Best Solar Charge Controller? And Series vs Parallel Wiring

[Scalf77]

Tare loss refers to the efficiency of the controller, while it would be true that you would use more power in a MPPT system, the extra power it gets from the panel in most cases make up for it. So again it comes down to if your voltage head room is enough to give you that advantage. With a good vendor, I don't think that would be my highest priority in choice. Tare loss will usually be specified as %.

While the actual power consumed by a PWM controller would be less, than a MPPT, the MPPT usually makes up for it by harvesting more power from the panel. So you most likely will see PWM controllers specifying just the conversion efficiency, while a MPPT controller may specify it as a whole.

Power of the controller to just to stay alive (at night) is usually specified in as self consumption.

Both of these areas is where you pay the extra money, and why the generic controller on Ebay is so much cheaper. You can usually design it cheep or efficient, not usually both.

-greg

[E350]

Thanks Scalff77!

Apparently tare losses (or idle converter losses or nighttime losses or consumptive losses) are not so important to grid-tied systems, but for small off-grid systems like ours can be a real battery drain.

From June/August 2013:

http://midniteforum.com/index.php?topic=153.15

mtdoc: "I'm actually fine with a 6 watt idle draw since I am grid tied and have a fairly large system - though of course lower is always better. But for those with smaller, off grid systems every little bit is important. I know that the poster Willy seemed quite concerned about this number as he had posted over at the NAWS forum as well."

Willyarnold: "I bought my Classic 150 on Black Friday of last year (2012) and when I checked, I believe it was drawing about 4 watts on idle (Klien clamp meter). I guess if you have a big system or a grid tie system, that's not a big deal, but right now I have a standby/emergency system and until I go out and invest in a battery bank, just one 4D battery. 4 watts x 16? hours will cycle my single battery (which is not otherwise being used) more than I would like. And please forgive me for bringing up the competition, but Outback has got theirs down to less than 1 watt on standby. I had read the above quoted statement when (or maybe before) I bought my Classic believing that in time you could bring the idle draw down in firmware.

"The idle draw is important to us and I can assure you we will work to bring that way down. Possibly even having a super sleep mode based on sunset and sunrise where we turn almost everything off." - Halfcrazy

I guess at this point I am asking if there is anything I can do to bring my idle draw down as much as possible. For instance, if arc fault is a constant draw, can I disable it completely? (even by cutting a wire?)

If nothing else, maybe I can set up a way to just disconnect it every night.

Thanks in advance for any input you guys can offer."

I remember that tare loss or "idle draw" occurred in my Xantrex MPPT charge controller so much that I was also turning it off at night. So I guess when looking at controllers it is important for us to distinguish between controllers designed for grid-tied applications where idle loss is not so important and those controllers designed for small off-grid applications where we fight for and want to keep inside the battery every amp we collect.

So, I will be comparing tare loss numbers across the controllers I compare and I will be including Outback in my comparison.

BTW, from the above link, I liked this succinct formula:

"Well 4w times 16 hours is 48Wh so at 12 volts that is 4AH"

which was posted by halfcrazy and showed how he calculated the tare/idle loss to be 4 amp hours over a 16 hour night. I guess the only thing to add to that formula would be how watts are calculated which is: volts x amps = watts

http://www.crownaudio.com/ohms-law.htm

I have a Victron BMV 600 battery monitor which is way too smart for me, so I am considering installing the 5Amp version of these things in line on every amp drawing item in my van:



http://www.ebay.com/itm/131269460493?var=430549583129

[daveb]

I find this thread as great ammo for my limited knowledge of solar, but really I’m not worried about the small difference between the type controllers. I do see the need for being able to pull as much out of an array in fog, overcast or low light situations but feel the issue should be directed more towards battery reserves. I agree that the solar array needs to be sized to the battery bank to some point but there is a fairly large gap to play with. Grid tie systems need to pull out as much as they can because it offsets the power bill in most situations. I don’t need that. With both PWM & MPPT controllers, 90% of the time I’m charged up by 10AM. Even with a single 135 watt solar panel, on a sunny day I found my dual 4-D batteries were brought back up to full SOC even with the refrigerator running. What counts is the nightly load and if the battery reserves can get you through the evening and how well the battery is charged which promotes battery health. Batteries are a very expensive item on board. So I look at how the controller charges more than I worry about grabbing an extra amp or two of sunshine. That said I really have drunk the salesmen’s kool aid and just went with their recommendations…MPPT.

