Advice on refridgeration unit please
 

On Sat, 19 Jul 2008 16:02:44 -0700 (PDT), "
wrote:

On Jul 19, 2:32*pm, Larry wrote:
...
200A x 12V = 2,400 watts.

No danger of overheating and warping AGM plates with only 2.4 kilowatts
forced into them at all. *You should crank up the charging even further.
...

Just for the record, my electrical system was designed and installed
by Gary Pacey of Outback Marine. He's an EE specializing in marine
power systems. He's installed virtually the same system on lots of
boats. In the small world category, the boat three down the dock from
us was built in the same year in the same part of Oz and with the same
power system as my boat. I know Gary did a lot of in house testing and
had good relationships with the suppliers of the batteries and
controllers. In short, this isn't something that I just threw
together out of catalogs.

Also, I don't follow you point. Are you saying 2.4Kw is too much
power for any battery bank or were you making a specific point?

-- Tom.


Not to disparage anyone but have a look at the battery manufacturer's
specs and see whether they recommend that high a charging rate. I
suspect you'll see something like 10 - 15% of rated capacity.


Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)

Advice on refridgeration unit please
 

On Jul 18, 9:34*pm, Larry wrote:
Ryk wrote :

You would be much better off filling the freezer with a phase change
fluid that melts/freezes somewhere in the desired temperature range.
Water, for instance...

I have lots of freeze packets, both in plastic bags and hard plastic cooler
packs made to go between the cans. *I'll try them, too, as a cold plate..

If you have two sets of the freezer packs you can freeze one during
the night and morning, move it to the fridge compartment just prior to
the hottest part of the day, simultaneously moving the other (thawed)
bunch of freezer packs to the freezer. I've found it works wonders.

Advice on refridgeration unit please
 

On Sat, 19 Jul 2008 21:42:34 +0000, Larry wrote:


The AC compressors synchronize to power line frequency (50 or 60 Hz), which
gives them a steady power output regardless of condensor pressure loading
which would drive a DC motor crazy trying to maintain counter EMF.

I don't think so - they are integrated induction motors and
compressors in a can. There's a capacitor that splits the phase, but
they slip the rotating field depending on load - if I recall

Brian W

Advice on refridgeration unit please
 

On Sat, 19 Jul 2008 16:02:44 -0700 (PDT), "
wrote:

On Jul 19, 2:32*pm, Larry wrote:
...
200A x 12V = 2,400 watts.

No danger of overheating and warping AGM plates with only 2.4 kilowatts
forced into them at all. *You should crank up the charging even further.
...

Just for the record, my electrical system was designed and installed
by Gary Pacey of Outback Marine. He's an EE specializing in marine
power systems. He's installed virtually the same system on lots of
boats. In the small world category, the boat three down the dock from
us was built in the same year in the same part of Oz and with the same
power system as my boat. I know Gary did a lot of in house testing and
had good relationships with the suppliers of the batteries and
controllers. In short, this isn't something that I just threw
together out of catalogs.

Also, I don't follow you point. Are you saying 2.4Kw is too much
power for any battery bank or were you making a specific point?

-- Tom.

Larry is possibly supposing that the 50 ampere hours you are charging
with will show up as 2.4 kW of heat - but he will remember that most
of that energy goes to electrochemical storage.
Still, give a person credit for gun-shyness from a battery fast-charge
accident!

Brian W

Advice on refridgeration unit please
 

On Jul 19, 5:04*pm, Bruce in Bangkok
wrote:
...
Not to disparage anyone but have a look at the battery manufacturer's
specs and see whether they recommend that high a charging rate. I
suspect you'll see something like 10 - 15% of rated capacity.
...

Nope. My battery manufactuer recommends charging with a voltage
regulated charger at 14.2-14.4 volts.* That's what I do. And as I
say, many other boats are doing this, too. It has worked well for me
for years and AFIK it works well for other folks also.

Not to disparage anyone, but where are you getting your information?
You sound very sure of yourself. However, what you are saying doesn't
fit with my experience or with the advice I have taken from a pro. Do
you have any sources or experience you can point to?

-- Tom.

*http://www.lifelinebatteries.com/mch...procedures.php

Advice on refridgeration unit please
 

Larry wrote:

Does someone make a 12VDC compressor? I've never seen one, here.

You're pretty much admitting that you've never seen a custom marine
refrigeration system and know nothing about them. Most of the small
boat systems in the last 20 years have used DC Danfoss hermetic
compressors. The larger systems use a belt or direct drive from a DC motor.

I do see
AC inverters built into fridges driving standard AC-powered compressors
that have relays or electronics to switch to shore power if shore power is
available to run the compressor straight off shore power, however.

Perhaps the AC/DC units on powerboats do it this way.


