Keeping blower turning when engine turned off

[Vicarage]

Ahoy
At the moment we've got a snail cam blower for the engine outlet ventilation. It comes on with the ignition first position and stays on whilst the engine is running. When the engine is turned off it goes off as soon as you turn the ignition off.
I'm keen to try and get it set up to stay running for 5/10 minutes after the ignition goes off - to pull the heat and fumes etc. Does the committee have any bright ideas of a way of cheaply and easily doing this?

The current setup is wired directly to the ignition barrel, with no wires to the battery or anything, and no desire to run miles of wiring. I'm wondering whether there's some way of installing a tiny inline battery that is charged as the ignition is on, and then kicks in when the ignition goes off to continue running the fan for a few minutes.

I'm certainly not competent to make such a device but I'm wondering if something similar exists already - I'm sure it must.
Thanks

 

[peteK]

Plenty of 12v delay timers on ebay.

 

[Vicarage]

Plenty of 12v delay timers on ebay.

It would need power as well though, once the ignition is off then the power is off

 

[Daverw]

+1 for12v delay off timer, you will have a supply to the panel already, Thame that to the timer then the ignition supply you already have to the timer, when you then turn off switch the timer will hold supply to the fan for the set period. Very commonly used in process equipment control panels. Make sure it’s delay off not delay on, multi function available but can take some working out and setting up.

this an option

CAR DRL LED DELAY TURN OFF TIMER SWITCH 3 TO 750s 12V 1A BOX POSITIVE ACTIVATING | eBay

 

[[159032]]

I'm certainly not competent to make such a device but I'm wondering if something similar exists already - I'm sure it must.
Thanks

Will a 1 amp one be sufficient?

Something like this? DC 12V Trigger Delay turn off / turn on Switch Timer Relay Module High Power 30A | eBay
I'm not an expert either, but it's cheap enough. Probably need an enclosure.

More expensive, but all the hard work done 12V, 10A Adjustable Delay Timer Relay (Delay ON or OFF)

Search for "12v timer delay relay"

 

[Slowboat35]

How much difference would it make - running for just 10 minutes?
There shouldn't be any fumes in the engine bay anyway - if there are there's a serious underlying problem that needs attention, plus a great clod of cast iron doesn't cool by any appreciable degree in just 10 minutes so the residual heat will not be significantly different. Run it for an hour - maybe you'd see a little effect. But still not a great deal, I suspect.

 

[Spirit (of Glenans)]

Clean the engine with degreaser, clean up any spills from filter changes etc, then there shouldn't be any fumes.
If there is still evidence of fumes, (a) check your exhaust for leaks, (b) check for back pressure in your crankcase by removing the oil filler cap and pressing the palm of your hand down on the opening. (If you drove bangers in your youth you'll know what I mean). If there is back pressure you've got a problem with bore wear or broken rings or perhaps a head gasket, which will present further symptoms .

 

[William_H]

I would reckon a temperature controlled switch wired directly to the battery power. This will delay turn on until after engine start (more power for starter) and continue until temp has gone down in compartment. XH-W3001 Digital Control Temperature Microcomputer Thermostat Switch 12V/120W | eBay might suit.
On the other hand if it is a petrol engine you should run blower for a period before starting engine to clear potential petrol fumes. So would need an over ride switch and flame proof blower.
ol'will

 

[Catalina36]

It would need power as well though, once the ignition is off then the power is off

So run it through a 30amp relay, a fiver in a car electrics shop. RS do 12v timers which can be configured in various ways. You need a timer which carries on running for a set time after the original supply to the fan is turned off, like an extractor fan in a loo. Other formats run for a set time after it's turned on, then turn if off (runback timer, like a wall heater) which is not what you want.

Another option is just to rig a manual switch in parallel so you simply keep the fan running for as long as you like independently of the ignition. I have two fans, one blowing cold air directly on to the alternator and its belt and running on the ignition so always on when the engine runs, the other drawing hot air from the top of the engine bay adjacent to the exhaust to remove heat and any possible exhaust leak and blow it out of a stern vent. That one's on a manual switch and I only put in on for prolonged hard running, but it could equally be wired via the ignition.

