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Old 06-21-2014, 08:07 AM   #1
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Tachometer problem

I need some help solving a tachometer issue. I recently installed two high output alternators. With both engine running the starboard tach turns off when the port one is on but it comes back on when the starboard engine is above 1500 rpm. After the install both tachs work fine but only if there is only one engine running at a time. The port tach always works.
The voltmeter and ammeter readings indicate that they are both charging correctly. The tachs are driven off the alternator stator. The lowere helm and bridge tachs do the same thing. I have a 1989 6BT5.9. I cant figure out how one tach could influence the other. Hope someone has some insights to point me in the right direction.
Dave
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Old 06-21-2014, 08:15 AM   #2
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I tracked a similar problem to noise. My engine room LED lighting scrambles one tach signal. Both original alternator tachs are wrong a good part of the time. I suspect poor connections, no dedicated negative wire, and no shielding. One these days I'll pull new, shielded 2-conductor cables.
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Old 06-21-2014, 06:48 PM   #3
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Well after some troubleshooting it is the regulators that are doing it. For some reason the first regulator to start becomes the tach that works all the time. This happens when there is no demand on the batteries. If the alternators need to charge hard the regulators both turn on and both tachs work. There has to be an adjustment in the Sterling regulators that will fix this. On to more research I go!
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Old 06-21-2014, 08:17 PM   #4
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Both alts charging the same batt bank? If so, one alt will "sleep", one will charge and on the sleepy one the tach will not work.
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Old 06-21-2014, 09:43 PM   #5
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Both alts charging the same batt bank? If so, one alt will "sleep", one will charge and on the sleepy one the tach will not work.
The alts feed a Promariner 2 alt, 4 bank combiner, that feeds an 8B for each engine and a 920 amp-hr house bank. The combiner is supposed to make use of both alternators.
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Old 06-23-2014, 10:25 AM   #6
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A "combiner" is usually a device that combines batteries.

Can you start again with the problem description....

a. for the first engine to start the tacho works immediately on starting...correct? test and confirm please by starting the test with both stopped, start one, observe & record tacho, stop engine and then start the other, observe & record tacho, stop engine

b. the second engine to start, whichever it is, tacho doesnt work until the 2nd engine rpm is over approx 1500 rpm...correct? test and confirm please by starting the test with both stopped, start one, observe & record tacho, then start the other, observe & record tacho, then increase speed on second engine until tacho kicks in, record tacho for both engines at this point. stop both, repeat but starting with opposite side first

or, describe the problem again in your own way !!

I think what is happening is that you start one, it's generator starts generating, you can tell it has done so because you can see rpm on the tacho. Once it has started generating the combiner senses the generator voltage on one side and "combines" the batteries so that both banks are now being charged from the only running generator (the one on the first engine to be started). You then start the second engine, it's generator has to get up to the voltage of the first generator before it can start delivering to it's battery, because it's battery load is already at an elevated voltage from the first engine's generator through the "combiner" this does not happen until you speed the engine up somewhat, after that it kicks in and you get rpm indication

I will know better once you give the result from the above described test routine, the final question, if it is happening as I have described above.... when you slow down the second engine to tick over after the gen has kicked in does it continue to give rpm indication ?
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Old 06-23-2014, 10:58 AM   #7
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I think the problem is the 2 source combiner. I'd try disconnecting one alternator and having that alternator just charge one stand alone battery or (1) battery bank. I know this might mess with your battery banks charging scheme but it might help us better understand the problem.
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Old 06-23-2014, 11:09 AM   #8
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The tach signal is a rectified fractional output from the stator. So your signal strength is dependent upon the voltage output. If you are in float stage on your charger, the alternator output voltage is low, and the tach signal output is a fraction of that. Likely cause of why you are losing your signal.
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Old 06-23-2014, 11:09 AM   #9
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I think the problem is the 2 source combiner. I'd try disconnecting one alternator and having that alternator just charge one stand alone battery or (1) battery bank. I know this might mess with your battery banks charging scheme but it might help us better understand the problem.
Bill
I had this exact problem with two alternators feeding that first bank. One was an old internally regulated Delco, and one a high amp externally regulated alternator. Regardless of which engine was started first, the old Delco would always shut down the smart regulator/alternator as the "dumb" regulator was set at a higher voltage. Also had a combiner, but it wasn't the underlying issue.
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Old 06-23-2014, 11:15 AM   #10
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I'm thinking if you want to keep the current set up and have reliable tach signals external tach senders might be needed so your tachs don't rely on the alternators output for reliability.
Bill
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Old 06-23-2014, 11:28 AM   #11
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I'm thinking if you want to keep the current set up and have reliable tach signals external tach senders might be needed so your tachs don't rely on the alternators output for reliability.
Bill

Yup. Use a mag tach shooting the teeth on the flywheel.
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Old 06-23-2014, 11:34 AM   #12
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Quote:
Originally Posted by stone beach View Post
A "combiner" is usually a device that combines batteries.