Inversion and synthsized AC power creation from battery power is now in the
range of 98-99% efficient with switching power supply technology using
pulse-width-modulation to accomplish a near-perfect sinewave output to
drive loads. These powerful synthesizers are very cheaply constructed and
very profitable.

It can be done, but if you buy a general purpose inverter it will likely
run at about 80%,


The AC compressors synchronize to power line frequency (50 or 60 Hz), which
gives them a steady power output regardless of condensor pressure loading
which would drive a DC motor crazy trying to maintain counter EMF.

It makes little difference in efficiency running a switching inverter
outside......or building one inside for another $1500 to sell at the boat
store. The price difference is phenomenal!


OK, I just checked the energy efficiency of a GE compact fridge, 5.7
feet with a tiny freezer. It uses 360 kWh's a year, or 1 kWh per day.
Supplying this with an inverter would take over 100 AmpHours. However,
a similar sized fridge built with a small Danfoss will only use about 35
Amp-hours. My system includes this size fridge (bigger, actually), plus
a 5 foot deep freeze which keeps a summer's worth of burgers and steaks
at about 5 degrees only uses 55-60 AmpHours in New England, maybe 75-80
in the tropics. (Mine is a belt driven 12V compressor with holding
plates and water cooling. In the tropics, if I had to do it over, I'd
be considering two small Danfoss air-cooled systems, one for the fridge,
the other for the freezer.)

I'm a fan of faster charging, either with a high output alternator or a
Honda 2000i pushing a 100 Amp charger - either way I can do most of my
charging at 75-95 Amps, even though its only a 440 AH bank. But still,
adding 65 AH a day to save some money doesn't work, even assuming the GE
fridge would fit in a boat. Frankly the cost is irrelavent; there's no
way I would double my charging time to have less capacity. Since you're
claiming you can't charge at over 25 Amps, running the commercial fridge
would take an extra 2 and a half hours, and a system like mine would
require even more hours.

Of course, you're saying that a marine fridge *could be* built for on a
few dollars more than a commercial unit. Possibly true, but the market
is tiny by comparison, and that's what its all about.

Advice on refridgeration unit please
 

On Jul 19, 5:22*pm, Brian Whatcott wrote:
..
Still, give a person credit for gun-shyness from a battery fast-charge
accident! ...

Oh yes. An exploding battery while offshore is a nightmare! I
appreciate the concern. I think Larry is incorrect in his assertion,
but I'm listening because if he convinces me that he isn't then I'm
going to change my ways fast.

-- Tom

Advice on refridgeration unit please
 

On Jul 19, 2:42*pm, Larry wrote:
...
Does someone make a 12VDC compressor? *I've never seen one, here. *I do see

http://www.rparts.com/Catalog/Major_...ss/danfoss.asp
(http://tinyurl.com/2tkja3).

"Like the smaller BD35F and BD50F models (below), the BD80F uses an
electronically commutated permanent magnet brushless DC motor."

They're pretty much everywhere. I've got two.

-- Tom.

Advice on refridgeration unit please
 

On Sat, 19 Jul 2008 18:52:14 -0700 (PDT), "
wrote:

On Jul 19, 5:04*pm, Bruce in Bangkok
wrote:
...
Not to disparage anyone but have a look at the battery manufacturer's
specs and see whether they recommend that high a charging rate. I
suspect you'll see something like 10 - 15% of rated capacity.
...

Nope. My battery manufactuer recommends charging with a voltage
regulated charger at 14.2-14.4 volts.* That's what I do. And as I
say, many other boats are doing this, too. It has worked well for me
for years and AFIK it works well for other folks also.

My battery manufacturer recommends charging to 14.8 and then dropping
back to 13.2, see:

http://www.trojan-battery.com/Batter.../Charging.aspx

If you stop when the batteries first reach 14.8 you never fully charge
your batteries.


Not to disparage anyone, but where are you getting your information?
You sound very sure of yourself. However, what you are saying doesn't
fit with my experience or with the advice I have taken from a pro. Do
you have any sources or experience you can point to?

Try
http://www.trojan-battery.com/Batter...Selection.aspx

Note that my figures were too low for some batteries. Trojan
recommends 20% but other recommendations are in the 10 - 15% range
see: http://www.solarnavigator.net/battery_charging.htm


-- Tom.

*http://www.lifelinebatteries.com/mch...procedures.php

Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)

Advice on refridgeration unit please
 

Bruce in Bangkok wrote:

Not to disparage anyone but have a look at the battery manufacturer's
specs and see whether they recommend that high a charging rate. I
suspect you'll see something like 10 - 15% of rated capacity.


That's what Trojan says for their wet cells, though I've done a lot of
charging at more like 18-20% will no ill affects. My first set did die
after 7 years (they might have gone another year or so if I had tended
to them better over a harsh winter), but frankly, they are the cheapest
part of the system.

For their gel and AGM batteries, they say 20%.