Bulk and float voltage options.

[GILow]

Hi Cruisers,

My second attempt at an interim battery bank is ready to go, I found a pair of flooded lead acid batteries from a reputable local supplier at a very good price. Now I would like to make sure I don't kill them over the next three years, before they are replaced with the "real" battery bank of 6 or 8 Trojan T105s.

The scenario is:

1. 280 watts of solar hooked up to a Votronic MPPT controller.

2. 2 new 12V, 105AH flooded batteries, quote "low maintenance", meaning you can check and top up the electrolyte, but in theory this should not have to happen more than once every couple of months. (more on this below.)

3. The boat is a serious dock queen at the moment, spending a week in the pen before doing the odd overnighter. Power consumption for the weekending tends to be trivial, the most I have seen so far is 80 amp hours consumption in a 24 hour period, most of which I have been able to get back straight away between the panels and the wind gen. The boat usually comes back to the pen with at least 80% charge (at least on paper).

4. I have a mains power smart charger that I would like to avoid using, because that would involve plugging the boat into the mains power at the pen, which is a PITA, and I just know I will forget to unplug the cable one day if I use it.

5. A 300 watt wind generator, which I only untether when I am actually using the boat. It cuts out at 14.2 volts from memory.


Before purchasing, I phoned the battery company, got through to their technical guy and asked him what voltages I should be using for the bulk/absorption and float phases. To my surprise he said anything between 14.2 to 14.8 for bulk/absorption and anything between 13.2 to 13.8 for float. I was kind of surprised at this, some of those numbers sounded high to me, and he said yes, at the higher end of that range I would be expecting to be doing reasonably regular electrolyte top-ups. OK, I said, so how about if I use the lower range of those values? 14.2 and 13.2. Any problems? He said no problems, he just assumed I would want to charge the batteries as fast as possible, hence the higher range voltages. And he reckoned at the lower voltages I would see no electrolyte loss.

So, given I have all week to be sure the batteries are completely topped up again, can anyone think of a problem using the lower voltage range? Or would you use a different range? For instance, the MPPT controller has a 13.4/14.4 preset program for lead acid batteries, so clearly it thinks that is the best voltage range to use. But it can be programmed for other voltages if needed.

Matt

[smac999]

bulk high and float low. like 14.8 / 13.4

then it'll charge faster when you need it but not kill them when full.

[GILow]

Originally Posted by smac999

bulk high and float low. like 14.8 / 13.4

then it'll charge faster when you need it but not kill them when full.

That fast charge will cause significant outgassing I would think? Then I will have to extra care of electrolyte levels.

Also I am in no rush to charge, as noted the boat is a dock queen with a whole working week to restore charge.

But then I don't want to inadvertently kill these batteries with kindness by using voltages that are too low, which is the key point of my question.