Alternator overcharge?

[Observer]

I have a brand new 90hp 2-stroke Yamaha on a RIB. Last weekend, running (I think) at a range of mid-throttle settings (say 3000-4000 rpm) the charge indicator (digital) showed 16.2 and was flashing.

I have two batteries connected in series. Battery 1 is always on and battery 2 has an isolator, which was switched to the "on" position at the time.

Having read the earlier threads, do I have an overcharging problem which could damage the batteries? I couldn't find anything helpful in the engine handbook.



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[mtb]

AS I recall it if the regulater is iffy then it can over charge and cook your batteries, the output would be unregulated so the higher the engine speed the higher the voltage.
It does sound high, did you zero the avo before testing !!.

Cheers
Mick

<hr width=100% size=1>One day son all this will be yours #### off I dont want it

 

[tcm]

I think that is too high, and will fry batteries. I believe a Zener diode regulates the max charge, and yours is busted. But I am no expert. Check battery levels a lot and turn on lights or anything to use/waste charge till fix found. That old bloke wassiname in Portsmouth, Ron Hale is useful 023 92732 2985, but these days Suzuki i think.

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[burgundyben]

if batteries are in series then should be 24 volts?

I think you mean paralell.

Yes, 16 and a bit sounds a little high.

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[Observer]

Don't know how to "zero the avo" (is the "avo" the voltmeter?) and why does that matter? Could it be reading wrong?

Just spoken to dealer and they say problem is either: (i) second battery is lower rated so alternator is pushing through more charge; or (ii) second battery is on its way out so same effect. Battery 1 is new and battery 2 is old so this explanation seems to make some sense. Not sure about ratings, have to check next time I'm there.

I'm not too worried about slowly cooking battery 2 as it is old anyway (and I assume I can top up levels more frequently to compensate?) but I don't want to bugger the new one. I guess the answer is to buy a new equal rated second battery - seems a shame if the present one still has some useful remaining life.

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[alan]

I don't agree with your distributors comments. As far as I understand it, the alternator is a constant voltage device and should be outputting about 14.2 volts, the amount of current will vary depending on the load(s).

I would check the voltage at each battery with an external digital voltmeter (you can pick up a simple one at Halfords or your local market for about £5:00 or so).
Note the voltage when you have battery one connected, battery two conected or both connected. You should not have 16v at any time or you will cook the battery(ies); I don't believe the problem is with the batteries unless possible the old battery has developed a really high resisitance and the alternator regulator sensor is external to the alternator or something else weird. In any case a test with only the new battery connected should resolve this.

Good luck.

<hr width=100% size=1>Alan Cloke

 

[Observer]

Thanks for the advice, Alan. I'll take my multimeter down this w/e. However, and I need to confirm this, I don't think I experienced this problem when I only had battery 1 connected so bringing battery 2 on line does seem to be the catalyst if not the problem.

Just to clarify, I should measure the voltage on battery 1 with battery 2 disconnected and then on battery 2 with both batteries connected? Will engine speed make a difference?



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[tcm]

i agree with alan. The zener diode limits the voltage hence current is available to charge batteries. The voltmeter might drop a bit if large charge taken, batteries knackered or whatever, but not increase to 16+, imho.

mtb's "avo" is indeed a voltmeter - he's assuming you used a test meter (brand name is an Avometer)

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[tcm]

engine speed does make a difference to the output of the alternator - but if voltage is measured beyond the regulator, the regulator is busted. The purpose of that regulator is to limit the output to the circuit to 14-15 volts, regardless of input voltage (ie engine speed). Remeber old british bikes with those black diode things - a zener diode, which dumps everything above 14.5 ish depending on performance. All imho.

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