In order to try and show what the impact can be on a high performance charging system I set up to recreate a scenario I had on a customers boat.


This was a race boat and light and fast was the game. As such the bank was designed to be cycled to approx 35% SOC as opposed to 50% most cruisers would do. The cost of the batteries was not the issue for this owner. Battery weight and getting as much energy back into them, in the shortest time, was the main goal. He chose TPPL AGM's (thin plate pure lead) for their ability to take a high charge current rates yet he was not happy with how long his batteries were staying in bulk.


With a .5C charge capability on-board (.5C = 50% of bank Ah capacity) and Odyssey TPPL AGM batteries he should have been doing better than he was. I ran his alternator in bulk charge and measured a .73V drop from the alternator end to the battery end. Not a good find on a boat demanding the utmost in fast charging.... I fixed this issue by addressing the placement of the voltage sensing wires and beefing up both the positive and negative alternator output wires.. Performance increased, and all was good..


For this article I took a brand new Odyssey PC2150 battery (Group 31 12V AGM), that I had just tested at 100.2Ah's of capacity at the 20 hour rate.. I then discharged the bank down to 11.85V at 77F and the 20 hour rate of 5A. This left the battery at 35% SOC or about 65% discharged. The battery was then recharged with an approx .7V drop at 50A. I set the charger for a 14.7V absorption voltage. The results are in the graph above. Click on the graph to make it larger.



Points to Ponder:


*In 1 hour of charging, at a .5C charge rate, the battery never exceeded 14.3V.


*At just 14.0V, measured at the battery terminal's, the charger began limiting voltage. When measured at the charger end, it was seeing 14.7V and it began holding the voltage steady.


*Once the voltage is held steady current tapers off and charging speed reductions are happening.


*Maximum bulk time was limited to 30 minutes at 50A, due to the voltage drop. This resulted in just 41.93 Ah's delivered to the battery in the 1 hour recharge period.