Wire size from Battery ON/Off switch to Electrical Panel

[smokey73]

What size wire do you have from you Battery ON/Off or On/OFF/BOTH switch to your electrical distribution panel. My run is about 16 feet one way and the wire size looks like 6 AWG? Just wondering as I'm seeing about a 10% voltage loss on this stretch of power wire. Input would be appreciated. Yes, I'll be looking at the wire size charts but thought I'd get an idea of what is normally used.

Thanks in advance

 

[CarlN]

10% voltage drop is not good just getting to the panel. Your problem is that long16ft run. For things like electronics you really want not more than 3% voltage drop. My boat has a shorter run and there's AWG 2 cables from battery to panel. Here's a good calculator. The site, Genuinedealz, also makes beautiful custom cables for a very reasonable price. I use them for any wire bigger than AWG 10. Just stick your numbers in the calculator and solve for 3% -

Voltage Drop Calculator

Custom Battery Cable Marine Grade | By The Foot

8 AWG to 4/0 AWG Custom Battery Cables made to order from our marine-grade tinned copper battery cable which is very flexible and an excellent choice for many battery cable options including automotive, RV, motorcycle, golf cart and solar battery strings. Use the custom cable designer to build...

www.genuinedealz.com

 

[smokey73]

10% voltage drop is not good just getting to the panel. Your problem is that long16ft run. For things like electronics you really want not more than 3% voltage drop. My boat has a shorter run and there's AWG 2 cables from battery to panel. Here's a good calculator. The site, Genuinedealz, also makes beautiful custom cables for a very reasonable price. I use them for any wire bigger than AWG 10. Just stick your numbers in the calculator and solve for 3% -

Voltage Drop Calculator

Custom Battery Cable Marine Grade | By The Foot

8 AWG to 4/0 AWG Custom Battery Cables made to order from our marine-grade tinned copper battery cable which is very flexible and an excellent choice for many battery cable options including automotive, RV, motorcycle, golf cart and solar battery strings. Use the custom cable designer to build...

www.genuinedealz.com

@CarlN Thanks for the link. I think I'd like to be closer to 1% for the main power lead since everything downstream of that is added to the loss in the power lead. To that end I'm going ot have to figure out how to run at least a 1awg and preferrably a 1/0 awg wire for the power lead and the ground.

 

[Jackdaw]

Remember the length of wire runs are considered to be the round trip distance... so 32 feet is a LONG way for your panel to be from your house bank.

 

[twalker H260]

You mention in a previous post that you have a voltage drop of .27v in the 16’. At a nominal 12v this gives a voltage drop of 2.25%. To have a drop of over 10% you would need a voltage drop of over 1.2v.

The .27v drop is higher than what it should be for a 6g wire by about .07v. This could easily be in the connections - both cable to post and the crimp connections. (In previous photo it looked like you had some corrosion on the cable crimp at the pop up breaker)

 

[smokey73]

Remember the length of wire runs are considered to be the round trip distance... so 32 feet is a LONG way for your panel to be from your house bank.

You're right but it is what it is. It is a 40 foot boot and my estimate of 16 feet one way is an estimate but I imagine it is not very different than that (could be a little less) I can't think of a reasonable place to put the house batteries much closer and can't even imagine where else to appropriately put the electrical panel.

The only solution seems to be to increase the wire gauge to reduce the loss to some reasonable number, preferably 1% rather than 3%. Except for the bilge pump, all the equipment including sensitive instruments, see the voltage at the panel as the starting point for any voltage drop calculations so this is problem I need to address.

 

[smokey73]

You mention in a previous post that you have a voltage drop of .27v in the 16’. At a nominal 12v this gives a voltage drop of 2.25%. To have a drop of over 10% you would need a voltage drop of over 1.2v.

The .27v drop is higher than what it should be for a 6g wire by about .07v. This could easily be in the connections - both cable to post and the crimp connections. (In previous photo it looked like you had some corrosion on the cable crimp at the pop up breaker)

Excellent point @twalker H260 . Correct on percentage - my bad math . You are also correct that it may be the connections including the crimps. I've cleaned all the connections in the path but not redone the crimps. Looking at the voltage drop calculation it seems that 2.52% is about right for 32 feet round trip on 6 AWG wire at 12 Volts and 12 A. Still, that puts the voltage down to 11.7 V when the bank is at 12 V and I'm not comfortable about that. So, maybe its operating at design specs from Hunter based on their installation of 6 AWG but I think I'll increase the wire AWG to minimize the losses. Thanks for the correction

 

[Ron20324]

What size wire do you have from you Battery ON/Off or On/OFF/BOTH switch to your electrical distribution panel. My run is about 16 feet one way and the wire size looks like 6 AWG? Just wondering as I'm seeing about a 10% voltage loss on this stretch of power wire. Input would be appreciated. Yes, I'll be looking at the wire size charts but thought I'd get an idea of what is normally used.

Thanks in advance

Don't go by "normally", go by the charts. More than one, if possible.

 

[JamesG161]

You don't have to change gauge of the original wire.

You can add a new smaller gauge in parallel with the existing one.

Jim...

 

[smokey73]

You don't have to change gauge of the original wire.

You can add a new smaller gauge in parallel with the existing one.

Jim...

That's what I like, thinking outside of the box!! BZ

 

[twalker H260]

You might want to do an energy budget with the timing of your high amperage uses. Your instruments likely use relatively small amounts of power and likely have a fairly broad operating voltage range - typically 8-16 volts or so. Typical incandescent lighting can be higher power draws but are less troubled by voltage drops.

