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Old 10-01-2015, 12:40   #1
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Quick fix? Expanding DC electrical capacity

Hey Sailors! Quick question about DC electrical:

My DC panel, circa 1980, just doesn't have the wiring to support the modern demands I'm putting on it. This sucks, and its really limiting that shiny new 6x6v house bank.

I believe the current main DC leads are 8g, and I have a long length of brand new 6g marine wire. If I replace the Hot main DC lead with the bigger 6g wire and expanding amp 12v capacity on the + side, will this make any difference? Do I have to make an equal change to the negative side for this to work?

Thanks a lot! Its really getting old having my fridge shut down when I'm running other things....
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Old 10-01-2015, 12:55   #2
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Re: Quick fix? Expanding DC electrical capacity

6a is only one size bigger.

You need to do a load calc. What is your normal amp load at panel. And how far from battery. You want less then 3% drop on panels. Lots if calculators on line. Note distance is normally both ways. Ie if panel us 10' away. Use 20 in calc

Because yes. Neg also needs to be bigger.
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Old 10-01-2015, 13:44   #3
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Re: Quick fix? Expanding DC electrical capacity

As I have mentioned in another thread, there are many advantages to using the metric system.
To calculate a voltage drop of 3% you to in the following way:
Measure the distance between the battery and the user, one way, in meter.
Measure the current flowing through the cable, in ampere.
Multiply the distance with the current and divide the result by 10.
There you have the cable area in mm².
And you should have the same area on both the plus and minus side.

If you take an extreme case:
The plus side is very thick (25 mm²). There will not be any drop in the voltage.
The minus side is very thin (0.5 mm²). There will be 12 V voltage drop.
What use did you have of the thick plus cable?
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Old 10-01-2015, 13:57   #4
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Re: Quick fix? Expanding DC electrical capacity

One option, if you only have enough 6AWG for the one-way trip, is to use the 8AWG you remove to parallel the existing negative conductor. I'm sure there are plenty of code violations in doing that (and someone will be along to point them out), but, if your main breaker/fuse is sized for a single 8AWG conductor (and you're only using the paralleling to reduce voltage drop, not increase ampacity) then from a protection standpoint you would be safe.

That way you'd end up with 0.39Ω/1000ft on the positive side and 0.31Ω/1000ft on the negative side. Close enough, and much better than your existing 0.63Ω/1000ft on both sides.
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Old 10-01-2015, 15:05   #5
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Re: Quick fix? Expanding DC electrical capacity

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Originally Posted by TenaciousH View Post
.......... Do I have to make an equal change to the negative side for this to work?....
Of course you do. The same current flows in the positive and negative legs of a circuit.

Based on your question, I suggest getting and studying a good book on marine electrical systems at the very least. Better would be to have a qualified marine electrician do the work or at least supervise.
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Old 10-01-2015, 15:08   #6
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Re: Quick fix? Expanding DC electrical capacity

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Originally Posted by Dsanduril View Post
One option, if you only have enough 6AWG for the one-way trip, is to use the 8AWG you remove to parallel the existing negative conductor. I'm sure there are plenty of code violations in doing that (and someone will be along to point them out), but, if your main breaker/fuse is sized for a single 8AWG conductor (and you're only using the paralleling to reduce voltage drop, not increase ampacity) then from a protection standpoint you would be safe. .
if you only have enough 6AWG for the one-way trip, go to the store and buy what you need to do a proper job.

Replacing #8 cable with #6 cable is more trouble than it's worth. Think #4 or even #2 and do the job right.

Like I posted. get a book or an electrician.
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Old 10-01-2015, 15:22   #7
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Re: Quick fix? Expanding DC electrical capacity

You could also just put a ring of heavy gauge wire around the boat and use the existing wiring to drive relays, thus the power to your appliances comes from the ring, and the old loom just has the light load of the relay to do the switching.

Regards,
Richard
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Old 10-01-2015, 17:54   #8
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Re: Quick fix? Expanding DC electrical capacity

You would still need current protection devices for your bussbar or ring


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Old 10-01-2015, 18:13   #9
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Re: Quick fix? Expanding DC electrical capacity

If I understand the OP's question, he's talking about the DC panel bus being wired with #8, looped breaker to breaker. It was common to see that in the earily 80 boats.

Depending on the configuration #6 may be adequate to carry the load. But it depends on the total load on each section of the DC panel. Going to #4 would be even better.

As to the ground. Normally there is a ground buss or point where all the negatives connect to a big battery cable (#2 or bigger). If that is the case, then your fine.
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Old 10-01-2015, 18:21   #10
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Re: Quick fix? Expanding DC electrical capacity

In the 80's there was no led lighting or suitable solar instalations at a cost effective price also refridgeration has come a long way so has instrumentation ! I have an 80's boat and the wiring is well above what I require. I am curious to know what modern devices require so much power ?
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Old 10-01-2015, 19:40   #11
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Re: Quick fix? Expanding DC electrical capacity

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Originally Posted by boden36 View Post
You could also just put a ring of heavy gauge wire around the boat and use the existing wiring to drive relays, thus the power to your appliances comes from the ring, and the old loom just has the light load of the relay to do the switching.

Regards,
Richard

Is this common Richard? Seems like a simple arrangement which could reduce wiring cost. Cost of additional relays significant? Wonder if it becomes more useful in bigger boats.


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Old 11-01-2015, 07:00   #12
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Re: Quick fix? Expanding DC electrical capacity

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Originally Posted by boden36 View Post
You could also just put a ring of heavy gauge wire around the boat and use the existing wiring to drive relays, thus the power to your appliances comes from the ring, and the old loom just has the light load of the relay to do the switching.

Regards,
Richard
That's not a practical wiring plan.
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Old 11-01-2015, 07:39   #13
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Re: Quick fix? Expanding DC electrical capacity

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Originally Posted by rwidman View Post
That's not a practical wiring plan.

I think it's a nutso way myself, but it's big business when you call the components Nodes.

http://www.oceannavigator.com/March-...ributed-power/



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Old 11-01-2015, 09:04   #14
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Re: Quick fix? Expanding DC electrical capacity

I am going to refrain from any design issues that are quite apparent and just suggest that you procure a DMM and watch your system voltage, your DC compressor motor is starving and you are possibly slowly destroying your batteries/capacity. A system designed and installed by a pro will save you a lot of headaches.

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Old 11-01-2015, 09:18   #15
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Re: Quick fix? Expanding DC electrical capacity

I added a second new BlueSea panel for new heavy loads. Actually two new panels, DC & AC. Just 6 breakers each which has been enough for 'modern conveniences' (DC:cold plate, Chartplotter, fans,... AC: inverter, toaster, microwave, hotwater heater, hairdryer, sometimes electric heater)
I splurged with amp/volt meters on both to monitor these loads more carefully... but later installed a amp-hour battery monitor that is better than glimpses of DC load. With all LED and little Hella fans and more efficient electronics these days... max load for what's left on main panel went way down (lights, fans, bilge, pressure pump,...). With the BlueSea built to take modern loads... and reverse polarity protection (AC) the boat mains now first go to them and their main breakers and last breaker in the stack feeds the old panel. Works for me and no real modification of old panel.


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