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10-06-2018, 05:37
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#1
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Registered User
Join Date: Dec 2009
Location: Quebec (boat currently in Sardinia)
Boat: Bruce Roberts 45 (steel) - Armonid
Posts: 96
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Installing Battery Monitor - cable gauge
I am in the process of replacing my battery bank and installing a battery monitor.
All would be fine and dandy, with the exception of the windlass (1500W, powered by the house bank). Cables are 000 AWG.
My understanding is that all negative should be captured by the shunt. Would be easy to bring the panel's and windlass' negative to a post and connect the post to the shunt.
My question is whether I should (must) use 000 cables to connect the battery monitor's shunt, or if I can use smaller gauge, since the shunt is a few inches from the battery (ex. AWG 3).
In other words, gauge calculators assume constant wire diameter to compute the expected voltage drop. If a very short section of relatively smaller gauge is inserted in the circuit, what happens?
Sorry if this is a simplistic question.
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10-06-2018, 07:02
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#2
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Registered User
Join Date: Jun 2009
Location: BVI
Boat: Leopard 40 (new model)
Posts: 1,385
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re: Installing Battery Monitor - cable gauge
ok to have a short section of smaller gauge. In order to calculate drop add up the drop in volts for each segment. If you want to use American tables that dont give drop in volts you can " adjust" the length of the piece of different gauge to use the table. Example: If you will use 1 foot of wire that has half the cross section (circ mils or mm2) of the main wire, then count that as 2 more feet of main wire.
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10-06-2018, 07:10
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#3
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Commercial Member
Join Date: Dec 2008
Location: St. Petersburg, FL
Boat: Gulfstar Long Range Trawler; 53'; BearBoat
Posts: 1,524
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re: Installing Battery Monitor - cable gauge
Why would you want to do this? What is the advantage?
__________________
Charlie Johnson
ABYC Master Technician
JTB Marine Corporation
"The Devil is in the details and so is salvation."
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10-06-2018, 07:10
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#4
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Registered User
Join Date: Dec 2009
Location: Quebec (boat currently in Sardinia)
Boat: Bruce Roberts 45 (steel) - Armonid
Posts: 96
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re: Installing Battery Monitor - cable gauge
Ok. Thanks
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10-06-2018, 10:26
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#5
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Registered User
Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 10,208
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re: Installing Battery Monitor - cable gauge
The current leaving a load is the same as entering the load. Down sizing wire gauge?
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10-06-2018, 11:01
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#6
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Registered User
Join Date: Dec 2009
Location: Quebec (boat currently in Sardinia)
Boat: Bruce Roberts 45 (steel) - Armonid
Posts: 96
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re: Installing Battery Monitor - cable gauge
Quote:
Originally Posted by CharlieJ
Why would you want to do this? What is the advantage?
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I'll have to run a 1 foot cable from the shunt to the battery. AWG 000 is stiff and would complicate things.
AWG 2 can handle close to 200A and voltage drop is insignificant.
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10-06-2018, 11:09
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#7
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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re: Installing Battery Monitor - cable gauge
The OOO is I’m sure to prevent voltage drop, due to wire run length.
Surely it isn’t there cause it needs to be that size to keep from overheating, or he has God’s own battery bank.
We ran smaller wire than that to start a Honeywell (Garrett) G-10 engine, that drew a sustained 1000 amps at 24 V for likely 30sec during starting.
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10-06-2018, 11:11
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#8
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Moderator Emeritus
Join Date: Aug 2005
Location: Carlsbad, CA
Boat: 1976 Sabre 28-2
Posts: 7,505
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re: Installing Battery Monitor - cable gauge
Thought the PO was looking for input on laxatives from the title. Sometimes better to spell out what you are looking for in the title.
__________________
Peter O.
'Ae'a, Pearson 35
'Ms American Pie', Sabre 28 Mark II
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10-06-2018, 11:17
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#9
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Moderator
Join Date: Aug 2009
Location: Solent, England
Boat: Moody 31
Posts: 18,398
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Re: Installing Battery Monitor - cable gauge
Quote:
Originally Posted by roverhi
Thought the PO was looking for input on laxatives from the title. Sometimes better to spell out what you are looking for in the title.
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Second one today, I have edited the title for him.
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10-06-2018, 11:43
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#10
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Registered User
Join Date: Dec 2009
Location: Quebec (boat currently in Sardinia)
Boat: Bruce Roberts 45 (steel) - Armonid
Posts: 96
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Re: Installing Battery Monitor - cable gauge
Quote:
Originally Posted by a64pilot
The OOO is I’m sure to prevent voltage drop, due to wire run length.
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yes yes, I understand this and do not question the size of the main cable.
Again, my question was whether it is OK to insert a short length (1 foot / 30cms or so) of smaller cable in the circuit. Turns out that it is perfectly possible. I am set on a short length of AWG 2 (50mm2) to connect the battery to the shunt.
thanks for your input
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10-06-2018, 14:04
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#11
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Registered User
Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 10,208
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Re: Installing Battery Monitor - cable gauge
Just remember the radius of the wire size is a squared function when it comes to circular mill area and current carrying capacity.
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10-06-2018, 15:31
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#12
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Registered User
Join Date: Dec 2009
Location: Quebec (boat currently in Sardinia)
Boat: Bruce Roberts 45 (steel) - Armonid
Posts: 96
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Re: Installing Battery Monitor - cable gauge
Yes. I am in Europe at the moment. The metric is the cable cross section, expressed in square mm. Actually easier to understand and work with.
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10-06-2018, 17:01
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#13
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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Installing Battery Monitor - cable gauge
I’d still fit as large a wire as will fit without undue stress.
Just can’t hurt having large cabling, and we are talking about a short run, so cost isn’t likely an issue either.
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10-06-2018, 20:45
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#14
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Registered User
Join Date: Aug 2008
Location: Sydney, Australia
Boat: Roberts 45
Posts: 1,033
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Re: Installing Battery Monitor - cable gauge
Quote:
Originally Posted by gauvins
I am in the process of replacing my battery bank and installing a battery monitor.
All would be fine and dandy, with the exception of the windlass (1500W, powered by the house bank). Cables are 000 AWG.
My understanding is that all negative should be captured by the shunt. Would be easy to bring the panel's and windlass' negative to a post and connect the post to the shunt.
[...]
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Correct, you should capture all current with the shunt, but you don't have to. The simplest option would be to leave the windlass out of the "BM picture", if it causes undue efforts and costs to include it.
Compared to other consumers, the windlass only runs on rare occasions for short periods anyway. It all depends on what you really want to achieve with and expect from the BM.
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11-06-2018, 06:37
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#15
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Registered User
Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 10,208
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Re: Installing Battery Monitor - cable gauge
Quote:
Originally Posted by gauvins
Yes. I am in Europe at the moment. The metric is the cable cross section, expressed in square mm. Actually easier to understand and work with.
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It makes more sense than AWG.
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