Attention a Electrical Sleuths

[Terrapin]

Mr. Grandby,

Well, so far nothing has been fixed although I've convinced, myself at least, what's to be done.
FWC has agreed that exterior fridge venting should be in place and committed to installing both upper and lower exterior vents. We are waiting for the vents to be shipped to Oregon where the Tigard distributor will do the installation. Once vents are in, we need to close up and seal off ineffectual interior vent spacing above and below the fridge to mitigate intrusion from dust and insects through the new exterior vents.

My plan here was to use expanded foam board above and below the unit to both close those gaps and increase insulation to the box itsself. I thought I could additionally use foam sheets attached to the unit back not only as additional insulation to the fridge box but as baffling that would serve to channel incoming air through the bottom vent, up and across the compressor, cooling fins, the compressor fan, then out the upper vent. The convection and flow of this air stream is to be assisted by 2-120mm BB fans blowing the heated air out through the upper vent. My thinking is that if all new air is directed past, over and through the cooling mechanism there is no need to cool the lower dead space behind the fridge unit. The two small fans theoretically draw .22 amps each at full speed 1350 rpm. Of course, that's manufacturers specifications when new. Even though they have twin ball bearings I suppose that number will increase over time with wear etc.
I'm not the sharpest tool in the drawer when it comes to refrigeration or electricity for that matter, but I do have a sense for fluid flow and aerodynamics.
The lower part of my 2-way Dometic is just a cooler box. The upper is the mechanism for dissipating heat. Doesn't it make sense to channel all available air past that heated area rather than have it swirling around where it only would serve to warm the area we're trying to cool?

Grandby, I like your idea off a temperature switch. No use running the fans if unnecessary.
Although thinking I'm a smarty pants with the foam baffling...I don't know. I suppose the compressor fan and convection would do the work. After all, any air movement has to go right over and through the only open path. Can you give me some recommendations about a good switch and where I can get one and some additional details about your installation?
I'm all ears if someone wants to chime in here. I've been known to overthink just about everything I come in contact with!

I appreciate every comment, truly!

T


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[Terrapin]

Jim,
about the insulation. I think I'm on the same page. I was thinking of attaching the insulation directly to the box below the cooling fins
I was thinking of the u
Insulation foam from Corning with foil on one side which I thought should face out away from the fridge..reflecting heat?
As per my last post, I'd also shape the foam to direct the incoming air up and across the cooling unit.
Your thoughts?

Ted

 

[ntsqd]

FWIW I bought this t-stat switch: http://www.amazon.com/Emerson-3F05-1-Adjustable-Snap-Control/dp/B000PY7T7I?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o09_s00 and this t-stat switch: http://www.amazon.com/Thermostat-Switch-Circuit-100%C2%B0F-Flange/dp/B0026RYU4W?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o07_s00 each controlling one of these fans: http://www.amazon.com/TECHNOLOGIES-5920PL-04W-B40-D00-AXIAL-172MM-12VDC/dp/B00MEIR298?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o08_s00


I think 85° is too low. I need to re-wire them to both work with the adjustable and take the fixed one out.

 

[97grandby]

Jim,
about the insulation. I think I'm on the same page. I was thinking of attaching the insulation directly to the box below the cooling fins
I was thinking of the u
Insulation foam from Corning with foil on one side which I thought should face out away from the fridge..reflecting heat?
As per my last post, I'd also shape the foam to direct the incoming air up and across the cooling unit.
Your thoughts?

Ted

Hi Ted, I didn't add anything more to the back of the fridge as the manual says you need 4 inches minimum behind the fridge of clear space. I would guess that is only needed around the compressor at the top but as it didn't say and I have left a gap around the opening for a bit of flow I thought more at the back would hurt more then help. I remember a post but can't think of it, from someone who added a ton of insulation around the the fridge and the fridge and had issues with the freezer staying frozen. Seemed the temperature sensor is in the fridge and if it doesn't run every so often the freezer won't keep cold. But in any case I for the most part try not to stray to far from the engineers who designed it specs. Once i looked at the manual and got the correct venting and wiring works like a champ. Here is the switched I used. And below it is a screen shot of the manual about the rear of the fridge.
Let me know if you have any other questions I can help you with. -Neal




1990 Ford F-250
1997 fwc grandby

 

[Terrapin]

Regarding the refrigerator venting, insulating and addition of fans.
I finally found a local RV refrigerator wizard in Portland. An enlightening character who indeed pointed out how I was overthinking everything. He dissuaded me from adding additional insulation around the box and strongly suggested I only add one fan...a slow one at that. He explained that too much air movement can change the pressure and air flow in the small area between the fridge and camper wall to where the natural flows could become confused with turbulence. I suppose like cavitation around the prop of an outboard motor. Monday we're installing both upper and lower vents each with access doors for service, and a single 120mm fan which draws about .2 amps, pushing air out the top vent. We'll see how this works before deciding on a panel size for solar upgrade.

