Freezer alarm for shed freezer - how to make one???

Submitted: Saturday, Jun 13, 2015 at 18:28
ThreadID: 119169 Views:2008 Replies:3 FollowUps:9
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Hi All, I have seen some pretty smart ideas on here from others and this is a bit over my head.
A bit off topic, but also not as its required for freezer safety while away from base. (which is part of being able to get away)
We have a great neighbour whom keeps an eye on things while we are away but I want to make a freezer alarm so he can be alerted quickly if
1/ Power to the freezer stops
2/ The freezer temp warms up to say minus 9
I have searched the net and can only find little miniature battery units with no usable outputs and very quiet alarms, or high tech expensive units.
I was thinking of using a 12volt -50-110°C W1209 Digital thermostat Temperature Control Switch 12V with sensor off ebay with a trickle charger on a small Gel battery, then use the thermostat to have a set point at which the contacts will close and then use battery power to turn on LED and sound an audio alarm.
As well I was hoping to have a normally closed relay held open by the trickle charger (with a diode to stop back current from battery) so that if power was interrupted to the trickle charger (which would be on the same power circuit as the freezer) then the relay would close also setting off the alarms.
But the trickle chargers I have seen kick in / out and so my idea here would not work as I planned.
Is there anyone out there whom has a solution as to how to set up wire such a unit?
Regards Geoff 17
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Reply By: OBJ - Saturday, Jun 13, 2015 at 19:19

Saturday, Jun 13, 2015 at 19:19
I use an Acu-Rite Digitial thermometer at home, and take it with me when I travel. I have two Engels, one as a freezer and the other as a normal fridge. The Acu-rite has two sensors which enables me to monitor the temperature in both units. You are able to program them to alert you to temp variations.

I know this is not directly dealing with your question, however it is a simple fix and works well for me.


Acu-Rite link
AnswerID: 555917

Follow Up By: Annie M - Saturday, Jun 13, 2015 at 19:34

Saturday, Jun 13, 2015 at 19:34
Thanks for info
Its unreal how much net search I did but didn't find that one.
Unfortunatly the link says its unavailable.
How far do the remote monitors work from the freezer?

Geoff 17
FollowupID: 842010

Follow Up By: OBJ - Saturday, Jun 13, 2015 at 20:39

Saturday, Jun 13, 2015 at 20:39
Hi Geoff.

My freezer is in our garage which is about 15-20 metres from the gauge. Not so when in the car of course. I have not tried to see how much further that that they operate.

That website I put up is Fishpond. It may be possible to purchase them from another source. As always Google can be your friend :)

I'm pretty happy with mine. I do use Lithium batteries (as recommended) in the sensors. It seems they may handle the extreme cold better than alkaline.

Good luck. I thought it may save some effort if you were aware of these.

FollowupID: 842012

Follow Up By: OBJ - Saturday, Jun 13, 2015 at 20:46

Saturday, Jun 13, 2015 at 20:46
Found some on eBay. Postage is a bit stuff, but it usually is from the USA.
I heard recently that Aust Post have set up an address where purchases made in the US can be sent there and they are then sent to Australia for much lower rates than US postage. I can't find anything about it after a quick search through Aust Post, but clearly remember reading about it a while back. It may suit you if you can find it. Maybe you post office has the clues. Good luck.
FollowupID: 842013

Reply By: Allan B (Member, SunCoast) - Saturday, Jun 13, 2015 at 19:45

Saturday, Jun 13, 2015 at 19:45
Hi Geoff,

I have looked at the specs of the W1209 unit on eBay and it would appear to meet your needs.

As it operates from 12vdc, simply use a 240v/12v plug pack fed from the same 240v supply as the fridge and ensure that the W1209 is programmed to de-energise its relay coil as the temperature rises. This would be programming as a 'heater'. Then connect your alarm device to the normally-closed contacts of the relay.
In this way two actions would be achieved........... (1) As the fridge temperature rose to the alarm point, the relay will de-energise and the contact close to operate the alarm, and (2) If the power fails then the relay will of course de-energise and again sound the alarm. No need for an additional relay.

As the audible alarm will only consume power when it is sounding, a simple dry battery of suitable voltage (6v?) could be used. No need for chargers and Gel battery. Jaycar and eBay will have suitable audible alarm components which will operate from 6vdc.


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AnswerID: 555919

Follow Up By: Annie M - Saturday, Jun 13, 2015 at 20:29

Saturday, Jun 13, 2015 at 20:29
Hi Allan
I think you idea makes sense (ill read again tomorrow when no red)
I guess I ws stuck on the trickle chark / Gel as we use them at work for timer back ups and the batteries last for 6-7 years and would have a reasoble reserve of power incase neighbour away for a couple of days.
When you say dry battery I am not sure? - like a 6v dolfi torch battery?
I though 12v I could just use LED side lamp as a light alarm and maybe a reverse buzzer for audio??
AH I just read your point 2 again and it sunk in, you are correct no need for extra relay set up for power loss.
Battery option still not clear to me yet.
Geoff 17
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Follow Up By: Member - Geoff 17 - Sunday, Jun 14, 2015 at 11:03

Sunday, Jun 14, 2015 at 11:03
Hi Allan

got myself confused with the Annie, but I was using someone elses pc and didn't realise she was auto logged on!!

