Wiring Thread: This stupid safety device started alerting that there wasn't safety!

The Something Awful Forums > Discussion > Hobbies, Crafts, & Houses > Wiring Thread: This stupid safety device started alerting that there wasn't safety!

Tom Guycot: Oct 15, 2008; Chief of Governors

I hope this is the right thread for this kind of thing since I see some recent posting about solar systems, but I'm curious if anyone can point out any red flags in my DIY solar project. I'm looking to make a solar system for my parent's cabin. This is a 100% off the grid place, no running water, will never have electrical hookups, etc.

At the moment there is power from 1x 100w panel going into a PWM controller and 2x 12v 100ah batteries which I put together and installed for them. This gives all the power ever needed to run the lights at night, and charge people's phones, run small fans, etc (there are 12v USB outlets, and circular car outlets inside). They also have a small 2200w generator which goes into a completely separate circuit (theres no chance at all of cross connecting things between the 12v wiring inside, and the 120v wiring), split into 2x 15a ones in a little breaker box. This powers a small AC unit on really hot summer days, coffee machine, a TV, vacuum etc when needed.

I've had the idea for a while and finally want to act on it, to add a solar system that can mostly replace the generator, as I hate the idea of consumable fuels, and they would have 120v power available without having to go start the generator. To simplify things I'm not going to touch the cabin wiring, so all the lights, phone chargers, etc will still run on the isolated 12v circuit, the solar system will just plug into the 30a RV plug the generator now plugs into to do the 120v activities. This will also let them plug in and use the generator if there isn't power available in the solar system.

This is a real rinky dink DIY log cabin, thats been added onto and onto for decades, and no one is looking to do some extravagant build, BUT I have a very very healthy fear of electricity and how much it wants to kill you. This wasn't as much of a big deal with the one little 100w panel at ~20v and 5amp or so, but with this bigger build, that can scale up higher, I want to make sure I've crossed every T, dotted every i, and that I don't have any red flags. I've been doing months of research on all this, solar systems configurations, controllers, wire sizing, etc. On that note a lot of the wiring is over designed for what It could probably get away with (at least i think so...), but I'd prefer to err on the side of caution and have margins for any future expansion.

This is a diagram I did of how I envision the system, though I plan to only start with 2x series of 4 panels for 800w total, but I wanted space to expand it in the future if it proves successful:

If anyone has any opinions on red flags I'm missing here, please call me a loving dumbass for dancing with the electricity gods and let me know, or even just any advice/suggestions for things I'm looking at wrong.

# ¿ May 28, 2022 23:51

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# ¿ May 9, 2024 12:16

Tom Guycot: Oct 15, 2008; Chief of Governors

Thanks for all the responses! I really appreciate all the advice.

babyeatingpsychopath posted:

This seems OK. I would ensure that you're breaking both legs on your circuit protection devices, and not just the + all the time. Fuse both the + and - of the panels, definitely both the + and - of the batteries, and use a breaker that's DC-rated for the maximum current your system can supply before your inverter.

Rest of it seems solid; good job.

So, to make sure i'm understanding correctly, all the places I have fuses or a breaker just on the positive line, i should put another fuse/breaker of the same capacity on the negative side as well? So for example I have in my spreadsheet of all the parts i'm looking to get the 200a DC breaker to go on the positive line between the batteries and the inverter, I should buy a second identical breaker to go on the negative line? and do the same for the other spots?

Also, when you say 'a breaker thats dc-rated for the maximum current to the inverter' I'm a bit confused, as I was understanding it, the breaker between the batteries and the inverter sizing should be based on the inverters watts/batt voltage, with a 1.25 safety factor, so 3000w/24v * 1.25 puts that at a 156amp breaker, and rounding that up getting a 200a breaker there. Is that not correct? What should I be sizing that one on then?

H110Hawk posted:

Just tips and tricks since an actual person who knows what they are doing has commented on your picture - have you ever wired up a high voltage/current DC system? You're going to want to keep some blankets around to cover your panels while doing the hookups so they aren't producing while you are messing around - remember it's a chemical reaction. I think they make specific things, but soft moving/furniture blankets should be fine. Once you have your strings hooked up you should be fine. Remember not to become a path to ground.

