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Small Cabin Forum / Off-Grid Living / Final off-grid wiring
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beachman
Member
# Posted: 17 Feb 2015 09:07
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Hi all. I have been trying to put together this solar set up and I need some final assistance. I have researched this thing, gone to the NAWS forum, and everywhere else. My next step is professional help (some say I really need this in other ways). Anyway, here is where I am at. I have small needs about 750KWH per day max! A few lights, a 12v water pump, a cell phone booster, a satellite radio and maybe a small TV screen for movies at some time.

I have a 235 watt 12v panel that gets about 60% full sun each day (when it is shining). To get 100% would be a long trek from the cottage. This is connected to a Blue Sky 2025 MPPT charge controller (CC). I have 2 6v L16 Trojan batteries in series (I think) to make 12 v and 370 AH at 20 hours. I also have recently purchased a Trimetric battery monitor, shunt and SPD, and a 1000W pure-sine inverter that I will hook up to a Square D distribution box to fun to various outlets and switches around the cottage. The system is properly grounded as far as practicable and works reasonably well so far (there is no ground attachment to the CC).

My questions relate to the setup of the breakers, disconnects, fuses and SPD before the connections to the inverter. I was thinking of putting a disconnect in between the panels and the CC, (I currently have a 30A fuse between the CC and the batteries (close to the + battery terminal), putting a 15A breaker on the #14 wire to the 12v water pump + side, getting a small (combiner??) box to house the small bus bars G, - and +, the shunt and the Trimetric SPD. Then run wiring to the inverter with a 60A breaker on the + side to protect the inverter and to disconnect when needed. I will run the system ground to the ground bus in this box, to the SPD and to the inverter taking care not to bond anything as the inverter has an internal bond.

I have a generator that I can use with a charger to cook the batteries occasionally as the CC will not equalize. All of the YouTube stuff and everything else glances off these topics and one has to glean as much as possible from pictures and momentary comments. Does any of this make sense? I kind of feel like a new welder at a used gas tank factory.

sparky1
Member
# Posted: 17 Feb 2015 09:58
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I have small needs about 750KWH per day max!
your kidding me---huh.
750 thousand watts? ?

MtnDon
Member
# Posted: 17 Feb 2015 09:59
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Quoting: beachman
putting a disconnect in between the panels and the CC

Good idea if only because it makes it easy to disconnect for any maintenance. Keep the fuse

Quoting: beachman
putting a 15A breaker on the #14 wire to the 12v water pump

Definitely

Quoting: beachman
a small (combiner??) box to house the small bus bars

Anything to keep from accidentally shorting them

Also it is a good idea to have some tools dedicated to whatever nuts and bolts may be needed to tighten, etc from time to time. Wrap the entire thing with tape, except for the one end that will be used. Wrap screw driver shank if any used near the batteries, etc.

Quoting: beachman
60A breaker on the + side to protect the inverter and to disconnect when needed.

As long as the breakers are all rated for DC use at the system voltage or higher. There should also be a fuse (preferably a type T) in case of an accidental short. Both sized to maximum inverter draw at surge rating of breaker. Fuse close to battery; breaker wherever handy but away from batteries.
Quoting: beachman
30A fuse between the CC and the batteries (close to the + battery terminal)


You want the fuse close to the batteries but placed where if it blows there is no danger of the fuse arc igniting any hydrogen. Or a fuse that is fully encased to prevent an arc in the air.


Quoting: beachman
have a 235 watt 12v panel that gets about 60% full sun each day

If by that you mean it is shaded; that is not too good. Has this system been running and does it charge the batteries sufficiently? With a 370 AH capacity I would say you are under paneled. That does depend on how much you draw out of the batteries.

I have to run out right now , no time for the math, but I'll check back later

MtnDon
Member
# Posted: 17 Feb 2015 10:47
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I think you must mean 750 watt hours, not 750KwH, not with only 370 AH x 12 volts = 4440 Watt-hours or 4.4 KwH of battery.

So assuming that is right 750/4440 = about a 17% draw down. A conservative amount.

Those batteries could safely be charged at a rate of 37 amps (10% of the AH capacity). The single panel can not come close to that. If there is sufficient sunshine the panel could re-charge to 100%. If not you could run into deficit charging. The battery getting a little more discharged every day. That's not good for the battery health when that occurs regularly over time.

With a tall case battery like the L-16 the higher amps has a second use. It stirs up the electrolyte. That is necessary to prevent stratification; more dense acid solution at the bottom, lighter at the top. That promotes sulfation and that shortens battery life. You get enough voltage to make the CC think everything is okay but it is not.

I would also check to see that the CC is using the voltage set points that Trojan recommends for absorb and float. Trojans recommendations are a little higher than some. Under volting those can also lead to early battery deterioration.

