Don & Karen's Cargo Trailer to Camper Conversion

Started by MountainDon, January 21, 2014, 08:35:16 PM

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I received the 90 CFM fan, so now have two.

Latest data...

Water heater burner on to heat water to 136 degrees then turned off.
Water pump and fans turned on and left to run to stabilize. (two 45 CFM fans)
Measured temperature every minute until temperature began to fall.
Started timing.
Trailer interior at 46 F.
Hot line (surface of PEX pipe) from water heater measured just before radiator @ 131 F.
I left the trailer and let the pump & fans run for 15 minutes.
Hot line then measured @ 119 F, a difference of 12 degrees

Water tank volume is 6 gallons. I don't know how accurate that is or if the volume takes into account the space occupied by the burner heat exchange tube. 6 gallons @ 8.34 pounds per gallon = 50 pounds. I reduced that to 48 lbs. to help compensate for the burner tube, if necessary.

48 pounds with a 12 degree temperature drop, 48 lbs x 12 degrees = 576 BTU's.
(temperature change of 1 degree F on 1 lb.of water = 1 BTU by definition)

576 BTU per 15 minutes = 2304 BTU/hour, call it 2300 BTU/hour. For the curious that converts to 675 watts. Not a high capacity heater for certain, but the trailer is a small enough space and insulated well. The interior volume of the trailer calculates to about 440 cu ft, BTW.

BTW, the interior temperature rose to 50.3 F in the 15 minutes. Call that 4 degrees and that works out to 16 degrees an hour, more or less.

Keep in mind that temperature change slows down as the difference between the hotter and the cooler decreases, so the interior temperature rise will slow down from the initial 4 degrees per 15 minutes. Also the transfer of heat from the radiator to the air will slow down as the interior warms. Slightly compensating will be that the water temperature will return to 131 and even higher when the burner is allowed to be turned back on by the water heater controller.

Next I think will be to change the fans to the higher output 90 CFM and retest tomorrow morning or late tonight. It's too sunny to get any really meaningful data during the day.
Just because something has been done and has not failed, doesn't mean it is good design.


New trial this morning; new data

I changed the fans to the twin 90 CFM models.

I repeated the warm up process as done yesterday.

Initial temperature at the pipe = 138 F
After a 15 minute run the temperature  measured at the pipe fell to 113 F
Temperature difference = 25 F
48 lbs water x 25 degrees F = 1200 BTU per 15 minutes or 4800 BTU / hour

4800 BTU/hr = 1406 watts, call it 1400 watts.

The increased fan volume makes quite a difference!

I messed up with the before and after interior temperature readings so I do not have that data.   :(   However,  that is of minor importance.

I also measured the temperature at the pipe after 7.5 minutes. At that point it was 119 F, a drop of 19 F.  (The second 7.5 minutes saw a drop of only 7 degrees F.  This reflects the faster rate of heat transfer that occurs with greater temperature differentials)  48 lbs x 19 degrees F = 912 BTU/hour.  If we round that to 900 BTUH and then multiply by 8 we get 7200 BTUH or the equivalent of 2100 watts. That would be more or less what the output would be if the water heater burner was left turned on so as the water temperature dropped the burner would cut back in and bring the water temperature back up. (That water temperature is achievable with the heater control set on high. Depending on the weather or the need to heat quicker/slower the water heater could be used at a lower setting.)

The twin 90 CFM fans are noisier, but still not bad. We use an air filter device at home in the bedroom in part to act as a white noise when one of us goes off to bed earlier than the other. The twin 90 CFM are quieter than that bedroom unit so I don't see any potential issue there.  Just in case, though, I am pondering whether or not I should wire the trailer fans up with the PWM speed controller I have. I did re-find it yesterday! And then that raises the question of slowing the pump as well, or not?   ???

One more thing, the current draw increased from 0.67 amps to 0.77 amps with the twin 90 CFM fans. (Pump and fans total)
Just because something has been done and has not failed, doesn't mean it is good design.


It's been a long time... I finally completed the installation and setup of the PV panels and charge controller today. The panels have been on the roof for a month or so. I ran into an issue with the charge controller and had to send it in for warranty claim. I received a replacement, a brand new unit yesterday.

The panels are attached to the roof using Instapark mounts and sikaflex 252 adhesive. The 252 is sold only through industrial dealers; very tenacious stuff. It is rated as a structural adhesive.

It's been windy blowing dirt mixed with rain so there is some dirt dried in place. The two panels are connected in parallel. 140 watts each.

The 10 AWG wires from the panels are routed to the hinge line and down the left rear corner.

Then to the Midnite Solar Brat charge controller.

This is a PWM controller, made in USA. There is a fuse in the + from the PV array, mainly to make disconnecting and reconnecting a tool-less job. Also a fuse on the output to the battery very close to the + terminal. The brat did a short bilk and then stepped into absorb as the batteries were fully charged. In a hour and a half from now it should shift into float. There are 4 LED indicators used to show what is happening. After I let it run for a week or so my plan is to paint most of the clear case white to match the trailer.

The Brat is mounted under the A/C that hangs out the left rear door and above the spare tire.
Just because something has been done and has not failed, doesn't mean it is good design.


Here's a shot of my wires when they pass through the lower wall to under the floor. The black fitting has a rubber sleeve that gets compressed when the nut is tightened. In case it is not 100% water proof there is a weep hole at the bottom.

Just because something has been done and has not failed, doesn't mean it is good design.


Don when my wife and I were traveling all over in our trailer I replaced our noisy bathroom vent fan with one of those CoolerMaster fans. It had a blue LED light when running  :)

"Specialty" products, RV being one of them, get marked up so much. Ah, I can't even remember the name of those RV vent fans.. but they are like $300 vs $11 for a computer fan.

Brings back good memories. Cool project.

For our solar setup I just bought the Renogy 200 watt kit with a cheapo PWM charge controller off amazon. Still going strong as far as I can tell.


Don I can't tell from the pictures but I take there is no adjustment on the panels.


No, no tilt adjustments.  With the roof some 11 feet up in the air I didn't feel it was worth the effort and the climbing. It may not be ideal but it is better than nothing and the panels were a good deal.  The charge controller was a good deal as well as I got it for about half the normal retail selling price.
Just because something has been done and has not failed, doesn't mean it is good design.