HOT IN THE ’HOLE
QI have sound insulated the engine bay on a semi-trad narrowboat, but on a hot day the temperature in the bay now rises to 45-48C. Will this damage the sealed lead acid batteries? The alternators are okay up to 70C.
PETER CASWELL, via the CB website
ATONY REPLIES: If that really was the ambient air temperature in the engine bay (rather than something that has been heated by radiation or conduction) I would be concerned about the efficiency of the combustion in the engine.
How well is the engine bay is vented? At 1,500rpm a 1.5-litre engine will consume about 900 litres of air a minute at 80% volumetric efficiency, which even on a hot day would help keep the area cool. I expect the engine alternator will be okay because after half an hour or so it will have virtually shut down. But the domestic alternator might be subject to high loads at any time. The amount of heat transferred depends upon the temperature difference between the air and the alternator parts; you only have just over 20 degrees difference, so cooling must be compromised.
I have found references stating that every 8C above 25C halves the life of a lead acid battery, but that probably only applies when the battery is operated above 25C for the whole of its life. Unless you are a very keen long-distance cruiser your batteries will only be above 25C for a small fraction of their life. Any reduction in life might not be noticeable if sulphation and excessively deep discharge are also contributing.