Auxillary battery charging question.

Quote:

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Originally Posted by Vern

Charge voltage for the dcs is 14-14.6v, so alternator shouldn't be a problem.

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All good if the alternator can do it....

OP has a DC-DC, I’d be keeping it

Quote:

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Originally Posted by drivesafe

Hi Vern and yes you could charge straight from the alternator, but you need a way of separating the batteries ( lead acid cranking battery from the Lithium battery ) when the motor is not running.

NOTE, I specifically stated when the MOTOR is not running, not when the IGNITION is turned off.

This is one of the many potential problems of mixing the two types of batteries.

In Bazzle's case, not having a STOP/START vehicle, the problem is just separating the batteries when the alternator is not working, otherwise the lithium will continually discharge back into the lead acid battery.

This is great for the lead acid battery but it will continually discharge your lithium battery and if you do not drive the vehicle fo a while, you may actually flatten the lithium battery.

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So if both batteries could be charged from an alternator, then any isolator could be used? Including yours?
Just trying to get my head around it.

Quote:

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Originally Posted by Vern

So if both batteries could be charged from an alternator, then any isolator could be used? Including yours?
Just trying to get my head around it.

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Hi again Vern and NO, you can not use my isolators or any standard isolator with lithium batteries.


I better explain how lithium batteries operate so you will understand the problem the pose.


Lead acid batteries have a fully charged voltage of 12.7v, and while some will be as high as 13.1v, but as soon as any form of load is applied, they will quickly settle to around no more than 12.8v and the voltage of all lead acid batteries reduces as they are being discharged.


Lithium batteries have a fully charged MINIMUM settled voltage of 13.1v, but 13.3 or more is common place.


Furthermore, while lithium batteries are being discharged, the voltage in a Lithium battery will stay at 13.1v almost till the lithium battery is about to go flat.


Now, with the above info, standard isolators turn on at 13.2v and turn off at around 12.7v.


So with a lithium battery in the setup, while the voltage will easily rise above 13.2v with the motor running, but when the motor is turned off, the lithium battery will hold the vehicle’s voltage at 13.1v, and this means as the voltage never drops down to the 12.7v turn off voltage of a standard isolator, it remains on.


But as above, a lead acid battery has a sealed voltage of 12.7v and ANY voltage above that, will continue to charge the lead acid battery.


So the lithium battery will continually discharge back into the lower lead acid battery, and as above, if left long enough, this will flatten the lithium battery.


Vern, does this help?