What gauge wire needed to parallel 12v deep cycles

BFL13 wrote:

mrad wrote:

enblethen wrote:
1200 watts would be about 100 amps.
You could go to auto parts store and get a #2 battery cable with ring terminals on each end.If you have no plans on more load a #4 battery cable would work.

Hmmm... so if I have two 109 hour at @ 1 amp, deep cycle, how long can hope for it to last before falling to 50% discharge ?

EDIT--how will you know you are down to 50%? It is not so easy to tell.
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A 27 will have about 90AH at the "20 hour rate" that rate is the current it takes to go from full to empty in 20 hours. So 90/20 = 4.5 amps. So it takes 10 hours at 4.5 amps to get to 50%.

You have two batteries, so now you can go more than twice that 10 hours at 4.5 amps. (Your 20 hour rate is now 9 amps, and you go longer at lower than that rate --Peukert says so)

I don't know the Peukert factor for those batts but say somewhere like 12 hours or so at 4.5 amps?

BTW I think your problem will be generator time recharging that 180AH pair with your little Vector charger at 12 amps. Say you want to go from 50% back up to 90% and stop the gen.

50-90 is 40% of 180 = 72AH and 72/12 = 6 hours. If the gen is on anyway for some other reason that long, then no problem

The gen will most likely run 8-10 hours a day. I came up with the battery power idea on Black Friday while getting my ice fishing gear ready and brining my boat batteries in for the winter. I thought it would be nice to have some quiet time and to have backup power in case of genny problems (which can happen in -20 and n30 mph winds blowing snow at the gen)

I was thinking I may be down to 3 hours per battery when I read that 700 watts could be 30 amps ( I have limited electrical understanding)

Single aught twelve inches in length can pass 900 amps continuously with very little volt drop. The problem with using extremely heavy cable is lateral shear force on the battery terminals. It doesn't take much to shear Pb. I dislike the work but I resoldered dozens of battery terminals a majority of which were caused by a loose cable in a 24-volt system failing under a starter motor load.

I see now Silicone 1 AWG is available on eBay. This stuff is far and away the most flexible electrical cable I have ever worked with. It is to welding cable what welding cable is to THHN construction wire.

I have seen idiot sailboat builders connect a 120 amp alternator with 2/0 cable. The ring terminal is frightfully close to the bearing boss.


the 150 amp charger I am building has several short-length 6 gauge component to component bridges of silicone wire. The actual charger to clamp duplex wire is # 2 cable.

I base my decisions on electrical engineering discipline plus actual MEASURED full potential voltage drop. Methinks many misjudgements are afoot :)

mrad wrote:

enblethen wrote:
1200 watts would be about 100 amps.
You could go to auto parts store and get a #2 battery cable with ring terminals on each end.If you have no plans on more load a #4 battery cable would work.

Hmmm... so if I have two 109 hour at @ 1 amp, deep cycle, how long can hope for it to last before falling to 50% discharge ?

EDIT--how will you know you are down to 50%? It is not so easy to tell.
--------
A 27 will have about 90AH at the "20 hour rate" that rate is the current it takes to go from full to empty in 20 hours. So 90/20 = 4.5 amps. So it takes 10 hours at 4.5 amps to get to 50%.

You have two batteries, so now you can go more than twice that 10 hours at 4.5 amps. (Your 20 hour rate is now 9 amps, and you go longer at lower than that rate --Peukert says so)

I don't know the Peukert factor for those batts but say somewhere like 12 hours or so at 4.5 amps?

BTW I think your problem will be generator time recharging that 180AH pair with your little Vector charger at 12 amps. Say you want to go from 50% back up to 90% and stop the gen.

50-90 is 40% of 180 = 72AH and 72/12 = 6 hours. If the gen is on anyway for some other reason that long, then no problem

A “what size of wire” question should always also state the distance.

enblethen wrote:
1200 watts would be about 100 amps.
You could go to auto parts store and get a #2 battery cable with ring terminals on each end.If you have no plans on more load a #4 battery cable would work.

Hmmm... so if I have two 109 hour at @ 1 amp, deep cycle, how long can hope for it to last before falling to 50% discharge ?

wa8yxm wrote:
You use at least the LARGEST cable hooked to the battery.. Figure either battery may be called upon to deliver the total current of the load should it's partner fail "High Resistance" so the biggest cable is the jumper size.

Correct answer IMO. There is no good reason to use a jumper that is larger than whatever leads are supplying the coach. If you've got some additional large leads, for an inverter for example, you will want to at least match those, or go up a size to handle the combined load.

I use #4 store-bought for that job. Never a problem. Length depends on how close you get the batteries to each other--end to end or side by each. Be sure to balance the load though, so each battery takes about half.

That is, put your inverter and other wires across the pair with pos to one battery and neg to the other battery

If you want the load wires to go to the same end of the pair, put your parallel links cross-wise X so your load posts are both closest to the inverter or whatever.

I would use two #1 from inverter to batteries as short as you can in the set up.

I see the point above about if one battery fails the other takes all the load, but IMO in real life the one battery would then have such a voltage drop the inverter would shut down and now no problem!

You use at least the LARGEST cable hooked to the battery.. Figure either battery may be called upon to deliver the total current of the load should it's partner fail "High Resistance" so the biggest cable is the jumper size.

1200 watts would be about 100 amps.
You could go to auto parts store and get a #2 battery cable with ring terminals on each end.If you have no plans on more load a #4 battery cable would work.

Two LED tv’s, one satellite receiver, 27 wats in LED lights and a ceiling fan. I calculated it out to about 600 watts