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 16-05-2019, 07:33   #1
Tim. Keith-Lucas
 
tkeithlu's Avatar

Cruisers Forum Supporter

Join Date: Feb 2012
Location: Carrabelle, Florida
Boat: Fiberglas shattering 44' steel trawler
Posts: 1,157
Voltage on alternator ground?

I use a full Balmar alternator/regulator system to charge my house battery bank from my engine. It works beautifully. However, I was checking my bonding system yesterday with the engine off and noticed a small spark from the Balmar alternator ground to the engine block. My trusty multimeter revealed house voltage on the ground, but zero current. Could this be reading through my instument panel voltage meter, or some other un-measurably small use of current? I've not noticed any current drain from the battery bank. Thoughts from someone who knows DC better than me?
__________________

tkeithlu is offline   Reply With Quote
Old 16-05-2019, 08:10   #2
Registered User
 
thomm225's Avatar

Join Date: Aug 2011
Boat: Bristol 27
Posts: 5,345
Re: Voltage on alternator ground?

Is the ground connection loose at the block?
__________________

thomm225 is offline   Reply With Quote
Old 16-05-2019, 08:17   #3
Registered User
 
Stu Jackson's Avatar

Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 7,762
Re: Voltage on alternator ground?

If your alternator is connected to the house bank, it is always LIVE. Of course, it should be fused, but Maine Sail also suggests a service disconnect switch so that when you work on the engine you disconnect the alternator. I just remove the fuse.


Tighten that connection, Sparky!


You might consider learning some more about your electrical systems, too. Good luck.


Electrical Systems 101 Electrical Systems 101
__________________
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
Stu Jackson is offline   Reply With Quote
Old 17-05-2019, 04:09   #4
Tim. Keith-Lucas
 
tkeithlu's Avatar

Cruisers Forum Supporter

Join Date: Feb 2012
Location: Carrabelle, Florida
Boat: Fiberglas shattering 44' steel trawler
Posts: 1,157
Re: Voltage on alternator ground?

The connection is normally tight; I'm not that inept. But, thank you for the guidance.
tkeithlu is offline   Reply With Quote
Old 17-05-2019, 04:16   #5
Registered User
 
thomm225's Avatar

Join Date: Aug 2011
Boat: Bristol 27
Posts: 5,345
Re: Voltage on alternator ground?

Sometimes you have to loosen, clean, then retighten for a good connection even though it feels and appears tight especially if there are multiple wires attached.

Kinda like when your car won't start but when you tap the battery cables at the terminals/posts with a small hammer or heavy enough screwdriver etc it starts right up. (even though the cables felt tight to begin with)
thomm225 is offline   Reply With Quote
Old 17-05-2019, 04:57   #6
Tim. Keith-Lucas
 
tkeithlu's Avatar

Cruisers Forum Supporter

Join Date: Feb 2012
Location: Carrabelle, Florida
Boat: Fiberglas shattering 44' steel trawler
Posts: 1,157
Re: Voltage on alternator ground?

Thank you. I designed and built a rather complicated AC and DC system for our boat, with multiple sources of power for just about any task. I found this "problem" when I installed a heavier bonding cable for the starter battery for the main engine. It had not occured to me that the alternator ground would be live, given devotion to avoiding using the steel hull as a current return.
tkeithlu is offline   Reply With Quote
Old 17-05-2019, 06:27   #7
Registered User

Join Date: Oct 2015
Posts: 1,397
Re: Voltage on alternator ground?

Quote:
Originally Posted by tkeithlu View Post
Thank you. I designed and built a rather complicated AC and DC system for our boat, with multiple sources of power for just about any task. I found this "problem" when I installed a heavier bonding cable for the starter battery for the main engine. It had not occured to me that the alternator ground would be live, given devotion to avoiding using the steel hull as a current return.
Does your alternator have an isolated ground?

That is the way marine alternators SHOULD be, but all too often are not. That's the way that you avoid using either the engine block or a steel hull as the return path for the alternator output.
billknny is offline   Reply With Quote
Old 17-05-2019, 06:49   #8
Tim. Keith-Lucas
 
tkeithlu's Avatar

Cruisers Forum Supporter

Join Date: Feb 2012
Location: Carrabelle, Florida
Boat: Fiberglas shattering 44' steel trawler
Posts: 1,157
Re: Voltage on alternator ground?

Damn! That's good. Thanks so much. I'll just run it to the battery negative rather than the block.
tkeithlu is offline   Reply With Quote
Old 17-05-2019, 09:54   #9
Registered User
 
RossD's Avatar

Join Date: Dec 2018
Posts: 45
Re: Voltage on alternator ground?

Good information here, thanks!
RossD is offline   Reply With Quote
Old 17-05-2019, 10:10   #10
Registered User

Join Date: Jul 2016
Location: East Coast USA
Boat: Boatless at the moment
Posts: 335
Re: Voltage on alternator ground?

Quote:
Originally Posted by billknny View Post
Does your alternator have an isolated ground?

That is the way marine alternators SHOULD be, but all too often are not. That's the way that you avoid using either the engine block or a steel hull as the return path for the alternator output.
I agree if you have a metal hull but it's not necessary on a fiberglass hull. Many engines come standard with 1 wire sensors that require the block for ground. Unless you have 2 wire sensors you need to ground the engine block.

I think the problem arises when you use the alternator case as the ground rather than a separate but equally sized ground wire for the alternator. I also see a lot of problems when multiple ground points/planes are created by improper wiring.

