What is the best way of measuring the power drawn by a boat's refrigeration
unit?

Is there a way to do this without any expensive instruments?

I was thinking of installing an ammeter in the line to the compressor to
determine the current draw, but manufacturer does not recommend this. Even
with that, I would need an hour meter or some such device to know how often
and for how long the compressor runs.

I would like to test existing installation, then add some "temporary"
insulation to the inside of the box and then test again to see what
improvement I might get if I added permanent insulation.

GBM

GBM,

I'm curious why the manufacturer recommended against adding an ammeter
to the circuit. Generally these devices have very little measurable
effect on the current flow or voltage, so I'm puzzled about the
recommendation.

As to measuring current, there are several solutions but the problem is
that most of the "cheap, common" hand held devices will measure amperage
instantaneously, where as I believe what you are looking for is a graph
of the consumption over a very long period of time. In other words, I
think you really want the total amount of energy consumed by the system
over a given period of time, which in your case appears to be at least
one or more complete refrigeration compressor cycles.

To my very limited knowledge I'm aware of nothing "off the shelf" that
will do this, but just a very quick search on Goggle produced this link:

http://www.ferret.com.au/articles/16/0c006616.asp

which offers a TOPTRONIC T202 multimeter with a built in inductive
ammeter which can be then coupled with the CABAC TBM515 data logging
device. NOTE: I've no interest in either of these companies, nor have I
ever used either product. The above information is only an example of
how to capture the current draw over time. Any other product that can
measure current and log the data would work.

The advantage to this approach is that virtually no expertise is
required to capture the information you require, nor would you need to
modify the existing circuity in any way (the ammeter clips around the
wire and measures the current flow inductively), but you will need to
purchase two devices that you might otherwise not need. In my opinion,
I'd think both of these types of instruments would be useful for
debugging additional electrical issues in the future, but I tend towards
overkill in these matters.

Alternatively, one could build their own embedded system using a few ICs
(I would suggest checking out the PIC16 micro-processor line from
www.microchip.com) but this approach presumes some familiarity with
electronics.

Hope this helps,

Robb



GBM wrote:
What is the best way of measuring the power drawn by a boat's refrigeration
unit?

Is there a way to do this without any expensive instruments?

I was thinking of installing an ammeter in the line to the compressor to
determine the current draw, but manufacturer does not recommend this. Even
with that, I would need an hour meter or some such device to know how often
and for how long the compressor runs.

I would like to test existing installation, then add some "temporary"
insulation to the inside of the box and then test again to see what
improvement I might get if I added permanent insulation.

GBM

AMPowers wrote:
[snip]
Alternatively, one could build their own embedded system using a few ICs
(I would suggest checking out the PIC16 micro-processor line from
www.microchip.com) but this approach presumes some familiarity with
electronics.

my thought too, then you could have it stay in place and give you
readings from now until whenever. there are a number of really good
hall effects sensors for measuring current that are easy to interface
to a pic processor's a/d. but then of course you've got a "new"
problem of needing to find a way to measure current/voltage so that you
can calibrate the pic and it's sensor ... which is the same problem you
started with haha.

maybe the OP could borrow a data logger or multimeter/laptop setup ...
that's what most people do when they need an expensive tool, borrow it,
or rent it

purple_stars wrote:
[snip]
maybe the OP could borrow a data logger or multimeter/laptop setup ...
that's what most people do when they need an expensive tool, borrow it,
or rent it

actually i just looked around and radio shack has a multimeter that can
handle 10amps that has a serial interface on it, even comes with pc
software. costs 70$us, i think i'm going to go get one for myself and
try it out haha

purple_stars wrote:
purple_stars wrote:
[snip]
maybe the OP could borrow a data logger or multimeter/laptop setup ...
that's what most people do when they need an expensive tool, borrow it,
or rent it

actually i just looked around and radio shack has a multimeter that can
handle 10amps that has a serial interface on it, even comes with pc
software. costs 70$us, i think i'm going to go get one for myself and
try it out haha

i purchased one of these meters (46-range digital multimeter part
number 22-812) from radio shack earlier this evening, it's pretty nice.
it has all the usual things on it and includes a serial port so that
you can hook it up to your computer. there is some software that comes
with it for the PC but i didn't install it so i don't really know what
it does, i think it does have data logger functions in it. i wanted to
use the meter's output under linux so i had to write some code to parse
the weird binary data coming out of the meter into something
understandable. anyway, since it took over and hour to write a parser
for the data i thought i would post the code and maybe save someone
else the trouble. it should be trivial to write a data logger based on
this.

