Just when I thought my generator was sufficient (& how to get rid of hot air in the truck)

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paulnye
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2019/07/08 19:06:07 (permalink)

Just when I thought my generator was sufficient (& how to get rid of hot air in the truck)

So I measured all my appliances using a watt meter. I was using 1200-1400 after testing for 1-2 hrs straight. I just bought a 13500 btu Dometic rooftop AC unit which should draw 1450 watts. I tested it before install and it drew around 1430-1500 when the compressor was on. On my next event in the truck, the power started to flicker a bit. My Preditor 3000 signalled that it was overloaded a bit (it can peak at 3500 watts). But the AC kinda stopped working, as if there was a minor brown out and the compressor couldnt kick back in immediately. Next day I ran just one of my fridges and it ran 240 wats, but when I left the door open for 30 minutes it raised to 300 watts. Maybe both fridges do this when its 110 deg inside the truck and the door gets opened a lot.. which means my initial calculation of the power needs was too low as it didnt take into consideration the gradual higher power consumption over time when its hot.  Do appliances do this? .. keep increasing the draw over time? I thought it just ran at maximum, and not keep increasing. 
post edited by paulnye - 2019/07/25 09:38:23
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    edwmax
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    Re: Just when I thought my generator was sufficient 2019/07/09 07:43:42 (permalink)
    !)   You need to work in amperage (amps) not watts.    Amps is electrical current supply; while watts is power used.    watts / volts = amps  or    volts X amps = watts
     
    2)   List & total the amperage of ALL appliances that will or may be running at the same time.  Note some appliance have a 'start up' amperage (some do not), USE 'start-up' amps for the total instead of 'running amps' where listed.    Appliances that have a motor will have a 'start-up' amperage that is much greater than its running amperage.    Appliances like toaster oven, hair dryer, lights, hot water heater do not have  'start-up' amperage surge.  .... The gen-set must be able to supply this TOTAL amperage demand.
     
    3)   The gen-set should be size so the Total amp load is only about 50% to 60% of the gen set's output capacity.   This will allow for a little extra capacity and allow the gen set to run more efficiently.    It's not good for the gen to run wide open at max. capacity all the time.   ...  If appliances with large start-up amperage are tightly controlled, not allowed to start at the same time, the gen-set could run at 70% to 80% of its load.
     
    4) To answer your last question: "Do appliances do this? .. keep increasing the draw over time?"   .... YES,   when voltage output drops then the amperage draw INCREASES.   This could be due to improperly adjusted gen-set or an OVER LOADED gen-set.   ... But when the voltage is at the proper steady rate and amperage is increasing, the appliance is going bad and needs replacing/repair.    As well as running appliances on low-voltage from an over loaded gen-set will damage the appliance;  thus the need to insure adequate power supply by keeping the gen-set loading to 50% -60% of its total output.
     
    5) Your Preditor 3000 has a steady run rating of 25 amps (3000 watts/ 120 volts) with a surge peak of 29 amps (3500 watts / 120 volts).   You basically should not load it more than 25 amps X 90% = 22.5 amps   ...  Your total loading is likely between 30 to 50 amps (just my guess/estimate).    ... Yes, you can run the gen at its peak output but this take very close monitoring to insure the output voltage is correct and to prevent damaging your appliances and/or the gen-set.
     
     
    post edited by edwmax - 2019/07/09 07:53:27
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    edwmax
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    Re: Just when I thought my generator was sufficient 2019/07/09 08:15:14 (permalink)
    OH   ... the 13500 btu AC with a running load of 1450 watts (1450W/120v = 12 amp) as you stated would have a 'start-up' load of 2800W - 3000W or 25 amps.     This max out you gen-set capacity by itself.
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    Blakkmoon
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    Re: Just when I thought my generator was sufficient 2019/07/15 00:07:33 (permalink)
    Looks like you need another predator just for the a/c
     
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    paulnye
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    Re: Just when I thought my generator was sufficient 2019/07/15 16:58:34 (permalink)
    Edwmax,
    I did measure both Amps and watts. The Predator is rated at 27amps peaking at like 31amps
    Before buying the Dometic AC I spoke to one of their engineers who explained that the unit has a device inside which can lessen the startup load drastically. I measured it on startup and it was approx 25 amps then immediately back to 13amps.  It seems like the fridges can draw more power over time.  I became discouraged because I originally had a Firman 3000/3300 and loved it, but ended up buying the Predator 3000/3500 and when intially testing, it ran everything plus the AC fine for about an hour, but little did I know that after 3hrs (pretty much the end of the shift) it would get overloaded.
     
