Voltage Regulator

[NRolfe]

Hi-- I have a 1993 Mercury 75-HP outboard engine on a similar-age 15-foot boat. I bought the outfit privately last year because both the boat and the engine looked to be in very good condition.

Last weekend we were out on the sea water skiing. By the afternoon there was smoke coming from the engine and a smell of burning. After switching off and letting it cool down, I opened up the engine side panels and saw that the regulator and its wires had burnt out. I realise this is an old engine and maybe we had be been giving it a hard time.

What would cause [the regulator] to overheat and burn out?

I have read somewhere that the battery should be a non-maintenance free type, which mine is not. Any help would be very much appreciated. Cheers--Neil Rolfe

[jimh]

Electrical or electronic devices "burn" when too much current flows through them. The excessive current generates heat. Heat is the enemy of all electronic and electrical devices, and with more head usually comes more problems. Solid-state devices tend to increase their forward-bias current flow with heat, so heat begats more current which begats more heat which begats more current. The end comes when the melting temperature of something is reached. Sometimes the first thing to melt is the silicon junction, which becomes just a junction and allows even more current. Then things get hot.

The principal cause of this in older Mercury voltage regulators is either poor design or poor manufacturing quality--they were farmed out to Mexico for production.

Outboard engines with poor voltage regulation on their charging output should not be used to charge sealed valve-regulated batteries.