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Old 07-27-2016, 08:56 AM   #15
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Originally Posted by lewster View Post
The original pic is how a parallel battery setup should be done. Positive to #1 battery and negative to #2 battery with a cable running POS to POS and NEG to NEG. This doubles the amperage while leaving the voltage at 12VDC nominal.

My only issue with Airstream's wiring is the gauge used for both parallel cables. They use a meager 6AWG.

I NEVER use smaller than 2/0 for inter battery connections. I can assure you that even inside the lowly Interstate batteries, the individual cell inter-connect busses are far heavier than a measly 6 AWG!!!
Perfect, thanks Lewster.

Thanks too for the link. To confirm the 30-300 fuse block is the correct size for the 6AWG or the 2/0 for inter battery connections.

These are two very easy fixes. To quote Pat... is the ticket.

Thanks
Bob
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Old 07-27-2016, 08:58 AM   #16
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Please explain how that doubles the amperage vs connecting both trailer leads to one battery and jumpers to the other one
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Old 07-27-2016, 09:24 AM   #17
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We just have a single battery in the Classic so the cabling is very simple - 12Vdc 600 amp hour Lithium. The wire sizes are larger in diameter than my thumb with the appropriate sized fuses (400 amps).
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Old 07-27-2016, 10:18 AM   #18
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How are your batteries connected?

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I don't believe it matters electrically to which battery each of the two load cables are connected so long as the two batteries are paralleled and the paralleling jumpers are at least the size of the load cables. The addition of fuse protection at the positive battery per Lewster is a good idea.

All battery manufacturers recommend wiring the load cables at opposing ends of any battery bank that includes multiple units.

This assures that all of the cells participate EVENLY in both charge ad discharge cycles.
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Old 07-27-2016, 10:20 AM   #19
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How are your batteries connected?

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Originally Posted by CruizinDux View Post
Perfect, thanks Lewster.

Thanks too for the link. To confirm the 30-300 fuse block is the correct size for the 6AWG or the 2/0 for inter battery connections.

These are two very easy fixes. To quote Pat... is the ticket.

Thanks
Bob

Remember to size your MRBF (ice cube fuse) appropriately to match the ampacity rating of your cables.
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Old 07-27-2016, 10:23 AM   #20
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How are your batteries connected?

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Originally Posted by leedav View Post
Please explain how that doubles the amperage vs connecting both trailer leads to one battery and jumpers to the other one

Your method will also double the available amperage but as I explained above, cross-connecting your load cables using both batteries assures you of evenly using all of the battery cells at the same rate.
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Old 07-27-2016, 11:59 AM   #21
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When I re-did my system, I added an easy-to-find big knife switch, as a fast way to disconnect all batteries (4 Trojan T-105s). I also like to use those big fuses that the car stereo enthusiasts prefer.
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Old 07-27-2016, 12:34 PM   #22
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Quote:
Originally Posted by lewster View Post
......

My only issue with Airstream's wiring is the gauge used for both parallel cables. They use a meager 6AWG.

I NEVER use smaller than 2/0 for inter battery connections. I can assure you that even inside the lowly Interstate batteries, the individual cell inter-connect busses are far heavier than a measly 6 AWG!!!
Lewster, so I understand this correctly, your referring to the two batt to batt jumper cables not the POS & NEG battery post to the converter (or what ever is under our bed before the converter) cables, is that correct.

AS as it stands now, I need to have a fuse sized to the 6AWG capacity and when I upgrade to the 2/0 the size fused to that capacity.

It finally kicked in...the 30-300A is the terminal that accepts 30A to 300A sized blade(?) fuses.

Thanks

Bob
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Old 07-27-2016, 12:41 PM   #23
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How are your batteries connected?

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Originally Posted by CruizinDux View Post
Lewster, so I understand this correctly, your referring to the two batt to batt jumper cables not the POS & NEG battery post to the converter (or what ever is under our bed before the converter) cables, is that correct.

