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Old 06-27-2017, 07:10 PM   #1
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Magnetic Tachometer

Hi Folks:

My port tachometer shuts down after my alternator is told by the voltage regulator to stop charging the house bank. I can't increase the voltage on the Regulator because it would overcharge my new AGM Fullriver batteries, which are located in my hot engine room. So I'm told the only way to get around this problem is to install a magnetic tachometer.

Does anyone have experience with these, and if so what brands are you using. Is installing one easier than the other etc.

Please don't hold back. Looking forward to all input. Thanks.

Jim
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Old 06-27-2017, 09:18 PM   #2
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You could turn a few lights on, like we did back in the days of automotive generators, thus giving the alternator something to do and continuing to run the tach.
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Old 06-28-2017, 12:13 AM   #3
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Aetna Tachs make good units. Usually they tie to a sensor that counts the teeth on a flywheel but there are other ways of dealing with this. The units are programmable for the tooth count.

Talk to them.
Aetna Engineering Products | Aetna Engineering
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Old 06-28-2017, 04:47 AM   #4
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Which engines do you have? I'm interested in hearing what you come up with as I'm contemplating a change from the mechanical tach drive on my 453s.
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Old 06-28-2017, 05:08 AM   #5
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"I'm contemplating a change from the mechanical tach drive on my 453s."

Just all at the DD dealer or troll the net.

While the mechanical tachs are usually great , if a drive is there, its just parts to purchase a sender for an electric tach.

The alt tachs are never accurate , the mechanicals can be fine and the pulsed electric from a real tach drive is probably the most accurate.

Accuracy is most desired by folks with twins that do not have an engine sync system.

For most cruisers 1580, 1609 or 1650 RPM as a number is useless , repeatability is desired so you get repeatable speed , fuel burn , day after day.
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Old 06-28-2017, 05:45 AM   #6
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Jim- if you have 4-53's they should have a tach drive somewhere on the engine, ready to install a pulse generator. If you have a Glendinning synchronizer box, pulse generators can be installed on it. The sync box would already have cables going to the engine tach drives.
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Old 06-28-2017, 06:36 AM   #7
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So I'm told the only way to get around this problem is to install a magnetic tachometer.

Does anyone have experience with these, and if so what brands are you using. Is installing one easier than the other etc.
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Aetna Tachs make good units. Usually they tie to a sensor that counts the teeth on a flywheel but there are other ways of dealing with this. The units are programmable for the tooth count.

I changed our original analog tachs to Aetna digital tachs. Good tachs, easy swap, BUT we already had magnetic senders at the flywheel... so it was literally swapping only a few wires at the gauge end of the system.

Don't know what it might take to install magnetic senders if they're not already in place...

BTW, CruzPro also makes digital tachs, in a smaller diameter. I'd guess those work equally well.

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Old 06-28-2017, 05:06 PM   #8
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Thanks Brooksie, good idea!

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You could turn a few lights on, like we did back in the days of automotive generators, thus giving the alternator something to do and continuing to run the tach.
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Old 06-28-2017, 05:07 PM   #9
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DD 453s

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Which engines do you have? I'm interested in hearing what you come up with as I'm contemplating a change from the mechanical tach drive on my 453s.
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Old 06-28-2017, 05:10 PM   #10
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I have DD 4-53s. I'm that informed enough to be able to look for the "tach drive". I do have a Glendinning synchronizer but don't use it, but suppose that I could. Will consider this...one more device to learn....hm....

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Jim- if you have 4-53's they should have a tach drive somewhere on the engine, ready to install a pulse generator. If you have a Glendinning synchronizer box, pulse generators can be installed on it. The sync box would already have cables going to the engine tach drives.
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Old 06-28-2017, 05:12 PM   #11
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Thanks Chris....lots to consider...

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I changed our original analog tachs to Aetna digital tachs. Good tachs, easy swap, BUT we already had magnetic senders at the flywheel... so it was literally swapping only a few wires at the gauge end of the system.

Don't know what it might take to install magnetic senders if they're not already in place...

BTW, CruzPro also makes digital tachs, in a smaller diameter. I'd guess those work equally well.

-Chris
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Old 06-28-2017, 06:28 PM   #12
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I have DD 4-53s. I'm that informed enough to be able to look for the "tach drive". I do have a Glendinning synchronizer but don't use it, but suppose that I could. Will consider this...one more device to learn....hm....

Whether you use the sync box or not, the tach cables spin with the engines and with signal generators on the box the tachs will get good signals. Sync box does not need to be on.
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Old 06-28-2017, 06:48 PM   #13
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Tiny Tach - Diesel
https://www.tinytach.com/diesel-tinytach
Don't think it will work on a DD though.
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Old 06-29-2017, 04:11 AM   #14
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The alt tachs are never accurate , the mechanicals can be fine and the pulsed electric from a real tach drive is probably the most accurate.
Alternator driven tachs have long been known not to be accurate. However, I recently replaced my old Motorolas, the type that may be adjusted using its potentiometer which derives accuracy only within ranges, with VDO's on the lower helm and Isspro's on the upper. I used the original alternator feeds on my 1983 vintage boat.

These tachs, once adjusted, quite simply by following directions, are, indeed, quite accurate throughout its range. How do I know? Photo-tached my engines and then compared to tach output. Spot-on, all four. And, tach drop-out is rare and brief when it does occur. As others have suggested, just maintain some demand on the charging system. Also, I have Balmar externally regulated alternators which I think mitigates drop-out but that's a guess on my part.
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Old 06-29-2017, 05:36 AM   #15
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"These tachs, once adjusted, quite simply by following directions, are, indeed, quite accurate throughout its range."

Until the belt wears , gets thinner , the belt heats & loosens under load , the pulley changes size as it heats , all change RPM output.

But in most cases any repeatable reading is fine, as unless synchronizing engines even 100 RPM error is meaningless.
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Old 06-29-2017, 07:50 AM   #16
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So all I have to do is install "tach generators" onto my glendenning and whether I engage the synchronizer or not, the new tach generators will grab the signal from the box and provide accurate readings, correct?

Do you recommend a brand of tach generators? Thanks Ski.

Ji

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Whether you use the sync box or not, the tach cables spin with the engines and with signal generators on the box the tachs will get good signals. Sync box does not need to be on.
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Old 06-29-2017, 08:33 AM   #17
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So all I have to do is install "tach generators" onto my glendenning and whether I engage the synchronizer or not, the new tach generators will grab the signal from the box and provide accurate readings, correct?

Do you recommend a brand of tach generators? Thanks Ski.

Ji
Correct, tach cables and sync box guts spin all the time with engine running, regardless if sync is on or off.

Post a photo of the sync box, need to see if anything is installed on the end caps.

Have not shopped for signal generators in a long time. Glendinning is probably a good source. Fittings whether on the box or on the engine are somewhat standardized. All that stuff is interchangeable although sometimes it is not!!!
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Old 06-29-2017, 10:54 AM   #18
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On my old engine I have a magnetic tach that gets its input from the teeth of my oil pump. I am not certain of the brand but it looks to be a faria tach sender.

L.
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Old 07-02-2017, 07:00 AM   #19
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Hi Ski:

Here are three shots of the Glendinning. Standing by for your comments. Thanks.

Kokomo Jim



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Correct, tach cables and sync box guts spin all the time with engine running, regardless if sync is on or off.

Post a photo of the sync box, need to see if anything is installed on the end caps.

Have not shopped for signal generators in a long time. Glendinning is probably a good source. Fittings whether on the box or on the engine are somewhat standardized. All that stuff is interchangeable although sometimes it is not!!!
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