----
#include stdio.h
#include stdlib.h
#include fcntl.h
#include string.h
#include termios.h
/**
simple scrap of code for 22-812 46-range digital multimeter from
radio shack that compiles on fedora .. listens to the serial port
at 4800 baud and converts all the weird bits the meter sends
across the line into something human readable, hopefully gives
some poor ******* (you) the chance to watch television re-runs
instead of having to figure out what the bit pattern was, like i
had to. i could have cleaned the code up a lot and cut down on
the amount of code but i left it fat and ugly so you could figure
it out with ease and use it for whatever you want. hardly any
error checking in it. cheers.

LEGAL: public domain, no warranties expressed or implied. if it
burns your house down that's your own fault, you should
have been out sailing anyway. enjoy.
**/
char *mode_str [] = { /** string descriptions of modes **/
"DC V ", /* 0x00 */
"AC V ", /* 0x01 */
"DC uA ", /* 0x02 */
"DC mA ", /* 0x03 */
"DC A ", /* 0x04 */
"AC uA ", /* 0x05 */
"AC mA ", /* 0x06 */
"AC A ", /* 0x07 */
"OHM ", /* 0x08 */
"CAP ", /* 0x09 */
"HZ ", /* 0x0a */
"NET HZ ", /* 0x0b */
"AMP HZ ", /* 0x0c */
"DUTY ", /* 0x0d */
"NET DUTY ", /* 0x0e */
"AMP DUTY ", /* 0x0f */
"WIDTH ", /* 0x10 */
"NET WIDTH ", /* 0x11 */
"AMP WIDTH ", /* 0x12 */
"DIODE ", /* 0x13 */
"CONT ", /* 0x14 */
"hFE ", /* 0x15 */
"LOGIC ", /* 0x16 */
"dBm ", /* 0x17 */
"UNKNOWN ", /* 0x18 */
"TEMP " /* 0x19 */
};
#define VAL_1 0 /* array ptrs for digit positions on lcd screen */
#define VAL_2 1
#define VAL_3 2
#define VAL_4 3
typedef struct {
unsigned char match; /* bits to match */
unsigned char value; /* value if matched */
} bit_patterns;
#define MAX_PAT 18
#define CHAR_BLANK 0x10
#define CHAR_MINUS 0x20
#define CHAR_C 0x30
#define CHAR_F 0x40
#define CHAR_P 0x50
#define CHAR_E 0x60
#define CHAR_N 0x70
#define CHAR_L 0x80
bit_patterns pats[] = {
{ 0xd7, 0 }, /* 0 */
{ 0x50, 1 }, /* 1 */
{ 0xb5, 2 }, /* 2 */
{ 0xf1, 3 }, /* 3 */
{ 0x72, 4 }, /* 4 */
{ 0xe3, 5 }, /* 5 */
{ 0xe7, 6 }, /* 6 */
{ 0x51, 7 }, /* 7 */
{ 0xf7, 8 }, /* 8 */
{ 0xf3, 9 }, /* 9 */
{ 0x00,CHAR_BLANK }, /* (special, blank character) */
{ 0x87,CHAR_C }, /* C (special) */
{ 0x27,CHAR_F }, /* F (special) */
{ 0x64,CHAR_P }, /* P (special) */
{ 0xa7,CHAR_E }, /* E (special) */
{ 0x37,CHAR_N }, /* N (special) */
{ 0x86,CHAR_L }, /* L (special) */
{ 0x20,CHAR_MINUS } /* - (special, minus sign or dash) */
};
unsigned char vals[4];
int make_value()
/**
ok, basically this is the deal. there are 4 bytes (out of 9) that
come out of the serial line that are stored in vals[] and each bit
in those bytes is one of the lcd elements ... yes, that is to say
that for instance the character "8" is made up of 7 different
lcd segments, four vert ones and 3 horizonal. we have to match
those bits against what we have in pats[] in order to get a
real value back that is useful. then we print that and the
various decimal points out. you would probably want to make and
return a string or something and use it somewhere else
**/
{
int val;
int n;
int i;
for(n = (int)0;n 4;n++)
{
for(val = (int)-1,i = (int)0;i MAX_PAT;i++)
{
if(pats[i].match == (vals[n] & 0xf7))
val = pats[i].value;
}
if((vals[n] & 0x08) == 0x08)
printf(".");
switch(val) {
case((int)-1):
printf("[BAD(%02x)]",vals[n]&0xf7);
break;
case(0): case(1): case(2): case(3): case(4):
case(5): case(6): case(7): case(8): case(9):
printf("%d",val);
break;
case(CHAR_C): printf("C"); break;
case(CHAR_F): printf("F"); break;
case(CHAR_P): printf("P"); break;
case(CHAR_E): printf("E"); break;
case(CHAR_L): printf("L"); break;
