Fan selection

Airbag · June 30, 2009, 06:07:48 PM

I replaced my forward roof AC today with a new Dometic Duo Therm Brisk Air. I drove around and it made a big difference in the temp. When I got home I left it run on the 8kw gen for a while. After about an hour of use with both Duo Therms running the 30 amp breaker located in the generator bay popped. I reset it and turned both units on low and it did it again in a short period. The generator shares the same coolant as the DD. I believe it to be a case of just being too warm in the bay when stopped.

I would like to put a fan on the door to the bay blowing air out of the bay. I would like it to be a 120V fan that I can tap into the breaker box in the gen bay. My gen bay is the old OVR AC bay. Any suggestions for a good fan that will perform this duty?

Tenor · June 30, 2009, 06:17:02 PM

Airbag,
Does your genset have an enclosure? Since you are using the DD cooling system, is there any chance it is not flowing past the DD's thermostats? Are there electric fans on the DD radiators? I was looking at doing that combination, but there were just too many obstacles. Could you post some pictures?

Glenn

Airbag · June 30, 2009, 07:07:57 PM

Hello Glenn
Here are a couple of pictures. It is as the PO installed it. I have no idea how he has plumbed it into the cooling system of the DD. It is not overheating. I can dig further into it if you like and maybe I can find out.

Notice the screen on the door has been covered with a sheet of aluminum, Maybe I should try removing it. Any thoughts anybody?

luvrbus · June 30, 2009, 07:41:11 PM

Rick, I would check your voltage and the rpm on the set, all of the Isuzu powered generators like yours I been around seem to run a little warmer than the one using the Kubota engine when not having the correct rpm good luck

Tenor · June 30, 2009, 08:00:13 PM

I agree with Loverbus. I just did that check after finding out that I had the same problem that you did. I had my wife watch the hertz number on the inverter while I adjusted the rpm. It brought me up a couple of VAC and my air conditioners, inverter, fridge ran sweet.

I would definitely learn how your system is plumbed. It's a nice unit!

Are the original vents in the floor still open and do you have a round access door from that compartment to the first bay? (my mci 7 does). You could put a squirrel cage fan in a box in the first bay. Pull the air out of the AC compartment and push it out the floor of the first bay with a hole/screen. The original louvers in the AC bay would make good intake ports. I did the reverse on my bus. The genset is in a box in the first bay, the round access port connects to the squirrel cage in a box in the AC bay with the radiator facing the front.

Airbag · June 30, 2009, 09:41:14 PM

Quote from: luvrbus on June 30, 2009, 07:41:11 PM
Rick, I would check your voltage and the rpm on the set, all of the Isuzu powered generators like yours I been around seem to run a little warmer than the one using the Kubota engine when not having the correct rpm good luck

I have an appointment at 8:00 am tomorrow at Paulson's RV service and I will ask him if he can check the rpm. I have a remote panel in the cabin and when it starts it rev's right up to operating rpm. I sure would like to be able to do a warm up at idle before it throttles up. It shuts down the same way from operating rpm, that can't be right?

Glenn I like your set up it must be quiet.

Thanks guys

gus · June 30, 2009, 10:02:55 PM

Rick,

An 8KW gen is capable of a lot more than 30a, my 6KW puts out 50a! Why are you running it through a 30a breaker?

You don't say what size your new AC is but even 13.5s draw around 15 amps running in really hot weather (Like AZ for instance).

If one is running and one is in the start cycle the amps are probably much higher. If two happen to start at the same time the amps are way up.

I don't think my gen 30amp output will run two AC. I have one AC on 30amp and one on 20amp gen output coils and breakers.

Airbag · July 01, 2009, 05:50:31 AM

Quote from: gus on June 30, 2009, 10:02:55 PM
Rick,

An 8KW gen is capable of a lot more than 30a, my 6KW puts out 50a! Why are you running it through a 30a breaker?

You don't say what size your new AC is but even 13.5s draw around 15 amps running in really hot weather (Like AZ for instance).

If one is running and one is in the start cycle the amps are probably much higher. If two happen to start at the same time the amps are way up.

I don't think my gen 30amp output will run two AC. I have one AC on 30amp and one on 20amp gen output coils and breakers.