    Anyway, after doing more research and consideration, Im giving up on all the expense and effort to run AC since the temp only goes down from 110 to 105 since the extractor fans suck out a good amount of the cool air produced by the AC. They say the juice isnt worth the squeeze.
     
    It seems I should focus on extraction. I need powerful fans to extract the hot air from the ceiling and pull in cooler air from outside.  Something like this...
     

     
     
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    edwmax
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    Re: Just when I thought my generator was sufficient 2019/07/15 18:12:37 (permalink)
    paulnye
    Edwmax,
    I did measure both Amps and watts. The Predator is rated at 27amps peaking at like 31amps
    Before buying the Dometic AC I spoke to one of their engineers who explained that the unit has a device inside which can lessen the startup load drastically. I measured it on startup and it was approx 25 amps then immediately back to 13amps.  It seems like the fridges can draw more power over time.  I became discouraged because I originally had a Firman 3000/3300 and loved it, but ended up buying the Predator 3000/3500 and when intially testing, it ran everything plus the AC fine for about an hour, but little did I know that after 3hrs (pretty much the end of the shift) it would get overloaded.
     
    Anyway, after doing more research and consideration, Im giving up on all the expense and effort to run AC since the temp only goes down from 110 to 105 since the extractor fans suck out a good amount of the cool air produced by the AC. They say the juice isnt worth the squeeze.
     
    It seems I should focus on extraction. I need powerful fans to extract the hot air from the ceiling and pull in cooler air from outside.  Something like this...
     

     
     




    Yes exactly  ...   As the day goes on,  the frig doors are opened and closed so they are running more continuously to keep up; as the trailer heats up, the AC is no longer cycling but running contentiously;  all the appliances are running at the same time.     ... Thus the need for the gen set to be size 1.6 X's the total load.   ... !2 amp running & 25 amp starting is what I estimated the 13500 BTU Ac rating was.
     
    I agree the AC should be powered by a separate gen set or eliminated.       ...   Large exhaust fan in the exhaust hood would help by drawing air though the windows or door across work ares.   But be careful of other large exhaust fans as it will foul the air flow of the hood and draw hot air & smoke from the range into work areas.         ...   A swamp cooler could help to cool the outside air temp and give the makeup air needed by the exhaust fan.
    post edited by edwmax - 2019/07/15 18:15:52
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    paulnye
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    Re: Just when I thought my generator was sufficient 2019/07/16 12:27:49 (permalink)
     
    Edwmax,
    In my exhaust hood I have 2 of these 110v fans. Its the Fantech 2SHE1021 which claim to be up to 585 CFM @ 0 S.P.  They pull the fumes and hot air from the griddle. 
    https://smile.amazon.com/dp/B001TR3ZIW



     
    I also have a 3rd fan up front to pull fumes/air from a small crepe griddle..
     

     
     
    Should I just focus the extraction to the hood area? and replace the ones in the hood with twice the CFM ? Or even add a couple more inside the hood?
    Then I would have more exhaust rate just at the hood, which would pull fresh air from the front window which I leave open.  You made me think that if I add 2 or 3 in the ROOF then I will have fans competing and possibly end up pulling smoke into other areas which I dont want, even though its logical to think that the heat is up there in the ceiling and needs to be sucked out.  
    Whats the best strategy here? Thanks!
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    edwmax
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    Re: Just when I thought my generator was sufficient 2019/07/16 17:56:33 (permalink)
    Let the exhaust hood fans ventilate the trailer.      .... Look at it this way:    Trailer volume (height X width X length) divide by the total CFM of the fans (585 cfm X 2) equals 'air change per minute'.   ... You have to watch that all the incoming air is not though the front window as this would likely leave each end of the kitchen hot.    ...   Close down the front window some and the close the middle roof vents so the 2 end roof vents and the front window draw air equally.    ... At 2 air changes per minute, the inside air temp should be about the same as the outside air temp.     You have to work this out and a comfortable air speed though the windows and equal air flow though the trailer.
    post edited by edwmax - 2019/07/16 17:58:32
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    paulnye
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    Re: Just when I thought my generator was sufficient 2019/07/25 10:06:29 (permalink)
    thanks edwmax,
    Seems you are suggesting to exhaust all thru the hood fans (mine is at the rear) and balance the incoming air between drivers window, serving window & roof vents until a balance flow is achieved. Cool
     