case(CHAR_N): printf("N"); break;
case(CHAR_BLANK): printf(" "); break;
case(CHAR_MINUS): printf("-"); break;
default: break;
}
}
return((int)0);
}
int main(int argc, char **argv)
/**
main()
**/
{
int i;
int s;
int bit;
int len;
unsigned char c;
int neg;
struct termios newtio, oldtio;
/** set the serial port up for 4800 baud, 8n1 /dev/ttyS0 **/
if((s = open("/dev/ttyS0",O_RDWR | O_NOCTTY | O_NONBLOCK)) (int)0)
{ fprintf(stderr,"open(): (int)0\n"); exit((int)-1); }
tcgetattr(s,&oldtio);
bzero(&newtio, sizeof(newtio));
newtio.c_cflag = B4800 | CS8 | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR;
newtio.c_oflag = 0;
newtio.c_lflag = 0;
tcflush(s,TCIFLUSH);
tcsetattr(s,TCSANOW,&newtio);
fcntl(s,F_SETFL,FASYNC);
bit = (int)0;
/** start reading from the serial port and processing whatever bits
we get from the multimeter. we do this strictly by position,
each "packet" that comes out of the meter is has 9 bytes of
data associated with it, and we just process them in order **/
for(neg = (int)0,len = (int)0;
(i = read(s,&c,1)) = (int)0;usleep(200))
if(i (int)0)
{
switch(bit) {
case(0): /* byte 1 from meter says what the mode is */
printf("[MODE] %s ",mode_str[c&0xff]);
bit = (int)1;
break;
case(1): /* byte 2 from meter contains bits that represent
the actual icons on the lcd screen like the
"OHM" or "HZ" symbols */
printf("[LCD] "); /** print the symbols from LCD **/
if(c & 0x80) printf("Hz ");
if(c & 0x40) printf("OHM ");
if(c & 0x20) printf("K ");
if(c & 0x10) printf("M ");
if(c & 0x08) printf("F ");
if(c & 0x04) printf("A ");
if(c & 0x02) printf("V ");
if(c & 0x01) printf("m ");
bit = (int)2;
break;
case(2): /* byte 3 from meter is more lcd symbols */
if(c & 0x80) printf("u ");
if(c & 0x40) printf("n ");
if(c & 0x20) printf("dBm ");
if(c & 0x10) printf("S ");
if(c & 0x08) printf("% ");
if(c & 0x04) printf("hFE ");
if(c & 0x02) printf("REL ");
if(c & 0x01) printf("MIN ");
bit = (int)3;
break;
case(3): /* byte 4 from meter is one of our lcd values. the
lcd has four actual digits on it, these are what
you are going to be most interested in. each
byte of data has seven "segments" which are the
actual lcd segments which make up the digit, and
another bit for decimal on or off */
vals[VAL_4] = c&0xff;
bit = (int)4;
break;
case(4): /* byte 5 from meter, another digit and decimal */
vals[VAL_3] = c&0xff;
bit = (int)5;
break;
case(5): /* byte 6 from meter, another digit and decimal */
vals[VAL_2] = c&0xff;
bit = (int)6;
break;
case(6): /* byte 7 from meter, another digit and decimal */
vals[VAL_1] = c&0xff;
bit = (int)7;
break;
case(7): /* byte 8 from meter, more lcd symbols */
if(c & 0x80) printf("BEEP ");
if(c & 0x40) printf("DIODE ");
if(c & 0x20) printf("BAT ");
if(c & 0x10) printf("HOLD ");
if(c & 0x08)
{
neg = (int)-1;
printf("- ");
}
if(c & 0x04) printf("~ ");
if(c & 0x02) printf("RS232 ");
if(c & 0x01) printf("AUTO ");
bit = (int)8;
break;
case(8): /* byte 9 from meter, checksum, ignored in this
code but you'd probably want to actually use
it for error checking in your own code */
printf("[CHKSUM] %02x ",c&0xff);
printf("[VAL] ");
make_value(); /* process the digits and make something
out of them. they are stored in the
global variable vals[], 4 bytes worth,
so go parse it and print it out in human
readable form */
printf("\n");
bit = (int)0; /* get the first char all over again */
neg = (int)0; /* reset global negative bit */
break;
default: break;
}
fflush(stdout);
}
tcsetattr(s,TCSANOW,&oldtio);
close(s);
exit((int)0);
}

GBM wrote:
What is the best way of measuring the power drawn by a boat's refrigeration
unit?


