Chinook RV

Thanks, guys - adding room temperature items is a rookie mistake I made with my LP fridge but I thought I'd beat that by putting the items in a day in advance - just made it harder for the compressor to catch up. To make matters worse we stopped on the way up and picked up some fried chicken. I let it cool down for a couple of hours but it was still a bit warm when I moved it into the fridge. And parking it with the sun beating down on that side and NOT putting the awning out was a product of haste/stupidity and I won't make that mistake again.

Insulating the chimney is good idea but I'm wondering how hard it will be for me to pull the fridge out to do this. It appears that its held in place by the outside flange (front) so I'm hoping I can just disconnect the wires and pull it out. I'm somewhat handy but a bit nervous about doing this myself. Probably wait until after the 4th of July weekend so there will be time for my mechanic to fix whatever I break before the next trip!

Blue - on that terminal that I can run a second fan off of how can I tell which ones I need to tap into? Also, where do I buy the polystyrene insulation?

On both the DP150 and the 130 the refrigerator is held in just by the front flange (screws), so I would think the DP2600 might be the same. It does rest on four feet, but they aren't fastened down. Then there is just the wiring in the back (which should be accessible by the lower vent hole from outside).

I got the extruded polystyrene at a home store (Home Depot, etc.).

On the Danfoss, it will have labeled terminals where the wires are. If you put the two fan wires on terminals C and F then that fan will come on whenever the compressor is on.

There are a couple of other nifty things you can do too. If you put a light across terminals D and +, then it will give you error codes with specific flashes (should there be any).

You can also change the stock resistor, which governs compressor speed. I forget which one they set it to by default, but it's one of the middle ones, IIRC. Not that that's a bad choice. But, for example, if you slow it down to 2,000 RPM (the slowest) then I think it may run more, but at a lower amp load (it's been awhile since I read about the details, but it's kind of like how the most efficient furnace would be one that ran constantly, but that worries people (or they don't want to hear it) so they wouldn't probably choose that for default.

Here is a page that explains these things a bit more for the BD35. I can't remember if you have the BD35 or the BD50, but they are very similar (and I'm sure there is a page for the 50).

http://files.danfoss.com/TechnicalInfo/ ... 00m602.pdf

Blue - you're The Man! Great info, especially the part about removing the unit. I was wary about doing this myself but now I feel confident that its not going to be beyond my skill set. Once I pull the unit out I'll also be putting Dynamat over generator enclosure in addition to the foam - hopefully kill some of the interior generator noise.

The diagnostic info will also be helpful. I'm not sure that my installation is a direct run back to the battery so I'll need to check it to make sure its getting enough voltage as its currently set up. I'm also going to raise the unit up higher, as the DP2600 isn't quite as tall as the Dometic it replaced so I wound up with about 4 inches of dead space above the unit. By raising the unit I can eliminate most of that dead space and allow for adding the foam insulation. This will move that dead space to beneath the unit so I can install a vent of some kind to allow the compressor to pull cool air from inside the rig while adding a fan to pull the hot air up the chimney.

Not sure when I'll be able to do all this but at least now I have more info to execute this modification - probably in September when boating season ends.

Yeah, as it sounds like you already know, the electronic compressor control (or whatever the official term is) is very sensitive to low voltage. As in, you don't want to have to buy a new one type of sensitive. They always suggest a direct run to the battery, but if you took everyone's advice on that, you'd have forty lugs on each battery terminal. What they really mean is that you should drastically minimize voltage drop, and also not use a breaker that has a bunch of other stuff on it lest that influence things. Upon measuring, I found that it was pretty much an equal distance run either "around the horn" to the rear, or around the overcab to the front. Kinda long either way (which can be overcome, but I felt the stock 8AWG wire was a bit small for that length of run, plus the run to the batteries, etc. I'm considering running a wire across under the chassis (which is basically the path the generator start wire takes already). That's not only much shorter, but running a larger wire (which would be less necessary with a shorter run) would be less "gross" than running it around the rig by the other two routes. Actually, one could consider re-purposing the 6AWG generator start wire, and then running a larger wire to the gen start (which is a bit under-wired with 6AWG). You could then use a chassis ground for the negative, although I'm never sure what they "equal out to" in wire size, so I might be tempted to simply run a negative 6AWG wire as well.

You can probably find some sort of sketch of the DP2600, but the DP150 had four legs on the bottom; the two at the front were wide set, and then the two rear ones were narrower set. We wanted to insulate tightly around the bottom so had to take those into account (all of DP150's ventilation is "outside" at the back - none of it comes from or to the living space).

If you have an "intake" on the inside of the coach, but then the exterior "exhaust" you can get negative pressure inside the rig. Not that that's necessarily a bad thing (and it's not like the compressor is pulling a huge volume), but just something to consider. For possibly unnecessary reasons, I decided I'd rather either have all inside or all outside venting (so no negative or positive pressure on that "circuit").

Boating season IS sacred, after all

Hi Blue - I know I need to improve the insulation - particularly in the chimney area. For power I think they used the 12 volt line that fed the 12 volt heating element in the old absorption fridge. Since that heating element draws around 10 amps I'm assuming its large enough to feed the compressor but I could be wrong. Any thoughts on that?

I do have some thoughts, because I had the same situation in my planning. If yours is the same, the feed wire that went to the absorption fridge is an 8AWG and is a dedicated circuit. That is plenty to supply the amps needed, BUT. The "but" is that the electronic compressor controls on this type of refrigerator are very sensitive to voltage drop. They can fail prematurely if they are subjected to more voltage drop than they'd like to see. This is stressed in the manuals, and from what I can tell is true. It's not a Vitrifrigo thing, but has to do with the Danfoss compressor controller.

