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Old 08-26-2018, 12:47 AM   #1
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need to add a battery disconnect (a "coach" question, not a "house" question)

("house" batteries to be a separate system to be added later, this is not related to anything above the floor boards, so to speak, bus operations only)

i have 2 of those 8Ds in one of them older crown coaches

both positives are connected to a isolated post bolted on the frame near the batteries, then a separate lead from there to the main panel

both negatives are connected to a bolt to the frame proper and terminate there

i want to add a battery disconnect switch (something like this: https://l.facebook.com/l.php?u=https...AGzib2VQvUMW-X) so that power can but positively shut off @ the source for work on the coach system or for long term storage or such

what should be put in and where ?

and separating these two posts (incorporating some type of bus bar or the like) so they are more than 3" apart from each other wouldn't be a bad idea going forward, no ?

looking to add a fuse or breaker between the batteries and anything being powered by them also too

the batteries themselves are: #1 a 1400 CCA / 450 reserve and #2 a 1200 CCA / 420 reserve, should they be replaced looking @ #2 being a minimum spec

hi by the way, 1st posting
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Old 08-26-2018, 07:59 AM   #2
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step 1 clean those cables
step 2 bus bar mounted on the frame to separate cables on the positive,
step 3 install cut off switch between positive cable for power out to coach and bus bar, the switch you showed, in my opinion, would be too light duty for starting loads, from 2 batteries, that switch is usually used for boats which draw nowhere near the cranking amps of a large diesel.

something more like this https://www.amazon.com/Fastronix-Cur...ZMS3FQHFF&th=1

make sure it has enough amps continuous to handle your alternator and amp draw for your starter, the one you posted only could handle 250-350 amps for staring this one can handle 1000.
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Old 08-26-2018, 11:42 AM   #3
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thanks, good suggestions all, especially regarding the switch specifications

having an idea of what you want and knowing what will work in any given specific situation is why you ask questions and appreciate knowledgeable answers
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Old 08-26-2018, 12:19 PM   #4
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Definitely clean and protect those cable lugs! I would run a separate ground 4/0 cable directly from the batteries to the starter, not relying on the frame itself for any heavy electrical loads. My bus has a Cole-Hersee M-705 (now superceded by the M-750) battery master switch that allows me to switch each of the start batteries separately or combined - why not use one of them? Blue Sea also makes similar switches.

When I completely redesigned my starting electrical system I ended up using a quarter of the length of the original cables, and I ran the ground directly to the starter - the engine now turns over noticeably faster when starting. It's well worth spending some time cleaning lugs and protecting them from oxidation, especially if you live somewhere cold.

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Old 08-26-2018, 01:41 PM   #5
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Whichever style you go with, you need mighty big lugs for your cables.
Those smaller switches and cheap ones do not have lugs physically able to handle those. nothing comes to my mind but an industrial type disconnect, say 2/o lug size or more. They can be fused also so are a good choice.
Those cable ends have never been off or cleaned by the look of them. When they look that bad, usually there is something going on beneath the insulation also. That means high resistance and heat when in operation. Maybe consider new cables and lugs and save the old ones for spares.



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Old 08-27-2018, 08:26 AM   #6
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I just bought that fastronix switch and am working on hooking up

I'm torn on what gauge wire, and where to buy. Using calculators online it says 2/0 or 3/0 awt wire, and NAPA wanted like $13/ft for it. Lowes or google has 3/0 for $4 a foot, but it says max amps is like 225?

https://www.platt.com/platt-electric...spx?zpid=70214

https://www.lowes.com/pd/Southwire-S...-Foot/50101592
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Old 08-27-2018, 09:46 AM   #7
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It's not only the gauge of the wire that determines it's rating, but the copper used and the number of strands. The wire from napa will be referred to as automotive wire, which is highly flexible and has a high strand count. The wire you linked from lowes only has 19 strands, which is why the 225 amp limit and also the cost discrepancy. The stuff from lowe's is ideal for stationary items like houses, it's not ideal for automotive use.

Go with the stuff from napa, or go to a weld shop and get some welding cable.

Whatever you get, just make sure it's high strand count, and rated for the chemicals it might be in contact with.
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Old 08-27-2018, 09:51 AM   #8
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Try to find a big electrical wholesaler. The Kind that sells it by the foot or mile. HUGE difference in price, The outdoor 10/3 stranded I bought for .40 cents was about a buck-fifty at Home Depot as I recall and theirs was not outdoor rated.
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Old 08-27-2018, 11:37 AM   #9
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you guys have next weekend for me booked solid (if i can get all the requisite parts over the next few days, of course)

yes, those cables prob haven't been cleaned for a bit, but i do have to say, the bus starts IMMEDIATELY upon turning the key, never had to hold it on for more than a second (batteries seem good also, but was told one of them "was well used" when it was put in just to sell it to me with two installed, will be getting them checked also)

i done broke my multimeter, gotta getta new one of those, was looking @ this https://amzn.to/2odrnt5 (could go with cheaper $50 version or spend $500 or more, this seemed to cover the bases of what type of elec work will be needed going forward, from basic 12v coach stuff to later when the work of the house 110v stuff - and later still: the solar stuff)
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Old 08-27-2018, 01:06 PM   #10
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Quote:
Originally Posted by mmime View Post
you guys have next weekend for me booked solid (if i can get all the requisite parts over the next few days, of course)

yes, those cables prob haven't been cleaned for a bit, but i do have to say, the bus starts IMMEDIATELY upon turning the key, never had to hold it on for more than a second (batteries seem good also, but was told one of them "was well used" when it was put in just to sell it to me with two installed, will be getting them checked also)

i done broke my multimeter, gotta getta new one of those, was looking @ this https://amzn.to/2odrnt5 (could go with cheaper $50 version or spend $500 or more, this seemed to cover the bases of what type of elec work will be needed going forward, from basic 12v coach stuff to later when the work of the house 110v stuff - and later still: the solar stuff)
My Harbor Freight multi meter works just as well as the others, they are free on any sale they have and are only like $5 when they are not free.
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