Further to post #32644 Re: my Ammeter...

Derek, it's a 110L Waeco. The fridge is running as all fridge, no freezer and it's empty... I'll test it with the globe and see how we go... I thought it may be too low as "Alloy c/t" had mentioned that his 80L uses 64A/24hr but mine was cycling very infrequently(at a guess, only about twice an hour) and only for about 2 mins at a time.

So the git is coming out in me again... Just had a revelation, I think... I am using the Waeco power supply while the fridge is in the garage. The power supply delivers upwards of 24V, actually about 27V... Do I theoretically double the consumption for this scenario...???

Forgot to add, the CF110 has two 10 litre water containers in the fridge section.

Geoff.

Wonder if our leccy engineers dept has a chart recorder. That would indeed make life easier, especially if I could take it away to a couple of van parks(I presume I'd require 240v to run one) and have a look-see over differing ambient ranges...

Hi Blue,
A chart recorder generally requires say 240 Volt AC to power the instrument (Some will run on 110 Volt AC others on 24 Volt DC)

For recording the unit requires an input to measure. In my application I'll feed the "voltage drop" from the ammeter shunt into the measuring terminals of the chart recorder. That's how I intend to form my graphical reading of the fridges performance.

Just had a thought, on the same chart I can actually record ambient and cabinet temperatures. Now I'm becoming a real wanker.

But a wanker with a true understanding of my fridge and from that battery requirements.

Geoff.

Blue, if you don't want to get involved in the complexities of a chart reader, a simple hour meter also does the job nicely.
I have one of those inexpensive little LCD hourmeter modules. Fitted it in a little plastic box and also fitted a reset pushbutton.
Then I took the glass reed switch out of a domestic door alarm and wound a small coil of enamelled copper wire as long as the glass tube and so that the reed switch was a good fit inside the coil. (use a dowel for the winding, the glass breaks too easily). Use wire of about 1.5mm diameter, the short length required would add very little extra resistance to your wire run.

The switch contacts triggered the hour meter.
The coil was connected in SERIES to one lead of the fridge supply.

Each time the fridge cycled on the current flowing in the coil would set up a magnetic field which in turn switched the reed contacts on, thus recording the hours the fridge ran until a push on the reset button zeroed the meter for another recording session.

Its as small as your ampmeter and easily set up as a permanent indicator to tell you how busy your fridge was.

Klaus

Hioki used to make 12ch chart recorders that ran off 12volts.

If you want to do the job properly measure:

Outside vehicle temp (careful how you set it up)
Inside vehicle temp
Inside cabinet - bottom of fridge
Inside cabinet - top of fridge
Current draw
Voltage at battery
Voltage at fridge

The results could be very interesting.

Measuring breath temp (temp 150mm below head lining in drivers seat) of a Commodore a few models ago (in a previous career) we recorded a temp rise of to 75°C from ambient when the aircon was switched off in a car parked in the sun on a 35°C day.

The fridge would be cycling pretty hard then, me thinks.

Dave

Scary isn't it Dave,
When I worked for a large American company who are quite well known in computing and process control we setup a similar test between two commodores.
One had tinted windows, the other didn't.
Middle of summer in the carpark. The one without tinting hit a back seat temperature of 76 degrees C, the one with tint was less than 50 degrees C.
The purpose of the test? We had a new boss who said tinting was a wank.
Someone else came out a wank from that test.

You're so right on a fridge in a closed car in summer!

Geoff.

Klaus & Dave,
I'm trying to keep this as simple as possible... My record with all things 12V has led to much frustration and one fire... And Dave, I have a dual range thermometer which I had running in the canopy(black) and on a day of37°C, I recorded 67°C in the canopy so I'm well aware of just how hot it can get in there... And to think people leave kids in their cars on hot days...???

Hi Geoff,

A bit off topic but your story about your boss reminds me of a funny story re: testing things and looking stupid as a result.

Apparently (this predates me by many years but was still talked about by those who remember or had been told), when Holden first started putting seatbelts in cars in the early '70s they set up a demonstration for the journo's to demonstrate the amazing life saving strength of these new fangled seatbelts.

The idea was that they would demonstrate their faith in the product by suspending a new Torana over the big chief's Premier (top of the range at the time) by a few lengths of seatbelt and a crane, outside the building that is/was the Plant 3 cafeteria at Fishermans Bend. (In those days it was used for publicity & social functions like the regular company dinner dances - back when companies felt a social responsibility for the big family that were employees, sometime before they all became payroll numbers.)

The day arrived and all was in place. Some bright spark (probably an engineer or a marketing person ;) ) decided they better do a dry run before the journo's and dignitaries arrived and they hoisted the Torana into position. All was well, a sigh of relief was probably uttered and pats on the back all round.

The hour approached and all assembled to be astounded by the strength of modern materials. The Torana was hoisted into position over the Premier and all were impressed - until just shortly after when some of the belts snapped with a predictable result!

What was more than adequately demonstrated was that seatbelts are only rated for ONE use to their maximum working load and should never be used again afterward (such as after a serious accident where the car is repaired).

I'm not sure that it was widely reported, but then not many things in automotive journalism that involve egg on faces of either journalists or the big aussie car manufacturers ever are - the journo usually doesn't get the next big story if he makes them look bad.

Dave