#1 12-04-2017 14:44:15

Ziggy
Owner
From: basecamp
Registered: 29-04-2016
Posts: 44

Battery charging - why the standard setup disappoints

Our first CT  storage setup was two batteries charged off the car alternator with an isolator to protect the cranking battery and it worked OK.  Big plus was that it didn't have a voltmeter.

The second setup has been the Argyle SE with two batteries also charged off the alternator with isolator. 

We struggled for two years with this rig and the batteries never fully charged despite us driving long days on occasion. 

Why?

Battery manufacturers recommend 14.6-14.8 v for AGM bulk charge.  When the circuit from the alternator is delivering the typical 13.6 - 13.8 v to the batteries it takes many hours to make up the voltage deficit.    Collyn Rivers reports makers saying that it can take 30-70 hours of charging at a lower voltage to reach float - that's when starting at below 50% state of charge which we try to avoid of course.

The common response to running out of power is to add a battery.  We specc'd the Pioneer with two to begin with.  But given the low charge voltage that was just spreading inadequate charging power more thinly.

Like a lot of folk we have since installed an in-vehicle DC charger.  That can deliver 14.4 volts.

How long would  this take to fully recharge the two batteries?   Let's say we've used half the capacity, so 110 A. The formula is twice this divided by the charger current, which is 40 amps max.  So 5.5 hours.  In practice though it's taking longer.  There are losses in the system which I've yet to measure, and I have trouble understanding how a device can take an alternator output of 14 volts and 19 amps and turn it into 14.4 volts and 40 amps.  But that's my ignorance.

Sources:
http://www.batteryfaq.org/
https://www.exploroz.com/vehicle/electrics/solar.aspx

Edited 4.5.17

Last edited by Ziggy (04-05-2017 13:45:25)


Cheers,
Ziggy

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