Batteries. How hot is too hot?

[Porthandbuoy]

Two 110 Ah house batteries and one 110 Ah engine start battery. All identical sealed lead acid, 4 years old and giving no trouble.
Batteries are located in the engine bay, and while I had my temperature probe on board to commission the fridge, I thought I'd see how warm the batteries got while the engine was running.
The engine bay, at cruising rpm, stabilised at 42 degC.
That, according to t'internet, is pushing the upper limit for charging SLA batteries so looks as though I need to make some changes.
1) Forced ventilation. Probably the cheapest option.
2) Battery charging temperature compensation. Although the Hitachi alternator is temperature compensated in itself it is not looking at the battery temperature. Some sort of smart alternator regulator may be a good idea. I have a spare Balmar 80A alternator, but the regulator died a couple of years ago. Perhaps I should treat it to a new regulator and replace the Hitachi.

Or am I worrying needlessly?

 

[geem]

Two 110 Ah house batteries and one 110 Ah engine start battery. All identical sealed lead acid, 4 years old and giving no trouble.
Batteries are located in the engine bay, and while I had my temperature probe on board to commission the fridge, I thought I'd see how warm the batteries got while the engine was running.
The engine bay, at cruising rpm, stabilised at 42 degC.
That, according to t'internet, is pushing the upper limit for charging SLA batteries so looks as though I need to make some changes.
1) Forced ventilation. Probably the cheapest option.
2) Battery charging temperature compensation. Although the Hitachi alternator is temperature compensated in itself it is not looking at the battery temperature. Some sort of smart alternator regulator may be a good idea. I have a spare Balmar 80A alternator, but the regulator died a couple of years ago. Perhaps I should treat it to a new regulator and replace the Hitachi.

Or am I worrying needlessly?

Forced vent may help but you have a radiant problem from the engine that will heat up the batteries regardless of air temperature. Can you install a reflective bulkhead between engine and batteries? Can you relocate batteries out of the engine compartment? Forced vent would need to be extract. That is best from high level. If you can create a cool air inlet by the batteries, high level mechanical extract and a reflective/ insulated bulkhead between the engine and batteries, I think it would make a difference. The only problem you then have is when you have finished motoring, the whole engine space heats up and unless you continue running ventilation for several hours after you have switched off thr engine, the batteries will warm up to the space temperature. Moving the batteries is by far the best solution, but may not be easily achieved

 

[vyv_cox]

My Red Flash 1100 starter battery is alongside the gearbox inside the engine space. In Greece, I feel certain it becomes pretty warm at times. Despite that it has lasted 10 years and only recently failed.

 

[Supertramp]

I have all my sealed lead acid batteries in the engine bay. It is large, under the pilothouse floor with a decent amount of exposed hull. I have forced ventilation and it makes a big difference to the engine bay temperature (and the engine temperature as measured by exhaust water temperature). Geem is right about the temperature soaring after you switch off.

That said, I recently checked the batteries using a temperature probe which I use to monitor the engine and all 3 were at 24C after over an hour running with outside ambient at 16C. I don't know the engine bay temperature, but it will be significantly more than 24C.

Perhaps check the batteries with an IR probe before considering the difficult options.

My forced ventilation makes as much noise as my engine!

 

[Skyenergi]

Most Lead acid batteries are okay up to 50ºc some up to 80ºc, so check the specification of the battery. Maybe a long shot but the cabling is up to spec? As this could potentially be the cause of some heat. Or even a bad connection to the battery.

 

[Neeves]

It may be impossible to achieve in a mono-hull but....

We have domestic trunking from the anchor locker (being the coolest location on the cat) to the fridge compressor, then to the deep freeze compressor to the engine bay. The trunking is supported by computer fans drawing 0.5 amp when they cycle on. The computer fans cycle on when the compressor cycles on and the air is directed at the compressors. The trunking enters the engine bay forward and there is a vent under the deck hull joint, aft, in the hull so a through flow of air which operates when the fridge and/or deep freeze is switched on. We keep the anchor locker clean.

You need to be prepared to drill holes for the trunking through the bilges (which might be less easy to achieve in a monohull). It also needed that you have access to the compressors - but cooling the compressors and using the air warmed by the compressors, using that forced draft (forced is a rather strong word ) to refresh the air in an engine bay seems an objective that is positive.

Because we rely on the fridge/deep freeze cycling to control the computer fans we overcome Geem's issues with the radiant heat from the engine when the engine has been switched off. Our fans are 'extra' but you could simply use the fans in the fridge for the airflow (though they only use the air already in the yacht and/or the air warmed by the compressor.

Jonathan

 

[geem]

I have all my sealed lead acid batteries in the engine bay. It is large, under the pilothouse floor with a decent amount of exposed hull. I have forced ventilation and it makes a big difference to the engine bay temperature (and the engine temperature as measured by exhaust water temperature). Geem is right about the temperature soaring after you switch off.

That said, I recently checked the batteries using a temperature probe which I use to monitor the engine and all 3 were at 24C after over an hour running with outside ambient at 16C. I don't know the engine bay temperature, but it will be significantly more than 24C.

Perhaps check the batteries with an IR probe before considering the difficult options.

My forced ventilation makes as much noise as my engine!

Our engine room runs at 60degC without ventilation switched on. 40degC with ventilation running. The surface temp of kit stored close to the engine is much higher as the block is radiating at circa 80degC.