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toomuch
toomuch

Posted: Thu May 25, 2017 9:09pm

Post Subject: Battery Operating Temperature

Hi Tony I have sound insulated the engine bay on a semi trad narrowboat. This of course has also meant there is now thermal insulation. On a hot day, say 25 deg.C, the temp. in the bay rises to 45/48 deg.C Is this going to have a detrimental effect on the sealed lead acid batteries. I believe the alternators are OK up to 70 deg.C. Would apprecite your comment. Thanks Peter C.

Tony-B
Tony-B

Posted: Fri May 26, 2017 6:12am

Post Subject: Battery Operating Temperature

I would be more concerned about the alternators if you use high current devices when the engine is running but after the temperature has reached maximum. I expect the engine alternator will be OK because after half an hour or so it will have virtually shut down unless you have a fault. The domestic alternator that may be subject to high loads at any time is different. The amount of heat transferred depends upon the temperature difference between the air and the alternator parts so on your figurers you only have a bit over 20 degrees difference so cooling must be compromised. If that really is the ambient air temperature in the engine bay and not something that has been heated by radiation or conduction then I would also be concerned about the efficiency of the combustion in the engine. I wonder how well the engine bay is vented? At 1500 rpm a 1.5 litre engine will consume about 900 litres of air a minute at 80% volumetric efficiency. Even on a hot day that would help keep the actual engine area cooler. This is why I question the true ambient air temperature in the bay. I have no data on the maximum battery temperature allowed but apart from potentially increasing the water consumption to some degree and maybe causing stress in the plates by expansion I doubt it will do significant harm. If any readers are battery experts please respond.

Tony-B
Tony-B

Posted: Fri May 26, 2017 9:19am

Post Subject: Battery Operating Temperature

I have been doing further research and found it stated that for every 8C above 25C a lead acid battery is operated at it halves the design life of the battery. This is caused by an exponential increase in corrosion of internal parts. I think that you need to double check that the ambient engine room temperature, then ensure at least a minimum of a 3" X 3" vent into the engine bay. If that does not reduce the ambient temperature closer to 25C then move the batteries into one or both side lockers/seats, possibly with thermal insulation under them.

Tony-B
Tony-B

Posted: Fri May 26, 2017 7:44pm

Post Subject: Battery Operating Temperature

The above is not a bad as it may seem. That "rule" probably only fully applies when the battery is operated above 25C for the whole of its design life. If you think about it unless you are a very keen long distance cruiser your batteries will only be above 25C for a small fraction of their life so I suspect any reduction of life will not be notable when other things like sulphation and excessively deep discharge are also contributing to reduced life.

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