So came up with my proposed wiring diragram. Anyone see anything I missed or have wrong?
That… sure is a lot of disconnects you’ve got there.
Ha! Yeah, sure is. Especially needed for the solar and the battery, but I figure I’ll just leave whatever I’m not actually using to charge disconnected, so it can’t possibly draw any power in from the battery to have the electronics turned on. And I like to be able to isolate sections juuuust in case.
It’s 12V. Use a wrench and remove the bolts. You’ve got at least twice as may disconnects as you need there. If your concern is battery draw when shut down, a single disconnect at the battery is sufficient. Are you seriously going with solar, shore power, and charging from an alternator? Skip the 12V-12V converter, put an inverter on your car, and charge from that if needed. I might want more than 100Ah at 12V, depending on loads, but for a couple times a year, it’s probably fine.
Personally, I wouldn’t bother fusing/disconnecting solar panels to the MPPT, the panels are a current limited source, so as long as the wiring handles max current (156% rated short circuit, if you want to go with NEC), those can go. I’d not bother with the disconnect from the charger to the busbar either - if you’re shut down, just disconnect the battery. Same goes for the various charger outputs - they’re not going to drain the battery when connected, and you’ve got the battery disconnect for that. About the only thing the fuses there do is protect things if the charger shorts internally on the DC side, which… eh, OK, but your battery fuse will protect against that, if it’s a dead short.
You’ve got an awful lot of money in useless fuses and disconnects. Get rid of most of them and you’ll have a cheaper, more reliable system.
The 7-pin trailer connector has a 12v up to 30a pin, so I can charge while towing. Which is also when I won’t be using solar, since solar will be ground mount, not roof mount, so they’ll be put away inside the trailer or car. It’s not to charge while stationary, although that’s a last-ditch option that is a safety blanket I don’t ever expect to use, and more while I’m going somewhere.
You make a solid point. I don’t necessarily expect to be anywhere with the kind of problem I’d face, not like something permanently mounted. I will keep the disconnect switch so that I can connect/disconnect without possibly having a spark event. Should I change it to a 2-pole disconnect or breaker? Or a single pole disconnect should be fine?
I’m going to re-read the manuals, I thought I remembered reading they all wanted a fuse on the output, but that might just have been at the battery, not directly on the output. Which that single fuse right at the battery does protect. I guess the only thing they’d help is a short which is less than the fuse on the battery, but still causes heat to build to the point it burns the connection open which could potentially cause a fire.
I probably am way overdoing the disconnects, you’re right. For fuses, I’m a bit OK spending extra to have some extra safety, but putting them everywhere might, indeed, be a bit much.
I guess my thought was every charger which actually isn’t being used might have it’s internal electronics turned on (e.g. the BT, etc) from the 12v side, but fundamentally that means the battery is connected and one of the chargers will end up be in use. Either from towing, or I’ll be setting up the solar, or I’ll be at a campground with hookups. And so any small parasite drain, even at night with no solar, is really going to be quite minimal.
As usual, you’re usually right that the extra wiring/parts/etc isn’t all that worth it, and have very minimal to nothing in terms of practical end result.
For the battery size, pretty sure 100Ah will be plenty. The highest possible draw would be during the day when the solar is up and producing. I suppose I could go the DIY, but as I say, if something should ever happen, even with a well made DIY and comprehensive, insurance might get sticky. And I’m not going to spend the money on no-name random battery pack with who knows what inside.
Expected loads for shorter trips (1-4/5 days):
- Basic LED 12v lighting, some LED strips, some LED string lights or the like on the awning outside. If I have everything blasting probably 50-80W, but I rarely expect that, and I’ll have interior vs exterior on separate circuits.
- 12v pump for clean water tank (no model yet picked, I expect ~10a or less, on rarely)
- Some 12v->USB chargers for phones/tablets and the like
- Small speakers (guesstimate 40-50W speaker system, maybe less)
- 12v compressor RV fridge, 50-80W depending on model/size that will fit
- Possibly my laptop, might just do a 12v->19v boost direct to it
- Possibly a fan or two
Expected additional loads for longer trips (up to 2 weeks perhaps):
- Evap Cooler for hot dry locations (2-4a for fan and water pump), running for a few hours during the day
- Charging Li-Ion battery packs for e-bike/lighting (think festivals), 12v balancing charger, up to 30a total load, would only do during day when solar is producing and expect 2-3 hours total charging time. Will have the 2x235W solar for these things, so should be neutral or only slightly draining on the battery, with plenty of time to make sure the battery is topped off from overnight usage.
Hm, just saw a video where someone uses a ferrule to put on the end of wires for screw terminals. Worth doing? Or is just the usual being careful for stray strands don’t go into neighboring terminal should be fine?
