Voltage Drop at Battery
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=41676
Printed Date: November-10-2024 at 4:43pm
Topic: Voltage Drop at Battery
Posted By: Yako
Subject: Voltage Drop at Battery
Date Posted: August-04-2017 at 11:51am
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I have a 1973 Correct Craft Skier. I purchased it knowing of a few mechanical issues. One was a bad alternator. I installed a new alternator and I know that it works. I am getting 14.5 volts at the alternator. Problem is that I am getting 13 v at the battery and 13 v at the starter (back of boat). As a result, the battery is not charging. The alternator has an orange charge wire, that seems to run from the alternator, via a harness to the back of the boat. Then it runs to the dash, through an Amp Meter, and then back to the starter (as a red wire). I have been very perplexed as to why this is happening. In troubleshooting I took a 10 or 8 Gauge wire from the alternator to the starter and the battery started to charge. This is not a solution, just proof that it can charge and that the alternator is not the problem. The contacts on the charging wire, battery contacts and starter contacts are all clean and shiny. Any ideas on what to do next in order to identify the problem to root cause? |
Replies:
Posted By: 8122pbrainard
Date Posted: August-04-2017 at 12:00pm
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Mark, Depending on the load (charging battery in this case) the wire size and the length of the wire, I don't consider a 1.5 voltage drop to be abnormal. What type of battery are you trying to charge? IE: starting, deep cycle, dual purpose. AGM, etc. Do you have a DC clamp on ammeter to check the amps? ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: KENO
Date Posted: August-04-2017 at 12:58pm
Here's an early wiring diagram that should be pretty representative of what you have, complete with ammeter. Maybe it will help you, maybe it won't  I'll disagree with Pete and say you should be getting 14 or so at the battery like you're thinking. It's a long and winding road from the alternator through the 8 pin connector,through the ammeter, through the key, back through the 8 pin connector and then to the connection on the solenoid that the battery also connects to. I'd look at that 8 pin connector on the back of the engine assuming you have one and make sure those connections are all clean. Lots of connections to check clean and tight 
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Posted By: 8122pbrainard
Date Posted: August-04-2017 at 1:04pm
Ken, http://www.calculator.net/voltage-drop-calculator.html" rel="nofollow - This will save you from doing the math! ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
KENO wrote:Posted By: WinterTurtle
Date Posted: August-04-2017 at 1:13pm
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So firstoff I am not a boat mechanic - but I am an automotive mechanic. So that said some here may / should correct anything I mention that is considered a safety hazard in this environment. Also I understand the perspective of wanting to keep everything original if that's your cup of tea. Check over the two poles of the ammeter and see if that's your trouble spot. I've owned several 70s vehicles and over time the ammeters become a big source of voltage drop. On most that I own (drivers - not collectors) I bypass the ammeter by cutting off the rings - soldering inside an uninsulated butt connector - and shrink wrapping with marine sealant inside. Maybe the Correct Craft ammeters used are a better quality unit than older cars but this has benefited me many times on the road. If that's not it then it's time to get a schematic and trace the path of the charge wire looking for your trouble spot. Depending on the electrical design (obviously I am not familiar with the design and any critical nautical features) I don't see it as inappropriate to run a nice heavy cable with an appropriate fusible link or fuse from the alt output to the battery. I like this particular mod because it's simple and takes the load off the original wiring without disconnecting anything - just makes the charge light (if equipped) and ammeter void. Lots of old Dodges I've worked on have overheated and at times melted charge circuit wires around ammeters and bulkheads. Are there any bulkhead type fittings on boats like vehicle firewall connections? **Edit: looks like some of this addressed above while I hunt and pecked away! ------------- 1979 Southwind 18 351w Not Running - All Potential! |
Posted By: KENO
Date Posted: August-04-2017 at 1:27pm
Don't need the math Pete, Go fire up your boat and see what the voltage is at the battery coming from the alternator. I do agree with what winter turtle said about ammeters though, bypass it/ jumper around it and see what happens |
Posted By: KENO
