels are mounted higher to avoid A/C shadows and serial connected for increased shade tolerance with the panel bypass diodes. It's interesting how much misinformation there is on raised panels, serial panels and bypass diodes.

However it's obvious to me that anything electrical is the most misunderstood topic on RVs.

"Sizing should be 125% of the maximum harvest. So for a 20 amp harvest--the controller needs to be 25 amps. The reason for this is partly "cloud" effect. Essentially the clouds may act as a lens and temporarily increase solar irradiance"

This applies to PWM controllers, which will heat up and eventually fry when doing more than their rated amps for extended times. Brief cloud effect overages should be harmless though.

MPPT controllers can be over-panelled somewhat, as recommended by Morningstar for greater daily AH haul --see their blurb on that. That is because unlike PWMs, MPPTs "clip their amps" to their amp ratings.

What happens when a PWM controller is over amped? Zap = bad?

MPPT overpaneling can be very benefecial. It can allow maximum MPPT power over extended hours surrounding noonish. Most systems will not reach their maximum at 1:00 on a clear summer day in the south, let alone in the north. So who cares if there is amp clipping for a few minutes at 1:00 vs say increased battery amps for say +- 2 hours if one chooses to over panel?

And a oversized PWM controller will not see and real cost/performance benefit of 25% oversizing. But they do cost less.

take the sizing rules with a grain of salt. they were made up when solar panels were 30X the price you can get them now and are a minimum requirment to get you somthing that will work. when I now plan a system I go for a bigger controler for future upgrades, and as much pannel as I can afford and or have room for.

on my new camper I went with the renogy rover 40 amp mppt controler, and since I am running a 24V 325 watt pannel that is only about 1/4 if its capacity, but I wont be running any 110 stuff for now and I have room to add one more panel if I find I need it. this is going to charge 210AH of 6V GC batteries.

what my theory is now, is why wouldnt you want to charge the batteries as fast as you can so the panels can supply more of the house load during the day. I like to size my batteries at 4x or more of my daily AH usage (not sure if i can do it in the camper with out going to homemade li batteries) my 5th wheel is set up at 6-7X. so I can go 6 or 7 days in total darkness with out losing power, but when that cloud breaks I want that battery charged up as much and as fast as it can be.

for example the new system I am putting on the camper has the potential at 70% output due to where I am to put 93 ah back into my battery a day based on 6 hours. I cant see my camper using more than 40AH over night for furnace and such.

my 5th has 480 watts of 12v panels on a PWM and I cant see it putting much more than 105 amps on a good day, so that one is slated for a controler and panel upgrade eventualy

if you only have one panel now, might be time to thing about selling that panel along with your old controler to some one who just bought something and take advantage of that MPPT controler you are thinking about by going with 24V panels. I just got that 120 split cell 24V 325 watt panel for 200 cdn so would probably be in that 150ish US range. two of thoes and a deicent mppt controler would probably rock. My 40 amp controler can run 3 of these panels.

just some more to think about..

Steve

I start with wanting to run a MW at 125 amps draw from 12v battery bank via inverter. Have experience that says make that 125 approx 25% draw on the bank. Means need four 6s or equivalent. Can last for days with good solar and two 6s, but then that goes way over the 25% draw with the MW. So needs four even though really only need two.

Truck camper can take four 6s if you put them or half of them in the truck bed in front of the wheel wells before sliding in the camper. Connect the wires when the camper is part way in so the wires will reach, then slide in the rest of the way.

I don't believe in the usual rule of thumb for how much solar to have for how much battery. Solar helps keep the battery from going down so fast between generator charging sessions. It can stall the next generator session till October from the last one in June, but it is still a stall. At some stage, depending on the weather, out comes the gen.

What counts is how much battery you need to get by no matter what. If your scenario is a long weekend and recharge back at home, or maybe you have to go to storage and no 120v there, so now what? Or you do a month or two off-grid with lots of sunshine---scenario is everything.

Once you have the battery bank issue solved, "some solar" is gravy. Generator and charger is more important because it works no matter what the weatherman does to you.

12V panels have a use. But not for me as the panels are much more expensive than 24V panels per watt and take more space per watt. Even in 2014 my 750W MPPT system was only $100 more with less space and less installation than the equivalent 12V panel system.

OK, this introduced another tangent to the process... what is the difference between 12V and 24V panels, and why should it matter?

obiwancanoli wrote:
OK, this introduced another tangent to the process... what is the difference between 12V and 24V panels, and why should it matter?

12v are usually 36 cell (~.5v/cell or 18v Imp) less than 200w
'24' can be 60 or 72 cell, usually >200w

For a '12v' batt bank, '24v' needs mppt.

You can consider 24v as 2 x 12v in series although not a good analogy when it comes to 60 cell!