AS as it stands now, I need to have a fuse sized to the 6AWG capacity and when I upgrade to the 2/0 the size fused to that capacity.

It finally kicked in...the 30-300A is the terminal that accepts 30A to 300A sized blade(?) fuses.

Thanks

Bob

CORRECT!!!

You can always use a smaller capacity fuse (like a 50A MRBF on a 2/0 cable but not a larger fuse on a smaller capacity cable (200A MRBF on a 6AWG cable).
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Old 07-27-2016, 01:59 PM   #24
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Quote:
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All battery manufacturers recommend wiring the load cables at opposing ends of any battery bank that includes multiple units.

This assures that all of the cells participate EVENLY in both charge ad discharge cycles.
Wiring other than your recommendation must cause one battery to recognize a different resistance to the load than the other, although I wouldn't think it significant unless one battery was some distance from the other. I think I would need to be a designer of batteries to fully understand the charge/discharge differences that are said to occur, but I don't want to go that deep The differing opinions and useful information that turn up on the Forum are what make it so interesting. Thanks for the insight.
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Old 07-27-2016, 05:31 PM   #25
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Quote:
Originally Posted by lewster View Post
CORRECT!!!

You can always use a smaller capacity fuse (like a 50A MRBF on a 2/0 cable but not a larger fuse on a smaller capacity cable (200A MRBF on a 6AWG cable).

Thanks!


Lewster if this is your business, I'd be glad to call directly as a customer.

One last question. This winter I'm dropping the bottom of the batt box so I'll be ready for the new 2X6v's when the 2x12v's become terminal.

Can I stay with the 2 new 2/0' jumpers or should I plan for the future. And carrying that forward, you recommend up sizing the cables entering the trailer (to the bus bar?). I presume they should match the 2/0 (or higher depending on the answer prior) jumpers?

I have a 30 a service line & 1 ac and think my panel is 30A
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Old 07-27-2016, 08:38 PM   #26
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Lewster has it right. As an electrical engineer, I can add a little insight into this. Battery interconnects, whether the size of the main feeds or not, provide some resistance to current. That resistance causes voltage drop when current is passed through it.

If the feeds are connected to battery #1, some power sourced by battery #2 will be lost due to that resistance. Thus battery #1 will support more of the load. And during charging phase, battery #2 will see less voltage, and possibly less charge.

Thus, over time, battery #1 will be doing more of the work to provide power to the rig.

Arranging the feeds so that positive goes to one end of the parallel bank, and negative to the other end of the bank, equalizes the interconnect resistances seen by each battery in the bank, thus equalizing the voltage drops in the bank. Then, each battery contributes equally to satisfying current demand.


Quote:
Originally Posted by WGreg View Post
Wiring other than your recommendation must cause one battery to recognize a different resistance to the load than the other, although I wouldn't think it significant unless one battery was some distance from the other. I think I would need to be a designer of batteries to fully understand the charge/discharge differences that are said to occur, but I don't want to go that deep The differing opinions and useful information that turn up on the Forum are what make it so interesting. Thanks for the insight.
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Old 07-27-2016, 11:58 PM   #27
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Thanks everyone, This has been a great education and has been very helpful.

I truly appreciate the depth of the knowledge.

Bob
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Old 07-28-2016, 04:18 AM   #28
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. . .
Arranging the feeds so that positive goes to one end of the parallel bank, and negative to the other end of the bank, equalizes the interconnect resistances seen by each battery in the bank, thus equalizing the voltage drops in the bank. Then, each battery contributes equally to satisfying current demand.
Thanks steverino. To clarify one further aspect of this set up -- if one removes the Negative-to-Negative jumper cable between the two batteries, does this isolate the batteries from all loads, including:

-- the tongue jack motor connected directly to a Positive terminal, and grounded to the chassis;
-- the parasitic loads like the propane detector and sub-woofer which some folks have; and
-- storage area lights which might have been left on accidentally?

It seems to this lay mind that the missing negative jumper would prevent any 12-volt use. Or have I missed something?

Thanks,

Peter
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