How are you planning on racking and mounting this stuff? I would just love to see this setup in general. I would get the batteries up off the ground in a rack of some sort, and strap them down. If they're going to be inside or at least directly accessible/attached to the primary building consider a polypropylene tray and acid neutralizing pads, or a BIG box of baking soda. PIG pads seem to be pretty spendy, and you definitely don't need a 50 pack. If it's in an outbuilding I would store a couple of the like 10lb boxes of baking soda. It's a couple of bucks, and if a battery decides to boil over you will be glad you have it as a way to turn a big pool of acid into neutralized slurry. Heck I bet those pig pads are just doggy piddle pads impregnated with baking soda. I only suggest spill control stuff because you're _so_ remote. Don't breathe the H2S they let off it's very bad for you.

Remember you need to ventilate this room. I don't care how sealed the batteries are, slap a low vent on the door and a high vent on the opposite side of the room, you just need a basic convection draft. If they have vent tubes, which are just a few mm OD, loosely zip tie them together and extend them out away from your living space. If it gets hot where you are putting these you might need a little fan just to pull the draft, but try to make passive convection your friend.

Set a calendar reminder in your phone to annually isolate the batteries (turn off both disconnects) and unstring them, test their voltage, clean their terminals, and generally inspect them for premature wear. They shouldn't be bulging, warmer than the rest, or showing excessive (or really any) corrosion. Buy a tube of dielectric terminal grease and leave it on site. At 5 years you need to be considering replacement, at 7 years just do it. Or at least test fire your generator. If you want to do a load test, string them back up, hook up your meter, and turn on the load (house), and then turn on a space heater or something to max, maybe two. If your voltage drops more than it did the year prior you might have a cell starting to go in one of your batteries. Note this down in a notebook you leave on the rack with your equipment. You will thank me if one day your usual 26V nominal string that goes to 25.5V dips to 23.5V under the same load. I'm just making those numbers up, but it can help you get ahead of problems before they ruin a weekend.

https://www.autozone.com/greases-and-gear-oil/dielectric-grease/p/permatex-dielectric-tune-up-grease-3oz/34495_0_0 (I think this is right, you want the tube not the little "so you're changing your car battery" packet.)
https://www.amazon.com/HAMMER-Baking-Soda-13-5-Pound/dp/B002SKVZIQ (Get this at a bulk discount store in the laundry section. If a battery _goes_ you will be using the whole box don't be shy.)

Overkill? Probably. I just like people to be prepared with their dumb ideas.

Thanks! Thats some super helpful advice on the batteries and their maintenance, and I added those links to my spreatsheet to look at later.

I already planned to put all the batteries and inverter, and well... everything, out in a shed thats next to where the panels would go as I wanted to at the very least physically isolate everything away from the cabin. I know theres vents up near the ceiling, but thats a good idea to make sure its vented down below too, and I was looking at doing a little hood with a fan over the charge controller and inverter to take away heat if it needs it, so it sounds like I may want to do that too over the batteries. My original idea was I wanted to sort of build a shallow insulated tub around where the batteries would go to insulate them in the winter, and it sounds like I need to make that tub idea a lot more robust. Thanks!

As far as the mounting for the panels, they're going to go on a treated wooden A frame stand of sorts, like the one I built for the existing panel, but lengthened, anchored into the ground, and with a heavy beam across the top to try and mitigate any trees that might fall over on it. Nothing fancy there.

babyeatingpsychopath posted:

Meant Current, not Voltage. Good catch (edited).

Also worth pointing out that lead-acid batteries are positively subtle and sedate when it comes to dead-short conditions. The battery boils and pops, spraying hot, pressurized acid everywhere, and perhaps there's a bit of a hydrogen explosion. Then it's done with its drama.

Lithium batteries just catch fire in a way that makes the fire hot enough that spraying water on it breaks the water apart, which immediately recombines in a hydrogen-oxygen flame, making everything so much worse. Cover the whole thing in a few feet of sand bad. Bad enough that, if it were a car, the easiest way to extinguish is to drop the car into a dumpster full of water and just let it soak for HOURS.

If those are dirt-quality cheap-rear end batteries, then you will be able to pull out 3000A for an entire hour without any component of the system being stressed. If they're good batteries, then you can probably do 8000A for half an hour, or 100A for 100 hours. A hundred amps, continuously, for four straight days. And that's within limits: that's what they're DESIGNED to do.