Date Posted: August-04-2017 at 2:14pm
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Went out and fired up the boat and got 14.2 volts at the battery with one of them VOM thingies through basically the same wiring setup as the diagram running at about 2000 rpm's. The ammeter in this particular boat was bypassed years ago. I just hooked the "goes in" wire to the "goes out" wire I should add in also 14.9 volts at the alternator output |
Posted By: KENO
Date Posted: August-04-2017 at 2:35pm
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Nice calculator by the way Pete. I plugged and chugged some numbers and my real life voltage drop is only a little more than the calculated numbers. I probably went a little long on the wire length since I didn't measure it. Well within what you'd expect from wiring with many connections or at least I'd expect
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Posted By: 8122pbrainard
Date Posted: August-05-2017 at 10:24am
Ken, I too "plugged and chugged" numbers when Mark first posted his problem with the voltage drop and used a worst case scenario. Keep in mind he did say he cleaned up his wiring but didn't mention the harness plug(s). Good point BTW! First you must use the total wire distance with DC and not half like the calculator states. That's for AC. I used 25 feet. Next I plugged in 10 gauge wire which is typical with an ammeter set up. Then for a load I figured a battery in need of a charge so I used 35 amps which would be the approximate output of the alternator for at least several minutes when the engine is started. That come out to a 1.75 voltage drop. I also asked Mark what type of battery he has since that too can make a difference. BTW, if I went and checked my voltage drop per your recommendation, I'm sure I'd get the same results as yours since the battery is fully charged and new. I wish Mark would respond and fill in some of the blanks we both asked about. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: Yako
Date Posted: August-05-2017 at 12:08pm
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Ok. So this morning I took apart all of the harness connections and cleaned them out, greased (for protection with the correct stuff) and checked continuity. Charging wire to Bat had continuity and minimal resistance, Then I took all ground wires in the engine area, unscrewed, cleaned and re assembled Next, I verified that my NEW 800 CCA battery was still good with a load tester. Check Then I started the boat up and did the following: Checked voltage across Bat - , Ground (manin) and the ground on the solenoid. All read 0.00v Next, at 2000 rpm, I have the following results: Ground to Bat + 14.0 volts Ground to Amp Meter out 14.10v Ground to Amp Meter in 14.10 v At idle, I am getting 13.90 - 13.95 v Then, I connected an 8 gauge wire directly from the Alternator + to my solenoid + Now I got 14.5v Good news, is that I am now getting an extra volt. Work paid off. Questions: I realize that the amp meter is causing a 0.05v drop, not sure this is the problem. Could I have a problem with my orange charge wire? I cleaned that off as well. Questions Is 13.9v at idle satisfactory? Seems ok 14.0v at 2000 rpm feels a bit light, does anyone with skills share this view? Finally, if I were to take off the OEM charging wire and replace with 8 gauge wire and run directly to the solenoid + , are their any downsides. Only thing is that the ampmeter would not work (may read discharge), Again, referring to the last question, can someone confirm that the red wire from Amp Meter to solenoid + is still required, since this energizes the solenoid on ignition. Thanks Mark |
Posted By: KENO
Date Posted: August-05-2017 at 3:20pm
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I don't see any problem with the voltage readings you have now, but your 8 gauge wire to the solenoid would work and give more voltage like you saw. The red from the ammeter isn't needed because it goes to the BAT terminal on the switch and there is a red 10 gauge wire already there from the solenoid.serving the same purpose of supplying 12 volts to the key switch See the diagram earlier in the thread If you're ditching the ammeter you could wire a voltage meter to the same orange wire that now feeds the ammeter. Might be a confusing explanation from me , but you don't need it. You can unhook it to verify that the boat still starts and runs, you'll just not have a working ammeter |
Posted By: 8122pbrainard
Date Posted: August-05-2017 at 7:31pm
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Mark, Ken's comments are all good except I'd like to comment on what he said about the ammeter. I happen to prefer them since they show the true state of charge or discharge whereas a volt meter does not. I'd keep the ammeter and just run heavier wire. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |