I've got a Universal M-18 diesel in my 84 Catalina 27. I'm wondering if anybody can shed some light on the operation of the tachometer after starting the engine. Typically, my tachometer (a Teleflex, which gets its signal from the alternator, a 55amp Motorola, which I believe is original) remains at zero right after starting. It takes a blip of the throttle to get the alternator to kick in, which then immediately starts the tachometer. I'm told that this is normal, and allows the engine to be started without the extra load of an alternator that is "engaged". In fact, this is how my setup has worked since I got it in '99. On my last two starts, (yesterday) the usual blip of the throttle got some response from the tach, but it was not normal--it seemed to be reading low, and moving in slow motion. This lasted less than a minute both times, and then the tach returned to "normal", and gave correct readouts of rpm, and responded instantly to rpm changes. Any idea what could have caused this? Is my alternator on the way out? Or is it something in the tach, or in the wiring in between? By the way, alternator output is still good, giving me voltage in the high 13 range when the engine is on. Thanks for any input. Randy
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tacho
Randy; It's probably the voltage regulator, which doesn't "ignite" the alternator for about five seconds after engine start-up to allow the engine to start without the drag of the alternator. Plus, the engine has to be turning over at about 900 RPM to start up the alternator, too. If the tach is fluky, suspect the voltage regulator, especially when the regulator shifts from the CHARGE mode to FLOAT. This is normal. I'm assuming the alternator has a separate, three-stage, regulator. How much current does the alt. put out when the batteries are really low?
Randy; It's probably the voltage regulator, which doesn't "ignite" the alternator for about five seconds after engine start-up to allow the engine to start without the drag of the alternator. Plus, the engine has to be turning over at about 900 RPM to start up the alternator, too. If the tach is fluky, suspect the voltage regulator, especially when the regulator shifts from the CHARGE mode to FLOAT. This is normal. I'm assuming the alternator has a separate, three-stage, regulator. How much current does the alt. put out when the batteries are really low?
Tachometer reading at startup
Randy Am I correct is assuming that you leave your boat "plugged in" all week? If so, your batteries are full, and there's no reason for the alternator to kick in. Once there's a load on the batteries (i.e., instruments, refrigerator, VHF, stereo, etc.), the regulator will tell it to start. The tachometer works off the alternator, if it isn't running, the tach won't either. I doubt if you have an external three stage regulator in your boat, unless you put it in yourself. The 55 amp Motorola alternator is OEM with a relatively useless internal regulator. Check the link for a bit more discussion on your question, you're not alone. Check some other recent C34 Message Board questions, too, about alternators. It seems your alternator is doing fine. Wouldn't hurt to check connections regularly. Internally regulated alternators are very poor in recharging batteries, and also aren't very good to the batteries, for a number of reasons all well written up by people who have already written books about them, so I won't copy that here. Try Nigel Calder's Boatowner's Manual, very good boat electrical systems discussions. Voltage in the high 13 range isn't so good, either, so you may choose to do some reading on correctly charging batteries. A good regulator (say $200 installed) will be paid for in less than a year by keeping your batteires in good charge, and making them last longer. Good luck, Stu
Randy Am I correct is assuming that you leave your boat "plugged in" all week? If so, your batteries are full, and there's no reason for the alternator to kick in. Once there's a load on the batteries (i.e., instruments, refrigerator, VHF, stereo, etc.), the regulator will tell it to start. The tachometer works off the alternator, if it isn't running, the tach won't either. I doubt if you have an external three stage regulator in your boat, unless you put it in yourself. The 55 amp Motorola alternator is OEM with a relatively useless internal regulator. Check the link for a bit more discussion on your question, you're not alone. Check some other recent C34 Message Board questions, too, about alternators. It seems your alternator is doing fine. Wouldn't hurt to check connections regularly. Internally regulated alternators are very poor in recharging batteries, and also aren't very good to the batteries, for a number of reasons all well written up by people who have already written books about them, so I won't copy that here. Try Nigel Calder's Boatowner's Manual, very good boat electrical systems discussions. Voltage in the high 13 range isn't so good, either, so you may choose to do some reading on correctly charging batteries. A good regulator (say $200 installed) will be paid for in less than a year by keeping your batteires in good charge, and making them last longer. Good luck, Stu
ground wire
One place to look when instrumentation is erratic is the ground wire on the particular instrument. Check continuity from the ground terminal on the tach to a known ground. Insure the known ground is good. The sensing wire from the tach to the alternator may be suspect as well.
One place to look when instrumentation is erratic is the ground wire on the particular instrument. Check continuity from the ground terminal on the tach to a known ground. Insure the known ground is good. The sensing wire from the tach to the alternator may be suspect as well.
More info
Hi all--I appreciate the suggestions. The Motorola alternator is the original unit, as is the voltage regulator. I don't remain plugged in while away from the boat, so the batteries aren't freshly topped up when I get aboard. The strange part is that I am now getting this extra 30-60 second "slow motion" phase where the tach responds slowly, like it was "stiff". It happened again twice last night. Previously, the tach would simply remain dead after a start, then spring to life when rpms went above 900 or 1000. Now, it takes a minute, and 1500rpm to get the tach back to normal. I will recheck all wiring and connections to try to find something... Randy
Hi all--I appreciate the suggestions. The Motorola alternator is the original unit, as is the voltage regulator. I don't remain plugged in while away from the boat, so the batteries aren't freshly topped up when I get aboard. The strange part is that I am now getting this extra 30-60 second "slow motion" phase where the tach responds slowly, like it was "stiff". It happened again twice last night. Previously, the tach would simply remain dead after a start, then spring to life when rpms went above 900 or 1000. Now, it takes a minute, and 1500rpm to get the tach back to normal. I will recheck all wiring and connections to try to find something... Randy
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