Temperature Compensation Myth

[Sunking]

I see this subject coming up a lot in the forum. Every time I see the same wrong answers. Yes every good battery manufacture gives you a formula to use to determine how much to raise the voltage as temps go down. So you must think I am nuts which is perfectly fine with me. But I know something most of you you do not know after working 35+ years with battery manufactures; Manufactures give those formulas to be used in Stationary Float Service for Emergency Back Up Power. You are a Daily Cycle Application user, not a Stationary Battery Plant in a telephone office or cell tower. Only place a Telecom or Utility would ever think of using Temp Comp is a remote installations outdoor equipment cabinets exposed to the elements (heat).

So should you use Temp Comp?

Not unless you are talking about, using an FLA in a remote location where the battery is exposed to the extreme cold, where the temps fall well below freezing for extended periods of time. Jacking the voltage up adds a few more degrees of protection. But folks we are talking -40 degrees C or F. If you live where it gets that cold, solar is not for you unless you live on Mars.

Here is something else most of you do not know. Temperature Compensation was not developed to protect your batteries from the cold. It was developed to control thermal runaway in AGM batteries. Thermal Runaway on a solar system is almost IMPOSSIBLE, cannot happen unless your batteries are grossly undersized for the amount of panel wattage you are using. Thermal Runaway is only a concern for AGM and Gel batteries. Not a problem with FLA batteries.

So if you are using Temp Comp, ask yourself why and what conditions require you to use it. Otherwise you are doing more harm than good.

[PNjunction]

I would respectfully disagree with that on the basis that we are always looking for maximum battery performance, not just edge-case extremes of hot and cold operations, nor just thermal runaway issues with vrla.

It is also worth mentioning that temperature compensation should be done at the battery itself, since the mass of lead at the mountaintop, or just outside your door, is going to acclimate very slowly in comparison with ambient temps. Remote could be 10 feet away while you are sleeping.

Can you get away with no temp-comp other than in extreme temps? Sure, but do you want to, knowing that proper battery maintenance / performance adds up when all the parameters are adjusted for best performance?

For most of us running quality CC's, with at least ambient temp comp, the point kind of becomes moot and we are NOT doing more harm than good.

[PNjunction]

Wait, I think I see where you are going with this. Allow me to quote myself (not a good sign).

It is also worth mentioning that temperature compensation should be done at the battery itself, since the mass of lead at the mountaintop, or just outside your door, is going to acclimate very slowly in comparison with ambient temps.

Right - I see the problem that can occur depending on condition. Let's take a hypothetical extreme from my area in the summer:

1) 105f temp conditions all day.
2) Massive blob of lead acclimates to becoming nearly that hot after exposure all day.
3) After sundown, a quick ambient temperature swing over an hour or two forces my controller to INCREASE voltage
4) BUT, my massive lead blob has not cooled down significantly enough to warrant that temp comp!

So in this case, IF one is running ambient temp comp, and not "at the battery" temp comp, and ambient temp swings are swift, you run the risk of doing more harm than good.

I think I get it.

3a) Doesn't make sense. After sundown, my CC isn't charging!

Probably should go to bed but you got my mind boiling over...

How about the opposite:

1) Batteries cool all night
2) After sunup, a quick ambient increase change takes place
3) Huge mass of lead is slow to acclimate
4) CC applies a lower, less than optimal voltage if using only ambient temp comp early on in the day until you get lucky with ambient and batt being the same after many hours.
5) Battery may finally acclimate, but later on the afternoon ambient temp is dropping, but batteries, seriously big ones with a lot of mass, arent! Back to less than optimal voltage if you haven't finished charge.

Ok, going to go unconscious and think about it some more. Either way, maybe it is a way of saying that unless you are operating in total extremes, that if the bank is sufficiently large enough not to acclimate quickly with moderate swings of temp, you ARE doing more harm than good IF you are only using ambient, and not at-the-battery temperature compensation.

Wow - food for thought in moderate climates with only ambient temp sensing. Maybe best to disable or zero that out, or just bite the bullet and get that temp-probe you promised yourself you would and put it on the battery.

[Sunking]

PN you were on the right track for a moment, but allow me to mess with you a bit.