Storage is hard.

I haven't decided on what type of batteries to use yet, though with as cold as it gets there in the winter i've been thinking li-on is pretty much out. Some kind of battery warmer idea was getting things too complicated. I'm still not sure on if those sealed, or gel, or just traditional lead acid will be better and which to go with, let alone which brand. I've seen some of those big all in one high capacity units and stuff but they really just seem to get way too expensive compared to just putting together a bank.

On your last point, I'm a bit confused on what that means, does that mean the batteries will fail if under a load of 100A after those 4 days? What, I guess is what i'm trying to come up with the words for, what is the "safe" continuous draw you could pull from the batteries of a 300ah*24v system with good batteries? At what point does it become a ticking bomb?

# ¿ May 30, 2022 03:47

Tom Guycot: Oct 15, 2008; Chief of Governors

An update on the solar system I'm putting together for my parent's cabin that I posted about a month ago, and thanks for all the advice from people in this thread!

I've got most of the equipment for it now (still a few small things needed), and this past week finished constructing the stand for the panels and got the space ready for the batteries and electronics to be installed in. The frame has space for 12x 100w panels, though I've only got 8 to start with to see how things go. Its going to be anchored into the ground as well, but for now as theres not as much worry of an empty frame getting picked up by wind I just have some blocks on it.

There are some things I'm wondering about though, if anyone has any advice.

One of the things I still need to get is the heavy 2/0 AWG cables for the battery interconnects and to the inverter, however I'm not sure what (if any) difference there is between using a cable connector that clamps onto the battery terminal post, or a cable with a ring terminal to get screwed down to the lug? Is there any difference in connecting it one way or another, IE any sort of max ratings for amps or anything? The circuit breakers I have, have connectors on them to screw down a ring connector, so I just kind of assumed that connector would be fine on the batteries as well but.... I know assuming things can get yourself into trouble, and I haven't been able to successfully google an answer to that question so if anyone knows I'd be appreciative.

I'm probably just being overly cautious but, well I'd rather be that than the alternative.

Another thing I'm a bit uncertain about, as I've read conflicting things online, but should the ground wires coming off the inverter, charge controller, and even combiner box, be all tied together, or just all be independent to the ground? Does it matter with distance as well, because the inverter and charge controller are next to each other, but the ground from the combiner box is maybe 25-35 feet away from the rest of it?

babyeatingpsychopath posted:

Note that, like with all electricity, you must have a complete circuit, and current flows in all conductors of that circuit. It's possible to have the - wire be the faulted one, and you'll still get massive current -- except that current must now go through all the devices in order to blow the fuse on the + wire. There's no reason NOT to fuse both lines. Use 2-pole fuseholders on everything, and 2 fuses. DC fuses can be very small even at extremely high current ratings, so it's not much space. A single-pole fuseholder is $30 and the fuse is $3. A two-pole fuseholder is $40, and two fuses is $6.

As far as the breaker, here's a "find this at Home Depot" breaker: Example link. Note that the "voltage range" is 120/240VAC. It is not rated for DC at all. It is not designed to interrupt DC current, and may fail to trip, fail to open, or explode if used to interrupt DC current. However, a breaker like this is rated "120/240VAC, 120VAC, 48VDC" and will properly interrupt DC current. It's not sizing, it's rating. Sizing all comes out of the applicable sections of the NEC.

To the last point, it's a battery. If you have a AA battery that says "1250mAH" then you can pull 125mA out of it for 10 hours, then it's discharged. You have to recharge it now. Same with your batteries. 300AH of capacity gives you 300A for an hour, or 30A for 10-15H, or 3000A for a couple minutes, or 30,000A for a few seconds. Then the battery is dead and needs to be recharged. If your BMS is at all intelligent, it will be connecting and disconnecting batteries as the voltage indicates charged/discharged depending on whether or not you're asking for or supplying power. Which, I just noticed, you don't have at all, unless your MPPT has integrated battery management.