Check the charge with a good hydrometer instead of relying on voltage. I know creeky is going to say you should have LFP and avoid all that. Might be some truth to that but they are more $$ and not perfect for all applications, IMO. Let's just say we all make our own decisions on what batteries to use, for whatever reason is valid to ourselves.

beachman
Member
# Posted: 17 Feb 2015 12:32
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Yes 750 WH - Sorry! 750KWH would run a small town! Thanks Don - and Sparky for the heads up on the usage. I will try to get a box to house the items as mentioned. The 30A fuse from the CC is housed so it should be safe. With the battery monitor operating, I should be able to keep an eye on the battery health. If the batteries are showing signs of depletion, then I will probably add a panel and maybe switch to a better MPPT CC that will equalize the batteries. I have a hydrometer and I will put it to good use this year - Thanks again.

creeky
Member
# Posted: 17 Feb 2015 13:51
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ah. MtnDon. he's already got the batteries. too bad. could have saved quite a bit of money in the long run.

not to mention no worries going away for a couple of months. no maintenance. no off gassing. no worrying about sulphation with partial discharge. etc etc etc.

but I wasn't the first to point out that LFP looks perfect for off grid. and, what, 3 months after I posted my discovery Princeton Phds released a report proving my point. But, hey, sometimes it's better to spend a little less money a lot of times over a long period than a bit more money once. for sure.

beachman you've got a really good system there.

MtnDon makes some good points tho. i'll just fill in a few details

a 60A breaker between your batteries and the 1000 watt inverter.
1000 watt inverter, on surge, 1600? 2000? = 150 amps plus/minus. so as MtnDon suggest. you might want a bigger type T. say 2-300 amps.

this is a good system, but: for those looking at similar systems.
1) get a CC that can equalize. most chargers can't. even run by the genny. the RN/BN series from Tracer has equalization. equalization is very important.
2) a smaller inverter using less idle draw??? a 300 watt morningstar would suffice here. but with the 1kw beach has some future proofing for sure. run a small microwave with that thing.
3) and as I've seen/noted many times. most solar systems that people are happy with, use 1 amp storage at 12v to 1 volt charging (or better). so your 235v vs 370a. beachman if you get a chance I'd toss in another panel. you will like.

but. just like LFP. There's the "perfect" way. and there's the "good enough" way. and with solar good enough is great. and, to my mind, you've got a great system. it will treat you well for years to come. enjoy.

creeky
Member
# Posted: 17 Feb 2015 14:11
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oh. and another two things.

you mention #14 wire to the pump. but for those who are looking to build systems similar. wire gauge is really important.

so what is the gauge between the batteries, the fuse, and the inverter. If you want 150 amps ... #1?

the CC will run up to 25 amps. So #10? should do it.

remember. with wire sizing. it's the amps that counts. that's why higher voltage is good. because it means the amps are lower and thinner (cheaper) wire can be used.

and I only recently discovered that running a genny based charger is hard on the electronics of your inverter. so an ATS (automatic transfer switch) that bypasses the inverter and runs your "loads" while charging is a real good idea.

whew.

beachman
Member
# Posted: 17 Feb 2015 14:58
Reply 


Creeky - Too late for me about LFP as I got the batteries a year ago. Maybe next time around. Good point on the increase in the inverter breaker (and fuse) - will do. The wires from the battery to the inverter are #1STD which is equivalent to about #2AWG (or a little better). The run is about 5 feet in total (or less) to the inverter but will run to a shunt on the - side, and a fuse and a breaker on the + side. I plan to use #10AWG to run from the inverter to the Square D distribution box - about a 2 foot run - then #14AWG for the general house wire off of 15A breakers. For the novice - you really have to dig to get wire sizing right. I have had the luxury of the winter to do research and will put plans into action this spring. Gotta love this forum!

creeky
Member
# Posted: 17 Feb 2015 17:59
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square d. they're DC capable. nice choice.
I'm not sure: QC breakers I think?

ya. you just need a bit better than #2. That's only good to 120 amps in copper if I remember right.

great job.

MtnDon
Member
# Posted: 17 Feb 2015 18:37
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Quoting: creeky
square d. they're DC capable. nice choice.
I'm not sure: QC breakers I think?



QO Good for use on up to 24 volt DC systems, with a caveat.

Don't use them on large gauge wire that connects directly to the battery. The QO does not have a very high AIR rating; only 5000 amps IIRC. A shorted battery can easily go over that. Best practice would be to have a type T fuse from the battery to all other circuits. Those circuits can then be safely protected with a QO breaker. Or use a Midnite DIN rail mount breaker; good to 10,000 amps.

Steve961
Member
# Posted: 17 Feb 2015 19:12
Reply 


The problem with the Square D QO breakers, at least for me, is that the enclosures for them are so large. I have started using the Midnite Solar DC breakers and Baby Box enclosures for them. The breakers are only $11.35 from NAWS and come in many more amp sizes than the QO breakers.

