Tachometer

[Randomwake]

For some reason my tachometer cuts out when the
Engine heats up. Anyone have any common causes?

Also oil pressure gauges work backwards? Needle starts at 100 psi then once engine fires up its lowers to 70psi. This is both gauges on helm and fly bridge.

Thanks very much everyone!

 

[diver dave]

Does your alternator feed the tach using the "W" terminal? If so, does it actually continue to charge when tach goes inop?

ps; 70 psi sounds high. I would check with a mechanical gage. Not sure where the needle lays when off is otherwise pertinent.

 

[Randomwake]

Does your alternator feed the tach using the "W" terminal? If so, does it actually continue to charge when tach goes inop?

ps; 70 psi sounds high. I would check with a mechanical gage. Not sure where the needle lays when off is otherwise pertinent.

Not sure about the alternator I’ll check it out.

I’ve got a manual oil pressure gauge it’s about 50 psi cold and 35 warmed up. Like I said the gauge actually workes back wards so the more pressure there is the less it reads. So when it’s cold and 50psi(mechanical gauge) it actually reads 60psi then once it’s warm and 35psi(mechanical gauge) it reads 80psi.

 

[diver dave]

OK. In that case its pretty clear the gauge is wired backwards. Hopefully, the terminals are marked. Another cause could be the POS and NEG power to gauges is reversed.
Are the senders simple, one wire devices?

 

[High Wire]

On my old Phoenix with Crusader gas engines and VDO gauges, the oil pressure gauges also worked backwards. The engines came with Teleflex pressure senders which worked exactly opposite of VDO senders. The error should have been caught on the original commission. The gauges read mid scale (40 psi) when running. I found that the oil pressure gauges went UP when the oil got hotter, not down.
Bottom line, check that your senders are the same make as the gauges or at least compatible replacements.

 

[rgano]

Try this when the tach shuts down: Turn on some more 12-volt item to make the alternator to charge to see if the alternator comes alive.

As I understand it from the folks here who know about these things, the alternator, depending upon which battery it is connected to, can finish charging said battery in fairly short order, maybe as long as it takes to warm up the engine. Then it shuts down taking the tach feed with it.

Let us know you progress with your two issues. I'm with High Wire on the gauge issue.

 

[kchace]

Try this when the tach shuts down: Turn on some more 12-volt item to make the alternator to charge to see if the alternator comes alive.

As I understand it from the folks here who know about these things, the alternator, depending upon which battery it is connected to, can finish charging said battery in fairly short order, maybe as long as it takes to warm up the engine. Then it shuts down taking the tach feed with it.

Let us know you progress with your two issues. I'm with High Wire on the gauge issue.

Yup, certain situations can cause the alternator(s) to shut off, also cutting off feed to the tach. It happens to me if my batteries are close to fully charged at the beginning of a passage and I leave my solar running. The solar pushes the voltage up enough that the alternators can start turning off - along with the tachs since my tachs get their feed from the alternators.


Ken

 

[koliver]

Yup, certain situations can cause the alternator(s) to shut off, also cutting off feed to the tach. It happens to me if my batteries are close to fully charged at the beginning of a passage and I leave my solar running. The solar pushes the voltage up enough that the alternators can start turning off - along with the tachs since my tachs get their feed from the alternators.


Ken

Same here. Port engine drives a 120 amp alternator, through a smart regulator, that goes to the house battery, where the solar also goes.
The Stb tach feed is not affected, as it isn't connected through the house batteries, but only to the Start battery.
It has been so long since I have seen a reading on the port tach I have stopped looking for it. I feel the harmonics to synch, and run the engines to the same temp, theory being they are then doing the same amount of work.
I recently bought a trio of little digital electronic tachs, for which you glue a little magnet to the hormonic balancer on each engine, mount the sensor within 1 cm, mount the readout wherever you like and B'sYU. Third one for the genset, as it doesn't have a tachometer.
Not yet mounted, as the pigtails on the readouts are way too short.