Using a current shunt to monitor current flow through my motorcycle's battery

I've gone through a couple batteries on my '95 VFR750 recently, so I've been wondering if it's just a coincidence or if I have other problems. The regulator/rectifier seems to be charging the battery fine, starting at close to 14V at idle, and quickly maxing out at 14.8V when revved just a little. So the output voltage is neither too high nor too low, at least whenever I've checked.

At present, I'm thinking either my starter gets sticky at times and exceeds the CCA rating of the battery (180A), or something is happening during rides that causes the R/R output to be too low. Neither is easy to catch, so installed a 50A/75mV current shunt on the negative terminal of the battery to monitor whether the battery is being charged or discharged.

I had the shunt installed differently earlier so that I was measuring current flow to the bike (sourcing from the battery and/or R/R), so I was able to gather a few figures on total current draw (not just in or out of the battery):
* Headlights take around 9A to run.
* Cruising around took about 12-14A. Turn signals and brake lights would add 2-3A to this load. Higher RPMs would push current draw toward 14A, I assume to run the spark coils.
* The starter would usually spike 100-150A briefly at the start of the crank.
* If I cranked the starter extra long, even after the bike had started, I would see a draw of around 30A.

After moving the shunt inline with the negative terminal of the battery, I noted a few other figures:
* Cranking the starter after the bike was warmed up, but without the bike actually starting, would draw 70-100A when sustained. I don't know if this is normal, but it's below the battery's 180A CCA rating.
* Even at idle, the R/R would push a few amps into the battery, although turn signals and brake lights could occasionally nullify this and discharge the battery. But even approaching 2000 RPM would quickly bring the charging current up, and revving it would top out around 10A. It didn't take long for the charging current to start decreasing as the battery recovered from cranking the starter, and it would settle in around 1.5-2A while driving around.
* The radiator fan draws enough current to discharge the battery a little at idle, although revving a little would bring it back into charging.

FYI, these shunts and meters can be picked up relatively cheaply. I bought mine (RT3-5135) off eBay, and I've also ordered a 200A/200V meter that can switch between displaying voltage and amperage (uses an extra sense wire for voltage).

The 200A shunt will be a more work to mount since it doesn't have an insulated mounting base, so I'll probably need to make a couple more wires to mount the shunt further from the battery. In the video, the wire going from the battery to the shunt is 6-gauge house wire, with 1/2" copper tubing crimped, flattened, and soldered to the ends, and a hole drilled through them so a bolt could pass through it.

Category:

Autos & Vehicles

Tags:

• current shunt
• battery
• motorcycle
• vfr750
• current
• shunt

[9DragonMaster]

Did that LED come with the shunt? 

[phasm42]

@9DragonMaster Yeah it did. Check 'em out on eBay.

[RoadWarsOnSky1]

What is the rating of the ammeter not the shunt the ammeter its self

[ludrock2]

I got some thing similar from jaycar and mine shows-0.2 when no power is being used as well

[photolodge]

got same meter an shunt. i noted -.2 when you turned it on with no load. mine does same thing. wonder if pot on meter should be zeroed out.

[cabach34]

i like to know whats the problem?

my bike its doing the same.