Thermal grease and ground wire for CDI voltage regulators

[hkeiner]

I bought two new CDI voltage regulators for installation on my 1996 Mercury 150HP outboard. The regulators are sandwhiched between the engine and a thick metal plate upon which the coils are attached. Two bolts per regulator hold everything in place. There is no ground wire on the voltage regulators and grounding is accomplished, I believe, by the physical contact between the body of the voltage regulators and the motor, bolts, and thick metal plate to which they come in contact.​

Thermal grease question:​

The instructions that came with the CDI regulators advise the use of a thermal grease for installation. I am not quite clear, however, on where to put the thermal grease without negatively affecting the the grounding of the regulators. I understand that thermal grease does not conduct electicity and fear that using it improperly could affect the grounding of the regulators. I believe that the thermal grease could be placed between the regulators and the engine (thus allowing the heat from the regulator to transfer to the motor block) and NOT between the regulators and the metal plate (to allow proper grounding of the regulators to the think metal plate). Is that right? Alternatively, does anyone advise NOT using thermal grease at all in order to better ensure a good ground?​

Ground wire question:​

I called my local Mercury boat shop about the risk of having a bad ground when using thermal grease and they said that their Mercury OEM voltage regulators have a separate ground wire (which the CDI regulators do not) and advised that I use the OEM regulators. Because I already bought the CDI regulators, I prefer to use the CDI's that I have. Does anyone have an thoughts on installing an additonal ground wire, say between the bolt heads for each regulator and then to the engine block?​

(notes: I generally do not like to jury-rig or redesign things and prefer to follow manufacture's specifications. However, since the CDI and OEM regulators are apparently different in regards to the the ground wire setup this might be one situation where it may be appopriate. Also, I once tried using dielectric grease on the posts of the battery in my car and it kept the car from starting. I had to clean the posts for the juice to flow again. As a result, I am skeptical that sufficient amount of thermal grease will get squeezed out to make a good GROUND contact when the parts are tightened together.)​

Thanks​

 

[Laddies]

Re: Thermal grease and ground wire for CDI voltage regulators

The gease they taking about is just a dielectric grease that is used on many differant electric connections you can get a small tube at a autoparts or radioshack store

 

[Texasmark]

Re: Thermal grease and ground wire for CDI voltage regulators

I understand your concern and personally prefer to use thermal grease on such an application. Actually had a CDI in a Buick fail once because the grease had dried out and no longer allowed for the sinking you mention.

If you are concerned, after installation with grease, you can take an ohmmeter, zero the leads and then connect between the case of the CDI, attachment plate, and engine block. You should read within 0.1 ohm of the zero'd leads reading for what I'd call a good ground.

If you are still not happy, a lugged, short, wire of 16 or so AWG could be attached under a mounting screw on the CDI and the other end connected to the engine block (preferably under a non functional screw.....like one holding a bracket on). The connections need to be clean and bright and if you could use a star lug or lug and star washer it would help to bite into the surfaces to be grounded.

An overspray with Phantom Black or clear acrylic would help to preserve your joint.

Radio shack also carries electronics type (white) thermal grease. It's loaded with alumina powder which is an excellent thermal conductor.

Mark