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ContinuousWave Whaler Moderated Discussion Areas ContinuousWave: Small Boat Electrical Connecting Cables To The Battery
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Author | Topic: Connecting Cables To The Battery |
Tom W Clark |
posted 01-19-2014 03:37 PM ET (US)
Many modern Marine batteries have threaded studs in addition to the conventional clamp-on terminals. So if one is having brand new battery cables fabricated, should one have cable clamps put on or are ring terminals sized to the threaded studs adequate? |
jimh |
posted 01-19-2014 04:07 PM ET (US)
I'd use ring terminals on the cables. The large battery clamp and fat and soft post connections are a legacy from old automobiles and early batteries. Today many of the imported AGM batteries have neither big posts or threaded studs, but rather a threaded land or conductive area on the top, and cables are attached with ring terminals and a machine screw. The threaded land for connections is seen in this Cabela's AGM battery. Those types of connections use a rather small hole in the ring terminal compared to a 0.313-inch or 5/16-inch threaded stud. If going with 4-AWG and a 5/16-inch stud, use a terminal like a MOLEX 0192210231. For 2-AWG and 5/16-inch stud use Molex 0192210233. |
jimh |
posted 01-19-2014 04:31 PM ET (US)
I think the Cabela's AGM battery lands are threaded for a M6x1 fastener. That is a 6-mm fastener. [Here I had to change my calculations due to some bad math and wrong equivalence; thanks to tmann45 for the hint--jimh] In inches, 6-mm is about 6/25.4 = 0.236-inch, or just under a quarter-inch. The 6-mm terminal won't fit on a 0.250-inch stud. And 5/16-inch is 0.3125, so the 6-mm connector does not fit on a 5/16-inch stud. You can find some specialized ring terminals with the hole size for the stud set for metric and the wire crimp housing sized for AWG. For example, a ring terminal for a M6 stud and 2-AWG wire is http://www.digikey.com/product-detail/en/5580635/732-4300-ND/3844680 |
tmann45 |
posted 01-19-2014 09:26 PM ET (US)
Be careful of the ring terminal size, some batteries have 5/16" and some have 3/8" studs on the negative side. 1" = 25.4 mm [Thanks for the reminder--jimh] |
swist |
posted 01-20-2014 08:21 AM ET (US)
Relying on the pliability of soft lead (or whatever those terminals are made of) to make a good connection does seem pretty "low tech". After a long enough time, many seem to ooze yellow crud. But this discussion begs the question of why automobile batteries don't use some other form of connector. |
jimh |
posted 01-20-2014 07:01 PM ET (US)
Most car batteries now use side terminals, which have a large area of connection between the battery land and the wire terminal. Re the wire terminal hole sizes for the post or fastener: it is actually quite hard to enlarge the size of the ring terminal hole without messing up the terminal. I recommend getting the terminal with the correct hole size for the threaded post or fastener that will be used. You can make up some difference by using large washers. |
jimh |
posted 01-20-2014 08:35 PM ET (US)
This might be helpful: 6-mm 0.2362-inch. Used on many AGM battery terminals. 1/4 0.250-inch. Found on some threaded terminal posts. 5/16 0.3125-inch. Common on threaded terminal posts. 3/8 0.375-inch. Very common on threaded terminal posts. In looking at the drawing for a ring terminal rated for an M6 fastener, the actual hole diameter in the terminal is given as 6.4-mm, or 0.252-inch. It should be a snug fit on a 1/4-inch post. Another terminal, said to be sized for 1/4-inch studs, has a hole diameter of 7.06-mm or 0.278-inch. This is an easier fit on a 1/4-inch threaded post. According to a Wikipedia article at http://en.wikipedia.org/wiki/Battery_terminal marine batteries are said to typically have different diameter posts for the positive and negative terminals, with the convention to be POSITIVE = 3/8 x 16 thread NEGATIVE = 5/16 x 18 thread I have not made a wide survey to see if that is universally true. I have an Interstate Marine Battery on hand, and the two terminals are the same size; both are 3/8 x 16. Based on that exception to the supposed rule, don't automatically assume a marine battery will have terminals of either the same or different size; you should check the particular battery. Also don't assume the terminal polarity orientation will always be the same. The positive and negative terminals often change position on some models. |
jimh |
posted 01-20-2014 08:38 PM ET (US)
The concept of the Group Size is a bit frustrating to track down good information. The Group Size is set by the Battery Council International (BCI) but they do not publish their information on-line. They would rather sell you a printed copy of the specifications for $125. On that basis, I don't know of any really authoritative source of information about battery size, terminal location, and threaded post size as set by a BCI Group Size designator. (But try this PDF file; it looks interesting, if even you are warned against using it.) |
jimh |
posted 01-21-2014 10:04 AM ET (US)
The use of side terminals on an automotive battery is perhaps something which has mostly been adopted by General Motors, and the old-fashioned soft lead posts, which, by the way, come in a variety of diameters and tapers, are still in use on many brands of cars. I think my 2011 FORD has a battery with those tapered lead posts. In the so-called marine batteries one often finds both lead posts and threaded terminals. Sometimes having two connections on the battery can be useful; for example, if you want to connect more than one conductor to the battery. You could connect one conductor to the lead posts, and connect a second conductor to the threaded posts. |
kwik_wurk |
posted 01-21-2014 12:32 PM ET (US)
Fundamentally, you are always looking for the most contact area to make your electrical connection. So a large lead post has it's advantages in large current (but low voltage 12-48 VDC) applications. For small recreational boating applications, screw terminals make much more sense out of practicality versus the theory of needed surface area. If I was running a electric propulsion system on batteries, it would likely use lead posts, with 00 cables. Some of my battery sets have dual posts. I have liquid taped a cap on the lead posts, to avoid touching them with a tool or something. |
Tom W Clark |
posted 01-21-2014 11:02 PM ET (US)
It sounds as if the Sears group 34 Marine Platinum Die-Hard is perfectly typical. The screw studs are 3/8-16 on the Positive side and 5/16-18 on the Negative side. The battery cables we are ordering from genuinedealz.com will have 5/16" (M6) and 3/8" (M8) lugs. There is the option of ordering "Heavy Wall" tinned copper lugs for a trivial added cost. Any reason not to order "Heavy Wall" lugs? |
russellbailey |
posted 01-22-2014 10:37 AM ET (US)
Tom, I think the heavy-wall lugs are preferable. That being said, it is possible you may find a connection where the smaller, standard wall size fits better. I would suggest you plan to use the heavy-wall but get a few standard as backup. This is a great instructional for cable choices - I followed it closely. (the recommended crimper is great also) |
jimh |
posted 01-22-2014 11:43 AM ET (US)
Tom--your mention of the Sear battery terminals reminded me: I had to run to the hardware store to buy new hardware for that 5/16-inch threaded post when I changed to the Sear marine battery from the Interstate marine battery. So much for consistency among "marine" batteries. |
17 bodega |
posted 01-23-2014 03:02 AM ET (US)
I use the ring style in tinned copper. They work fine. I use the Costco Kirkland marine batteries and they still tested good from 2006. I changed them just out of paranoia that they would fail in the middle of the ocean. Steve |
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