Team,
Hoping to get some help from people who may have faced this situation before.
Background: Have a Tach plus hour meter that stopped showing RPM. Checked AC voltage output at Alt and the wire leading up to the Tach and found voltage coming/changing okay. Hence procured a new Tach=hour meter from VeeThree instruments (https://www.veethree.com/). The new Tach has quite different programming than my old one that just had a rotary switch which I had set the # of cylinders on the engine (3 for my M25). Here is a link to the programming instructions to the new Tach - https://www.yumpu.com/en/document/read/28790533/instructions-veethree-instruments
Question: The formula for calculating the FSF to program the new Tach is as follows:
FSF = (# of poles on Alt x Pulley Ratio x Full Scale RPM) / 60
Given that I have the stock 55 Amp Alt on my M25, here are the questions I have:
- What are the number of Poles on the Alt?
- What is the pulley ratio?
I know that the full scale RPM is 4000. So if I have the above two parameters I can calculate FSF and program the DIP switches behind the new Tach. I am attaching the pics of my new Tach so you'll can get a good idea...
Can anyone help?
Thanks!
Mahendra
P.S. Side clarifying question: What is the voltage I should be seeing at idling out of the AC Tap on a Motorola 55 Amp standard issue Atleernator? Is that DC or AC voltage? I an just checking as it is supposed to be coming out straight from the Stator winding and I think from before the rectifier (hence AC voltage...?).
Mahendra, I somehow recall 12 poles on the OEM Motorola alternator. When I installed my new Blue Circle alternator back in 2003 or so, that's what I think I asked and it was the same as the OEM.
I'd try that first.
Another way to approach it is working with "knowns" like the WOT of 3000 rpm. Set the tach with something to start off with (like try 12) and see what it does, adjust accordingly.
It's a boat. Who says you have to get it right the first time? :D :D :D
Thanks Stu. Agreed. I can also check the actual RPM on the engine with my contactless RPM meter I bought for my EV project.
Actually I am now second guessing myself and wanting to check if the output from my Alt is OK. Talked to Vinnie at Gen Star (John was out) and he was suggesting that even the voltage from the 'AC Tap' is a DC voltage. Is that correct? Anyone measure that on a Motorola Alt? If that is the case, I may have to take the Alt out and take it to them for repairs and my Tach maybe okay!...:-)
The tach signal voltage is a nominal 12v AC (not DC.)
The voltage value isn't that critical.
The terminal on the alt **should** read "AC tap."
Hi KW,
Is the output of the Alt at AC Tap 12VAC at idling or max RPM or both? What changes as RPM goes up? The voltage or frequency? Therefore the Tach's variable input is varying AC voltage or varying Frequency?
Thanks!
Mahendra : Look in the Mainsheet tech notes. You'll find an article I wrote on the programing/reprograming of the Teleflex Tach dip switches.
It was so long ago, I seem to recall? that I might have even given the OEM alternator dip switch settings.
Look in those old Mainsheet tech note - there are TONS of information!!! :clap
A thought
Quote from: SeaFever on February 25, 2021, 01:09:32 PM
varying AC voltage or varying Frequency?
Hint: think about this. When you're setting up the tach to the alt, you're matching up the frequency output from the alt at any given RPM (dependent on the # of poles, pulley size, etc.) to what the tach expects to see for that given RPM. Varying the voltage doesn't affect the tach set up.
That's why the signal is on-off (AC), otherwise it could be a DC signal.
Quote from: Ron Hill on February 25, 2021, 02:02:07 PM
Mahendra : Look in the Mainsheet tech notes. You'll find an article I wrote on the programing/reprograming of the Teleflex Tach dip switches.
It was so long ago, I seem to recall? that I might have even given the OEM alternator dip switch settings.
Look in those old Mainsheet tech note - there are TONS of information!!! :clap
A thought
Hi Ron.
How are you? It's been a long time...:-)
Could you point me to the month/year? That would help very much.
Mahendra
Quote from: SeaFever on February 25, 2021, 05:33:19 PM
Quote from: Ron Hill on February 25, 2021, 02:02:07 PM
Mahendra : Look in the Mainsheet tech notes. You'll find an article I wrote on the programing/reprograming of the Teleflex Tach dip switches.
It was so long ago, I seem to recall? that I might have even given the OEM alternator dip switch settings.
Look in those old Mainsheet tech note - there are TONS of information!!! :clap
A thought
Hi Ron.
How are you? It's been a long time...:-)
Could you point me to the month/year? That would help very much.
Mahendra
Here's the link to Ron's article: https://c34.org/mainsheet/pdf/1999_no1.pdf
How did I find it (so easily)? I used The Knowledgebase.
This is discussed in this link: A Quick Start Guide -- a.k.a. Too Much Information on this Website https://c34.org/bbs/index.php/topic,5260.0.html
which includes this text:
NEW!!!-Jan. '07 -: Tech Notes, Projects, and FAQ Articles KNOWLEDGEBASE & Index http://c34.org/bbs/index.php/topic,3362.0.html is also helpful.
Ron often says: "Read those old Mainsheet articles." He's right, and he has written so much with such important information, but never gives any links. Most likely it's from the sheer of the quality material he's provided for us over the decades.
So, I learned to use The Knowledgebase. It's a very handy tool.
Guys : Stu is correct in that I was the writer and He is the librarian (BTW, doing a great job). I should have made an Index, but never bothered.
I was too busy writing and gathering information by telephone and word of mouth (before there was an internet!!) and sailing myself!!
I have used my C34 more than most - averaging over 110 overnights (away from the dock) a year for over 25+ years. Wore out one M25XP!
Sorry bout that!! Do the Knowledge base search!!
A thought :think
All,
Thanks everyone for your comments/suggestions. Wanted to provide an update:
- Measured my o/p at AC TAP again and found to be very low AC voltage
- Removed the alternator and took it to Gen Star along with my original Tach=Hour meter
- Gen Star found that they need to repair alternator
- They ended up replacing the stator winding
- Checked the alternator on their jig and also connected Tach
- Everything tested okay. AC TAP o/p was 7.4 VAC
- Brought them back and fitted them on boat and checked with engine. All OK!
So ultimately my Alternator winding was an issue and my Tach was okay.
Now I have a 'brand new' alternator and SeaFever is a as happy as I am ... :D
Thanks again to all!
Guys : I just looked at my Feb. 1999 article and find that I did make a diagram of the Dip-Switch settings (up or down) for the M25/ XP / M35 engines with the OEM alternator. :thumb:
I had to do some adjusting when I change to my Balmar Hi-Output alternator, because of its different pully.
A few thoughts