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Author Topic: Generator Enclosure Heat  (Read 3834 times)
ArtGill
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« on: March 14, 2009, 07:25:39 PM »

I'm beginning to design and build my generator enclosure.  I'm planning to use a 110v AC fan to cool the enclosure and generator.  The radiator is external form the enclosure with it's own fan that is temperature controlled and 12v DC.  My concern is will the box get too hot when I shut the generator off and the fan goes off at the same time?  The generator is an Onan 7 KW marine that is water cooled 2 cylinder diesel. 

Art
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Art & Cheryll Gill
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Sean
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« Reply #1 on: March 14, 2009, 08:08:32 PM »

Art,

I, too, ruminated about this quite a bit.  Even going so far as to design a circuit that would allow the fans to continue to run, from the inverter, for some period of time after the generator shut down.

I am happy to say that I have not had to implement this circuit.  Yes, the temperature in the enclosure does go up somewhat after the genny shuts down.  But not so much that I worry about it.  After all, nothing is still spinning in there to be adversely affected by heat, at least not in moderation.

Bear in mind that, in most "normal" engine applications, the cooling fan is clutched to the crank -- when the engine stops, so does the cooling.  So it is only the genny head you are worried about, and, when static, it should be easily able to handle the extra heat load.

Hope this helps.

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« Reply #2 on: March 14, 2009, 08:27:07 PM »

For cooling my gen compartment (I too have a remote mounted radiator-which is a 12" squirrel cage blower with single inlet and belt driven with a 1/2hp 2spd totally enclosed fan cooled motor. I don't believe a 12v fan is going to move that kind of air.) I use an 8" bathroom ventilator rated at 250cfm from Graingers, since my compartment is next to the drivers seat like a front engine, and the air intake has the possibility of picking up water-hence the bathroom ventilator that can take moisture.  It works well.  If I run the gen during the day driving with the A/C on, then if I check into a campsite, I'll run the fans for about 15 minutes after switching to land line.  Otherwise, just turn it off-it won't hurt anything.  Good Luck, TomC
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« Reply #3 on: March 15, 2009, 12:26:53 AM »

When it comes time to shut down the generator, it has been my habit in the mobile applications that I have been involved with, to run the generator for a couple of minutes with the electrical loads shut down in order to take some heat out of the electric bits.

Nothing particularly scientific, more belt and suspenders, superstitious/spiritual. I feel good doing it.

Certainly won't be hurting anything letting it spin a bit with no load at the end of it's work day.

happy coaching!
buswarrior
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« Reply #4 on: March 15, 2009, 05:24:56 AM »

Our generator compartment (radiator is outside the compartment), is cooled by 3 bilge blower fans (240 CFM each). When running, the compartment is about 10-15 degrees above outside air temperature. When the generator is shut down, the compartment temperature increases about an additional 20 degrees before startingt to cool down. I had thought about adding a timer or thermostat to keep the compartment fans running for a while but have not done it yet.  Jack
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« Reply #5 on: March 15, 2009, 07:10:44 AM »

I've mentioned this before but I think it bears repeating.  For those of you using remote radiators with electric fans, I strongly suggest a sail switch in the radiator air stream to trigger an alarm or activate the shut down circuit. I would not depend on the generator over heat protection to do this.

Len
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« Reply #6 on: March 15, 2009, 07:22:13 AM »

I have a small 9 inch automotive fan inside my compartment with a toggle switch on the dash I run for a few minutes after shut down.Never could make a thermostat control work.    good luck
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« Reply #7 on: March 15, 2009, 08:24:09 AM »

Hi Art,

If your concern is about rising temps after the gen/fan shut down, you have a very viable concern. Especially with a highly insulated box around it.

Engines usually rise anywhere form 15 to 50 degs. after shut down. Why wouldn't you want to cool it down further?

A fairly simple "Delay on Brake" would keep the fan running for a period more. [2 to 5 mins would work] You mentioned the engine fan is 110v, I

could come up with a couple different ways to make that happen. One would be a small, inexpensive timer board that we use in the HVAC industry.

Second would be a thermister in contact with the engine that would brake current at  150 degs, "open on temp drop" "close on temp rise" These are

also available in our industry.

Hope this helps
Nick-
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Nick Badame Refrig/ACC
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« Reply #8 on: March 15, 2009, 08:40:59 AM »

Examples,

The following pics are 2 aquastats and 1 fan timer board.

Nick-
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« Reply #9 on: March 15, 2009, 08:54:35 AM »

When it comes time to shut down the generator, it has been my habit in the mobile applications that I have been involved with, to run the generator for a couple of minutes with the electrical loads shut down in order to take some heat out of the electric bits.

