Hey all

[Hedges]

Diagram is 2S4P so only 45Voc so plenty of room for really cold temps even on a 100V max input SCC.

Yup.
Just wanted to point out the earlier posting I responded to was risky.

8 x 100 watts panels is 800w on a 40A SCC into a 12V battery?

14V x 40A is only 560 watts so you are leaving a lot of wattage on the table.

Or a perfect fit, no watts left on the table, if strings are given multiple orientations.
Not the most convenient thing to do for a "camper trailer" unless set up at a fixed location, but potentially worth it for 50% more power.

 

[Noflers]

Is your system meant to be positive ground?

Four strings of PV panels in parallel, ought to be individually fused. MC4 fuses are one way to go. Four individual wires to circuit breakers is another, doubles as PV array disconnect shown as [2] in your picture. With (polarized) breakers, I favor ganging them to operate together by sliding a stiff wire through the hole in their handles (my safety upgrade because I dispute manufacturer's assertions.)

Suggest quality fuse on battery. Your planned breakers probably don't have AIC rating sufficient to interrupt the short-circuit current lithium battery can deliver. I calculate 20,000A (haven't seen a value from manufacturer or test result), and a class-T fuse is rated for that.

I would use something like 250A class T fuse (regardless of whether that exceeds ampacity of wires) and rely on breaker working in case of overload. Fuse should never blow, but in case of a short circuit it will clear faster than breaker.

1000W inverter is nominally 80A at 12V, a bit more for inefficiency. So 200A breaker is probably higher than required. It is OK if wires can handle that. Midnight has a 175A breaker with high ratings. That could be put right at battery (interrupting not just inverter but everything else too) and could be used in place of the class T fuse I suggested (that 175A breaker is rated 50kA interrupting)

You lost me a bit there in paragraph 3. By "fuse on battery", do you mean between the individual cells? Or are you talking about between battery and inverter? Ohhh wait, are you saying a fuse and a breaker between the battery and inverter, with the breaker sized below the breaker... I've redone the diagram and I got the breaker ratings from here https://www.altestore.com/howto/recommended-inverter-cables-sizing-and-breakers-or-fuses-a62/

Nowhere on your diagram does it say 12V battery or inverter.
You say Lishen which is irrelevant but omit voltage.
8 x 100 watts panels is 800w on a 40A SCC into a 12V battery?

14V x 40A is only 560 watts so you are leaving a lot of wattage on the table.

Apologies there. Fixed in the update.

 

[Hedges]

You lost me a bit there in paragraph 3. By "fuse on battery", do you mean between the individual cells? Or are you talking about between battery and inverter? Ohhh wait, are you saying a fuse and a breaker between the battery and inverter, with the breaker sized below the breaker... I've redone the diagram and I got the breaker ratings from here https://www.altestore.com/howto/recommended-inverter-cables-sizing-and-breakers-or-fuses-a62/

OK, you've now got negative terminal of battery grounded.

I meant a class T fuse very close to battery positive terminal. Then all other breakers/fuses/loads coming off that fuse. That is one way to go.

You can use the 175A breaker of suitable rating and no fuse is needed for circuit to inverter.
But 50A breaker to SCC needs to be able to interrupt battery short circuit too. I'm not sure it is rated high enough. Also watch out for "polarized" breakers.
Wire to 12VDC fuse panel is unprotected, and I'm sure those fuses don't have much short circuit current interrupt rating.

I don't know how badly a shorted 12V lithium battery behaves, it 12V is enough to arc through the fuse. I do see fuses with varying interrupt ratings, like 5000A at 12V and 2000A at 32V.

One guy shorted out his 48V pack, through a fuse without blowing it because a bad busbar connection went first and splattered metal all over (under a cover.) So these things do have destructive power. That's why I say class T fuse or something else just as good, with all paths going through it.

 

[Noflers]

OK, you've now got negative terminal of battery grounded.

I meant a class T fuse very close to battery positive terminal. Then all other breakers/fuses/loads coming off that fuse. That is one way to go.

You can use the 175A breaker of suitable rating and no fuse is needed for circuit to inverter.
But 50A breaker to SCC needs to be able to interrupt battery short circuit too. I'm not sure it is rated high enough. Also watch out for "polarized" breakers.
Wire to 12VDC fuse panel is unprotected, and I'm sure those fuses don't have much short circuit current interrupt rating.

I don't know how badly a shorted 12V lithium battery behaves, it 12V is enough to arc through the fuse. I do see fuses with varying interrupt ratings, like 5000A at 12V and 2000A at 32V.

One guy shorted out his 48V pack, through a fuse without blowing it because a bad busbar connection went first and splattered metal all over (under a cover.) So these things do have destructive power. That's why I say class T fuse or something else just as good, with all paths going through it.

Any recommendations on videos or resources to read about this stuff? Because apparently everything I've read/watched has taught me nothing as I still dont understand any of this. As soon as I think I have it figured, I'm only knocked back on my ass realizing I dont know anything...

 

[Noflers]

In other news, I was just gifted a 6'X12' flatbed trailer. It's got brakes, lights, and good tires. Will need a bit of stiffening to make a proper base for a camper, bit holy wow this is awesome.

Solar budget may be increasing a bit due to this revelation ???

 

[Hedges]

Any recommendations on videos or resources to read about this stuff? Because apparently everything I've read/watched has taught me nothing as I still dont understand any of this. As soon as I think I have it figured, I'm only knocked back on my ass realizing I dont know anything...