    So I was hoping to increase the rate of exhaust because I have 2 side mount fans in the hood with max 580 CFM at zero S.P., which probably means Im realistically getting only 200 CFM each. My plan is to add a 3rd exhaust fan in the hood...
     

     
    ... plus add 2 roof vents with outward blowing 700 CFM fans also.
    This would give me 6 exhaust fans (see pic..)
     
     
     
    Then when all fans are on I could start opening different incoming vents (like drivers window, serving window) to see what happens and if Im getting more flow of cooler outside air
     
    Is this experiment worth doing?  
     
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    edwmax
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    Re: Just when I thought my generator was sufficient 2019/07/25 11:47:06 (permalink)
    Hood exhaust fans were how kitchens were cooled before people started thinking they could cool the kitchen with an AC.
     
    Now your kitchen.
    1)   Too much exhaust fan CFM it will feel like your standing in a tornado.  And have blowing paper & items in the kitchen.
     
    2)   Air temp above mid 80 deg is not going to feel cool.   It will be fast moving warm/HOT air.  This is where a swamp cooler  could be a low cost help depending on the humidity.
     
    3)  The best you can do is to keep the inside air nearly equal to the outside temp.   I don't think you need a lot CFM do do that.     Your interior truck volume is about 700 cu ft. (estimate); the 2 exhaust fans are 580 cfm/each => total 1160 cfm.   This is about 1.6 air changes per min (1160 cfm/700 cu ft)    ... Now if the 2 roof vent are 18"x18" and the open window is about 24"x30" for a total of about 9.5 sq ft (???)'   Then air flow thought the kitchen/windows is 1160 cfm / 9.5 sft = 122 ft per min. or a little less than1 1/2 miles per hour  (redo the calc with the actual windows sizes).   
     
    4)  Yes try the experiment.    ... With the fans drawing all the heat from the range/grill then I don't think there is enough heat gain from the truck shell & other appliances to raise the inside air temp more than 1 or 2 degree it that much.   Fast moving hot air is not going to feel cool.
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    paulnye
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    Re: Just when I thought my generator was sufficient 2019/07/25 15:54:25 (permalink)
    My truck is about 1300 ft2 inside minus the volume of the equipment, so maybe 1000 ft2 ish at a guess.
    I would expect your estimates and calcs are good.
    I understand that warm air coming in isnt cool, but its more survivable than 120+deg and back at the ceiling close to the grill it reached 131 deg last week.  
    With just the 2 fans in the hood you can see my primitive tissue test, and theres not much suction.
    Once I add the 3 additional fans, if its too much flow, I can always turn the variable switch down a bit to suit my needs.  What do you think?
     
    [tube]https://youtu.be/1B8PdFagg14[/tube]

    post edited by paulnye - 2019/07/25 15:56:41
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    edwmax
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    Re: Just when I thought my generator was sufficient 2019/07/25 17:29:44 (permalink)
    Your getting there.   
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    paulnye
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    Re: Just when I thought my generator was sufficient 2019/07/29 14:33:24 (permalink)
    Just added 3 more exhaust fans:
    Now have 3 in the hood (prev had 2), 2 new ones on the roof 

     


    Although using 110v 800 CFM fans in the roof was tricky to install, they are way better than the weak 12v plastic ones that are about 150 CFM. 
    Now I am starting to feel air flowing in and around the truck.
    Ill post an update after being out on the road selling
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