Added a 12v Fridge Fan...

[charliem]

[font size="3"]PEIslander,

And the number is.....................On the 21RBS with everything "off" the residual current as measured with a good DVM is 0.19 Amps. This includes the fridge keep alive current (fridge off) the propane detector, the radio keep alive current with the clock display off, and one usb charger I have hardwired in but nothing connected to it. Most of that current is the propane detector though some current goes to the radio, the fridge, and the usb charger. Turning the radio clock display on increases the current to 0.25A. So at 0.19A the battery usage is 4.56AH/day, not at all insignificant if dry camping. For perspective, in ten days this is half the capacity of the typical 86AH Group 24 "Marine" battery supplied with our campers. Whoofit thinks his propane detector draws 0.3A so I'm suspicious of your low reported currents. Do you have a digital multimeter to check against?
[/font]

[whoofit]

I'm going measure mine across the fuse tomorrow. I suspect the calibration sequence it goes through on power-up uses more juice.

[peislander]

Regarding that residual current -- I have no radio, television, money counter, card shuffler or charger. I do have a cassette toilet that monitors the tank level with some form of float switch. The grey & fresh tanks have no monitoring. The Victron Energy Monitor uses 4mA when the backlight is off & it is not in an alarm state. I have it set up so the backlight only comes on when using the display. It is not in an alarm state. The resolution of the monitor when measuring current between 0 & 10A is +/- 0.01A.

Sorry I don't have a digital multimeter.

I just went and looked at the Victron Energy Monitor. It indicates it has been 4.1 days since I had 100% charge and that in those 4.1 days it consumed 5.2Ah. That consumption includes the 12-hour test I did running the fridge fan and 4 or 5 minutes of running one of my Fantastic-vent ceiling fans a few days ago & a minute or so of testing my LED cabin lighting (StarLights Brilliant Lights -- one fixture with dimmer & night light modules). I also confirmed the operation of the 300W inverter for a minute or so using a transistor radio with a 110v power adapter. I also confirmed the operation of the water pump but it just ran for several seconds. The 12-hour fridge fan test consumed 3.45Ah. Subtracting that 3.45Ah from the 5.2Ah I'm left with 1.75Ah being used in the four days -- and that includes the testing of the fan, pump, inverter, lights, and fiddling with the energy monitor.  ---- I did not confirm the propane detector is operational.

[charliem]

[quote source="/post/12461/thread" timestamp="1434587448" author="@whoofit"]I'm going measure mine across the fuse tomorrow. I suspect the calibration sequence it goes through on power-up uses more juice.[/quote][font size="3"]I watched the current during the 10 minute power up. It toggled between 0.19 and 0.21. After the green light came on continuously it read 0.19. I didn't think of the calibration routine. That may be what I was seeing. We're awaiting your report.
[/font]

[charliem]

[font size="3"]PEIslander,

Something still doesn't ring true. That would mean you were seeing about 17.8 mA for the 4 days. Everything I've read about propane detectors suggests something in the 100+ milliamp range depending on type and manufacturer. Does your propane detector have a green light that stays on all the time, two test/mute buttons, and a red light that come on for test or alarm?
[/font]

[david]

In addition to this fascinating conversation about how much current the fan draws, a more interesting issue for me is how it is wired to DC. It would be much preferable for me if it was wired in to the fridge's circuit so it only came on when the fridge was on. If it is wired to the DC supply to the Fridge then it will run continuously as long as the batteries are connected and have juice.

We often camp overnight and I don't bother cooling down the fridge in that case. We just take a small cooler for food and drinks for that single day.

So could you describe exactly where you picked up power and if wired into the DC supply is there a place where you can safely pick up power that is switched by the fridge.

David

[charliem]

[font size="3"]David,

I agree the preferable connection would be to a point switched by the fridge on/off function, but that will  depend on the particular fridge. The CL11, CL16, CL21 all have different fridges. Best bet is to look at your particular fridge schematic and try to find the proper point. Failing that, the switch mounted on the fan assembly can be used.

I also question the need for two fans. I use just one of the little blue cube fans in a 7 cu. ft. fridge and believe it make a noticeable difference. Maybe the best solution would be to replace the supplied switch with a single pole three position on-off-on switch. This switch plus a diode would allow one fan for dry camping and both for max cooling on shore power.
[/font]

[peislander]

[quote source="/post/12472/thread" timestamp="1434633010" author="@david"]It would be much preferable for me if it was wired in to the fridge's circuit so it only came on when the fridge was on. If it is wired to the DC supply to the Fridge then it will run continuously as long as the batteries are connected and have juice.[/quote]The fan is switched so it comes on only when you turn it on. When you use it is therefore optional. You could for instance just use it when running the fridge on propane or shore power.

[drdave]

[quote source="/post/12477/thread" timestamp="1434645848" author="@peislander"][quote source="/post/12472/thread" timestamp="1434633010" author="@david"]It would be much preferable for me if it was wired in to the fridge's circuit so it only came on when the fridge was on. If it is wired to the DC supply to the Fridge then it will run continuously as long as the batteries are connected and have juice.[/quote]The fan is switched so it comes on only when you turn it on. When you use it is therefore optional. You could for instance just use it when running the fridge on propane or shore power.[/quote]My brainstorm was a rheostat to dial down the fan speed (and amps needed) or some sort of timer that would turn the fans on and off every so often...say for 1 minute every 4 to still circulate the air but use only 1/4 the run-time/amp-hours?     I don't know how expensive or possible either of these ideas would be....