Can you start again with the problem description....

a. for the first engine to start the tacho works immediately on starting...correct? test and confirm please by starting the test with both stopped, start one, observe & record tacho, stop engine and then start the other, observe & record tacho, stop engine
If engines are run independently the tachs work fine.

b. the second engine to start, whichever it is, tacho doesnt work until the 2nd engine rpm is over approx 1500 rpm...correct? test and confirm please by starting the test with both stopped, start one, observe & record tacho, then start the other, observe & record tacho, then increase speed on second engine until tacho kicks in, record tacho for both engines at this point. stop both, repeat but starting with opposite side first
The first engine to start always has tach indication. Raising the 2nd engine to >1500 rpm causes the 2nd tach to kick in. Lowering the rpm <1500 causes the tach to kick out. This is repeatable with both engines when they are the 2nd engine started.

or, describe the problem again in your own way !!

I think what is happening is that you start one, it's generator starts generating, you can tell it has done so because you can see rpm on the tacho. Once it has started generating the combiner senses the generator voltage on one side and "combines" the batteries so that both banks are now being charged from the only running generator (the one on the first engine to be started). You then start the second engine, it's generator has to get up to the voltage of the first generator before it can start delivering to it's battery, because it's battery load is already at an elevated voltage from the first engine's generator through the "combiner" this does not happen until you speed the engine up somewhat, after that it kicks in and you get rpm indication

The Promariner combiner I have is designed to share the load between the two alternators. That is its primary function is to increase charging capability.

I will know better once you give the result from the above described test routine, the final question, if it is happening as I have described above.... when you slow down the second engine to tick over after the gen has kicked in does it continue to give rpm indication ?
If you slow below 1500 rpm it drops out. Above 1500 it kicks in. When the tacks are indicating they have accurate rpm readings
Thanks, Dave
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Old 06-23-2014, 10:52 PM   #13
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guessing a bit without the technical info for the new alternators with external regulators, but I suggest you connect your tacho(s) directly to the tacho output(s) from the alternator(s), I think from the above they are presently connected to the tacho output(s) from your new regulator(s), I would have expected a dip switch or something to select this operating mode, you can check the regulator manual for this first if you prefer
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Old 06-23-2014, 11:15 PM   #14
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Quote:
Originally Posted by stone beach View Post
guessing a bit without the technical info for the new alternators with external regulators, but I suggest you connect your tacho(s) directly to the tacho output(s) from the alternator(s), I think from the above they are presently connected to the tacho output(s) from your new regulator(s), I would have expected a dip switch or something to select this operating mode, you can check the regulator manual for this first if you prefer
The tachs are wired directly off the stator connection on the back of the alternator. It is a connection that is specifically designed for alternator input.
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Old 06-23-2014, 11:43 PM   #15
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It is a connection that is specifically designed for alternator input
I think you intended to say ....specifically designed for tacho input....
in this case what your tacho's are telling you is that the 2nd generator output is "switched off" (by your control system).
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Old 06-24-2014, 07:30 AM   #16
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...your signal strength is dependent upon the voltage output. If you are in float stage on your charger, the alternator output voltage is low, and the tach signal output is a fraction of that. Likely cause of why you are losing your signal.
I can confirm that. Underway after two nights on the hook the other day, my wife said "hey, look - both tachs are reading correctly now!"

This is the first time the port tach has consistently worked right. It's also the most load we've ever put on that alternator. I expect it'll be back to showing twice or three times the actual RPMs next time we leave the dock with a fully-charged house bank.
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Old 06-24-2014, 07:48 AM   #17
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I think we are back to either changing alternative charging systems not likely or changing the way our tachs get their signals. I'm with the change the tach senders and leave the alternative charging systems alone. This has been a good thread for me because I'm new to diesels and the way these older diesels in my case Perkins 4-154M's get their signals from the alternators. There seems to be a direct correlation between changing alternators regulators and alternative charging of battery banks and the loss of reliable tach signalling. I guess if I was to add a 2nd alternator for alternative charging and leave the original alternator and it's dumb regulator in place for the starting battery the tach signalling would be ok, however this is a pretty expensive undertaking.
Thanks,
Bill
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Old 06-24-2014, 09:45 AM   #18
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...I'm with the change the tach senders and leave the alternative charging systems alone...
This is exactly what I did on my Perkins 6 cyl. engines. I used this product:

It says it's for "perkins engines" but doesn't say which ones. I could see the blank plate that this replaces, so I knew I was on the right track. Very easy install. If I had it to do over again I'd use shielded cable rather than a pair of primary wires.
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Old 06-24-2014, 10:00 AM   #19
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I solved it by wiring the old dumb alternator to the start batteries and the high amp, externally regulated unit to the house bank. I moved the combiner (ACR) to interconnect the engine start batteries to the genset start battery (all dedicated start group 24s). A device such as the Xantrex "center fielder" might work to do what you originally had in mind.
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Old 06-24-2014, 01:15 PM   #20
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I can confirm that. Underway after two nights on the hook the other day, my wife said "hey, look - both tachs are reading correctly now!"

This is the first time the port tach has consistently worked right. It's also the most load we've ever put on that alternator. I expect it'll be back to showing twice or three times the actual RPMs next time we leave the dock with a fully-charged house bank.
This is how my stbd tach behaves sometimes. I find that if I add a load (e.g. heater, coffee maker, microwave) to the house bank which is fed by the stbd alternator, the alternator comes back online to feed the load and the tachometer displays accurately.

Next week, with the help of a professional, I'm installing a Balmar 110A alternator and Balmar MC-614 external smart regulator on the stbd engine feeding my house bank. I'm hoping my stbd tach continues to operate normally. (fingers crossed)
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