What and Why did temp comp come about.
What stage is Temp Comp applies to> example EQ
Where MUST the temp probe be placed.
What Industry uses the most AGM's

[sdold]

I'm following along, we have a few sites using AGMs with no air conditioning (because they are solar) at some mountain tops, some of them probably range from around 0F winter to 100F summer. I've wondered if we should use temp compensation.

[Sunking]

Steve I think what you are over looking and many over look is; What Does Temp Comp Accomplish or What Is It Used For?

There is only one answer; To lessen the chance of Thermal Runaway in Stationary DC Battery Plants in Float Service. Solar is NOT a FLOAT SERVICE operation.

Temp Comp was developed for Telecom battery plants and UPS users who use VRLA batteries with chargers capable of delivering 1C charge rates and higher in Float Service. Now stop and think about that for a moment. That is not how any Solar System works.

First understand that application does not use 3-Stage Charging, they are strictly Float Service where voltage never changes 24 x 7 x 365. It is all but Impossible for an AGM battery to go into Thermal Runaway in any solar application. There is just not enough power or daylight to do that. Additionally Temp Comp is a Float Mode only operation. Solar systems spend little if any time in Float Mode. 90% of th etime operating at much higher voltage of Bulk and Absorb, so Temp Comp has no function or purpose.

In addition to use Temp Comp requires the sensor to be attached to a cell buried in the middle of the string as close to center of Thermal Mass as you can get it. Having the sensor in the Charge Controller is just stupid. At no point does the Controller internal temp ever equal the battery temp. That means your temp comp voltage is always WRONG doing more harm than good.

So for a solar application where the battery is being cycled every minute of the day, temp comp has no purpose or function. To drive an AGM battery into Thermal Runaway takes days of a Float Charge Voltage applied with high charge rates and no or little load on the batteries. That cannot happen on a solar system.

The only argument you can make for using Temp Comp is with FLA batteries in extreme cold well below 0. Night comes around, charge stops that never completed. Now morning comes around, the sun rises, and the Controller turns on and does What? It immediately starts in BULK mode. If you are lucky by the end of the day you reach Absorb mode at 14.6 volts before the sun sets. You never reaches FLOAT voltage where Temp Comp would be applied to raise the voltage.

When it comes right down to it. Temp Comp is only usable to a Consumer using a AC powered Float Charger on an AGM battery being stored long term on a shelf. Who does that? One thing that comes to my mind is RV and Boat users who store their toys away for winter.

[sdold]

Thanks for the info, good to know. I thought it had more to do with not reaching 100% SOC in really cold temps.

[PNjunction]

Wow - thanks Sunking, consider me schooled!

I think one takeaway from this - at least for an agm user presented with a manufacturer's option of running between 14.4v and 14.6v setpoint for CV / absorb, choose the HIGHER value! You have nothing to fear, especially since we're talking typically low solar charge currents, and quick tapering of current anyway in the CV stage.

That is, for quality batteries, and not the trash-recyclers.

Awesome wakeup there, buddy.

[inetdog]

Wow - thanks Sunking, consider me schooled!

I think one takeaway from this - at least for an agm user presented with a manufacturer's option of running between 14.4v and 14.6v setpoint for CV / absorb, choose the HIGHER value! You have nothing to fear, especially since we're talking typically low solar charge currents, and quick tapering of current anyway in the CV stage.

That is, for quality batteries, and not the trash-recyclers.

Awesome wakeup there, buddy.

A critical feature is that as long as the gassing (overcharge current)stays below a certain level the AGM battery can effectively recombine the evolved gasses and not have to vent or otherwise lose electrolyte.

[PNjunction]

Right - I won't go to the extreme of ripping out my sensors, or disabling it completely with my agm's.

I think Sunking pointed something out to me about being application aware that I harp on and missed - that we can be a tad relaxed based upon our unstable, time limited application, rather than that of an industrial ups type backup with a stable charge source. At least between say 50F and 85F, with a charge current of say 0.2C or less, which should be pretty fast once into CV / absorb, or dark skies, etc. And for many, finishing CV is sometimes a luxury many might not enjoy on a regular basis. Thus exposure to long time periods of CV, even if on the high-ish voltage end is reduced enough that gassing (vent-blowing type) and thermal runaway won't be a major problem.

