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Old 24-12-2014, 14:19   #16
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Re: Batteries

Amen, rwidman. Have been looking but just can't seem to find a DC fan with the CFM of my 10" AC box fan. Based on my study, I am losing 10-20% of the power to inverter in-efficiency. However, all the DC fans I've seen don't have enough capacity or are intended for long term, slow ventilation (like an RV roof fan).

When it gets hot and still in the sub-tropics bringing in a lot of high velocity air makes all the difference. Do you have any leads on high capacity DC units?
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Old 24-12-2014, 14:25   #17
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Re: Batteries

An automobile electric radiator fan is the only serious 12V fan I have found, they come in many different sizes and CFM, some are very quiet, some sound like a model airplane engine so watch for that.
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Old 24-12-2014, 14:41   #18
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Re: Batteries

a64pilot, terrific idea! I would have never thought of that. Probably can get a used one from a junk yard for next to nothing and mount it in a box frame. As stated previously, I knew this thread would bring in some pay dirt.
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Old 24-12-2014, 14:59   #19
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Re: Batteries

Not sure of the current but its got to be more efficient than running an AC fan on an inverter. Gets high marks elsewhere on CF.

Amazon.com: Fan-Tastic 01100WH Endless Breeze Stand alone Fan: Automotive

I'm using these to replace dead Hella fans.

120mm 25mm New Case Fan 12V DC 124 CFM Ball Brg 2 Wire PC Computer Cooling 350A | eBay

A bit more current than a Hella but they move more air.
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Old 24-12-2014, 15:22   #20
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Re: Batteries

I have 4 banks of 2 ea T105 Trojans as house and two fairly small cranking batteries all of which are connected to 500 watts of solar panels. I also have an 85 amp alternator belt driven from a 5.5 hp Honda engine and a second 85 amp alternator on the main engine. I live aboard mostly in the tropics and with the above set up have managed to get 7 years of life out of some of the T105s.

One of the ways I extended the life of the house batteries was to run my 12v fridge as a eutectic on a timer so that it did not switch on until 0800 then switched off for the night at about 1530. This arrangement allowed the batteries to fully charge and the eutectic to re-freeze during the day when I had plenty of power during the day then minimized electricity use overnight.

On the fans thing.

I have just fitted a 16" 12V auto fan in a forward hatch and have found it to be very effective in keeping the hot air from heating up the boat during the day. I mounted it in a piece of 3/8" ply and have used 4 barrel bolts to hinge it. The barrel bolts allow me to remove it to clean out the fly screening. It is too powerful and noisy to run at full speed so at the moment I am running it from 6V whilst I build a motor speed controller.
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Old 24-12-2014, 15:23   #21
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Re: Batteries

I incorrectly stated my fan size. It is a 20" box fan I got at Walmart for about $25. Literature says it does 2500 cfm on high. Many nights don't need that much air. Probably could get by with something that does about 1500 cfm.
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Old 24-12-2014, 15:29   #22
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Re: Batteries

RaymondR; very nice fan setup. I am definitely going to look into auto fans. Do you have any data on cfm and current draw?
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Old 24-12-2014, 16:16   #23
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Re: Batteries

RaymondR. That looks great. What brand, where did you buy it? N how much did it cost? Thanks
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Old 24-12-2014, 16:30   #24
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Re: Batteries

sparrowhawk1; i was just doing some checking on the auto fans. They aren't real expensive (around $100 new) and cfms are in the 2000 category. What is currently mistifying me is the amperage (around 20 amps) which seems really high considering that when I run my 2500 cfm AC driven fan at it's 0.8 amps at 120 volts it equates to only 8 amps at 12 volts. Even with a 20% inverter loss, the battery draw would be 10 amps, not the 20 amps specified for the DC powered auto fans.

Anyone understand why this is so? Are AC inductive motors that much more efficient than DC?
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Old 24-12-2014, 16:45   #25
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Re: Batteries

new radiator fans can be had for about $30, try Amazon for instance, bigger ones are in the 2300 CFM range or so and should pull about 8 to 10 amps, depending on voltage of course, remember cars run at 14+ or- and fully charged we are about 13 and under load maybe less.
You should be able to get one from a junkyard for next to nothing.
I'm still with the walmart 20" box fan myself and last summer when it was really hot, I tied it between our grab rails and a port on line above the setee, called it my Redneck ceiling fan. Wife hated it for the looks.
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Old 24-12-2014, 16:47   #26
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Re: Batteries

Quote:
Originally Posted by Cal31 View Post
sparrowhawk1; i was just doing some checking on the auto fans. They aren't real expensive (around $100 new) and cfms are in the 2000 category. What is currently mistifying me is the amperage (around 20 amps) which seems really high considering that when I run my 2500 cfm AC driven fan at it's 0.8 amps at 120 volts it equates to only 8 amps at 12 volts. Even with a 20% inverter loss, the battery draw would be 10 amps, not the 20 amps specified for the DC powered auto fans.

Anyone understand why this is so? Are AC inductive motors that much more efficient than DC?
AC is more efficient but that isn't the issue with electric fans used for automotive radiator cooling. With the alternator output while the engine is running, being energy efficient just wasn't a design criteria.

The fans that jcapo recommended are designed for the RV market and as such, efficiency was a design criteria. If 900 cfm will work for you, that can be had for about 35 watts with his fan suggestion. For $57 that is hard to beat.

Fantastic Vent Endless Breeze Fan - $56.99
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Old 24-12-2014, 18:56   #27
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Re: Batteries

Thank you every one for great input. a64pilot, I am going to do more homework. The amps you indicated sounds a whole lot more reasonable than the information I was finding via a cursory look on the internet.

Merry Christmas!

Brian & Carol McMahon
s/v Windchaser
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Old 24-12-2014, 19:42   #28
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Re: Batteries

For example. 37' cruising sailboat. adler barbour 3.5 cf fridge, vhf radio, navtex, interior lights, occasionaly playing a dvd movie. We are probably at the low end of electric 'toys' for boats our size. Of course there are bilge pumps, which never run unless i'm testing them, and an anchor light which is LED and hardly counts.

Battery Bank. House is four golf cart batteries, engine start is one size 29. All are flooded lead acid. The size 29 should be replaced with two more golf cart batteries in the future. The boat has a built in battery box for six golf carts.

Charging. We spend a lot of time anchored in one place. The main engine can charge the battery of course, but I don't run it much. We have one 135 watt solar panel. It supplies about half the power we need. A second one would be an ideal addition and might make us totally solar powered. We also have a honda 1000 generator and a 35 amp smart automobile charger which we have to run for two hours or so every third day.
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Old 24-12-2014, 19:52   #29
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Re: Batteries

For example. 37' cruiser. Adler Barbour 3.5 cf fridge, VHF, Navtex, lights, occasional DVD movie.

Batteries. Four golf cart batteries for house bank, one size 29 'start' battery. All are flooded lead acid. The built in battery box is designed to hold six golf carts, and it eventually should.

Charging. We anchor a lot, so I don't depend on running the main engine just to charge batteries. We have a 135 watt kyocera solar panel, which provides about half our needs. A second one might make us totally solar. So every three days or so I have to run our Honda 1000 with a 35 amp smart automobile charger for maybe two hours to bring the batteries back up.
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Old 25-12-2014, 03:31   #30
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Re: Batteries

I am not sure of the brand having thrown the packaging away, I bought it at one of the discount auto parts stores for about A$120.

Since I am running it on 6V it only pulls 4 amps, it is mounted above my V berth and I will probably run it even slower after I install the speed controller. On 12V it blows too hard to be comfortable underneath it.
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