Erratic Gauges

[svfinnishline]

Originally Posted by mrm

A multimeter across this suspect wire will show what voltage drop and fluctuations are there.

Marius

OK here's the test results- V1 is battery voltage, V2 at end of negative cable (attached to shunt) and V3 at the bus bar:

MIN SOC V1 V2 V3 AMP
0 42 13.15 13.34 13.39 177
1 44 13.29 13.46 13.50 177
2 45 13.35 13.52 13.56 179
3 46 13.37 13.54 13.57 178
4 47 13.38 13.55 13.58 175
5 47 13.40 13.56 13.59 174

It seems OK to me - but let me know if there is something I have missed.

I did find the negative batt cable to batt post connection was loose by 1/2 a turn or so, maybe this was the root cause?

The fluctuating gauge problem has not reappeared and the shut off switch has been working fine the last 3 times.

Thanks again for the help!

[svfinnishline]

There's as usual more to this story! I believe the root cause of this issue was a poor ground connection. I found the one negative battery post heating up relative to the other 3 battery posts. I had used multiple steel washers to separate the negative battery cable lug from the battery parallel cable. Despite all the connections being clean and tight the resistance was too high and the post temperature increased to >52C during high rates of charge.

Lesson #1 is use washers sparingly, and use copper washers.
Lesson #2 was just learning about how useful a simple temp sensor (in my case a fluke meter and thermocouple wire) can be to diagnose poor (high resistance) battery connections. Just by comparing the temperatures I was as well able to find the same problem with the positive battery post as well. For me its worth rechecking this every time a terminal connection comes apart.

Thank you for the help - it definitely saved my bacon and made me understand the importance of 'minor' issues; before they became major!

[boatman61]

Gonna have to get new reading glasses...
I thought you said 'Erotic Gauges'....
Hence my interest...

[Bill S]

I have a similar problem with erratic gauges, but have a single alternator set-up. When the alternator output is high, the temperature gauge reads high, which is a decrease in voltage in the temp sensor circuit. I have been resaerching this for some time. I found that automobiles have voltage stabalizers feeding power to the gauges, but the sailboat does not have these and the voltage could vary from 12 to 14 volts. (How many volts should a gauge have?).

I too suspect a ground problem and plan to run a temp gnd wire from the temp gauge to the sensor. I have been considering putting in a non-electrical type of temperature meter. I have thought that the engine was running hot for years, but it may be that the gauge is off.

[roanokejim]

Hi Bill S. I think you are right. I tried the ground problem and it shocks me that it is really the problem. I will try to work it out. Thanks.