Battery warning alarm comes on when in tickover with new alternator

[tony_lavelle]

I replaced the alternator on my MD2030 and the new one (from a motor factor) delivers 14.4V to the batteries, except when in tickover, when the battery warning light and audible alarm come on.

Tickover is about 850 rpm, which I believe is correct, but alarm and warning light only extinguish when the revs are increased to about 1000 rpm.

This problem did not happen with the old alternator and nothing else has changed. The revs on the tachometer seem correct so the pulley sizes are right for the engine.

Any ideas about the cause please?

 

[Beneteau381]

I replaced the alternator on my MD2030 and the new one (from a motor factor) delivers 14.4V to the batteries, except when in tickover, when the battery warning light and audible alarm come on.

Tickover is about 850 rpm, which I believe is correct, but alarm and warning light only extinguish when the revs are increased to about 1000 rpm.

This problem did not happen with the old alternator and nothing else has changed. The revs on the tachometer seem correct so the pulley sizes are right for the engine.

Any ideas about the cause please?

Is it definitely the same size pulley?
S

 

[tony_lavelle]

Is it definitely the same size pulley?
S

I'll double check.

 

[earlybird]

Annoying rather than an electrical fault I suggest. Assuming that you don't have an alternator driven tacho then one cure would be a slightly smaller pulley on the altnator if you can source one. Alternators can withstand lots of revs and your low-speed charging would be better. I bet the old alternator wasn't doing much at tickover anyway.

 

[yotter]

I have a VP2030 and replaced the standard alternator with a Presolite (Bosch), mine also does not charge at tickover, but kicks at just over tickover. I did increase the tickover speed slightly but there was not enough adjustment to get the alternator to excite at tickover. Its annoying but not a big issue.

 

[Deleted member 36384]

Could it be fan belt tension reducing. My own does exactly as you indicate when the fan belt is new and when they get worn out. In the former case, it quickly resolves itself with retightening, in the latter case, it just keeps happening as the belt wears further.

 

[jac]

Had the same fault on a 2040. Never got to the bottom of it but found that reving made the alarm stop even when then going back to idle So lived with it as it charged fine.

 

[Sea-Fever]

This could be described normal behaviour for an alternator and occurs on cars as well. The alternator won't charge until the field is excited at which point the charge light extinguishes. I look at it as a positive indictation the alternator is working properly. If the rpm has to increase slightly to kick start the alternator I dont think that's a biggie.

I dare say there will be other takes on it.

 

[Hydrozoan]

See also down-thread here Starting a Beta Diesel | YBW Forum - similar experiences (and some similar views of acceptance) with alternator 'kick-in' on some Beta engines.

 

[tony_lavelle]

Thanks everyone, a few things to try there. As you all say, annoying but no biggie.