Battery ventilation fan

[Relax]

I have fitted a little computer cooling fan (draws 0.07A) to vent the battery compartment - 3 x 110Ahr house + 1 x 75Ahr start with a motorised VSR.

The thing is - what do I wire this to to control it? Don't really want either have to switch it on and off and at the same time it doesn't need to be on all the time.

Any bright ideas?

 

[Shibumi]

What is your primary motive for fitting the fan.

Is it to cool the batteries or to vent hydrogen when equalising etc?

Steve

 

[sarabande]

assuming that the purpose of the fan is to extract any nasty gases, I do hope that you have fitted a 'safety' fan, and not one that has little sparks around the internals when starting and running. And where is it venting to ? Atmosphere, or the cabin ?

Provided the battery box is not sealed, hydrogen opts for the quickest route to the heavens. If you know that your batts are gassing out, then the charge routine / system is incorrect.

Sorry. Good idea, but probably creating more risk than existed previously.

 

[vyv_cox]

I have fitted a little computer cooling fan (draws 0.07A) to vent the battery compartment - 3 x 110Ahr house + 1 x 75Ahr start with a motorised VSR.

The thing is - what do I wire this to to control it? Don't really want either have to switch it on and off and at the same time it doesn't need to be on all the time.

Any bright ideas?

Here's a pic of mine. I bought it in a chandlery but I doubt if it is anything more than a computer fan. The main aim of fitting it was cooling, as the box surrounding it is foam filled, bunk cushions on top, so batteries tend to get hot. It blows air into the compartment, discharge is via the row of one inch holes visible aft, into the engine compartment.

The intention is that it only runs with the engine so I wired it to a connection in the ignition switch that becomes live with the switch on.

It has been there a long time now, no problems at all and definitely helps with the cooling.

 

[prv]

If you know that your batts are gassing out, then the charge routine / system is incorrect.

Not necessarily. Charging quickly, accepting some gassing, and replacing the water as part of normal maintenance, is a perfectly valid way to treat proper deep-cycle batteries. It's in the instructions for Rolls traction batteries.

I agree that if you're expecting enough hydrogen to need a fan, a fan that generates sparks isn't a very sensible choice.

Pete

 

[Relax]

The fan is a tiny brushless computer cooling fan - purely to vent gases.

I do have other charging sources - 130W solar panels and a windgen (Aerogen4) - but the applied charge is obviously going to be greater through the engine - good idea thanks Vyv - easily solved.

I should say that several times with the previous system (Sterling) the smell of the batteries gassing (difficult to define - shades of gooseberry, hints of gear oil....) was obvious on opening the battery box. The water consumption was also significant. Gone now with the VSR, although I suspect the batteries are never as fully charged - but hey I've never run out of leccy.

 

[BlueChip]

The batteries presumably will only be gassing when they are charging, so why not fit a voltage sensitive switch that will turn the fan on when the battery voltage reaches a charging voltage - 13V?
In your shoes I think I would seal the battery boxes and vent them overboard, then use the fan to circulate air around the boxes. Alternatively vent the batteries overboard and install a positive pressure fan to blow air into the battery box.

 

[Malabarista]

The batteries presumably will only be gassing when they are charging, so why not fit a voltage sensitive switch that will turn the fan on when the battery voltage reaches a charging voltage - 13V?
In your shoes I think I would seal the battery boxes and vent them overboard, then use the fan to circulate air around the boxes. Alternatively vent the batteries overboard and install a positive pressure fan to blow air into the battery box.

Thank you very much from the future. Answered my conundrum very nicely ta
Dave

 

[halcyon]

Thank you very much from the future. Answered my conundrum very nicely ta
Dave

Back in the 80's the mains battery charger I made had a control to operate a fan, when the charger was on high charge, your the first person that's required that function, just did not wait long enough

Brian

 

[Seajet]

Presumably what's really required is a mobo engine compartment ' bilge blower ' - I'd ask on the mobo section.

Years ago I bought a for the time quite pricey solar day / night extractor fan with nicad for night, to go above the remote petrol tank in my boat - the salesman swore blind it was ' spark safe ' - I made a point of asking.

Within a year the bearing / spindle wore making a horrible noise then the thing failed - the suppliers were of course bust by then so I gave it to my chum who's an ace electrician to see if he could fix it - he came back to me " spark safe ? This thing's more like a spark generator ! "

So I'm lucky not to be in orbit.

 

[Malabarista]

Back in the 80's the mains battery charger I made had a control to operate a fan, when the charger was on high charge, your the first person that's required that function, just did not wait long enough

Brian

I am wanting to ‘assist’ the passive ventilation i am just installing as it’s a fairly large installation of lead acid with multiple charging sources. The spare output on an AC charger would be handy if there was also one on the mppt controllers and the alternator ( maybe someone clever can juggle with a vsr ?)

 

[halcyon]

I am wanting to ‘assist’ the passive ventilation i am just installing as it’s a fairly large installation of lead acid with multiple charging sources. The spare output on an AC charger would be handy if there was also one on the mppt controllers and the alternator ( maybe someone clever can juggle with a vsr ?)

Just a matter of setting one channel on a multi-bank VSR to run a fan on high charge voltage, and drop out on float voltage. Or base it on charge current, high current turn fan on, low current turn fan off.

Brian

 

[simonfraser]

0.07A = that's 12Ah a week
if you solar / mains charger can't handle that you'll likely run out of charge when you do use the boat, so why even put a switch in it ?
KISS leave it on ?

 

[thinwater]

The flammable limits of hydrogen are 4-75%. This is MUCH broader than gasoline, for example. Adding an ignition source in a battery box (or in the hose--same thing) is a Darwin award act. There is also the corrosive of H2SO4 to consider, the most probable reason the fans didn't last long.

Hydrogen dissipates very rapidly due to very low density. If you have any reasonable ventilation, you're chasing a red herring. Remove the fan.

 

[Paulg25]

Computer fans are brushless so no brushes to cause sparks.

 

[William_H]

I would suggest simply wiring the fan to the "ignition switch circuit of the engine. The small current draw will not matter whne starting the engine. However if you want it to ventilate when using a mains charger as well then you need a VSR on the batteries to switch the fan on when charge voltage rises. However VSR may consume some power possibly comparable to the small fan even when not actuated so not such a good idea to leave on battery full time. (check VSR current) Much depends on current capability of the mains charger. I would suggest fit the fan as an input ie pressurising the box with outlet over board. Or use diode isolation of the fan supply from either engine ignition or a switch for use on mains charger.