Alternator problem?

[concentrik]

When I first start the engine the RPM dial stays at zero. It takes a bit of throttle to wake it up, thereafter it settles and reads normally. During its 'no reading' period the charge light stays on. After a bit of throttle it goes off and settles to a normal 13.8v charge. Its a Bosch 55A alternator, built in regulator/brushes module.

I wouldn't worry too much except the other day, during normal cruise revs, the RPM dial dropped to zero momentarily; the engine reduced revs slightly; the Raymarine auto helm beeped 'low battery'. It all seemed to happen at once but I think the Autopilot warned first. It was over in a couple of seconds, returned to normal.

I had noticed that the battery voltage was around 13.5v at the start of the trip. The drivebelt is correctly tensioned. I have removed the brushes/reg module and cleaned the sliprings - and replaced the capacitor, whose lead was corroded and broke off in my hand and the plastic case was swollen and looked like it had melted a bit on one side.

The question again - is it normal to have to 'blip' the throttle at first? And what of the unusual events during yesterdays trip?

 

[halcyon]

When I first start the engine the RPM dial stays at zero. It takes a bit of throttle to wake it up, thereafter it settles and reads normally. During its 'no reading' period the charge light stays on. After a bit of throttle it goes off and settles to a normal 13.8v charge. Its a Bosch 55A alternator, built in regulator/brushes module.

I wouldn't worry too much except the other day, during normal cruise revs, the RPM dial dropped to zero momentarily; the engine reduced revs slightly; the Raymarine auto helm beeped 'low battery'. It all seemed to happen at once but I think the Autopilot warned first. It was over in a couple of seconds, returned to normal.

I had noticed that the battery voltage was around 13.5v at the start of the trip. The drivebelt is correctly tensioned. I have removed the brushes/reg module and cleaned the sliprings - and replaced the capacitor, whose lead was corroded and broke off in my hand and the plastic case was swollen and looked like it had melted a bit on one side.

The question again - is it normal to have to 'blip' the throttle at first? And what of the unusual events during yesterdays trip?

Check brushes for wear, or if brushes are sticking in brush holder.

Brian

 

[concentrik]

Check brushes for wear, or if brushes are sticking in brush holder.

Brian

Brushes look ok and no sign of sticking....

 

[nigelmercier]

Mine does this by design, it doesn't start to ramp up the field voltage for about 30 seconds. This is about the time it takes to notice the rev counter, and blip the throttle, the "fix" being an illusion.

 

[concentrik]

Mine does this by design, it doesn't start to ramp up the field voltage for about 30 seconds. This is about the time it takes to notice the rev counter, and blip the throttle, the "fix" being an illusion.

If I don't 'blip', it will stay at low idle and never indicate any RPM, nor battery charge......

 

[Bosun Higgs]

Its not that unusual. I've had cars that did that and certainly my pals boat does so and has been doing so for 14 years now.

 

[pheran]

The question again - is it normal to have to 'blip' the throttle at first?

Mine does that. Always has. Six cylinder Perkins Sabre.

 

[VicS]

If I don't 'blip', it will stay at low idle and never indicate any RPM, nor battery charge......

As said its not unusual.

Maybe, but don't know if this is applicable to your alternator or not, maybe fitting a slightly higher wattage bulb in the warning light will increase the initial field current a little and get it to start charging without blipping the throttle.

Most people probably start their engines with a partly open throttle anyway so would never notice.

Yesterdays events though suggest there might be a bad connection, intermittent fault worn brushes or something to keep an eye open for