I have either a fan or heater that runs along with the fridge I need to take into consideration and sized my panels and battery bank to that.
IMO what hits RV owners is the battery reserves and how far down your battery voltage is reduced overnight. Solar does nothing for that. I also don’t expect solar to “run” things during the day. The difference in an amp is negligible unless I’m subjected to low light conditions. The problem I see with low light conditions is there just isn’t enough room for panels to make much difference in charging. I feel rooftop storage is more important than a couple extra panels. YMMV. I do see the shading effect as being a problem for those who like to hide in the trees but at some point during the day I get enough sun to bring two 4-D batteries to full charge. The times I have problems are when the panels are stuck in a day or more of overcast and being the charge current is so low, even with my two 135w panels there’s not enough to do much. In most situations I have either very low charge current (limited sun) or fairly high charge current (normal sun) in respect to two 135w panels. IIRC, when I had a single 135 watt panel (which was a very short period in time), don’t quote me but think I saw a charge current of about 7-8 amps. It was rare when I wasn’t up to full charge by 11AM. My issue was when running the Espar heater at night, some lighting and the refrigerator. I found I was treading towards a 50% battery voltage before morning. I then added an extra 4-D battery. I believe having two 135 watt panels probably did help to shorten the time it took to bring the bank up a full SOC on a normal day, but after adding the second battery, the real plus was seeing a battery bank voltage of 12.4 - 12.6vDC in the morning before sunrise.
I think that those people who frequent the type of weather conditions where the sun don’t shine are better off with a generator and adding a ton of solar to the roof is just a waste of money. Each owner has to figure their daily load but 90 percent of the time my load is less than 3a continuous. I guess if I sat inside running a flat screen TV or massive stereo system (or some other kind of heavy daytime draw) I might have to look at things differently. Besides I'm not much at sitting in camp and usually drive a bit. My alternator does a fairly good job and even in limited sun, the batteries get topped off most of the time with a minimal solar charge. JMO

[Viva]

Good "real life" info, thanks!

My two main power "hogs" are the laptop/mi fi, and my future 12-volt refrigerator. Other than those things I'm used to camping/boating (in the ye olden days when it was iceboxes and kerosene lamps), so conserving seems normal to me. But, there were no laptops and internet then. Nor Eneloops/digital cameras/etc. The thing that is driving my solar install for the most part though is my desire to remove an absorption refrigerator (propane) and put in an Isotherm or Vitrifrigo 12-volt compressor unit. I know that will be a bit of a slave driver, electrically. I had a compressor type Norcold in my '97 SMB (with no solar or generator) and I always felt like I had to just keep driving to keep it going! I do have a generator now in this rig, and would also be willing to live with ice/cooler when necessary, although hopefully that won't be too often. Interesting point about strings of cloudy days being worse then partially shaded sites on sunny days.

I'm in the midst of re-doing the whole charging system (which is all circa 1998 "you will drive from shorepower to shorepower and then plug in" style, and I don't even like campgrounds, much less shorepower). I have three Group 31 AGM's, so that is 375 amp hours (they are not hooked up yet, as I'm not about to subject them to the stock "stupid" charger, which is all I have right now), and could fit up to 470 watts of solar (but not sure how much of that I will fit). I tend to be a night owl, but with LED's that's not so much of a factor.

I'm in the midst of figuring out what size the various wire runs should be, where/how much over-current protection to install, etc. (not speaking just of the solar here, but more the rest of the system). I hope to get things figured out within the next month or so and then rig it up over the winter.

It sounds like you have a compressor/12-volt fridge and manage to keep it running okay most of the time?

Viva

[daveb]

Yup, standard norcold. Most of the time the PC is used at night along with my DVD and surround sound. I'm also an inside night owl when camping by myself. With my heater running when it's cold outside, it does force the fridge run more but I still have plenty of battery left by morning. If I add that all up it's a fairly large load. I can even run the microwave for a couple of minutes on a medium to low setting and not be below 12.3 in the morning. Adding the 2nd 4-D was one of the best moves I've made for my style of camping but it did and will come at a cost when it's time to replace them.

[Viva]

I just looked up the 4D -- so that must mean you have 420 amp hours with two of them. Nifty! Spacewise, I was able to fit the three Group 31's (I got the ones with "extra" amp hours in them), so I will "only" have 375 amp hours, but that's not too far below what you have, so hopefully it will work out. I could possibly fit a fourth battery in a pinch (but would wait to see if it were necessary, as it would be a bit of a hassle). At any rate, hearing your real-world experience is super helpful. Thanks so much for reporting in.

I'm keeping an eye on the Lithiums.... a bank of those would be fanastic - less weight and more effective amp hours since you can run them down below 50% without undue life-shortening. Since I just bought the AGM's, maybe by the time it comes to replace them Lithiums will be "easy" for people like me, who aren't early-adopter-techy types (seems like they are juuuust becoming ready for "normal people").