T


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[craig333]

Sounds right to me, I don't think it takes a whole lot of cfm to exhaust the hot air. Might be interesting if someone had a flir to see the difference.

 

[Jack]

Just came across this thread and I have some comments.

First, the standard load test does not tell the right story for deep cycle batteries (unless they are pretty much dead). What you want to know is how many amp-hours are left. As deep cycle batteries age, they provide less and less amp hours. See below for how to test.

Second, the way FWC originally wired two 12V batteries together was incorrect (they have mended their ways). The way your batteries were originally connected resulted in one battery supplying more power than the other. If you started out with two 60 amp hour batteries, after a year of moderate use, one will be reduced to, say, being a 50 amp-hour battery and the other a 40 amp hour battery. This imbalance then ages both batteries even more. The level and frequency that a battery is drawn down determines it's life. Rule of thumb is to stay above 30% draw-down (30 amp hours for a 100 amp hour system). Drawing a deep cycle battery down to 0 (10,6V) greatly shortens its life. The correct way to wire two 12V batteries in parallel is to jumper the two positive terminals together and the two negative terminals together. Then connect your load wires to one terminal on one battery and one terminal on the other battery.

Third, a much better solution to wiring two 12V batteries in parallel is to wire two 6V batteries in series. FWC ought to offer this option instead of dual 12V batteries - they cost out about the same.

Fourth. The Exide batteries that FWC sells are marine batteries - dual starting / deep cycle batteries. Marine type batteries cost less than true deep cycle but they don't last as long. The Concorde Sunsaver batteries are at the top of the list - but pricey. (If price doesn't matter at all, go for lithium ion). The sweet spot for AGM deep cycle batteries are the golf-cart batteries. There's enough volume and competition to make them a good buy (make sure the golf cart batteries are deep cycle AGM - not flooded). Trojan is a well known and reliable brand, but that's not what I'm buying this Thursday (we are retiring our 2005 Eagle and getting a new Fleet on Wednesday). I'm buying a pair of 6V Fullriver batteries (http://www.fullriverbattery.com/main). The people in the battery business that I have talked with and my online research say that Fullriver is as good as or better than the Trojans, at a lower price. Jeff in Tigard sells both Trojan and Fullriver.

Fifth. All deep cycle batteries have a life. A good 100 amp hour battery, treated nicely, can still supply 80 or more amp hours three years later. I suspect that your Exide batteries, given your level of usage, including frequent draw down to 10.9V, your batteries have probably reached end of life..

Finally, I agree with others that the refrigerator cycling is a protection behavior for low voltage. Also, check the seal around the refrigerator door frame. Our Eagle has a Norcolde 3-way, and a service tech once told us that Norcold stopped insulating behind the door frame. When we re-insulated behind the fame, the door didn't open quite as easily - because the refrigerator was more air-tight. I assume Norcold stopped insulation due to complaints, but their solution allowed some cold air to seep out, making the refrigerator less efficient.

To test a deep cycle battery, do the following. Fully charge the battery, run a small load (lights) for a few minutes, and then measure the voltage at the battery. You then connect it to a constant load that draws about 4 or 5 amps - some appliance that operates continuously. You will need to measure the precise current with a clip ammeter or by insrting a shunt on the negative side of the battery and measuring the voltage across it. Current = voltage divided by the shunt resistance. For example, 0.5V across a 100mOhm (0.1 ohm) shunt is 5 amps. Let it run for 4 or 5 hours and then disconnect the load. Keep track of the exact time. Now measure the voltage at the battery. Hours x amps = amp-hours. Assume you ran for 4 hours at 5 amps - you used 20 amp-hours. Now look up a per-cent draw-down chart of an AGM battery (http://caravansplus.com.au/catalog/help-12v-battery-size.php). If your battery dropped by 0.2V from 12.8V, then 20 amp-hours is 75% of the battery capacity. Your battery is roughly capable of supplying 100 amp-hours.

A simple digital multimeter (DMM) will give good enough results to know how good your battery is. Harbor Freight gives a DMM away about every 6 months, and $15 to $25 buys a halfway decent one on Amazon (I have a decent Fluke, but I carry the https://www.amazon.com/INNOVA-3320-Auto-Ranging-Digital-Multimeter/dp/B000EVYGZA/ref=sr_1_3?ie=UTF8&qid=1465875014&sr=8-3&keywords=DMM because it's much smaller). Everyone should carry a DMM - even if you'r not sure how to use it, you can likely find someone nearby who does and who will help you out.

