[MarkofSeaLife]

No fumes. Totally sealed batteries. Its the temperature I'm trying to keep down.

 

[AWT2_Sail]

Sucking or blowing is really in the eyes of the beerholder, ehem, beholder, no? I miss Megamaid. I really do.
A fan sucking air out of the battery box and ducting it away and outside seems best.
If it's just heat inside the box, you might get away with a passive convection set up that draws cool air in through a bottom vent (from the bilge?) and up through a top vent into a lazarrete.

 

[MastUndSchotbruch]

Agreed. Muffin fans are not appropriate for ducted applications at all!

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For all types of fans: Is ignition protection an issue? Maybe not for Mark's sealed batteries, but flooded lead-acid batteries generated hydrogen gas.

 

[oldmanmirage]

No fumes. Totally sealed batteries. Its the temperature I'm trying to keep down.

In that case I definitely think you want to suck the hot air out and let cool air in.

 

[dcmeigs]

Mark, you know how pumps hate restrictions on the suction? Cavitation right? Fans are the opposite. They are built to have an unrestricted discharge. The current requirements for fans are based on density times volume. With a restricted inlet, density drops and volume goes close to zero; current falls close to zero also. With a restricted discharge, density goes up and volume remain close to the rating because pressure increases causing leaks. Current increases. This is why furnaces have the filters before the blower. You want to suck the air out.

 

[vbiz59]

Definitely out... but geeze,, I have the same situation. I guess it wasn't a thing 37yrs ago ;/
Though it should have been even more obvious with old battery technology.

 

[Nico-Zeil]

If you are ventilating due to potential fumes such as batteries gassing or engine compartment odors then you want to maintain that compartment at a negative pressure. If you blow into it and create a positive pressure you will force those fumes and odors to migrate throughout the boat.

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I am going with ShockT on this. Although heat is a concern, the hydrogen gas is explosive, so negative pressure. /Nick

If you are ventilating due to potential fumes such as batteries gassing or engine compartment odors then you want to maintain that compartment at a negative pressure. If you blow into it and create a positive pressure you will force those fumes and odors to migrate throughout the boat.

Sent from my SM-G981W using Tapatalk

I am going with ShockT on this. Although heat is a concern, the hydrogen gas is explosive, so negative pressure. /Nick

If you are ventilating due to potential fumes such as batteries gassing or engine compartment odors then you want to maintain that compartment at a negative pressure. If you blow into it and create a positive pressure you will force those fumes and odors to migrate throughout the boat.

Sent from my SM-G981W using Tapatalk

I am going with ShockT on this. Although heat is a concern, the hydrogen gas is explosive, so negative pressure. /Nick

 

[MarkofSeaLife]

Im in the tropics this summer. In the hurricane season theres not much in the trade wiinds. So the aft cabin doesnt get much cooling. Cooler batteries are much more efficient. Thats whey theres a batter temperature sensor to change the charging voltage. I think in Grenada they could lownly heat over a few weeks and be quite hot, soooo its just to have some air movement in a small space. Just knocking those top few degrees down might be well worth it.



Mark

 

[rdwentsailing]

I probably shouldn't be on a forum this early in the morning. The only thing I thought of reading this was this and I feel bad about myself, a little.

View attachment 147001​

I am curious about the opinions to the question. Seems like most engine areas on sailboats have a large hose which is attached to a blower, the intent to suck the hot air out and full in fresh air from anywhere there is an opening/egress.

 

[rdwentsailing]

 

[SanderO]

Im in the tropics this summer. In the hurricane season theres not much in the trade wiinds. So the aft cabin doesnt get much cooling. Cooler batteries are much more efficient. Thats whey theres a batter temperature sensor to change the charging voltage. I think in Grenada they could lownly heat over a few weeks and be quite hot, soooo its just to have some air movement in a small space. Just knocking those top few degrees down might be well worth it.



Mark

Even in summer my battery compartment and the bilges are pretty cool... probably because the water temp is much cooler than the air temp.

 

[LouK]

Faced with the same dilemma will be installing a computer fan on a timer exhausting into the lazarette,

 

[Barquito]

Engine ventilation fans are usually at the terminal end of the hose. However, I suspect that this is only for the practical reason that you wouldn't want a fan down in the bilge under the engine.

 

[SanderO]

My batts are sealed but I suppose they do produce some gas. It is exhausted into the bilge with a small fan via a 3" diameter hole. There are multiple large diameter holes at the top of the batter box for passing wires/cables and.... gases. As the boat has adequate ventilation I am not concerned about noxious gas. I have a gas sensor / alarm as well.

 

[willywaw]

Depends on boat architecture. My batts sit aft of the engine... above the bilge... I exhaust into the bilge. I have a bilge blower which exhaust bilge air.

And, I'd be willing to bet you don't run that Bilge B enough to keep hydrogen gasses out of your bilge.

 

[colemj]

Hydrogen will leave the bilge almost instantly without any blower at all.

 

[MarkofSeaLife]

Leaves the bilge quicker if you drop in a match.

😂😂😂

 

[SanderO]

You'd lose the bet.

 

[pdqaltair]

a. Unless you tell us how much heat you want to remove (BTU/hr) it is a trick question. Assuming you are charging a single battery at 30 amps, with typical resistance (30mOhm), the heating during charging is only a few BTUs. You can Google this. Batteries don't really heat when charging at a moderate rate, only when they are failing and resistance is high, and that number can aproach the power output of the charger (if 30 amp, as much as 500-700 BTUs, or 300 times more than normal charging) is possible. Natural movement of air should be pleanty for normal charging. Have you observed that the batteries are hotter than the surrounding area when charging (measure with IR thermo)? To remove 600 BTU, then about 50 cfm could required to maintain a 10F rise (check my math), which is a lot, which is why failed batteries can really cook. A smart charger with a temperature sensor will shut down.

If it is the sun beating on the side of the boat that is a different calculation.

b. No, the fan cannot tell push vs. pull unless the pressure is reduce dramatically (at least a few PSI) on the suction side. Comparing this with pump cavitation is a false comparison. For the purposes of this exercise air is an in compressible fluid, like water. More important is whether the fan is rated for the temperature and contaminants in the air stream, and whether the fan is rated for the pressure drop (most non-duct fans assume free air on both sides).

----

So I think the answers are:

• Normal charging. Forget about it if there are some openings.
• Run-away charging of shorted batteries. Only a temperature cut off is going to save them from cooking.