A Simple Way To Add Ground Wire Capacity

cr0ft said:

1500 watts at 12 volts theoretically equals 125 amps for the R3 starter.

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It's not as simple as that though - it can vary considerably because of the engine load;
The starter pulls in proportion to what the mechanical load on it is - 1500 would be the max.
Increased mechanical load means higher starter current; even simple things like the oil temperature, or grade of oil, can make quite a difference.
It'a also exacerbated by where in the cycle the engine stops when you shut it down; you will find your engine always stops in the same position. It stops when it meets resistance on compression stroke. That means when you go to restart it has to initially move against a compression stroke.
And the current required to INITIALLY get things moving is a lot higher than the sustained current once it starts cranking:
We all remember 1st Year High School Physics Class experiments on Friction - takes a lot more force to initiate motion.
And we've all pushed our motorcycles and experienced same thing.
From my experiences with the KeyLess systems I know that initial surge current on a Rocket is HUGE - enough to sag the battery voltage significantly at first instant of press of the button (this is happening too quickly for anyone to see with a meter)

So coupled with the starter cables upgrade, I would encourage to get the 'most' battery you can afford. Most in this case means CCA, not Ah (although typically higher in one will be higher in other anyway)
The LiFePO4 batteries are a great choice for BIG CCA punch, while not having as much battery voltage sag as a conventional lead-acid, due to different internal resistance.

Yep, that's why I wrote "theoretically", assuming it would vary.

Some people like the Lithium Iron, some people claim it won't do the job. There was a battery thread where the guys with higher compression and the like just didn't find it had enough "depth". My Shorai with 540 CCA equivalent has worked flawlessly for two years for me, though, but I think AGM might be the sweet spot between cost and capability. $300 for a battery is kind of nuts if you think about it.

The largest Ballistic Parts lithium battery shoots past $400.

DEcosse said:

Back to the original subject:
Apologies to the OP for being contradictory, however I would not personally advocate to ground to the chassis - the chassis is not an active current-carrying circuit component on a modern motorcycle, this is not like a car.
There is ZERO current flowing through your frame. Every component's negative return goes through the negative return wiring system directly to the battery negative;
the exception being those engine components - starter, spark plugs, oil pressure and neutral switch- which return via the engine block, then directly to the battery negative via the engine ground cable.
Engine contact to the frame is purely spurious, through painted surfaces; And you will encourage galvanic corrosion at the aluminium - steel interfaces.

So while I am complete agreement with the general premise of increasing the wire size (it has nothing to do with increasing the current capacity, but reducing the resistance) my recommendation would be to just make the cable a bit longer and connect it directly to the engine ground point.

But, similar to the headlight relay upgrades, where to get the maximum benefit, you need to not only augment the positive circuit to the lamps, but also the negative return, you need to do both sides of the starter circuit, which means the battery positive to the solenoid and also the solenoid to the starter.
You need the whole round-trip to maximize the starting efficiency.

This is the result on my Daytona - the difference in cranking speed is significant on that and KNOW the Rocket starter pulls a LOT more current; I guarantee you that it is a lot more than 70A. 4ga might have been overkill on the Daytona - I would probably go with that on the Rocket.


Here's a simple test you can do to determine the upside potential you might have:
Put your bike in gear, leave the side-stand down and tie your clutch lever to the bar with a zip-tie or similar; (that is how I disabled mine from starting in the attached video)
Run your starter (it will crank but won't start) and measure the voltage between the starter lug (on starter itself) to the starter body. Also measure the voltage directly across the battery terminals - this will show how much loss you are getting for the 'round-trip'
If you want to break up the supply and return, measure voltage from battery + to starter terminal and from starter body to negative terminal;

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I'm not sure how to address your reply to my post, but I will begin by saying you have made some valid points about my effort to show a simple way to improve the ground capacity of the Rocket 3. Your comment that.... "the chassis is not an active current-carrying circuit component on a modern motorcycle, this is not like a car".... is a point to be well noted. This point would be even more valid though if the the engine were mounted in total isolation from the chassis....which, of course, it is not. My question is....although it is not intended to be an active part, could it be used to enhance grounding in this scenario? It is true that grounding for much of the electrical system is done through separate wiring on the bike. I would consider that to be important for maintaining integrity and guaranteeing a dedicated path to negative as compared to relying on a chassis connections to provide a pathway to ground. I would think it would also factor into providing a more direct feedback path to the ECU which controls much of the bikes functions.

