12 volt freezers?

[Jeff S]

We bought a small AC model from Home Depot for $79.00 and use it on an inverter. Popcorn and cold beer after a day of sailing--Can't be beat. We use it on shore power when in port.

Can you use it on battery power through the inverter?

Jeff S

[GBroga]

I have owned or own both of the Honda's. It seems these knock-offs are priced $150 less than the lowest price I paid. Knowing the reliability of the Honda name I would cough up the extra $$$ to have piece of mind. I had 1800 hrs on the 1000 when I sold it and met a guy with the 1000 with almost 6000 hrs on it. The only non maint parts were 3 of the eco-throttle switches and gas caps and a set of rubber feet. My Brother in law bought one of those Chinese enduro dirt bikes and it ran good for about 100 hrs or so. No it eats chains and other parts are failing. He saved about $1800 off a name brand but if things keep up he will be at that price soon enough. I have bought knock-offs before and have been satisfied. These items include baby strollers, watches, handbags for the bride. I have been generally happy with them but am weary about an engine knock off. If you could buy a honda civic for $1000 more than a Daiwoo would you do it? Whats with the $800 microwave? I would buy the Honda 1000 and a cheap dial operated micro at WalMart before that came into my life-no battery switching or motor running...Then you could even buy a small A/C and be cool or use the power to charge the batteries with a charger...

[kmclemore]

I'd sure like to have one but 12 volt microwaves are expensive.
http://www.caravansplus.com.au/product_ ... ts_id=5939

Whats with the $800 microwave?

Keep in mind, that's in Aussie dollars... converted to US dollars it's $627. Still way more expensive than an AC unit from WalMart, though.

[Chip Hindes]

Can you use it on battery power through the inverter?

You'll need a pretty big inverter, and even then, not for long. A small AC will draw 750-1000W continuous; lets say 750 for argument. You need about 1.5X surge capactiy to start an AC. So first, you need an inverter with a 750 watt continuous rating and 1125 watt surge capacity.

Then, once you get it the AC started, and figuring 85% efficiency on your inverter, you will draw 74A DC continuous. A standard 65A-h deep cycle Mac battery discharged to 50% will be done in less than half an hour. Even several good sized batteries totalling (say) 250 A-h will last well under 2 hours. You can cycle the AC and keep adding battery capacity to give more hours of operation, but that becomes impractical in a hurry.

Eventually you will need to recharge the batteries. A typical 50HP outboard alternator will put out around 10 amps max. So, for every continuous hour you run the AC, you have to run your outboard at full alternator output (i.e., something close to max speed) for seven and a half hours.

Your AC, batteries, alternator etcetera, will differ from these numbers but they are in the right ballpark. Bottom line, it's simply not practical to run AC off an inverter. If you really can't do without it, plan to dock at a marina where you have access to shore power, or save up for an auxiliary generator.

[GBroga]

even at the conversion rate $627 is some real expensive popcorn. What ever happened to Jiffy POP on the grill? That neat metal pan with foil over it? At that price you might as well take a chance on the cheap Honda knock-off generator and a wal mart special micro unit and for the saving you will have from having to buy 3 huge batteries to run the inverter you can even buy a cheap a/c unit. With the rest of the moeny you have left buy 8 cases of micro popcorn and keep those sea gulls well fed..Electric usage on these boats are simple. Wind gens and solar barely keep up with normal usage of lights, gps, cd players,etc. There is not much room to add monsterous solar panels although I have no doubt duane would find a spot. Those huge panels would just about end the trailerability. I have a small solar unit that lays on the cabin top to keep the batts charged when not in use but other than that these inverters, microwaves, a/c, tv's just suck juice from a small battery bank. Save the money and buy a small genset for the times you must use ac power.

[Jeff S]

Chip, Actually I was referring to the microwave not the A/C. I quoted the wrong part of Tom's message. Good discussion on the A/C but I never would consider running A/C off an inverter. I have a microwave in the boat I have used with shore power- just wondering if anyone uses and inverter on the boat to power the microwave since the time would be relatively short- what size inverter and how well does it work.

Jeff S

[Dimitri-2000X-Tampa]

Actually, there was a boat for sale a few months ago that we talked about on this board which ran A/C off an inverter. The boat was in Bradenton Florida and had a built in A/C under the front dinette seat with about 7 batteries onboard. He had a big inverter on board, maybe 1500-3000 watts, and wrote that he could run the A/C for nights at a time without shore power. The boat had a bunch of other electrical loads on board too, microwave, other kitchen gadgets, etc. I don't remember what type of recharging situation he had on that boat.

[mike]

Actually, there was a boat for sale a few months ago that we talked about on this board which ran A/C off an inverter. The boat was in Bradenton Florida and had a built in A/C under the front dinette seat with about 7 batteries onboard. He had a big inverter on board, maybe 1500-3000 watts, and wrote that he could run the A/C for nights at a time without shore power. The boat had a bunch of other electrical loads on board too, microwave, other kitchen gadgets, etc. I don't remember what type of recharging situation he had on that boat.

Nukular?

--Mike

[Catigale]

Snip

. He had a big inverter on board, maybe 1500-3000 watts, and wrote that he could run the A/C for nights at a time without shore power.

unsnip

...Some bad math here...with a battery cap at roughly 1 kW hour per battery you need one battery per hour of operation - so for 'nights of operation' I calculate 20 batteries

Maybe he ran the AC without the compressor....