A single disconnect is fine. NEC is a bit belt and suspenders IMO on that point. A load break disconnect on your positive or negative is fine, if you’re doing a solidly grounded system (negative and ground tied somewhere), disconnect on positive.
There should be a fuse somewhere that will open on the charging side, but you can also have all your chargers gang together and then go to the battery through a fuse. Honestly, for a portable system like this, I wouldn’t worry that much about it. Fuse the battery terminals, and accept that there are some screwball, one-off, edge-case failures you can’t really protect against. Solve for dead shorts, but that’s fuses, not disconnects. Fuses are a lot cheaper than load-break rated disconnects.
Correct. Any halfway competent charger shouldn’t have a significant load from the battery side being connected, and if it is, it would be something like an LED. But I usually see that on cheap Chinesium, not anything competent.
Fair enough regarding capacity, I live in a different space where 1.2kWh isn’t useful. Office has 10, power trailer now has 20…
As long as you’re able to shift most of your loads to daylight hours, you’re right, it should be fine. It’s more of a buffer in the system at that point.
If you’re working with “fine” stranded wire (welding cable or such), you should do that before going into a screw terminal (though you can crimp an end on just fine). For normal “course” stranded wiring, no need - just ensure they don’t go splaying off all over.
//EDIT: Regarding the connections for disconnects and such, yes, there’s some safety from them, but there’s also “more connections,” and if you’re going to have a thermal issue, it’s likely to be at a connection, not in a random chunk of wire. So I think it’s entirely possible to build a system with so many connections that you actually end up reducing net system safety. I have a number of disconnects in my office system, but I’m also running ~160V open circuit on the panels (4S), and 48V on the battery bank, so there’s more that can go wrong. A single panel voltage system isn’t nearly as likely to arc, for instance.
I’m not referring to the disconnects, but the fuses I have marked between the chargers and the bus bar. I agree not the disconnects are excess, and of no particular value, but I’m seeing $20-30 or so for Class-T fuses, which seems like a relatively low investment for extra peace of mind for an unexpected edge-case short.
Then again, everything battery-side will be in the same physical space (except the battery, which will be fused at the terminal) and all wired up together right there. So any edge-case short would be something major that probably would hit the entire system and cause the battery fuse to isolate.
I’ll still keep the DC-DC fuse on the car side of things, that makes a lot of sense, and the breaker for shore power should stay there just in case.
As for the rest, I think you’re right, they’re superfluous. And on the rest of the DC side, that’s what the blade fuse panel is for, and they’ll be a lot smaller fuses, so I expect them to go before the Class T on the battery. Which of course I’ll keep one or two spare with me just in case, and have a small multi-meter on hand to trace/tone to check for a short circuit if the battery fuse goes and nothing else.
Which leads me to having just 2 disconnects. Solar to safely connect/disconnect, and battery. The solar will go next to the MPPT, but should the battery go right next to the battery, or should it be on the board with all the rest? I’m kinda thinking right next to the battery, have the shortest possible hot wire.
LOL, yeah, I’m certainly not looking at Solar Trailer storage needs, that’s for sure. I can’t even contemplate needing anything vaguely near even your office. And worst case, if I find I’m starting to get close to that, I can always buy another 100Ah and put it in parallel (after making sure both charge levels/voltage is the same).
I just wish the Victron batteries weren’t so insanely expensive. It’d be nice to tie their built-in BMS system into the rest natively, but being $350 or more expensive, PLUS needing to buy another component to get other components to talk to the BMS, my system fundamentally doesn’t need any of that.
And this is why I so enjoy ya’ll on here. You help get me to check myself and assumptions so whatever I come up with is improved and more rational.
If you want to use them, have at it. Put them directly on the busbar, as the high current path for a charger is going to be from the battery down into the charger, not from the (current source/limited) charger up. Unless something’s gone terribly wrong, at which point the charger is likely to blow up first.
Yup! They’re there to protect the wiring.
You definitely want a good multimeter in the system, and I might consider a good shunt and meter on the battery as well - something that will show you system voltage as well as net current in and out of the battery. You don’t care so much about the amperages flowing elsewhere, but knowing what’s coming out of the battery is nice.
Something like this might work, though I’ve not used it personally - look for charge/discharge in search terms: DC 120V300A Dual Ammeter Voltmeter Red LED Charge Discharge Indicator Volt Gauge | eBay
That’s much more reasonable. Fuse the other stuff, but you don’t need all the disconnects.
As far as the battery disconnect, I’m not sure it really matters. If the wire has rubbed through, you’re going to have a bad time of things anyway. However, that battery might have an internal BMS that shuts things down if there’s a short, which is one advantage of that kind of thing vs lead acid that will just dump a few thousand amps into a short until something fuses.
