need voltage drop ideas...(long with details)

[rsfeller]

30' (1984) year old Cruisers Inc avanti vee (twin 351 pleasurecrafts with port engine on two deep cycle and starboard on one starting battery (all new)). My buddy and I have the same boat with the same 12v voltage drop issues. To the panel I’m good (12.5v or better) but by the time it runs to the dash (from the master switch at the panel) I’m at 11.4v or worse under any load. I’ve done a few cleanings and r&r on connectors and gained a 0.5v here and there to improve things, but overall connections look good and wiring diameter is correct for all main lines and grounding blocks.<br /><br />Two issues now I want to resolve.<br />When I toss on the nav lights the oil pressure gauges go 100% until the engine is turned on and then the oil gauge reads correct. I think the nav light issue is causing another issue as I’ve had the radio (new unit this summer that works down to 10.5v) drop out (low voltage) with a few two many lights on, but voltage at duel house battery are still 12v+). NOTE: Nav lights work fine. What should I look for, a bad ground at a light location?<br /><br />Running the head (macerator 14amp) will cause the stereo to drop out to and the voltage will go to 10.5 volts, lights take a big hit on the boat at night. I’m thinking of by passing the panel (for the head) and my house batteries and hooking the head directly to my starboard engine starting battery (port has duel deep cycles) to get it on another circuit (of course with proper fuses inline). any thoughts here? I’m hoping the 12v starter will do fine with the “hit” of the high amps for a few seconds and keep it isolated from my house battery bank and the problems the 14amp draw causes, is my logic good. Remember this head is only going to run two or three times a night tops…so it shouldn’t hurt the starting battery.<br /><br />thanks.<br />shawn

 

[Ralph 123]

Re: need voltage drop ideas...(long with details)

How big (what gauge) wire is running from the master switch on the panel to the dash and how far is the run? How big is the fuse in that circuit? What is on that circuit? Same questions for the primary feed from the battery to that panel. <br /><br />My gut tells me one or more of these could be undersized causing an excessive voltage drop. Sounds like something that got built-in at the factory since both boats are exhibiting it.<br /><br />[edit]<br /><br />Use this wire size calculator to determine what size wire should be used in these circuits for a 3% voltage drop at load. Note the distance is the round trip distance. So, if it is 20 feet from the battery to the panel, you put in 40 for the distance...<br /><br /> http://www.ancorproducts.com/Technical_information/Wire_calculator.php <br /><br />Example. let's assume your current load off the panel totals 20A and the panel is 20' from the battery. Then you'd expect a 4 awg wire (pretty hefty) running from the battery to the panel to see 11.64 (3% drop) at load. Sounds like you're all ready seeing that much of a drop with less than full load...right?

 

[rsfeller]

Re: need voltage drop ideas...(long with details)

i'm seeing well over 3% drop for sure. i don't know the gauge and distance for sure, but i'm guessing that that the wire is 8 gauge for close to 15-20ft round trip from the master to the dash. same size from the battery to the master at about 15 round trip. i'll do some figures with the wire calc and see about the need to rewire to the dash. i'm quite sure it's not 2-6 for sure...<br /><br />i haven't determined where the head/macerator wires into the system yet (no fuse on the panel just inline at under the sink) so i'm guessing it ties into the dash (all on starboard side)...so anything come from "dash power" really is at 10% or more votage drop. i did wire the stereo direct to the master panel and gained almost .5-.7v just from that...<br /><br />any thoughts why the nav lights toss my oil gauges (both) to 100% unit power until the ignition is turned on?<br /><br />UPDATE: the wire from the factory for the macerator is approx. 10-12 gauge but the calulator says it should be 8AWG!!!!!! that is a hell of a WRONG size for 3%...how it worked well even 20 years ago is a surprise to me but obviously their standard was a 10% acceptable drop.

 

[Ralph 123]

Re: need voltage drop ideas...(long with details)

This will help you understand how that gauge works and how to test it:<br /><br /> http://www.tflx.com/pdf/oilpre~1.pdf <br /><br />It sounds like, for some reason, the Nav lights are putting a voltage onto either the Ignition line (I in schematic above) or causing the voltage on the ground to rise causing the gauge to act strangely. Once "I" is truly activated, the gauge then operates correctly. Flick the lights on and measure the voltage from "G" to "I" without the key on... Has the Nav switch or wiring been worked on?