Now here is an thats real.....

Drop a 3/4 inch pipe overboard and suck up >70F water from your location. A small pump will pull about 30 Watts, so if you run it for 8 sleeping hours you discharge you battery about 240 W hours, or 1/4 of its capacity, which is reasonable. On shore power of course, you can just use juice from the marina

Now send this water through a Copper coil heat exchanger like an automotive heater core. This you locate either near a Day/Night Vent (no more electrical draw) or a small 12 VDC blower (another 20 Watt draw or so).

The whole unit could be nicely mounted in the galley area with the discharge Tee-D into the galley sink - you might need a small drip pan to take care of the condensate.

The idea is you use the thermal mass of water around you to cool the boat instead of a relatively inefficient compressor.

In the fall, the same system can heat the boat, where there is often a 15F difference in air and water temp the other way.

[TampaMac]

Uh, in the summer when you need AC here the water keeps about 85 to 90 degrees F, or about the same as the air at night.

So that system just would not work here, in the west with the cold Pacific maybe.

http://www.dcbreeze.com/finding_power.htm

Check the above link for a discussion about running a AC system from batteries and etc.

[Chip Hindes]

In order to get decent cooling or heating out of a small tube type heat exchanger, the delta T between the tubes and the air you're heating or cooling needs to be substantial; 70-100 degrees. 10-30 degrees won't do it.

You can use the thermal mass of the water to build a fairly efficient water source heat pump. Somebody has already done this; I've seen it somewhere; but as I recall the cost was pretty steep, and it still takes quite a few amps to run it.

[deacm]

I have been looking at both the WAECO COOLMATIC CF-50 and the ENGEL 45 12 volt freezers. The big difference for me seems to be the power draw. As far as I can tell the COOLMATIC draws 5 amps max. and the ENGEL draws 2.5 amps max. Is this difference worth worrying about. Other difference worth considering? Anyone have experience with either of these units.

I'm wanting to put some refrig in the boat next year as well and looking at the Waeco CF-50. The Waeco Coolmatic 52 Quart consumes an average of 45 watts (which if my high school science class memory is still there should be 3.7 amps (45W divided by 12v, right?)) which is maybe 33% more than the Engel. The Waeco weighs less (44lbs vs 53 lbs), holds more (68 beer cans vs 60) and has a lockable lid. If I have a 150 amp hour AGM battery, what would the 'running time ' difference be would you guess without running the battery dead?

[Moe]

The rule of thumb is not to discharge deep-cycle batteries below 50% charge for a good life. That being said, where space and weight are a consideration, some of us RVer's take 'em down lower, to maybe 35%, knowing we're going to have to replace them maybe twice as often.

Battery charge rate is also not linear throughout it's entire range. It takes about as long to charge from 80% to 100% as it does from 20% to 80%. Many, if not most, of us with generators, shut them down at about 85% charge (i.e. we operate in the "bulk mode"). So depending on how often you want to replace batteries, after the first day off shorepower, where you got to 100% charge, we'd have between 1/3 and 1/2 of the rated amp-hours for actual daily use.

Refrigerator power consumption, RV or boat, is hard to figure because it varies quite a bit with ambient temperature. In mild weather, the "duty-cycle" ("on" time percentage) is about 25% of the time, and that's what manufacturers use for "average" consumption. So for 24 hours a day, you'd multiply that by 0.25 (or divide by 4) to get 6 hours, and multiply that by the current draw, when on, to get the daily amp-hours used. In hot weather, duty-cycle can be 50% or more, so you'd double the amp-hours. But since many of us run the generator for 4 hours/day (you have to put back about 110% of what you use), we only calculate the power used over 20 hours, since the charger/converter is powering the frig (and other things) during that 4 hours of charging.

BTW, even though RV refrigerators are generally absorbtion type and run off LP when not on 120VAC, we still have a 1 amp gas valve and some milliamps for the circuit board to have to worry about.

Hope this helps,
--
Moe

[trapeze]

I have been looking at both the WAECO COOLMATIC CF-50 and the ENGEL 45 12 volt freezers. The big difference for me seems to be the power draw. As far as I can tell the COOLMATIC draws 5 amps max. and the ENGEL draws 2.5 amps max. Is this difference worth worrying about. Other difference worth considering? Anyone have experience with either of these units.

I'm wanting to put some refrig in the boat next year as well and looking at the Waeco CF-50. The Waeco Coolmatic 52 Quart consumes an average of 45 watts (which if my high school science class memory is still there should be 3.7 amps (45W divided by 12v, right?)) which is maybe 33% more than the Engel. The Waeco weighs less (44lbs vs 53 lbs), holds more (68 beer cans vs 60) and has a lockable lid. If I have a 150 amp hour AGM battery, what would the 'running time ' difference be would you guess without running the battery dead?

Deacm,

Are you comparing the average consumption rate of the Waeco unit to the maximum consumption rate of Engel?

As Moe pointed out, the average rate is hard to pin down, because of all of the variables.

I would think the Manufactures of both of these units are optimistic about the average rating. This is why I am considering the comparison of the maximum consumption rate of these two units, given all other variables being equal.

I must say that 8 beers difference is a very important consideration.

[deacm]

Are you comparing the average consumption rate of the Waeco unit to the maximum consumption rate of Engel?

I'm just going by what the brochures say............Waeco say 45 amps average and Engel says just 2.7 amps