Low voltage up on the port motor flybridge guage?

Twin 454 Gen IV Crusaders --1984 Egg Harbor Tournament Fisherman

Try not to laugh...

Port motor voltage gauge shows 12.6 volts at start up and idle but decreases with increasing RPMS both underway at cruise and at the dock in neutral if the engine is reved up. Drops down to slightly under 12 volts if underway at cruise for 30 minutes or so. Will recover to around 12.5 volts in gear at low RPMS (1200 or less) while underway or at the dock. Voltage readings were verified at the gauge by digital volt meter. The gauge is accurate.

Down in the engine room the port alternator and at the port battery bank the voltage is rock solid at 13.4 volts regardless of RPMS.

Power to the flybridge goes through a circuit breaker at the power distribution panel and then up to a main bus bar on the flybrige. I suppose there could be a bad connection at the flybridge breaker (had one once that affect my trim tabs).

More likely there is a bad connection at the flybridge bus bar or perhaps at the ignition key switch where high resistance causes a voltage drop as the ignition call for more power with increasing RPMS.

I've been too lazy to check the voltage at the main flybride bus bar to see if it drops with increasing RPMS.

Anyone seen this? Trouble shooting tips?

Not at all uncommon. The ignition system is run by the same switched +12volt line as that connected to your gauge. More rpm, more sparks, more current on that wire. That wire is likely over 20 feet long to run up to the bridge. You are seeing voltage drop in the wire, shown by the dash gauge. Actually, each connection, the breaker, the wire itself all contribute to the voltage drop. You could take a DMM and measure across each contributor. You could redesign the system, so the ignition system uses an engine mounted relay to supply the current. Or, you could do what I did, and run the voltmeter + term directly to that engine's master On/Off switch; use a fuse near the switch, though.

Yes, very common, especially on older hulls.

the short answer - stop procrastinating and start making those measurements. If the result is many distributed drops, I'd take the redesign approach. If the issue turns out to be one or two, I'd fix them.

I'm looking at it from an efficiency viewpoint. You've verified the gauge reading so the voltage drop is real which means the wiring and the rest of the ignition system isn't operating as it should. Any cost effective means to improve efficiency will result in more fuel to burn (or less money to get the fuel needed). This can then be redirected to the wine cellar, the bait locker, or the electronics budget, as desired.

Thanks Guys. Very Helpful.

I will make some measurements at the flybridge bus bar and see if the bad behavior is present there. Then perhaps the ignition key switch and anything else that's in series with the ignition circuit. Perhaps temporarily jump across the main flybridge breaker to the port engine and re-check the behavior--that's easy enough.

Hopefully a corroded connection or wire will reveal itself.

I would very much prefer to have the ignition running off full battery voltage while underway. I don't like to see any number below 12 on my engine volt meter--a value right around 13 volts is what I'm looking for.

Best wishes,

Tom

And yes, I've been procrastinating. But consider this year's completed tasks.

Installed new 5 kW genset, complete with new exhaust system and remote start.
Replaced hydraulic steering completely including new Helm pump, cylinder, hydraulic lines and autopilot.
New Risers and elbows Port Engine
Installed new A/C in salon with digital controls.
Installed a queen sized futon couch (really needed that one).
Installed a stereo with iPOD connectivity.
Installed a 1000 Watt inverter
Installed an HDTV anntenna (to watch football on the water)
Installed a dingy lift and davits

And of course general maintenance for the big boat and two inflatables...

major_tom said:

Installed new 5 kW genset, complete with new exhaust system and remote start.
Replaced hydraulic steering completely including new Helm pump, cylinder, hydraulic lines and autopilot.
New Risers and elbows Port Engine
Installed new A/C in salon with digital controls.
Installed a queen sized futon couch (really needed that one).
Installed a stereo with iPOD connectivity.
Installed a 1000 Watt inverter
Installed an HDTV anntenna (to watch football on the water)
Installed a dingy lift and davits

...

Click to expand...

WOW; your 33 convertable is a whole lot bigger than my 32 express! I can't even stand up in my cabin...

Yes, the cockpit is a little small but the salon is huge for a 33' footer.

Diver Dave, I'm a lttile confused by the following statement, and a more detailed explanation would be appreciated.

"Or, you could do what I did, and run the voltmeter + term directly to that engine's master On/Off switch"

Best wishes,

Tom

major_tom said:

Diver Dave, I'm a lttile confused by the following statement, and a more detailed explanation would be appreciated.

"Or, you could do what I did, and run the voltmeter + term directly to that engine's master On/Off switch"

Click to expand...

