Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 13-05-2017, 19:16   #16
Registered User

Join Date: Feb 2016
Location: So Cal
Boat: Lancer 44 Motor Sailer
Posts: 542
Re: Negative Ground vs Positive Ground History Question.

My long gone 1965 MGB roadster was 12 volt positive ground. was a pain in the rear to put in a newfangled AM-FM Cassette player. I used a small square of plywood under the dash to mount it with negative ground.
__________________

Diesel Bill is offline   Reply With Quote
Old 13-05-2017, 19:17   #17
Senior Cruiser

Cruisers Forum Supporter

Join Date: May 2013
Location: Oregon to Alaska
Boat: Wheeler Shipyard 83' ex USCG
Posts: 2,487
Re: Negative Ground vs Positive Ground History Question.

If your boat with a positive ground has one improperly wired item it can eat the underwater metal in a very short time. Commercial fishing trollers were commonly wired with a positive ground before many electronics were common. The reason was to put a +0.5 volt charge on the fishing lines. It was known to better attract fish.
I had a fishing friend who installed a new radio and wired it backwards. Everything ran ok. One day, three weeks later, backing down, the blades on his 44" prop came off.
__________________

Lepke is offline   Reply With Quote
Old 14-05-2017, 01:26   #18
Registered User
 
Snowpetrel's Avatar

Join Date: Jul 2012
Location: Hobart
Boat: Alloy Peterson 40
Posts: 3,919
Re: Negative Ground vs Positive Ground History Question.

Quote:
Originally Posted by Lepke View Post
If your boat with a positive ground has one improperly wired item it can eat the underwater metal in a very short time. Commercial fishing trollers were commonly wired with a positive ground before many electronics were common. The reason was to put a +0.5 volt charge on the fishing lines. It was known to better attract fish.
I had a fishing friend who installed a new radio and wired it backwards. Everything ran ok. One day, three weeks later, backing down, the blades on his 44" prop came off.
Yeah, this was my understanding as well, but I dont have the technical understanding to back it up with anything substantial.

For what its worth one old steel boat engineer told me the big plus to a negative earth was it would potentially trip the circutbreaker of any positive feed that leaked to the hull. Preventing this kind of rapid electrolytic corrosion. He reckoned wiring the whole boat above earth was a recipe for problems, as a positive leak could do real damage before it was spotted. I am still not sure if the negitive earth protecting the hull is an urban myth, or real? But the reading I have done seems to support the idea.

This seems to make the idea of a positive earth pretty bad from a corrosion point of view?
__________________
My Ramblings
Snowpetrel is offline   Reply With Quote
Old 14-05-2017, 05:16   #19
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 9,644
Re: Negative Ground vs Positive Ground History Question.

Quote:
Originally Posted by Snowpetrel View Post
Yeah, this was my understanding as well, but I dont have the technical understanding to back it up with anything substantial.

For what its worth one old steel boat engineer told me the big plus to a negative earth was it would potentially trip the circutbreaker of any positive feed that leaked to the hull. Preventing this kind of rapid electrolytic corrosion. He reckoned wiring the whole boat above earth was a recipe for problems, as a positive leak could do real damage before it was spotted. I am still not sure if the negitive earth protecting the hull is an urban myth, or real? But the reading I have done seems to support the idea.

This seems to make the idea of a positive earth pretty bad from a corrosion point of view?
Yes, this seems to a common POV. I wonder if it is myth or not???????

Presumably we are talking corrosion of the chassis / hull etc rather than corrosion of the hot side wiring?
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 14-05-2017, 06:11   #20
Registered User
 
Snowpetrel's Avatar

Join Date: Jul 2012
Location: Hobart
Boat: Alloy Peterson 40
Posts: 3,919
Re: Negative Ground vs Positive Ground History Question.

^^ my thoughts are that it has to be the case, look at how impressed current systems work, they drive the hull into the negative voltage, effectively pumping it full of electrons to prevent corrosion (at least thats my non technical mental picture of what happens...)

Now I am figuring cars and other stuff like planes or electrical gear really do not have the same issues, because generally speaking cars and such aren't continuously immersed in an electrolyte soup like our boat is, so nothing particularly bad happens most of the time. Just as an impressed current system and anodes don't work very well above the water(though galvanising does...)

I think it takes more than just a positive earth to cause a problem. There has to be a volatage difference somewhere. If the whole hull is at +12 or -12v there is no issue, but if one part is at +12v and another part is at -12v and they are connected electrically and are also floating in the same electolyte bad things can happen to the positive part. This is my very fuzzy understanding. And it is probably wrong, hence posting here to hopefully have the errors of my ways corrected.
__________________
My Ramblings
Snowpetrel is offline   Reply With Quote
Old 14-05-2017, 11:43   #21
Senior Cruiser
 
senormechanico's Avatar

Cruisers Forum Supporter

Join Date: Aug 2003
Boat: Dragonfly 1000 trimaran
Posts: 6,768
Re: Negative Ground vs Positive Ground History Question.

Quote:
Originally Posted by Viking Sailor View Post
It had to do with the evolution of the vacuum tube. As the complexity of the vacuum tube and the surrounding circuit design increased it became more efficient to use a negative ground and a positive plate supply. When tube based radios were installed in cars it was much simpler to tie the negative battery terminal to the chassis then to "float" the radio on a positive ground.
Could be a contributing factor, but the old tube car radios power supply went from the DC input through a vibrator and a transformer to supply 150 volts to the tubes.
The transformer secondary was isolated from the primary, so the input voltage could have been either positive or negative ground.
Actually, the radio worked without regard do the DC input polarity.
Input polarity only became an issue in about 1963 when GM cars had a DS105 transistor for the output stage, and the tubes were designed for 12 volts operation.
GM went from generators to alternators in 1964.
Before that with generators, you could get them to charge with either battery polarity if you "flashed' the field winding.
As there were no solid state items in the car before that, everything worked without regard to polarity of the battery.

Back in the day ('60's) the shop I worked at used to repair car radios IN THE CAR for $1.50 + parts. If it couldn't be repaired in the car, we removed the radio, fixed it on the bench (usually while the customer waited for it), reinstalled it in the car, and charged $1.50 each way + $1.50 + parts.
Believe it or not, we made a living doing that.


Edit: I see Wotname beat me to the generator flashing bit.
__________________

__________________
One should try to "Die Young" as old as possible.
senormechanico is offline   Reply With Quote
Reply

Tags
history

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
24v negative and 12v negative totalrefitdan Electrical: Batteries, Generators & Solar 11 15-05-2016 10:24
negative power supply and 12v negative battery supply same thing? er9 Marine Electronics 8 02-03-2016 08:06
Why fuse on positive but not on negative? cszosler Electrical: Batteries, Generators & Solar 6 22-05-2014 09:38
12v positive and 24v negative possible? heintje23 Marine Electronics 17 27-07-2013 19:11
Positive and Negative Charges Srah 1953 Electrical: Batteries, Generators & Solar 19 16-01-2011 05:42

Advertise Here


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 08:08.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×

ShowCase vBulletin Plugins by Drive Thru Online, Inc.