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Old 08-08-2022, 10:04 AM   #1
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12vdc Wired in Parallel

I'm in the process of completing a battery upgrade. I originally had 1 8D starting batt. and 1 8D house batt. I've added a new starting battery so that I could combine the 2 8D's into a single large house bank (I replaced the 8D's with new as part of this project).

Starting Batt.: 4D (AGM)

House Bank: 2 x 8D (AGM)

The existing wiring for the engine is 1/0 gauge. I used 1/0 for the run to the new battery as well.

For the cross-overs to wire the 2 x 8D in parallel.......can I use 1/0 or should make them larger (e.g. 2/0 instead)?

Full Disclosure: I used 1/0 and now I'm second guessing whether that is large enough.
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Old 08-08-2022, 10:18 AM   #2
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A lot depends on the length of each run, what kind of engine you have which will tell how much current it takes to start and other factors.

1/0 sounds small to me.

BTW you must be a tough guy to install another 4D. I suspect a G31 would have worked fine.

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Old 08-08-2022, 10:49 AM   #3
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DavidM is correct, with out knowing the length of your run we would not know if 1/0 is large enough. You can Google this info. We also don’t know what type of engines you are starting, big difference between a small Yanmar and a big Cat.
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Old 08-08-2022, 12:18 PM   #4
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I removed 2 8D's and installed 2 8D's and a 4D by myself. I'm not sure how tough that makes me, but my shoulders were sore the next evening.

The engine is a Yanmar 6LP-STp2. The battery is sitting beside the engine. The entire run from the starting battery to the switch to the engine is maybe 12 feet. The existing engine config. used 1/0, I only added a battery, I didn't add distance.

However, I'm talking about the positive and ground jumpers between the 2 house batteries, which wire them in parallel. The posts are about 1 foot apart.

Will I have to calculate the highest anticipated load on the house bank at a given time along with the longest potential active circuit to figure out how large to size the parallel connector?
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Old 08-08-2022, 02:47 PM   #5
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The Yanmar 6LP was originally developed by Toyota for use in their Landcruiser. So I bet they didn't use a 4D or 8D to start it. I am guessing here that normal starting current is 500 or so amps and that is why a Group 31 battery which runs from 800-1,000 CCA can be used to start it and most diesels up to 6 liters. I know member Ski in NC uses a G31 to start his 8.3 liter Cummins.

So with that 500A figure in mind and a total of 13' 1/0 one way, you will have a voltage drop of 1.3 volts which brings the voltage at the starter terminals down to 12.6-1.3 = 11.3. I think anything better than 11.0 is ok. But with a 50% discharged battery it might not start since your no load voltage will be down to 12.0 volts..

2/0 brings the voltage drop down to 1.0 volts and 4/0 down to 0.7 volts.

So I would wire it with 2/0 at least.

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Old 08-08-2022, 02:51 PM   #6
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You can’t go wrong with bigger wire. It is a one time cost and it will give better voltage for the life of the boat. Money well spent IMO. I calculate the wire size needed for a 3% drop and then go one size larger when I am doing electrical work. It may be overkill but more voltage is always a good thing.
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Old 08-09-2022, 08:37 AM   #7
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The Yanmar 6LP was originally developed by Toyota for use in their Landcruiser. So I bet they didn't use a 4D or 8D to start it. I am guessing here that normal starting current is 500 or so amps and that is why a Group 31 battery which runs from 800-1,000 CCA can be used to start it and most diesels up to 6 liters. I know member Ski in NC uses a G31 to start his 8.3 liter Cummins.

So with that 500A figure in mind and a total of 13' 1/0 one way, you will have a voltage drop of 1.3 volts which brings the voltage at the starter terminals down to 12.6-1.3 = 11.3. I think anything better than 11.0 is ok. But with a 50% discharged battery it might not start since your no load voltage will be down to 12.0 volts..

2/0 brings the voltage drop down to 1.0 volts and 4/0 down to 0.7 volts.

So I would wire it with 2/0 at least.

David
I appreciate your advise. The Yanmar 6LPA-STP2 specs call for a battery with at least 120 amp hours.