So at first I was all, oh goodie, a dedicated 8AWG wire for a refrigerator that draws 3.8 amps. I'm on Easy Street! But then I did some calculations.... Well, that wire is close to 30' long (one way). Now the negative is a chassis ground, but there is a fair bit of 8AWG wire leading to the chassis ground on each side, and then I'm not really sure what "wire size" a chassis is. So I presume for the sake of calculation that the entire round trip (erm... sixty feet, ouch) is 8AWG. I can't remember right now if the compressor uses more when it starts up, but it runs at around 3.8 amps, so I figured 5 amps (or maybe back then I looked it up). This is for the BD35, if you have the BD50 it might be a higher figure.

So, heading over to the trusty voltage drop calculator, I put in the figures and come up with.... around 2% for the dedicated refrigerator leg. But, you also have to add the voltage drop on the main panel feed wire. If you have the stock setup in a 21-er, that's another ~30' of 8AWG wire from the Brown Box to the batteries. That's another 2% if no other loads are running at the same time. Then you have the battery jumpers, but we'll leave those out for now as I can't remember the sizes/lengths. I wouldn't be happy with 4% voltage drop. I have very little voltage drop in the main feed leg and jumpers, but I still may consider running a new wire pair (and not using the chassis ground). If I had the stock main feed I'd definitely do something different.

I calculated and it's close to the same distance going around either way with the wire (forward or aft), so there's not much savings there. Running 6AWG around would be fairly big/clunky. So I considered running a 6AWG duplex cable (because I have a lot of 6AWG and little 8AWG) across under the rig. The generator wire already takes basically the same path. That would be something like a 12' run for me, much better.

Okay, after all that, I re-looked at the Danfoss recommendations. They list 30' (one way) as the very maximum length for 8AWG wire, but they specify that that be directly to the battery terminals. In other words, you don't "get to have" any more length (like, oh, say the 30 more of 8AWG from the Brown Box to the batteries...

Now you don't actually have to run straight to the battery posts (if you listened to every mfgr who said you had to do that, you'd have thirty lugs on each battery terminal ), but the concept is that it should have very little voltage drop, and should not be on any other busy/droppy circuit (like say on the same breaker as a pump or something).

So the short version is that no, with the stock Chinook setup I would not want to use that 8AWG wire - especially in combination with the lengthy 8AWG wiring that goes on to the battery. In my case the 30' of 8AWG is basically the only wire I would have, effectively (because I have large wire and short distance from panel to batteries), but I'm pretty sure I'm still going to make a new shorter/larger run to keep the refrigerator blissfully happy I'll run duplex cable, so no chassis ground for that circuit.

(For the moment I'm running a Dometic "cooler shaped" refrigerator which also has the BD35 compressor. I took the original "thin" cigarette lighter cord that Dometic supplied (I think it was 14AWG, IIRC) and changed it to 10AWG and also hard wired it (vs. the cigarette lighter plug). So I have around 12' of 10AWG, and then right to the heavy battery cables. I do have a second cord that is the stock type in case I want to temporarily put it somewhere else.

BG

Hi Blue - well, I won't shoot the messenger!

Given my skill level it looks like I may need to take my rig back into my RV mechanic to have them put in a heavier wire. If I understand all this correctly would the heavier, shorter wire run from the panel to the fridge outlet? If so, is there a way to come underneath the chassis and wind up at the panel without going all the way around the back?

Well the issue you've got (presuming you still have the original Chinook electrical system -- and that yours isn't different than the typical for some reason), is that the ~28' 8AWG wire run from the Brown Box to the batteries is already right at the maximum allowable run. And that doesn't even count the next 30' 8AWG run from the Brown Box to the refrigerator, OR the fact that you have other loads sharing that first 8AWG wire from the Brown Box to the batteries.

So, if it were me, and presuming you don't want to change anything else out right now (if you do, we can talk it over and amend the plan), I would want to run wire from the refrigerator pretty much right to the batteries (well, to a bus right near the batteries, and you'd fuse it separately, since it wouldn't be fused at the brown box).

If you ran that wire across under the coach (you could follow the same path as the generator wire, basically), then that would be around an 18' run. I'd probably still run 6AWG, just because why shave it close, and then the other little losses would easily be absorbed; but you could run 8AWG for that distance. Not saying everyone has to do their own work, but that would not be a particularly difficult job, presuming you are able to lie under the coach and are willing to do some relatively basic work. Or you could explain to an electrician what you'd like done.

If you want to make a nice improvement to the main wiring that feeds your charging to the batteries and all of your loads (and then still run the refrigerator wire from the Brown Box vs. right to the battery area), you could run a new wire from the batteries to the brown box. This is already a woefully small/long wire even not considering the refrigerator. If you take a route inside, under the couch and against the outside wall, you can make a ~28' run into a ~16' run. Plus you can up the wire size to 6AWG or 4AWG say.

If you did THAT, then you could consider running the fridge-specific wire from it's original fuse in the Brown Box, but if you take it across under the coach (from the Brown Box), that makes a(nother) 28' run into something like a 14' run.

If you'd like, I can run the numbers through a voltage drop calculator, plus check the ampacity (for fusing) if one or the other of these paths appeals to you.

Okay - this is starting to become clearer. I like the idea of a run directly from the batteries and an inline fuse of some kind. Will look at all this more closely after the weekend. We're headed up to our lake for 5 days (its cooled down to only 98 degrees!) so I'll have to check all this out when I get back. I'm sure I'll have more questions but as always thanks so much for your detailed response.

This heatwave is something, isn't it? I hope you have a great trip - we can pick up when you get back.