How to insulate batteries from heat in engine room

[SV__Grace]

Any ideas?

My house batteries are in a box next to the engine, not a great location, but it's a 1200 amh bank of heavy AGMs and the mass and weight would be really, really hard to locate elsewhere.

You might be interested that my electrician constructed the house battery box from a $20.00 Home Depot storage tote, encased on all 4 sides in a plywood enclosure that is bolted to the engine room floor. Inside the box the batteries are held in place by a wood frame that is bolted to the floor and sides. The whole thing is designed to withstand capsizing.

There is space inside the box for insulation, I could add insulation between the plastic box and wood enclosure, and I could add insulation on the outside of the box.

But what to use and would it make a difference?

Any CF experience or wisdom on protecting batteries from heat in the engine room?

[Stu Jackson]

I'm an hvac engineer. Insulation in that example will do absolutely nothing other than just delaying the time it takes for the heat gets to the batteries.


If you just use the engine for short periods of time, it may help.


But once you motor for more than an hour or so, there will be no advantage.

[sailingunity]

I have had the same thought and had planned to put a computer fan in the battery box with a air duct somewhere else in the boat. It would push cool air into the box and be tied to the blower fan on the motor.

[SV__Grace]

Thanks Stu, I appreciate hearing from an HVAC engineer!

I have one possible trick up my sleeve that I might use if you think it would make a difference- directly above the battery box is an old exhaust fan ducted to outside. It seems to move a lot of air.

If I were to run that exhaust fan (or someone were to install one if they didn't have on) while motoring, or even install a duct from the fan to the battery box (assuming I create an intake vent someplace cooler, such as the floor area underneath which is the hull) do you think that would that make enough difference to be worthwhile?

[a64pilot]

I disagree, insulation will help, how much depends on how much insulation.
Heat really kills batteries, I believe 10 degrees F above 77f, will reduce battery life by 50%.
Eventually of course given enough time and the batteries will reach the engine room temp, just like the inside of an ice box will, but insulation will slow the ice from melting and the heat gain.

[rslifkin]

What about adding a heat extraction blower in the engine room to keep temperature down in the general space? You could duct it so that the incoming replacement air gets pulled through the battery box, keeping that coolest. Or insulate the box and ventilate it to the outside to avoid heat buildup in there.

[guyrj33]

You could loop your raw water intake around the battery box and actively cool the batteries.

[PeteG1943]

I have 4 6v gel cell batteries in house bank (360 ah @12 volts, two on either side and just forward of the engine and one 12v 125 ah gel cell starting battery next to engine. I typically get 10+ years of battery life from this arrangement. I did not know that engine heat good be a problem. I am thinking I should reinstall the engine room blower for additional cooling. I would like to hear opinions.

[tarian]

Fit a bilge blower to pull the hot air out of the engine allowing fresh cool air to be sucked in via the engine vents if you have any
But getting rid of the hot air is the issue here, 900 amps in my engine room and have seen no detrimental effects in my batteries 3 years now lead acid. I have vents and air blower batteries contained in fiberglass boxes moulded into the hull

[Cheechako]

Nah, dont insulate those. It's minimal, you might even end up keeping the battery heat in!
If you really want improvement put a bigger fan that extracts hot air from the engine compartment, or an extra fan. Or multiple ducting that extracts with the chimney effect. It's amazing how much flow there is with 6 feet of height differential...

[CarlF]

I’d use a computer fan to blow air into the box from a hose led to an interior space outside the engine room (like the forward bilge). It takes very little fresh air to avoid heat buildup in a box like that. If necessary, cut a small hose in the box to let air out.

While you’re at it, add a few fans to exhaust from the engine space.

This will cool the boat off much quicker after a day of running making the cabin cooler in the evening

Leave the fans on 24/7. It will reduce odors and mildew throughout the boat.

I’ve had two Noctua fans on full time since I bought the boat six years ago - exhausting from the engine space. These are from an Austrian company and very high quality. Draws 0.96 watt and almost silent - 16DBA six year warranty.

https://www.amazon.com/Noctua-NF-A14...WXK1T94T1M1YPA

[mvmojo]

I'd recommend pulling cooler air from a bilge or cabin and blowing it across the batteries then into the engine space. Diesels like a lot of air and like for the intake air to be within 30 degrees of ambient if possible. Pulling air from the engine room out will help but the air flow will be diffuse over the batteries. Pumping air directly to the batteries will have the most impact. And, I agree, don't insulate. It won't help keep heat out for very long but may hinder getting rid of heat in the battery box. If you can't duct air to the batteries, if possible consider opening the battery box while underway to allow heat to rise from the box to the surrounding space.

[Cadence]

Insulation is pissing up wind. Evacuate the heat.

[Captain Bligh]

My engine is uses a lot of air as it has a turbo . My engine room only gets hot after i shut the engine off. If yours is similar, maybe insulation will work or a fan to evacuate air after you shut the engine off?

[StoneCrab]

I have a similar configuration and blowing air does not get the job done...
Plus engine room blowers are very loud and inefficient.

I plan on water cooling the batteries by making up battery boxes with pex tubing surrounding the batteries. It will not be hard to pump water through the tubes, keeping the batteries at lake or ocean temperature without the noise.