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Old 21-01-2007, 19:06   #436
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This is the way the DC current usage could add up at happy hour (just after dark)

2 fridges running for 2/3 of our hour...........................66 amps

1 freezer running for 1/3 of our hour..........................17 amps

of 40 odd lights, lets say 75% are on.........................30 amps

stereo............................................ ......................17 amps

Fans an other misc.............................................. ....3 amps

Total amps DC used in one hour......133 amps

Now lets see how this affects the standard 2 battery system

2- 140 amp-hour batteries hold a total of 280amp-hours, so to take them down 20% would be .20 X 280 = 56 amp-hours used.

If you take them down 40%, that would be twice as much or 112 amp-hours used.

Now lets combine the drain on the batteries with the input from the 2X25 amp chargers or 50 amps/hour at peak efficiency, most chargers are no better than 90%, so lets say we get 45 amps/hour.

So in our happy hour we consumed 133 amps,(this is just DC, and is not counting showers and the like AC draw off your inverter) and replenished 45 amps. This means that our 2 house batteries are down a net 88 amps in 1 hour or 88Ah. This means that at the end of happy hour our batteries are at 31.4% discharged. If happy hour continued for another 1/2 hour the batteries would be down 47.1% and damage is occurring.

It seems fairly clear, that to be safe on a charter boat, that we either add batteries, add battery chargers, or both. The easy fix is add 1 or 2 more house batteries, but that is also the one that add the most weight.

What say ye all!

Fair Sailing _(\_
Quiet Riot 420
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Old 21-01-2007, 19:15   #437
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With the extra fridge it sounds like you do need to do something about it. Which route are you taking? This just makes me want to measure actuals before I act further.
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Old 21-01-2007, 19:16   #438
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The water heater has an on/off breaker on the AC panel.
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Old 21-01-2007, 19:22   #439
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I have ask Lagoon all alone to give me more 12V battery chargers,(or bigger ones) but its like talking to a brick wall. I was considering ordering 2 as replacement parts before the boat reaches Tortola, depending on how much Lagoon wants to gouge me in price for them. If they are way to much, I will probably just add more batteries.
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Old 22-01-2007, 00:07   #440
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I just zoom in again on the 2 units that I though were 12V battery chargers, and they are really just 72V to 12V converters, this is not right, as Nick's new Elec Engine file, that he sent to us, clearly identifies 2 x 25 watt battery chargers in their schematic. I going to try and clear this up, as they should definitely be 3 stage chargers and not just converters if you want your batteries to last! Their must be a float stage to keep from over charging or wasting 72V capacity.
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Old 22-01-2007, 05:28   #441
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I think you need to do your calculations based on realistic numbers. 66 amps for two small fridges is extremely excessive. The small 100-120 ltr fridges usually use a bd 35 compressor. The maximum draw is 78W or 6A @ 13v, in practice more like 4A, allowing 6A and a 75% duty cycle 4.5A x2. the freezer may use a bd50 109w max or 8.4, same duty cycle 6.3A. Even if everything used bd80 compressors at maximum it only comes to 29A @75% duty cycle or 38A @ 100% duty cycle a long way short of 83A.
Danfoss Brushless DC Hermetic Compressors

If your stereo was drawing 17A there wouldnt be a happy hour if I was next to you. There would be a stream of bricks being sent you way to get you to shut up, 220W RMS is loud.

40 halogen lights in this day and age, crazy. Havent Lagoon heard of the alternatives, things like this would be higher on my list of things to bitch about before more batt chargers.

I do totally agree with your idea to shift the ac load to 72v inverters.

If the power used was in line with your estimates the gen set will see some serious duty. I would certainly make sure the hot water has a heat exchanger off the gen set.

Mike
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Old 22-01-2007, 05:32   #442
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Quote:
Originally Posted by Quiet Riot 420
I just zoom in again on the 2 units that I though were 12V battery chargers, and they are really just 72V to 12V converters, this is not right, as Nick's new Elec Engine file, that he sent to us, clearly identifies 2 x 25 watt battery chargers in their schematic. I going to try and clear this up, as they should definitely be 3 stage chargers and not just converters if you want your batteries to last! Their must be a float stage to keep from over charging or wasting 72V capacity.
Is it possible the two units you photographed have some other purpose apart from cross-charging and that the actual cross-chargers are elsewhere?
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Old 22-01-2007, 08:07   #443
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Steve,

There would be no other reason to convert 72V to 12V, other than to help charge the house batts, which power the whole 12V system by themselves.
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Old 22-01-2007, 08:28   #444
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Whimsical,

You may be right on the friges and freezer, as I was just trying to make an educated quess. The Waeco site is no help at all, so today I am having my brother go around to measure the draw on different small refridgerators when they are running to see if we could get more reliable figures to use. Maybe we can get some radio readings also. I'll let you know what we find in real world situations.

