Monitoring Battery Temperature

[bristol27]

Hello Everyone,

I hope you're doing well and it's been awhile since I've posted, but I'm still plugging away on the project. 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 - http://www.bristol27.com/projects/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.

[LazyGuy]

It is true, Battery temperature makes a difference. When the battery is hot, chances are the electrolyte is hotter, expanded and less dense. For heat, it is more of a density compensation in determining specific gravity which, as you probably already know, is the most accurate method of determining battery condition. One the other hand, cold is the enemy of the battery. Battery capacity decreases with cold. But the real question is how closely are you using your battery. If you are a weekend sailor that goes for the annual 2 week cruise, I would not worry that much about it. If you are a live aboard on a mooring or planning on an around the world cruise, it might become important. Big loads such as air conditioning and refrigeration are big loads which can heat a battery during discharge. Also, charging equipment such as wind generator can add a lot of current in a short time which also adds heat. Even a solar panel "can" add heat depending on size. If you are adding all that then get temperature compensated monitor. For 99 percent of us (including me) temperature is not too much of a worry.

This is my opinion and should be taken as nothing more than that.

Dennis

[earlylight]

Dennis,
I believe you are spot on. I feel that for the average weekend boater money spent on battery temperature monitoring could be put to better use on other items.

[bristol27]

For reference, this boat will be my world cruiser. I plan to be living on the boat for a good number of years. I also should have mentioned that I plan to use 4 GC2 Lead Acid batteries

I've also posed the question to other online users. The general consensus seems to be that it would be nice, but it's not that important.

What's most important is that the battery charger know the battery temperature. Also, for Lead Acid batteries, it's less important, because they aren't as temperature sensitive (apparently).

If you're the diligent type or want to track these things closely, then battery monitoring might be a good call. I probably do put myself in that category - mainly because I want to maintain the batteries in top-notch condition. However, the ~$300 price difference and fact that it may not be overly necessary makes me think I can live without temperature monitoring for now.

So, I think I'll go/start with the monitor that doesn't measure temperature, and if I find later that I really need it, I'll upgrade to a monitor that has this capability.

[Maine Sail]

The vast majority of battery monitors I come across on boats, like 98%, are horribly programed and due to this they are also horribly inaccurate.

Temp monitoring for the battery monitor is the least of the worries. Most batteries on most sailboats are at or near ambient temp or closer to sea water temp, unless in an engine bay. They should never be in an engine bay but often are. HEAT MURDERS BATTERIES..... Keep them below 80F and they will be very, very happy..

Contrary to popular misconception specific gravity tells you zero about the actual "capacity" left in the battery bank. It can tell you when cells become out of balance or let you know that sulfation is setting in & you're ready to equalize or equalize more regularly, but it tells you nothing about the capacity of the battery bank. The only test worthy of telling you the current capacity is a 20 hour load test at the 20 hour rate. You will need to count the Ah's delivered before the bank hits 10.5V.... A 100Ah battery would have a 5A load applied and held steady until the battery hit 10.5V. This should all be done at 77-80F battery temp to make it easier.

The place to spend money on temp sensors is for your charge sources, charger, charge controller, or alternator regulator not necessarily the battery monitor.

If you want your battery monitor to remain as accurate as possible:

*Program for the correct capacity and reduce it each year after conducting a 20 hour capacity test. Capacity testers are ungodly expensive but they can be built with a simple battery monitor, and adjustable load, or fixed for your batteries, and some relays.

*Program the correct Peukert value! 99.9% of monitors I see are NOT touched when it comes to Peukert. An Odyssey AGM has a Peukert of 1.11 and a bank of Trojan L-16H's is 1.79.. That is a HUGE range and changes everything in terms of accuracy. Heck the Lithium bank on our boat has a Peukert of 1.01..... If you don't program the correct Peukert there is no way it can be accurate for % charged.

*Program the correct charge efficiency, the manufacturer can tell you this.

*Turn off auto synchronization to "full" and do your re-sets manually when "known full". I have been doing this for 20+ years.

What is "known full"? When at 14.4V (at the battery terminals) and less than 2% accepted current is flowing into the battery bank you can then safely re-set the monitor to 100%. I use 1.5% and 14.4V. If your absorption voltage is set to 14.6V - 14.8V then use 2.5% instead.

*Solar has a nasty habit of re-setting battery monitors before the bank is actually full. This is why manual re-set when "known full" are the best way to keep them accurate.

I once had a Link 2000 reading -575 Ah's on a 70Ah starting battery. That can't physically happen.... Owner had never programed it correctly, had solar and never manually re-set it. It was also wired incorrectly....

Focus on temps sensors for your charge sources then if you have some extra boat green a batt mon temp sensor can be good.......