Charging Voltage

[me3@neuralfibre.com]

Can anyone confirm / deny the following.

Normal vehicle alternators are set to a voltage limit of between 14.2 and 14.8v that may or may not be temperature compensated.

Truck alternators are set to 13.2 - 13.8v. (yeah, double it for 24v systems - 26.4v - 27.6v)

The theory is that short haul vehicles need to fast charge the batteries, hence the higher voltage. The normal wet cell is relatively tolerant of overcharging and is not frequently subjected to this charge for a long period of time.

Interstate long haul trucks on the other hand are subjected to very long charge cycles and the higher voltage would result in overcharging with resulting outgassing and frequent maintenance required to stop batteries drying out.

Any knowledge appreciated. Also any information on temperature compensation in Landcruisers would be interesting if anyone knows anything / anyone.

Why am I Iconcerned? Well I am now running AGM cells under the bonnet. There are 3 impacts.
1 - overcharging will result in outgassing and possible failure of the cells.
2 - Underbonnet heat is more likely to result in thermal runaway during charging.
3 - Limited electrolyte will result in decresed ability to handle loss from outgassing.

Thanx
Paul

[-Scott-]

The theory sounds fair, but I can't confirm or deny.

I have a FullRiver AGM as a second battery, and recall that charging voltage & temperature specs seemed fairly tolerant - I haven't measured underbonnet temperatures, but I don't expect a problem.

Having said that, I think it's a great question, and look forward to others' opinions.

Cheers,

Scott

[drivesafe]

Hi me3, the truck voltages are probably correct as the Europeans have been setting long distance truck reg to 13.6 to 13.8 while delivery truck regs were still being set to 14.2 to 14.4, so that would correspond to what you posted.

13.2 is a tad low as very few batteries and certainly no standard vehicle batteries will charge properly at that low a voltage.

Now having said that, the Europeans may well need to have a slightly high voltage as their average climate temperature is lower than ours.

As to the AGM under the bonnet, you pretty well covered the answer yourself save to say that the location of the second battery under the bonnet will also be a factor in the life span of the battery, in other words, batteries located at the front of the vehicle’s engine bay are going to get cooler air running past them while batteries mounted further back are going to get much hotter air flows. The further back, the more chance of overcharging.

Cheers.

[KiwiBacon]

So what life are people currently getting from their batteries and at what charging voltage?

My 4wd uses a couple of NS70's that are about four years old. I've had charging voltage issues for all that time that I have finally got to the bottom of. My batteries were getting just under 14v but got 16v for a few months when a sparky wired in a new alternator wrong.

[drivesafe]

Hi KiwiBacon, I’m guessing here that the NS70’s are wet cell batteries because they can take that sort of voltage for a short time and not be damaged. In fact it can actually rejuvenate old batteries.

PS, I do not recommend to anyone to try this high voltage charging unless done with a battery charger that has the feature included in it’s charge cycles.

Whereas sealed batteries, gels or AGMs will most certainly be damaged in a very short time.

Cheers.