How does the alternator work?

[Tyler_h]

So I have a 2nd deep cycle battery that I use for remote camping and I want to charge my 2nd battery faster, thread here: https://www.ramforum.com/threads/need-a-high-idle-switch.214026/#post-2962429

Today, for testing, I hooked up my 2nd battery with a pair of jumper cables with an amp meter to find that I was charging at only 33A. Even holding the rpms up at 2500 did not increase the charge output. When my electric fan kicked on, I was only charging my battery at 26A. I expected more.

Is there something wrong with my charging system or do I not understand how this alternator works.

Help is appreciated.

 

[dsherman26]

You've got all the other devices in parallel with this second battery, and all are requiring current. The rate that it charges at is largely determined by what voltage the system is operating at, and generally a second battery charges very slowly off the alternator. RV owners have the same problem when they try to charge their RV batteries off the alternator. Just what level of current were you expecting?

 

[Tyler_h]

Thank you. Its refreshing to know that RV owners have the same issue. I had concerns my alternator was failing, I do have a bit of a startup whine but no other issues.

According to this, https://www.ramtrucks.com/assets/bbg/pdf/2016/docs/ram/ramaltoutcrv.pdf I was expecting around 100a output.

650 rpm x 2.9 = 1800rpm of the alternator = 100a output. Also revving the engine and seeing no amp change was concerning.

At 33amps per hour on a 100ah battery, it would take 3ish hours to charge a battery, that seems wrong.

 

[andymax]

Deep Cycle batteries are not designed to accept a fast charge, nor are they designed for rapid discharge (IE starting). Attempting to do either will damage the battery due to it's high internal resistance. You could probably look up the max charge rate on the battery manufacturer's website.