Battery choices again

[Bobbie54]

OK- bought a second 12V. But I threw away the old wires when I disconnected the old 12V last year so need to get wires for it. I obviously have the plus minus wires for one battery. What type of wiring should I use to connect (and a review of how to connect them in parallel would be nice) the two batteries? I'm charging up #2 soon before I try connecting them.

[rubicon327]

Originally Posted by Bobbie54

OK- bought a second 12V. But I threw away the old wires when I disconnected the old 12V last year so need to get wires for it. I obviously have the plus minus wires for one battery. What type of wiring should I use to connect (and a review of how to connect them in parallel would be nice) the two batteries? I'm charging up #2 soon before I try connecting them.

The wiring type and gauge can be the same as what is there now. See diagram for connecting.

[Bobbie54]

I don't know what's there now. It's the wiring coming from the trailer to the battery; I assume the original. I didn't keep the connector wires so I don't know what gauge to use. It looks fairly heavy but I can't tell by looking.

[jxoco]

these might be the ones you want.

https://www.amazon.com/Gauge-Copper-...4348350&sr=8-2

you pick the length, you probably need the shortest
and the size of the hole that the bolt goes through. just measure the batterys oyu have, 3/8 inch or 5/16.

there is also an 8 inch long set, I don't know if they are too short for you.

https://www.amazon.com/Battery-Inver...1HPJ42399AHPVP

[Bobbie54]

Thanks!

I have to figure out lengths. I read they should be equal but they won't be- the way the wiring is running from the trailer, I can't reach the black to the second battery unless the batteries are head to head- (or black to black) in the boxes, which are end to end. So that means red-red will be a long connector and black to black a short one. Not sure how much the length thing matters (the comment was made for banks of batteries, not just two.)

Though this might be possible but most of the other diagrams I've seen have one wire going to battery #1 and the other leaving battery #2, not both on one battery like this. (Ignore the 6V part; these are 12s going to the 12V system.)

[Brian B-P]

Originally Posted by Bobbie54

I have to figure out lengths. I read they should be equal but they won't be- the way the wiring is running from the trailer, I can't reach the black to the second battery unless the batteries are head to head- (or black to black) in the boxes, which are end to end. So that means red-red will be a long connector and black to black a short one. Not sure how much the length thing matters (the comment was made for banks of batteries, not just two.)

The lengths are important to balancing the current between the batteries. If you're just going to connect these batteries and not going to manage them yourself (with a selector switch and monitors), it would be preferable for them to be matched. I would use equal length and just loop the extra length of one out of the way. If you really want to do the design work, you could use a smaller gauge for the shorter wire, calculated to have the same resistance.

You could also extend the cable which doesn't reach so that the batteries can be placed in the desired arrangement. The challenge then becomes a suitable connection to make the extension.

Originally Posted by Bobbie54

Though this might be possible but most of the other diagrams I've seen have one wire going to battery #1 and the other leaving battery #2, not both on one battery like this. (Ignore the 6V part; these are 12s going to the 12V system.)

The other diagrams are preferred; this will cause imbalanced current in the two batteries due to the extra cables for one battery.

[Bobbie54]

Thanks, Brian. Extra length on one is a good idea to keep it equal. This afternoon's project is to measure lengths and check post size and see what I need.

[Bobbie54]

I figured out by turning both batteries around and undoing a bit that had attached the red and black cables together I can get them in with 18" cables between the batteries. So now to the store to check the post size and get two more wing nuts for them, and see if they carry the right cables before I order online.

[gbaglo]

Originally Posted by Bobbie54

So now to the store to check the post size and get two more wing nuts for them, and see if they carry the right cables before I order online.

I'm sure the store appreciates your business.

[Bobbie54]

Originally Posted by gbaglo

I'm sure the store appreciates your business.

Well, they got the sale of the wing nuts but not cables- they didn't have any the right size. I did buy the battery there, though.

[gbaglo]

Originally Posted by Bobbie54

Well, they got the sale of the wing nuts but not cables- they didn't have any the right size. I did buy the battery there, though.

Good.
Soon we won't be able to buy anything from any other than Amazon.

[Bobbie54]

We don't have a lot of choices here without going north almost an hour or off-island but we definitely want to keep those we do have in business.

