Erratic Gauges

[svfinnishline]

My engine oil presssure, water temp and tachometer fluctuates wildly at high rates of alternator charge (>150A). This is a new problem found after adding a balmar 150A alternator, running in parallel with an Amptech 125A alternator to charge the new Odyssey house battery bank.

Once the charge level decreases it seems as though the gauges are much more stable.

The wildly fluctuating gauges are a little un-nerving on initial engine start up with the batteries down to 50%. Any ideas or suggestions on what I should be looking for?

Many thanks,
Michael

[osirissail]

Running dual alternators at the same time usually requires a special control unit that takes control of the regulators so one doesn't try to overpower or get confused due to the voltage present from the other alternator. Balmar makes such controls.
- - Does the problem exist if you are running only one alternator or the other but not both at the same time? If it doesn't then I suggest you redo your alternators regulation system to conform to dual alternator operation.
- - If the problem exists when only one alternator is operating then probably there is a main power feed to the instruments problem. Watching the voltage of the whole system when the alternator(s) is charging is quite important. You might be over-volting the system which is neither good for any instruments and other electrical equipment or the batteries themselves. Over-volting can cause boiling of the batteries and expensive damage.

[svfinnishline]

I'm using the Balmar MC-612-Dual voltage regulator. It seems to be controlling the voltage output quite nicely, but have not as yet tried to run one alternator at a time. Just now plotting the recharge time curves noting voltage, amps and SOC every 5 minutes and there are no anomalies. Any other ideas? Thanks for the input.

[osirissail]

Then I would suggest my last idea that you have a feed problem to the instrument bus. Corroded terminals or intermittent/defective wires might be causing problems. Try using a "bypass" wire from the both before and after the instrument bus c/b (fused wire) directly to the distribution terminal block for the instruments. Then see if the problem is present. Also some installation have the power for the instruments running through your ignition on-off switch which could also be faulty. Which is not uncommon.

[svfinnishline]

Now that rings a few bells! Just recently have had an intermittent problem shutting the engine off via the key - sometimes it works as expected and other times I need to open the engine access hatch and shut the engine down manually.. Thank you for your help!

[chris_gee]

Is this a diesel engine? If so you don't stop the engine via the key, rather a choke like knob which shuts off the fuel. Using the key can damage the electrics.

[anjou]

If you were wired to 200a plus, i bet you would fluctuate too.
Were your instruments designed for this?

[osirissail]

Originally Posted by anjou

If you were wired to 200a plus, i bet you would fluctuate too. Were your instruments designed for this?

Huh? what is "200a plus"? Over-voltage or intermittent voltage will cause instrument fluctuation but the system is on a fused or c/b protected bus so over-current cannot be a factor.

[mrm]

A wild guess: overloaded ground wiring between main ground bar and batteries?

More than doubling charging current without wiring upgrade might have caused the gnd bar voltage to float somewhat and this may give erratic gauges behaviour.

[osirissail]

Originally Posted by chris_gee

Is this a diesel engine? If so you don't stop the engine via the key, rather a choke like knob which shuts off the fuel. Using the key can damage the electrics.

I've always like the manual compression release or fuel shutoff cable system but unfortunately there are an awful lot of boats that have electric solenoids that are operated by the key switch or a separate electric push button to shut down the diesel engine.

[svfinnishline]

Well as osirissail suggested the gauges are powered off the ignition switch, see wiring diagram attached. I have had intermittent issues switching the engine off using the switch (Volvo MD22L designed this system to shut down the engine using the switch), which have occurred since the charging system was upgraded.

The wiring was upgraded 2/0 gauge from the 150A alternator, on both positive and negative sides, from the alternator to battery (+) directly, and from the IG negative to the negative bus bar. But I have not as yet upgraded the battery negative cable from the battery (-) to the ground bus.

So as mrm suggests, could this be the root cause of the erratic gauges, and the intermittent failures to shut the engine down via the switch? Can I test or measure something to confirm this (ground bar voltage float?) - if so how? What are your thoughts mrm & osirissail?

Thanks for the help!

[osirissail]

Svfinnishline - wrong diagram. you need to post the ship's DC wiring diagram that includes the alternators, controllers and ground system.
- - Normally, alternator positive feeds are cabled to the positive DC distribution system but the alternator negative is through the mounting frame directly to the engine or with a short ground strap to the engine frame/block. In short there is no "negative cable" from the alternator to the ship DC distribution system panel.
- - Normally the Battery negative cables are connected to your amp-hour shunt then to the engine block.
- - From the DC distribution system panels the negative bus terminal bars are also routed to the engine block.
- - Only the negative wires from the batteries to the engine need to be sized to accommodate the total alternator output loads. The negative cables from the ship's DC distribution system are sized to the handle the total load of the DC distribution system - not the alternators.

[svfinnishline]

The wiring diagram attached previously was only to show that the gauges are indeed powered through the ignition switch. I need to draw up a new DC wiring diagram, for the new installation..

This boat has an isolated ground system - there are separate ground wires from both the alternators negative posts to a large central ground bus.

The battery negative cable is connected to the amp hour shunt and from there to the central ground bus - this cable - perhaps 9 feet in length, has not been upgraded or increased in diameter.

As mrm suggested "More than doubling charging current without wiring upgrade might have caused the gnd bar voltage to float somewhat and this may give erratic gauges behavior."

Can I test or measure something to confirm this (ground bar voltage float?) - if so how?

[osirissail]

Originally Posted by svfinnishline

. . . This boat has an isolated ground system - there are separate ground wires from both the alternators negative posts to a large central ground bus.

The battery negative cable is connected to the amp hour shunt and from there to the central ground bus - this cable - perhaps 9 feet in length, has not been upgraded or increased in diameter. . . .

Usually the "AmpHour Meter" also includes a volt meter. It measures the DC voltage from the battery to the central ground bus, measured at the shunt. If the central ground bus has a potential above zero the volts on the meter would be less than actual across the battery.
- - I find the idea that the central ground bus is "floating" above battery zero strange and unusual. "Never say never" but highly unusual. A meter across the actual battery terminals compared to the meter across the battery positive and central ground bus should read very close to each other. The difference would be accounted for in a resistance to current flow caused by an improperly sized battery negative cable from the batteries to the central ground bus.
- - Forget the instrument fluctuations - if that battery negative cable system is under-sized then you have a potential fire hazard as that battery negative cable cannot handle the ampere load of the whole system at maximum. That is a serious problem that needs correcting immediately if not sooner.
- - I also find it unusual that the DC system could be "isolated" from earth/water grounding. There are electrical sensors on the engine that usually have only one wire to them. The return DC wire is the engine itself which through the propeller shaft is grounded to sea water. And the alternators would have to totally non-standard as the case of the alternator is part of its "grounding" and is mechanically bolted to the engine. Again, never say never, as I have seen some unusual electrical systems coming out of other countries that are not bound by the US ABYC system of conventions.

[mrm]

Originally Posted by svfinnishline

Can I test or measure something to confirm this (ground bar voltage float?) - if so how?

A multimeter across this suspect wire will show what voltage drop and fluctuations are there. For fluctuations a scope would be preferred, but just measuring with a multimeter should help verify. Look for changes in voltage between negative battery terminal and ground bar and see if they correlate to erratic behaviour in gauges.

Marius