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
Hi BFL,
When battery manufacturers define the temperature compensated charge values they are referring internal temperature of the battery (specifically the temperature of the electrolyte). This is chemistry after all...
However the practical answer to your question is; "It really depends."
In many installation and use scenarios the ambient temperatures at the charge controller and at the battery storage location are very nearly identical, and it is reasonable to expect that the internal temperature of the battery is fairly close to the ambient temperature as well. I do agree with you that in these cases there is no issue with using the temperature sensor that is integrated into the charger/controller…. especially with FLA batteries.
On the other hand, there are installations where the batteries and charger, although physically close to one another, are in locations with huge temperature differences… for example; I own a TT that is stored and used in a climate that is both very warm and fairly cold (northern NV desert). The battery is mounted outside on the tongue of the trailer and the charger is inside the climate controlled living space. It's easy to imagine that there might be a 40ºF difference between the two locations (in both directions and on the very same day!). If I had a fancy battery (I don't) and a fancy charger (nope) I would most definitely choose to mount a remote temp' sensor directly to the battery!
Another scenario may be found in RV's that place heavy demands on their batteries. For example; In my TC I frequently see discharge loads as high as 150A and charge current of ~100A. Even though my chargers(s) and batteries are in the same climate controlled space, the batteries are often 15-20ºF warmer than the ambient temp' (that is; the temperature indicated by the chargers' internal temp' sensors vs the external probes). In addition I my batteries are expensive AGM's (mounted in my basement, where I would really prefer that they did not vent)… oh and each of my (3) chargers has an (optional) external temperature probe. It was a no-brainer (cheap, easy) to choose to fasten the probes to the battery terminal posts.
So again, it depends… I suggest that folks take a look at their specific situation (equipment, installation, climate, usage, finances) and do what works best for their needs.
Here's a sample temperature compensation quick reference chart I made that will give you an idea for the difference in charge voltages vs temp'. It assumes float and bulk charge voltages of 13.6 and 14.7 voltages respectively with a temp' coefficient of ±0.024V/Cº
CLICK HERE to download a customizable version of this chart in MS Excel format :)
In terms of "battery management outcome"… well I haven't owned any RV batteries long enough to come up with a dollar/watt/year calculation yet. Most of my batteries have been in operation for a long long time and I haven't' had any unexpected failures. On the other hand, I'm one of those people who regularly checks electrolyte levels and keeps the batt's pretty close to 100% SOC all the time.
Cheers,
-Mark
When battery manufacturers define the temperature compensated charge values they are referring internal temperature of the battery (specifically the temperature of the electrolyte). This is chemistry after all...
However the practical answer to your question is; "It really depends."
In many installation and use scenarios the ambient temperatures at the charge controller and at the battery storage location are very nearly identical, and it is reasonable to expect that the internal temperature of the battery is fairly close to the ambient temperature as well. I do agree with you that in these cases there is no issue with using the temperature sensor that is integrated into the charger/controller…. especially with FLA batteries.
On the other hand, there are installations where the batteries and charger, although physically close to one another, are in locations with huge temperature differences… for example; I own a TT that is stored and used in a climate that is both very warm and fairly cold (northern NV desert). The battery is mounted outside on the tongue of the trailer and the charger is inside the climate controlled living space. It's easy to imagine that there might be a 40ºF difference between the two locations (in both directions and on the very same day!). If I had a fancy battery (I don't) and a fancy charger (nope) I would most definitely choose to mount a remote temp' sensor directly to the battery!
Another scenario may be found in RV's that place heavy demands on their batteries. For example; In my TC I frequently see discharge loads as high as 150A and charge current of ~100A. Even though my chargers(s) and batteries are in the same climate controlled space, the batteries are often 15-20ºF warmer than the ambient temp' (that is; the temperature indicated by the chargers' internal temp' sensors vs the external probes). In addition I my batteries are expensive AGM's (mounted in my basement, where I would really prefer that they did not vent)… oh and each of my (3) chargers has an (optional) external temperature probe. It was a no-brainer (cheap, easy) to choose to fasten the probes to the battery terminal posts.
So again, it depends… I suggest that folks take a look at their specific situation (equipment, installation, climate, usage, finances) and do what works best for their needs.
Here's a sample temperature compensation quick reference chart I made that will give you an idea for the difference in charge voltages vs temp'. It assumes float and bulk charge voltages of 13.6 and 14.7 voltages respectively with a temp' coefficient of ±0.024V/Cº
CLICK HERE to download a customizable version of this chart in MS Excel format :)
In terms of "battery management outcome"… well I haven't owned any RV batteries long enough to come up with a dollar/watt/year calculation yet. Most of my batteries have been in operation for a long long time and I haven't' had any unexpected failures. On the other hand, I'm one of those people who regularly checks electrolyte levels and keeps the batt's pretty close to 100% SOC all the time.
Cheers,
-Mark
