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Old 23-07-2018, 12:21   #91
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Re: Sizing Main Battery Cables

Quote:
Originally Posted by mitiempo View Post
Lots of room for a 6" bus. It is common sense to keep battery wiring to a minimum and simplifies battery maintenance as well.

First thing I look at on a battery bank is the number of wires on the bank. More than 2 load carrying wires is sloppy.

Positive post to bus. MRBF fuses on the bus for individual loads. This way a blown fuse does not kill everything unless it is the main fuse.
The current wiring diagram is here

mitiempo:

I have the same issue with my current setup, even after moving a lot of wires and fuses off the positive battery post! Now there are even more wires like that.

I have shown all those fuses moved into the "Battery 24hr Fused Panel", run a heavy wire direct from the House positive terminal (bypassing the main battery fuse) to the "Battery 24hr Panel". From there each device, source or sensor has the appropriate fuse in one place. I have 3 solar sources, and a number of positive sensor wires with their fuses, the two bilge pumps and the nav/anchor light.

Quote:
More than 2 load carrying wires is sloppy...Positive post to bus. MRBF fuses on the bus for individual loads. This way a blown fuse does not kill everything unless it is the main fuse.
I was trying to reduce the energy robbing voltage drops that Mainesail so completely illustrates here. It seems you have to use larger size fuses to have less of a voltage drop, thus you need to have larger sized wires! Or, you need to have fewer connections or interruptions in your main wiring! I will have to do both of these techniques, but I am trying to reduce the number of connections first.

By having the Alternator and the 1both2 SW1 cable bolted direct to the 250a - 300a MRBF Fuse which is directly off the Battery + Terminal, I am eliminating two voltage drops due to extra connections.

I appreciate your observation that there is lots of room for the pos & neg bus and that it will simplify maintenance, all good. I am also concerned about the exposed positive and negative buses under my port seat, with my lines bin (sheets, docking, etc) right next to the that bulkhead, and on top of the House battery bank.

Don't know if the voltage drop issue will change your mind, but that is my thinking. Will be interested in your response.
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Old 23-07-2018, 13:01   #92
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Re: Sizing Main Battery Cables

Here's how I would wire it:

MRBF fuse on battery positive.
2/0 cable from there to covered bus.
All solar, alternator, and shore power charger wiring to this bus, fused appropriately.
One lead from this bus to a fuse panel for 24 hour loads.
One lead from this bus to main switch, also 2/0.
Cover this bus.

Negative post to battery monitor shunt.
Shunt to negative bus.
Negative from start battery to this bus.
2.0 cable from this bus to engine block.
Cable to main panel negative.
Cable to 24 hour panel.
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Old 23-07-2018, 13:06   #93
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Re: Sizing Main Battery Cables

I have missed a lot of the prior posts, but thought I would let you know that there are also circuit breakers available that may benefit you. While often hard to find in appropriate capacity, there are 250 amp surface mount breakers that may be useful. This breaker, for example, is stocked by Waytek:

I don't believe that Bussmann makes surface mounts larger than 150 amp - which may be sufficient for you - but this would allow you some added capacity. They are also available in 200 amp.

Breakers give a visual indication of actuation, while sometimes fuses can be hard to tell if blown or not. Especially in low light situations. And fuses must be replaced, as opposed to simply re-setting a breaker.

Note that some breakers are available which automatically re-set. Use those with caution, and only in the proper application.
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Old 23-07-2018, 13:09   #94
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Re: Sizing Main Battery Cables

DC Power - here some old and new tricks.

1. Used Copper anti-seize paste to light coate all wires to terminals connections and connections to attachment points...this lowers resistance and greatly improves DC current.
2. Use marine cables or go one size higher.
3. Clean all connections and lub...do not forget to clean “Battery Switch” inside switch and Diode battery charging separators
4. Gauge wire - One size for Starting, and one size for other uses
5. “Most failures” in DC is ground or return...some owners double the return on separate returns and terminal strips. Think about and makes good sense!
6. Use color code wires and if possible Red & Yellow - Wht & Blk is for AC, Blk will kill you.
7. “Note” - Double the size is one gauge size larger or two separate wires.
8. Grounding properly...most have proper BONDING to all metal, shaft, rudder hinges, through hulls (metal), metal fuel fill.

