January 13, 2016

Today's post is one that will hopefully be very helpful to mechanics and riders alike. I spend a good deal of time every day talking with people about their battery and charging system issues, and as a result I have a lot of experience in this area.

It is not often that I get to use real data captures to explain a battery concept. Often, clients dont want their data displayed publicly. Mostly, people dont have data recorders when they have electrical failures, so I am usually forced to work through the issues after the fact. Not easy.

This is different. This time, I have a screenshot of the data trace that I need to explain why this battery was killed, and permission to post it on the blog. Also, this was a beautiful bike built and tuned by one of the best tuners in the US. Top rate stuff all around. First, the email from him:

Hi Jason-

I sold a P2 battery to a customer for a ZX10 Marelli project bike that we built a few months back and seem to have run across an issue with it.  I just completed a two day test with my customer and on the second day, last session the bike began to cut-out and stop running as he reached the pits.  I downloaded the data and looked at the battery voltage throughout the session and noticed that the voltage began to drop and finally ended up at 7 volts, thus shutting off the bike.  I attached a screen shot for you of the voltage drop from my data. 

Could it be possible that the battery has had a failure inside it?  I did put another battery in the bike after the session and started the bike, the voltage was charging at 13.5V at 4000RPM, which is normal.

Could you possibly send me two P2 batteries?  I'd like to have one on the shelf as a spare?

Let me know- B

This is the image of the data trace:

 Troubleshooting a lithium battery

And the response:

Hey B-

I think Ive got this figured out- but if you would rather call, Im always available for troubleshooting for you.

This graph is really helpful. Wish everyone could supply these! Here is what I am seeing in this graph.

This trace is a textbook example of a stator/regulator failure. Here is why:

A slow voltage decrease over time/distance, like what you see in that graph, indicates a loss of current supply from the stator- or shutdown of reg/rec- forcing the bike to use all of the battery reserves to power the electronics. Remember, a running motorcycle is drawing current from the stator- not the battery- so a slow voltage decrease means charging system failure, not battery. As the battery reserves run out, you get a voltage decrease, resulting in symptoms which you described.

I am guessing that the event at 17.8k on the X axis corresponds with the bike shutting off? Since the bike is no longer loading the battery, it is going to rebound in voltage. A good analogy is to watch the start event. As the starter draws from the battery, voltage sags. Once the bike is running (even without a charging system) voltage rebounds and stabilizes.

I also estimate a typical Mag Mar inline 4 system will draw 14-17 amps, depending on sensor and fuel pump configuration. This means that if you start a session with a fully charged battery, you would get around 15 minutes of run time from a P2. (The P2 is a 5 amp hour battery, so you should get around 15-20 minutes of run time with no charging system on this


Also- 13.5 is not normal charging voltage in my experience. Assuming you are using a kit stator- that is low for sure. At 4k, you should be just over 14v, with a peak of 14.7v over 6k. While the kit stuff will produce less watts/amps, voltage should also be similar to stock- above 14v.

Were you able to continue the day with the replacement battery? Id like to see a trace from the bike post swap.

Have you tried recharging the battery? Curious to see it recharged. Put it on a balance charger and Id bet it will be fine.

The failure modes for these batteries are generally on/off. If something fails inside one of these it will go to zero volts. Again, generally- there is always a new and exciting way to kill stuff that I haven't seen! :-) Ill get a few P2's in UPS for you.



In a phone call later that day, we looked at other session data from before and after, and found that this bike was never charging at greater than 13.4-13.6v, which is way out of spec, and is too low. A few quick checks with the multimeter verified that the stator winding was shot, and was the cause of the issue.

Ive said many times that lithium batteries (good ones) are usually "killed"- they seldom just "die". This is one example of that in action.