Something sticking....

MJ24

MJ24

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Joined
26 Apr 2012
Messages
362
Location
West Wales
www.markjohnsonafloat.org.uk
Just fired up the Bukh 20hp after a month unuse.

The alternator/regulator would not allow a charge to go into the battery. The red light was on faintly, and flickered.

I restarted the engine a couple of time and eventually pulled full revs. After a moment or two, we got full charge with the red light well and truly out.

Something seemed have got stuck, and was eventually released by brute force.

Is this symptomatic of a future problem, or just something that happens?

Mj
 
one possibility is that the battery had gone down a lot, and the alternator sensed a big charge rate was needed. This load was too much for the drive belt and the belt slipped, until the V surfaces warmed up, grabbed the alternator pulley and charging started.

If that is the case, you might have some black belt dust as evidence. Is the belt at the proper tension ?
 
sarabande said:
one possibility is that the battery had gone down a lot, and the alternator sensed a big charge rate was needed. This load was too much for the drive belt and the belt slipped, until the V surfaces warmed up, grabbed the alternator pulley and charging started.

If that is the case, you might have some black belt dust as evidence. Is the belt at the proper tension ?
Click to expand...

I did check voltages on both batteries, they were 12.84v, and of course they did start the engine after a couple of attempts.

Thanks anyway

Mj
 
VicS said:
A little surface corrosion of the slip rings?
Click to expand...

Yes the dim field current light would indicate that there was a problem getting initial filed current through the light and through the field coil. The current goes through the field coil via the brushes and slip rings.Could be sticking brushes or dirty slip rings. Often these can be exposed by removing the box that holds the brushes and often the regulator. By rmeoving this you cna see the slip rings which can be cleaned with a solvent on a rag or even fine sandpaper. The brushes can be checked for length and spring force.
good luck olewill
 
I have a DV24 (same as the DV20 except the head has direct injection) and I have similar charging symptoms however it is quite normal. When one starts a DV20/24 the injection timing is auto adjusting so it will run rough for a few seconds while the timing is adjusting itself and reves will be low and uneven and the red charging light stays on. Once the timing has settled down the engine runs smoothly but the red light sort of flickers from dull red to off - blip the throttle and all is well. I have overhauled the alternator (new bearings, new brushes and regulator and cleaned / polished the slip rings) which subsequently passed bench test at local automotive engineering test facility so I am confident there is SFA wrong with the alternator - just needs to be spinning at some minimum speed before the regulator kicks in. Once the throttle has been "blipped" the regulator takes over and charging proceeds even at tick over (engine 750~800 rpm). Note: I do not need to thrash the engine to get the regulator to kick in - just blip it briefly
 
cliff said:
I have a DV24 (same as the DV20 except the head has direct injection) and I have similar charging symptoms however it is quite normal. When one starts a DV20/24 the injection timing is auto adjusting so it will run rough for a few seconds while the timing is adjusting itself and reves will be low and uneven and the red charging light stays on. Once the timing has settled down the engine runs smoothly but the red light sort of flickers from dull red to off - blip the throttle and all is well. I have overhauled the alternator (new bearings, new brushes and regulator and cleaned / polished the slip rings) which subsequently passed bench test at local automotive engineering test facility so I am confident there is SFA wrong with the alternator - just needs to be spinning at some minimum speed before the regulator kicks in. Once the throttle has been "blipped" the regulator takes over and charging proceeds even at tick over (engine 750~800 rpm). Note: I do not need to thrash the engine to get the regulator to kick in - just blip it briefly
Click to expand...

You might find it useful to try a higher wattage globe in the indicator light. (Or a resistor across the lamp about 50 ohms might do.) This will allow more current to the regulator before the alternator itself supplies field current. Hence more inclined to come to life at lower revs on start up. Or maybe a change of pulleys to give more alternator RPM but don't overdo it. good luck olewill
 
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