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Old 10-06-2018, 06:37   #1
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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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Old 10-06-2018, 08:02   #2
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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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Old 10-06-2018, 08:10   #3
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re: Installing Battery Monitor - cable gauge

Why would you want to do this? What is the advantage?
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Old 10-06-2018, 08:10   #4
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re: Installing Battery Monitor - cable gauge

Ok. Thanks
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Old 10-06-2018, 11:26   #5
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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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Old 10-06-2018, 12:01   #6
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re: Installing Battery Monitor - cable gauge

Quote:
Originally Posted by CharlieJ View Post
Why would you want to do this? What is the advantage?
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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Old 10-06-2018, 12:09   #7
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re: Installing Battery Monitor - cable gauge

The OOO is Iím sure to prevent voltage drop, due to wire run length.
Surely it isnít there cause it needs to be that size to keep from overheating, or he has Godís 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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Old 10-06-2018, 12:11   #8
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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.
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Old 10-06-2018, 12:17   #9
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Re: Installing Battery Monitor - cable gauge

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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.
Second one today, I have edited the title for him.
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Old 10-06-2018, 12:43   #10
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Re: Installing Battery Monitor - cable gauge

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The OOO is Iím sure to prevent voltage drop, due to wire run length.
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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Old 10-06-2018, 15:04   #11
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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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Old 10-06-2018, 16:31   #12
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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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Old 10-06-2018, 18:01   #13
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Installing Battery Monitor - cable gauge

Iíd still fit as large a wire as will fit without undue stress.
Just canít hurt having large cabling, and we are talking about a short run, so cost isnít likely an issue either.
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Old 10-06-2018, 21:45   #14
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Re: Installing Battery Monitor - cable gauge

Quote:
Originally Posted by gauvins View Post
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.

[...]

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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Old 11-06-2018, 07:37   #15
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Re: Installing Battery Monitor - cable gauge

Quote:
Originally Posted by gauvins View Post
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.
It makes more sense than AWG.
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