Identifying sources of electrical interference

[Derek - Raymarine - Moderator]

Electrical interference onboard a boat can have many effects, random or erratic equipment operation, loss of performance, complete loss of sensor signals or constant resetting of displays. The cause can be many and various and there is rarely a single quick fix.

A steady process of logical elimination is required, also what may work on one boat will not necessarily work on another. Each case is individual and specific to the boat, the installation, the cabling and small variances in cable runs, location of product etc..

The first area to be checked is the Power supply to the equipment.
Voltage level alone is not the sole determining factor for stable operation of equipment. The power requirements (P=IV) of the equipment must additionally be satisfied.
- loose, corroded, or poor electrical power connections, defective in-line fuses or fuse holders, fatigued or damaged cables will all have en effect ... inspect from the unit's power cable right through the distribution / breaker panel, through to the batteries. any high resistance joint or switch will drop some voltage and restrict current flow, thereby affecting the product. Check all connections both positive and negative. If the voltage is lower than the battery voltage, run a temporary heavy duty cable direct from the batteries, through an in-line fuse to the equipment,bypassing all other electrics onboard - if this fixes the issue then there is some problem still with the power distribution onboard. click here for further information regarding power supplies.

- the gauge of the wire used supply power or ground to the panel and/or MFD are of insufficient grade ... click here to view a web page addressing wire gauge.
- weak battery(s) ... have the batteries load tested, note that even when almost discharged a battery will still show 12v, however as soon as a load is attached the voltage will drop almost immediately and little current will flow. A fully charged 12v battery will register 13.6v.
- the regulated power supply cannot supply sufficient current to satisfy the power requirements of the unit
Remember that if there is insufficient voltage there will also be limited current to power the equipment

A poorly charged battery will also not be effective in providing a smooth and stable power supply that electronic equipment requires.

Electrical noise can become superimposed on the power supply to equipment and this can trigger shutdowns or erratic performance too. click here for further information

Other equipment onboard could be triggering this electrical noise and by turning off all other equipment, unplugging shore supply or even running the affected units from a completely independent battery, this may be isolated. Examples can be bow thrusters, electric pumps and motors, generators etc, all of which can trigger brownouts onboard affecting electronic equipment. Once the source is identified, power circuits can be re-routed, seperate batteries installed or alternative arrangements made to enable a stable supply to be provided for the electronics.

Charging systems or inverters can output a 'ripple' onto the power supplies and this can be enough to trigger issues, in this case power supply conditioners, previously referred to, will help smooth the supply. To test for the latter, the engine(s) and all equipment (except for the MFD) should be powered ON. The MFD's power cable would then be unplugged from the back side of the MFD and the DC voltage level would be measured at the cable's power pins using a multimeter configured to measure DC voltage. The voltage level should be approximately that of the engine's charging system or the electronics battery(s). The multimeter would then be configured to measure AC voltage and the voltage level would again be measured at the cable's power pins. if an AC voltage measuring 0.01 VAC or greater is measured, then a power condition would be recommended for the system.

Cables carrying high voltages or currents bundled with power supply cable to electronics can also induce electrical noise into adjoining cables, often separating these cables by 6" or so can be enough to eliminate the issue.

RAYFAQ#