Oh, that’s OK, I don’t need anything vaguely near my office either. It just happens to be an overkill system at this point. I’m actually debating hanging another inverter off the battery bank to do EV charging via the solar trailer, but then I have to upgrade my charging system wiring, because I can now exceed the 50A charge current I designed for (back when there was no way I’d ever see that on the panels I had). With 5.2kW hung, I can source the amps now!
Of course, the solar trailer can now source even more…
Building overkill isn’t the real challenge in engineering. Building something safe and affordable, while also meeting the requirements? That’s a lot harder, and it’s not a skill I’m amazing at yet.
That’s what the BMV-712 is, good quality shunt/voltage monitoring and such, plus provides BT to talk to the MPPT (rather than a separate BT dongle or USB->VE.Direct interface) to put in the correct settings for the battery charging/cut-off/etc.
The Battleborn does, and the BatterySpace one does have an internal BMS, I’d have to read back up on it to check on short shut-off kind of thing.
With the original thought I went for excessive “safe”, met the requirements, and was affordable to me, even if some of the extras were more than I needed. Of course, I could probably build it a lot cheaper using something other than Victron, and doing a safe DIY BMS like what @Symbioquine linked. However Victron has the reputation from what I’ve seen in the trailer/RV communities of being basically bulletproof and well integrated, and given the $$$ I have available to throw at this, I figure being bulletproof and a great warranty is worth it, plus being well integrated. Rather a piece from A, separate from B, another from C, etc for the major electronics pieces.
As a side note, something of potential interest in the future if I use more parts for a bigger system, they have the full embedded Linux system in their GX line of monitoring/control hardware which can run on beaglebone/RPi, and probably others if you do the work of cross-compiling or what not.
Based on the sales pitch, this actually can interface with a ton of other hardware besides just Victrons own, with good support for a lot of standards/formats apparently. I imagine sometimes you might need some separate hardware dongles to interface with the bus.
Actually, I wonder if it might be handy for you with some of the solar builds you’re doing for some other folks, as part of the sales pitch is remote monitoring, dual rootfs, watchdogs, remote console. If it doesn’t already have a driver/interfaces for the stuff you’re getting which has some sort of serial interface, you can add your own driver. At least for monitoring it seems straightforward, not sure about control.
I may have to take a closer look at that - thanks! For now, we’re using Midnite hardware for charge control, and playing around with an integrated Midnite unit for charge/inverting (120V only). I wonder if they can interface with the Aims inverters - they’ve got a serial control panel interface.
If they don’t, should be easy enough for you to write a driver to put the data on the D-Bus to have it pop up onto the dashboard. I haven’t looked at the samples they have, so don’t know what you might need to do, but from the docs it sounds like they have some decent samples.
Ok, other parts:
4 post 3/8" bus bar (one red, one black). I’ve got 5 things, but it shouldn’t be a problem to put 2 ring terminals to a single post, should it? Especially if it’s something like the Orion charger & 110v charger. It’s so highly unlikely that both would be active/charging at the same time. Not impossible, but chances are essentially nil.
For disconnect, the basic cheap-ish 12-48v 275A continuous should be fine, the black ABS body with red knob. Or should I seek out something more than $15/switch?
I actually found a solar isolator switch, although it’s not the cheapest (~$58 on the big A), so not sure if it’s worth it rather than using the same disconnect switch as above that will be for the battery.
For wiring:
4 awg THHN for the 6-8’ from the battery to the bus bar (fuse at the terminal, or at least as close as I can get).
For the Orion & SmartSolar, the terminals are 6awg max size, so for them and the 12v blade fuse block I’ll use the same. I’m thinking 6 awg because I’m crazy like that, but really I think 8 awg should be fine for the loads, especially given the short runs. Probably no more than 12". I might actually have some/enough 8 awg around, if I do, I might just use that.
The BMV-712 monitor has an optional temperature monitoring probe (P/N ASS000100000), so I’m going to get that as well and install it.
I’m going to get a short VE.Direct cable to connect the SmartSolar MPPT + BMV-712 monitor. At least I think I need to, I’m not seeing clear documentation on whether they can talk to each other over BT, or VE.Direct, or if I need something else between them.
Then need the MC4 external pass-through, I’m going to have to figure out which specific one and how to have it setup. Might just be a very short cable through cable glands with MC4 ends.
Class-T fuse holders, for the fuse from the car 12v and the battery fuse, and 2 of each fuse size. Always carry a spare 
Other than the ring terminals, any heatshrink, screws to mount, etc I think that’s it.
EDIT: Ok, here’s a proposed general wiring layout for a 19x19" mounting area. I might (probably) will have more space, but I’m pretty certain of 19x19. Am I being a bit too much trying to not cross wiring?
The green circles are the mounting for the plexi over top, with a hinged plexi over top of the bottom 1/4 or so where the disconnects and fuse blocks are, so I can access them easier.
