Temperature Compensation--Battery or Ambient?
OK I have had my fill of why you need a temp comp probe to the battery casing or battery post (whichever one this week it is supposed to go on, the neg or the pos :) ) I understand temp comp and ag...
Forum Discussion
I think BFL has very valid questions, here. He asks the questions from a complete sceptical point of view and that's a good agenda to get good answers.
As I understand them:
1) Does temperature compensation aid in battery charging and if so, how much?
2) Is a separate probe attached at the battery necessary or can the ambient temperature around the batteries be close enough to establish correct values for temperature compensation?
I'd answer from my own experience like this:
1) I believe temp compensation does matter and more so for a user that experiences very high temperatures in Summer than for a user that has low temperatures in Winter. The risk of reaching internal battery temps with the electrolyte starting to boil in Summer is the most critical, IMO, and if the charge can be lowered so that threshold isn't crossed, the benefits are big. This also entails typical maintenance habits of a typical user, one that isn't observing and changing charge set points frequently.
I see a seasonal voltage change using the Morningstar MPPT-15 w/attached probe, of about .6V when in float. This is in MN, ambient ranging from typical 80-90f in Summer and -20-30f in Winter. I'm able to program the controller to individual charge setpoints for bulk, abs, and float, along with some changes to duration of those. The combination of these variables seems to keep my banks in perfect health, although life duration of the batteries hasn't been established. Without temp compensation, I might either shorten the life cycle by a short period of time or, if that boiling threshold is crossed, by a significant margin of life cycle, depending on how I replenish electrolyte levels.
2)I think the probe/sensor at the terminals is more accurate. In the case of an ambient probe at the controller, sensor mounted exterior of the controller heat, with the batteries at the same ambient temperature, the accuracy is probably very close to what the on-terminal probe measures. There may be induced noise into the probe wiring or a unique temperature situation where the controller mounted sensor is more accurate. Barring those, the sensor at the battery is "best".
Since this is all a "game of inches", the user will have to decide how much or little all of this plays in their own situation. Also, like Mex cautions, is the charge derated in the higher temperature example to the point where battery health is effected, i.e. an under charged situation. This too, is in the "game of inches" realm. The formulas used in the Onsemi application notes show the two "high limit" and "low limit" charge curves getting into "fractions of inches game".
As I understand them:
1) Does temperature compensation aid in battery charging and if so, how much?
2) Is a separate probe attached at the battery necessary or can the ambient temperature around the batteries be close enough to establish correct values for temperature compensation?
I'd answer from my own experience like this:
1) I believe temp compensation does matter and more so for a user that experiences very high temperatures in Summer than for a user that has low temperatures in Winter. The risk of reaching internal battery temps with the electrolyte starting to boil in Summer is the most critical, IMO, and if the charge can be lowered so that threshold isn't crossed, the benefits are big. This also entails typical maintenance habits of a typical user, one that isn't observing and changing charge set points frequently.
I see a seasonal voltage change using the Morningstar MPPT-15 w/attached probe, of about .6V when in float. This is in MN, ambient ranging from typical 80-90f in Summer and -20-30f in Winter. I'm able to program the controller to individual charge setpoints for bulk, abs, and float, along with some changes to duration of those. The combination of these variables seems to keep my banks in perfect health, although life duration of the batteries hasn't been established. Without temp compensation, I might either shorten the life cycle by a short period of time or, if that boiling threshold is crossed, by a significant margin of life cycle, depending on how I replenish electrolyte levels.
2)I think the probe/sensor at the terminals is more accurate. In the case of an ambient probe at the controller, sensor mounted exterior of the controller heat, with the batteries at the same ambient temperature, the accuracy is probably very close to what the on-terminal probe measures. There may be induced noise into the probe wiring or a unique temperature situation where the controller mounted sensor is more accurate. Barring those, the sensor at the battery is "best".
Since this is all a "game of inches", the user will have to decide how much or little all of this plays in their own situation. Also, like Mex cautions, is the charge derated in the higher temperature example to the point where battery health is effected, i.e. an under charged situation. This too, is in the "game of inches" realm. The formulas used in the Onsemi application notes show the two "high limit" and "low limit" charge curves getting into "fractions of inches game".
