Mobile Grounding and Negative Power Fuses

My radios all have fuses on both positive and negative power leads.  An interesting article  

  • Do not connect the negative power cable directly to the battery negative post.
  • Do not fuse the negative power cable.

W8JI argues that a negative fuse is unnecessary and unsound.   W8JI also argues against connecting directly to the negative battery post as is recommended by some manufacturers including Yaesu ( e.g. FT857D Manual pg 8).

The reasons not to connect to the negative battery post  are 1) to reduce alternator noise and whine, and 2) safety reasons. Yaesu advises to connect directly to the battery to reduce alternator noise.  If the automotive ground is lost for some reason, the radio ground provides the return path to the battery.  If the negative fuse blows, w8JI argues the radio is still grounded through the antenna or key. The reason not to fuse the negative ground are that if the fuse opens, the radio is still grounded through the antenna ground, through a morse key, a direct chassis ground, or any other inadvertant path to ground.  Then these paths provide the ground path.  The negative lead to chassis conducts the high currents to the chassis ground, and reduces possibility of burning traces in the radio.

Another reason to ditch the negative fuse  is a likely voltage drop  and a potential cause of low voltage and resultant transmission splatter.

The FT857-D Operating voltage is 13.8V +- 15%  ( low == 11.73 V  high == 15.87V ). Yaesu warns not to operate if voltage falls below 11.73 V to prevent erratic operation, shutdown.  


~ by marksun on August 12, 2014.

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