[daveb]

I can't wait till they come down in price and it seems like it won't be long. The only thing is I still want to do is to solar maintain my starting batteries and I haven't read up on banking standard batteries with the lithium's. Not too sure about charging them either but saw they make some that use regular standard charge methods. I might have to split the panels and have separate controllers for each but I'll do that research down the road. For you Viva, building a new system, you might want to look into it. I feel that it's better to have a small solar panel that charges the starting batteries only, keep the larger system for the house system, and keep the two battery systems separate unless there is a need to jump start the vehicle. It's not really good to bank different types or sized batteries together. Not that I haven't been doing that, but I did switch to AGM starting batteries and think it helped. Before I did I was going through wet cell starting batteries like $#!t through a goose.

[Viva]

Good points and stuff to think about. When I was at AM Solar last spring, they were just running some Lithium batteries on their test panels at their shop. When I stopped in last week, they had already installed a few banks in customers' RV's. I believe they are ones wherein they are basically fit and forget (in other words these customers are not designing charging parameters or etc.). Since I had already bought the AGM's I'll be sticking with them for now, but when they go....

I'm not sure I am mentally grasping exactly how the whole system is going to work yet (part of why it is not installed!). I have a more basic system on my boat, which I do mostly understand and did install myself -- but there is more going on in the van. Some parts I have or will have, but have yet to figure out exactly how to rig up:

1) Three Group 31 AGM's (vs. existing single Group 27 flooded cell - inadequate!)
2) Blue Sea ACR (7622 IIRC) (vs. existing recalled Surepower 1315)
3) Blue Sea On/Off switch (vs. a rocker switch in the ceiling with mystery wiring)
4) ProNautic 50 amp charger (vs. single stage "converter")
5) Blue sea fuse block (maybe? vs. converter fuses)
6) Victron battery monitor (vs. low-voltage disconnect, etc.)
7) New solar panels and controller (vs. 40 watt panel, outdated tiny controller, and miles of probably 18 gauge wiring!)


Where my questions lie is mostly in overcurrent protection (how big), how to wire in the "jump start" feature (which rig already has but I think the ACR will now handle that), how to wire up ACR to not use the house bank to start UNLESS I ask it to, what to do with the converter box once I don't need the charger any more (I would like to use a separate Blue Sea fuse block not all the "built in' stuff), whether I need the automatic transfer switch (for the generator) vs. a manual switch, etc.

This is sort of getting off topic, I realize (except that it's all connected!).
So I am close to having all the components, but have to figure out how to connect them all properly. It will be nice to have a robust system of the type I am more used to vs. all the "automatic" or thinly wired or non-smart things that are in there now. I also can't really do much unless I am plugged in or live like I am in a tent (which is not all bad, but I'd like to step it up a little bit!).

[Scalf77]

E350,
Don't get to carried away, you should be able to get the current draw info using the victron. For every one of those current Ammeters that you installed you would be using 5.5 watts of power per day. See it can turn into a vicious circle. You can always put switches on things that pull power when unneeded. I have things that are disabled when i am in "Boondock Mode" but operate fully while plugged in or running.

Dave,
I agree with you, I think the most important thing is to take care of the battery. That is the area I am willing to spend more money on. It is just as important to look at charging profiles versus just the power you are getting out of solar. I like features such as temperature compensation, voltage sensing, user programmable voltage set points.

Viva,
Where you located, if your going to AM solar, you are probably not to far away, I am in Beaverton, and could probably sit down with you to help you figure some your topics out.

also just throwing out another controller http://www.bogartengineering.com/content/solar-charger The SC2030 from Bogart Engineering is designed to work with the TM-2030 TriMetric Battery System Monitor. (It can also run independently )

[Viva]

Originally Posted by Scalf77

E350,
Don't get to carried away, you should be able to get the current draw info using the victron.

I'm not totally "smart" about all of the Victron functions, but figuring out how much various things are drawing seems pretty simple. Is that what you are trying to figure out, E350? I really like the Victron.

Originally Posted by Scalf77

Viva,
Where you located, if your going to AM solar, you are probably not to far away, I am in Beaverton, and could probably sit down with you to help you figure some your topics out.

What a nice offer. Not only would it be really helpful, but it would be fun to meet a forum member in person That said, I was in Oregon but am now in Arizona. However, I may be heading back to Oregon in a month or so (which will be before I start to tackle the systems upgrades), and if I do I will send you a PM. It would be great to sit down together.

I will look at the controller you linked to. I was provisionally thinking of the Blue Sky 3024 (I think it is), but am in no way committed to it. Have also browsed Midnite Solar's Classic Lite 250 (although I think it is overkill). That's the one component I have not really chosen yet.