Thread: Puma Alternator charging voltage

Hello All,

I have a 2009 Puma and the Denso alternator charges at 14v no load and 13.7v with lights and driving lights on. I was wondering if there is any easy way to bump up the initial charging voltage to 14.3-14.5v no load as this will better charge the 2 AGM batteries I have as auxilliaries?
The Toyotas now can change a fuse/diode to up the voltage approx 0.4- 0.5v which would be ideal for me.

I for those interested I have one 100AH battery added under the P/S seat with the original starting battery still there and with the addition of a Mulgo Exbox I have another 100AH under the D/S seat on its side- tight fit but it does fit.

Any suggestions would be greatly appreciated.
Thanks

Giles

Originally Posted by quaddrive

Hello All,

I have a 2009 Puma and the Denso alternator charges at 14v no load and 13.7v with lights and driving lights on. I was wondering if there is any easy way to bump up the initial charging voltage to 14.3-14.5v no load as this will better charge the 2 AGM batteries I have as auxilliaries?
The Toyotas now can change a fuse/diode to up the voltage approx 0.4- 0.5v which would be ideal for me.

I for those interested I have one 100AH battery added under the P/S seat with the original starting battery still there and with the addition of a Mulgo Exbox I have another 100AH under the D/S seat on its side- tight fit but it does fit.

Any suggestions would be greatly appreciated.
Thanks

Giles

Hi Giles,
Technically a 12 volt charging system should charge at a voltage of 13.5 to 14.2 volts.
The available amperage supply and demand needs to be considered.

With charging 12 volt batteries the lower the charging voltage technically the higher the amps going into the battery, as the battery gets further charged the amps lover and the voltage rises,
In your case the starting battery has been drained to start the car, thus lovering the surface charge voltage and you also have an axillary battery that the alternator is also trying to charge, thus it will take longer for both batteries to fully charge and the alternator voltage to reach 14.2 volts.

You have 13.7 volts with the lights ON and still trying to charge both batteries and supply power to all the system electronics.
Technically a automotive battery is never fully charged as the internal resistance is greater as the voltage increases, so it takes longer for the battery voltage to reach 14.2 volts,
So what is the answer....a bigger amp output alternator so that it can push more amps into the battery ( overcoming the internal resistance) and charge quicker to reach the required 13.5 to 14.2 volts.

An example of above is,
I have a Honda petrol motor with a 55 amp alternator attached to it to top up charge my AGM solar batteries, if the battery standby voltage is 12.5 volts 80% discharge, the alternator will try and supply 45 amps to the batteries ( alternators never supply rated full amps), it will charge at 45 amps only for several minutes and then drop off, as the battery voltage rises the amps drop back to 20 amps, at 13.5 volts and it will stay at 13.5 volts 15-20 amps for hours, as the battery voltage has risen and the internal resistance is greater....basically this is what is happening with the car battery.

As long as the battery voltage is 13.5 to 14.2 you do not have a charging problem...it just takes a bit longer to reach 14 volts.