 

[Terrapin]

Jack,

Than you for the informative post, much of which I have surmised over the last month.
Yesterday we finished adding venting and an additional CPU Fan for the poor refrigerator. Previously their was virtually no venting. The camper has run off the 2-Exide batteries since yesterday morning. That is, the LED lights day during while installing the vents and then with the fridge (Dometic 110) all night.
My Trimetric showed a starting voltage of 13.1v @ 100% charge. This morning it's reading 12.1v @ 84% charge and my fridge is again cycling although not drawing as much amperage as it had been before the venting. It was cold last night so the fridge did not have to work hard. Regardless of the numbers, I believe the batteries too are damaged. Likely aided by the faulty wiring from the factory and insufficient cooling from the lack of venting for the fridge compressor. Their is no question that heated air is now exhausting from the upper vent!
Your right about the weatherstripping on the fridge door. Twice I've found it hanging at the bottom where of course the seal was faulty. I check it regularly now. Thankfully the fridge runs fine on 110 so I don't think it's damaged....yet.

Lastly, my Trimetric history suggests the batteries have not been getting a full charge during the day; even if driving for several hours in full sun. From what I read, the alternator is providing little more than a trickle charge and the single 90-95 watt panel is insufficient for the large fridge.
No wonder. It's taken two years to finally get a handle on this system and equally irritating that we pay $$$ to learn this stuff from hard knocks.

Today I'm buying two Full River 224-6v AGM batteries but need to make room for them in the cabin. We are heading out for a couple of weeks so I'll have to find supplemental110 charging so as not to run the new batteries down too far before upgrading the solar power.

Oops, I almost forgot, as a test, I ran the batteries low, individually. The second battery (originally jumped by the faulty factory setup), ran down faster than the main battery which always received a full proper charge.


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[billharr]

Please post a diagram of the faulty wiring of the batteries. I assume the load and charge wiring was to just one of the two batteries and not across both.

Correct way

Wrong way

 

[DrJ]

I'm not sure there is any difference in how those two batteries are being wired in the previous picture.
They are both the usual parallel way used for two 12 volts together.

 

[Wandering Sagebrush]

I'm not sure there is any difference in how those two batteries are being wired in the previous picture.
They are both the usual parallel way used for two 12 volts together.

The difference is where the negative lead is coming from one battery, and the positive from the other. Electricity tends to take the shortest path, and by doing it the optimum way, the first battery is no longer the shortest path.

 

[Terrapin]

Precisely!

If wired improperly, the second battery is simply "jumped" from the first battery. Battery two then may not fully charge creating an imbalance that drags the fully charged one down during practical use.
They become unbalanced over time with the one battery continually degrading the other, shortening the life of both.
Oddly, over the last year I've had the batteries tested 8 times in virtually every western state, always with a clean bill of health. Both of batteries measure 13.1-12.8v shortly after a full charge and measure a 100% charge on my Trimetric. Finally, suspicious of the testing methods performed with a multimeter, I ran a practical load test on each battery independent of the other. One of the batteries wore down noticeably more quickly than the other. Apparently, a simple metering voltage is not necessarily accurate unless the batteries are actually being tested uniquely with a load.
Unfortunately, my experiences have shattered my confidence in RV service departments at least in their abilities to problem solve electrical issues.

A huge drawback of the modern plug-and-play culture.

I'm starting afresh today with 2-224 6volt AGM batteries and a Trimetric meter to help me learn and better track their performance and health......I'll learn anything for ice cream in the fridge!

Just Kidding......


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[Jack]

All wire has some resistance - that's why the two diagrams are different. Insert a light bulb (a resistance) in each jumper wire for each diagram and you can see the difference.

 

[Happyjax]

Hmmm never looked at it that way. Good info!

 

[Terrapin]

FOLLOW UP...

