Battery temperature sensor - worth it?

[gauvins]

Just about to install a Balmar regulator. Looking through the instructions, I see optional battery and optional alternator temperature sensors. Is it really worth the cost/trouble, or does it fall in the "nice to have" category?

Partially related - Balmar sensors are quite expensive. Is it possible to install another brand (say, Victron) or are gauges using different proprietary signals?

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In case context matters: 2x100A alternators shaft driven. Balmar 6120 dual regulator. 3x230Ah FLA batteries. 3x70W solar panels. Victron MPPT 75/15. Victron BMV 700

[denverd0n]

I think so. The temperature of the battery is a key element in determining the optimal charging voltage and current. If you're going to spend the money for a quality charging system it seems to me to be penny wise and pound foolish to try to save money on the temp sensor.

[billknny]

Originally Posted by gauvins

Just about to install a Balmar regulator. Looking through the instructions, I see optional battery and optional alternator temperature sensors. Is it really worth the cost/trouble, or does it fall in the "nice to have" category?

Partially related - Balmar sensors are quite expensive. Is it possible to install another brand (say, Victron) or are gauges using different proprietary signals?

---

In case context matters: 2x100A alternators shaft driven. Balmar 6120 dual regulator. 3x230Ah FLA batteries. 3x70W solar panels. Victron MPPT 75/15. Victron BMV 700

Context does matter... because it is about a cost benefit analysis.

Batteries will last longer with a temperature sensor. You will charge them more fully in cold temperatures, and avoid overcharge when it is hot. You can mimic the behavior and get 90% of the benefit for no cost if you seasonally adjust the absorption and float voltage, but on a balmar regulator that can be a bit of a pain. Your batteries are (relatively) inexpensive, so if they are not charged optimally, and they died 10% early, who cares?

My recommendation would be to keep the alternator absorption voltage set a tiny bit low, and let the solar system top off the batteries. It has built in temperature compensation, so will deal with the end of the charge cycle (where temperature IS critical) in a smart manner.

The alternator temperature sensor is in my opinion, much more important. Alternators are not designed to run at full output continuously, but are significantly downrated (10-20%) when "hot". They get hot fast and if run that way for any length of time will suffer. They are NOT cheap and should be protected. The regulator will manage this problem automatically with a temperature sensor.

[sailorboy1]

Personally I don't see a big value in the alternator temperature sensors unless you have a real big alternator in a real hot engine compartment. And the same for the battery sensors unless they are installed in some place that gets hot.

Of course anyone who has spent cash to get them will disagree, but I think it will take 20 years for most people to save enough on extending battery life to pay for the sensors.

[john61ct]

It's not just the temperature compensation, adjusting voltage

which I agree with a cheap bank will take a long ROI period

But the overtemp **protection**, de-rating current

which will have a much more dramatic impact

if your setup gets hot

[Zil]

battery temperature is important charge parameter.

[sailorboy1]

Today I almost heat stroked out on the boat.

But I bet the batteries down on the nice cool bilge were among the coolest temperature items outside the freezer/frig!

It's like everything boat electrical, yes it is "better" but is it worth it

[Dsanduril]

In principle I think you should have both a battery and an alternator temperature sensor. In the real world, however, I've found battery temperature to be less than useful. The most they are likely to change charging voltages is about 0.1V. I have three charge controllers of various kinds and a battery monitor on the boat and they disagree as to measured voltage by more than that. Not one of the vendors provides specifications that include the accuracy of their voltage measurement. In that scenario what use is the 0.1V change from the temp. sensor when the charge controllers aren't getting the basic measurement correct? (And I know they aren't getting it correct because I had access to a highly accurate, calibrated voltmeter at one point).

The alternator temperature, on the other hand, can quickly kill your expensive, high-output alternators. If your batteries have a high acceptance current (in comparison to alternator output) and you run them down regularly then a temp. sensor for the alternator is almost a necessity.

[a64pilot]

My alternator derates based on temp, I feel pretty sure without the sensor it would overheat and likely fail, I’m sure it would shorten its life. I have an AGM bank which means it will work the alternator hard for the first 30 min or so, regular flooded not so much, an LFP will eat alternators if you don’t protect them.
However I have watched my chargers for a few years now and really don’t see much difference in charge voltage, it will go up as much as .2 VDC when it’s real cold, but I have yet to see it drop, maybe .1V in real hot weather, but I’m allowed plus or minus .1V, so you decide.
I figure what the heck, I have so much money in all this stuff, what’s a little more for the protective sensors?
I have four battery temp sensors by the way, one for each charge source. The Magnum will display battery temp and the Balmar 614 displays both battery temp and alternator temp.

[wsmurdoch]

Originally Posted by gauvins

Just about to install a Balmar regulator. Looking through the instructions, I see optional battery and optional alternator temperature sensors. Is it really worth the cost/trouble, or does it fall in the "nice to have" category?

The answer is yes, buy both. I have both. Both while expensive are worthwhile. If you are really good with electronics, you can make your own for far less. I bought both although I could have made them myself for less. It is insane that they are not standard with the regulator. The sensor on my alternator catches my attempts to overload the alternator. The sensor cuts the regulator to 50% field voltage to my alternator regularly when charging overly discharged batteries at anchor. The battery temperature sensor watches the batteries. I have never felt them to be overly hot. So far, so good, after eleven years.

Bill
Irish Eyes to the Bahamas

[noelex 77]

Battery temperature is an important charge parameter.

Fortunately batteries have great deal of temperature inertia and as they are usually stored below the waterline the temperature fluctuations are not great.

High current charge sources can heat up batteries. I have never sailed on a boat that has enough charge capacity for this to be a significant issue, but it will be interesting to see if this is the case my new boat.

Nevertheless, for most boats, where the charge sources are insufficient to cause significant battery heat, simply manually modifying the battery set points to cope with different seasons, or locations, is generally close enough, but take the trouble to make the changes.

To charge the batteries as quickly as possible the battery voltage set points make a big difference. If you want to adjust the battery set points close to the limits battery temperature compensation is important.

Alternator temperature is very different. This has nothing to do with health of the batteries but the the health of the alternator. It is not practical to manually control the alternator temperature. The alternator may be 60°C or more above the air temperature.

So the options are to install:

A large frame modest output alternator that will never overheat
A small frame very low output alternator that will never overheat
A large frame high output alternator with alternator temperature compensation
A small frame modest output alternator with alternator temperature compensation.

All of the above can work reliably, providing you are aware of the limitations and compromises.