Hot water question for Larry
 

The AC element on my hot water heater is 1250 watts.

Can you safely draw from an inverter while the engine is running? If
I put in a 1500 watt inverter and used it carefully to only run the
water heater (which would also be getting waste heat from the cooling
water coil) and was sure that my other 12 V loads were minimal at the
time, could I get my hot water tank heated up in the 5 - 10 minutes
that I do with shore power? (It takes motoring half a day to do it
with the waste heat alone from my 20 hp diesel).

Or, will this burn up my little 35 amp alternator? I have a 55 I can
put in but it needs a different voltage regulator.

I would never try to make hot water from the batteries through the
inverter for obvious reasons.

--

Roger Long

Hot water question for Larry
 

Roger Long wrote:

(It takes motoring half a day to do it
with the waste heat alone from my 20 hp diesel).

Something may be wrong with your setup, Roger. IIRC, you have a very
similar engine to my Yanmar 2GM20FC. I run the coolant through an 11
gal heater, and it get quites hot in well under an hour, maybe even 30
minutes. Actually for a few years the engine was running a tad hot
(180 degrees) but after cleaning out the heat exchanger its normally
at 165-170, which probably slows the heating a bit. Even if all I do
is run the engine for a little while to set an engine, it usually
heats enough for showers for the day. When I run for charging, the
engine never gets above 160, so in that case after an hour run its
still not quite as hot as when we're pushing hard.

If you had a large alternator (like my 110 Amp) then by putting a
large load on it you might be able to raise the engine temp enough to
heat the water faster!

Hot water question for Larry
 

Roger Long wrote:
The AC element on my hot water heater is 1250 watts.

Can you safely draw from an inverter while the engine is running? If
I put in a 1500 watt inverter and used it carefully to only run the
water heater (which would also be getting waste heat from the cooling
water coil) and was sure that my other 12 V loads were minimal at the
time, could I get my hot water tank heated up in the 5 - 10 minutes
that I do with shore power? (It takes motoring half a day to do it
with the waste heat alone from my 20 hp diesel).

Or, will this burn up my little 35 amp alternator? I have a 55 I can
put in but it needs a different voltage regulator.

I would never try to make hot water from the batteries through the
inverter for obvious reasons.

Your 35 amp alternator puts out 35 amps x 13 volts (approx) = 455 watts.
Your 80 amp alternator will deliver 1040 watts... both running flat
out and probably overheating. Neither would supply the 1500 watts your
heater needs, or the approximately 1700 watts your inverter would need
to make the 1500 watts your heater needs. Not even both together would
be enough.

Further, this electrical energy comes from the mechanical energy that
the engine develops. 1700 watts represents about 2.25 HP, or in your
case, about 10 % of your engine's maximum output. If you are not
running at full throttle, you could be delivering as much as 25% of your
engine's output to the alternator(s). Much better to use the waste heat
in the cooling water loop - that is free from an energy standpoint.

bob

Hot water question for Larry
 

The heat exchanger in your set up is the key. Simple raw water
systems like mine run way too cool for best diesel engine operation.

As described in my response to Tom's Atomic 4 cooling question down
below, I'm looking into a keel cooler to get the operating temperature
up.

I'm glad to hear that your engine does put out that much heat. That
means that the keel cooler setup, which would cost about the same as a
big inverter, would give me hot water in more reasonable time.

--

Roger Long



"Jeff" wrote in message
...
Roger Long wrote:

(It takes motoring half a day to do it with the waste heat alone
from my 20 hp diesel).

Something may be wrong with your setup, Roger. IIRC, you have a
very similar engine to my Yanmar 2GM20FC. I run the coolant through
an 11 gal heater, and it get quites hot in well under an hour, maybe
even 30 minutes. Actually for a few years the engine was running a
tad hot (180 degrees) but after cleaning out the heat exchanger its
normally at 165-170, which probably slows the heating a bit. Even
if all I do is run the engine for a little while to set an engine,
it usually heats enough for showers for the day. When I run for
charging, the engine never gets above 160, so in that case after an
hour run its still not quite as hot as when we're pushing hard.

If you had a large alternator (like my 110 Amp) then by putting a
large load on it you might be able to raise the engine temp enough
to heat the water faster!

Hot water question for Larry
 

OK Larry, you don't need to chime in and make me feel even more
foolish. I did something wrong in my head with that calculation.

Damn, where is that calculator?

--

Roger Long



"RW Salnick" wrote in message
...
Roger Long wrote:
The AC element on my hot water heater is 1250 watts.