But a few nice vessels “do not Bond” when hull uses copper rouge on outer hull surface in place of bottom paint.

So a OHM check is a must, at time of all pulls out of the water. (Salt water is a must)
Do not forget all exposed metal like Metal Cutless Subports....Ground on engine block to all metals check...Recheck return DC batt.,(Battery Negtive) to engine block.

9. Zinc should be grounded...Zinc last 9 - 14 months if not, not bonded, the metal underwater (props) will be damaged.

10. New ways - the Zinc is being replaced with Aluminum ???

11. Fish finders work better when connected to a separate and isolated battery not connected any vessel circuit - the generator or alternator will put spikes out and limit your fish finder.
So as you see - Electric on vessels is very in-depth subject.

“The wood sailing craft and oars...learn how to tie knots. Light with lanterns. The world has changed....now you need a PHD to run or understand your vessel.”

Now let the fun begin - it is your big bucks vessel - pull out the manuals and keep asking questions.

GOD Speed - captpage
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Old 23-07-2018, 13:10   #95
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Re: Sizing Main Battery Cables

Most breakers do not have an AIC rating appropriate for a large battery bank. Fuses (ANL, MRBF, and class T) have high to very high AIC ratings.

ABYC does not allow breakers that automatically reset. They can be dangerous.
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Old 23-07-2018, 13:20   #96
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Re: Sizing Main Battery Cables

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Originally Posted by mitiempo View Post
Most breakers do not have an AIC rating appropriate for a large battery bank. Fuses (ANL, MRBF, and class T) have high to very high AIC ratings.

ABYC does not allow breakers that automatically reset. They can be dangerous.


Yes, to all above. Application specific.
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Old 23-07-2018, 13:57   #97
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Re: Sizing Main Battery Cables

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Originally Posted by curtis742 View Post
Use 1/0 or 2/0 for all of your heavy load circuits. You should size these wire runs for a worst case scenario. A starter going bad, an inverter shorting, etc. Often battery cables are undersized due to cost and are insufficient to properly carry loads causing cables to get hot. When calculating loads add at least 30% safety factor for catastrophic failure. Once past the breakers or fuses normal sizes can be run since these circuits are protected.
Thank you Curtis. I am now leaning toward using 2/0 for all heavy load circuits, as it will be one size up from what Yanmar prescribes for my installation with 12' of wire (+ and - cables) for the starter. I believe the maximum fuse size will be 250a but I am going to check this again.

Quote:
Often battery cables are undersized due to cost and are insufficient to properly carry loads causing cables to get hot. When calculating loads add at least 30% safety factor for catastrophic failure. Once past the breakers or fuses normal sizes can be run since these circuits are protected.
I am pretty sure this is going to be expensive, particularly with the right tools as suggested by MaineSail, but best to do it once and do it right.

Is sizing up one cable size from 1/0 to 2/0 equal to a 30% safety, ..I hope? I cannot imagine going any bigger!!
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Old 23-07-2018, 14:12   #98
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Re: Sizing Main Battery Cables

I was an A&P aircraft mechanic. My nickname was 'Sparky'.

Anytime I fussed about with wiring, all the fellows gave me plenty of room. My go-to phrase was "Well, it looks like that's working..."

From outside the hanger door came a chorus of "So far..."

On your boat, you are less concerned with weight and balance. I would go at least one size larger than the most conservative Yacht Council requirement.

And that depends on cable type. Thick stiff wire carries less juice than equivalent-rated thin flexible, and because of this, has greater resistance.

Greater resistance causes higher heat. An electric space heater or water heater works because of controlled resistance.

Please consider going at least one size larger than the most conservative recommendation.