... and next phase. FWC agreed that our rig needed venting behind the fridge and did install both an upper and low vent at their dealership in Tigard ,Oregon. We added an additional Pancake fan wired to the compressor fan to push air out the top vent. Domestic service advice not to use additional fans as it may disrupt the pressure in the area behind the fridge. The nifty fan draws 125 ma so did not think it needed its own wiring. Incidentally both vents have access doors for cleaning maintenance. I also replaced my Factory Exide batteries with 2-6V 224amp AGM batteries in series.
Our first road test stretched over 2400 miles, nearly 3 weeks through Oregon, Idaho Washington and Montana, lots of sun and heat! Our solar panel (95 watt) and several hours of driving failed to keep the batteries fully charged. except for 3 nights where we had AC at the Old Time Fiddlers Championships. The batteries slowly measured lower and lower. We decided to reduce the fridge's power usage (Dometic 2-way 110) by keeping one drawer stocked with block ice and shutting the fridge down at night. Admittedly, I was a nervous wreck about running the the $660 dollars worth of new batteries but there simply was no where to plug in. So except for lack of charging, the vents and new batteries seemed to have eliminated at least the fridge cycling problem
.
​Charging is my new issue and I'm looking for information. A generator is easy but I don't want to carry or hear one running. The Trimetric indicates the truck alternator contributing inconsistently with current dropping noticeably after the initial start up. Then, one day it seems to charge to a full 100%. I seems I am ignorant about the isolators function and its requirements. One thing seems sure that the 10ga. wiring from the truck to the isolater needs to be upgraded to 6 or 4 ga. Apparently I also need a larger plug and some fuses. Also FWC says I need to replace my small solar panel with a 160 watt one but I'm leaning towards at least 200. We are very frugal with power but I'm tired of always worrying to the point of turing my fridge off at night if its cool out.
My question to the community is will upgrading my wire from truck to home with 6 ga. be adequate or must I go to 4ga.? Is a 200 watt panel adequate if I only use the 2 way fridge 24-7, a couple of LED lamps and occasionally the furnace fan to take the chill off?
Ideally I'd like to be off grid for at least 5 days without concern for the equipment or the condition of our food.

Thanks,

Ted

 

[K7MDL]

The size of wire is hard to say. There is an element of diminishing returns. Other factors influence the choice
Cost, length of run, available alernator output useful for charging (voltage it wants to run vs. what your batteries want), temperature difference between the alternator and camper batteries, size and length of the camper side run, choice of connector (contact resistance and other losses), and run time from your truck engine. Sounds like a lot doesn't it?

Some of this you might not know except for trial and error. If you can measure a large voltage drop from alternator to camper battery then that is a good place to start. It only helps ensure you are topped off on the way out and back though. You can add a smaller wire in parallel with your existing wire and lower the cost and perhaps install time. If you have a 10GA size wire run now, adding a 8GA in parallel will give you the equivalent of 6GA. Resistance of a length of copper wire of 4GA is 25% of 10GA, 6GA copper is 40% of 10GA. 8GA is 63%. So you can then see if you are measuring a voltage drop of 1.2VDC with 10Ga wiring, roughly speaking you can more than halve that drop to 0.5VDC by adding 8GA in parallel (equivalent to 6GA). Of course as current drops off when the battery charges, this becomes moot, but it is all about the engine running time then to get topped off fully. It at least leaves less work for your solar charging capacity. Once you fix your charging wire size, it is possible you have all you need at peak light, but are lacking solar capacity in the off peak light hours, so would be good to measure that and see where your problems really sit .

If you are running out of power on station, then in addition to ensuring you start off topped up, you simply have to add more solar, use less power, or be more efficient with the solar you have, such as pointing it more directly at the sun.

Given all you have done so far, I would measure your charging cable voltage drop and deal with that part. Try to measure your power deficiency - if you are drawing too much then you should be able to calculate how much you will need. Consider borrowing a portable panel of near that estimated size needed and plugging it in appropriately to see what it does - being additional power and pointed better you might find it is enough. Not sure where you are located but I have a 120W Zamp with controller sitting in my garage I never use that could be borrowed. I am near Seattle. IF cost is no object then you can just add a lot more solar and it will probably work out .

 

[JaSAn]

My question to the community is will upgrading my wire from truck to home with 6 ga. be adequate or must I go to 4ga.? Is a 200 watt panel adequate if I only use the 2 way fridge 24-7, a couple of LED lamps and occasionally the furnace fan to take the chill off?
Ideally I'd like to be off grid for at least 5 days without concern for the equipment or the condition of our food.

This is the calculator I use to determine wire size; pick how much voltage drop you can tolerate and the length of wire run (round trip) and it will tell you what size wire to use:
http://circuitwizard.bluesea.com/#

As to your second question: I spent 5 weeks in Utah this spring and my batteries were at 100% by 1 PM each day.
I have 2 x 100 Watt panels, 208 amp hours of battery and 4 AWG cable running from panels to charge controller (16 ft RT) to battery. I did not use my truck to charge house batteries.
I run a refrigerator (4.5 amps), MaxxFan and portable USB fan (sometimes over night when hot), LED lights, cell booster, and charge a MacBook, iPhone and InReach emergency beacon. Refrigerator was kept at ~ 35°F .
I was taught ~ 1W solar to 1AH battery.

jim