Did you mean like a 6 volt dolphin torch battery for a "dry battery"?

I guess they would be ok but how long do they last just sitting I wonder?
I guess if I added a small readout volts then that would end up draining it in any case, but I could just have a cheap tester and do it every few months maybe - if I don't forget.

Geoff 17
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Follow Up By: Allan B (Member, SunCoast) - Sunday, Jun 14, 2015 at 13:20

Sunday, Jun 14, 2015 at 13:20
Yes, a 6v lantern battery would do it, but so also would a 9v lithium (Jaycar SB-2397) with a piezo buzzer (Jaycar AB-3462) and a flashing LED (Jaycar ZD-1965). The alarm only draws current when actually alarming and the lithium battery will have several years shelf life.

I guess that the system design depends on the desired arrangement. Will the buzzer and LED be in the neighbour's premises or will they be on your house and visible to your neighbour? If the latter then they may need to be louder and brighter.
Just what is the likelihood of freezer failure? How many of your acquaintances have suffered?

But what happens if your neighbour is absent? If monitoring your freezer is important maybe a Phone Dialler such as this one could be worthwhile? It is a GSM (mobile phone) system and will require a SIM card (prepay or Telstra Casual $10/month) but systems such as this are available for connection to the wired phone network.

There are also apps for your mobile phone which will allow you to 'call home' when desired and view your fridge temperature readout.

Then again, perhaps it may be desirable to install a full home security system incorporating a phone dialler to which your freezer alarm can be connected.


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Follow Up By: Member - Geoff 17 - Sunday, Jun 14, 2015 at 18:20

Sunday, Jun 14, 2015 at 18:20
Hi Allan

thanks for the Jaycar part #, I will have a look.

the lithium type battery I only recently even knew of, which were advised for a "spot" epirb type think we bought for a present - not cheap but had shelf life into the 2020;s

The end of the shed is close to the neighbour car port and so a flashing light / buzzer would certainly alert him.

yes risk if he is away I guess, but if something goes wrong I also need someone to help in anycase.

We have had 3 bad freezer experiences over the years - almost 4

1/ CFA bloke kicked lead and separated when getting out of boat in shed (freezer still in boat from trip with fish in it) when he decided to service the fire extinguisher whilst doing the shed ones and no one noticed unltil it was real bad!!!!!!

2/ Had a power failure for a few hour and when came back on bait freezer never did (it was very old) and we were away = BAD

3/ Again bait freezer and we were away and had a short and blew fuse so freezer was OFF = BAD

4/ Electrician decide to test / tag lead on freezer sitting in shed while doing work items, BUT FORGOT to plug in again, LUCKY this time we went to get some fish and found it 1/2 thawed and so were able to give all the fish away so it was not wasted and frezzer ok.

so you can see why I am thinking alarm!

Maybe our bad luck run is over and I should be fine from now??

thought about a full home security set up but don't have land line so would add another ongoing cost, I guess it could be done with a data mobile type phone (we have some of those GSM set ups you speak of on soil moisture probes and quite reliable but again an ongoing cost and when they do play up its a tech job.)

Thanks for the range of ideas, I will ponder for a few days to see what may suit best.

Geoff 17
FollowupID: 842045

Reply By: Member - Jim B8 - Sunday, Jun 14, 2015 at 16:04

Sunday, Jun 14, 2015 at 16:04
Evacool do a great little remote monitor - wireless, $35, I have used them for years, two in the truck to show fridge and freezer temps. I like them because my fridges are very thick, and these units use a fine wire to the sensor, and the wireless transmitter outside the fridge. So the transmission distance is much greater. I put the receivers inside the truck.
I think they have alarms, but I have never bothered with setting them. 2 x AAA batteries last for ages. Its not exactly what you are asking, but worth a look?
Good Luck
AnswerID: 555949

Follow Up By: Member - Geoff 17 - Sunday, Jun 14, 2015 at 18:21

Sunday, Jun 14, 2015 at 18:21
Hi Jim

thanks for that, will ask them what max range they will work

Geoff 17
FollowupID: 842046

Follow Up By: Member - Jim B8 - Sunday, Jun 14, 2015 at 18:36

Sunday, Jun 14, 2015 at 18:36
They work to 100 meters, within their design, that is
They are designed to show the temperature to a remote display. They are not a setpoint controller, if they have an alarm, it would just be a buzz or something. (if at all) No relay, no led's, and external switching. So not exactly what you asked.
I love them, awesome. Cheap, Quite a few suppliers have the exact item, rebadged. My first one was badged a "Dualzone", the current 2 are Evacool, same thing, last for years
FollowupID: 842047

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