12v schematic, safety check, and a few random questions...

[Yurtle]

apologies for the kindergarten level scribble scratch... hopefully legible; obviously not to physical scale
this is for a 4x4 van install
red = + side
black= - side
green = OCP
blue = devices

2 @ 280aH LiFePO4 batteries, 200A continuous (ea) BMS
2 @ 200W panels

The component accepting the two battery pos+ cables is a Bussman 1BS103 modular fuse block; so two wires in, two wires out.

https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/fuses/data-sheets/bus-ele-ds-1208-1bs103.pdf

Depending on stuff I haven't figured out yet I may try to use Class T rather than MRBF at the battery posts if I can figure out a good way to mount it all up.

To simplify the drawing I left out a few neg conductors and minor downstream stuff, though that is one of my questions, regarding using vehicle frame as neg current path.

Two components I'm thinking of using frame as neg are the air compressor and winch. (Not sure yet max winch amp draw but planning for a max of 400A)

Assuming correct ampacity wire and good solid connections between frame and conductors, is there a danger to other components in the system, esp vehicle computer, etc in using frame as a major current path? Also, wondering if Orion dcdc can use frame as neg?
(I was thinking I'd upgrade the engine battery ground but have realized 4/0 is overkill in that location)

I'm especially concerned after reading this post about "big kick back Voltage (back EMF)" and from Will P, "I don't think a solar specific lithium battery running a large inductive load, controlled by a semiconductor switching device is ever a good idea. It might work for a few months, but it will fail eventually. The kickback can be massive." https://diysolarforum.com/threads/how-close-can-bare-copper-bus-bars-be-12v.30555/#post-368595

Can't say I fully understand kick-back voltage and its consequences, also confused/worried about potential ground loop issues. Need further education on these topics.

Also, what is best practice for location of solar disconnect?
and, would this be an appropriate device?
MNEPV30-600-2PP

https://www.midnitesolar.com/productPhoto.php?product_ID=757&productCat_ID=16&act=p

Last question... the Bussman device is "tin plated aluminum". If I put tin ferrules on the copper cables and use "no-ox-id a special" in the sockets, would that be appropriate and sufficient to prevent galvanic corrosion?

 

[12VoltInstalls]

Bussman 1BS103 modular fuse block

Nice fuse block for ClassT - they only accept 6ga conductors? That’s insufficient for two 200A+ capable batteries I think.

may try to use Class T rather than MRBF at the battery posts if I can figure out a good way to mount it all up

Check this out: https://diysolarforum.com/threads/mrbf-vs-class-t.102175/

one of my questions, regarding using vehicle frame as neg current path

I do not do this, ever.
The frame AND body should have a ground cable to your busbar, but the frame itself should not be used as a conductor: single earth/ground wire equal or bigger than your battery cables.

Two components I'm thinking of using frame as neg are the air compressor and winch. (Not sure yet max winch amp draw but planning for a max of 400A)

Use slinky-sheathed “loom” over welding cable neg(-) and pos(+) from battery(-ies) to the winch high-side relay(s). Don’t use the frame. Frame grounds have caught underhood PDC’s on fire due to poor conductivity of the grounds: electricity takes every available path, and at high current (and usually small/poor frame ground conditions) you can have rogue current passing through all kinds of places. Underhood fires sorta suck especially if off road.

Related to this:

Not sure yet max winch amp draw but planning for a max of 400A

I’d suggest two things:
A]
3/0 winch cables, though many people settle for 2/0 but they can get hot.
B]
That 400A fuseholder is gonna blow that 400A ClassT if you have a decent winch. How many HP is your winch? Just 3HP is ~2300W 175A and that’s an optimistic 175A. Do a hard pull on 3HP winch and you can see 300A; on a decent 5HP that’s 3800W 300A. A hard pull or extended pull will easily bury that 400A ClassT.

is there a danger to other components in the system, esp vehicle computer, etc in using frame as a major current path

I have worked on a bunch of Jeeps, offroad trucks, and utility trailers with winches. Utility trailers aren’t really in the vehicle circuits and only melt cables. Trucks and Jeeps on the other hand have burned stuff up from PDC’s to random wiring to alternators themselves; I know because I’ve repaired them.
Just don’t use the frame for neg(-) conductor(s), just ground your system to the frame in one place only.

I don't think a solar specific lithium battery running a large inductive load, controlled by a semiconductor switching device is ever a good idea. It might work for a few months, but it will fail eventually. The kickback can be massive.