A lot of it gets taught in safety classes given to employees with engineering degrees who have been working in the field for years, so don't feel bad.

"Grounding, Bonding, and Shielding" "Arc Flash and Arc Blast"
There's lots of scary stuff, and the worst ones involve either 120/240VAC at high current from utility transformers in an industrial (not residential) neighborhood, or 12KV circuit breakers.

But lithium batteries have a degree of risk too. "Vent with fire" which is well known for other lithium chemistries and is rare but not impossible with LiFePO4. What is common is for cells to swell up and be ruined by charging or discharging outside allowable voltage range. Also common is melting and splattering aluminum or copper conductors because a 12V battery can deliver 100,000W into a short circuit. People on the forum have melted terminals of batteries.

Mostly, the protection we have comes from NEC for house wiring. Main breaker is rated to interrupt a short circuit. Wire gauges and grounds keep voltage on appliance frames safe and wires don't overheat, last long enough to trip breaker.

When you work inside electrical panels or on car batteries, accidents can happen. Lithium batteries can deliver several times as much power. People short them out with a wrench or wire.

Once you've assembled a system successfully, the idea is that it should be protected even if you connect excessive load or a wire gets shorted. That's why I suggest a class T fuse close to battery positive terminal, with everything else wired through it. I know from its ratings that it can open in milliseconds and stop current flow.

The other parts also need to be correct size and suitable quality. For instance, many people get off-brand breakers through Amazon or other sources, then find it gets hot or trips under normal load. Some vendors like Blue Sea and Midnight have quality products made by Busmann, LittleFuse, and other good manufacturers.

If you stick with quality name fuse/breaker/switch and look up wire gauge in ampacity tables that takes care of most issues.
I see you have 2 awg and 175A breaker, which looks OK according to table for single conductors in free air, 90 degree insulation.
But if it is a long wire run, could be too much voltage drop at high current, so calculate resistance and check.

 

[Noflers]

A lot of it gets taught in safety classes given to employees with engineering degrees who have been working in the field for years, so don't feel bad.

"Grounding, Bonding, and Shielding" "Arc Flash and Arc Blast"
There's lots of scary stuff, and the worst ones involve either 120/240VAC at high current from utility transformers in an industrial (not residential) neighborhood, or 12KV circuit breakers.

But lithium batteries have a degree of risk too. "Vent with fire" which is well known for other lithium chemistries and is rare but not impossible with LiFePO4. What is common is for cells to swell up and be ruined by charging or discharging outside allowable voltage range. Also common is melting and splattering aluminum or copper conductors because a 12V battery can deliver 100,000W into a short circuit. People on the forum have melted terminals of batteries.

Mostly, the protection we have comes from NEC for house wiring. Main breaker is rated to interrupt a short circuit. Wire gauges and grounds keep voltage on appliance frames safe and wires don't overheat, last long enough to trip breaker.

When you work inside electrical panels or on car batteries, accidents can happen. Lithium batteries can deliver several times as much power. People short them out with a wrench or wire.

Once you've assembled a system successfully, the idea is that it should be protected even if you connect excessive load or a wire gets shorted. That's why I suggest a class T fuse close to battery positive terminal, with everything else wired through it. I know from its ratings that it can open in milliseconds and stop current flow.

The other parts also need to be correct size and suitable quality. For instance, many people get off-brand breakers through Amazon or other sources, then find it gets hot or trips under normal load. Some vendors like Blue Sea and Midnight have quality products made by Busmann, LittleFuse, and other good manufacturers.

If you stick with quality name fuse/breaker/switch and look up wire gauge in ampacity tables that takes care of most issues.
I see you have 2 awg and 175A breaker, which looks OK according to table for single conductors in free air, 90 degree insulation.
But if it is a long wire run, could be too much voltage drop at high current, so calculate resistance and check.

Thanks for that little explanation. Still trying to wrap my head around it all.

Started thinking about the idea of using one of the all in one units from MPP. Heard a few talking about the noise level of the cooling fans being a bit much, so that and the efficiency level have me worried....

I'm also wondering what cells I have on order. They came from a link on Wills page on raw LFP cells. https://s.click.aliexpress.com/e/_9fYkO3

I was under the impression that I had ordered LISHEN cells.

But the pics one Micheal B Caros group buy thread, the cells have a different pressure relief valve (oval, silver) , and in another thread I saw that they differentiate further saying the cells I have on the way are ETC cells . Reason I'm worried/wondering is because I want to order 4 more cells from Michael, but I want to make sure they are from the same manufacturer.

 

[Noflers]

My batteries finally arrived!



I dont think they're LISHEN, definitely not what was pictured in the listing when I ordered. Oh well, what can ya do?

I'm wanting to order another set of 4 from Michael B Caro, but these don't have labels with the ir rating. I'm thinking about ordering something like this so that I can measure myself, to work with Michael to orders cells from him that closely match mine. Any thoughts on this unit? https://www.amazon.com/gp/aw/d/B07S7NKZ45/ref=ox_sc_act_image_1?smid=A18TWJ2XIUOEX9&psc=1

This is turning into a bit longer of a project than I'd anticipated due to my wanting to wait for the price of lumber to come down some (if you didn't know, the prices are outrageous right now!).

 

[Noflers]

Well, hello all... I'm sad to say I have to bow out if this battle. I have literally everything to build this system, minus panels. Selling as a bundle would be amazing, though I know it's probably not possible.

I'll be back in the next few days to make a formal sale thread....