What type is it? Danfoss or big DC compressor? AC? Holding plate?

Is there a way to do this without any expensive instruments?

I was thinking of installing an ammeter in the line to the compressor to
determine the current draw, but manufacturer does not recommend this.

Why? This seems odd.

Even
with that, I would need an hour meter or some such device to know how often
and for how long the compressor runs.

That's just what I do - I have a "2 bank" amp-hour meter, actually a
Link 2000, which I use in the normal way for the first bank, but I
measure the fridge usage with the second bank.

This is not a cheap solution, but if you have AH concerns, maybe you
want at least a simple amp-hour meter that you could use in either mode.




I would like to test existing installation, then add some "temporary"
insulation to the inside of the box and then test again to see what
improvement I might get if I added permanent insulation.

GBM writes:

Is there a way to do this without any expensive instruments?

(If this is DC power you can't use a clamp-on meter as some others
suggest.)

If you're trying to measure duty cycles, you can improvise a cheap logging
meter with an inexpensive multimeter from Radio Shack (etc) that has a PC
interface, and a laptop or other computer. You can even simplify by
omitting the computer and just pointing a video recorder at an ordinary
meter, and fast-forwarding through to find the on and off times. No need
for expensive logging instruments for a one-time procedure.

Adding insulation is not typically an improvement in anything of recent
construction. That's a fantasy factoid lingering from the 1970s energy
crisis, endlessly repeated by people who've never measured the realized
benefit.

"Richard J Kinch" wrote in message
. ..

Adding insulation is not typically an improvement in anything of recent
construction. That's a fantasy factoid lingering from the 1970s energy
crisis, endlessly repeated by people who've never measured the realized
benefit.

Richard - Unfortunately our boat is not of recent construction. The original
icebox had just 1/2" of polyurethane insulation. When I installed the refrig
unit, I added as much as I could on the outside. But, it is still not as
much as is often recommended. Only way of adding more, is on the inside.
But, if it won't make much difference in compressor run time, I would prefer
not to do this because of cost of so-called "space-age" insulation or space
taken by conventional insulation.

Perhaps this explains why I would like to measure present power usage, then
add temporary sheets of foam using 2-way tape and measure again.

Thanks for all the input so far guys!

GBM

Adding insulation is not typically an improvement in anything of recent
construction. That's a fantasy factoid lingering from the 1970s energy
crisis, endlessly repeated by people who've never measured the realized
benefit.

Richard - Unfortunately our boat is not of recent construction. The
original
icebox had just 1/2" of polyurethane insulation. When I installed the
refrig
unit, I added as much as I could on the outside. But, it is still not
as
much as is often recommended. Only way of adding more, is on the
inside.
But, if it won't make much difference in compressor run time, I would
prefer
not to do this because of cost of so-called "space-age" insulation or
space
taken by conventional insulation.

Perhaps this explains why I would like to measure present power usage,
then
add temporary sheets of foam using 2-way tape and measure again.

Thanks for all the input so far guys!

GBM

This topic (now moving away from recording to efficiency) has had a
great deal of exposure.

As one who has taken a sawzall to his original box (anyone wanna buy a
very cheap, perfectly good, 110/engine drive, dual split-system cold
plate[s - 2], quite large system?), without getting technical about it,
BTU are BTU. However many it takes is what it will require for the
cooling system.

An advantage to the older engine drives (techumseh compressors like
used to be on 60s era Ford products) is that they can make a ton of ice
in an hour, properly set up, so there's ample capacity if you have the
right cooling plates, regardless of how poorly insulated your box might
be.

However, if it's not adequately insulated, it will sweat - and
eventually rot stuff, usually behind the fascia, where you don't see
it. That's why, in our boat, the galley sole was skinned before I
bought it, and why the area under the reefer, inaccessible until we
tore it out, was mostly gone. Ample pix of that removal in the late
04/early 05 galleries if you wanted to see what happens.

So, back to the story. You can either live with it, add mechanical
(could be attached to a genset or the main engine - or rigged with a
110 motor and pulley, if you're dockside most of the time) cooling, or
(unless you don't mind losing the space occupied by the original
housing/insulation, in which case you could build it from the inside)
rebuild it from scratch, as we did.