Midnite Solar DC Breakers

MtnDon
Member
# Posted: 17 Feb 2015 20:25 - Edited by: MtnDon
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NAWS also sells lengths of DIN rail for them so you can mount them anywhere, in anything. Darn near. Doing that might not meet code, but for a non-inspected site that works.... only as safe as the build though. I've used them before and after the charge controller which is in a cabinet with a lock; so it's safe enough for our situation.

DIN Rail

beachman
Member
# Posted: 27 Feb 2015 17:55
Reply 


OK, More research and questions. One thing that still bothers me is why I should have fuses if I have breakers. Aren't they the same thing? Why both?

MtnDon
Member
# Posted: 27 Feb 2015 19:03 - Edited by: MtnDon
Reply 


Not fuses, but a fuse. A type T fuse in the heavy wire from + battery to + inverter terminal. That fuse as close to the battery as practical. Type T is a fast blow, virtually instant blow fuse. It is also completely encased so if/when it does blow there is no visible flame arc so it can be very close to the battery and have no hydrogen ignition danger.

Then a big DC breaker, probably closer to the inverter for convenience. This is to use as a disconnect, a big on-off switch for the inverter DC power supply.

Batteries are capable of delivering huge amounts of current if there is a short in a large gauge wire. A circuit breaker may not react fast enough to prevent damage at times. Hence the type T fuse which will blow rapidly when the overcurrent reaches the value of the fuse.

That is the safest battery to inverter connection. many don't bother and most never have any problems. Cheap safety insurance.

beachman
Member
# Posted: 27 Feb 2015 19:20
Reply 


Got it! Thanks.

Steve961
Member
# Posted: 27 Feb 2015 21:32
Reply 


The easiest battery fuse to use, IMHO, is the terminal fuse block from Blue Sea Systems. It's easy to install, is as close to the battery as you can get, and has fuses ranging from 30 to 300 amps. The fuse block and fuses are available from Amazon for about $20 and $15 respectively.
BlueSeaTerminalFuseB.jpg
BlueSeaTerminalFuseB.jpg


Bret
Member
# Posted: 28 Feb 2015 09:17 - Edited by: Bret
Reply 


http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=26&productCa tName=Combiners,%20Disconnecting
Any thoughts on using these for a small sysrtem? Two uses in one.

Truecabin
Member
# Posted: 28 Feb 2015 11:44
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beachman my system is about same size as yours but my batteries are 5 years old and dont hold what they used to. my inverter charger can equalize but i havent been doing it. in the beginning all the details were overwhelming and i somehow did not start the habit of equalizing now i see my inverter instructions recommend equalizing at least 4x per year and even every month i bet i have equalized 4x in 5 years but im on the program now

Quoting: creeky
and as I've seen/noted many times. most solar systems that people are happy with, use 1 amp storage at 12v to 1 volt charging (or better). so your 235v vs 370a


creeky can you clarify this benchmark with regards to beachmans numbers 235watts and 370 AH?

creeky
Member
# Posted: 28 Feb 2015 15:05
Reply 


Yup. I developed this basic rule of thumb about 5 years ago. When I did my initial research I noticed that off grid, either full time or RV boondocking, the folks who were happy with their systems typically had 1 watt of solar panel per 1 amp of battery capacity (measured at 12v).

The rest grumbled about "genny time" and worse. with lead acid over discharge & under charge = dead battery. There could be a topic on this.

so with Beachman, mid summer 235 watts of power is probably fine. Six hours of sunshine x 235 less line/battery losses. He's all good. But in the shoulder seasons and winter. He's probably gonna want more panel. Couple of rainy days... etc.

Math: with 370 amps x 12.7v = 5kw power. His usable power for max. lifespan on the batteries is then @ 20% discharge. 1kw. Using .75/day. That means he wants to fill his batteries daily.

I don't have a problem with that. Basically that's what I need to do too. And I've been doing that for the last two years. 365/24/7. So it works. (previous 2 years with this system my fridge was propane so I wasn't using as much power. I had 2-3 days if nec. And spent $450/yr on propane.)

But back to the few rainy days. Now you really want extra power. A rainy/cloudy day. His panels are making 1/2 power, 1/4 power, 1/20th the power. And he needs to make up 1/2 kw min.

I think that's the thing about off grid power. You, to some extent, have to build for the 30-70% days. The top 30% is gravy. The bottom 30% is genny time. (pick a ratio...

There is also the issue of getting enough power to quickly charge the batteries (avoiding sulphation) and equalizing. Which is best done with solar, imho.

hope that helps. (and points to why I like LFP batteries so much. Didn't get a full charge on your batteries? LFP doesn't care. Lead acid ... yikes! Left your batteries partially charged. LFP doesn't care. Lead acid. Dead!)

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