solar/ engel calculations

Submitted: Friday, Feb 24, 2006 at 14:17
ThreadID: 31114 Views:6045 Replies:9 FollowUps:2
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Im have just rung my local engel dealer to find out the power consumtion of my fridge. I have a Engel SR70F-G4-Gl, 70 litre front door type with freezer.

He reckoned it _Affordable_Storage_Drawers.aspx 2.5A with a 40% duty cycle depending on ambient temp, beer consumption etc. So here goes....

2.5A x 40% = 1A
power consumption = 1A x 12v = 12W

A 64W solar panel mounted flat (80%) in perth (5.5.peak sun hours)produces :
64 x 0.8 x 5.5 = 281W

The efficiency of a battery is about 80% so usable power is :
281 x 0.8 = 225W

Therefore 2 of these panels would be required to be self sufficient.

The main problem I have is the 40% duty cycle rate for the fridge and would appreciate any information anyone has regarding this number, or experience with actual power usages.

Steve M
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Reply By: V8troopie - Friday, Feb 24, 2006 at 15:50

Friday, Feb 24, 2006 at 15:50
Steve, the fridge duty cycle depends on a number of variable so really you can't expect an answer that has any relation to your set up.
What I would suggest is to fit an hour meter to your fridge circuit. I have done that on my boat and its quite simple if you're handy with building things. The heart of the system is a reed relay that turns on when the fridge runs. I used the biggest N/O contact reed RLY I could find and wound a coil around its glass tube with 1mm enammelled wire. You will have to experiment with the number of turns. The lot was covered in heat shrink tubing afterwards.
One side of the fridge power wire is routed through this coil. When the fridge is on a current flows in that wire, setting up a magnetic field in the coil which turns on the reed switch.
The red switch contacts turn on a small 12V LCD hour meter ( got mine from RS components) and tell you for how many hours in a set period, eg. 24 hours, your fridge ran.
With that figure you are well on the way to calculate a more precise power consumption figure.

The neat thing is that no mod to the fridge itself is required. You could even make the gadget transportable for lending to your mates for the appropriate consideration.

I would agree with you on the number of panels you calculated as a ball park figure.

AnswerID: 156879

Follow Up By: Steve M - Friday, Feb 24, 2006 at 18:02

Friday, Feb 24, 2006 at 18:02
Bloody good idea with the hour meter

Thanks Steve
FollowupID: 411047

Reply By: Ken - Friday, Feb 24, 2006 at 16:13

Friday, Feb 24, 2006 at 16:13
Steve, the 40% duty cycle figure is like most figures given by equipment suppliers, optimistic !
The actual running time will vary considerably depending on ambient temp, location, use etc, I'm sure you understand the variables.
I don't have any experience with the door type Engels but this type of fridge loses cold air more rapidly than a chest type when the door is opened; the cold air falls out ! This will increase the running time of the motor.
Also Engels [chest type anyway] have fairly poor insulation compared to other makes and their efficiency suffers a bit through this, again adding to the run time.
I would also question the value of 2.4 amps as the current drawn. Again for the chest type, it is more like 5 to 6 amps. I would be very surprised if the fridge only _Affordable_Storage_Drawers.aspx 2.5 amps. You may have been quoted 2.4A as the 40% duty cycle value of the full current. If this is the case your 288Wh/day is now 720Wh/day.
Try measuring the current when the fridge is running to confirm the real current being drawn.

AnswerID: 156883

Reply By: muzzimbidgie - Friday, Feb 24, 2006 at 18:30

Friday, Feb 24, 2006 at 18:30
They tell you 2.5 amps, but that is what is should draw over an our.

When it's running it will be more than double that, but luckily for you it only runs maybe 15 - 20 minutes in an hour

On the bottom of my 50l waeco it states 7 - 8 amps current draw, but over an our, cutting in and out, comes down to 2 - 3 amps per hour.

Hence the term "amphours" as it's stamped on your battery.
AnswerID: 156899

Reply By: sav - Friday, Feb 24, 2006 at 19:16

Friday, Feb 24, 2006 at 19:16
What about using something like this to measure the power consumption over extended time periods...

It's meant for ebikes, but I don't see why it wouldn't be useful for us lot.

AnswerID: 156907

Reply By: sav - Friday, Feb 24, 2006 at 19:17

Friday, Feb 24, 2006 at 19:17
I'll try that again....


AnswerID: 156908

Reply By: Member - Collyn R (WA) - Friday, Feb 24, 2006 at 19:58

Friday, Feb 24, 2006 at 19:58

Your the sums and results are impeccable - but are based on the not unreasonable but nevertheless wrong, assumptions that solar modules and batteries actually do what seems clkaimed for them!

Most 64-watt modules will at best produce about 53 watts (mounted flat, that's about 42-45 watts). It actually says that in the (very) small print.

The PSH estimate is also optimistic for February. Work on 4.5 PSH. Assume about 200 watt/hr/day for each right now and 7.5 PSH in July.

As others have said, there's a heap of variables re fridge draw but with this year's summer in Perth that 40% could well be about right!

The battery estimate is way too high! At BEST work on 50% of the Ah capacity being accessible (reality is really lower). Truly.
Trust this helps
Collyn Rivers

AnswerID: 156915

Reply By: waynet - Saturday, Feb 25, 2006 at 14:43

Saturday, Feb 25, 2006 at 14:43
If your Engel is a relatively new model it will draw 2.4amps when running, slightly older models draw 3.5 amps, and the very old models draw 5.4 amps, the only thing that will change these figures is ambient temperature, ie. higher ambient =higher discharge pressure=higher current draw, but the increase is only about 0.1 or 0.2 amps. I have fitted a LINK 10 battery monitor to my auxiliary battery system and am very happy with it. It will give you all the information you need to monitor your battery: voltage, current draw and charge, amphours used and replaced into the battery from whatever charging system you are using. I bought my LINK10 from I have no affiliation with this company
but I am happy to recommend them as I found them very good to deal with and very knowlegeable about solar and other low voltage systems.
AnswerID: 157002

Follow Up By: Tim HJ61 (WA) - Saturday, Feb 25, 2006 at 16:52

Saturday, Feb 25, 2006 at 16:52
That'd be folks, without the .au

FollowupID: 411195

Reply By: Mike DiD - Sunday, Feb 26, 2006 at 08:29

Sunday, Feb 26, 2006 at 08:29
At 30 degrees air temperature, a fridge will draw 50% more power than at 20 degrees.

AnswerID: 157100

Reply By: Mike DiD - Sunday, Feb 26, 2006 at 12:19

Sunday, Feb 26, 2006 at 12:19
I just found this extract of a test published by 4WDMonthly mag.

They tested in a cycle ranging from 15 to 55 degrees and for a Waeco CF40 the total consumption over 24 hours was 22.5 amphours (not amps). Even at 55 degrees the AVERAGE consumption was only 2.2 amps - or 2.2 amphours for one hour.

No wonder people have trouble understanding electrical units if authors can't be bothered checking their own text for accuracy. The measure of how much a load _Affordable_Storage_Drawers.aspx at an instant in time is Amps - the measure of how much it _Affordable_Storage_Drawers.aspx over one hour is AmpHours.

AnswerID: 157133

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