low voltage cutoff 12v system 2 12v batteries lead acid

[motomarc]

Broke down went the cheap route to start my setup before going all out with a all in 1 growatt and solar.

I got the ps1003 go wise 2000watt inverter going to use a 300 amp anl fuse ,1/0 welding wire rated for insane amps per foot , 20 amp 110 breaker on output .

I have got in my basket a 350 amp blue see cut off switch , post connection battery terminals with 1/0 x 2 connections making a simple plug and play, if I should be going with the 3/8 threaded let me know please.
I also have battery monitor capacity voltage led cost $8.

I have no low voltage cutoff from what I read the ps1003 has a 10.6v cutoff way to low for lead acid or anything for that matter.
How do I connect 1 up when I have a potential of pulling up to 300 amps??
I have looked can't find the high amp units I saw tons of 30 amp units.

any help is greatly appreciated I am trying to get everything installed in 5th wheel by the 15th for a trip to Carlsbad NM.

MM

 

[Short_Shot]

Those low voltage cutoffs usually are that low because under load you have a voltage drop. Especially if you're talking about 300 amps.

My fridge has a low voltage cutoff that I've got set to 11v and it's not an issue. When it cuts out my battery is still actually at a higher voltage.

Battery voltage for lead acid really needs to be checked only after "settling" and normally after a load is removed the voltage will actually climb back up.

Also 1/0 is nowhere near large enough for 300a

You'll need minimum 4/0 or you're going to see even higher voltage drop than that 10.6 would imply. Wire is not sized by "amps per foot" because adding more feet rapidly decreases the current rating.

 

[motomarc]

Those low voltage cutoffs usually are that low because under load you have a voltage drop. Especially if you're talking about 300 amps.

My fridge has a low voltage cutoff that I've got set to 11v and it's not an issue. When it cuts out my battery is still actually at a higher voltage.

Battery voltage for lead acid really needs to be checked only after "settling" and normally after a load is removed the voltage will actually climb back up.

Also 1/0 is nowhere near large enough for 300a

You'll need minimum 4/0 or you're going to see even higher voltage drop than that 10.6 would imply. Wire is not sized by "amps per foot" because adding more feet rapidly decreases the current rating.

all the research I have done says 1/0 - 0 gauge is fine for the 166 amps maximum continuous from a 2000watt inverter, the 300amps I spoke of is for surge capacity and in case of short for safety the fuse will let go thus saving the system and my home.
it will be less then 7ft total round trip for wires from battery to inverter.
https://www.arc-zone.com/ultra-flex-welding-cable-DWC-UF-Bulk look at the ampacity chart for 50ft can handle 350 amps all day. google says same thing 1/0 welding cable good for 350 amps. research is key .

Back to the real ? that is, how the low voltage works to stop the power going through such a big wire and load?? I understand load and voltage drop from many years of RC cars etc & that voltage comes back up after load is removed.

just wanting to know how it works & how to hook it up correctly, safely .

thank you for your recommendations.

MM

 

[Short_Shot]

If you want to hook it up correctly and safely then you should be a bit more open minded, because your research is based on data for an application that does not apply to your installation.

1: You are right about less current because I didn't notice the 2kw inverter and falsely assumed 350a was a load.
2: However, you are incorrect about a 2kw inverter pulling only 166a. After 0.85% efficiency it will actually pull 196 amps. With power factor issues on the AC side it might even be a bit higher, depending on the model.

3: Welding is rarely ever done at a 100% duty cycle and that usually does not significantly factor in voltage drop because a welder can just increase the voltage a bit. An inverter is not a welding application and is subject to a very different set of current rating charts. Your own link explicitly states under the chart in question: "There are variables in welding applications therefore it is recommended the user consult an electrical engineer for a particular welding application."

