Alternator Charging Voltage

[Paringa]

Hello all,

 

I hope you can help me with this "issue" I am having with my alternator output voltage. Or put my mind at ease by telling me not to worry...

 

After installing a new set batteries - Exide ER650's

 

http://www.tayna.co.uk/Exide-ER-650-DUAL-Marine-Battery-P8739.html

 

And also new wiring - which I am very pleased with - I checked my alternator output and got a healthy 29V as measured by my Smartgauge. However my new batteries only want 28.8V max according to the book of words that came with them. I only went on a short journey of about 30mins but I could hear them bubbling away so I stopped to consider things...

 

I have not put the multimeter on the battery terminals or the alternator output as yet to see the exact figures but I believe the Smartgauge is near enough at this stage. I could not tell you the alternator type but it does have a regulator panel held in by a couple of bolts. There are no other external regulators fitted.

 

So questions....

 

Am I worrying unduly? If so great the rest is irrelevant!

 

If not what can be done about it?

 

How can I reduce the voltage output from my alternator if this reading proves to be too high?

 

I do a lot of cruising so would like to see a voltage nearer to 28.6V or 28.4V

 

Also as an aside I have set my Smartgauge to battery type 6 for sealed batteries is that correct?

 

Thanks all for your time. I shall do my best to supply any additional info as best I can.

 

Cheers

 

 

[nicknorman]

That is the trouble with sealed batteries, and the reason I wouldn't have them - you do have to be careful not to overcharge. That said, you are only 0.2 v over and a couple of thoughts spring to mind:

 

Check the SG voltage against an accurate DVM - the SG voltage calibration is not always that good. Ours was at least 0.1v out at 12v until I re-calibrated it.

 

You might find that, when the alternator heats up after a long run and/or when the batteries start out needing plenty of current, the voltage drops slightly. It certainly does with our Iskra alternator.

Edited October 19, 2013 by nicknorman

[Tony Brooks]

It should drop with all alternators while they are on maximum output.

[nicknorman]

It should drop with all alternators while they are on maximum output.

Yes but what I find is that the light load voltage drops with increasing temperature. Its 14.6v when cool vs 14.4 when the engine bay is hot. Thus when starting out with lowish batteries, the voltage is low due to the high load, but then never gets above 14.4 because by the time the batteries are fully charged, the alternator is hot not from its generation, but from the proximity to a hot engine and hot engine bay. Whereas when starting with fully charged batteries (from shore power) the alternator voltage goes straight to 14.6.

[Sir Nibble]

What kind of alternator is this? perhaps A picture?

[smileypete]

What sort of level does the charge current tail off to?

 

Also might be worth reading the voltage across each 12V batt.

 

cheers, Pete.

~smpt~

Edited October 19, 2013 by smileypete

[by'eck]

To the OP - I wouldn't worry. 0.2 volts (for a 24 volt system) is very little over the max recommended. I regularly charged sealed AC Delco 12 volt batteries at up to 14.8 volts (equiv to 29.6 volts) for five years without issue.

 

If however you find through long cruises your batteries are bubbling for extended periods an external multi-stage alternator regulator such as the Sterling DAR will drop your alternator output to float at around 27 volts, when it decides the batteries are fully charged. It will also offer user adjustable upper regulated voltage according to one of several battery types.

[Paringa]

After a bit of research on here and a bit of ebaying, i found a new regulator that matched the shape of the one i had - I was away from the boat at the time so did this from memory. It was an A127 type Lucas fit that also had Perkins - my engine type - in the matches. It had a lower voltage output so at under £20 i thought i would give it a go, It arrived and i fitted it,,,and it worked!

 

I am pleased to say my cruising voltage is now 28.4V (14.2V) which is below the 28.8V (14.4V) where my batteries gassed, and below the 29V (14.5V) my previous regulator charged at...after a couple of hours cruising no gassing was evident.

 

Only one question remains re the Smartgauge battery type for these:

 

http://www.tayna.co.uk/Exide-ER-650-DUAL-Marine-Battery-P8739.html

 

Type 1 or Type 6

 

Thanks all for your input. Problem solved and with the minimum of outlay.

[nicknorman]

You would think it would be Type 6, but in the past IIRC Gibbo has said to use Type 1 for "dual purpose" batteries even if they were sealed. Maybe it won't make much difference.

[bottle]

Type one. Type 6 is for a specific type of battery, not checked but calcium/calcium rings a bell.

 

note: I have sealed AGM and Gibbo confirmed that even they are type one. I had dual lead acid, sealed and they were type 1

Edited October 27, 2013 by bottle

[Paringa]

Thanks