Group 31.....105 amp hrs (x2 =$910.40 w/tax)
4D..............210 amp hrs ($852.85 w/tax)

So I'm either a bit under min. spec., or I'm way over min. spec. If I compare the cost of a single 4D vs 2 x Group 31 in parallel, the 4D is cheaper. I'm sure I could get away with installing an undersized battery, but I would prefer too much than too little. As that undersized battery gets older, so does its capacity and ability to discharge.

The entire cabling for the engine has not been changed, it has been in place for many years, and I suspect came from the factory. It is 1/0 from the starting battery to the battery switch to the engine. The entire run can't be more than about 15 feet. At 20 feet a 12v circuit at 60 amps can be handled by an 4 gauge wire.



Now, that being said. Please allow me to clarify....

While I outlined my entire project, I'm specifically asking about the 2 x 8D batteries which comprise my HOUSE BANK.

Specifically the cable which connects Pos. to Pos. and Ground to Ground between the 2 8D's in the house bank wiring to the 2 8D's in parallel.

In my caser, I suspect the largest amp load on the circuit could potentially be the alternator (80amps). The alternator is only 5 feet from the starting battery and about 8 feet from the house bank.

I did notice that the windlass and 2000W inverter were both using 2/0. I suppose if I go to 2/0 it will at least be as large as the largest circuit and, as mentioned can't hurt anything.

I continue to welcome all thoughts, opinions, suggestions, and corrections.
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Old 08-09-2022, 08:44 AM   #8
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1/0 is more than enough for a house bank.
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Old 08-09-2022, 08:45 AM   #9
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You have good intentions however I think that you are going way overboard. I started my Yanmar with one of these for 10 years. (Same battery) I finally changed it before I got bit. It never failed.

https://www.google.com/search?q=walm...hrome&ie=UTF-8
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Old 08-09-2022, 10:20 AM   #10
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I don't know where you got the 120 Ah spec for the Yanmar starting battery. The only spec that is meaningful for a starter is the CCA or MCA rating.

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Old 08-09-2022, 10:46 AM   #11
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Quote:
Originally Posted by DavidM View Post
I don't know where you got the 120 Ah spec for the Yanmar starting battery. The only spec that is meaningful for a starter is the CCA or MCA rating.

David
Was wondering that too.
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Old 08-09-2022, 10:50 AM   #12
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Quote:
Originally Posted by DavidM View Post
I don't know where you got the 120 Ah spec for the Yanmar starting battery. The only spec that is meaningful for a starter is the CCA or MCA rating.

David
David
While I agree My - Yan manual cites the same batty reqm't which I find less meaningful than CCA/MCA

Shrew
When I combined my 2 8D battys I just added a flag terminal to the 4/0 pos lead that went to the farther batty terminal. The Neg already had 2 terminals and tied the battys together. With a short run I would go with the same Ga as the leads to the batty sw.
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Old 08-09-2022, 11:54 AM   #13
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Amp hours is usually used for house banks. The cranking amps is usually used for starting banks.
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Old 08-09-2022, 11:56 AM   #14
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Formula used connectors similar to that since each engine has 2 starting batteries. It is a slick way to get 2 cables on one connector.
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Old 08-09-2022, 02:14 PM   #15
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Shrew,

I will assume the 8D’s are 255 AH for a total of 510. The thing to look at for your house bank is the total highest draw from your house bank. So, the 2000 watt inverter would pull 16.66 amps AC if it was maxed out. Let’s use 15 amps AC. That translates to 150 amps DC. You may never reach that level, but that is what it can do.

I would assess the AC draw of the connected appliances for the inverter, and use that (converted to DC amps) for the inverter. On top of that your house will be feeding navigation equipment, lights at night, both inside and out, a fridge, and possibly other miscellaneous DC draws (water pump). So, the battery cable you size for would be the total possible amperage draw from that bank, taking into account the round trip distance of the cable from the battery to the DC panel, or the inverter. You will want to use the 3% drop in this case. Using a 30 foot round trip and assuming 150 amps for the highest draw, for a 3% drop, would require 2/0 cabling.

There are many AWG calculators out there. I use the Blue Seas calculator.
Circuit Wizard - Blue Sea Systems
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