Jegs
Well-Known Member
I have a single cylinder diesel genny; without an alternator. Can any kind soul advise me how I might measure the number of revs?
Hopeful thanks,
John G
Hopeful thanks,
John G
Rev Counter?
- Thread starter Jegs
- Start date
tinkicker0
Well-Known Member
Put a line of white paint on the shaft or pulley and count very fast.
alternatively, buy one of these:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=4459557
TrueBlue
Well-Known Member
Get a non contact tachometer Like the one shown here
But it'll cost you over £30, so I wonder if it's worthwhile for a one-off?
It might be easier to see if there's a label with model No; etc which you could research.
If it's a marine unit it's most likely to be a 3000 rpm unit as 1500 sets are quite large and heavy.
PCUK
Well-Known Member
Do you need to constantly monitor the revs, or is this for a one-off test?
aquatom
Well-Known Member
You can get multimeters with a frequency function for not vere much money. connect this to the 220v output and measure the frequency.
stuartwineberg
Well-Known Member
Genny Speed
Generators only run at one fixed speed - its part of the way they generate a stable alternating current. Is this useful info or does your machine have a fault?
Generators only run at one fixed speed - its part of the way they generate a stable alternating current. Is this useful info or does your machine have a fault?
Jegs
Well-Known Member
Thank you for your helpful responses.
The genny is designed to run @ 3000 rpm but the voltage is 200/205 not 230. I thought that the problem might either be with the engine or the electrickery & decided that If I could measure the rpm I could either alter that, if incorrect, or eliminate it & go on to the electrical side.
The optical counter might be difficult to use without removing genny from outer case - awkward & heavy. It's at least 20 years old!
Many thanks,
John G
The genny is designed to run @ 3000 rpm but the voltage is 200/205 not 230. I thought that the problem might either be with the engine or the electrickery & decided that If I could measure the rpm I could either alter that, if incorrect, or eliminate it & go on to the electrical side.
The optical counter might be difficult to use without removing genny from outer case - awkward & heavy. It's at least 20 years old!
Many thanks,
John G
Bilgediver
Well-Known Member
The voltage is determined by the AVR (automatic voltage regulator) Which will be in a box strapped to the machine or beside it . Changing the speed will increase the cycles and this you don't want to do.
What make is it and have you got the manual?
Jegs
Well-Known Member
Laser
Thank you - didn't someone once say that wisdom is knowing how little you know?
The manual for the Laser generator, with Faryman diesel, is in Italian & does not appear comprehensive. My thinking [?] was that if the revs were down the output would drop, but it would seem from your reply that I was wrong. Would I be right in reading your reply to mean that even if the revs drop the voltage would not?
Thank you,
John G
Thank you - didn't someone once say that wisdom is knowing how little you know?
The manual for the Laser generator, with Faryman diesel, is in Italian & does not appear comprehensive. My thinking [?] was that if the revs were down the output would drop, but it would seem from your reply that I was wrong. Would I be right in reading your reply to mean that even if the revs drop the voltage would not?
Thank you,
John G
grumpy_o_g
Well-Known Member
Normally the main factor governing the voltage produced is the DC windings field strength which is controlled by the voltage regulator. The field is produced by passing a current through DC windings in the generator. It's by rotating another winding through this field that the electricity is produced.
Think of an old toy dynamo with just a magnet and and rotor with some wire windings on it. Effectively you're now using an electro-magnet to create the magnetic field instead of the permanent magnet. Increasing the current through the windings is just like using a more powerful magnet. You may have an "exciter" on the generator. This is simply a small dynamo that creates the current to power the DC windings.
Changing the RPM will actually change both the frequency and the voltage from what I remember but the voltage compensator will adjust the field strength until the voltage is at the required level so you won't actually see it change.
Increasing the electrical load will make it harder to turn the generator rotor which would normally slow the rotor but, again, some circuitry automatically determines how much to open the throttle to keep the speed constant.
If the voltage is low then the voltage regulator is the prime suspect, especially if the frequency is correct.
Having said all the above there's more than one type of generator but I'd have thought that's how yours works. If it's a different type (e.g. brushless) then I'm talking rubbish. It's a while since I worked on a small generator (the last one was powered by a brand new Lister diesel I think!!)
Jegs
Well-Known Member
Grumpy
Many thanks.
John G
Many thanks.
John G
