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Old 10-09-2013, 14:21   #1
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Monitoring Battery Temperature

I have a question for you all related to battery monitors:

How important is it to have a monitor capable of monitoring battery temperature?

According to my research (partially updated here - Bristol27.com Batteries), I get the idea it's important. As I understand it, the temperature of the battery affects things like:
  • Calculating how much capacity a battery has (higher temp = higher capacity, lower temp = less capacity)
  • Calculating battery voltage (higher temp = lower voltage)
  • Required charging voltage, which can help prevent thermal runaway (e.g. At low temperatures, increased internal resistance and reduced chemical activity require a higher charging voltage and visa-versa).
  • Timing of off-gassing (Gassing is directly related to battery voltage and electrolyte temperature. If the battery temperature rises to 120F, gassing starts at just 13.4 volts, but hold the battery temperature at 100F, and you delay off gassing until the battery voltage rises to 13.8)

I'd prefer if we could focus this discussion on why it is or isn't important to know a batteries temperature. However, the reason I ask this question is because I'm trying to choose between the Victron BMV 600S and the Xantrex LinkPRO. A key advantage of the LinkPRO is that it has the ability to monitor battery temperature, while the BMV 600 does not.

I appreciate your input and look forward to the discussion.
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Old 10-09-2013, 15:04   #2
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Re: Monitoring Battery Temperature

The answer, of course, is YES and NO.

Depends on where you sit, what your objectives are, and how diligent or paranoid you may be.

For longest life of batteries, yes, it's good not to overstress them with the wrong charging voltages at high or low temps.

Calculating residual AH can be more accurate if you have temp sensing; but only marginally, since many other factors intervene. And, in a large house battery bank where, exactly, do you place the temp sensor?

Sensing an overheated battery to prevent boiling or "thermal runaway" is theoretically possible, but temp sensors themselves are notoriously unreliable and can lead to problems.

What kind of problems? Well, if the temp sensor under-reads, i.e., reports the battery temperature to be lower than it actually is, this could lead to overcharging and/or overheating/gassing, etc. If the temp sensor over-reads, this could lead to severe undercharging.

Consider this statement,
"According to a report from Ward's Auto released last week, the global number of cars exceeded 1.015 billion in 2010, jumping from from 980 million the year before."

There are over one billion cars on the worlds roadways. All of them have lead-acid batteries. Virtually NONE of them has temp-sensing to change their alternator's charging profiles. It's 13.8VDC or, if newer, 14.4VDC charging voltage all the time, whether in sub-zero freezing temps or in 100 degree plus summer temps. Car batteries don't typically last quite as long as many boat batteries, due to such treatment, but one would be hard-pressed to make the case that they really should have temp sensors :-)

Bottom line: for some folks in some situations temp sensing, properly implemented and monitored, may be a good idea. For others it's unlikely to be of much benefit, if any.

Bill
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Old 10-09-2013, 15:29   #3
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Re: Monitoring Battery Temperature

It is important to be able to change the charge the voltages based on temperature. This is a job for the regulators so it is better if they can measure the battery temperature and adjust the charge parameters. The temperate has to change significantly to make a meaningfull difference so you can usually achieve an acceptable performance (if your batteries are not in the engine room) by tweaking the charge parameters manually a few times a year based on the season, but automatic is nice.

There is not a great advantage having this information on the battery monitor as most cannot communicate with the regulators. It is possible to pick up a defective battery by noticing the temp rise that sometimes occurs, but a single temperature measuring point is not very likely to show this.
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Old 11-09-2013, 11:13   #4
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Re: Monitoring Battery Temperature

You the operator don't need to know. Your battery charger would like to know.
Ask yourself: do you really need a monitor to tell you what temperature the batteries are?
Since your charger doesn't have your 5 senses and intelligence, it would like to have an idea.

I have the BMV600...awesome.
I have a Newmar charger with temperature compensation as highly recommended by the OEM. I can only assume this inexpensive investment will help prolong the life of my batteries.
With that, I could give a rat's @$$ what the exact temperature of my batteries are.
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Old 14-09-2013, 00:55   #5
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Re: Monitoring Battery Temperature

Quote:
Originally Posted by btrayfors View Post
....There are over one billion cars on the worlds roadways. All of them have lead-acid batteries. Virtually NONE of them has temp-sensing to change their alternator's charging profiles. It's 13.8VDC or, if newer, 14.4VDC charging voltage all the time, whether in sub-zero freezing temps or in 100 degree plus summer temps. Car batteries don't typically last quite as long as many boat batteries, due to such treatment, but one would be hard-pressed to make the case that they really should have temp sensors......
This could open a can of worms. I don't think you can compare automotive charging of a starter battery to charging of a deep cycle boat service battery.

Ample Power introduced the first alternator regulator that was temperature compensating in early 1987. Today many automotive regulators are temperature compensated BUT they monitor the temperature of the engine compartment not the battery.

Automotive internal regulators are designed to provide power to the cars electrical systems. Charging the battery - which is only discharged about 1% or less of it's capacity - takes such a short time that multi stage regulation was always considered unnecessary.

On a boat that discharges to 50% SoC then a multi stage regulator is best practice with a temperature sensor on the batteries. This is especially important for sealed batteries. A temperature sensor on the alternator is also a sensible precaution, especially with AGM batteries that can take more amps out of the alternator for longer.

I burnt out my 100 amp Balmar alternator because it didn't have an alternator temperater sensor.
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Old 14-09-2013, 01:53   #6
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Re: Monitoring Battery Temperature

Big difference between automotive starting batteries and deep cycle banks.
At the start of charging a deep cycle bank the batteries are at ambient temperature.
As the current goes in they warm up. The absorption voltage needs to be lower at higher temperatures so as not to overcharge the bank....so the temp sensor on the battery is needed so the reg can back off a bit as the battery temp increases.
A temp sensor on the alternator is provided with some regs (Balmar?) so the reg can back off the field drive to be sure not to burn out the alternator as Sailinglegend's experience.

I've had temp sensors for years on battery charging systems, both battery and alternator and never had any trouble with them. They are generally Type-K thermocouples and these devices are exceptionally reliable.

As a previous poster said, YOU don't need to know what the temperature is, but your reg does.
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