Thread: Alternator voltage a bit high?

Well I have run my AGM with a separate alternator for about 3 years now, and the voltage is always 14.2-14.5 when fully charged.
This is a quote from a US website. Arizona Windsun.
AGM batteries have several advantages over both gelled and flooded, at about the same cost as gelled:

Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also means that since they are non-hazardous, the shipping costs are lower. In addition, since there is no liquid to freeze and expand, they are practically immune from freezing damage.
Nearly all AGM batteries are "recombinant" - what that means is that the Oxygen and Hydrogen recombine INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost.
The charging voltages are the same as for any standard battery - no need for any special adjustments or problems with incompatible chargers or charge controls. And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. The Concorde (and most AGM) batteries have no charge or discharge current limits.

Regards Philip A

Thanks PhillipA,
That kinda puts my mind at rest but it's amazing how much contradictory info is out there, I read that AGM batteries were more sensitive to higher charge voltages.
I had 3 of these batteries (ex-Telstra) and cooked one recently on a drive from Wangaratta to Melbourne, however they are mounted under the rear seat of my D130CC, and the cooked one was above the muffler and I couldn't hold my hand on it for more than 1/2 second it was so hot! I have since put a heat-shield above the muffler, and want to rule out over-charging.
I have also read about a "runaway" condition AGM's can have when charging at high temperatures where they start to heat themselves and end up destroyed. It was 42 degrees that day, and the batteries were pretty low when I set off.
perhaps it was a conbination of:
Ambient temp
Muffler heat
Low initial charge state
Alternator capable of large current? (not like the old 35A ones)

Any thoughts?

Cheers,
Fraser

Hi Fraser130 and PhilipA.

First off, Fraser, your alternator sounds like it is working fine so don’t stress.

Next, Philip, be very careful of info relating to AGM batteries, as you stated, the info you posted is for AGM batteries made in the USA. These batteries are made much better than the Chinese ones and have different specs but regardless of where the AGM battery comes from, unlike ordinary flooded wet cell batteries, where you can pretty well use the info provided by one brand of battery and the specs will be near the same for all other flooded wet cell batteries, you need to have the exact specs for the brand of AGM battery you are using because there can be a HUGE difference between makes of AGMs.

Most AGM batteries are NOT designed for automotive use and as such, have some limitations that most of the users have no idea of, so again, go check the specs for your AGM battery at the battery manufacturer’s web site.

Cheers

Here are the specs on mine.You will see max voltagw is 15Volts.

http://www.absorbedpower.com/battery/pdf/GT12-90C.pdf

Regards Philip A

Thanks to both of you, I feel much better now, mine are top quality American ones (GNB Marathon) so I'm guessing they are similar in spec to PhillipA's ones, If they can handle 15V then they will be fine as the 14.7V only lasts maybe 10 mins, then it srops to high 13's/ low 14's.
AAAAAhhhhhhhh,
(sigh of relief as I don't have any more spare and can't afford to cook another,
I guess it was the hot day and the muffler heat)

Cheers,

Fraser

Hi Phil, I’m not trying to be a smartass but what do you think is your operating specs are?

I’ll explain after you reply.

Cheers.

"Charge Voltage" in the specs.
Regards Philip A

Interested in what you have to say drivesafe.

In the process of installing a AGM battery as a second unit into the defender, and made the same assumtion to stay away from the Chinese units probably go with an optima or similar USA manufactured and a high amp trickle charge system rather than a standard dual battery system.