Those doing specialty type of finishing charge with CC rather than the usual CV - (IUIa protocols, etc) must be on top of things of course.

Truth be known, slight controlled overcharge (at least for agm) is more beneficial than slight undercharge! But yeah, don't go nutzo to the extreme.

I do see however the chance that 1 in 100 ops might consult temp-comp charts and make a big mistake - not knowing that CC's that do temp comp START from a default of about 68-72F and go plus or minus from that range automatically.

BUT, by mistake, they wander into the shed where it is 20F cold, look at the chart, and program their controller's CV/Absorb for that temp! When it warms up, OUCH. I guess the warning here is that if one is going to choose their CV / absorb based on manufacturer's recommendations, do so at the 68-72F charted data, and not outsmart the controller by reprogramming at what is the current ambient temperature! If one didn't have a manual or know this already, it might save that 1 out of 100 ops.

The only reason I mention this is that I have a tendency to overthink things, and could see myself doing just that if I was starting out.

[Sunking]

Right - I won't go to the extreme of ripping out my sensors, or disabling it completely with my agm's. .

No that is not what I meant or was trying to say. If you have your sensors at least attached to the batteries are ahead of most. Hope you did not take it that way.

Temp Comp came about the same time I entered into the scene professionally sometime in the 70's, It came out not long after VRLA batteries. FWIW most folks are unaware why VRLA batteries came about. They were like many things a product of the Aircraft Industry, developed exclusively for aircraft for the obvious reasons. It did not take long for VRLA to enter consumer hands and was a desaster in the late 70's early 80's.

Not long after that they found their way into telecom offices which seemed like at the time the greatest thing since sliced bread. No more expensive spill containment or ventilation required. But there was a Gremlin hiding inside waiting to surprise the world called Thermal Runaway. VRLA batteries had never been used in Float Service before. For those who are not familar with Telecom and Utility battery plants they are extremely large battery plants up to 10,000 amps of Rectifiers (charger) with 40,000 AH 48 volt batteries. Enough batteries to fill a large home. Even a tiny Cell Tower will have a 2000 AH 24/48 volt battery with a 1600 Amp Rectifier. Point here is no AGM at that time had ever been used and connected to a Float Service DC Battery Plant with 1C capable charge currents. Anyway the early VRLA batteries were prone to Thermal Runaway. Today's models are less prone and use Temp Comp.

Back in 1990 I was C&D largest customer, or my company was MCI, and every year there is a Power Conference in Cleveland where all manufactures in Telecom show up. Lots of parties. lectures, and entertainment. Richard Black was lead development scientist for C&D. He gave a 90 minute lecture on AGM batteries and Temp Comp I had forgotten about. In that lecture was the intro to Temp Comp battery plants. Then some damn fool wet behind the ears engineer asked why not use Temp Comp in Planes and Auto's that used AGM batteries. Dick laughed and explained that unless you are talking about a 18-Wheel Tractor Trailer where engines are left running for extended periods of time of 24 or more hours was no added value, and small form factor single batteries thermal mass was just to small to make it a likely candidate. Dick and I became good friends after that, and he taught me a lot. I miss him RIP Dick.

So bottom line Temp Comp is not for COLD weather like many of you are thinking. It is for a battery sitting in a building at normal room temps preventing Thermal Runaway. So unless your solar system can provide very high charge currents for a given battery size, solar is just not capable of causing an AGM to go into thermal runaway.

So should you use it? I leave that up to you, bu twill say if you do use it put the damn sensor on a battery buried deep in the middle of the string and not on the end.

[PNjunction]

No problem - I didn't take it that way and found it extremely enlightening - but not to the point where I abandon all reason!

Interesting about C&D. Although I don't have any of their batteries, I put their documentation at the very top of my list. Quite frankly, C&D's docs are my bible for agm. They get right to the point with a minimum of marketing, but provide enough information for the battery-geek to understand and be confident they are doing the right thing without a lot of fluff. If I were an industrial user, the documentation alone would be enough for me to buy sight-unseen. Heh, they've been at it since what 1908 or so?

My interest in agm was started in the 70's as a kid, marveling at the Gates Cyclons, and I suppose John Devitt's early work with them. Which of course branched out into the Optima, Odyssey/Hawker/Enersys, which I find fascinating. Especially the transition from Gates > Gilling Group > JCI etc etc.

