Overloading the alternator - what happens?

[peter_mcc Senior Member Find all posts View Profile Close peter_mcc]

What happens if you overload the alternator? My Dad's 120 diesel Prado has a 40A DC-DC charger under the bonnet for his 2nd/3rd batteries. He's just added an anderson socket at the back of the car (from the main battery) to connect a camper trailer with a 30A DC-DC charger in it.

From searching PradoPoint it seems the factory alternator is 80A - if both the DC-DC chargers were going flat out that would be 70A. I'm guessing that charging the starter battery pls running the car, A/C, lights, etc would be more than 10A.

Does he need a bigger alternator? Or does it gracefully cope with being overloaded? He's keen for it to not die in the middle of nowhere (next trip will be Tassie over Christmas - not the best time to get something fixed in a hurry!)

I saw that 130A alternators are available - do they need upgraded wiring and fuses or can you just slot one in?

[JimmyC Advanced Member Find all posts View Profile Close JimmyC]

From my knowledge it gets to the limit of its capacity and starts working against you. So if your alternator is 80 amps and you're trying to draw 90 the load will find the remaining 10 from the battery and your battery will begin to discharge. It will be so rare that you will be drawing the full 30 and 40 amps from the chargers I wouldn't really be too concerned about it.
The upgraded alternators are just bolt in. No upgrading of wiring required.

[Brodad Junior Member Find all posts View Profile Close Brodad]

If max capacity is reached the overall voltage in the system would reduce/collapse and if it gets below ~12.7volts then the start battery would start to drain, however low voltage could also cause the dc-do chargers to shut down, recovering the situation. . Running an alternator at full capacity for extended periods wouldn't be great for it (duty cycle) and could fail abruptly. It could be a monitor and see situation, or upgrade alternator for piece of mind.

[bricat Junior Member Find all posts View Profile Close bricat]

http://www.piranhaoffroad.com.au/pro...management/aoc

I have heard about this and it might be of help.

[Anth120playdo Banned Find all posts View Profile Close Anth120playdo]

You risk killing it, while reducing its life.
But, you can get very lucky, many do.

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

http://www.piranhaoffroad.com.au/pro...management/aoc

I have heard about this and it might be of help.

Voltage boosters do not increase the alternators output power, they trade reserve capacity for
an increase in output voltage.

The output capacity of an alternator is determined under lab test conditions, and with the alternator supplied with unrestricted free airflow at approx. 22C, it is unlikely that these conditions will exist in an engine compartment in a vehicle therefore the alternators maximum continuous output will no doubt need to be derated for normal use.

To complicate things more, some manufactures (good quality units) rate their alternators as being able to maintain 100% output indefinitely under test conditions. Others only rate them for a short time at their nominated max output.

Overloading an alternator means that the alternator is unable to shed its heat load, this will result in the alternator over heating, initially its output may actual increase as the rectifiers overheat then fail.

[peter_mcc Senior Member Find all posts View Profile Close peter_mcc]

Thanks for the comments guys. He's decided to install a 130A alternator to be safe - it would only be heavily loaded when he's away which is the time/place you don't want it to break down!

[red hilux Member Find all posts View Profile Close red hilux]

Which 130amp alternator did he buy and has he had any problems?

[peter_mcc Senior Member Find all posts View Profile Close peter_mcc]

Which 130amp alternator did he buy and has he had any problems?

He got one from eBay - subject was "ALTERNATOR TOYOTA PRADO D4D 1KD-FTV 3.0L Turbo Diesel 130A 100A 2005-2014" and it was $249 in Nov 2016. It was installed shortly after and has been working without any problems.