 

[Skylark]

Another vote for solving the cause, not its affect. The fan shouldn’t need to over-run. Find the cause of the fumes and smell. It could be early symptoms of a bigger problem.

 

[prv]

I’m a little curious what the fan is supposed to be doing in the first place. There’s already a 30hp air pump sucking in air from the compartment and throwing it outside; how much extra flow does the electric fan add?

Agree with others about fumes - fuel or exhaust leaks need fixing, not covering up, and what else is in there making fumes?

Pete

 

[pvb]

I’m a little curious what the fan is supposed to be doing in the first place. There’s already a 30hp air pump sucking in air from the compartment and throwing it outside; how much extra flow does the electric fan add?

Agree with others about fumes - fuel or exhaust leaks need fixing, not covering up, and what else is in there making fumes?

In sailboats, the fan is often fitted to reduce engine compartment temperature. My Bavaria came with one, a Rule 4" inline blower which incidentally is a 24v version, presumably to reduce noise.

 

[Paulg25]

Turbo timer for cars.

 

[NormanS]

I can see some logic in running an extraction fan, both before and after engine use, but I can't see any point in it when the engine is running. The engine will already by sucking out huge quantities of air.

 

[coopec]

I’m a little curious what the fan is supposed to be doing in the first place. There’s already a 30hp air pump sucking in air from the compartment and throwing it outside; how much extra flow does the electric fan add?

Agree with others about fumes - fuel or exhaust leaks need fixing, not covering up, and what else is in there making fumes?

Pete

Well I have a squirrel cage blower blowing air into the engine room as the motor will use 125 cu ft of air per minute. (I think my calculations are correct. 4.108 Perkins 108 cu inch X 2000 RPM = 216000 cu in = 125 cu ft. Forget volumetric efficiency)

I certainly don't want my motor to be trying to suck hot air into the motor. The motor cannot suck air from the bilges as I have deliberately closed them off to stop the engine room being flooded in the event of a disaster. (keep the pumps going as long as I can). And the engine room is fully enclosed.

Engine Room Ventilation
Engine Room Ventilation for Cat® engines
This guide addresses engine room ventilation considerations that apply to the successful installation, operation and maintenance of Catengines, generator sets, compressor units, and other packaged units.The primary aspects of a properly designed engine room ventilation system are cooling air and combustion air. Cooling air refers to the flow of air that removes radiant heat from the engine, generator, other driven equipment and other engine room components. Combustion air describes the air the engine requires to burn fuel.Cooling and combustion air directly impact engine and package unit performance and dependable service life; these must be considered in the design of an engine room ventilation system. It is also important to consider all engine room equipment in the design of a ventilation system and provide a comfortable environment for service personnel to perform maintenance.

https://s7d2.scene7.com/is/content/Caterpillar/CM20160713-53120-44971

 

[NormanS]

There is nothing to prevent the air being used for combustion in the engine, being used for cooling beforehand. It is good practice for air to be drawn into the engine room, as far away from the engine intake as practicable.

 

[PCUK]

Disconnect from ignition and wire through a separate switch. Full control whenever you want it!

 

[pvb]

Well I have a squirrel cage blower blowing air into the engine room as the motor will use 125 cu ft of air per minute. (I think my calculations are correct. 4.108 Perkins 108 cu inch X 2000 RPM = 216000 cu in = 125 cu ft. Forget volumetric efficiency)

I certainly don't want my motor to be trying to suck hot air into the motor. The motor cannot suck air from the bilges as I have deliberately closed them off to stop the engine room being flooded in the event of a disaster. (keep the pumps going as long as I can). And the engine room is fully enclosed.

You'll have more than enough air! The engine will use half as much air as you think, because it's a 4-stroke cycle.

 

[lw395]

The residual heat from the engine keeps the boat warm and dry. It shouldn't smell (at least no worse than the rest of most boats.....).
Maybe sailing in a warmer climate you don't want that heat.

 

[Spirit (of Glenans)]

Turbo timer for cars.

That's an optional extra, (at least for Isuzu D-Max), which will allow the engine to run for a time at tickover, after you have switched off and got out, so as to allow a hot turbo to cool down to normal engine temperature, after you have been driving hard on turbo, not what the OP requires.