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Old 08-07-2019, 10:40 PM   #1
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How to hookup disconnect switch.

Batteries on my dt466e keep running down so I bought a disconnect switch. Had originally intended on switching the negative. But there is a cable running from each of the negative terminals as well as one that runs between them. Any recommendations on the best way to do this.
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Old 08-07-2019, 10:41 PM   #2
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those clips are the charger i have hooked to it
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Old 08-07-2019, 11:00 PM   #3
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I can not really see the negative terminals from that picture. You may be able to install the disconnect between the grouding cable and the batteries.
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Old 08-08-2019, 08:09 AM   #4
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Will try to get better pic. That was my original plan. But there is a wire running from each of the negative terminals to somewhere on the bus. Along with 1 between them
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Old 08-08-2019, 09:13 AM   #5
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Question:

Every rig I have owned, that had a disconnect, had the disconnect on the positive side.

I never questioned it. What are the advantages and disadvantages of installing it on the positive Vs negative?

Thanks.
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Old 08-08-2019, 09:40 AM   #6
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Originally Posted by PNW_Steve View Post
Question:

Every rig I have owned, that had a disconnect, had the disconnect on the positive side.

I never questioned it. What are the advantages and disadvantages of installing it on the positive Vs negative?

Thanks.
It seems that the main concern with installing it on the positive side is that the switch itself (depending on the type) can significantly increase the amount of positive-wired exposed metal that is inside the battery box, increasing the chance of an accidental short.

I thought that the general guidance on removing batteries was to disconnect the negative and then the positive leads. If this is correct, I guess it would also make sense to attach the disconnect switch to the negative side.

I am sure of none of this, so I'll happily be corrected. I'm also wondering about what kind of switch has the necessary amperage rating for this, and whether the $6 Harbor Freight cheapie would work here (I'm guessing no).
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Old 08-08-2019, 09:46 AM   #7
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The disconnects that I am familiar with are enclosed and don't have any exposed copper.

Like this one: https://www.amazon.com/Disconnect-Ve...54685735&psc=1
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Old 08-08-2019, 09:49 AM   #8
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The disconnects that I am familiar with are enclosed and don't have any exposed copper.

Like this one: https://www.amazon.com/Disconnect-Ve...54685735&psc=1
That seems pretty clear that it's intended for the positive lead.

I was thinking more of this type: https://www.amazon.com/Battery-Disco.../dp/B07MTXDHNV which is intended for the negative post. I don't know why anyone would use this instead of the one you linked, except that it doesn't require any additional cables or splicing, I guess.
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Old 08-08-2019, 10:13 AM   #9
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Originally Posted by PNW_Steve View Post
The disconnects that I am familiar with are enclosed and don't have any exposed copper.

Like this one: https://www.amazon.com/Disconnect-Ve...54685735&psc=1
This is actually the one that I purchased.
Think i will just put it on the positive lead. May have to figure out where the 2 additional small fused wires on the positive terminals go. They may be the source of my drain.

Thanks guys!
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Old 08-08-2019, 11:43 AM   #10
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Originally Posted by MambaJack View Post
This is actually the one that I purchased.
Think i will just put it on the positive lead. May have to figure out where the 2 additional small fused wires on the positive terminals go. They may be the source of my drain.

Thanks guys!
dave
The fused wires go to the negative. That switch is designed for the neg terminal and the added wires also go to ground. I would not hook them to ground and hook it to the pos lead.
The only disadvantage to being hooked to the pos. is in the event of and accident or shift of the batteries, the terminal ends could contact the body or frame and short the circuit. NHRA requires cutoffs on the Pos.. Use one that has covered terminals.
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Old 08-08-2019, 02:25 PM   #11
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Quote:
Originally Posted by PNW_Steve View Post
Question:

Every rig I have owned, that had a disconnect, had the disconnect on the positive side.

I never questioned it. What are the advantages and disadvantages of installing it on the positive Vs negative?

Thanks.

Strange but every vehicle I have is disconnected from the battery on the negative side. Done by a habit I have got used to since trade school.
Not really remembering those classes much no I searched direction of current in a dc circuit.
Seems the dc electrons flow in one direction, from high potential to low potential.


Now I am positive of why I placed the disconnect switch on the negative post of the battery. This may seem unconventional to many but is the way dc current works with regards to batteries.


Don't believe me, do the search I just did as above.


John
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Old 08-08-2019, 03:04 PM   #12
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My bus has a Cole-Hersee M-705 battery isolator/selector for the two start batteries, connected to their positives and directly to the starter motor. That's how Crown did it, and I have no reason to doubt their rationale. The M-705 has now been replaced by the essentially-similar M-750, and they work well; if you don't have space for one, the Blue Sea 9001 and 9002 are also very good quality and take less space than the C-H. I recommend not buying some cheapo generic switch for something that can briefly pass hundreds of amps.

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Old 08-11-2019, 02:40 PM   #13
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Originally Posted by musigenesis View Post
That seems pretty clear that it's intended for the positive lead.

I was thinking more of this type: https://www.amazon.com/Battery-Disco.../dp/B07MTXDHNV which is intended for the negative post. I don't know why anyone would use this instead of the one you linked, except that it doesn't require any additional cables or splicing, I guess.
I would have some concern about the current rating on that one. Looks like 750 amps surge. I suspect that your starter may exceed that. I would get that question answered before pulling the trigger.
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Old 08-17-2019, 06:31 PM   #14
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Someone mentioned NHRA... if itís good enough for race cars, itís good enough for me...

No direct bus experience here, but I have wired off-road winches through Blue Sea manual marine disconnects (the big red ones that let you connect one, two, or no batteries) with great results. Check the current ratings; theyíre higher than the automatic charging relays, generally.

Iíve also used those ACRs, and theyíre great for dual battery systems in a 4x4.. For winching current levels, I always thought the manual ones were more appropriate, so I used them for that.
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Old 08-18-2019, 05:23 AM   #15
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I think the concept of disconnecting the negative side first (on negative ground vehicles) was simply practical, if your tool on the terminal accidentally hit the chassis you get no short. Other than that I don’t see why it matters which side you disconnect.
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