To the OP you might want to check the diodes in the alternator's bridge rectifier, especially the negative diodes.
kenbo is offline   Reply With Quote
Old 17-05-2019, 14:13   #11
֍֎֍֎֍֎֍֎֍֎

Cruisers Forum Supporter

Join Date: Apr 2006
Posts: 15,352
Re: Voltage on alternator ground?

"It had not occured to me that the alternator ground would be live,"
FWIW, I've never heard an electrician refer to a ground as "live". Live is reserved for "hot" wires, meaning they are carrying voltage above ground level. There can be various types of "ground" but they are always assumed to be connected, GROUNDED not LIVE or HOT, at all times.

If your alternator made a spark to ground when it was not running? Then some component in the alternator was passing power when it should not have been. The alternator may be wired wrong (in the control circuits) or you may have a diode failing, passing reverse current. Before you start moving the ground, it may pay to start checking the alternator for internal or configuration problems. There's still going to be something wrong--regardless of where you move the ground to.
If you disconnect the ground from the block, and insert an ammeter, either it will read zero, or it will show there's a current flow. ANY current flow when the alternator is off, means a problem.
hellosailor is offline   Reply With Quote
Old 17-05-2019, 14:25   #12
Senior Cruiser
 
Captain Bill's Avatar

Cruisers Forum Supporter

Join Date: Apr 2008
Location: Punta Gorda, Fl
Boat: Endeavourcat Sailcat 44
Posts: 2,661
Re: Voltage on alternator ground?

Check for voltage between the block and battery negative. I once had a corroded ground connection at the engine block and there was 8 volts between the block and the battery. Oddly enough the bolt head had zero volts to the battery as it was making good contact with the cable. The block however was not. While trouble shooting I was assuming that the bolt head would be the same as the block, but it wasn't. The ultimate source of the problem was a leaking exhaust elbow which had dripped on the ground connection. I cleaned the connection and replaced the elbow and all was good.
Captain Bill is offline   Reply With Quote
Old 18-05-2019, 09:12   #13
Registered User
 
Boatyarddog's Avatar

Join Date: Nov 2014
Location: Olympia, Wa
Boat: 1979 Mariner Ketch 32-(Oberly build) - Hull 202
Posts: 824
Re: Voltage on alternator ground?

Quote:
Originally Posted by tkeithlu View Post
I use a full Balmar alternator/regulator system to charge my house battery bank from my engine. It works beautifully. However, I was checking my bonding system yesterday with the engine off and noticed a small spark from the Balmar alternator ground to the engine block. My trusty multimeter revealed house voltage on the ground, but zero current. Could this be reading through my instument panel voltage meter, or some other un-measurably small use of current? I've not noticed any current drain from the battery bank. Thoughts from someone who knows DC better than me?
You said "house voltage" is that 120 or 12vts.
Bonding systems are usually connected to 12 Vt.DC circuits and 120 Vt in vessels to stop or reduce corrosion of metal.
But, only the neutral.
Could there be an issue in your dockside pedestal power box? Problem with your bonding?
SV Cloud Duster
Boatyarddog is offline   Reply With Quote
Old 29-05-2019, 05:28   #14
Tim. Keith-Lucas
 
tkeithlu's Avatar

Cruisers Forum Supporter

Join Date: Feb 2012
Location: Carrabelle, Florida
Boat: Fiberglas shattering 44' steel trawler
Posts: 1,157
Re: Voltage on alternator ground?

Lots of good thinking here, which I appreciate. I'll start with checking the diodes, which didn't occur to me given a Balmar alternator that is only a few years old and is charging the house bank of six size 27 lead-acids just fine.

I found house voltage between the alternator ground wire (not to the alternator case) and the engine block, but zero current, at least to the level that my multimeter could detect.

Yes, we are talking about the 12vDC circuit, not the 120vAC circuit. Our shore power goes directly to a 1:1 transformer, isolating the boat.
tkeithlu is offline   Reply With Quote
Old 29-05-2019, 07:00   #15
Registered User

Join Date: Feb 2019
Posts: 27
Re: Voltage on alternator ground?

Quote:
Originally Posted by tkeithlu View Post
Lots of good thinking here, which I appreciate. I'll start with checking the diodes, which didn't occur to me given a Balmar alternator that is only a few years old and is charging the house bank of six size 27 lead-acids just fine.

I found house voltage between the alternator ground wire (not to the alternator case) and the engine block, but zero current, at least to the level that my multimeter could detect.

Yes, we are talking about the 12vDC circuit, not the 120vAC circuit. Our shore power goes directly to a 1:1 transformer, isolating the boat.

I'm curious how you are measuring current. If you are just clicking your meter to "current" and measuring the same way you measured voltage (ie, with the meter connected in parallel to the target circuit) it won't work.
__________________

SwellGuy is offline   Reply With Quote
Reply

Tags
alternator

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
9 V difference between ground and ground Arrandir Electrical: Batteries, Generators & Solar 12 19-07-2018 22:51
Negative Ground vs Positive Ground History Question. Wotname Electrical: Batteries, Generators & Solar 20 14-05-2017 11:43
Low voltage vs higer voltage solar Singleprop Electrical: Batteries, Generators & Solar 11 06-07-2015 19:35
To ground or not to ground an aluminum arch...that is my question. chrtucke Electrical: Batteries, Generators & Solar 9 06-10-2014 23:17
Floating Ground on Aluminum Boat: Voltage Reading? msponer Electrical: Batteries, Generators & Solar 15 31-08-2013 05:44



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 02:04.


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.