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Hi Guys 

I am trying to trouble shoot a non charging issue aboard my mates boat. He’s running a R N engine and I suspect that it revs to low to activate the alternator. Alternator has been bench tested and performs as it should , however when on board it doesn’t? Can this be down to size of lamp in exciter circuit or do these engines req special alternators ?

cheers in advance 

 

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I ran a RN DM2 for a number of yars and it had a similar problem..

 

My solution was to wire a push button switch (it was a Lucas horn switch) so that each time I started the engine I could manually excite the alternator. 

 

It might be resolvable with a lamp. I don't know if what I was doing was liable to damage the alternator but it was just a momentary switch not an on/off latching sort of thing. 

The original pulley on the engine was rather small considering the low rpm of the engine.

Edited by magnetman
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27 minutes ago, Sneill said:

Hi Guys 

I am trying to trouble shoot a non charging issue aboard my mates boat. He’s running a R N engine and I suspect that it revs to low to activate the alternator. Alternator has been bench tested and performs as it should , however when on board it doesn’t? Can this be down to size of lamp in exciter circuit or do these engines req special alternators ?

cheers in advance 

 

 

As always, the missing piece of information is did it ever work?

 

Or has it been fine for years and this a newly presenting problem?

 

 

 

 

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3 minutes ago, Sneill said:

The alternator hasn’t worked since the boat was bought 8 months ago

I would try magnetman’s idea. It’s certainly true that fewer revs is needed to operate an alternator than to get it going. Nothing lost by trying anyway. Momentarily short the D+ directly to the B+

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6 minutes ago, Sneill said:

The alternator hasn’t worked since the boat was bought 8 months ago

 

 

Hmmm... probably the reason the boat was sold then!

 

Get a bigger flywheel pulley.

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One of the negative side effects of running the alternator off a larger diameter pulley can be irritating noise. 

 

Given how nice a Russell Newbery sounds when running slowly the added whine of an alternator working hard to recharge the batteries is rather unpleasant. 

 

Just worth being aware of before going to the effort of altering it. 

 

A better approach may be to fit a good size solar panel and mppt controller wired to domestic batteries. That would save quite a bit of alternator work during cruising season. 

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10 hours ago, MtB said:

 

 

Sticking plaster concealing the real problem.

 

 

Well not really if once alternator is excited it starts charging. I made the stupid mistake of replacing the filament bulb on our charging circuit with an led.

Spent ages wondering why it then wouldnt charge before the light dawned and the led was thrown out.

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11 hours ago, Sneill said:

Can this be down to size of lamp in exciter circuit or do these engines req special alternators ?

 

Yes it can, especially if the warning lamp has been replaced with an LED or one using a grain of wheat (dolls house) bulb. Neither will allow an alternator to energise on almost any other engine.

 

Assuming a normal 9 diode alternator. Do what Nicknorman advises and if it energises then you know the problem is with the boat wiring. Stop the engine and turn the ignition back on. The warning lamp should come one, if so  pull off the warning lamp cable (D+) off the alternator and the lamp should go out. Touch the cable onto any clean metal and the bulb should light up. If all that works, then the problem is the bulb power or something else.

 

It would not surprise me if the alternator (and possibly the warning lamps and instruments) were not energised by a rising oil pressure switch, If that fails to close when the engine runs the alternator won't energise. 

 

The smallest bulb I would use is 1.5 watts and preferably 2.2 watts, but ob slow revving Listers @bizzardsuggest 6 watts (a car side lamp bulb).

 

As others have said, it could be down to the pulley ratio. The alternator pulley is normally the easiest one to change, fit the smallest you can get - ask an alternator & starter specialist for advice - but ensure that you used a notched/cogged belt because they grip small pulleys better than a standard belt.

Edited by Tony Brooks
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4 minutes ago, magnetman said:

My DM2 had a bourdon gauge for the oil pressure with no switch in it just fed by a 1/8 copper pipe. 

 

The alternator was a 70a Lucas and was designed to be excited by a lamp. 

 

 

 

That is most likely in this case, but by no means certain. Without a photo or positive alternator identification, it could be anything.

 

If it does use a mechanical oil pressure gauge, it makes it slightly more likely that there may be a rising oil pressure switch involved.

 

29 minutes ago, Tracy D'arth said:

Or shunt the bulb with a resistor, 72 to 100 ohm should do.

 

Agreed, but it is an extra component introducing another potential failure point.  I would always go for a larger bulb if possible.

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4 minutes ago, Tony Brooks said:

 

That is most likely in this case, but by no means certain. Without a photo or positive alternator identification, it could be anything.

 

If it does use a mechanical oil pressure gauge, it makes it slightly more likely that there may be a rising oil pressure switch involved.

 

 

Agreed, but it is an extra component introducing another potential failure point.  I would always go for a larger bulb if possible.

This should do it.

1942 Sperry 60" Anti-Aircraft Searchlight | Searchlight, Army truck,  Military gear

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Thanks guys 

lots to think about 

so if there is a rising oil pressure switch in circuit. I assume switch closes once pressure is sufficient ? Any ideas where to look to Identify

it ?

 

thanks again

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17 minutes ago, Sneill said:

Thanks guys 

lots to think about 

so if there is a rising oil pressure switch in circuit. I assume switch closes once pressure is sufficient ? Any ideas where to look to Identify

it ?

 

thanks again

 

Rather than answer that for now, please tell us if the warning lamp comes on the instant you turn on the ignition. Can you also post a photo of the warning lamp.

 

If the lamp comes on as soon as the ignition is turned on, then almost certainly there is no rising oil pressure switch. Yes, it closes when the oil pressure has built up. Often used on engines with just a push button to start them or manual start engines.

 

 

If the lamp looks a bit like these, it may well be an LED or grain of wheat bulb.

 

0609: Panel warning light - Dashboard - Lamps - Vintage Car Parts

Edited by Tony Brooks
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