Tachometer issue

[coyote454]

Electrical question: I run an electric tach off the alternator of my T6.354 Perkins. Since purchase the tach works about half the time, showing accurate RPM and then a few minutes later back to zero. I've run a new ground but no change. The question I have is this: Can I check for the alternator pulse at the tach, using a volt meter or continuity tester to see if the tach is getting a constant signal? This tach is new as I replaced the original when it had the same problem.

 

[SeaDogAK]

I have exactly this problem with the same engines. I think the problem (with mine) is that my Balmar regulator shuts down the alternators when the batteries are full, which shuts down the tachs. My fix is to junk the alternator tach senders and replace them with old style mechanical tach senders, which I’ve bought from Aetna Engineering. I hope to have them installed next week, and I’ll let you know if they work. Here’s a link to info about the Perkins senders: https://www.aetnaengineering.com/wp-content/uploads/2016/01/perkins.pdf

 

[STB]

Yup. Somewhat common problem, depending upon how charging is set up.Magnetic or mechanical senders are the usual solution.

You can watch the wave, but you'd need to use an oscilloscope.

Some multimeters have a frequency coubter function thst might work, but sometimes the signal is too noisy.

 

[PhilPB]

I also have the same engine with the same problem(s). My lower tach would sporadically work and zero out at 1k rpm, the suggestion from my mechanic at the time was to change the tach, so we did. That fixed the lower helm tach. Now about 2 years later the flybridge tach is acting a bit wonky. Also, I have new alternator from Tadiesels that was replaced before the tach replacement. In my case it wasn't the alternator signal.

 

[High Wire]

When the tachs are bouncing or reading zero, turn on a significant DC load like an incandescent spotlight or washdown pump. That should drop battery voltage off enough to reactivate the voltage regulator to begin charging again. If the tachs return to reading ok then it was just a case where the alternator shuts down from having nothing to do. Another thing to do is connect a digital voltmeter to a DC fuse panel near the tach to watch what happens to system voltage at the same time as the tach bouncing.

 

[jgwinks]

Real common problem in boats with big solar panels or those that are plugged in all week. If the batteries are fully charged the alts won't output and the tachs won't work. Turning on a DC load fixes it. If you have incandescent nav lights, that might be enough and there's nothing wrong with running them in broad daylight.

 

[26permacraft]

Had a similar issue with my tach on a different rig. Checking for alternator pulse at the tach sounds like a good move. You can use a voltmeter or continuity tester for that. I'd start there and see what readings you get.

 

[Bmarler]

I have experienced tach dropout as with my balmar regulator as well. The regulator has a couple of terminals on it that are supposed to help with this problem. I will be hooking them up this season to see. There’s a stator terminal, and a tach terminal. Instead of running the tach direct off the stator tap on the alternator, you run the stator lead to the regulator and then to the tach.
I don’t know if it affects the field current or not till I try it.

 

[Barking Sands]

These threads pop up often. And the issues are already described above. I always add what my solution was on my Perkins. It was easy and very inexpensive, and several years on has been bulletproof so far. And if it breaks is extremely easy and cheap to fix. It also ditches the W signal which is unreliable and not very accurate especially considering it is belt wear/slip and pulley size dependent.

There are several videos covering details but I will just post the final result and then links to how it was done and all the options.

It is basically adding 2 very small magnets on the balancer via epoxy, bending a 90 degree bracket and mounting on one of the bolts near the balancer and then running a few small wires to the tach. Then using a compatible tach or use a tach adapter if you want to keep you existing W signal tach.

Here is the end result

And here are two videos covering more details. May not be for everyone but it is a viable option that was not difficult and has eliminated tach issues for me.

 

[PhilPB]

When my old/original tach on the flybridge starts to have a mind of its own, I tap on the face and it will settle down and eventually display a correct reading. I've checked the wires on the back of it but all are tight and not corroded. Also, when it's reading correctly and I tap on it, it starts acting like a crazy person (why do I tap on it? I don't know, except to experiment). I may just replace this one as I did for the lower helm.

 

[Bmarler]

When my old/original tach on the flybridge starts to have a mind of its own, I tap on the face and it will settle down and eventually display a correct reading. I've checked the wires on the back of it but all are tight and not corroded. Also, when it's reading correctly and I tap on it, it starts acting like a crazy person. I may just replace this one as I did for the lower helm.

if there's a dial on the back for calibrating the tach to match the engine rpm, try rotating it a few turns each direction, or just back and forth, and see if it helps. i had a tach that had that instruction in the manual, and it worked for me. remember where you started though.

 

[PhilPB]

if there's a dial on the back for calibrating the tach to match the engine rpm, try rotating it a few turns each direction, or just back and forth, and see if it helps. i had a tach that had that instruction in the manual, and it worked for me. remember where you started though.

I don't think it has the dial but I will double check. The new one does have the dial but, after all, it's 40 years
newer!

