36 replies to this topic

[NorCalSteve]

I am not against running the refrigerator on gas while driving. If I am worried about the level of charge on my batteries, I will run the refrigerator on gas. It is not that big of a deal. I just see some room for improvement with my particular configuration. I think, once I have increased the wire size between the truck battery and the camper battery, I will learn when to run the refrigerator on batteries and when to use the gas. I am still new at this whole thing. But having fun both tweaking stuff as well as going out an using my camper! Yeah, I wish the existing wires were #6 to begin with.

I ran an experiment on the truck that I don't feel real great about because there is so much room for error but will go ahead and mention it. I set the refrigerator to DC with the truck off for a few hours just to get the battery discharged a little. The battery in the camper dropped to about 12 volts with the refrigerator still on DC. I then started the truck (refrigerator still on). I was alone so I could only idle the truck while I took measurements. The truck battery was at 13.9 volts and the camper battery was at 12.6 volts. I am comfortable saying there was at least a 1 volt drop or greater between the truck battery and the camper battery. I then ran my jumper cables from the truck battery through the cab to the camper battery. Then, the truck battery was at 13.7 volts and the camper battery was at 13.2 volts. So I might have gained .5 volts after the jumper cables were attached. I have no idea how much current was flowing so I have to be careful how I use these results.

Again, I don't expect a real great improvement but it will be fun to see what happens.

Steve

[pods8]

As I mentioned in another post, I ran #8 wire directly from the battery to the refrigerator.

Which battery are you referring to here? When I mentioned running a line directly to the fridge I meant from the TRUCK, it sounds like you went to your camper. If that is the case I honestly can't see the point. Why would you ever want to run a 13amp load off your camper batteries? I can't ever see a reason, you're either going to drain them or impede charging or both. You'll want to supply those amps from your alternator if you're ever going to bother with the DC mode on the fridge. So run a dedicated line for the fridge back to the truck and also a dedicated line for the batteries, if you do that I think you won't see the voltage drops you're dealing with right now at the camper battery. Otherwise you're always going to have a 13amp load off the bat contributing to your voltage drop regardless of wire size (6ga you've already got 1.5% drop at 20' in that case).

Or look at the DC-DC charger to boost the voltage back up to something useful. Wiring is cheaper though...

[NorCalSteve]

Hey pods8,
The 3-way refrigerator was installed by FWC. FWC used #10 wire from the camper battery to the fuse box and then from the fuse box to the refrigerator. There was a little more of a voltage drop than I wanted between the camper battery and the refrigerator when the refrigerator was operated on the 12 volts DC. So I ran #8 wire directly from the "camper" battery to a fuse and then directly to the refrigerator.' I did this rather than replace the factory #10 wire because it was pretty easy. This gave me a slightly higher voltage at the refrigerator when it operated at DC. I am happy with the small improvement this made. I think that many people who use the Dometic 3 way refrigerator don't even bother to run it on 12 volts DC. I do and it works for me (if I am careful).

[K7MDL]

To avoid needing to run the fridge on gas or DC while in transit, I use several "Blue Ice" plastic freeze blocks. Keeps it cold for more than a day, and when I stop for the day, I switch to propane and move the blocks into the freezer comparment. Pull them out the next morning. In cooler weather I never turn on the gas for a short weekend and use a few more freeze blocks since I need less stuff in the fridge. I do empty the fridge when not traveling and thus only carry what I plan to use on the trip which leaves me plenty of room for the extra blocks.

[NorCalSteve]

Cool Idea K7MDL. That is something I figured I would try sometime. I have driven in warm weather where the refrigerator creeps up to 50 degrees. It was on a trip to Texas about a month back. 75MPH in hot weather. The Blue Ice would be a great way to assist the system on those hot days. Glad to hear it helps! And my freezer usually has space for at least one blue ice block.

Steve

[pods8]

I think that many people who use the Dometic 3 way refrigerator don't even bother to run it on 12 volts DC.

I agree 13amps isn't something to shrug off.


Again to reiterate I think lots of good suggestions are out there now, just gotta choose what you want. Run a dedicated wire from the truck to avoid the voltage drop to the camper battery, use a DC-DC charger to boost it back up, don't use DC fridge, use ice packs, etc. Without doing a dedicated line I'd say you'll rob any worthwhile solar charging so discount that while on DC.

Just my thoughts.

[ntsqd]

A point of "Handy Bob's" that I came away with from reading his blog is that a .1 volt drop (or gain) isn't a small percentage loss or gain since we're not dealing with a range of zero to twelve volts. We're dealing with a range from ~12.1 volts (50% discharged) to ~13.6 volts (fully charged), or roughly 1.5 volts total charging range. Suddenly a .1V gain is a whole lot more significant when talking about battery charging. This is, I think, his foundation realization. What he builds everything else on. Once you accept that, and I don't think that it will be too difficult to do, then everything else that he has to say about wire sizing and voltage drop is a logical deduction.

My early days as a bachelor in my own home (no roomies etc.) taught me that "thermal mass" in the fridge is a good plan. I didn't have a lot in the fridge in those early days (or money to fill it with) and it was running almost constantly. Simply by filling used gallon milk bottles with water and leaving them in the fridge cut the run time significantly.

[White Dog]

I think ntsqd made HandyBob's point in much less space - I don't see a single rant. Thanks ntsqd.

Voltage drop is the real issue. HandBob uses the analogy of trying to blow up a tire. If you have a compressor set at 75 psi, it is quite easy to reach 50 psi in the tire. The last 10 psi takes longer than the first but it's still relatively quick. If you try to do the same with the compressor set at 51 psi, it takes forever. The volume of air (analogous to amps) is the same but the higher psi (analogous to volts) makes the process much faster. The problem is to get the highest voltage that will not damage the battery to the battery (typically (but not always) 14.8 VDC for lead-acid deep-charge wet batteries). This is impossible from the truck's alternator since it is limited to 14 VDC. Voltage drop from the alternator to the camper battery just makes it worse. Plugging in the camper will continue this process but unless it has a 'smart' charger built into it, the charge will continue at the same poky rate. The stock Iota DSL-30 that FWC uses puts out 13.4 VDC. However they do offer an upgrade module called the IQ4 which turns the DLS-30 into a 4-stage charger.

Personally, I would prefer to never camp anywhere I could plug my FWC in but that's just me. So I continue on my quest for 120 VAC independence at affordable cost.

[ntsqd]

Thank you for posting that link. It has proved to be the beginning of my truly grasping what a well designed and installed solar charging system is and has led to a sequence of further reading that I've learned a lot from.

My first purchase is going to be a Tri-Metric meter. After I have a handle on our usage, then I'll start sizing & spec-ing a solar system.

[White Dog]

My first purchase is going to be a Tri-Metric meter. After I have a handle on our usage, then I'll start sizing & spec-ing a solar system.

TriMetric is just one brand. These monitors are used quite often on boats so if you look at some marine suppliers like Jamestown Distributors you will see they have other models. This will help with pricing and features before you make a decision. Some of these will even data log to your laptop.

Good luck. Let us know what you find out