While I like agm's for convenience, I have no qualms about them not being the single-answer to every application. Despite the recent quality, there is a price to be paid for their convenience, which I don't go into blindly.

To be on top of things with agm, you have to be kind of a chess-player and get the "end game" right, which involves different strategies depending upon application and charge sources.

But back to temp comp - you surely got me thinking about how the average solar user never truly finishes a proper CV in the first place, and hence never sees float (unless their controller drops the cv stage too early), where temp-comp at extremes is vital - especially so if they are using constant-current and not constant voltage for float....

Heh, don't worry - it's under control here, but your information has helped me fine tune my setup.

[Sunking]

But back to temp comp - you surely got me thinking about how the average solar user never truly finishes a proper CV in the first place, and hence never sees float (unless their controller drops the cv stage too early), where temp-comp at extremes is vital - especially so if they are using constant-current and not constant voltage for float.....

Bingo, you got it. Winner Winner Chicken Dinner.

Well in the event you have not noticed or followed the automotive technology and EPA requirements the battery scene for automotive has made a shift to almost exclusively AGM batteries. Soon FLA in all new cars will be a thing of the past. The extremely high demand new car electronic systems put on the battery, and coming EPA requirements to shut down the engine while stopped at traffic lights and such demands a AGM to handle that. The point I am driving at if you have taken note all new cars Voltage Regulators are set to 14.2 volts which is a curious voltage. Perfect to Float an AGM and LFP. Something can be leaned from that info. Actually makes life real easy as far as a charger goes. Just a simple CC/CV Float Charger. Well truth be told if I stored a AGGM would be at 13.X volts recommended by the manufacture.

C&D is a very good battery manufacture. If you think the docs you have are good try to get your hands Industrial User Guide. They provide detailed discharge curves from 100 to 1 hour fore testing. They also if you beg them will give you MHO charts of Age vs capacity. With those charts and a Midtronics Analyzer you can tell real quick if the battery is good or not.

I will tell you another secret I know you will like Go here and look. Priceless info. I will warn you as a battery junky, be careful, some powerful chit and easy to over dose on. You gonna like if you know what you are looking at.

[PNjunction]

Oh yeah, been on top of that. See my rant..er comments of the latest ALABC.

Yep, the whole micro-hybrid (start stop), high parasitic draw thing. JCI going nuts with AGM now.

Previously kept an eye on the whole carbon, graphite, graphene thing along with Firefly/CAT, Axion, and now the Deka licensed UltraBattery psoc.. NONE of which ever show up for the average human to install. Vaporware as far as I'm concerned.

From an agm standpoint, most of us are left with 70's tech. Lead calcium vs pure-lead. Improved separators, yadda yadda. The question of recycling lead-calciums vs mining of pure-lead up front etc. All fascinating discussions as long as one doesn't get swept into a marketing vortex.

Love the charts. Sure looks like short-circuit current measurements (aka related to internal resistance) to me. Might have to print that out and paste it on my wall.

[Sunking]

Love the charts. Sure looks like short-circuit current measurements (aka related to internal resistance) to me. Might have to print that out and paste it on my wall.

No sir, they are not Short Circuit, better than that, it is Mho's of a new battery Reference Library to use with a good Battery Conductance Meter.

From that you can most certainly calculate short circuit. In a way it does tell you how much current produce at 1-Volt. Invert Mho's and you have Ohm's or the Internal Resistance of the battery under test.

The real purpose of the Library is so you use a Conductance Meter and determine Pass Fail. End of Life is reached when Mho's equal or less than Reference Mho's / 2. When At that point of half the Mho's or double the resistance the battery is at 80% rated capacity. Now a lot of folks 80% is good enough. But once you get down that low, it is a short ride to unusable. So it might have taken 3 years to 80%, and 1 more year to unusable.

But you can tell who the beast batteries are. The higher the Mho's, the larger the battery. When you get up to 5000 Mho's you are in the 2000 AH battery territory. FWIW Conductance meters stop at 20,000 Mho's. There is no such thin gas a battery with 20,000 Mho's I know of except maybe sub marine batteries.