And remember:
*** Every junction or connector increases resistance.
*** Length increases resistance.
*** Heat increases resistance.
*** Running cables side-by-side increases resistance. Why? FIIK.
*** Dirty contacts in your fuses and circuit breakers increase resistance.
*** Aluminum has greater resistance than copper. What type contacts in your circuit breakers?

A lot can go wrong. Fuse everything. Everything. Fuse it.


Sparky says so.
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Old 23-07-2018, 14:25   #99
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Re: Sizing Main Battery Cables

Quote:
Originally Posted by mitiempo View Post
Here's how I would wire it:

MRBF fuse on battery positive. -agreed
2/0 cable from there to covered bus. -agreed
All solar, alternator, and shore power charger wiring to this bus, fused appropriately. -Fuses: Alternator=150a, Charger=80a, Solar=I had each PV panel + Controller fused on the "Battery 24hr Fuse Panel"
One lead from this bus to a fuse panel for 24 hour loads. - Even with the voltage drop due to two connections? This panel has in it all the + voltage sensor wires for Balmar Regulator, Link10, SmartGauge etc. I would prefer to take it directly off the Battery + terminal before the main battery fuse. Also I wanted the solar to be efficient. Would this location be bad? Why?
One lead from this bus to main switch, also 2/0. -Agreed
Cover this bus. - Yes, but the covers look pretty incomplete and flimsy!

Negative post House to battery monitor shunt. - Agreed.
Shunt to negative bus. - I am not so sure I need a negative bus, maybe just a single post?
Negative from start battery to this bus. - Agreed, has to be changed.
2/0 cable from this bus to engine block. - Agreed, has to be changed.
Cable to main panel negative. - Yes.
Cable to 24 hour panel. - Yes

Thank you mitiempo.
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Old 23-07-2018, 14:28   #100
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Re: Switches: Emergency Switch, DCPanel and Starter, etc

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Originally Posted by rgleason View Post
I am torn about whether to include the emergency switch or not
You should.

Some say "a small bank" can go without, but not me.

The cutoff should be immediately past the master CP at the bank.

Blue Sea makes ones with an AFD feature to ensure you don't blow your alt diodes.

Also remote operated ones if the cutoff location would be hard to get to in an emergency.
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Old 23-07-2018, 14:31   #101
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Re: Sizing Main Battery Cables

Sensor wires can be behind the CP an master switch, ideally right on the post.

You are already aware enough about voltage drop issues, do not overly fret further unless your measurements post-install show a problem.
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Old 23-07-2018, 14:53   #102
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Re: Sizing Main Battery Cables

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You should. - OK, I will have an Emergency Switch right after the main battery Current Protection CP (fuse about 250a-300a), with AFD.

Some say "a small bank" can go without, but not me.

The cutoff should be immediately past the master CP at the bank. - Agreed

Blue Sea makes ones with an AFD feature to ensure you don't blow your alt diodes. -OK

Also remote operated ones if the cutoff location would be hard to get to in an emergency.


Sensor wires can be behind the CP an master switch, ideally right on the post. - Ok. There are a lot of sensors/pwr (Balmar ARS Regulator, SmartGauge, Link, etc) all requiring fuses, so I have them in a fuse panel. Isn't that ok?



Also I was hoping the 3 Solar PV & 3 Controllers could also lead to this location, to improve the solar recharge of the Battery. Must it go through its own fuse and the 250a-300a main battery fuse?

You are already aware enough about voltage drop issues, do not overly fret further unless your measurements post-install show a problem.-Ok That is a big help!


Thank you John
I have some more changes to make now. This looks like a job for thee fall to me! Too much to do in a weekend.
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Old 23-07-2018, 15:12   #103
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Re: Sizing Main Battery Cables

Quote:
Originally Posted by mitiempo View Post
Most breakers do not have an AIC rating appropriate for a large battery bank. Fuses (ANL, MRBF, and class T) have high to very high AIC ratings.

ABYC does not allow breakers that automatically reset. They can be dangerous.


