charging problem - something sticking?

[deep denial]

I have a new alternator fitted to my dolphin engine. when the engine starts and runs, we get only about 12volts showing on the voltmeter. however if we rev the engine very hard for a few seconds, it suddenly flicks up to about 14 volts, and then stays there even when revs drop back to normal. What's sticking?

 

[sailor211]

I have a similar symptom on ours. I do not see it as a problem, A quick blip of the throttle sorts it. I am no expert but suspect its in the control pack, but as we are battery voltage sensed it may need a kick to get flow through the diode.

 

[lw395]

The initial field current for an alternator (or dynamo for that matter) to start up is supplied via the charge or 'ignition' warning light. If the light does not come on brightly, it may be worth checking its circuit. Also check the bulb rating.
When this starts to happen on an old alternator, it can also be the brushes worn out or sticking in their holders, in this case the lamp may be dim or intermittent.

 

[deep denial]

unfortunately the burst on the throttle needs to be very hard, up to max revs, and so I don't think it should be doing this!

 

[deep denial]

I don't think it's a problem with the initial charge current - apart from anything else, the engine starts fine, and the problem persists indefinitely until revved

 

[Ballistix]

It'll be fine, lots of meters do it.
T

 

[VicS]

There is nothing sticking and and the alternator does not have the old electromechanical control box that dynamos used to have.

The problem is almost certainly because your alternator is not getting a sufficiently high initial field current via the warning light to start it generating at idle speed.

(The belt is Ok I assme and the new alternator has the same size pully as the old one)

You could investigate the warning light circuit from ignition switch through the bulb to the connection on the alternator for poor connections but you will probably find all is well. You could then try a slightly higher wattage bulb in the warning light. That will increase the initial field current and with luck you may get to a point where it will start to generate with little or no increase in revs.

If there were any other problems or symptoms then inspection of the brushes and slip rings would be advisable but not with a new alternator.

Edit sorry repated a lot of what others have said. Must learn to type faster. Cant all be wrong though can we.

Yes it will persist until you rev the engine to the speed where it starts generating with the field current its got. Once its going it'll generate its own field current evn though the revs are dropped back

 

[deep denial]

thanks everyone

 

[DaveS]

It is just possible that the needle of an analogue meter might be "sticky", though I would not agree that it is common. Checking with an independant meter (at £5 for a DVM every boat should have one IMHO) would only take seconds and would easily confirm / eliminate a voltmeter problem.

 

[Billjratt]

I had the same "with a new alternator" in other words it needed more of a spin than the old one. They all need some whizz to get the field current running, and I think (from two personal instances) that the bigger the alternator capacity, the more it needs to rev before it kicks in. It's also normal to replace with a higher rather than lower capacity unit, so we are all beginning to notice this syndrome. Remember the electicity generated is a function of the strength of the magnetic field and how fast it's lines are cut by the rotating coil.- so if there's a low-ish current, it needs to go faster. Want to experiment? - start the engine and leave at low revs with the ingition bulb glowing/pulsing. then try shorting out the bulb and see if it comes up at lower revs than before. If so, you could try a higher wattage bulb and make sure all the connections (including the ign switch points) are good.