[solds88]

[p]
[/p][p]Todd,

This is an elementary drawing of the repeat interval timer that you were suggesting in your post. This is old school relay logic, but it's very effective in terms of reliability and only uses two components, and does not require an external trigger as SW1 is the trigger. Yes, there are more sophisticated applications available but may cost more and may be more complicated to apply? I haven't priced any of these components and now days you may be able to get a, Chinese made, dedicated repeat interval timer for less than the price of the two relays? Keep in mind that the relay holding coils also require current to operate. You need to do a study to determine the current draw of the holding coils verses the fan motor. And, you may find that this is not a worthwhile project and that a small fan running full time may work just as well.  I still use the little blue cube fan with a D battery.[/p][p]
[/p][p]


001 by james M, on Flickr      
[/p]

[drdave]

[quote source="/post/12508/thread" timestamp="1434739036" author="@james"][p]
[/p][p]Todd,

This is an elementary drawing of the repeat interval timer that you were suggesting in your post. This is old school relay logic, but it's very effective in terms of reliability and only uses two components, and does not require an external trigger as SW1 is the trigger. Yes, there are more sophisticated applications available but may cost more and may be more complicated to apply? I haven't priced any of these components and now days you may be able to get a, Chinese made, dedicated repeat interval timer for less than the price of the two relays? Keep in mind that the relay holding coils also require current to operate. You need to do a study to determine the current draw of the holding coils verses the fan motor. And, you may find that this is not a worthwhile project and that a small fan running full time may work just as well.  I still use the little blue cube fan with a D battery.[/p][p]
[/p][p][a href="https://flic.kr/p/uSs4Ui"]

[mitch]

The blue fan will run for a very long time, I used one all last summer and didn't have to change the batteries until the fall.

[daplumbr]

The electrical stuff is pretty interesting (really), but I'll raise a question about thermodynamics. These are small refrigerators. I'll hazard a guess that a very small fan would help the natural convection and improve the eveness of temperature inside as well as improve the efficiency a bit. However, at some point there is overkill and the fans themselves will be adding excessive heat. As well, I wonder if there is such a thing as too much air circulation that may add excessively to the conduction of heat to the interior. Bottom line is that I think (but I don't know) that a very small fan inside would be useful but not any more than that. On the outside, however, I can imagine a larger fan helping a lot to move air through the coils. The refrigerator in my 16 does not have a fan in the outside compartment and I think I'll add one that comes on when things get hot. 

[drdave]

[quote timestamp="1434849146" author="@sandroad" source="/post/12525/thread"]The electrical stuff is pretty interesting (really), but I'll raise a question about thermodynamics. These are small refrigerators. I'll hazard a guess that a very small fan would help the natural convection and improve the eveness of temperature inside as well as improve the efficiency a bit. However, at some point there is overkill and the fans themselves will be adding excessive heat. As well, I wonder if there is such a thing as too much air circulation that may add excessively to the conduction of heat to the interior. Bottom line is that I think (but I don't know) that a very small fan inside would be useful but not any more than that. On the outside, however, I can imagine a larger fan helping a lot to move air through the coils. The refrigerator in my 16 does not have a fan in the outside compartment and I think I'll add one that comes on when things get hot. [/quote]
So this fan is out of the question?

[charliem]

[quote source="/post/12525/thread" timestamp="1434849146" author="@sandroad"]The electrical stuff is pretty interesting (really), but I'll raise a question about thermodynamics. These are small refrigerators. I'll hazard a guess that a very small fan would help the natural convection and improve the eveness of temperature inside as well as improve the efficiency a bit. However, at some point there is overkill and the fans themselves will be adding excessive heat. As well, I wonder if there is such a thing as too much air circulation that may add excessively to the conduction of heat to the interior. Bottom line is that I think (but I don't know) that a very small fan inside would be useful but not any more than that. On the outside, however, I can imagine a larger fan helping a lot to move air through the coils. The refrigerator in my 16 does not have a fan in the outside compartment and I think I'll add one that comes on when things get hot. [/quote][font size="3"]Merlin,

You're correct, there is a point of overkill. I think the twin fans are overkill. The best info I can find on the twin fan 3.5" HD coolers is 10.5 CFM and 0.12A at 12 VDC. I think a single fan would suffice. At 5.25 CFM it would move all the air in a 5 cu.ft. fridge around each minute. I use the blue cube battery powered fan in my 21RBS and it seems to be effective and it moves a whole lot less air than 5 CFM. I put batteries in it last summer, before a month+ trip, and the batteries are still good. I think a slightly bigger fan may help somewhat, but it's not high up on my todo list.

My 7 cu.ft. fridge does have outside fans controlled by a thermostat. I hear them come on frequently on hot days, particularly when the fridge is facing the sun. It probably would be a worthwhile addition to your fridge, but you should include the thermostat for noise and power considerations.
[/font]