Once you've selected equipment but before purchase, look at the equipments' install sheets and see what their recommended wiring is. There are some installations that want fusing on the input and output, some on the input only, and some on the output only. Regardless, check in the "rated voltage" section of everything and make sure it specifically says 24VDC or more. 120VAC is not more than any VDC; it's not the same kind of voltage, and a VAC rating does not compare in any way to a VDC rating.

Bit of a late reply, but I wanted to say I appreciate the advice. The circuit breakers I had sourced were DC ones specifically and all the specs look correct so I'm not worried about having the wrong kind, and I plan to put one on the + and - as suggested as I'd much rather be safe than sorry. However, I'm curious why it is every bit of advice and diagram I could find online, even from solar system manufacturers only ever says to put the fuse or breaker on the + side and doesn't for the negative?

I'm also planning on putting in a disconnect switch between the batteries and inverter, which again in every diagram and suggestion online only has that done for the + side. Is that another case where I would want to put a disconnect switch on the + and - side?

# ¿ Jul 11, 2022 00:42

Tom Guycot: Oct 15, 2008; Chief of Governors

Methylethylaldehyde posted:

https://www.solar-electric.com/lib/wind-sun/PV-Ground.pdf

That PDF gives you the NEC guidelines, and a decent picture showing all the parts of the system that need grounding, and where the grounding wires need to go. Assuming you do NOT have any utility service of any kind, the Figure 2 diagram on the pdf is what you should do. At least one ground rod, preferably two, tied together with wire based on the largest ungrounded wire in the system.

Rotohammer is the easiest way to drive a ground rod, though a sledgehammer and a helper can also work.

https://www.electricallicenserenewal.com/Electrical-Continuing-Education-Courses/graphics/sectionPics/large/qid867.jpg
This is the chart for determining the size of the grounding wire that ties the ground rods to eachother and to the service disconnect. Use the largest wire size your system uses (not counting the battery wires) to determine the sizing. All the grounding wires should be that size.

movax posted:

That is strange to me (putting stuff on both the positive and return sides) � I would only put it on the positive side, personally. I can only think of once in my career where I put a fuse or other element on the low-side / return of a system and it was a really weird case.

You optimally want return / �GND� to be an infinitely sized / zero resistance / equipotential plane � if it�s not, current flows anytime there is a potential difference. Adding fuses / other elements with some resistance that can vary will make what I just said harder. On a PCB for example w/ digital logic (so not solar at all), that can cause issues when you have an input who�s VIH is say 0.8 V, referenced to �ground�� but if ground is sitting 200 mV higher at one IC vs the other, you just lost margin.

Current flows in loops � as long as you can point to something near the start of that loop / the source of energy that is a protective element, you�re good.

babyeatingpsychopath posted:

I'll fully admit that the state of fusing may have moved since I was last into DC and solar heavily. I also lived in a state where just because something was touching the ground, didn't mean it was well grounded; very very low soil moisture and not many minerals. Myself, I tend to err on the side of caution. I would put fuses on both legs coming from the PV strings and batteries because it's just very very cheap insurance. For the rest of it, if the manufacturers don't say to put protection on the -, then you don't have to.

Cheers! Thanks for the links and advice everyone. I'm trying to operate everything on "better safe than sorry" rules, so more caution, even if it costs a couple bucks more is worth it as long as it isn't detrimental.

Regarding batteries, I initially was planning on the wires coming from the charge controller to the batteries, and the cables coming from the batteries to the inverter being on the same posts, but recently I was reading someone suggesting instead to have them on opposite ends of the bank (the dashed lines in this picture) to balance the batteries better. Is there truth to that, or does it not matter if they're on the same connection?

# ¿ Jul 13, 2022 04:26

Tom Guycot: Oct 15, 2008; Chief of Governors

Battery series/parallel stuff always gets me going cross eyed after looking at it too long lol.

So, as far as "from opposite sides" compared to what I was thinking before, is this wiring arrangement what would be appropriate to better balance the load for it? Where I have one lead on one of the "24v batteries" basically, and the other lead on the other "24v battery"?

Also, though this is of no practical concern, out of curiosity, where you have the series being made, is there a sort of... industry or regulation color for a cable going from + to - side? Like are those typically done in red or black or some other color? Again not that that matters in the slightest it just made me curious when I was shopping for 2/0 battery cables.

# ¿ Jul 15, 2022 21:05

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