I use an Edge Evolution to monitor various engine parameters one of which is battery voltage. Historically it has been spot on agreeing with my Fluke meter at the battery, but lately it does not. For example it might show 13.8 VDC when my meter says 14.25 VDC.

Now obviously I am monitoring right at the battery and comparing it to what the Edge reads off the OBDII and I am trying to figure out if this is an issue with my Edge or is there something else going down on my truck. I have also contacted Edge and am waiting for their response.

Any ideas?

 

You are within .5 vdc. You're okay. This could be cable temperature, minor corrosion, or probably nothing at all.


If you see more than a 1 vdc you have an issue that needs correction. For what it's worth, these OCM's are Pulse With Modulation. When you see something, it happened a few seconds back in time.


What's the difference at the post on the back of the Alternator vs the cable end on the battery vs the Battery Post?

 

Never was before. What changed?

 

Have you done this yet? Also, check for leakage between the (+) and the Battery Case.

 

If you really want to know the accuracy, you need to take the Fluke and look at the voltage right on the PCM connector - because that's where the reading originates for the OBDII port.

A loose ground, corroded connections, debris/oil "slightly" shorting something out... there are many reasons for a reading at one location to not match a reading at another. I suspect that by double-checking with a Fluke, you may have stumbled onto the early stages of an issue. Hey... we should name this stumbling onto something phenomenon - let's call it a "Fluke".

 

I will do this today. Overnight I have been running an open voltage test after fully charging the batteries and leaving the cables disconnected. That should also answer the (+) to case leakage question.

Here is my thinking on checking multiple points for voltage. Given I have 14.2 at the batteries with the engine running, the alternator has to be putting out at least that much as has historically been the case. If the batteries were less than that, I would be suspect of cabling or connection problems.

I think that leaves issues related to the PCM connection, the OBDII connection, or the Edge, although there may well be things I am not thinking of. The Edge seems to be consistent with historical data on EGT, boost, and temps.

I will gather more information on this later today.

Thanks,

Steve

Steve

 

Here is what I have so far.

My batteries are going on 6 years old and I still have 12.63 VDC this morning at the terminals using my Fluke. I think that is perfectly acceptable. My batteries also will hold a charge for long periods of time and my engine starts right up.

Today my Edge reads 14.1 VDC and I have 14.3 at the back of the alternator and 14.2 at the (+) battery terminals. I think those numbers are also in good agreement, unlike the variation I noted yesterday. I also know even when my Edge shows 13.6 VDC, I am still not in danger of discharging my batteries.

So what I think I have is an intermittent issue (oh joy) and it may be hard to nail down as I am going to have to capture data at the time the greatest discrepancy is taking place. Intermittent also means to me from work with RVs that I could be searching for either a component beginning to fail or a loose or compromised connection. This is something that may have to get worse and become consistent before I can make it better.

Steve

 

I think you're right.

 

I should note that the voltage varies as I drive (RPMs) and the power demands fluctuate (A/C engaged/not, brakes/lights on/not, various states of charge, etc....) . If I were to look at the gauge, then walk to the battery and take a reading - the voltage could truly change in that time. One way to avoid this possible scenario is to take my tablet to the battery and look at the gauge and the meter at the same time.

 

I can do that using extensions on my Fluke and alligators on the battery running the leads in the window.

Steve

 

That may very well give you some comforting results.