Do I need temperature sensor? Smartshunt + MPPT

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joaher asked May 31, '20

Do I need temperature sensor? Smartshunt + MPPT

I have one battery bank (an separate bank for starter) with 4 AGM 79Ah in different places in my boat. I have SmartShunt + MPPT 75/15 solarcharger + Ctek M300 Charger. The SmartShunt and solarcharger are inte the same space as the first battery and near the engine so the temperature will be higher for the first than the rest batteries. The second battery is under the kitchen and the rest two batteries are placed in front area. A temperature sensor is in the solarcharger. Early in the season we close the door to the front area in the boat and the temperature will be up to 10 degrees lower than in the rest of the boat. So it can be 40-50 degrees C near the engine an only 10 degrees C in the front. Should I use a Smart censor and where should I place it?

MPPT Controllers Smart Battery Sense

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Answer 1 · 2020-06-01T06:48:24Z

ejrossouw answered · Jun 01, 2020 at 06:48 AM

Hi @Joaher I am not a marine guy, but my casual observations are with 1. not having batteries close together and 2. all with different lengths of connections, 3. different temperature zones it will almost be lost on you to add a temp sense as your setup hardly constitutes a battery bank in the true sense of the word. Not knowing the space limitations etc. I would think your money will be much better spent on one large battery and then a separate starter battery.

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joaher commented · Jun 01, 2020 at 07:08 AM

Thank you ejrossouw for your answer. I agree that the batteries should be at the same place but it is a matter of space so it is not possible in my case. Normally the temperature is the same during the most of the time. When the boat is not used the temperature will be the same and near the water temperature. And during this time the solar panel is charging the batteries for longer times. When the boat is in use the battery bank is almost newer fully charged so I think the solar charger is in bulk state and delivering as much current it can. So this maybe are not a problem but I was curious about if anyone has any suggestions of get my installation as good as it can be.

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Answer 2 · 2020-06-01T12:24:12Z

JohnC answered · Jun 01, 2020 at 12:24 PM

Hi @Joaher

Battery imbalance is your issue with paralleled and separated batts. That's bad enough, but differing temps can worsen that situation even more.

If your charger struggles to keep up while you're aboard, you could consider lowering your Abs/Float settings down to somewhere they can't do damage, like even 13.5V (say, presuming 12V). Would that hurt?

Your 75/15 cannot temp compensate alone more than once a day, when it awakens. You could go with a networked temp solution to manage that, but then it would be best to apply the temp sensor to the hottest batt, so it won't be damaged. The others will just follow at a safer level.

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joaher commented · Jun 01, 2020 at 08:11 PM

Thank you JohnC for your answer. After checking the specification I think out are right about that I need to lower the voltage from 13.8V to 13.5V. My AGM batts specification says 13.40V-13,55V bulk charge and between 14.30V-14.45V in absorbing mode at 20 deg C.

It is difficult to read the exact values see below table. But its also says the you should not be out of min 14.4 - max 14.6. The standard AGM mode is in the solar charger 14.7V.

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