 

[coyote454]

tachometer

Thanks to all for the information concerning the voltage and how it affects the tach. You were all correct. I disconnected the shore power, turned on some lights and watched the voltage drop a bit. After a couple minutes fired up the Perkins and the tach started working. Now I understand how it operates. Whether I convert it to a mechanical remains to be seen.

 

[Tiffany]

I have the same situation with my electronic tach on my Perkins T6-354. Dead straight readings then sudden drops off and comes back 5- 10 minutes later.

 

[Bmarler]

I have the same situation with my electronic tach on my Perkins T6-354. Dead straight readings then sudden drops off and comes back 5- 10 minutes later.

are you using a programmable regulator like a balmar? try turning on some dc loads and see if it pops back on. when the regulator shuts down the alternator output the tach signal goes away. you might be able to route the tach signal through the regulator to solve the issue.

 

[hgd]

Loss of tack signal

Electrical question: I run an electric tach off the alternator of my T6.354 Perkins. Since purchase the tach works about half the time, showing accurate RPM and then a few minutes later back to zero. I've run a new ground but no change. The question I have is this: Can I check for the alternator pulse at the tach, using a volt meter or continuity tester to see if the tach is getting a constant signal? This tach is new as I replaced the original when it had the same problem.

I had this problem on my Seapiper 35 with a Beta 85 engine. The problem is the tach signal is derived from the field signal of the alternator. When the batteries are charged, the regulator reduces the field voltage and the tach pulses disappear.

I solved the problem with a device made by Design Technologies which derives its signal by using a Piezoelectric Sensor clamped to a fuel injector tube which is amplified and sent to the tachometer. It works very well.

To see what I am talking about go to https://mvkiwi.com. Page through the blog and you will find it.

 

[Barking Sands]

I had this problem on my Seapiper 35 with a Beta 85 engine. The problem is the tach signal is derived from the field signal of the alternator. When the batteries are charged, the regulator reduces the field voltage and the tach pulses disappear.

I solved the problem with a device made by Design Technologies which derives its signal by using a Piezoelectric Sensor clamped to a fuel injector tube which is amplified and sent to the tachometer. It works very well.

To see what I am talking about go to https://mvkiwi.com. Page through the blog and you will find it.

I tried the Tiny Tach driver from Design Technologies first and it worked good for a few months...then died. I messed with it for a bit but it was a bit finicky for me. I still have a few transducers and driver box.

 

[new2trawl]

I have the same issue with my starboard Lehman running the old 70A Motorolas; internally regulated. Hadn't happened in a while until last year up in the San Juans. Tach bounces and I get it to stop by turning off ignition switch momentarily then back on. Been looking to upgrade both engines to 100A Balmar 6-series but am debating on external regulation. Based on what I've read from a number of you with Balmars, voltage regulation with fully charged batteries seems to be the culprit. Like the Perkins, Lehmans have the mechanical tach connections also and I'm considering going that route when I upgrade my alternators. I'll give Brian a call for his thoughts and see if AD still has the externals for the mech connections.
What I have not seen here in these threads is nobody has put Inverters in mix as a solution to this tach problem. I would think with them on while cruising it would resolve the fully-charged battery issue so the regulators keep 'regulating'. Not sure as I don't have an Inverter installed yet to offer this advice.

 

[Bmarler]

I have the same issue with my starboard Lehman running the old 70A Motorolas; internally regulated. Hadn't happened in a while until last year up in the San Juans. Tach bounces and I get it to stop by turning off ignition switch momentarily then back on. Been looking to upgrade both engines to 100A Balmar 6-series but am debating on external regulation. Based on what I've read from a number of you with Balmars, voltage regulation with fully charged batteries seems to be the culprit. Like the Perkins, Lehmans have the mechanical tach connections also and I'm considering going that route when I upgrade my alternators. I'll give Brian a call for his thoughts and see if AD still has the externals for the mech connections.
What I have not seen here in these threads is nobody has put Inverters in mix as a solution to this tach problem. I would think with them on while cruising it would resolve the fully-charged battery issue so the regulators keep 'regulating'. Not sure as I don't have an Inverter installed yet to offer this advice.

I have a balmar regulator and an inverter. I leave the inverter on 24/7. Still have the issue when the solar output is high. Without solar, the issue is rare for me. I’m going to try the dedicated tach signal from the regulator next time I’m out and will report my findings.

 

[coyote454]

Interesting thought about the inverter. I hadn't thought of that but I'll leave mine on next time out with the radio on to see if that keeps the tach signal constant.

I run a Balmar 100Amp and as a test ran a few lights with the shore power disconnected to discharge the batteries just a bit and then started the Perkins. Viola, The tach stays on for a bit and then turns off when the batteries are charged again, so this definitely was the culprit.

 

[Mischief Managed]

When my old/original tach on the flybridge starts to have a mind of its own, I tap on the face and it will settle down and eventually display a correct reading. I've checked the wires on the back of it but all are tight and not corroded. Also, when it's reading correctly and I tap on it, it starts acting like a crazy person (why do I tap on it? I don't know, except to experiment). I may just replace this one as I did for the lower helm.

If it's a Faria tach, that's normal for them.