Notices
Marine Electronics Forum

Electrical Issue HELP

Old 05-04-2008, 08:46 PM
  #1  
Junior Member
Thread Starter
 
Join Date: May 2008
Location:
Posts: 1
Likes: 0
Received 0 Likes on 0 Posts
Default Electrical Issue HELP

Hello there. I have an issue with my boats DC system that I need a hand with.

I have a 32' cruiser with twins, 2 crank + 1 house batt, a 2 alt 3 batt isolator, and a Xantrex 40+ charger.

My voltmeters on both side very rarely hit 13 - in idle and even while underway they hover around 10. I hit the blowers, they drop to a hair over 8. When anything else happens - toilet flush, running lights, etc., the radio goes dead for obvious reasons. This is the scenario most of the time, but other times things seem much better.

While at the harbor with the batt charger cranking, the same happens most of the time. This is very frustrating. Hell, even underway with the Genset on giving the charger juice, the head still kills the radio.

I've replaced all 3 batts and the charger. My next stop would be to replace the isolator - as this seems to be common across all scenarios.

Thoughts?

Please advise.




Old 05-05-2008, 12:12 AM
  #2  
Senior Member
 
Join Date: Jan 2007
Location:
Posts: 2,154
Received 52 Likes on 30 Posts
Default Re: Electrical Issue HELP

Welcome to THT! Get a digital volt meter and check the voltage at your batteries. First with the charger shut off for at least an hour and after running the blowers for a few minutes to knock off the surface charge from the house battery. Then turn the charger on and check again. The start both engines and check the voltage at each battery after running the engines for about 5 minutes at a high idle. With o charge from the alternators or the charger the voltage should be around 12.6 to 12.8. With the engies runing the voltage should be around 13.5 to 14 or so. Same with the charger on. Given your description if your batteries show good voltage I would check to make sure the main feed and ground to the main panel are big enough for the load and the connections are good. That sounds like your problem most likely. Personally unless your alternators have the ability to externally sense the regulator then I would dump the isolator as with it you will not get the batteries fully charged using the alternators. Easiest way would be to add a combiner to feed the house battery from one of the starting batteries and put the autopilot, trim tabs and windlass (if you have them) onto the other starting battery to balance the alternator load.
Old 05-05-2008, 05:08 AM
  #3  
Senior MemberCaptains Club Member
 
Join Date: Feb 2005
Location: Falmouth, MA
Posts: 6,192
Received 693 Likes on 430 Posts
Default Re: Electrical Issue HELP

i agree that you need to get a multimeter and start taking readings with the engine off and then with the engine running and then with the charger on...check, at a minimum:
-at each battery
-on the alt sides of the isolator
-on the bat sides of the isolator
-all sides of any battery switches
-supply side of your distribution block/accessory fuse panel

record these numbers and compare. you are obviously looking for differences in voltage. the only place there should be a siginificant difference is from one side of the isolator to the other (0.7volts). if the readings show no significant differences then repeat with some accessories on (like a spotlight or blower). record these numbers as well.

i also agree that if you do not have externally regulated alternators then you need to either change that or switch out the isolator.

from what you've said, i think the most likely cause is corroded connection(s) and/or corroded wire(s). it also could be a corroded battery switch/breaker. i am guessing it is not a new boat?
Old 05-05-2008, 08:01 AM
  #4  
Senior MemberCaptains Club Member
 
Join Date: Jan 2005
Location:
Posts: 4,300
Received 309 Likes on 261 Posts
Default Re: Electrical Issue HELP

OK, lets try and keep this simple if we can. When you are reading 8 to 10 volts on your console voltmeters, what voltage do you read with a digital voltmeter across each crank battery and house battery?? Also what voltage does your GPS/Plotter or FF show at the same time.


Jim
Old 05-06-2008, 06:50 AM
  #5  
THT SponsorCaptains Club Member
THT sponsor
 
Join Date: Jan 2007
Location: Beaufort, SC
Posts: 692
Likes: 0
Received 68 Likes on 47 Posts
Default Re: Electrical Issue HELP

If the batteries are in good condition and holding a charge but the voltage drops when you apply a load, this suggests a wiring problem. Somewhere in the circuit there is a bad connection or a corroded wire. Since it seems to happen with different loads that would be using different positive cables, this suggests the problem is in the negative or ground return cable to the batteries since multiple devices would all share the ground return.

The first project is to thoroughly inspect all the wiring for problems, concentrating on the negative side and the vicinity of battery terminals in particular, including the actual connection to the battery.

If the wire gauge is too small to carry the loads due to extra loads applied to an original cable, or being modified at some stage with a wire that is too small, even though it is in good condition you will get a voltage drop. If you are flushing toilets, the circuit from the battery, through switch(es) and back from the toilet all the way to the negative terminal should be at least as heavy as 6 gauge wire. If it is a long run, 4 gauge would be better. Circuits that carry heavy loads should have their own positive and ground connections back to the battery. If your radio is sharing one of these leads, especially a common ground return circuit, then it will see a voltage drop when the heavy load is applied.