At that point, your options expand but as you've identified, it's a
tradeoff between foam for cheap but fat, or vacuum for dear but thin.

I vehemently (well, not to be angry, just strong) disagree with the
"70's hype" bit. If you don't keep the heat out, you have to remove
it. There's a point of diminishing return, but my marker is to take an
infrared thermo (cheap at the cheapo tool places, and even sometimes at
the Shack) and point it at the face of the insulated, cold, box. Then
point it at another similar face nearby which isn't near the
reefer/freezer. If they're within a couple of degrees of each other,
that's probably as good as you'll get. The less techie test is to use
your hand. If the reefer feels notably cooler, you probably don't have
enough insulation. However, if you have a face plate trim which isn't
in contact with the box (another barrier, good idea) then it masks the
truth. If you have a top loader, your countertop is a good place for
the test, even though the least amount of BTU go through the top (heat
rises, so the convection component is very small there).

As to your "temporary" sheets of foam, part of the equation is
preventing air movements. You have to be very aggressive about sealing
joints and overlapping as many times as possible (longer path for air),
along with as precise a fit as you can manage. Again with my pictures
for examples - I used paper patterns for exact fits, and at that
spoiled some of my sheets, doing them over.

FWIW, my original thought was to add insulation to the inside of the
box, too, replacing the countertop as I went. Without the gory details,
that proved impossible. Had I known the reality which might have
avoided all the gory details, I might still have cut it out, because
the original insulation, even if it's not sweated (as yours nearly
certainly must have, as thin as it is), loses most of its R-value over
the years. Technology today helps, and epoxy encapsulation retards it,
but you'll still lose some R over the years with new stuff, space age
or extruded Poly-x. However, 30 years from now, I'll not care about it
in my boat :{))

I have a lead on what used to be a very much less expensive (than
Rparts or Glacier Bay, the usual suspects) source for vacuum panels if
you decide to go that route.

Hope that helped and not just repeated what you already know...

L8R

Skip

Morgan 461 #2
SV Flying Pig KI4MPC
http://tinyurl.com/p7rb4 - NOTE:new URL! The vessel as Tehamana, as we
bought her

"Believe me, my young friend, there is *nothing*-absolutely
nothing-half so
much worth doing as simply messing, messing-about-in-boats; messing
about in
boats-or *with* boats.
In or out of 'em, it doesn't matter. Nothing seems really to matter,
that's
the charm of it.
Whether you get away, or whether you don't; whether you arrive at your
destination or whether you reach somewhere else, or whether you never
get
anywhere at all, you're always busy, and you never do anything in
particular; and when you've done it there's always something else to
do, and
you can do it if you like, but you'd much better not."

"Skip Gundlach" wrote


So, back to the story. You can either live with it, add mechanical
(could be attached to a genset or the main engine - or rigged with a
110 motor and pulley, if you're dockside most of the time) cooling, or
(unless you don't mind losing the space occupied by the original
housing/insulation, in which case you could build it from the inside)
rebuild it from scratch, as we did.

Skip,

We are done with the initial re-insulation and have the Waeco Coolmatic
installed. So let's not get into other types of compressors or changing the
external box insulation - that is behind us!

I just completed insulating the box - insulation now varies from about 1.25"
to 3" where I used polycyanurate board but is 5+" where I poured in foam
around the back and most of bottom.

If I have excessive compressor run time, I could add internal insulation on
the two areas where I could only fit in an extra 3/4" of foam. It would be
quite easy to temporarily add sheets of cyanurate with two-sided tape for a
test.

There's a point of diminishing return, but my marker is to take an
infrared thermo

Not a bad idea - I will try the hand feel first!

Had I known the reality which might have
avoided all the gory details, I might still have cut it out, because
the original insulation, even if it's not sweated (as yours nearly
certainly must have, as thin as it is), loses most of its R-value over
the years.

Our 1/2" insulation was at least totally encapsulated and was bone dry, at
least on the piece I cut out - I have sealed the openings I cut with epoxy
and sealed all edges of the new foam with aluminum tape or epoxy.

Basically now come down to testing and seeing if I need to add the internal
insulation. I am going to insulate the side of the engine room that faces
the icebox. I am also going to ventilate the cupboard that is between the
two.

Thanks guys for all the good ideas. I have several ways I can go and will
try the cheapest first

GBM