Re: [Amel] Isolated or non Isolated DC to DC Convertor

Herbert Lackner


We will install a Kenwood 480HX SSB with an MFJ 993BRT automatic antenna tuner on our SN #120. We do not have a HF ground plate (I think that was an only an option for the SN). To ground the antenna Tuner I planned to connect it to the rudder shaft where the thick yellow/green cables are connected (I assume they are for the VHF grounding).


is that ok?  (do not want to have a   Swiss cheese rudder shaft J )


Thanks, Herbert

SN #120 Kali Mera, Sukosan



Von: amelyachtowners@... [mailto:amelyachtowners@...] Im Auftrag von Joel F Potter
Gesendet: Freitag, 29. November 2013 17:16
An: amelyachtowners@...
Betreff: RE: [Amel] Isolated or non Isolated DC to DC Convertor



All Amel boats since at least as far  back as the Meltem in the 1970’s has a floating/full earth return 12 and/or 24 volt direct current system. Simply, this means all DC power comes out of the battery, to the device that needs the power, AND THEN RETURN COMPLETRLY AND DIRECTLY TO TH BATTERY BANK. This prevents many possibilities of corrosion and keeps noisy things like fans and fridge motors from ‘talking’ to your radio, stereo and so forth. It is extremely important to never corrupt this system as, depending on how much power has been corrupted, you can suffer serious problems with electrolysis and feedback.


All Amel’s that had a ICOM SSB installed at the shipyard came with a special ICOM 24-12 volt transformer/converter with an isolated negative to accommodate the floating/full earth return. If you provided your own equipment for them to install, they always insisted on the special isolated negative transformer and would not install transformers that were not compliant with this. SSB’s require a healthy amount of power that can cause trouble if not integrated into the DC system correctly.


If your Amel has been modified by those unknowing of the type of DC system it has, change it back to the way God and Captain Amel ( and Jacques Carteau! ) conceived it.


If an electrician or electronics installer comes to your boat, be sure to ask him if he is familiar with a floating DC systems. His answer should be in the affirmative with a compliment that this is the best way to power DC gear. If he says “no”, “that’s stupid”, or “Whuzzat”, send him away. Trust me, you don’t want to screw around with this. I sold a SM 53 boat where the rudder shaft was Swiss cheese because of an improper SSB install. When we dropped the rudder to replace it, I bent the shaft in half with my bare hands. They guy who bought this boat still owns it, I believe, and I invite you to chime in here. He spent $3500 to repair the wiring and more to replace the rudder shaft here in Fort Lauderdale. Amel was a big help with technical assistance but Carteau admonished me to not screw around with the DC electrical system even though it wasn’t I who ever messed with any DC system on an Amel.    


All the best,




Joel F. Potter - Cruising Yacht Specialist, LLC

Amel's Sole Associate for the Americas

Mailing Address:  401 East Las Olas Boulevard #130-126

Fort Lauderdale, Florida  33301

Phone:  (954) 462-5869   Cell:  (954) 812-2485

Email:  jfpottercys@...



From: amelyachtowners@... [mailto:amelyachtowners@...] On Behalf Of Richard03801
Sent: Friday, November 29, 2013 10:27 AM
To: amelyachtowners@...
Subject: Re: [Amel] Isolated or non Isolated DC to DC Convertor



Hi. Under the navigation station the doors on the right side have 12 V power supplies that should be your source for 12 V coming off the 24 bank. I believe the brand name is sailor. 

In the ass locker there should be a copper foil for grounding the A140 tuner. 


Richard Piller


Cell 603 767 5330

On Nov 29, 2013, at 8:27, <terencesingh@...> wrote:


Some advise is needed with respect to the replacement of the factory installed 24VDC to 12VDC DC to DC Convertor.

We are about to install our Icom M802/AT140 SSB Radio.

The existing 12VDC wiring system is quite mess and includes a separate 12VDC battery that was used for the previous SSB installation.

I have heard that an Isolated ground DC to DC convertor should be used. These are used in systems that are ether positive ground or with floating ground systems.

I am pretty sure that our vessel (SM#196) does not have a positive ground system. 

Did Amel built their boats with a floating ground?

What does this mean with respect to installing a DC to DC convertor?

What are the ramifications for using a non isolated DC to DC convertor?


Any help understanding this is much appreciated.



SV Libby SM#196

San Diego

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