15.1 volts from the Alternator!!!!!!!

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swanny

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Hi, I have all new batteries - sealed but vented lead acid. It is my understanding that the voltage intput to them should be limited to not more than 14.6 volts which is the maximum my Sterling Pro Digital 50 amp charger puts into them, even when they are very low. The engine and 175amp alternator are new. I thought alternators were limited in their output to avoid cooking the least accepting of batteries? 15.1 volts seems too much. Am I right or, I hope, wrong? Is it safe or will I boil them?!?!?
 
15.1 volt is a little high, but some cars are running at that voltage. The battery will actually need a higher voltage to fully charge it, but this area is not normally used.

So what voltage is the alternator designed to work at ?

If not 15.1 volt, return as faulty.

If it is 15.1 volt, get advise from the alternator supplier, as it is high.

Brian
 
"15.1 volts from the Alternator". Does this mean You measured the voltage at the alternator? More interesting would be the voltage measured across the batteries.. If there is a diode splitter in between the value would be correct.
 
[ QUOTE ]
"15.1 volts from the Alternator". Does this mean You measured the voltage at the alternator? More interesting would be the voltage measured across the batteries.. If there is a diode splitter in between the value would be correct.

[/ QUOTE ]Yes, that would be about right with remote sensing. The alternator would increase its output to offset the voltage drop across the diodes. But if there isn't a splitter and there's no remote sensing wire, and the voltage is definitely too high at the battery terminals, then you could make use of this voltage drop by installing a diode between the alternator and the battery (or a diode splitter as you have more than one battery).
 
Thanks for the input guys. More info - There is no diode splitter, I have two banks, starter and house and each has its own alternator. The 15.1 reading is from my sterling battery management digital panel and also on the Beta Marine Engine Panel which has its own voltmeter. I will go and take the voltage at the batteries to be sure. Beta Marine are looking into if my alternator has an unstrestricted or high power regulator in within it. I didn't order one. In fact, I ordered a 150amp alt but they had none so upgraded to a 175amp without my knowledge. I found out when the engine was installed. I guess it's a bonus, I have a 450ah house bank. I am reluctant to run the engine now as I don't want to boil the new batteries!!! If the voltage output is true I guess I will have to take of the drive belt to the alternator and have the regulator changed to a more restricted one. Alternatively I wonder, if I connected up my sterling alternator regulator, would this control the output of the alternator down to a max of 14.6 ???????
 
I think you are worrying unduly. It's not just a diode splitter that can cause high volts showing. High resistence in your charging circuit can too. If you have a stirling smart charger it should in fact be wired with the sensing lead straight back to the battery and control voltage to 14.6 or thereabouts AT THE BATTERY. However if your ammeter or digital panel is reading elsewhere it could be different. There are a series of dip switches in the stirling smart charger that allows you to change the charging voltage. I was a little unhappy that mine was showing a constant 151/2 volts but have "tuned" it back to 14.8 by changing the dip switches. If you wire this in and play with the settings you will get a reading that you are happy with as it should override the controller in the alternator. You do need to read the instructions carefully though to get the dip switches right and ensure that you set it to the readings at the battery not elsewhere.
 
My analogue meter shows about 14.8 when engine running and fully charged batteries, the Raymarine instrument readouts show 15.1v. Batteries don't seem to be cooking.
 
I had the same problem, voltage readings very high: I don't know which alternator you have but mine is a Prestolite and the regulator has a tiny screw allowing to trim the output; the screw has come somewhat loose and the alternator output skyrocketed
Restored the screw position, drop of thread glue, no problems since

Maybe worth having a look if yours is the same ?
 
Thanks for all that but the story unfolds. I have now read the voltage output from the alternator at the alternator and the batteries. Interestingly at the alternator it fluctuated between 14.95 and 14.97 and at the battery 14.3 to 14.4 the really strange thing is when I revved the engine beyond idle speed the alternator output dropped to 14.8 at the alternator and a tad less at the batteries! Is this normal? That an alternator voltage, not amps drops as it spins at higher speeds? It did not drop further the more I revved, just that initial drop. How strange. I await some more info from Beta before I do more.

I don't have a diode splitter by the way and the alternator controller from stirling is not connected yet. I heard from Charles at Sterling that external regulators like his can not reduce the output from an alternator, only increase it, so fitting it won't help. He told me that I should not put more than 14.4volts into sealed lead acid batteries but his pro digital charger regularly puts in14.6 to 14.8 and the settings are correct for sealed lead acid. I think though that the battery management panel from sterling that I have reads say .05 of a volt higher on average. Exciting stuff eh!
 
I wouldn't worry about it unless it's kicking out lots of amps at the same time. I am on a 24v system so my voltages are double. The alternator shows 30volts when fully charged. My battery charger (40/5amp) however will show 31.5v when fully charged, but any load, like switching a light on will drop it to 29.5v. It does not cause any problem in normal use. but I wouldn't leave the charger on when I am not about.
 
Get your tester calibrated or at least checked!! As VicS says the reading vary alot when their internal battery weakens - just had this with my multimeter.
Also on my boat the nav instrument voltage readings differ from my multimeter which is different from my in-line analogue voltmeter......
 
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