Jump to content

Lazy Alternator


mkn777er
 Share

Featured Posts

First of all I should explain I am not an expert with engine electrics, but I'm happy to learn! I was fortunate to inherit a few years ago a small 23 ft narrowboat. I had it serviced and checked over and at the time was told the alternator was 'lazy'. What this meant was that after engine start the warning light and buzzer need a few revs before extinguishing, and after that all appears to be fine.

 

I now want to sell the boat (we have subsequently purchased a grown-up version) but the 'lazy' alternator has progressively got worst to the extent that it needs some serious 'revs' for the warning light to go out. I decided it only fair to get the alternator re-furbished and checked over. It came back, gleaming, and fully functional. However, I have put it back on the engine and it is the same. The alternator warning light and buzzer are very reluctant to extinguish. So the question is, what else could be causing this?

 

It is a Mitsibishi alternator fitted to a Vetus M2.05 diesel engine supplying just the starter battery and one leisure battery.

 

Many thanks

Link to comment
Share on other sites

Most alternators need a few revs when you first start up. tick over is not fast enough. What rev's are you needing?

 

Other problems could be slipping belt, but if you have refitted after refurb then that shouldn't be a problem unless the belt is old and worn.

 

Check out all the wiring (there isn't that much) which includes the warning light and ignition switch, and ensure that there are no poor connections. Sometimes just pulling off the spade connectors and pushing them back on is sufficient to clean the connection.

Link to comment
Share on other sites

It must be the wiring or the batteries...

 

The wiring needs to be as short as reasonably possible, the high current path via any ammeter/shunt to the battery, both the =ve feed and the -ve return path/cable and with good connections at every single point, and the excitation feed also in adequate cable, and in good electrical condition, with no high impedances through e.g. a "dodgy" ignition switch circuit...

 

The batteries need to be in at least fair condition and with no cells down, and the alternator output voltage suited to the chemistry of the batteries. If the Alternator is getting a clean bill of health, that is all it could be ....

 

Nick

Link to comment
Share on other sites

Before you go spending a load of money replacing anything else, it may be worth checking the pulley sizes. The alternator will run faster or slower in relation to the engine speed depending upon this gearing ratio. If your alternator is being driven too slowly, say as a result of its own pulley being too large or the one on the engine being too small, it would need more revs to excite it in the first place and deliver less charge than it could.

Link to comment
Share on other sites

Apart from a slipping belt or lazy alternator a larger charge warning light bulb would excite the alternator to begin charging at much lower revs, possibly right away on idle, say 6w instead of probably the tiny pea bulb which are mostly used.

Link to comment
Share on other sites

If its something has slowly got worse and the alternator is OK then its not the pulley ratio, they don't shrink that much in the cold. More likely to be as pointed out earlier a mucky switch, poor contact on the bulb or a connection on the wire between the battery and the field connection on the alternator. The alternator needs a given current through the field to start working.

Link to comment
Share on other sites

Thanks for the replies. I did also fit a new belt when I re-fitted the alternator (genuine Vetus). The alternator is the original one, as fitted when new, so the setup should be okay. This is more than just a 'blip' of revs to get the light out - I'm talking about almost maximum throttle (and I don't like doing it, only did it today when the engine had warmed up and there was nobody about!). I couldn't tell you how many 'revs' that was, because the tachometer is not working either, that's another job on the list.

 

I suspect this is a wiring issue. I do have a split charge relay, and both the batteries were new back in the summer so they should be okay. As has been mentioned, there is not a lot of wiring involved so once I get a bit more time I will delve a bit deeper, or, probably more realistically seek the help of the experts! It just seems strange that I have noticeably watched this problem get worst over the years - what started as no more than a 'blip' of throttle (quite normal) to now needing almost full throttle.


ditchcrawler

 

thenks and sorry, posted at the same time, and came to the same conclusion.

Link to comment
Share on other sites

This is where I start getting a bit out of my depth. I'm not sure what a W terminal is. On the back of the alternator are just two terminals, one is a single wire terminal plug, and the other is a twin wire plug. They are both in use. I'm sure one of these, if not both are for the Tacho, but again I cannot be sure of the integrity of the wiring. The terminals on the alternator are good (newly cleaned and refurbished) but the plugs are in need of a good clean.