 

[Ralph 123]

Re: need voltage drop ideas...(long with details)

Just read your update. It probably worked because the wire was new - now it's corroded a little and the resistance has increased hence the voltage drop has increased... sounds like you have some wiring to do. Replacing and beefing up some of these lines may solve some of these issues..

 

[rsfeller]

Re: need voltage drop ideas...(long with details)

thanks again ralph. i don't think the NAV LIGHTS have been worked on, but i'm going to remove the switch from the circuit to test it properly. additionally, i was hoping to examine the ground point for this circuit and make sure there are is no chance the wiring has been compromised along it's path. <br /><br />i can tell you the oil gauges are original (as well as water temp) and they all have strange reading until the ignition is turned on. all new gauges read "0" when ignition is off. i'll check the voltage as you state. obviously there is some voltage cross the ground, but not enough to affect other gauges.<br /><br />i have a feeling the nav switch and/or new gauges would make the symptom disappear...just a hunch. thanks for your expertise and reinforcing that i'm on the right path...

 

[Ralph 123]

Re: need voltage drop ideas...(long with details)

My pleasure Shawn. Post back as you make progress and check back as others chime in with ideas...

 

[jlinder]

Re: need voltage drop ideas...(long with details)

One test that would be of interest would be to meter the voltage drop across each link in the circuit and record it.<br /><br />I think you may start finding the problem is in the switch or some one particular part. At the very least it will give you a guide as to where your biggest problem is.<br /><br />Let us know what your readings are.

 

[rsfeller]

Re: need voltage drop ideas...(long with details)

jack. i'm with you on the switch idea for sure. i'm going to have quite a "voltmeter" party this fall/winter. for now i'm going to solve the basics...but your idea is on my "to do" list.

 

[rsfeller]

Re: need voltage drop ideas...(long with details)

here is a slight update on my power drop quest. my head (which when activated can knock the voltage down to 10v on new deep cycles) was discovered to have an inline fuse hidden behind the head. this inline fuse which was not only unneeded because it was already fused at the panel but was to far from the source and also of the wrong gauge where it terminated. my 10gauge wire went to about 14 gauge at the incline, and boy did it heat up.<br /><br />upon future discussion with the previous owner whom had the macerator installed the year before i bought it i found it was done by a big sea ray dealer in cleveland. i'll not mention names, but very concerning. this is the stuff boat fires are made of!<br /><br />more voltage drop in the system to find yet to come...

 

[18rabbit]

Re: need voltage drop ideas...(long with details)

Originally posted by shawn feller:<br /> ... my 10gauge wire went to about 14 gauge at the incline, and boy did it heat up. ... this is the stuff boat fires are made of!

Well, you’re only about half way there. Your macerator is yanking only 14-amps out of that AWG 14 wire. The insulation won’t melt off that wire until you get closer to something like 30 to 35-amps going thru an AWG 14 wire. There is a huge safety margin figured into UL approved wire.<br /><br />Think of it as a sock dryer. When your socks get wet, hang them over that wire and keep flushing until dry.<br />

 

[seamegr]

Re: need voltage drop ideas...(long with details)

My 2cents Canadian, if this wiring is original and worked ok up until a certain point, my guess would be a ground/bonding issue. It sounds like too many related problems. Try running a temporary ground wire direct from the battery to one of the affected items and see if that cures any of the problems.<br /><br />Poor grounds do funny things.<br /><br />Greg

 

[CalicoKid]

Re: need voltage drop ideas...(long with details)

I was suspecting ground too. All too often the ground is way undersized and it's importance ignored. Put a lot of current on the ground like you're doing and it becomes pretty weak. Inspect you're grounds closely, look for big splices, undersized wires etc.

 

[rsfeller]

Re: need voltage drop ideas...(long with details)

i understand the 14gauge being acceptable to minimize fire with the UL margin...but the minute i cut the 14 gauge out of the loop (10 gauge from panel to macerator) it starts every time w/o concern and no heat up at the wire. plus the voltage drop at the panel and lights is almost eliminated...<br /><br />thanks again for all your comments. running a new ground is my first project this fall. i'll be running a new one from the battery system to the panel and another from the panel to the dash area. t

 

[18rabbit]

Re: need voltage drop ideas...(long with details)

Yeah, but now you have to walk around with wet socks.<br /> <br /><br />When you know what you are doing, it is amazing the stuff you discover boat manfs get away with.