Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 10-07-2013, 15:35   #1
Registered User

Join Date: Feb 2011
Boat: aluminium twin keel, Laurent Giles, 62 foot
Posts: 100
12v positive and 24v negative possible?

Is it possible to take the positive of my 12v bank and use the negative of my 24v bank? The max amp is 30.
__________________

__________________
heintje23 is offline   Reply With Quote
Old 10-07-2013, 16:00   #2
Senior Cruiser
 
atoll's Avatar

Cruisers Forum Supporter

Join Date: Mar 2010
Location: gettin naughty on the beach in cornwall
Boat: 63 custom alloy sloop,macwester26,prout snowgoose 37 elite catamaran!
Posts: 9,310
Images: 75
Re: 12v positive and 24v negative possible?

you mean to get 12v supply from your 24v bank?
__________________

__________________
my catamaran building project updates http://www.cruisersforum.com/forums/...36#post2502136
atoll is offline   Reply With Quote
Old 10-07-2013, 16:05   #3
Registered User
 
nathanp's Avatar

Join Date: Jun 2013
Location: Spring Hill, FL
Boat: Sea Ray 175BR 18'
Posts: 27
Re: 12v positive and 24v negative possible?

I don't fully understand what you are asking, but you have to complete the circuit back to the battery that the positive is coming from. If the 12v and 24v share their ground circuits, then it would work, but if not, no.
__________________
"Float on Bubbles, float on" - Capt. Alex Rust
nathanp is offline   Reply With Quote
Old 10-07-2013, 17:24   #4
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,022
Re: 12v positive and 24v negative possible?

I suspect the answer is 'yes' since damn near anything is possible, but without some specifics on how the batteries interconnect and what you are trying to accomplish, you may either get 36 volts out of the kludge, or nohting at all, or burn out the batteries, or set the boat on fire.

So, some specifics might be needed here. But literally, "yes".
__________________
hellosailor is offline   Reply With Quote
Old 11-07-2013, 00:18   #5
Registered User

Join Date: Feb 2011
Boat: aluminium twin keel, Laurent Giles, 62 foot
Posts: 100
Re: 12v positive and 24v negative possible?

I have replaced my electro hydraulic autopilot pumps with two new ones each drawing 27amp maximum. The old ones were running on 24v and the new ones run on 12v. I have put in new wires for the 12v positive supply. I was wondering if I could use the old 24v negative wire as the new 12v negative for the new pumps. I think the boat has a common ground so then it should be possible.

Is there any way to check if the boat has a common ground or not other then visually following the negative cables?
__________________
heintje23 is offline   Reply With Quote
Old 11-07-2013, 01:28   #6
Senior Cruiser
 
atoll's Avatar

Cruisers Forum Supporter

Join Date: Mar 2010
Location: gettin naughty on the beach in cornwall
Boat: 63 custom alloy sloop,macwester26,prout snowgoose 37 elite catamaran!
Posts: 9,310
Images: 75
Re: 12v positive and 24v negative possible?

check the resistance between a 12vneg and 24v neg.

though on an alumilium boat i would think the circuits would be isolated
__________________
my catamaran building project updates http://www.cruisersforum.com/forums/...36#post2502136
atoll is offline   Reply With Quote
Old 11-07-2013, 01:51   #7
Registered User

Join Date: Jun 2010
Location: Central California
Boat: Samson C Mist 32
Posts: 484
Re: 12v positive and 24v negative possible?

Ground is ground, no?
__________________
Steve Bean is offline   Reply With Quote
Old 11-07-2013, 05:56   #8
Registered User
 
nathanp's Avatar

Join Date: Jun 2013
Location: Spring Hill, FL
Boat: Sea Ray 175BR 18'
Posts: 27
Re: 12v positive and 24v negative possible?

I would just put a voltmeter on the new 12v+ wire that you ran and the ground wire you want to use, if there's 12v on the meter it'll work.
__________________
"Float on Bubbles, float on" - Capt. Alex Rust
nathanp is offline   Reply With Quote
Old 11-07-2013, 10:35   #9
Registered User

Join Date: Apr 2007
Posts: 718
Re: 12v positive and 24v negative possible?

I would not rely on just "having continuity" between the 12v negative and the 24v negative. Where does your 12v negative connect in relation to the 24v system? The grounding bus (if you have one) and it's conductors should not normally carry any current. If your 12v negative connects to the same point on the engine as your 24v negative or to the 24v main negative bus, your ok.

Eric
__________________
fairbank56 is offline   Reply With Quote
Old 11-07-2013, 11:28   #10
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Quote:
Originally Posted by fairbank56 View Post
I would not rely on just "having continuity" between the 12v negative and the 24v negative. Where does your 12v negative connect in relation to the 24v system? The grounding bus (if you have one) and it's conductors should not normally carry any current. If your 12v negative connects to the same point on the engine as your 24v negative or to the 24v main negative bus, your ok.

Eric
The term " ground " is frequently used in DC circuits to mean negative return ( hence the symbol)

" grounding " wires , protective earth etc are all different concepts

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 11-07-2013, 11:37   #11
Registered User
 
rw58ph's Avatar

Join Date: Jun 2013
Location: Seattle WA
Boat: Roughwater, pilot house, 58 ft
Posts: 485
Re: 12v positive and 24v negative possible?

You also have to make sure the wire is sized correctly. Wire size for 24 volt is usually smaller than 12 volts. You can run 24 volt on wire sized for 12 volt but you can not run 12 volt sized for 24 volts.

Regardless I would have a 12 volt and a 24 volt ground wired. Keep them seaparate.
__________________
rw58ph is offline   Reply With Quote
Old 11-07-2013, 14:12   #12
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,022
Re: 12v positive and 24v negative possible?

IF the negative lines (which ma or may not be isolated from ground and from each other) all make the same run to a common negative bus or ground point, you would be able to use the old 24v negative line.

But if the wiring was rated for less (half? the) amperage that your new 12v equipment draws, then it would be undersized and it might cause excessive voltage drop in the lines. Check the wire size and make sure that it is of sufficient capacity, otherwise, run a new negative line as well.

When you are sizing the wires, you need to measure the ground-trip length of the wiring run. That's positive and negative, both sides of the circuit, to get the total wire length to use with the current capacity and voltage drop.
__________________
hellosailor is offline   Reply With Quote
Old 11-07-2013, 14:59   #13
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
Re: 12v positive and 24v negative possible?

On DC circuits it is called positive and negative. On AC circuits it is called hot, neutral and ground.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 11-07-2013, 15:20   #14
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 13,022
Re: 12v positive and 24v negative possible?

"On DC circuits it is called positive and negative."
Ah, it is called by many names, whether they're technically correct or not. For instance in autos, there's hot and ground--and a ground cable attached to the negative post of the battery. No negatives. Boat systems being so similar to autos...The negative might or might not be the same. When one of the engine mounts has been used as the common point for the negative battery cables, panel distriution, bonding and everything else, does the engine block now count as "negative" or "ground" ?

Conventional versus electron flow : Basic Concepts Of Electricity

In grade school they still taught us that electricity flowed from the + to the - but these days, that is known to be incorrect, it actually flows from the - to the + so no matter which nomenclature you use, in some context it is wrong.
__________________
hellosailor is offline   Reply With Quote
Old 11-07-2013, 15:47   #15
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Quote:
Originally Posted by David M View Post
On DC circuits it is called positive and negative. On AC circuits it is called hot, neutral and ground.
Technically correct , but the term ground is used commonly to refer to tbe negative . Especially on split power supplies for example the negative may not be the " ground" hence the common term GND in circuit design. gND may be earth referenced or may not be

Dave
__________________

__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Reply

Thread Tools
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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 05:27.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.