I would not, however, characterize the connection between engine and chassis mounting to be spurious. I don't believe one can discount this as being simply a casual acquaintance or insignificant connection between the the engine and chassis together as a whole. One only needs to make the mistake of contacting a clean part of the frame with a wrench while tightening down the positive terminal of the battery to understand the potential of the engine to frame ground relationship. This, of course, being a foolish practice with the negative terminal connected. Yes, any painted surface complicates this relationship, but I find it hard to believe that all the bolts, nut, exhaust, crash bars, anchor points, and associated lock washers found throughout the bike, it would not negate some of the painted frame to engine connections. This total contact surface would certainly have to at least be equal the surface area found on a simple ground terminal connection located on the engine. In my situation, the chassis ground point was welded to the frame and not a bracket forming a point of contact by simply being joined to the frame of the bike with a bolt. Certainly the frame could be considered as a ground point for adding a simple accessory ground connection, but I believe your concern comes into play with my using it as a larger pathway to the negative terminal of the battery linking to the engine ground.

As for galvanic corrosion or electrolysis, the potential is there whenever to dissimilar metals, in this case an aluminum alloy and steel, are brought into contact with one another. Add some moisture and it becomes even more of a concern. This could take place even without encouraging an alternate pathway for the flow of electricity. The question is...whether this process would be accelerated over time by doing the additional connection...who knows. I have no point of reference nor have I looked for any specific documentation that would prove this to be of major concern, even over the long run. On many motorcycles, the engine is actually part of the structural frame. How this plays out in a ground situation I am not sure. It would have been interesting to see what effect a separate ground wire from the negative battery terminal to the frame of the bike would have had on starting the engine in the video using the original 8 gage wire. This, assuming the engine is bolted directly to the chassis.

In conclusion, your opinion is valued and your points are noted and well taken. Especially in light of your work on the keyless ignition. Pretty cool by the way! When summer gets here and I have better access for working around my bike, I will rethink my grounding alternatives as should anyone else who has read this post. Thanks for your insightful discussion and video on this post.

I have a shorai too - note that the CCA is not an equivalent, the CCA is real - only the 'capacity' is labeled as an 'equivalent' (but really just BS on that one)
For sure the resistance is much lower on a LiFe and it will maintain better terminal voltage at high starting currents.
Cost no object, you can certainly get higher CCA capability with the LiFe - but as you say can become hugely expensive.
It's not that it needs that higher CCA - we already know that the starter current is not as high as the rated CCA of even the stock battery; the key is in how well it can hold its voltage at whatever current its supplying. i.e. a lower CCA battery will sag more, compared to higher rated CCA battery.

I just doubled up on my ground wire from the battery to the engine. I ordered a triumph ground cable for my type of bike. That way the cables are the same length. When paralleling two cables they should be the same length because ohms law says the path of least resistance would be the shorter cable. Thats why you want the cable to be the same size and length.

Jag said:

When paralleling two cables they should be the same length because ohms law says the path of least resistance would be the shorter cable. Thats why you want the cable to be the same size and length.

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That is incorrect - the resistance is the parallel sum of both cables, irrespective of each individual cable's resistance possibly being different from the other.
Besides not having to be same length, they can be different wire gauges.
Current will flow through both cables - if they are exactly same resistance, the current would be divided equally;
if different the split would simply to be to have slightly more in the lower resistance cable, than in the other.
But you still achieve the primary objective, which is to reduce the voltage drop across the cable(s)

DEcosse said:

That is incorrect - the resistance is the parallel sum of both cables, irrespective of each individual cable's resistance possibly being different from the other.
Besides not having to be same length, they can be different wire gauges.
Current will flow through both cables - if they are exactly same resistance, the current would be divided equally;
if different the split would simply to be to have slightly more in the lower resistance cable, than in the other.
But you still achieve the primary objective, which is to reduce the voltage drop across the cable(s)

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You would want the current to be divided equally?? Also if the wire is under sized and one is shorter than the other all the current would or could travel on that wire??

Jag said:

You would want the current to be divided equally?? Also if the wire is under sized and one is shorter than the other all the current would or could travel on that wire??

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No - does not matter if divided unequally; that is not relevant.
Current does NOT all go through the lower resistance, it splits proportionately between them

DEcosse said:

Besides not having to be same length, they can be different wire gauges.

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And not necessarily pure 100% copper, never mind splashing out on Silver wire.