Special alternator needed for deep cycle (AGM) battery?

[RIP]

Info on this topic is sketchy and contradictory. I fitted a deep cycle Bosch AGM battery to my buggy to accommodate the winch. But now I've been told this battery needs a special alternator that outputs 14.4-14.7v. I've googled for two hours now and can't get to the bottom of this. Does anyone know?

 

[finyuk2005]

Info on this topic is sketchy and contradictory. I fitted a deep cycle Bosch AGM battery to my buggy to accommodate the winch. But now I've been told this battery needs a special alternator that outputs 14.4-14.7v. I've googled for two hours now and can't get to the bottom of this. Does anyone know?

there is a trick you can do with a standard alternator, using a diode or two in the sense wire, to trick the voltage regulator into outputting a higher voltage.
I did it to charge my vans leisure batteries a bit higher.

not a great video, but if you google "alternator diode mod" you will find what you need to know

 

[m_c]

The big issue with AGM batteries is they will accept charge far faster than a standard lead acid battery.

What this means in practical terms, is with older 'dumb' alternators, should the battery be low in charge, they will accept every possible bit of power the alternator is capable of producing, with the risk the alternator will overheat, especially if you just leave the engine running at idle to 'charge the battery'.
In terms of charging voltage, AGM is more tolerant of higher voltages, but they'll run just fine at standard charging voltages.
Run them permanently at higher voltages, and you'll still cook them just like you would a normal lead acid battery.

The reason for the higher voltage, is so they can be charged even faster.
With modern smart alternators, the alternator output is increased under deceleration to try and recover as much useful energy as possible, then reduced under acceleration to reduce energy use and improve fuel efficiency (minimal gains apply!).
Charging voltage can swing between 13Vto over 15V on a modern charging system, as an AGM battery will happily handle the higher voltage, whereas you couldn't push the voltage as high with a conventional battery.

So in short, no changes are needed, but if you do run the battery low, try and avoid just leaving the buggy idling after starting, as alternator cooling at idle is minimal.

 

[finyuk2005]

the other option would be a dc to dc charger, something like a c-tec,

DC-DC campaign

www.ctek.com

not the cheapest though, but i think they should be able to limit charge current to be kinder on the alternator, and they can do smart charging profiles for all different battery types to get the right voltage