So If You Want To Ventilate The Battery Box .......

D

Dave100456

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We are here thinking purely about temperature control of two batteries in a close fitting box (box only offers 10mm gap around each battery and 20mm gap between them). The batts are AGM so no need for a sealed box.

So how do you best keep them cool?

Do you;
1) drill as many holes as possible in the box (Swiss cheese like)

2) drill large holes as low as possible around the sides and have holes in the lid? Passive heat rise ventilation.

3) as above but add brushless computer fans to suck or blow?

4) add holes and computer fans in a strategic pattern to offer positive and negative flow?

Do you experts have any suggestions for the best method and/ or ”strategic pattern” of holes to achieve the maximum airflow?

The fans I’m considering are like these http://www.ebay.co.uk/bhp/50mm-silent-fan.
At around 0.1 watt each in terms of power consumption I can afford 4 fans (approx 0.5 amp)

Cheers

Dave
 
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I have battery boxes that seem the same as your description but have no intention of drilling any holes or adding any fans.
 
I would suggest you get one of those max min thermometers and install in the box perhaps on top of the batteries to just check if you have a high temp problem. Most battery concerns are centred around ventilation and removal of hydrogen rather than cooling. Certainly no one around here seems to be concerned with battery temp in their boats in a much hotter climate. I would think that any temp rise might be conducted through the hull to the sea so you might be able to enhance that aspect. Perhaps ali or stainless steel plates from battery sides down to close bonding to inside hull.
If you did go for fans make up a small comparator circuit (VSR) so that they only operate when battery voltage is over 13v ie being charged. olewill
 
My batteries are in a moulded box surrounded by insulating foam on five sides and a cushion on the top. They often got quite warm after long motoring trips and we have suffered them boiling on a couple of occasions over the years. So I added a small fan that comes on when motoring. It blows air in, which vents out through a few holes drilled into the engine compartment. You can just see them in the photo. I place plastic strips between the batteries to ensure that air can flow around them.
 
pvb said:
Why do you think the batteries are too hot?
Click to expand...

If you want to replace the 400Ah you have used (because no charging sources have been available) even with an intelligent charger the batteries will get warm. The warmer they are the longer it takes to charge them as the temp compensation reduces the charger's output.
 
To William

Thanks for the info. I'm referring to my 645Ah bank which with a 70% DoD will need lengthy high amperage replenishing. Whilst my last battery bank was 7 yrs old and with the increased resistance that comes with age (thats the batts not me!) they did get too warm on occassions despite have temp compensated charging. I may be wrong but I think its difficult to replace 400+ Ah without the batts getting (too) warm.

If I feel fans are necessary, as you suggest I would like to use a VSR type set up that switches the fans on at 13+v. Not being an electronics expert can you suggest a low power consumption switch please? Happy to source components and make it myself but designing it is beyond me. Thanks
 
vyv_cox said:
My batteries are in a moulded box surrounded by insulating foam on five sides and a cushion on the top. They often got quite warm after long motoring trips and we have suffered them boiling on a couple of occasions over the years. So I added a small fan that comes on when motoring. It blows air in, which vents out through a few holes drilled into the engine compartment. You can just see them in the photo. I place plastic strips between the batteries to ensure that air can flow around them.
Click to expand...

Vyv
Thanks for the picture and info. it looks a good setup. Can I ask why the "insulating foam on 5 sides" is it to secure the batts in place or isolate from outside ambient temps?
I can see why you went for the 120mm? fan in that location. Can I ask; is the fan a 12v computer type and does the airflow reach the exhaust holes at the back side?

edit:
Just zoomed in to the pic and can't see the foam you refer to, I presume its in the FRP structure.

Thanks
 
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Dave100456 said:
Vyv
Thanks for the picture and info. it looks a good setup. Can I ask why the "insulating foam on 5 sides" is it to secure the batts in place or isolate from outside ambient temps?
I can see why you went for the 120mm? fan in that location. Can I ask; is the fan a 12v computer type and does the airflow reach the exhaust holes at the back side?
Thanks
Click to expand...
The boat is a Sadler 34. The foam is a build feature for flotation purposes.
The fan is a computer type although I bought it in a chandlery. Airflow definitely extends right through to the engine compartment.
 
Dave100456 said:
If you want to replace the 400Ah you have used (because no charging sources have been available) even with an intelligent charger the batteries will get warm. The warmer they are the longer it takes to charge them as the temp compensation reduces the charger's output.
Click to expand...

The temperature compensation will slightly reduce the charge voltage, but at the same time a warmer battery will accept charge more readily due to reduced internal resistance. The net result is probably about the same. Unless your batteries are getting very hot under charge, I wouldn't worry. In my old boat I had 660Ah in a domestic bank and the batteries never got hot.
 
If anyone is fitting fans near their batteries I hope they are the ' spark proof ' type; I believe bilge blowers usually are or certainly should be.

I don't have a cooling problem with my battery but did fit a vent tube; as it's hydrogen which is given off, the tube goes up to a ventilator which is open when at the mooring.

Incidentally I used to have a solar vent in the locker top above my ( petrol ) fuel locker; I went to some pains to interrogate the salesman at Earls Court that this day / night solar & nicad job ( not made any more ) was spark proof and was assured that was the case.

When it failed just out of guarantee I gave it to a very good electrician chum to see if he could fix it; he reckoned it was more like a spark generator and I'm lucky not to be typing this from orbit, so now I just have a closeable tannoy vent above the fuel.
 
pvb said:
The temperature compensation will slightly reduce the charge voltage, but at the same time a warmer battery will accept charge more readily due to reduced internal resistance. The net result is probably about the same. Unless your batteries are getting very hot under charge, I wouldn't worry. In my old boat I had 660Ah in a domestic bank and the batteries never got hot.
Click to expand...

As I am planning this system I am trying to design out any potential problems. Its good to know your batteries did not get hot. Can you tell me what DoD you took them down to and how many amps you saw when you charged them back up at?
 
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