Greetings Everybody,

Please imagine a small watercooled motor confined in non-ventilated enclosure (it is noisy). It has its own 12V alternator and a led acid battery. I turn it on and off manually, as needed.
The motor overheats the enclosure space causing premature decomposition of rubber hoses and plastic components within the enclosure.
I would like to add a bank of 12v (20A max total draw) cooling fans to the side wall of the enclosure to push in some cold air.
I don't need fans going until the motor comes up to the temperature. I think about fitting a thermal switch into the motor water jacket to activate the fan circuit.
(1) Upon turning the motor "off", I'd like the fans to stay "on" for 3-5 minutes during the motor heat soak cycle.

So far, so good, pretty straight-forward.
Here is the rest of the story...

Let's assume that I run the unit for a while and shut it off. After 5 minutes fans are turned off by the timer. Cool...
Than, I may decide to turn it on, again. At this point of time the motor is still hot and the thermal switch in the waterjacket is "hot". Fans will create an instant excessive load in the alternator circuit and will burn the voltage regulator.
Not pretty.
So, to avoid this calamity, the delay timer, in addition to function (1), has to have an additional function built in.
(2) It needs to detect if the thermocouple circuit is "on" and delay turning fans by 1 minute allowing the alternator to come up to the normal working parameters.
The rest is the same... After I turn the contraption off, fans stay "on" for 5 minutes and shut off.

The first part (1) is not that complicated, but (2) needs some kind of a logic function switch.

Input 1 (thermo couple switch)
1a on/ motor hot, than-activate 1min delay and turn fans ON
1b off/ motor cold, than- turn fans ON

Input 2 (main powr switch(+12v) )
2a if on (+12v), than- keep fans circuit ON
2b if off (0v) , than -activate 5min delay and turn fansOFF

 

(2) It needs to detect if the thermocouple circuit is "on" and delay turning fans by 1 minute allowing the alternator to come up to the normal working parameters.

Couldn't you draw the fan current from the battery? Then it wouldn't matter if they run instantly when you turn on your system.

 

1b off/ motor cold, than- turn fans ON

Is this supposed to mean OFF? And does that mean, that as long as the main power switch is ON the thermo switch will immediately turn off the fan when open? without the 5min delay?

 

You have to 'turn on' some type of switch to get the motor to start right?

The switch can be your control logic input for a timer. After the fans have stopped 5 min. after engine shutdown. The timer logic will be waiting for you to turn on the engine. That on signal will initiate the countdown, which must complete before the fans can come on. At the point where the countdown completes, the thermistor input can be consulted and used to determine actual start time for the fans. If the engine is already warm the fans will start then, if the engine is cold the fans will wait for the thermistor to give the signal then start.

 

why dont you try starting the fans along with the motor, so that you dont need to get the motor 'heated up' to cool it down? So the motor will stay at a lesser temperature and you might not need running the fans after the motor is switched off..

 

I don't need fans going until the motor comes up to the temperature.
...
(2) It needs to detect if the thermocouple circuit is "on" and delay turning fans by 1 minute allowing the alternator to come up to the normal working parameters.

If the requirements for "hot" and "cold" are the same, why not just add a fixed one minute timer? no need for logic detect if it's already "hot" - just go ahead and delay a minute anyways - wouldn't hurt anything from what I read; even if it were cool.

 

Input 1 (thermo couple switch)
1a on/ motor hot, than-activate 1min delay and turn fans ON
1b off/ motor cold, than- turn fans ON

Input 2 (main powr switch(+12v) )
2a if on (+12v), than- keep fans circuit ON
2b if off (0v) , than -activate 5min delay and turn fansOFF

Can we rewrite this? (just to make it clearer )

1. turn main switch ON
1.1 if thermo switch is ON then delay fans for a minute
1.1 if thermo switch is OFF then do nothing

2. turn main switch OFF
2.1. if thermo switch was ON (and fans where running) then keep them running for 5min

3. main switch is ON and temperature activates the thermo switch: fan turns on
3.1 main switch is ON and temperature deactivates the thermo switch: fan turns OFF (or is there also a 5min delay?)

