Setting the Tachometer

Tags

Boat Tech, Calibration, Perkins-Sabre, Tach, Tachometer

Diesel engines use a signal from the alternator to synthesize a tachometer signal. When you change your tachometer or your tachometer pulley, you need to re-calibrate your tachometer.

Here is the Perkins-Sabre document on how to set the electronic tachometer on your brand-new engine. Read it if you want. It may be the worst tech writing to ever be thrust upon unsuspecting customers: PerkinsSabre Tach Programming.

It took me several years, but I finally figured out what they’re saying. Here’s the process.

Figure our your drive ratio. With an 8″ OD crankshaft drive pulley and a 2.625 OD alternator driven pulley, my ratio is 8/2.625=3. Multiply that times the number of poles on the alternator (usually 6). 3 x 6 = 18 alternator pulses per engine revolution.

This is a picture of the back of the control panel. There is a greenish/blue wire hanging out of the back of the tach. That is the programming wire (called pin 11 in the documentation). Right next to it, there are a bunch of black wires connected to the circuit board. These are all ground wires. Clip a test lead to the programming wire and a different test lead to the ground pins.

Get where you can see the front of the panel and hold both test leads at the same time. This would be a good time to find your reading glasses, too. There is a decimal point on the display that is approximately the same size as no decimal point.

Ground the programming wire (PW).

Turn the panel ON (do not start the motor). The beeper will beep. Ignore it.

Unground PW. The display will change. Pulse-ground PW to change the digit, hold-ground PW to move to the next digit. Beware of the tiny decimal point. Once you’ve got the ratio set correctly (18.0, in my case), ground PW and turn the switch off. This will save the setting. If you screw up or get confused, turning the switch OFF with PW un-grounded will not save your changes.

Clearly you can screw things up if you do this wrong. Also, you’re on your own. If you do something because somebody on the internet said to and it doesn’t work, it’s your fault. Feel free to contact Perkins/Sabre and tell them to fix their documentation. Tell them you know about this guy that can rite gud and is remarkably affordable.

 

Belt Slippage

Tags

Alternator, Balmar, Belts, Boat Tech, Cal 2-46, Tach

We have a great big alternator. 210 amps at 12 volts – over 2500 W. Huge.

It’s driven by two large V-Belts off the main crankshaft. In the olden days, you would buy a matched set of V-Belts to use in a dual application because it’s important that they are the same size. Exactly.

Modern manufacturing methods mean that the premium belts are uniform enough that you don’t need to buy them in pairs.

We’ve had a problem where the tach would jump around when the alternator was producing maximum power. I always figured it was electrical noise and would go wiggle the connectors. Eventually the tach would settle down.

I never suspected belt tension, since I regularly check and re-tighten the belts. However, the belts aged differently. The inner belt stretched slightly, and under heavy load would slip slightly, heat up, and transfer all the horsepower into the outer belt. Eventually that belt would also heat up and slip – just enough to show up in the tach needle (diesel engines get their tach signal from the alternator, since there is no distributor producing an electrical pulse). You can see the belts are now differently-colored from the aging.

So, two new belts from spares and everything was right in the world.

Solar versus Alternator, Tach Loses.

Tags

Alternator, Balmar, Boat Tech, Cal 2-46, DC Power, MPPT, Regulation, Solar Panels, Tach

This is a nerdy one.

We have a huge 210 Amp Balmar alternator on the engine.  It’s controlled by a separate Balmar MC-614 Charge Controller.

We also have a huge 400 Amp solar array mounted on the pushpit.  It’s controlled by a Morningstar TriStar MPPT charge controller.

The purpose of the two charge controllers is to give our huge(ish) battery bank what it wants.  What our battery bank wants is maximum amps until it’s at 14.4 volts, then 14.4 volts for a couple of hours until it’s mostly charged, then 13.2 volts for a long time to “top off” the charge.

Even though they don’t really communicate with each other, usually the solar charge controller and the alternator charge controller work well together, mostly because the batteries aren’t that picky.

However, we’ve had a few times where we’ll be motoring along on a sunny day and the tachometer signal will disappear, often while we’re anchoring or entering a harbor or are otherwise distracted.

Here is what the deal is:  The batteries are full but the charge controllers are somehow off synchronization.  The alternator controller is trying to hold a trickle charge of 13.2V, but the solar power controller has decided that the batteries really need 14.4V and pump in the juice.  The alternator controller sees the higher voltage, thinks that the world is coming to an end, and faults out.

It would be fine if all it did was shut down the alternator until we re-started the engine, but the alternator controller also puts out a synthetic tachometer signal that the engine control panel uses to tell the meat how fast the engine is running.

So, now, if the tach shuts down while we’re running, we close up or cover the solar panels.  Problem solved.