I should correct my earlier post. For the primary battery protection, the ampacity of the entire bank must be considered. While the fusing may be selected to protect the conductor, the potential ampacity is critical to ensure that the OCPD may work as intended, and not simply weld itself together when facing a short circuit. I should not have inferred otherwise. The interrupt capacity of the OCPD should exceed the worst case situation.

This is the type T fuse that I use, for example:
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Old 23-07-2018, 15:46   #104
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Re: Sizing Main Battery Cables

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Thank you mitiempo.
As I posted I would go from the positive post to a bus. All charge sources would go to this bus with fuses sized correctly. From this bus a short cable to the 24 hour fuse block.

Smartgauge wiring has to go to the positive post, not a bus or remote fuse block.

Alternator fuse should be 150% of the maximum alternator output.

I see no reason for the additional master switch. You already have one - the 1/2/both switch. The feeds to this switch are fused at the batteries. This adds extra complexity as well as extra connections.

I would use a negative bus. Too many wires for a post - negative from start battery, negative to engine block, alternator negative, solar and shore power negatives, as well as negative to the DC panel.
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Old 23-07-2018, 17:28   #105
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Re: Sizing Main Battery Cables

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Originally Posted by mitiempo View Post
As I posted I would go from the positive post to a bus. All charge sources would go to this bus with fuses sized correctly. From this bus a short cable to the 24 hour fuse block.

- That's clear


Smartgauge wiring has to go to the positive post, not a bus or remote fuse block. - Agreed,yes

Alternator fuse should be 150% of the maximum alternator output. - That's a new way to size the Alt fuse to me. I was using BlueSeas Circuit calc. & got 150a for 120a alternator.

I see no reason for the additional master switch. You already have one - the 1/2/both switch. The feeds to this switch are fused at the batteries. This adds extra complexity as well as extra connections. - Yes, I see your point about the extra connections and voltage drop potential. I am going to have to think about this more, as I respect John from previous posts and help, and I do realize that this is a personal thing too and situations are different, but you've given me another perspective which is very very helpful.

I would use a negative bus. Too many wires for a post - negative from start battery, negative to engine block, alternator negative, solar and shore power negatives, as well as negative to the DC panel.
-Now that I see this list, I get your point. Currently the shunt is around the corner from the House Battery mounted in the Engine area. I think it should be moved to be next to the main Positive Busbar just above the House battery case, less heat and more easily accessible.
I might build my own covers for these things out of 1/4" plexiglass with 1/4" vent holes drilled into them. The plastic covers provided are not robust and do not totally cover busbars and stuff. Then I won't mind having my Lines Box next to them in the port locker.
Thanks, very much for your help, time and expertise.
And I would like to thank everyone who has contributed to this thread and process.

I would like to quote smac999, because he just contributed to my understanding of how fusing works with this simple description:
From Critique my Wiring Diagram thread:
Quote:
Fusing does 2 things, makes a boat safer, and makes a boat more reliable. The single main fuse makes the boat safe if all cables are 2/0, but is horrible for reliability. If the alternator or alt wire shorts out, the main 300a fuse will blow, and you just lost VHF radio, nav lights, cockpit lights everything. A main fuse should never blow, each device, load should have it's own that goes first.
So, both Loads (DC House) and Energy Sources (Alternator, Charger, Solar, Wind, Water) can fail either in the device, or in the wiring or connections, and a fuse is needed for that size wiring to that device. Mainesail has an excellent link about voltage drops and sizing fuses as large as possible but not > than the wire ampacity. That's just on reason why it helps to size cables 30% greater or one size higher. The second reason is the larger wire size also reduces voltage drops.

Some other things I've learned from reading and other forum user input: To reduce Voltage Drop good connections are also essential. Use good Marine Grade tinned wire, clean and protect all wire ends before doing a proper crimp (see Mainesail's website). Use the right type and size of terminals with the right sized holes. Clean and protect all terminals and tighten nuts to the proper torque.

I know I am going to have other questions, and would appreciate some review of the next wiring diagram, there will undoubtedly be some differences in approach, but I hope it will be a good installation.

Thanks again to everyone, much appreciated. I've learned a lot here.
Rick Gleason
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