However there is a case that's not covered, but maybe it doesn't need to. You could turn on the main switch with the thermo switch ON for 50seconds, turn it off for 5 seconds turn it on again for 50 sec and so on...the fan would never turn ON...

 

If the requirements for "hot" and "cold" are the same, why not just add a fixed one minute timer? no need for logic detect if it's already "hot" - just go ahead and delay a minute anyways - wouldn't hurt anything from what I read; even if it were cool.

OK, that makes sense, adding a 1 minute delay timer in series w/thermistor would work in both conditions, motor warm or cool.

So it looks like I need two timers:
First timer sensing main "power On" (input +12V) and turning fans ON after 1 minute. I may use a Turn-on Delay, Loudspeaker Protection Module.
Or... even better: hook up an Intellitec Isolator Relay Delay 00-00629-120 RV

Second timer, armed when main switch is turned ON and first timer is ON and starting 5 min count down when the main switch is turned OFF. For this purpose, I can probably use one of the interior lights delay relays off the older car (I love my local junkyard).

I Usually they are 1 minute delay, but they can be modified. The car lights relay is activated by the door switch when one opens the door, stays on as long as the door is open (+12v is ON trough the switch) and starts the count down as soon as the door closes (the door switch turns +12v off)

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OK, that makes sense, adding a 1 minute delay timer in series w/thermistor would work in both conditions, motor warm or cool.

So it looks like I need two timers:
First timer sensing main "power On" (input +12V) and turning fans ON after 1 minute.

Second timer, armed when main switch is turned ON and first timer is ON and starting 5 min count down when the main switch is turned OFF

Assuming your power goes through the switch then to the first ONtimer, If the first timer is ON, then that that means that the main switch IS ON. no need to add the switch to the logic.

so all I see the need for here is 1 ONdelay timer set for 1 min and 1 OFFdelay timer set for 5min. no need for microcontroller or exciting circuitry. K.I.S.S.

 

For this purpose, I can probably use one of the interior lights delay relays off the older car (I love my local junkyard), or a Turn-on Delay, Loudspeaker Protection Module. Usually they are 1 minute delay, but they can be modified. The car lights relay is activated by the door switch when one opens the door, stays on as long as the door is open (+12v is ON trough the switch) and starts the count down as soon as the door closes (the door switch turns +12v off)
???

Sorry for the cross-post. I started to reply, then got called away and came back some time later to finish, after your edit. You may be able to make the door switch work but remember the door switch is just for lamp. A motor may excede the amp rating of it.

 

Thank you for all the support.
I will fit 12v/40A relay(s) into the fan(s) power supply.

In search for suitable timers, I found this 40A Turn-on Delay, Loudspeaker Protection Module, which may work as a hot re-start delay timer(function #2).

Here is a translation (probably from chinese) which comes with the unit:
[...]
This speaker protection module runs on 12V-CT-12V AC, 0-24V AC or 12V DC. 12V DC power supply regulator and 2x 40A relay included.
If your OCL amp doesn't have a protection circuit, you could potentially fry your speakers, unless you use something like this module.
Each module can handle up to 2x 800W ouput of your power amplifier DIY (2 channel). The module is used to turn on delay and to protect your expensive speaker system from amplifier damage. This module is installed between PA and speaker system. [...]

Is anyone familiar with how this board works? How to adapt this unit to my requirements? Can I add two relays at the output to handle fans power supply circuit? I'm sure the delay is not greater than 3-5 sec, but it could be sorted out later. My fans are 80W a piece, 4x80=320W.
Hmmm...
Looks promissing...
What say you?
Similar module diagram, here Datasheet: Connection diagram of the 2-channel loudspeaker protection for mono-bridged connections