[Bobbie54]

Back to questions. I got 18" cables and realized they won't work because I can't get the batteries wired end to end unless they are pos to pos or neg to neg in the two boxes. I did take a picture of the original battery (the one I replaced) and it was wired directly to the trailer so the second one (no picture) must have been added on with the additional cables.

So- any problem letting the batteries sit in boxes several inches apart as + . - | - +? It's two boxes, I think about 3 " apart. I don't think so- I don't think the polarity of these batteries works like magnets- but let me know if it does.

Second, the cables I got- 2 AWG- are heavier than the wires running from the trailer. (At least, the covering makes it look heavier, I didn't undo anything to look at the wires themselves.) From what I looked up resistance even if I go to a 3 foot cable is still extremely low for size 1 or 2 or even 4 cable, but should I go to a lighter cable? Or use the 2?

Third is related to the battery boxes- the lids are shattering. Boxes seem fine. Thinking of trying to replace the lids without trying to remove the boxes (8 rusty bolts, some looking very bad) as the boxes are in much better shape (not exposed to UV since the box was covered). Although if I did manage to remove them I could mount the new ones slightly closer together and solve the distance problem. I know some of you would tackle removing the bolts. I'm not at all sure that I can. But thinking I can nest a new box inside each one if I find the right boxes to fit. So interested in what you would do, although the odds I'll do it aren't too good!

[Ron in BC]

Sounds like the ideal time to install a battery selector switch and always have one isolated and fully charged battery in reserve.

Rusty bolts get more co-operative with heat, lots of heat. But you'd have to sacrifice the battery box, presuming it's plastic.

Ron

[John in Santa Cruz]

Originally Posted by Ron in BC

Sounds like the ideal time to install a battery selector switch and always have one isolated and fully charged battery in reserve.

Rusty bolts get more co-operative with heat, lots of heat. But you'd have to sacrifice the battery box, presuming it's plastic.

Ron

so how do you charge the isolated battery ? two separate AC to DC chargers, and two separate solar controllers so both charge at once regardless of the isolator switch setting ?

[cpaharley2008]

You only charge one at a time and then select the other battery to use. After awhile you switch to the first battery, so you are using only one battery at a time.

[Bobbie54]

I could, but the idea is to wire them in parallel which I imagine is less complicated than introducing a third component.

[John in Santa Cruz]

Originally Posted by cpaharley2008

You only charge one at a time and then select the other battery to use. After awhile you switch to the first battery, so you are using only one battery at a time.

so the switch connects the charger to battery 2 while battery 1 is connected to the load ? huh. in that configuration, you would never be running off the DC converter.

[alanmalk]

Originally Posted by John in Santa Cruz

so how do you charge the isolated battery ? two separate AC to DC chargers, and two separate solar controllers so both charge at once regardless of the isolator switch setting ?

https://www.etrailer.com/Battery-Cha...a/DW08770.html - diodes sold for this purpose.

But not very common in trailers - more for boats where having two independently charged batteries could be the difference between making it home, or not.

--
Alan

[Ron in BC]

Originally Posted by cpaharley2008

You only charge one at a time and then select the other battery to use. After awhile you switch to the first battery, so you are using only one battery at a time.

That's right. In my case I might go a week or two then switch to the other battery.

Originally Posted by Bobbie54

I could, but the idea is to wire them in parallel which I imagine is less complicated than introducing a third component.

Yes, there's the cost of a battery switch but there's the payback of knowing that if you loose a cell in one battery, which has happened to me, there is a fully charged other battery ready to go. Loose a cell in two batteries not isolated from each other and you end up killing the other if you don't catch it quickly. To me peace of mind is worth it.

Originally Posted by John in Santa Cruz

so the switch connects the charger to battery 2 while battery 1 is connected to the load ? huh. in that configuration, you would never be running off the DC converter.

No, you've got it backwards. If my selector switch is set to "1" then it's the active battery in use. Both getting used and getting charged whether it's the converter or solar. The other battery just sits there independent of the other. Previously I'd only switch to "both" when using the microwave. Now it's a moot point as I'm not going to bother having a microwave in the 21.

Ron