Here's an OT one for the wisdom of the group

"tdacon" fired this volley in news:m1pogh$haj$ snipped-for-privacy@dont-email.me:

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.

LLoyd

"Lloyd E. Sponenburgh" fired this volley in news:XnsA3C8D32D4A5D7lloydspmindspringcom@216.168.4.170:

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

L

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.

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

You might have a look at eBay item number:

321517372775

Dan

This meter, shunt and a laptop can log the power:

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:

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

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

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