Eva Dry 2200 too much for our bank?

[Clipper4730]

Hey y'all about to put the old girl to bed till it cools off and had a quick question on power usage. We want to run a dehumidifier or two on board and are wondering if we have enough juice to run them constantly. The model we are looking at uses 72w. Would this be per hour or per 24 hours? It is a 12v 6amp unit. Can anyone splain it in small easy to read words. We have a three of the large house batteries and am somewhat embarrassingly unsure of the total capacity. Think it is around 600 amp hours. We also have a 560 watt solar array with a midnite mppt controller taking care of things.

Anyways if you are electrically inclined and some time an explanation of how to calculate the usage of said device would be fantastic.

Thanks in Advance!

Will

[Dsanduril]

Watts are a measure of power, Wh and Ah are a measure of energy (although Ah is hokey, since without specifying voltage you can't know the energy value, we just assume 12V in most cases).

So the 72W rating indicates that is takes 72W of power to run the unit. At 12V this is 6A of current. If you run it for one hour then you have consumed 6Ah of energy (6A x 1 hour). So, for a 24-hour day you are looking at 6A x 24 hours = 144Ah of energy used every day.

Presuming your batteries are lead-acid the usable stored energy is about 50% of the rated capacity, or about 300Ah. So, you could run one unit for two days (300/144 ~2), or two units for one day (300/(144 x 2) ~1) before reaching the minimum desirable charge state on the batteries.

On the charging side, so much depends on the solar installation, the location, shading, etc. Making some gross generalizations, if everything is working perfectly you can probably see 4-5 hours equivalent of the rated output of your panels, (you may see full power for an hour or two, 80% for another hour or two, and lower for the remainder of the day, but it works out to about 4-5 hours of full output).

If we use 5 hours then 560W x 5 hours = 2800Wh/day. Dividing by 12 to get Ah, the solar might be able to deliver 233Ah/day. At four hours equivalent you might get 187Ah/day.

To run one unit you need 144Ah/day, and you have maybe two days total reserve in the batteries. So, you might be able to run one unit, will depend on actual solar output, and how many sunless days in a row you might have.

That's a lot of generalizations on very little information, but you might be able to get away with one unit, certainly could not with two.

[GILow]

Excellent explanation. I would just add what might be obvious but might not, and that there is a very high risk of running the batteries low enough to permanently damage them if there was a cloudy day or two. Based on the stated power draw I would not risk running the unit without some kind of protection factored in. Either a low voltage cutout or a timer that limited the number of hours the unit runs.


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[Dsanduril]

I agree, a low voltage cutout would be nice, and probably a timer to run them less than full time. Don't know the proposed storage location, but maybe run the units at night, and relay on warmer sun during the day to keep condensation at bay?

[HopCar]

I won't comment on the electrical side as dsandril has done a much better job than I could, but I do have experience with the EvaDry dehumidifiers. I use one on my boat and it works well. The problem is that the tank can fill in just a day or two. I solved that problem by getting a length of aquarium air hose, drilling a hole into the tank, shoving one end of the hose into the tank and leading the other end of the hose to the galley sink drain. Now it just drains overboard.

[JDMac]

Not sure where you're dumping the water from the dehumidifier, if it's in the bilge, don't forget to account for the bilge pump power consumption.

Hope it works out for you!!

[thinwater]

Small words... so funny.


Another thought is that it does not NEED to run 24/7. I have mine on a timer, though a day/night switch would work just as well. This is even better in the winter, as it allows for defrost during the day, when solar warming will often bring the cabin temp above freezing.

[mitiempo]

Originally Posted by Dsanduril

If we use 5 hours then 560W x 5 hours = 2800Wh/day. Dividing by 12 to get Ah, the solar might be able to deliver 233Ah/day. At four hours equivalent you might get 187Ah/day.

Good post.

One correction though is that a battery does not charge at 12 volts, but 14.4 to 14.8 depending on controller setting and battery requirements. When figuring solar charging I divide by 15 as it is a bit more conservative and easier math. That equals 187 AH per day.