Is the pain of having to throw the main disconnect or turning everything off before shutting down the generator really worth it?  If the generator is going off the high draw items will be turned off, but your refrigerator along with a few smaller loads are likely to still run off the inverter.

Maybe the ideal answer would be to use all manual transfer switches.  My inverter has problems with the transfer relay getting welded shut since I don't turn everything off when power transfers from shore/generator to inverter power.  Turning off all power would be a major pain on warmish days when the A/C might not be needed all day so the generator is run two or three or more seperate times in single day.  ( I am not happy my transfer relay in the inverter is fried after less than five weeks of total use on the coach.)
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Ray D
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« Reply #10 on: March 15, 2009, 10:21:10 AM »

I vented the generator head directly to the outside so the hot air does not go into the generator box and it made a huge difference.

Ray D
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« Reply #11 on: March 15, 2009, 12:06:17 PM »

I think one of the most overlooked assets laying around is the radiator electric fans in the junk yards.  I have used a Datsun Pulsar fan for 18 years for ventilation and it hasn't skipped a beat.  Admittedly it runs at maybe 1/4 speed but still.  On full power they are very loud but that can be dealt with.  The things are very powerful, move a ton of air and so very cheap.  I intend to stay with Datsun(nissan) or Lexus as a brand. Grin Can't get off a winner.  The thermostat for control is in there also.  Trans cooler?  Engine oil?  Engine bay?  Gen compartment?  Full house vent? 

I think the Anti Peacenic has the best "op shutdown procedure".  Run it for 5 minutes at zero load before shutting it down gets my vote no matter what else you do.  That Datsun fan should stay on also for a while after shut down, as well.  Might want to consider making that vent fan a "gosinta" cause that is way quieter than having it exhaust.

2 cents,

John
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« Reply #12 on: March 15, 2009, 03:37:02 PM »

About the compartment temperature fan control.
You need a “Snap-Disc Control”. Fan control version is automatic reset switch type. You want a contact to open at 120°F and close at 140°F which is called “close on rise”.
Caution…Do not get the manual “reset” type.
Example…Grainger has them in the HVAC Control/Snap-Disc section for under $12.00. …item # 2E248. Mounting bracket is available. These are 1200 watt at 240v or 120v rating…however, for the low 12v@60amps or 24v@30amps to run a fan motor should be sufficient.


About the mounting location for Snap-Disc Control.
Mount it at about 3” below or on rectangular box’s cover plate to the compartment ceiling with insulation around it…at perpendicular angle over in-between the top of the engine and generator.

About wiring the Snap-Disc Control to the fan. Just cut the hot wire or positive wire in-between fan and fused power source and install the wire ends to the tabs. Suggested to use ½″ metal conduit & rectangular box with 1⅛″ hole in center of box’s cover plate to mount the Snap-Disc Control on it and for being inside of the high-heat engine compartment for safety. BTW…you can wired a red dash indicator lamp from the fan wire after the Snap Disc Control switch so you can know when it on.

The bottom-line is you only need the fan on whenever the compartment temperature reach at 140°F, it will turn on the fan until it cooled down to 120°F. There no need to hard wired the fan with the generator output. There is no need of a timer in the circuit.

Remember…car under-hood temperature is around 200°F + on a warm day. That was one of my technician projects at GM Tech Center. Which means...it OK to be around 200°F and with hose connected to the outside cooler intake air for combustion.

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ArtGill
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« Reply #13 on: March 15, 2009, 07:10:24 PM »

Thanks everyone for your comments.  I think I going to use 12v fans with the"fan switches", like the one used in furnaces, to turn the fans on at 140F and off at 120F.  I also like the suggestion to put an air flow sensors on the radiator fan.  If I wanted to put a high temp switch or alarm in the generator box, what temperature should I set for the alarm?  It was mentioned that under an auto hood will be 200F.

Again, thanks for all the help.
                                                 Art
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« Reply #14 on: March 15, 2009, 07:23:36 PM »

Art, not to be counterproductive but bear in mind that a switch designed for switching high voltage ac may fail to  work or have a short life on dc.  Switching a high current inductive load on dc will cause some switches to not open the circuit and some will have a short life because of arcing.  Using a relay controlled by the thermal switch will negate this.  May be insignificant, just a thought.  And by the  way Gerald is one of the best sources for info and help on the board.  I was recently researching some of the high current low voltage thermal circuit breakers and discovered a big blog on dc versus ac in regards to interrupting high current loads in dc circuits.  Just My thoughts disjointed as they are.  Regards, John
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