In the fourth part of our deep cycle battery series, I provide an update on how charging and my attempt at reconditioning the trimmed down battery bank. I’ve run into some challenges and have possible ideas to overcome them. You may be interested in the previous article that explains why particular batteries were selected for reconditioning: deep cycle batteries [3] Reconfigure Array
About three weeks ago, I assembled the 4 worn out Trojan L16 batteries into our “new” battery bank, ready for reconditioning. Well, right off the bat this new system worked better than the original 12 batteries that had 5 dead cells in 5 batteries. I tried to keep this new array charged quite often, and ran the charger and generator up to 14 volts or more until the charging current went to 15 Amps or less. This is what a normal equalization charge would do.
Also during this time, I’ve dug into the details of Lead Acid battery construction and chemistry to understand better what the primary wear out mechanism of these batteries are. That is sulfation; leas sulfate is normally gray powdery substance that is part of the normal discharge process. When the battery is charged up, it dissolves back into the electrolyte. However, if a battery remains in the discharged state for long periods of time, the powdery substance crystallizes more and more. The crystallized lead sulfate no longer dissolves completely and the battery holds less and less “juice”.
Another effect is that the battery voltage rises higher with lower charge states, or percent charge. Smart battery chargers monitor the voltage and tend to back off charging to a trickle charge when the voltage rises. Now the battery with sulfation problems never really gets charged fully and the problem gets worse as the battery snowballs down the performance curve.
I measured the batteries the other day and was shocked to find one nearly dead cell!
Re-Configured Battery array (4 active batteries)
I think part of the problem with my charging may be involved with the Trace DR2412 charger we’re using. It has 3 states that change the amount of charge based on the voltage. They have a charging LED that signals which charge state it is in. In all my charging recently, I’ve had the charger set to “equalize” and always have the charger in the heavy charging Bulk mode. The charging current was 50A at 11.4V, but tapers off significantly above 13V.
Before throwing another battery out of the bank, I’m going to try to borrow a normal automotive 50A charger. I will then use this to continue some charging in this restoration project. Maybe it will put out more current above 14V.
Have you had any success restoring deep cycle batteries? Tell us about it below in the comments, let us all benefit from your experience!
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Marshall is the failed cell the one closest to the positive battery terminal. If so it could be the failure is due to post corrosion induced by the charging current.
You are right, it is the cell under the positive terminal. Have to open up case and inspect cable closely. All contacts are good, but maybe corrosion grew underneath the insulation.
Ambulance and taxi vehicles often suffer from positive post erosion due to prolonged idling. What happens is the plates gets fully charged and the acharging source continues to run (think solar panels) Current now flows directly through the electrolyte from positive post to negative post. In that situation the positive electrode immersed in the electrolyte erodes due to the continued current flow. The eroded post no longer has the cross section needed to maintain full current flow during normal charging and the cell fails to be charged enough. Sometimes the post is actually eroded enough to part and the whole string goes dead. In situations where several strings of cells are wired in parallel the loss of one string is not easily noticed as long as the other strings continue to take a charge. Only S.G.Readings of every cell will reveal a failure by which time it may be too late.
I see the comments could be misleading. Positive post corrosion takes place INSIDE the battery case in the electrolyter not externally where you can see it. When the sulfate builds up the plates increase the apparent resistance. Instead a strong charge current will short circuit from positive post to negative post directly through the electrolyte. Under such conditions the positive anode corrodes effectively reducing its cross section. This in turn means higher resistance which further increases self heating. It is a vicious circle.