For quite a while, I was have trouble with my alternators. The charge voltage was not stable, sometimes not charging at all, sometimes running over 14 volts. I have remote, adjustable regulators, and I was adjusting them and readjusting a week later. While I was dealing with that issue, I especially wanted accurate readings at the dash. Anyway, my voltmeters always read low, about a volt lower than the actual battery. I was bound and determined to fix this readout issue. My engines also have electric chokes, that also run current thru the switched 12v line, coded purple on the wiring harness. With my DMM, I read a voltage drop thru the engine wiring harness connector, and there was more voltage drop thru the long run of wire itself. Turning on the blowers increased the drop even more. I figured since I really wanted to measure the voltage across the battery, why not connect the voltmeters to the batteries? It turns out that my DC panel was only a few feet from my lower dash and there was already wiring that connected the DC panel voltmeter to each battery, (port, starboard, and house), thru a rotary switch. What I did was disconnect the engine voltmeter + terminal from the engine purple wire, and instead run a new wire from the engine voltmeter + term. to the power panel battery sense wire. Now, what happens is that whenever the engine master switch (on-off), is ON, the dash voltmeter indicates the actual battery voltage without any voltage drop. The various errors due to the engine power drains do not mess with the reading. It is stable and accurate. They also tell you if the master engine switches are on or off at a glance. I did this for both engines and they have been working this way for over a year. It's more important for me to know what the battery voltages are rather than the voltage midway thru a long harness to the engine.

Thanks for the explanation. I would like to remedy my low votage readings as well. At the same time it would be nice to ensure that the ignition system was being supplied with full batttery voltage while underway. Your solution above solves the voltage meter problem, but since it is no longer in series with the purple ignition wire, it doesn't solve the low ignition voltage issue and in fact you have no way of knowing if your ignition voltage is running low. Hence your suggestion of installing an engine mounted relay...

I have yet to locate my engine wiring "Harness". Maybe I'm looking for a connector that's not present. The best I can do is find a ball of wires wrapped up in electrical tape at the rear of the motor near the remote oil filter. Maybe its time to unwrap the mummy and see how well preserved the bones are. The starboard engine has the same ball of wires, so I think it came this way from the factory, but who knows after 26 years. I was kind of hoping for a nice in-line 8-pin connector or equivalent.

I have two new alterators and they charge the battery banks flawlessly (13.4 V) based on repeated measurements at the battery banks while underway. You'd never know it up at the helm though with the port meter a little below 12 V.

major_tom said:

Your solution above solves the voltage meter problem, but since it is no longer in series with the purple ignition wire, it doesn't solve the low ignition voltage issue and in fact you have no way of knowing if your ignition voltage is running low. Hence your suggestion of installing an engine mounted relay...

Click to expand...

The automotive world has tons of these 1" cube relays rated at 20 amps or so, and they are designed for a socket. If you feed the 12v coil of one of those, then the "purple wire" will suffer far less voltage drop on the round trip to the dash. It does add more points of failure to the existing, simple system, but it will bring the ignition system up to full battery voltage, and your gauge will read accurate charging voltage as well. Carry a spare relay.

Saturday I took Diver Dave and Mako's advice and checked all DC connections starting at the main breaker panel and then up on the flybridge. At the main breaker the main DC feeds to the bus (power and ground), flybridge circuit breakers, etc. were loosened, sprayed with Corrosion Block, and re-tightened. Corrosion Block literally disolves copper oxides on contact and leaves a protective coating--closet thing to a miracle in can I have ever seen and highly recommended).

(http://www.westmarine.com/webapp/wc...hanintel_google&ci_src=14110944&ci_sku=441942

Up on the flybride the 5 terminal strips where the engine and control wires are connected through to the bridge controls and instruments were treated the same way. Corrosion was visible on the terminal block screws at all connections before treatment.

Previously the gauges on the instrument panel had been treated in a similar way so these were left alone. Finally had a go at the ignition terminals for the port motor (the side where the voltage gauge read 12 volts while underway).

Preliminarly check revealed a modest increase in voltage but nothing to speak of and the voltage on the port side still dropped as RPMS increased. I was about to visit the engine room when I decided to jump across the ignition key switch "Bat" and "IGN" terminals with a screwdriver while the engine was running. Voila--13.0 Volts at the port gauge.

Replaced port ignition key swith with a new brass key switch from Autozone for $15.00 The new switch was indistinguisable from the old key switch except the "Made in USA" now read "Made in China".

Port voltage gauge now 13.5 volts while running and holds rock steady as RPMS increase, just like the measurements down at the alternator and battery banks. Starboard gauge shows 13.4 volts.

Thanks Diver Dave and Mako Mark for your advice and encouragement. I feel a lot better about those voltage numbers now....

Best wishes,

Glad that one is resolved!

Also, congrats on your "accomplished" list this year; much more impressive than mine. On the other hand, the "events with the kids" list is at an all-time high. Only one more event to complete this season.