Gus
I suspected that. The wiring is large enough to handle more than that. It will be replaced today.

Thank you sir.

luvrbus · July 01, 2009, 06:06:14 AM

Rick, you may need a larger breaker but have the rpms and voltage checked if they are low it will still heat a 50amp breaker and trip it.
The diesel generators do go from start to full rpm on start up me on shut down I remove all the load for a couple of minutes before shutdown.
One thing to keep in mind here in sunny AZ when parked your generator is picking up 140+ degree temps air coming from the pavement also. FWIW the S&S use a 30 amp for 2 Ac's good luck

edroelle · July 01, 2009, 07:22:45 AM

The following is guidance, in addition to your breaker popping comments.

Your generator head needs cool air to run efficiently and reliable. The generator head intake is toward your left, forward in the bus. You should have about 4" to 5" of clearance and a source of fresh air. The generator head exhaust is from the grille, adjacent to the engine housing. The air from the generator head should be routed outside your compartment and away from the intake.

The MCI 8 has marginal engine cooling. This should be considered in your generator cooling.

You have a very nice generator. You don't want to compromise it with a poor system design. Discuss this with someone knowledgeable and can look your design over, or you can contact me.

Ed Roelle
Flint, MI

Damn Yankee · July 01, 2009, 08:33:27 AM

My coach generator is cooled the sam way as yours. There is a 120v fan mounted on each side. Here is a picture

http://i734.photobucket.com/albums/ww347/Michigander_Bob/My%20Bus%20Conversion/gen_fan.jpg

I would highly recommend you follow Eds advice for cooling the head. Someday I'm going to rip out those fans and install a separate radiator cause they are very noisy in the bedroom and I really haven't driven it in high temps with the genny running yet. Open up your gen compartment and point a fan at the head and see if the breaker still trips.

Sojourner · July 01, 2009, 11:08:13 AM

Airbag...all of what Ed & Yankee posted and more.

About RPM check...you can use a simple 110v clock with a second hand. If it running too fast...the second hand move faster than 60 seconds or vice versa if it slow. Adjust the RPM until it match your watch. Very accurate every time. Sometime RPM meter is not calibrate correctly.

Sojourn for Christ, Gerald

Airbag · July 01, 2009, 12:08:56 PM

Well guys I just got back from Paulson's RV service and supply. He checked the rpm and cycles and found them to be OK. He did find the problem which was and I hate to admit it here because it is electricity 101. We had both units on one leg. Go ahead and laugh. The man is very knowledgeable and fair priced. he worked for over an hour and wanted to charge me 20 dollars, I argued with him and we settled on 30. It is a family business and has been around since 1953. I highly recommend them if you are in Tucson. He is a factory authorised Dometic service center. He owns an airplane so he can't be all bad.

As it turns out what I thought was a 30 amp breaker is really two 30 amp breakers ganged together one for each leg.

Ed and Yankee
I concure on the head temps needing cooling. I still would like to know what type of fan to get. I will call you Ed.

Nick: By the way he called Dometic and the installation manual has a misprint that says the fan stays running when the compressor shuts down during a temp cycle. That is incorrect the fan shuts off they are working on the miss print. I would prefer the fan to continue to run to de-ice the evaporator more quickly.

Gerald I will file the clock trick away in my tiny cranium. Sounds like a good one , makes sense.

Thanks all

bevans6 · July 01, 2009, 12:42:34 PM

brisk my brand new Brisk Air 15K leaves the fan on when the compressor cycles off. The fan runs constantly, the compressor come on and off as needed.. FWIW...maybe they changed the wiring to match the manual...

Also FWIW, I've been taught that a breaker is rated at 80% of nominal rating for constant use. So a 30 amp breaker is rated to 24 amps constant use. so your 30 amp breaker popping after a couple of hours is actually normal.

Brian

gus · July 01, 2009, 12:48:21 PM

Rick,

It is great how problems often turn out to have simple solutions!! I think I would have given him more than $30, AC is essential to busnut life!!

When you say both were on the same leg which leg do you mean, the generator output leg or the breaker leg? As I said before, my Honda gen has two output coils (Legs?).

Please post the phone number of Paulson's. We usually pass through Tucson every year, this year being the only exception for quite a while, and this is valuable info to have. What plane does he own?