And yes, as the Halogens burn out I do indeed intend to replace them with LED's to conserve current. How long do these halogen bulbs last?

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Old 22-01-2007, 08:55   #445
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Whim,

I'm not sure where you got you numbers from at the Danfoss site. The BD80F's capacity is listed at 274 watts, and this would be 22.8 amps just for the compressor, not counting the blower motor, right? If the blower motor used 9.2 amps to circulate the cold air, (a rough guess) then this would indeed add up to 33 amps/units if running for the whole hour. At 75% this would be 24.75 amps each or about 50 amps for the pair.

Their smallest unit the BD35F is 174 watts or 14.3 amps. At 75% this unit with a blower might draw around 15 amps alone or about 30 amps for 2 units.

We'll see what the real world reading are, and try to adjust the figures then.

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Old 22-01-2007, 18:43   #446
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Capacity is different to power input. Refridgeration does not make cold, it just pumps the heat out of the cabinet. For the BD80 Power Input (max): 168 Watts is what is drawn from the batts, Capacity: 934 Btu/hr (274 Watts) is the cooling capacity. No I have not discovered perpetual motion, if you look at any cooling systems the stated BTU is far greater than the consumed power.
Fridges don't use a blower to distribute the cold, the compressor pumps the liquid refridgerant through the evap. Some have a small fan to improve airflow over the condensor, the power consumption is tiny. The Kollmann site has a lot of interesting info.
KollmannMarine Boat Refrigeration Specialist

I haven't repaired low voltage entertainment devices for a long time and my memory has faded and I am too lazy to connect an amp meter into my car stereo. I do have a small DVD player with a 7" screen, this takes less than an amp @ 7V say 7 watts. A similar power consumption for a car unit would be reasonable, an allowance for the amplifier stages would be needed of course. Systems are often rated higher, needed for transient response etc, but 5 watts rms per channel is quite loud so 10 watts or 1A on average. Don't get sucked in by the advertised numbers for audio equipment. I have seen 10 W amps described as 400 watts peak to peak or music power or some other such bullshit. The only figure that has any meaning is RMS, a figure that equates ac to dc without the hype. I would think 2 or 3 amps for the stereo would be plenty.

Mike
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Old 22-01-2007, 19:13   #447
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I had a look at the Waeco catalogue. The only unit that has power consumption figures is the FR 145. This is a portable chest type fridge of 136 ltr. It uses the DB35 compressor. From the pics the insulation is not very thick. Average power consumption is claimed to be 2.9 Ahr based on an interior temp of 5C and 32C ambient.
In refridgeration consumption will be in proportion to the heat load placed on the compressor and not the power input maximum. The bigger the box and the poorer the insulation the greater the consumption. Front opening units consume more but this is a difficult thing to define. The fuller the unit the less the impact. Maybe take waecos 3A up to 5 but this is a big number for a fridge in a yacht from my research, 120Ahr per day.
How big are the fridges in the lagoon.

Mike
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Old 22-01-2007, 21:49   #448
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Mike,

I looked at the Waeco site(s) (many, and none were very good), and think the friges on the Lagoon 420 are model numbers RPD-0110U & PRD-0080U. I have attached pics of both friges. I found a CT phone # that I may call tomorrow to see if they actually have amp draw while running figures.

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Old 22-01-2007, 21:52   #449
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Lets see if I can get the galley frige to show up
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Old 22-01-2007, 22:04   #450
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Owners,

Notice the hand railing up to the helm in the first pic. This is the one they are suposed to replace, as this one is way to flimsey and would probably be broken off in the first few weeks of charter. I wonder if they will fit the US boat with a new railing before the Miami Show. Also in that pic, notice the propane cylinder to the left of the frige. It is stored here and not in the propane locker because the 2 bottles fit in the locker so snuggly that there is not room to mount the manifold, without removing one of the tanks. Thus us see it stuffed under the helm. This would be another "fix list" thing to check out at the Miami show.
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