how far apart can 2 batteries be in same bank:

[ColinR]

I want to get a second battery to increase my domestic battery bank as the one 130ah I have is not quite enough. The problem is there is no space near the battery box and the best place to site another battery is at some distance. I would need about 6m of wire to connect them. Is this viable if I use thick enough cable? How thick? I would get an identical battery to the deep cycle one I have which was only bought this year. The existing battery location is close to the engine etc. Currently there is one 130ah deep cycle domestic and one 108ah cranking battery.

thanks!

 

[NormanS]

I have that. I used commercial welding cable. No problems.

 

[ccscott49]

Depends on the maximum current you draw from the domestic bank, welding cable or battery cable is OTT unless you are using very high currents, like starting current, 5 would be adequate for most needs or bigger, but welding cable? No not really.

 

[neil1967]

It's not just about current drawn, but also about trying to equalise the drain across the battery bank, and about charging - my alternator can easily push 70 Amps into my domestic battery bank. Also, if you have an appreciable resistance in the cables leading to the more distant batteries, then the closer batteries will end up working harder. If you can afford it I would use welding cable - I have 70mm cross section, which I think was about £7/meter.

Neil

 

[ColinR]

I use the cranking battery to start the engine from cold but when underway I generally start it with the domestic battery so I don't have to switch over (1-2 off switch). I suppose that puts a load on it.

 

[ColinR]

It's not just about current drawn, but also about trying to equalise the drain across the battery bank, and about charging - my alternator can easily push 70 Amps into my domestic battery bank. Also, if you have an appreciable resistance in the cables leading to the more distant batteries, then the closer batteries will end up working harder. If you can afford it I would use welding cable - I have 70mm cross section, which I think was about £7/meter.

Neil

good point. I have a Sterling digital regulator which puts 50-60 amps into the battery when its bulk charging. It senses the domestic bank.

 

[prv]

Also, if you have an appreciable resistance in the cables leading to the more distant batteries, then the closer batteries will end up working harder.

It's always been recommended to put the incoming positive cable on one battery and the negative cable on the other (ie, connect to diagonally opposite corners in the usual side-by-side-in-a-box arrangement). This evens out the voltage and wear between the two. It would seem even more important to do this in the OP's distributed arrangement. Just needs him to extend one of the incoming cables a bit (or possibly re-route it).

Pete

 

[VicS]

I want to get a second battery to increase my domestic battery bank as the one 130ah I have is not quite enough. The problem is there is no space near the battery box and the best place to site another battery is at some distance. I would need about 6m of wire to connect them. Is this viable if I use thick enough cable? How thick? I would get an identical battery to the deep cycle one I have which was only bought this year. The existing battery location is close to the engine etc. Currently there is one 130ah deep cycle domestic and one 108ah cranking battery.

thanks!

You might like to read the advice on the "Smart gauge" website regarding connecting batteries into banks to balance the use/charging of the various batteries. ( This is what PRV refers to above)

http://smartgauge.co.uk/batt_con.html

Your interconnecting cables must be heavy enough to not only safely carry the maximum current but to do so with acceptably low voltage drop.

"Welding cable" comes in a range of sizes so as a specification without qualification is not very helpful. You need to determine the cross sectional area which will satisfy the current carrying and acceptable voltage drop requirements.

Now might be a good time to abandon the 1,2 both switch in favour of separate isolating switches for engine and domestic banks with a diode splitter to split the charging between the banks. A diode splitter will work well with a Sterling advanced regulator.

You might also look at the possibility of locating both batteries that make up the domestic bank closer to each other and having the engine battery separate.


Another route you could consider is to adopt the arrangement favoured in the US, and described in Calder's book, of having one large all purpose battery bank and a "reserve" battery.

 

[NormanS]

Quite right. I should have made clear that the welding cable that I used was 70sq mm. Also concur with using info from Smartgauge. That's what I did.

 

[ColinR]

very useful info, thanks. The Smartguage if a good link. Based on all this I might put the two domestic battery's together wired diagonally as described and move the cranking battery. Boat already has splitting diode.

 

[chewi]

You might like to read the advice on the "Smart gauge" website regarding connecting batteries into banks to balance the use/charging of the various batteries. ( This is what PRV refers to above)

http://smartgauge.co.uk/batt_con.html

Your interconnecting cables must be heavy enough to not only safely carry the maximum current but to do so with acceptably low voltage drop.

"Welding cable" comes in a range of sizes so as a specification without qualification is not very helpful. You need to determine the cross sectional area which will satisfy the current carrying and acceptable voltage drop requirements.

Now might be a good time to abandon the 1,2 both switch in favour of separate isolating switches for engine and domestic banks with a diode splitter to split the charging between the banks. A diode splitter will work well with a Sterling advanced regulator.

You might also look at the possibility of locating both batteries that make up the domestic bank closer to each other and having the engine battery separate.


Another route you could consider is to adopt the arrangement favoured in the US, and described in Calder's book, of having one large all purpose battery bank and a "reserve" battery.

I took out my 1-2 -both in favour of a diode splitter last winter, but it caused the Bukh charge alarm to be on the edge of sounding, a weak irritating whine. So I went back to my 1-2-both.

 

[symondo]

From my experience with car stereos - where you fit an alt and battery up front of the car and more in the rear - you should be able to run a decent length of 0awg cable (basically welding cable) and if in doubt regarding voltage drop - run 2 cables in parrallell. each cable should be able to take 300a easily - that what i had fused on it anyway.