Testing for DC based ground leaks

[ESGWheel]

To test if there is a DC based ground leak is straightforward. Three steps and only requires a good multimeter (MM) capable of both resistance and DC current.
Note: this process assumes no interconnected AC shore power or solar panels or chargers. If they exist, all need to be completely removed from the DC side.

1st - Validating there is an issue:
1) Turn off all equipment
2) Disconnect the positive side of the battery.
3) Leave the main battery isolation switch turned “ON”
4) Set the meter to VDC mode, range appropriate for your battery (i.e., 12 or 24VDC)
5) Connect the meter between the positive terminal and the disconnected positive cable

The meter should give no reading. This means there is no path for current (i.e., a ground leak) and there is a completely open circuit as expected. If it reads XX volts for your XX VDC system, one of two things is happening:
1) Some connected equipment is turned on. This could a power feed to a stereo for the radio's memory, or a hard-wired detector or some other device like lights or the bulge pump in the “on” condition.
2) After disconnecting all the "hard-wired" equipment / turning off any other gear and still get a reading, then most likely have a ground leak in the boat's DC system.

2nd - Ground leak check:
1) Set the MM in Ohm mode and set it to the lowest range (x1).
2) Connect the leads of the MM to the disconnected positive lead and the negative terminal of the battery.

The meter is now reading the resistance of any circuit to ground that exists in the boat's wiring. The reading on the Ohm meter display will help identify the cause of the leak.
0-10 Ohms means it is most likely a piece of equipment still left on
10-1k Ohms is a low-drain piece of equipment left on, or a serious ground leak
1k-10k Ohms is a minor leak
10k+ Ohms is an insignificant leak

3rd - Determine how big of a leak:
The ammeter function of the MM can tell what the current leakage is. If the MM can read up to 10ADC, then it can be used it to measure amperage for leaks down to about 1.3 Ohms resistance on a 12 VDC system, or 2.6 Ohms for a 24 VDC. (Ohms Law: Current = Volts/Resistance > so 12VDC / 1.3 Ohms = 9.2ADC and same for 24VDC at 2.6 Ohms). Using Ohms law and the value of your MM’s DC Amps determines how low the resistance can be. Most MM’s ADC are protected by a fuse but still be cautious doing this. To see how big the leak is:
1) Set the MM to Amps DC (may require using different MM probe inputs)
2) Connect the probes to the positive battery post and the disconnected positive cable.

The meter is now reading the current flow of any circuit to ground that exists in the boat’s wiring. The readings can be characterized as:
<1mA - insignificant leakage
1-10mA - minor leakage
10mA-1A - major leak or some equipment left on
>1A - Usually some equipment left on.

While I have used the above process in my automotive days, the logical outline, and values for determining leakage characterization came from another post of about 10 years ago that I ran across.
For those with expertise in this area, please provide any corrections or comments to help all of us with these sorts of troublesome issues.

 

[Chris1956]

DC Ground Leak? We just called it a passive drain or short.

I am not sure about new boats, but newer cars often have small current flows when everything is off, especially when the battery is first connected. It would not surprise me if boats start to have those as well.

 

[dingbat]

DC Ground Leak? We just called it a passive drain or short.

Ground leak, passive drain and a short are three very different conditions in electronics

 

[cyclops222]

There can be a few milliamps for some electronic devices. Some older equipment has a need to keep all MEMORIZED things powered. It would take a month to slightly drain down the battery.

I have had computer controlled Rule Bilge Pumps that tested for bilge water every 2 minutes for 2 second run times. Still not going to kill the battery.

 

[ESGWheel]

Using the term ground leak was to aid in searching as this is the term I have seen used in other posts. Agree there are possible parasitic draws on new boats and even older ones. My 2005 Larson has a sensor based (vs float switch) bilge pump fm Rule Mate. Their tech support confirmed the sensor has a parasitic draw but it’s so small it does not present an issue and would be considered insignificant (now that I say that I should measure it to see if it does fit in that category listed above

My hope is that for someone who has or suspects they have an issue, the above post will guide them to a proper conclusion. Sharing learnings and helping others are my way of giving back, hence the post.