Join Date: Jan 2003
Location: Maine Coast
Thanked 183 Times in 142 Posts
Rep Power: 16
PLEASE be very careful with the advice you were given. He should have forwarded you their charging profile sheet.
Some things that were missing from his explanation:
1 They like to see a four stage algorithm like are used in big industrial or golf applications. The four stages are Bulk (current up to 10% of capacity), Absorption (14.4V to 97% of capacity), Finishing (15.3V @ 3% or less of capacity) & Float.
2- The 15.3V they want to see as a finishing charge is current limited to 3% of the battery capacity and acts sort of like a mini-equalizing charge on each cycle. You WILL use a lot more water.
3- In marine applications we rarely have the time to wait for a charger that only pumps out 10% of the 20 hour capacity so the algorithm above likely changes. We also don't have chargers that know what the current is so it is tough to limit the current to 3% of C @ 15.3V..
4- In marine applications there are very few chargers that can do a current limited "finishing charge". Some may have the capability but I don't know of one. Most marine chargers are voltage regulated not current. If you raise voltage, you also raise the current, unless you have a way to "limit it". Some limit current in equalize mode but I can't think of a program on any of them that would allow you to include an equalizing voltage/current on each charge cycle.
5- Keep in mind that you will be cycling down to about 50% state of charge so BULK (below the chargers limiting voltage) will be from about 50% -80% SOC and ABSORPTION charging (@ 14.4V) to about 97% - 99%, depending upon your charger.
6- If you set up a marine charger the way you were told you'd have a MUCH higher voltage, & potentially current, for a much longer time and could really do some damage to your batteries. Unless your charger can do two "absorption" phases, or "absorption" & a current limited "finishing" charge, then I would urge you to reconsider the 15.5V recommendation from this rep. It is also .2V higher than any voltage I remember US recommending except for perhaps an equalizing charge. The "finishing voltage" US recommends in their own lit is 15.3V or 2.55V per cell X 6 = 15.3V..
7- If charging using what US calls "two stage charging" with "optional float", what most marine chargers do, then they want the absorption voltage at a max of 14.7V, then a float voltage but remember this is all predicated on a charger rated at 10% of the 20 hour capacity. They recommend an equalizing voltage of 15.3V for this type of charging. If your charger is larger than 10% of C a reduction in absorption voltage may be warranted.
Deep cycle wet cells in marine applications are usually charged at 14.4V - 14.6V and do just fine. They'll do even better with occasional equalizing. I have set up some regulators, like Balmar's that do dual absorption stages, to push 14.8V then cut back to 14.4V but in each of these situations they batteries use considerably more water. The gassing voltage really begins at around 14.4V..
I will try and see if I can dig up the US Battery charging sheet for you as they sent it to me a while back. BTW US Battery makes EXCELLENT batteries that are right up there with Trojan in terms of quality.
-Maine Sail / CS-36T
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Last edited by Maine Sail; 09-30-2011 at 07:54 AM.