The higher the current draw at any one time the higher the voltage drop for that period. Your 6g cable should have a voltage drop of .08v or .63% at 5 amps draw. At 20 amps the same wire should have .25v drop or 2.1%
At 12a with 32ft round trip you should have a drop of .15v for 1.26% at 12v. (According to A couple of different voltage drop calculators.)

Also keep in mind fully charged batteries should be in the order of 12.5-12.6v. By the time your down to 12v on your banks you should be recharging them - Assuming your using deep cycle lead acids.

On the other hand there is no harm in increasing wire size other than what it does to your wallet.

 

[smokey73]

OP Here: I did some digging and measuring and came up with some surprising information. Here are the numbers. Of course I can keep the current draw down to about 2 amps if I don't use the radar and don't use the autopilot but then again maybe the solution is to upsize at least the 6AWG wire.

The main power to the DC panel is 33 ft of 6 AWG Positive wire from the Battery On/Off switch to the DC Panel Switch. . That is a voltage drop of .299V alone at 12.5V and 11.5A. All the other main power lines are 2 AWG or 2/0.
There is also a 6 AWG ground wire in the circuit that is 12 feet long for another .109V With those two alone its .408 voltage loss at the 20 hour rate. Of course it is much less at more modest loads.

I am sure it was a cost consideration but 6 AWG for a run of 45 feet seems like a poor design decision to say the least. Do other 40.5 owners have a 6 AWG for such a long run? I have traced the wires and am certain of the 33 feet.

 

[Davidasailor26]

OP Here: I did some digging and measuring and came up with some surprising information. Here are the numbers. Of course I can keep the current draw down to about 2 amps if I don't use the radar and don't use the autopilot but then again maybe the solution is to upsize at least the 6AWG wire.

The main power to the DC panel is 33 ft of 6 AWG Positive wire from the Battery On/Off switch to the DC Panel Switch. . That is a voltage drop of .299V alone at 12.5V and 11.5A. All the other main power lines are 2 AWG or 2/0.
There is also a 6 AWG ground wire in the circuit that is 12 feet long for another .109V With those two alone its .408 voltage loss at the 20 hour rate. Of course it is much less at more modest loads.

I am sure it was a cost consideration but 6 AWG for a run of 45 feet seems like a poor design decision to say the least. Do other 40.5 owners have a 6 AWG for such a long run? I have traced the wires and am certain of the 33 feet.

Do you mean the positive wire is 33 feet, and the negative is another 12 feet of 6 AWG? If so then your total round trip distance is 45 feet, but for voltage drop calculators that’s equivalent to a one way distance of just 22.5 feet. So the expected drop at 11.5 amps is about 0.204V, or about 1.7%. At those distances you’d be good up to about 20A before you get to 3% drop.

 

[smokey73]

I'm probably overthinking this which is par for the course.

@Davidasailor26 - Thanks for correcting my misuse of the voltage drop calculator. @Jackdaw , its not 32 ft round trip, its 66 ft round trip Probably not how I would have layed out the placement of the battery but I see no way to get the house battery much closer. Except for the bilge pump, all my equipment and instruments see the actual voltage at the DC panel not the actual voltage at the Battery.

Sorry, I did not give all the wire lengths in the run, just the 6 AWG lengths (the smaller ones). The 12 foot of 6 AWG ground wire is back to one connection point and then it is 2 AWG for another 21 feet back to the negative bus near the battery. Don't know why they changed to 2AWG at that connection point so it makes the use of the calculators a little more complicated. I have calculated each leg separately and used 1/2 the one way length to approximate the equivalen "round trip." So to do some more accurate numbers at 12.5 Volts and 11.5A:

Positve leg 33ft yields 33/2 or 16.5ft 6 AWG for a loss of 0.15V
Negative leg 12ft yields 12/2 or 6ft 6 AWG for a loss of .055V
Negative leg 21ft yields 21/2 or 10.5ft of 2 AWG for a loss of .04V
Total loss to and from DC BATT ON/OFF switch to DC power panel and back = .245 V (not including any connection losses) or about 2%. This is very consistent with the .27 V drop I was measuring with my voltmeter if you also include connection losses.

That number is acceptable within the ABYC standards and within recommended norms of less than 3% loss to power panels.

This whole thing started when I was sailing and got a low voltage alarm of 11.5V on my Raymarine a98 chartplotter. I had left my frig and freezer on when sailing by accident and with the voltage loss I'm seeing plus some loss back to the plotter from the panel the alarm went off. Probably a power spike with the regular loads, refrig/freezer. water pump and autopilot motor all on at the same time but still I was taught to "Believe Your Indications." I did a 20 hr battery capacity test with a "load bank" and the battery tested at 94.17% capacity (18:50 to 10.5V) so I decided to check into voltage drops.

Shout out to this forum for all the help in thinking this through!

 

[JohnShannon]

Ray marine stuff seems ridiculously fussy about voltage. I upgraded to a ray marine autopilot when my old Robertson unit blew up and the RM unit would refuse to work due to low voltage where the Robertson was untroubled. Eventually I just stuck a motorcycle battery at the inputs to the pilot.

Good job chasing down the voltage drops. The only way to lower the resistance is shorter fatter wires, Shorter means relocating stuff, fatter means dropping a few gauges.