Thread: Alternator output

You are right - those numbers do not make sense!. I think you need to talk to the supplier of the charger about it. As far as the car is concerned, in my view the alternator and its system should handle the load OK, but it is another matter whether the smart charging system can handle it wiithout doing something silly - remember that the smart charging system is designed to give best possible fuel economy by only switching the alternator on when necessary to keep the battery charged. Talking to the dealer, and specifically someone who understands the system would seem to be a good idea.

As John said, those numbers make no sense.

The DC-DC won't care what the alternator output is, as long as it's enough.

Being a smart alternator, it will be important to connect it correctly, on a D4 it's important to never connect anything to the negative post of the battery, as this interferes with the car controlling the alternator, you must use one of the negative posts that are supplied.

I've never had anything to to do with smart alternators, DC-DC chargers or lithium batteries, but this is my understanding of them.

Hopefully Tim/Drivesafe will be along shortly.

Tony

Hi sharmy and as both the above posters have stated, that does not make sense.

You may have misunderstood what is in the instructions.

Next, regardless of that strange info, make sure your DC/DC device has an IGNITION sense and is not just a voltage sensing setup.

John was close to how SMART alternators work.

They do not actually turn off.

If the cranking battery is better than 80% charged, while you have your foot on the accelerator peddle ( or your cruise control is running your vehicle ) a SMART alternator will lower its output VOLTAGE to reduce the load on the motor while the motor is working.

Any time you take your foot off the accelerator, the voltage will rise.

The voltage can lower to as little as 12.2v, but usually around the 12.5v mark while the motor is under load, and it can rise to 14.7v while the motor is coasting.

If your DC/DC device is set to voltage sense, with a SMART alternator, your DC/DC device may spend more time off than on.

When set to IGNITION, the DC/DC device may reduce to OUTPUT current when the alternator voltage is low, BU it will still keep charging the lithium, all be it at a reduced charging current.

One more point, make sure the DC/DC device is mounted as close as possible to the lithium battery, as this will guarantee the correct charging voltage at the battery.

I was also baffled by the request, it doesn't seem to make sense. I will go ahead and fit it and hope for the best, the vehicle hand book gives no technical information at all. Here is the offending page.

Originally Posted by sharmy

I was also baffled by the request, it doesn't seem to make sense. I will go ahead and fit it and hope for the best, the vehicle hand book gives no technical information at all. Here is the offending page.

Hi again sharmy, before you fit that device, please post up more info about it.

There are DC/DC devices that are specifically designed for Alternator to Battery charging and have an INPUT CURRENT LIMIT.

This type of DC/DC unit is most likely NOT SUITABLE for charging lithium batteries.

If you can, post up a link to the manual for your DC/DC device.

Your vehicle has a 140 amp alternator which will easily exceed the limit of such a charger if it has a maximum input current of 720w.

NOTE, that DC/DC device is most likely intended for use with a marine outboard motor, which has a much smaller alternator.

Thanks for your info Drivesafe, I probably bought the wrong unit. I hope you can scan this, I can't, I am hopeless at such things.

Originally Posted by sharmy

I hope you can scan this, I can't, I am hopeless at such things.

I can.