I knew what Larry intended: why didn't you?

Brian W

On Wed, 14 Jan 2004 20:59:50 GMT, "Morex Support"
wrote:

Fatal Error.
The heating element is resistive. 120V 2KW element is approx 7 ohms. Reduce
voltage to 24 v and current draw drops to 3.5 amps. Power is not a constant.
"Larry W4CSC" wrote in message
...
Wouldn't actually make much of a difference. If the 2KW water heater
were running on 12V, it would draw 167A. On 24V it would still draw
83.3A, draining the batteries in a matter of minutes, not hours......

On Thu, 15 Jan 2004 13:09:01 GMT, Brian Whatcott
wrote:

I knew what Larry intended: why didn't you?

Brian W

Now I can stop shaking my head and wiping my glasses....(c;

"Morex Support" wrote in message
able.rogers.com...
Fatal Error.
The heating element is resistive. 120V 2KW element is approx 7 ohms.
Reduce
voltage to 24 v and current draw drops to 3.5 amps. Power is not a
constant.


I am sure that Larry wasn't suggesting that a 120 volt heating element be
used at 12 volts. What he was suggesting is that IF a 24 volt equivalent
device could be found, then it would draw 83 amps.

Oh, and by the way, your example is way off also. In most cases, heating
elements have a dramatic increase in resistance as they heat up. The element
in question may have a resistance of 7 ohms when it is dissipating 2KW, but
if you drop the voltage the resistance will drop also.

This resistance change is even more dramatic on a light bulb. Take a low
wattage light bulb and measure the resistance when it is cold and you may be
surprised! This is why cutting the voltage in half to incandescent lights
does NOT cut the current in half!

Rod McInnis

"Morex Support" wrote in message . cable.rogers.com...
Fatal Error.
The heating element is resistive. 120V 2KW element is approx 7 ohms. Reduce
voltage to 24 v and current draw drops to 3.5 amps. Power is not a constant.

I don't recall anyone suggesting to run a 2kW, 120V heating element
directly off of 24V. The question was to run an inverter on 24V to
make 120V, or to obtain a 2kW, 24V element (0.288 ohms).

%mod%

Mi,
I completely agree with you. Electric is the way to go for both safety and
convenience. I would not have gas unless CNG was available everywhere and
there is the rub. It isn't. The gas of popular choice is LPG and that is
heavier than air. CNG is not. So for me, the best of the rest was electric.
The other responders mentioned the impractcality of using 24V for heating
and cooking. They are correct. In order to be all electric, you must use
240V. Even 120V is impractical because of the wire size required. You need a
large generator, in fact you probably need 2. That means a big boat. The
other problem is the noise from a running generator. I have overcome this
problem with a shaft driven 6KW generator that is silent and a 35KW diesel
generator, but then I have the space. Please be careful of capturing heat
from your engine exhaust. Yes, it is possible, but if you take to much heat
out, you will create acidic deposits that will destroy 316. If you use a
fresh water exchanger and your hot water tank is up to temp and you continue
to run the engine, the exchanger overheats. So you need auxillary cooling,
when your heat demand is low. I guess there is no free lunch.
Steve
"misia" wrote in message
ail.from.there...
On my new boat I will have a powerfull 24VDC battery bank charged by a
diesel generator and auxiliary sources.

I did a bit of search but couldn't find much- are there any 24 VDC
appliances such as cooker/oven, fridge, AC and water heater you could
recommend?

I know I can run standard items through power inverter but I would
prefer not to do it for the sake of reliability/efficiency/cost. I wantMi,
to go totally electric (no gas)

Regards Mi

Steve Lusardi wrote:

If you use a
fresh water exchanger and your hot water tank is up to temp and you continue
to run the engine, the exchanger overheats. So you need auxillary cooling,
when your heat demand is low. I guess there is no free lunch.

??? Are you suggesting there are systems out there that use
the domestic hot water system as a heat sink for the engine
cooling requirements? Or that someone would install a heat
exchanger that is rated at a lower temperature than the
operating temperature of the engine cooling circuit?

Something is missing here.

Rick

Rick,
If you use a water cooled muffler as a heat exchanger to heat your fresh
water, at some point your freshwater tank will be hot enough. You now must
have a mechanism to dump the absorbed exhaust heat or damage will occur
somewhere in the system. Most colorifiers use the engine's cooling water
circulating through an imersed exchange coil in the hot water tank. In that
way, the engine's cooling system itself is the energy dump. If the exhaust
system is used, another mechanism must be found.
Steve
"Rick" wrote in message
nk.net...
Steve Lusardi wrote:

If you use a
fresh water exchanger and your hot water tank is up to temp and you
continue
to run the engine, the exchanger overheats. So you need auxillary
cooling,
when your heat demand is low. I guess there is no free lunch.

??? Are you suggesting there are systems out there that use
the domestic hot water system as a heat sink for the engine
cooling requirements? Or that someone would install a heat
exchanger that is rated at a lower temperature than the
operating temperature of the engine cooling circuit?

Something is missing here.

Rick

Steve Lusardi wrote:

If you use a water cooled muffler as a heat exchanger to heat your fresh
water, at some point your freshwater tank will be hot enough.

Just curious, no one mentioned using the exhaust waste heat
for domestic water heating. I have never seen such an
installation and suspect it is pretty rare since for the
reasons you mention it is a cumbersome means to avoid using
heat from the coolant.

Rick

That means a big boat.

Thanks to all posters for feedback.
I have the luxury of a big cat and big battery bank.

I'm not worried about the fridge , it's maybe 300W/24 hrs average in tropics
and half of this in the north.

As for the cooker- two hot plates at 1KW each seems a lot but given you use it
for 1 hour/day it translates to something like 2kW/24 = 83 Watts average @ 24
hrs and I think it's well worth it given the safety,cost, convenience and
simplicity advantages.

Same goes for coffee maker etc.

I did do my math before posting here and I understand how amps/watts etc add up.
I agree higher voltage would be nice but we are stack with 24V and don't expect
to be running generator at all times. Also we have luxury of designing
everything from scratch as the boat is being built and can acommodate locations.
In other words instead of long thick wires we can make them short for equipment
which consumes a lot of ampers. I'm trying to be smart but not always
conventional with this.

I agree electric heater might be the most energy hungry element, especially if
the water has to be retained and temperature maintained in the tank for 10
people onboard.

This is something that I'm considering to built around hybrid solution.

I came accross this Webasto heater:

http://www.navstore.com/pdf/webasto/Webasto%20TSL17.pdf

What do you think?

Another thing is - I'm wondering if we need a water tank at all? It takes lost
of gallons to shower 10 people- it cost money and space. I remember seeing in
some country (not US) showers with built in electric heater element which will
simply just warm up water passing through a piece of the size of grapefruit.

Regards M

On Sun, 11 Jan 2004 22:34:28 GMT, misia
wrote:

I agree electric heater might be the most energy hungry element, especially if
the water has to be retained and temperature maintained in the tank for 10
people onboard.

================================================== ====

To cruise with 10 people in the tropics, you're going to need a water
maker and lots of power. You might as well spring for a decent sized
generator with 110/220 volt power and not worry about finding 24 volt
appliances or stove fuel.