Hm. Just noticed something with the Battery Space battery, the charge temp is 0-40C, while the Battleborn is -3-57.2C. Especially on the heat end, that’s better for a trailer which may be out in the sun. And a higher standard charge rate of 0.5C vs 0.2C for the Battery Space.
Making me think twice about trying to save the $300. It’s not insignificant, but the wide temp rating is making me strongly reconsider.
Also just found info saying the BMV-712 is fairly dump, doesn’t store the information at all about about history. I’m contemplating building in an RPi Zero with the VE-Direct → USB to capture all that data. Then again, when I’m not actively using it, the battery will be disconnected, although the BMV will still be powered (uses maybe a few mA according to docs when display is off). So perhaps an old cell phone or small tablet with the Victron app installed, when I go to use the trailer, I turn it on, hook it up to one of the multiple USB ‘outlets’ I’m intending to have, and have it connect and keep track of things that way via BT. Simpler, cheaper, easier solution I think.
Not a problem at all, especially for things like that. In general, you’ll want the washer over the top of all of them, and make sure the rings are flat - sometimes if you start stacking rings, the wire bits coming off don’t let them sit flat, and that will be a problem.
I think any of the cheaper disconnects should be fine. They’re just breaking low current DC loads, and not that often, so no need for exotic stuff. IMO.
Awww, cute! 
That should be fine for your loads, though.
Check the NEC ampacity tables and you’ll be totally fine. If you want to be strict, remember that those ratings aren’t continuous, so you can only have 80% of that for >3h, but it shouldn’t be a problem in the slightest for your use case. You don’t have enough battery to run loads at the wire limits for that long.
That’s what the solar trailer has. Just a chopped PV extension cable with the MC4s on the outside.
Temp ratings matter more if you’re doing a lot of cycling. For infrequent use, I wouldn’t worry too much about them. Battleborn has a good reputation and can have an optional heater, which is nice. I suppose. Never used one. Around this point I usually make my normal muttering noises about how lead doesn’t have any of these problems, and a 200Ah lead acid AGM would solve most of those problems.
Trojan SAGM 12 205 Solar AGM 12V 205Ah Battery - Solaris perhaps? An extra 100lb over your LFP, but you don’t have to worry about temperature, and you can just store it on a battery tender without worrying about it.
I’m more concerned that the BMS will (properly) shut off charging during the hot (e.g. sunniest) parts of the day. I’ll be way over paneled I expect, but it’d still be nice to have the extra headroom to be able to keep juicing up the whole day if I do put on a higher load, like the e-bike batteries, during the middle of the day.
I’m not planning on getting a battery with a heater, don’t really anticipate doing much in the way of actually super cold usage. As long as I can use it down to around freezing (this past weekend up in Los Padres had a hard frost on the ground!), for at least lights and stuff, where I plan the days will warm up enough to get plenty of charging time.
Yeah, I need to start thinking about weight though. Especially as I’m going to be adding a fresh water tank, so weight will start becoming a factor getting closer to my vehicles tow rating. So an extra 100lb for just the battery is something for me to worry about. Or rather, not having it means I have less to worry about otherwise.
If the battery is in the shade, it shouldn’t get that hot while charging. See if you can find a spec sheet for the BMS - maybe call them to get details. Most of the over temp shutoff stuff I’ve seen is when it gets really quite hot, 80C+ or so, but you’d want to find that out beforehand.
Well, it’s in an enclosed compartment, with minimal ventilation. Or will be at least.
The Battery Space lists charge temps of 0-40C, discharge -20 to 60C, although the PDF docs says the PCM temp of -40-85C operating temps. Doesn’t list what the high temp charge cut-off is, I presume 40C, but doesn’t say.
Whereas Battleborn says on page 5-6 the BMS will charge -3-57.2C, and discharge -20C-57.2C. So presuming the BMS of the Battery Space one does the 0-40C charge temps, the range, especially on the high end, are significantly lower than Battleborn. I wouldn’t be surprised if, during the daytime in the desert, the interior does get >40C easily, even with some good shading.
Hmph. Class T fuses with the blade/bolt style seem to start at 80a, it’s ferrule cartridge style for 60a and below, which also seems to mean box lug, screw tensioning. Rather than a nice bolt terminal which would give me lots of warm and fuzzies when it comes to making sure the wiring stays attached and in firm contact. I was planning on using some Loctite blue on the threads, along with washer & lock washer, just to make sure everything would stay tightened down well with all the vibrations from going down the road.
Thoughts? Would box lug still be sufficiently secure when tightened down well, in an environment with regular significant movement and vibrations?
At least for the battery side fuse, 80a is still within the Battleborn max charge/discharge (rated for 1C, 100a), so good in terms of that.
On the other hand, the DC-DC charger to the 7-pin I was planning on a 25-30, don’t want to go any higher.
I’d use a RigRunner with blade fuses for less than 80A distribution, personally. And for >60A I prefer to use circuit breakers than fuses.