Link to comment
Share on other sites

Not familiar with the OP's Vetus, but some Vetus have a connector plug which can suffer with grotty connections. Might be worth a look.

Not just a single plug, one on the engine and one on the control panel and maybe another two if there is an extension cable (likely). Also the +12V from the battery passes through all these connectors to the control panel and back through them all (on different pins) to the alternator; possibly eight poor connections.

 

This is a common problem for Vetus wiring looms; the terminals in the AMP connectors corrode even in a fresh water environment.

 

Ideally I would use my Digital Voltage Meter (DVM) to determine where the voltage drop (high resistance) occurs.

 

It may be sufficient to re-seat all the connectors (disconnect and reconnect), a spray of switch cleaner and repeated re-seating may help. Better to inspect for corrosion, clean it with a small Swiss file and maybe tighten the female connector using thin nosed pliers or a tiny jeweller's screwdriver. Failing that you could use an AMP terminal removal tool and crimp new terminals;

 

The OP's symptoms fit quite well with increasing corrosion in the connectors. I had a problem with my 1985 Vetus M3.10 where the tacho. would intermittently drop to zero rpm (running at 1,200+ rpm) that coincided with zero charge from the alternator. The 'run' (ignition?) relay energised by the 'heat' or 'start' button 'dropped out' due to poor connections in the Vetus loom. The engine continued to run normally because the stop solenoid was not activated.

 

HTH, Alan

Link to comment
Share on other sites

Alan Saunders .....

 

Hi Alan

Many thanks for that post. What you describe is pretty much what I am experiencing. The Tacho used to work, then worked intermittently, and now does not work at all, although I do occasionally see it 'jump' only to drop back to zero. I suspect that it is connected with the other problem. I'm happy that the alternator is working (just been fully re-furbished) so I guess it must be down to wiring.

 

Might have to wait until after the festive season before I get the time to poke around in there again.

Link to comment
Share on other sites

I agree the tacho not working seems related. They are generally driven from the alternator.

 

Many alternators are capable of 'self exciting' if revved fast enough, even the ones not designed to be self exciting. I suspect this is how yours is starting to work when you say you rev the nuts off it.

 

I'd be looking closely at the excitation circuit. Who repaired the alternator? I'd also be asking them a few questions about how they tested it and what might cause these symptoms now it's back in the boat. Did you tell them the symptoms when you gave it to them for repair?

 

 

MtB

Link to comment
Share on other sites

Alan Saunders .....

 

Hi Alan

Many thanks for that post. What you describe is pretty much what I am experiencing. The Tacho used to work, then worked intermittently, and now does not work at all, although I do occasionally see it 'jump' only to drop back to zero. I suspect that it is connected with the other problem. I'm happy that the alternator is working (just been fully re-furbished) so I guess it must be down to wiring.

 

Might have to wait until after the festive season before I get the time to poke around in there again.

 

Ah, I confess I read your original post as the boat always having had a 'lazy alternator', so I was suggesting you make sure the original installation wasn't sub-optimal before moving on to more expensive solutions. If things have gradually got worse it certainly won't be cos your pulleys are changing size!

Link to comment
Share on other sites

Who's that for, Snibs?

 

This is clearly a developing fault. 2 things come to mind, bad connection or possibly the split charge relay coil resistance falling.

Thanks for the replies. I did also fit a new belt when I re-fitted the alternator (genuine Vetus). The alternator is the original one, as fitted when new, so the setup should be okay. This is more than just a 'blip' of revs to get the light out - I'm talking about almost maximum throttle (and I don't like doing it, only did it today when the engine had warmed up and there was nobody about!). I couldn't tell you how many 'revs' that was, because the tachometer is not working either, that's another job on the list.

 

I suspect this is a wiring issue. I do have a split charge relay, and both the batteries were new back in the summer so they should be okay. As has been mentioned, there is not a lot of wiring involved so once I get a bit more time I will delve a bit deeper, or, probably more realistically seek the help of the experts! It just seems strange that I have noticeably watched this problem get worst over the years - what started as no more than a 'blip' of throttle (quite normal) to now needing almost full throttle.

ditchcrawler

 

thenks and sorry, posted at the same time, and came to the same conclusion.

Disconnect the split charge relay and see how it cuts in then.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.