I promise you that 1/0 cannot handle 350 amps "all day". In fact when you do the math on 50 feet of 1/0 for DC12V application (round trip is 100 feet) then you get a voltage drop of 69.34%, or 8.32 volts lost attempting to run 350a for even a few seconds let alone "all day". Even if you don't round trip that the drop is still over 4v. No inverter can tolerate that.

At 166 amps over 50 feet both directions that vdrop is 3.95v (or almost 2v one way), which is still in excess of what the inverter can tolerate and will shut down. But, you aren't going 50 feet I hope, so...

If you are pulling 196 amps (after efficiency losses) AND have less than 5 feet of 1/0 (10 feet total) you will see a voltage drop from 12v to 11.53v. This may be sufficient, but still is far from ideal as it exceeds 3% voltage drop (3.88%) which NEC suggests as a maximum drop for any individual circuit.

If you surge to no more than 350 amps as you claimed, that same set of wires will see a voltage drop to 11.17 volts. Nearly 7% drop. Depending on the inverter this might trip the low voltage shutdown (yours might be fine at 10.6 if you really must go that light on wire). If you have any imperfect connections this almost certainly will trigger.

You need no less than 3/0 to fall below the 3% voltage drop at 200 amps over 10 feet, which would subsequently handle the 350a surge as well.

Can you do it? Maybe. Might still have issues. Do the guidelines suggest otherwise? Also yes.

To quote someone who is very confident: "Research is key."

My journeyman card and multiple engineering courses tend to back me up here, as does years of running this stuff at stupid high currents in automotive and industrial applications.

 

[motomarc]

If you want to hook it up correctly and safely then you should be a bit more open minded, because your research is based on data for an application that does not apply to your installation.

1: You are right about less current because I didn't notice the 2kw inverter and falsely assumed 350a was a load.
2: However, you are incorrect about a 2kw inverter pulling only 166a. After 0.85% efficiency it will actually pull 196 amps. With power factor issues on the AC side it might even be a bit higher, depending on the model.

3: Welding is rarely ever done at a 100% duty cycle and that usually does not significantly factor in voltage drop because a welder can just increase the voltage a bit. An inverter is not a welding application and is subject to a very different set of current rating charts. Your own link explicitly states under the chart in question: "There are variables in welding applications therefore it is recommended the user consult an electrical engineer for a particular welding application."

I promise you that 1/0 cannot handle 350 amps "all day". In fact when you do the math on 50 feet of 1/0 for DC12V application (round trip is 100 feet) then you get a voltage drop of 69.34%, or 8.32 volts lost attempting to run 350a for even a few seconds let alone "all day". Even if you don't round trip that the drop is still over 4v. No inverter can tolerate that.

At 166 amps over 50 feet both directions that vdrop is 3.95v (or almost 2v one way), which is still in excess of what the inverter can tolerate and will shut down. But, you aren't going 50 feet I hope, so...

If you are pulling 196 amps (after efficiency losses) AND have less than 5 feet of 1/0 (10 feet total) you will see a voltage drop from 12v to 11.53v. This may be sufficient, but still is far from ideal as it exceeds 3% voltage drop (3.88%) which NEC suggests as a maximum drop for any individual circuit.

If you surge to no more than 350 amps as you claimed, that same set of wires will see a voltage drop to 11.17 volts. Nearly 7% drop. Depending on the inverter this might trip the low voltage shutdown (yours might be fine at 10.6 if you really must go that light on wire). If you have any imperfect connections this almost certainly will trigger.

You need no less than 3/0 to fall below the 3% voltage drop at 200 amps over 10 feet, which would subsequently handle the 350a surge as well.

Can you do it? Maybe. Might still have issues. Do the guidelines suggest otherwise? Also yes.

To quote someone who is very confident: "Research is key."

My journeyman card and multiple engineering courses tend to back me up here, as does years of running this stuff at stupid high currents in automotive and industrial applications.

Thank you for your kind advice in going bigger now for sure or dbl up on 1/0 if that would do it. Getting 3/0 connections to a battery seems tough what connects are you using? Just copper ends on wire to the threaded post??