The problem could also be trying to squeeze blood from a stone. If the total electrical load you are trying to support is more than the alternator(s) can supply then the batteries are never going to get enough charge. If alternator output is below normal this is an indication of damaged rectifier(s) in the alternator and may need to be repaired/replaced. Damage to these rectifiers is frequently sustained when the alternator to battery connection is switched off while the engine is running. Think of it like water flowing from the alternator to the battery. If it is suddenly shut off (disconnected) all that fast moving water in the pipe suddenly has no where to go so it can temporarily build up too high a pressure (voltage) and damage the rectifiers.

Finally, you lose about 0.6 volts in an isolator so the batteries don't get a full charge. By connecting the alternator directly to the starting battery without the isolator you will deliver more charge. You can then use one or two Combiner100s to share that voltage with other batteries. Since there is no voltage drop in a Combiner100, all the batteries will get full voltage.
Old 05-06-2008, 07:37 AM
  #6  
Senior Member
 
Join Date: Jun 2007
Location: Boston, MA
Posts: 715
Likes: 0
Received 0 Likes on 0 Posts
Default Re: Electrical Issue HELP

Ditto..
Your batteries are obviously not getting any charge. To suggest even a simpler approach, take a multimeter and write down the charge readings on all your batteries. Start one engine off one crank battery and take a reading again. If she is not over 14v there is no charge from the alternator to the battery. Then as suggested above take readings right off your alternator. If that is 14 or over, it's the wiring OR your battery selector switches.

I had a broken battery selector switch causing no charge for me.
Old 05-06-2008, 09:13 AM
  #7  
Senior MemberCaptains Club Member
 
Join Date: Feb 2005
Location: Falmouth, MA
Posts: 6,192
Received 693 Likes on 430 Posts
Default Re: Electrical Issue HELP

to say the batteries are obviously not charged is incorrect. if there is a corroded wire/connection between the battery and the loads, then the batteries could be completely charged. in fact, because he is seeing voltages as low as 8 volts then i think it is much more likely that the batteries are indeed charged and there is a drop between the batteries and the loads. if his batteries were that dead then the boat would never start. his symptoms are very consistent with a bad accessory supply wire/connection/switch/breaker. the condition is bad enough (dropping 5~6 volts) that i would consider it dangerous. assuming you are drawing 20 amps when the voltage drops to 8 volts, you are generating over 100watts of heat somewhere it shouldn't be. unfortunately, that is another way you could diagnose the problem...turn some stuff on and feel for hot wires/connections/switches/busses/etc.

if an isolator is wired correctly with the alternator regulator's voltage sense wire connected to the battery side of the isolator, the batteries will charge fine. yandina is again trying to make a sale. it's not that i have anything against combiners...they've come a long way and i will admit they are easier to install, but to say that batteries won't charge correctly with an isolator is either stupid or misleading. when installed properly (external regulation) the batteriers will charge perfectly.

i have been using isolators w/very large battery banks and high output (externally regulated) alternators with absolute success for years. let's stick w/the facts
Old 05-06-2008, 07:43 PM
  #8  
Senior MemberCaptains Club Member
 
Join Date: Jan 2005
Location:
Posts: 4,300
Received 309 Likes on 261 Posts
Default Re: Electrical Issue HELP

We all know what it sounds like, but none of us know until Diverseyrink posts some voltage measurements. So Diverseyrink give us some data so we can help you out.

Jim
Old 05-06-2008, 10:19 PM
  #9  
Senior Member
 
Join Date: Aug 2007
Location:
Posts: 307
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Electrical Issue HELP

diverseyrink - 5/4/2008 8:46 PM

Hello there. I have an issue with my boats DC system that I need a hand with.

I have a 32' cruiser with twins, 2 crank + 1 house batt, a 2 alt 3 batt isolator, and a Xantrex 40+ charger.

My voltmeters on both side very rarely hit 13 - in idle and even while underway they hover around 10. I hit the blowers, they drop to a hair over 8. When anything else happens - toilet flush, running lights, etc., the radio goes dead for obvious reasons. This is the scenario most of the time, but other times things seem much better.

While at the harbor with the batt charger cranking, the same happens most of the time. This is very frustrating. Hell, even underway with the Genset on giving the charger juice, the head still kills the radio.

I've replaced all 3 batts and the charger. My next stop would be to replace the isolator - as this seems to be common across all scenarios.

Thoughts?

Please advise.


Why did you replace all 3 batteries? Were they replaced at the same time? Assuming all the accessories are connected to the house battery, we can eliminate bad accessories wiring as the likely reason the 2 "crank" batteries go dead. If those batteries are fairly new within its life span, then we can assume further the isolator, alternators or one of the two is defective. There is no other reason why the crank batteries should to go bad.


All the accessories and devices in your boat are wired in parallel. At least they should be. When you turn on a device or many devices, the volt reading should not dip down as you indicated. If it is the case then three scenarios is likely.

1) The devices are wired wrong. Two maybe mistakenly wired in series, thus the one with lower resistance gets most of the voltage causing the second device to go dead.

2) The wire feeding all the accessories is extremely of a small gauge. With a few accessories on, the wire gets hot and the voltage drop increases. Most DC electronic units do not operate when the voltage drop is more than 5 percents. 8 volts is more than 5%.

3) The charging system is not up to par. The battery is being drained faster than the alternator can replenish it. This can be the result of many things. Isolator/combiner defect. Bad wiring. Wire gauge too small

Not knowing your boat, of course, I would have to do a test to find the problem. Based on what you said, above is just an opinion.


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 On
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.