That sounds like great advice to me!

also confused/worried about potential ground loop issues. Need further education on these topics.

ground your system at one point to the frame and run your pos(+) and neg(-) as homerun cables. You will not have a DC ground loop. Similarly, any inverter should be homerunned with its ground/bare/green/earth in accordance with the manufacturer provided instructions grounded at the same single location.
Ideally you want to ground to the body with a solid bolt or stud that is welded, and the a jumper from that point to the actual frame.
The chassis battery neg(-) is going to be tied to the block and the firewall from the mfgr, and maybe to a/the PDC, and will have a maybe 40A or 50A strap to the frame somewhere. Just leave that be.

appropriate device?
MNEPV30-600-2PP

Yes

Bussman device is "tin plated aluminum". If I put tin ferrules on the copper cables and use "no-ox-id a special" in the sockets, would that be appropriate and sufficient to prevent galvanic corrosion?

i hate that.
Just get a different fuse holder that is copper, make your connections and tight, then and only after they are torqued final apply CRC dielectric or aerosol fluidfilm to inhibit corrosion.

On my phone- didn’t study your schematic but someone with a big screen can probably study it over.

 

[robbob2112]

Nice fuse block for ClassT - they only accept 6ga conductors? That’s insufficient for two 200A+ capable batteries I think.

Check this out: https://diysolarforum.com/threads/mrbf-vs-class-t.102175/

I do not do this, ever.
The frame AND body should have a ground cable to your busbar, but the frame itself should not be used as a conductor: single earth/ground wire equal or bigger than your battery cables.

Use slinky-sheathed “loom” over welding cable neg(-) and pos(+) from battery(-ies) to the winch high-side relay(s). Don’t use the frame. Frame grounds have caught underhood PDC’s on fire due to poor conductivity of the grounds: electricity takes every available path, and at high current (and usually small/poor frame ground conditions) you can have rogue current passing through all kinds of places. Underhood fires sorta suck especially if off road.

Related to this:

I’d suggest two things:
A]
3/0 winch cables, though many people settle for 2/0 but they can get hot.
B]
That 400A fuseholder is gonna blow that 400A ClassT if you have a decent winch. How many HP is your winch? Just 3HP is ~2300W 175A and that’s an optimistic 175A. Do a hard pull on 3HP winch and you can see 300A; on a decent 5HP that’s 3800W 300A. A hard pull or extended pull will easily bury that 400A ClassT.

I have worked on a bunch of Jeeps, offroad trucks, and utility trailers with winches. Utility trailers aren’t really in the vehicle circuits and only melt cables. Trucks and Jeeps on the other hand have burned stuff up from PDC’s to random wiring to alternators themselves; I know because I’ve repaired them.
Just don’t use the frame for neg(-) conductor(s), just ground your system to the frame in one place only.

That sounds like great advice to me!

ground your system at one point to the frame and run your pos(+) and neg(-) as homerun cables. You will not have a DC ground loop. Similarly, any inverter should be homerunned with its ground/bare/green/earth in accordance with the manufacturer provided instructions grounded at the same single location.
Ideally you want to ground to the body with a solid bolt or stud that is welded, and the a jumper from that point to the actual frame.
The chassis battery neg(-) is going to be tied to the block and the firewall from the mfgr, and maybe to a/the PDC, and will have a maybe 40A or 50A strap to the frame somewhere. Just leave that be.

Yes

i hate that.
Just get a different fuse holder that is copper, make your connections and tight, then and only after they are torqued final apply CRC dielectric or aerosol fluidfilm to inhibit corrosion.

On my phone- didn’t study your schematic but someone with a big screen can probably study it over.

Drawio.com - design tool that is free...

And i was just getting started responding when he posted..... everything he says.... especially the part about not using the frame as a current path.... you want the frame and body bonded together and to the negative bus bar so you can't get a shock from a voltage difference and to prevent galvanic corrosion..... car manufacturers do it to save money in some cases but for critical stuff they even run a negative wire along with the rest.

 

[Yurtle]

understood, thanks guys!!

Bussman accepts accepts 6 AWG - 250 kcmil.

regarding winch amps... the one I may use (HF Apex) maxes out at a little over 400A @ 12,000 pounds pull iirc. That's more than the full weight of my rig. I'm not a serious 4x4 guy, just have winch for emergency self extraction if alone and stuck in the mud somewhere; not going to be hauling myself up cliff faces I also have 2 pulleys and will pull enough line out so very unlikely I'll ever need the full 12k. maybe I'll go 450A anyway just to be safe though... looking at 4/0 DLO for the cable.

Still don't understand the kickback voltage though... and is it a danger to the LiFePO4 or the other equipment? and if so are there required/recommended devices to mitigate this effect? I'm not using a "semiconductor switching device", just the standard control that comes with the winch, so not sure if the discussion in the other post was particular to his set-up, or all winching systems in general?

I'll try out the drawing program, thanks!

 

[robbob2112]

When you pull a very large amount of current through an inverter and the cut it off suddenly there is an inductive kick as the magnetic field around the wires collapses. Typically if the dc wires are running exactly parallel and together the magnetic fields cancel each other out. But there will be sections where the are not together and in that case a magnetic field will develop and when the voltage/current goes away the magnetic field collapses and can put a spike of high voltage back along the lines.... same concept as long runs and nearby lightning strikes... they induce a voltage on the lines that a SPD will block by shorting it to ground.

