| Author |
Message |
Brian (Bigbusguy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 21, 2005 - 7:58 pm: | |
I fixed my Tachometer sender unit problem buy just buying a new Alternator Tachometer ISSPRO R85210 .
It was cheper then a new sending unit and becouse a GMC has a gear driven tach there is no loss in RPM becouse of belt ware or slipping.
I dont have a photo type tach and was wondering if any one has one or can bring one the the Oregon bus Rally in July.
I guessed at the calibration set it at 2100rpm no load and it shows a idle speed of 525 rpm .
I would like to check to see how close I got.
Also it was very easy to adjust this type it just has a calibration pot you just turn it until it shows want you want.
Brian 4905 Vancouver WA for now. |
Pete/RTS Daytona (Pete_rtsdaytona)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 21, 2005 - 10:51 pm: | |
Brian
Here's another way - got any of those cheap little 12volt power supplies that have the little black box that plugs into the wall - bet we all have a few around somewhere. Just about every one of them is an unfiltered full wave rectifier that puts out 120 pulses per second (a full wave rectifier inverts (flips) the bottom 60 cycles to form a 120 pulse wave
The "R" terminal is also a 12volt pulse source - just take the negative from your little 12 volt supply to ground - remove the tack wire from the "R" terminal and connect it to the positive wire of your little 12 volt supply
NOW - here the science behind this whole thing
The Detroit Diesel Delco 270 Amp 24 volt alternators is driven by (2.93 to 1 gears) x (3 pole stator) x (2 for full wave alternator rectifiers) = 17.58 pulses/rev and The "R" terminal output is 12 volt -
adjust your tach to read 410 RPM with your 120 pulse/sec 12v power supply.
You can take the engineer/instructor (me) out of the classroom (IBM 30 years) - but you can't take the classroom out of the engineer/instructor
Pete RTS/Daytona |
John Jewett (Jayjay)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 22, 2005 - 12:30 am: | |
Gads, I'm overwhelmed yet again by the fantastic wealth of knowledge of the respondents to this 'Board. Thanks Pete, You've given me info I needed desperately for a similar tach difficulty.
Cheers...JJ |
Brian (Bigbusguy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 22, 2005 - 12:52 am: | |
WOW Mr Wizard thats cool I will give that a try.
Thanks Pete
Brian 4905 |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 22, 2005 - 8:21 am: | |
Pete, great information and a great explaination. As a former instructor at JPL for NASA, I compliment on the great presentation.
Have to confess that I never heard of a three pole alternator before. If it was spinning at 2400 rpm, would it put out 60 hertz? |
Pete/RTS Daytona (Pete_rtsdaytona)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 22, 2005 - 8:49 am: | |
Richard
hmmm let's see now
if the engine turned 2400 RPMs then
2400rpms x 2.93gear ratio x 3poles x 2fullwave then divide by 60sec/minute would be approximately
700 pulses (fullwave rectified) per sec
Think you may have to stay after school till you get this stuff right - (just kidding)
Thanks for making my day guys
Pete RTS/Daytona |
Pete/RTS Daytona (Pete_rtsdaytona)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 22, 2005 - 9:08 am: | |
Richard
OOOPs - I may have misunderstood
If you meant:
a.- spin the generator itself 2400 RPMs
(no 2.93 gear ratio)
b.- remove the diodes (no neg pulse inversion)
thus no (times 2 multiplier)
Then you are absolutely right -- geeee- see what a big head will do to a guy - sorry Richard
Pete RTS/Daytoan |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 22, 2005 - 11:39 am: | |
Thanks, Pete. Wish I had thought of that many years ago when I was designing and manufacturing large flywheel type power conditioners for the main frame computer system.
The amount of kinetic energy stored in a 3-4 ton flywheel significantly increases when the rpm is raised from 1800 rpm to 2400 rpm. We could not use 3600 rpm and still keep the flywheel in one piece. LOL
Richard |
gusc
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 23, 2005 - 5:43 pm: | |
A system used to check aircraft tachs is to put a fluorescent light in front of the plane when dark and adjust the throttle until it appears stopped, then see how it compares to the tach.
This obviously only works at rpms divisible by 60 and if your ac supply is reasonable stable. We use 600, 1200 or 1800 for most aircraft.
I haven't tried this on a bus but see no reason it won't work if you can get the light behind something turning at engine rpm or a known ratio to engine rpm. |
James Maxwell (Jmaxwell)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 23, 2005 - 7:37 pm: | |
Gusc: Is this method approved by the FAA as a standard? My bus does not have a propellar, so what do I use, the radiator fans? |
Jtng
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 24, 2005 - 12:37 am: | |
I tried that, but the damn light kept getting sucked into the Jet's compressor fan. |
gusc
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, June 25, 2005 - 1:08 pm: | |
James,
The FAA doesn't have a standard and as far as I know they don't even address tach calibration. As I said, this is not precise unless you know your 60hz electric source is exactly 60hz, most vary somewhat. But it is close enough for 99% of uses.
Use anything that turns and has points or blades that can cause a strobe effect. You can even make a white mark with chalk, like timing a gas engine.
jtng,
You're supposed to put the light a few feet in front away from the suction and then go to the rear and look up the exhaust! |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, June 25, 2005 - 2:15 pm: | |
The US power grid is very stable and very accurate, so I have been informed. It is so accurate that every night, just before midnight, the overall grid is adjusted up/down by a few thousands of a cycle to make certain that electric clocks across the nation keep the correct time.
This does not effect the many battery operated clocks however.
Richard |