battery cable question

[Jack]

I know this has been discussed but I can't seem to find exactly the answer I need in the archives. we will be adding a starting battery this year and combining the 2 grp 27 dual purpose, wet cell deka's for the house. What is the wire recommendation to combine the two batteries, they will be right next to each other. I picked up new, in the package cable at a yard sale with this info on the side - Ancor Marine Grade 4 AWG (UL) Boat Cable 600V 105°C dry 75° wet oil resistant BC5W2 E67078 LL22035 CSA TEW 105° or AWM I A/B 105° C 600V FT1 (I know most of you won't need that much info) Will this be heavy enough for the job?



Thanks for the help
jack

 

[Roger Long]

Also, what is the groups thoughts on series vs parallel connections?

First, we have to know whether you want to fry all your electronics or not.

 

[Jack]

frying

Let's say, just for the sake of argument, in this particular situation that I would prefer not to fry all the electronics at this time, however, that does not mean we should completely rule out that option for future installs.

jack

 

[Ed Caldwell]

Also, what is the groups thoughts on series vs parallel connections?

Jack, you do know that connecting two 12V batteries in series results in 24V? Thus Roger's question...

 

[Jack]

that's it...

Thanks Ed,
that is what I thought...but just couldn't be certain...
this age thing can be so annoying at times...

any thoughts on the wire size for creating the house bank?

 

[Bill Roosa]

You should still be using the Positive and negative terminals from the old house to supply the boat. The connecting cables (plural, + to + and - to -) should be the same size. You could get by with a cable with half the amp acpacity but I would not recommend it unless you can still connect either house battery to the boat with the existing positive and negative cables. If the existing boat cables can reach both batteries you will be able to take out one if it fails and still have some capability. If you can only reach one battery with the boat cables then you will need the connector cables to reach it and they will need to handle the full house load expected.
You can get the ampacity of the cables by googling "wire gage" and compairing yours to the list and selecting one with half (if that will work for your setup)

 

[Jack]

thanks bill

Hi Bill,
The original cables are still in place and will be used to get the power to the breakers. I was just wondering about the size of the cable needed to go between two batteries to increase the ah. the batteries will be right next to each other. I have Ancor AWG 4 600v.
thanks
jack

 

[sail_4_me]

cable sizing

The cable sizing depends on distance and expected amperage. Long wire runs need larger wire to avoid DC voltage drops, but for battery-combiner cables this is not a problem.

If you are just combining these 2 batteries together to extend your usage time, and not adding any load to your existing system, then you can use a same-or-larger diameter cable to hook your batteries together, but that cable should not be smaller than your original battery cables.

Check that the battery wires running to your panel and big red switch are 4AWG. If they are larger, you should match their size when combining the batteries.

If your adding a small invertor to power a TV etc., you will connect it directly to the battery bank. Invertors pull a lot of amperage from the batteries, thats why its important that the battery-combiner cables are matched to your heaviest expected load. For example, if the invertor recommends 2AWG running to the battery, then you should also have 2AWG for the combiner cables. ( example - AC invertor of 1000 watts AC = 83 amps DC, at 12v. Your DC panel probably pulls 30 amps max with everything on )


Lastly, make sure the original cables are boat cable ( like the description of your new 4AWG wire ). If its not marine wire and its not 'tinned' then consider switching it out, especially if your in salt water.

I reccommend you buy a book or two from your local marine store if your plannng any upgrades to your electrical system. Older boats designs did not have all the 21st century toys we have now.

 

[Jack]

Thank you Sail_4_Me

Sail_4_Me,
That is exactly the info i needed. I know my limitations but I am pretty sure I can connect 2 batteries together if I know the wire size. The original cables are larger than the AWG 4 which was my concern.
Thanks again...off to the store we go...
jack