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Help please wire sizing

E

epsilon

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Feb 26, 2021
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wondering if I can use 2 AWG from my 50 amp circuit breaker to batterys and 4 AWG or 6 conecting 40 amp mppt to fuse box and neg bar, or should I keep all the same guage. Thank you.
 
I would guess that there is no problem using larger wire than required. Now practically, I don't do it because large wire is harder to handle and if you are fitting the wire into terminals, it may not fit, I am not a fan of shaving down a wire to get it to fit into the terminal. Not to mention that wire is expensive.
 
epsilon said:
wondering if I can use 2 AWG from my 50 amp circuit breaker to batterys and 4 AWG or 6 conecting 40 amp mppt to fuse box and neg bar, or should I keep all the same guage. Thank you.
Click to expand...
The wires and fusing is typically determined by your maximum load in amps.
The lions share of the load is usually the inverter.
What is the continuous rating of your inverter and what is your system voltage?
Do you have any significant pure dc loads?
 
For a long run, larger gauge is better to minimize IR drop so if breaker is far from battery the large gauge is good.
You might go to smaller wires for a short segment, especially after a breaker which limits the current it will have to carry.
Unless the 50A breaker is right next to the battery, you might want to put a (higher amperage rating) fuse right at the battery, to protect against shorts in the wire before breaker. Depending on battery short circuit capability and breaker AIC rating, the fuse could be a good idea regardless of breaker location.

The wire sizes you mention are all of sufficient ampacity for those breaker sizes.
Do calculate IR drop and compare to operating voltage.
 
so I have magnum ps 3ooo, its on my boat and all professionally done all AC and shore power upgrade before I bought the boat. I am adding 400W solar and was going to the batterys direct. so inverter and solar are stand alone, came across two new ancor 48" cables for cheep so thought I would use them for solar connection to batterys approximantly 3' run
 
What charge controller will you use?
 
OK, just making sure after you said "I am adding 400W solar and was going to the batterys direct... thought I would use them for solar connection to batterys" :)
 
epsilon said:
so I have magnum ps 3ooo, its on my boat and all professionally done all AC and shore power upgrade before I bought the boat. I am adding 400W solar and was going to the batterys direct. so inverter and solar are stand alone, came across two new ancor 48" cables for cheep so thought I would use them for solar connection to batterys approximantly 3' run
Click to expand...
Since you don't mention system voltage I will assume 12 volts.
Magnum inverters are all low frequency as far as I know.
3000 ac watts * 1.5 low frequency fudge factor / 12 volts low cutoff = 375 dc amps
375 dc amps / .8 fuse head room = 468 fuse amps
That is getting ridiculous.
I hope its 24 for 48 volts.
 
Hedges said:
I've unfamiliar with low-frequency fudge factor.
I see 88% efficiency, so I would use 1.14x multiple.
Does 355A sound better?
I think 350A is what I have in my 48V system, branching out to 2 inverters.

3000W 12VDC Pure Hybrid Inverter Charger MSH-RV Series | Magnum Dimensions

Pure sinewave hybrid inverter/charger for RV applications. Includes and RV-C connector.
www.magnum-dimensions.com www.magnum-dimensions.com
Click to expand...
Most of the low frequency inverters have non trivial surge capability that can flirt with the fuse's trip curve.
Hence the fudge factor.
The unit in question weighs 55 pounds so its a pretty good bet its got a big transformer.
 
it is 12 v 4 fl 225 ah in sieres 6 volt batterys. I am here to trying and learn . so, ridculous ? also, i am only conected to ac when at marina otherwise its solar or engine alt charging on sail boat. :)
 
Depending on how fast blow the fuse is.

This data sheet says "Peak Watts 3,500W" which wouldn't even reach the 25% extra allocated to avoid nuisance trips.
Mine can do 2x for 3 seconds, then similar overage as his for 30 minutes.

epsilon said:
it is 12 v 4 fl 225 ah in sieres 6 volt batterys. I am here to trying and learn . so, ridculous ? also, i am only conected to ac when at marina otherwise its solar or engine alt charging on sail boat. :)
Click to expand...

Not ridiculous if you have short, fat cables.
Mine, now that's ridiculous. 20 kWh of AGM and four inverters able to put out 28 kW for 30 minutes. Can you say, "Peukert"?
 
epsilon said:
it is 12 v 4 fl 225 ah in sieres 6 volt batterys. I am here to trying and learn . so, ridculous ? also, i am only conected to ac when at marina otherwise its solar or engine alt charging on sail boat. :)
Click to expand...
Yeah a 3000 watt low frequency inverter at 12 volts is pushing the limits.
Its doable but its pushing the limits.
The amp draw exceeds the capacity of 4/0 105C wire from the battery bank to the inverter.
 
If the surge capacity doesn't interfere with the fuse trip curve then it ok.
 
smoothJoey said:
Puny.
I hear Arnold saying that.
Click to expand...

I suppose he would have dead-lifted them.
I used an engine hoist on the deck above, with straps through the gaps between boards.
When TrukinBear had to rehang his, I reminded him the manual says to put a 3/4" pipe through the vents and have two people lift.

My inverters have breakers which protect cables against over-current, so fuse at battery is just for shorts.
 
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