adding battery

[Bat]

I have diesel with 2 starter batteries and a 110 amp alternator. I want to add a 3rd battery for a lighting and maybe a fringe. Should I come off the alternator or the batteries for charging and can I put in a isolator for the 3rd battery.Do you think there will be a problem for the alternator to keep up with 3 batteries.

 

[Stan@FourWheel]

Most customers will run the camper wiring or the aux. battery wiring to the battery posts for the "accessory" battery in your engine.

It is always best to use some in-line fuses or a thermal breaker for extra protection.

It also seems like a great idea to install the battery separator / isolator in-between the truck battery and the aux. camper battery too.

I haven't heard of any alternator problems.

The 2 batteries in the engine shouldn't need much of the alternators power to keep charged up.

Hope this helps a little.




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[Curmudgeon]

Do you think there will be a problem for the alternator to keep up with 3 batteries.

No.  It makes no difference how many batteries it has to keep charged.  The alternator only has to provide the amount of energy that you are using.  As long as the demand does not exceed the output of the alternator, the charge can be routed to any number of batteries.  



JP 

 

[John D]

Curmudgeon, I respectfully disagree. Of course, a modern 100 amp capacity alternator may be adequate for charging three batteries simultaneously without overheating. On the other hand, it depends on the type of alternator, how much work it will do without overheating, how much load is placed by the discharged batteries, and how much additional load is required by accessories such as headlights, fans, winch, etc. Some of the new alternators are liquid cooled, which means they are less likely to overheat.

For the batteries to be charged, the alternator must have enough capacity at the required output to hold voltage above 13.5 volts, and this could be problematic with very large batteries. Once a typical air cooled alternator has been under a load anywhere near its rated capacity, it will heat up and loose a significant portion of its capacity. Heat kills alternators. Thus, and alternator is more likely to fail when most needed, as under under exceptionally heavy loads. A good example is while winching. This could be catastrophic if it happens in a remote area.

Elsewhere in this forum, I have recommended a dual alternator arrangement and I do not understand why more off road campers do not adopt such an arrangement. Aftermarket mounting brackets for dual alternators are available for many newer trucks. The two alternators run independently of each other, electronically speaking. That is, one of your three batteries could be charged by one alternator and the other two by the other alternator. With this arrangement, little or no switching is needed. Plus, there is the added security of two alternators. Should one fail, a second alternator is readily at hand. The only extra item needed is possibly a spare idler pulley to exchange for a frozen alternator, should both be driven by a single belt.

John D