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  #1   IP: 108.2.122.5
Old 07-16-2020, 06:24 PM
masteriti masteriti is offline
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Looking for advice on adding a tachometer

Hi! Came across your webiste and forum in my research, great resource btw!

I recently bought a '81 Pearson 28 sailboat. She's got a beutifully running Universal Atomic 4 (model 5411), but the electrical system is a mess. So I'm planning to rewire it all, organise it into new panels, and add some new tech.

One of the items I bought for this project is the Blue Sea M2 SoC indicator. This nifty device will not only give me voltage reading for each battery, but also measure amp charge/draw and keep track of house charge level through a shunt at the negative house bank post. The boat currently has a simple Ammeter on the engine panel, but not a tachometer...so now I'm thinking: what do I need the Ammeter gauge at this point? Could I put a tachometer in its place...maybe one that will keep track of engine hours too? I'm not sure I have a signal feed for it from the Alternator or if there's a (reasonable) way around this. My alternator is a Motorola MR12V60 55A with attached external regulator.

Thanks in advance for any advice!
Cheers!
M
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  #2   IP: 100.36.65.17
Old 07-17-2020, 10:18 AM
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Hi! Welcome to the forum. You have found the best place on the web for all things A4. The folks here are knowledgable, polite, and eager to help.

Adding a tach is a great idea. Unlike a diesel engine, which requires an alternator feed for a tach, a gas engine like the A4 can run a tach off of the ignition signal present on the "-" terminal of the coil. This is, by far, the commonest way of driving a tach on an A4.

Tachometers of this type usually come with some sort of selection mechanism for the number of cylinders. This tells the tach how many pulses per revolution to expect.

Wiring is pretty easy, consisting of four wires: Ground, +12 power, ignition signal (from the coil "-"), and display illumination.
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Last edited by edwardc; 07-17-2020 at 10:19 AM. Reason: typo
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  #3   IP: 108.2.122.5
Old 07-17-2020, 10:44 AM
masteriti masteriti is offline
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Hi edwardc, thank you! I feel very welcome!

So, I should have specified that my engine is actually a diesel, therein lies my problem.

The research I've done so far, I've only seen a couple of options:

1. AutoMeter diesel tacho that straps an inductive pickup sensor on the alternator housing.

2. add some sort of a reflector tape somewhere with a light sensor.

Not sure if there's another option I've missed.

Cheers!
Marco

Last edited by masteriti; 07-17-2020 at 11:42 AM.
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  #4   IP: 100.36.65.17
Old 07-18-2020, 03:21 PM
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The AutoMeter seems rather pricey. By the time you've bought it, and a suitable tach, it looks like you'll be close to $200. And you'll have to modify your alternator.

A better choice might be to replace the alternator with one that has a tach output. As an example only, I found one on Amazon for just under $80 (not sure if this exact one is a fit for you, but you get the idea.) Then you could install a standard diesel tach, which can be had for as little as $30.

https://www.amazon.com/New-Mercruise.../dp/B00E9G07JK

https://www.amazon.com/MOTOR-METER-R...e%2C148&sr=1-6
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  #5   IP: 32.211.28.40
Old 07-18-2020, 10:34 PM
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[QUOTE= I should have specified that my engine is actually a diesel, therein lies my problem. [/QUOTE]
Love it!!!
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  #6   IP: 100.36.65.17
Old 07-19-2020, 10:50 AM
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Marco,

I found this 5411 manual if you don't already have it.
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Old 07-21-2020, 08:29 AM
masteriti masteriti is offline
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Thumbs up

I like the idea of getting a new alternator, the current one I can keep as a spare since it works fine. Thanks, edwardc!
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Old 07-21-2020, 12:28 PM
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You're quite welcome.

Spares are always good.

I carry a spare alternator and starter when cruising.
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  #9   IP: 137.103.82.227
Old 07-22-2020, 08:16 AM
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See this thread:
http://www.moyermarineforum.com/foru...ese+tachometer
I got a $30 FleaBay tach and so far so good.
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  #10   IP: 207.32.169.48
Old 07-22-2020, 12:35 PM
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1940's engineering still going strong

This tachometer discussion makes me appreciate my mechanical tachometer, so I thought I would send in a tribute.
It runs from the accessory drive, and spins a cable in a sleeve which extends to a needle on a large dial. It is easy to see from a distance. It never seems to need any maintenance as long as the engine has oil, which apparently works its way up inside the cable to the little gearbox on the back of the dial. You know it is accurate because it is a direct drive. It also shows engine hours. It is a primitive technology that seems foolproof. No electricity or electronics are involved. I have yet to see a mention of one on this forum. The older model accessory drives that support them are no longer available, and the only mention of them I see in the Moyer catalog is a plug for its port. The dial also has mounts for old timey temperature gauge and ammeter, which have been replaced by more modern versions. It still has the old school oil pressure gauge. The drive, cable and dial would no doubt be collector's items, if anyone cared. I think it is one of the more charming features of my boat, obsolete as it may be. Just like the A4 itself.
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  #11   IP: 24.15.42.198
Old 07-22-2020, 03:50 PM
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Along the same line on my 1966 Moran 34 I have a old school mechanical oil pressure gauge - oil filled copper tubing to the back of the gauge. The original Stewart Warner lasted about 35 yrs, found a replacement in an automotive catalog for replacement parts for antique cars.
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