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Author Topic:   Grounding
griffgil1 posted 07-22-2007 02:23 PM ET (US)   Profile for griffgil1   Send Email to griffgil1  
My array requires a 24v power supply- my boat power is 12v. I will be powering the array with a DC/DC step-up converter. Where can I ground the array? I don't think one can ground 24v equipment to the main ground bus of a 12v system. Also, the converter is NOT an 'isolated' coverter (not quite sure what that means either), so instructions say it is not meant for "floating" or "positive" ground systems. Thanks all.
jimh posted 07-22-2007 04:53 PM ET (US)     Profile for jimh  Send Email to jimh     
quote:
I don't think one can ground 24v equipment to the main ground bus of a 12v system.

Why not? It is entirely normal for DC voltages to share a common reference point, 0-volts, or ground.

Chuck Tribolet posted 07-23-2007 08:42 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I think you need to understand more about that converter --
I interpret what you say to mean that the converter will tie
the 24V and 12V negative together.

And that must be a pretty beefy converter. It takes a fair
amount of power to run an array.

What array? What converter?


Chuck

griffgil1 posted 07-25-2007 03:01 PM ET (US)     Profile for griffgil1  Send Email to griffgil1     
Let me re-explain:

The radar cable has three wires on the end that attaches to the converter- red, black, green. The end that attaches to the radar array has a red, black, and bare RF screen wire. The RF screen wire attaches directly to the metal radar housing via a metal saddle clamp. Where do I attach the green wire on the other end, since there is only a positive and negative output connection on the converter?

jimh posted 07-25-2007 09:13 PM ET (US)     Profile for jimh  Send Email to jimh     
If the device you call an "array" is a RADAR unit, consult with the manufacturer about where to connect the shield of the power cable. In most cases this would be bonded to the hull, but if your hull in not conductive, there may be alternative techniques which are recommended. The manufacturer of the device ought to be able to assist you in the installation with questions like this.

The power wiring of your boat will be configured like this:

+ 24 Volt --------Output of DC-to-DC converter

+ 12 Volt --------Positive of 12-volt battery

0 Volt common ---Negative of 12-volt battery; negative of DC-to-DC converter

On most boats with an outboard motor the chassis of the outboard is connected to the battery negative, and though the outboard motor gear case and propeller the battery negative is in contact with the sea. This provides a reference potential of 0-volts.

towboater posted 07-26-2007 12:40 PM ET (US)     Profile for towboater  Send Email to towboater     
IMO, trade the 24v in for a 12v radar asap.

sorry, I know you dont want to hear this but, I might be negligent to let it slide.

I cant tell you how many electrical problems I faced simply using 24v starters on my diesel engines.
2 8D bats. Sounds simple.
Primarily it was the isolators going bad...all flavors.
Forgive me if I put isloators in the same electrical context as a 12 to 24v converter. Arent they just the opposite of eachother in this situation?

Finally, after several isolators, expensive alternators & down time... my electrician talked me into buying 12v starters (twice as expensive as 24v starters) and I havent had a problem since. The biggest improvement is that the alternator feels the CORRECT draw and responds. I dont know what it is about isolators or the ones I had that would always send the alt the same message no matter how many deck lights and electronics I was using...thus, I would end up with low voltage after a long night on the water. Actually, we could never figure out why the alternator wouldnt keep the bats full and ended up going with 12v starters that solved the problem. I hope you wont have this problem...but, how the charging system reacts to your converter would be the first thing I would check.

12v Radar eliminates ALL that speculation and possibly arguement that a converter will or wont have issues.
Ive had a JRC (48" ant, crt screen, 12v) for so many years now I almost forgot the brand name. I can pick out boat swells with it. It absolutely kicks the ass of a 2003 Furuno (24" ant) and only cost 3k back then.

mk

griffgil1 posted 07-26-2007 01:08 PM ET (US)     Profile for griffgil1  Send Email to griffgil1     
OK, got it figured out! Thanks for the input all. A quick rundown for all those who may have similar questions in the future-

Normally (not always), most 12/24v systems on outboard boats DO NOT have a bonding/grounding system connected to the H2O. Some Mfgs. call it a "floating" ground because it is never truly "grounded" by the water/earth. In this case, most electronics mfg. either tell you to cut and insulate the ground wire (i.e. don't even use it), or like in the case of Raymarine, they say connect it to the negative side of the battery. Some, like Garmin, just give you a red and black wire period- no choice in the matter 'cuz there is no ground wire to worry about.

I don't know how other boat builders do there systems, but BW has what they call a "main ground bus". This is NOT a ground at all, it is the negative side of the connection, and is wired directly to the negative battery post. This is where I got really confused!

As for the radar and converter: same thing, just use red and black wires for everything (per mfgs. recommendations via phone call to Analytic Systems).

I would like to know if anyone has put in a true grounding system in their boat, and if it actually helped with noise, etc.

Thanks again, Griff

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