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Notes on SOB Charging from an early userΒΆ

The charger is actually two power supplies in one (capable of a positive and a negative voltage relative to a common ground), and we are using them in series, like two batteries. Each section of the charger can supply up to 30V at up to 2A, so in series we have a maximum of 60V at 2A. Each section can be set independently for max voltage and max current; if the current tries to go over the max, the voltage is reduced until the current drops to the max. With the two sections in series, it makes sense to use only one side as the controller for both voltage and current. I think we have left the current limiting at the default max, and we have the voltage on one side set to 30, and on the other side something like 28–I don’t recall the exact number. After a cast, I would expect the current to be pegged at 2A and the voltage on one side or the other, or both, to drop slightly; it might actually be best to set the current limiting to a value slightly under 2A, say 1.9A, on the same side as the voltage limiting is set, if it is not already that way. I think I already did that.

Lead-acid batteries have two typical charging modes, one for use when the battery has been drawn down, the other when it is fully charged–the latter is the trickle-charge mode. The voltages for the two modes don’t differ by much unless one is trying to charge fast, which we don’t need to do, and can’t with the 2A limit on our charger. Commercial “smart” chargers drop the voltage to the trickle level based on some criterion–I don’t know how they actually decide the battery has had enough. Probably it is based on charging time and/or impedence.

I think that our usual charging voltage is a little above the ideal trickle level–hence our practice of turning the charger off after a few hours.

The SeaBattery has more than double the amp-hour (A-H) capacity of the gel-cell packs we used to use (like the backup from Teri), which also means it will charge faster–accept more current–for a given voltage and state of discharge (in terms of A-H). Also, the trickle current will be higher. With our charger and the typical WOCE cast schedule, we did not have to turn the charger off much, if at all, between casts, but we also had no problem at all keeping the battery topped up. With the SeaBattery, I expect that either the charging voltage or the time would need to be reduced if the charger is to be left on between casts with standard spacing. I suggest backing off on the charging voltage by perhaps 0.5 V, and see if that reduces the outgassing. You might also try to find the minimum voltage that delivers 2A when the pack is first plugged into the charger after a cast. We using only a tiny fraction of the pack’s capacity with each cast, so we don’t need to run much current back into it, or for a very long time. I think a cast uses something like 1-2 A-H–probably closer to 1.

Some outgassing is expected, but we do want to minimize it. I hope that a small voltage reduction brings it down to very low rates.