Battery Cable Questions

[Guest]

Hi all,

I've done some searching and haven't found conclusive answers.
I'm relocating the battery to the back of the frame behind the seat (under the tail cover). Can I ground the battery to the frame in that location, as in the back of the bike, or does it need to be grounded to the engine?

Also, what gauge cable should I use one both the ground cable and the + terminal?

Thanks in advance.

[Steve]

You can use the chassis as a ground (just like the factory does), but the starter is your biggest current draw (which is why the direct wire to the engine), so make sure you use adequate wire. I would probably use 4- or 6-gauge wire.

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[koolaid_kid]

The gauge of the wire depends on the length of the wire. 4 gauge is fine unless you want to go the length of the frame.
The factory configuration is to ground everything to the frame, including the battery. There is another school of thought that everything should be grounded to one point and that one point should be grounded to the battery. A less radical method would be to connect all ground points to each other and then to the battery.
I use the factory configuration with no issues. Dealer's choice.
Sorry, Steve, you posted while I was typing. I'll just leave it as is to give the OP a bit more info.

[Collo]

Okay thanks for the help Gents.

The original ground went from the battery to the clutch cover. So now the battery is in the boot (for lack of a better expression) I'm hoping to ground it close. Sound like it shouldn't be a problem only that I have 8 gauge wire. Can always buy new stuff I guess.

I'm confused now about the starter... it has a big black cable which is now too short to reach the circular power thingy up near the 'boot'... is this the one you mean that must be adequate in size? The original one has pretty solid strands but not really that thick.

[koolaid_kid]

To clarify: If the cylindrical object has 2 terminals for thick cables and one small wire on it, it is your starter solenoid. Have you moved it to the back with the battery?

[bonanzadave]

I have 8 gauge wire.

Thats fine. 8 ga should be good for 50 amps. We use 4 gauge on 100 amp alternators on airplanes. Im guessing that little MC starter wont pull 50 amps. I would still run a ground to the engine.

[Steve]

I'm confused now about the starter... it has a big black cable which is now too short to reach the circular power thingy up near the 'boot'... is this the one you mean that must be adequate in size? The original one has pretty solid strands but not really that thick.

As Koolaid_Kid mentioned, the starter solenoid (your circular thingy) will have two large cables attached. One will connect to the positive terminal on the battery, the other to the starter. They both have to carry all the current to the starter, so should be as large as practical. You may need to go to your auto parts store to see what they have in the way of generic starter cables to see if any of them might work.

The starter also needs a return path, usually called a "ground" or "earth". The starter is bolted to the engine case (good connection), and the engine case is bolted to the frame, but there are so many connection points (bolts, nuts, etc.) with so many opportunites for corrosion, so there is a dedicated ground cable that connects the engine to the frame. There is also a dedicated wire that connects the battery negative terminal to the frame to complete the circuit.

In your case, since you have moved the battery to the "boot", you will need to extend the wire from the starter solenoid (assuming you have also moved it to the boot) to the starter and make sure your battery has a good ground connection.

Thats fine. 8 ga should be good for 50 amps. We use 4 gauge on 100 amp alternators on airplanes. Im guessing that little MC starter wont pull 50 amps. I would still run a ground to the engine.

8 ga will work fine for short-term use with 50 amps.

However, I have used my clamp meter to check the starter current and found that it averages just a bit over 50, it's closer to 80, but it varies widely with the crankshaft position. Still, 8 ga will work.

Depending on how you measure your wire, that would be 3 to 4 mm diameter or 8.3 to 13.3 mm^2.

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[Collo]

To clarify: If the cylindrical object has 2 terminals for thick cables and one small wire on it, it is your starter solenoid. Have you moved it to the back with the battery?

That's correct, under the seat now...

[koolaid_kid]

First, I tend to err on the side of caution. You are going from the "boot" all the way to the starter, and you are carrying a possible 80 Amps of current. I would not be comfortable on my bike using anything smaller than 4 gauge wire for that connection. It's only one run of wire, possible 4 feet. Use a heavier gauge than minimum wire with heavy duty ring terminals and you won't have to worry about it. And both the wire from the battery to the solenoid and from the solenoid to the starter need to be the same gauge.
But that's just me.

[Collo]

You lot are a great help, many thanks!

I would like to do things properly so I will buy some proper cable tomorrow. I found some 4 gauge cable from my car amp stuff, but I'm reluctant to use is as a starter cable and would prefer something like the original. The original ground cable for the battery is long enough to use again (only somewhere else) so that will be good. So it's just the positive terminal to the starter solenoid to worry about now

Can't wait to have this finished and back to the seat making.

[koolaid_kid]

The car amp cable is exactly the type of cable you want. Perhaps it is bright pink so you don't want to use it? Just remember, the cable on your bike now was made in the early 80s. Don't hesitate to put a newer, better cable on it now, almost 30 years later.

[Steve]

I found some 4 gauge cable from my car amp stuff, but I'm reluctant to use is as a starter cable and would prefer something like the original.

Electrons are blind and VERY indifferent.

Besides the fact that they are blind, it's dark inside the insulation, so they can't tell what color wire they are running through. They also don't care whether they are feeding the amplifier, speakers or a starter. Electricity is electricity. Like Kid said, what you have is PERFECT for the job. Just get some proper terminals (if you have to cut the wire) and support it to keep it tidy.

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