 

[Yurtle]

When you pull a very large amount of current through an inverter and the cut it off suddenly there is an inductive kick as the magnetic field around the wires collapses. Typically if the dc wires are running exactly parallel and together the magnetic fields cancel each other out. But there will be sections where the are not together and in that case a magnetic field will develop and when the voltage/current goes away the magnetic field collapses and can put a spike of high voltage back along the lines.... same concept as long runs and nearby lightning strikes... they induce a voltage on the lines that a SPD will block by shorting it to ground.

ok, interesting. guessing that's why I hear a crack/pop in my speakers when certain electric (household a/c) loads shut down?

the winch doesn't run off the inverter, but assuming that doesn't matter, right?
so run +/- cables parallel and add a spd.
Midnite Solar MNSPD-300-DC Surge Arrestor Protection Device ??

If the wires run along the vehicle frame, does all that steel help to mitigate the field collapse?
anything else to do in a vehicle mounted situation?

 

[Yurtle]

also, just for a little more clarity on the grounding...
the vehicle engine starting batteries/alternator/electrical equipment are all essentially grounded to the frame/body (I believe at multiple locations(?), but main ground point of the system would be where big neg battery cable connects right?

would it be ideal then to ground solar/LiFePO4 batteries/neg bus bar to that same point? I do have welders so can weld a big grounding lug to the frame too... just not sure what's best.

 

[12VoltInstalls]

Bussman accepts accepts 6 AWG

And that is too small imho

If the wires run along the vehicle frame, does all that steel help to mitigate the field collapse?

mmm. Not really.
If you run them twisted (aka twisted pair) they will alleviate themselves.

Still don't understand the kickback voltage though

Think of it like little electrons running along the wires like fleas, and then someone slams the little door at the end of the wire (switch) and fleas being small minded all run into the back of the next one like an interstate pileup. The running pixies have no where to go so there’s a V spike on both the load side and the line side. That’s not scientifically correct but it is a useful analogy.

I'm not using a "semiconductor switching device"

Inverters, charge controllers, electronics all have them. In miniature. A computer “chip” in all its forms (microprocessor) is essentially a bizajilion switches….almost everything is binary; dna is made up of ‘switches’ in a way.
Anyways, electronics can be affected by the fleas running willy nilly along the wire when the door slams and stops the load draw.

batteries/alternator/electrical equipment are all essentially grounded to the frame/body (I believe at multiple locations(?), but main ground point of the system would be where big neg battery cable connects right?

The starting battery’s main contact point is the engine block. Secondarily the primary ground to the body is grounded by a strap to the body; the body may be grounded through a PDC or another strap/wire incidentally but the ECU most likely gets its own ground from the main battery connection. “More” grounds are not usually beneficial.
But let’s be clear: the frame ground is probably a 30-40A wire. It is not a conductor. The positive (+) and negative(-) wires/cables are the conductors, neg(-) is not to be confused with ‘ground.’

ground solar/LiFePO4 batteries/neg bus bar to that same point? I do have welders so can weld a big grounding lug to the frame too... just not sure what's best.

I’M not sure either LOL
In my mind I’d leave the oem vehicle grounds alone. And then ground the neg(-) busbar to the nearest convenient spot to penetrate the body. A welded stud might seem like it has the advantage of not getting corroded behind a bolt, but the primary advantage is no possible movement. It’s picky-uni actually but a stud with clean metal behind it stands up longest on utility trailers so I learned to just do that.

My 2c

 

[Yurtle]

re Bussman: 6awg is the smallest size the fuse body takes, 250kcmil (next size up from 4/0) is the maximum, so 4/0 should just fit, which is what I'm planning to run.

right, sounds similar to water hammer, to make a plumbing analogy.
and a surge arrestor would be like a hammer arrestor, essentially a shock absorber...

cool physics and awesome advice, thanks very much!!

 

[Yurtle]

thought of another question.
would the best place to install SPD be where the winch hot wire bolts to the 400A class-t fuse block? thereby protecting all devices "upstream" of the kickback? (this is assuming that it makes more sense on the positive side of the circuit)

just scratching the surface here but it looks like understanding the parameters by which these devices are sized/selected is a bit complex... any advice on this front?

thinking back to Will's comment ("controlled by a semiconductor switching device"); does the speed at which a switch functions effect severity of kickback? again with the plumbing analogy, a "gradually" closed valve shouldn't cause water hammer, but a rapidly shut valve will.

 

[12VoltInstalls]

does the speed at which a switch functions effect severity of kickback

Well the electrons are essentially moving the speed of light so at the snail’s pace ‘we’ work in I don’t think it’s relevant