I know this isn't a metalworking topic, but you guys have a lot of
collective knowledge. I'm installing a refrigeration system in my boat. It's
a holding plate system, powered by 12V DC, turning a motor that draws about
25 amps when it's running. It will probably run about an hour or so a day,
at unpredictable times. I'd like to be able to measure how many hours in a
day it runs, without having to sit there and time it when it turns on and
off. How would you go about that?

Thanks,
Tom

"tdacon" fired this volley in
:

I'd like to be able to measure how many hours in a
day it runs, without having to sit there and time it when it turns on
and off. How would you go about that?


12VDC hour meter. You'll have the duty of recording and subtracting daily
times, but even if it ran for a week before you 'serviced' it, you'd still
have an average. And it will give you a relatively accurate total time.

http://www.mcmaster.com/#1877t81/=u6lif5

LLoyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com fired this volley in
. 4.170:

have an average. And it will give you a relatively accurate total time.

http://www.mcmaster.com/#1877t81/=u6lif5

PS... the "analog display" specification means it has mechanical digits
rather than an LCD display.

L

On 2014-10-17, tdacon wrote:
I know this isn't a metalworking topic, but you guys have a lot of
collective knowledge. I'm installing a refrigeration system in my boat. It's
a holding plate system, powered by 12V DC, turning a motor that draws about
25 amps when it's running. It will probably run about an hour or so a day,
at unpredictable times. I'd like to be able to measure how many hours in a
day it runs, without having to sit there and time it when it turns on and
off. How would you go about that?

Is the 12V cycled at the same time, or is the 12V stable, and
switched inside the holding plate?

If the former -- find an old automobile clock (which runs from
12V and hook it in parallel with the plate. The really old ones used to
have a spring which was wound once every few minutes (a "thunk" at that
time), so your resolution would be limited to how long to took to run
down without power.

Fancier would be a digital counter and an 555 generating a pulse
per minute or a pulse per second, depending on how much precision you
wanted. Just remember to read the data before you turn it off for the
day.

Or -- there are running time meters. Most that I have are 115 V
60 Hz, but I know that there are versions designed to run from 28 VDC,
and are likely also for 12 to 14 VDC.

O.K. Here is an aircraft one on eBay which works from 6V or 12V
DC:

#131238077504

And here is a cheaper one from 8V to 50V DC:

#161450172146

And some 10-80 VDC ones:

#161261318398

So -- I've found you several choices on eBay. The search string
is:

elapsed time meters

and just wade through looking for ones which will run on somewhere
around 12-14 VDC/ (All of the above which I have found will do so.)

Too late to go any deeper into the search results. And
specifying the voltage in the search string will miss a number, as the
voltage is not in the header. Sometimes you have to look at the box
images, or labels on the instruments.

Good Luck,
DoN.

--
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On Thursday, October 16, 2014 8:40:00 PM UTC-4, tdacon wrote:
How would you go about that?



Thanks,

Tom

You might have a look at
eBay item number:
321517372775


Dan

"tdacon" wrote in message
...
I know this isn't a metalworking topic, but you guys have a lot of
collective knowledge. I'm installing a refrigeration system in my
boat. It's a holding plate system, powered by 12V DC, turning a motor
that draws about 25 amps when it's running. It will probably run
about an hour or so a day, at unpredictable times. I'd like to be
able to measure how many hours in a day it runs, without having to
sit there and time it when it turns on and off. How would you go
about that?

Thanks,
Tom


This meter, shunt and a laptop can log the power:
http://www.amazon.com/dp/B000OPDFLM/..._26725410_item

http://www.amazon.com/Current-Resist...rent+shunt+75A
Any large enough shunt would do, that one reads directly at 1mV per
Amp.

You could also record the battery voltage with a second meter. I use a
Cardbus dual COM port card to read two more meters but AFAIK they work
on USB / COM adapters. Their separate log files can be combined in a
spreadsheet by aligning the time stamps if you start the second one
just after you see the first take a reading. The meter grounds are
optically isolated from the COM port and won't short-circuit the
battery through the laptop, but you should double-check that in case
of manufacturing flaws.

The laptop might cost you 2 to 3A for its Auto-Air adapter or 12-120V
inverter. The old one I use drops to around 10~12W between readings
with the screen and hard drive off. A Pentium II running Windows 2000
is good enough.

This will display the total Amp-hours, like a DC Kill-A-Watt:
http://www.amazon.com/dp/B00EYZS6R6/...332200_TE_item

It reads only (+) current source-to-load so don't hard wire it in. I
use 45A Andersons. The actual current resolution is 0.1A, not the
0.01A it displays. The shunt and DVM can measure and record both
charge and discharge. If you hard wire the shunt the safer place for
it is in the ground lead, so the dangling meter leads to it won't have
live +12V on them.

jsw

"tdacon" wrote in message ...

Thanks, folks. Great suggestions. Now to figure out which way to go.

Tom

It's looking like the hour meter is a quick and simple way to go. A quick
search on the web showed me how to wire it up, so it looks like I'm off and
running.

Thanks to everyone,
Tom

"tdacon" wrote in message
...

"tdacon" wrote in message ...
Thanks, folks. Great suggestions. Now to figure out which way to go.

Tom

The AODE is the cheapest and least intrusive and directly displays
battery voltage and total charge or discharge Amp-hours, like a
battery fuel gauge.

The TP4000 DVM can also measure temperature with a fairly thin
thermocouple that won't cause much heat loss where it goes into the
fridge under the door gasket, though I used a fine wire thermocouple
from Omega to record how my refrigerator cycles.

The program that came with mine allows up to four separate
installations assigned to COM1 through COM4.

-jsw