Can you safely draw from an inverter while the engine is running?
If I put in a 1500 watt inverter and used it carefully to only run
the water heater (which would also be getting waste heat from the
cooling water coil) and was sure that my other 12 V loads were
minimal at the time, could I get my hot water tank heated up in the
5 - 10 minutes that I do with shore power? (It takes motoring half
a day to do it with the waste heat alone from my 20 hp diesel).

Or, will this burn up my little 35 amp alternator? I have a 55 I
can put in but it needs a different voltage regulator.

I would never try to make hot water from the batteries through the
inverter for obvious reasons.

Your 35 amp alternator puts out 35 amps x 13 volts (approx) = 455
watts. Your 80 amp alternator will deliver 1040 watts... both
running flat out and probably overheating. Neither would supply the
1500 watts your heater needs, or the approximately 1700 watts your
inverter would need to make the 1500 watts your heater needs. Not
even both together would be enough.

Further, this electrical energy comes from the mechanical energy
that the engine develops. 1700 watts represents about 2.25 HP, or
in your case, about 10 % of your engine's maximum output. If you
are not running at full throttle, you could be delivering as much as
25% of your engine's output to the alternator(s). Much better to
use the waste heat in the cooling water loop - that is free from an
energy standpoint.

bob

Hot water question for Larry
 

In article ,
RW Salnick wrote:

Much better to use the waste heat
in the cooling water loop - that is free from an energy standpoint.

It is not free, but it is already paid for.......

Hot water question for Larry
 

Hi Roger,

Roger Long wrote:
The heat exchanger in your set up is the key. Simple raw water
systems like mine run way too cool for best diesel engine operation.

Whether an engine is raw-water cooled or cooled through a heat
exchanger should have nothing to do with the temperature
it operates at.

Somewhere in the system should be a thermostat which prevents
new coolant from being pumped into the engine until the
coolant in the block has come up to the proper temperature.
This will work whether the coolant is an antifreeze mixture
pumped through a heat exchanger, or raw water drawn through a
water intake.

Is your thermostat possibly stuck open, or missing? Or am I
missing something here?

Don W.

Hot water question for Larry
 

On Wed, 15 Mar 2006 15:24:13 GMT, "Roger Long"
wrote:

I would never try to make hot water from the batteries through the
inverter for obvious reasons.

You don't say how big your battery bank is, and whether or not it is
isolated from your starting battery.

If you have an isolated house bank driving the inverter comparable to
4 golf cart batts (about 440 A-H), you could run the inverter/heater
for at least 30 minutes or so. I used to do that on my old boat if I
wanted to shower in the morning without starting the generator.

The important thing is to make sure you don't run down the starting
batt, and that you fully recharge the house bank as soon as possible.
I wouldn't worry too much about the alternators. They will generally
take care of themselves if the voltage regulator is working properly.

I agree with the others that there is some issue with your water tank
not being heated properly from the engine. Is the heating loop on the
raw water side or the fresh water side? It really needs to be on the
fresh water side to get warm enough.

Hot water question for Larry
 

Sorry, I was thinking you had fresh water cooling. The thermostat on
your raw water system is set much lower than mine (140 degrees?)
making it real hard to get the hot water tank up to the 155-160
degrees that you'd like to see in order to have hot showers the next
day. You may even want to research the thermostat a bit - I've heard
conflicting setpoints, 125 or even lower.

Of course, you could always take a dip in ocean :)

Roger Long wrote:
The heat exchanger in your set up is the key. Simple raw water
systems like mine run way too cool for best diesel engine operation.

As described in my response to Tom's Atomic 4 cooling question down
below, I'm looking into a keel cooler to get the operating temperature
up.

I'm glad to hear that your engine does put out that much heat. That
means that the keel cooler setup, which would cost about the same as a
big inverter, would give me hot water in more reasonable time.

Hot water question for Larry
 

Don W wrote:
Hi Roger,

Roger Long wrote:

The heat exchanger in your set up is the key. Simple raw water
systems like mine run way too cool for best diesel engine operation.


Whether an engine is raw-water cooled or cooled through a heat
exchanger should have nothing to do with the temperature
it operates at.

Somewhere in the system should be a thermostat which prevents
new coolant from being pumped into the engine until the
coolant in the block has come up to the proper temperature.
This will work whether the coolant is an antifreeze mixture
pumped through a heat exchanger, or raw water drawn through a
water intake.

Is your thermostat possibly stuck open, or missing? Or am I
missing something here?


Yes, Yanmar (and other manufacturers) use a much lower temp for raw
water cooled engines. I believe it is to reduce precipitation of
salts. The thermostat and alarm are set to much lower temps - the
alarm is at 145 instead of 185 as on fresh water engines.