Battery size to use off peak power?

[Harry Bloomfield]

Whilst that is all theoretically true, power cuts of long enough duration to impact on the contents of a freezer are 'almost unknown' - I certainly have not experienced one in the 60 or so years for which my household has had a freezer.

Generally, the worst we have had, is a minute or two break in supply. Many years ago, we had an hour or so, when a cable failed. When individual addresses, or several have suffered failures, where a quick fix is not possible - they have brought temporary generators in. The only real concern, would be a massive area loss of supply, there is nowt much can be done about that, nor is it worth expending much on a backup system.

 

[JohnW2]

Generally, the worst we have had, is a minute or two break in supply.

Where we are, we fairly frequently suffer very brief cuts - anything from a couple of second to a minute or two - which I suspect are due to DNO 'devices' re-setting. They are a pain, since they upset any number of 'clocks' and cause any number of things tio re-boot, but are essentially of no consequence.

Many years ago, we had an hour or so, when a cable failed.

I recall a couple of cuts, presumably due to DNO equipment failures, which lasted for a small number of hours. Even when the overhead supply to my village was brought down by 'the hurricane of 1987', power was again restored within a small number of hours.

The only real concern, would be a massive area loss of supply, there is nowt much can be done about that, nor is it worth expending much on a backup system.

Quite so. I personally really don't think it would make any sense to spend appreciable money in anticipation of such a (very rare) event.

Kind Regards, John

 

[Harry Bloomfield]

Quite so. I personally really don't think it would make any sense to spend appreciable money in anticipation of such a (very rare) event.

and if the worst happened - I have the caravan in the drive, with a self-contained gas supply, and a blown air heating system, cooking facilities etc..

 

[JohnW2]

and if the worst happened - I have the caravan in the drive, with a self-contained gas supply, and a blown air heating system, cooking facilities etc..

Fair enough - but not many people have that!

In our case, if we didn't have the generator, then in the even of loss of electricity we would still have the ability to cook (two LPG cookers, fed from a 2000 L tank in the garden) and just a little heat (from the cookers, one of which is an Aga, and one {virtually never used} LPG 'gas fire').

 

[ericmark]

I seem to remember a time around 1978/9 when it seemed every other day we had a power cut of a reasonable time, but that was with a Labour government.

 

[JohnW2]

I seem to remember a time around 1978/9 when it seemed every other day we had a power cut of a reasonable time, but that was with a Labour government.

Indeed - but I thought it was appreciably earlier than that - I certainly experienced some cuts of that type when I was trying to study for A-Levels in the mid-60s.

However, those cuts were never moire than 'a few hours' at most - nowhere near long enough to be a problem for an (unopened) freezer.

 

[ericmark]

nowhere near long enough to be a problem for an (unopened) freezer.

I was rather surprised at how short the time can be, I was in the kitchen when I heard a freezer fail, lucky I had a spare in the garage used for brewing beer, so turned this on and waited ½ hour to allow it to cool, the contents then swapped between the two, the upper 6 inches to foot had already defrosted. Food lower down was OK, I would assume it had just finished the defrost cycle when it failed, and it was on restart it failed, however this pointed out to me it does depend on when the last defrost was completed as to how long a freezer will last.

My modern upright freezer actually displays the maximum temperature reached during a power cut, until a door is opened, but back in 1978/9 don't remember frost free upright freezers, and we did know when the power was going off. The biggest problem was loss of the central heating, which at that time was hot air type gas powered, so there was not even a hot radiator to keep the room warm, and windows at that time single glazed top to bottom front and rear of room, so cooled down very fast.

This house far better, central heating drops from 20ºC to 16ºC at midnight, and it is rare for it to kick in before it returns to 20ºC in the morning. But double glazed not single as it was back then.

If I was to loose power between sun down and midnight then the house would cool down, as battery would be unlikely to last the night, but by 2:30 am it would be charged again, and likely would last until sun up, and since not powering kettles etc once power has failed, there would not be a problem most days with a power cut.

However since what the labour party did, I have not trusted having an electric supply, once bitten twice shy, so have ensured I do have either a gas fire or solid fuel fire, and heat pumps are a non starter.

 

[JohnW2]

I was rather surprised at how short the time can be, I was in the kitchen when I heard a freezer fail, lucky I had a spare in the garage used for brewing beer, so turned this on and waited ½ hour to allow it to cool, the contents then swapped between the two, the upper 6 inches to foot had already defrosted. Food lower down was OK,

We've discussed this many times before, on the many occasions you have told this story, and I remain confused/surprised. Certainly in the case of a reasonably full fairly modern (well-insulated) freezer, the temp within the cavity should be reasonably maintained for at least "many hours" provided that the door is not opened.

I wonder if this may be partially due to what you regard as "defrosted"? Large items (e.g. joints of meat) can take many hours to thaw, even at room temperature.

I would assume it had just finished the defrost cycle when it failed, and it was on restart it failed, however this pointed out to me it does depend on when the last defrost was completed as to how long a freezer will last.

I suppose that the 'risk' is greater with a 'self-defrosting' freezer, since it's presumably possible that, by chance, the temp of the cavity may be appreciably higher 'than it should be' at the moment the power fails

However since what the labour party did, I have not trusted having an electric supply, once bitten twice shy, so have ensured I do have either a gas fire or solid fuel fire, and heat pumps are a non starter.

Fair enough, but your fears seem to be based on something which last happened best part of 50 years ago!

 

[Harry Bloomfield]

We've discussed this many times before, on the many occasions you have told this story, and I remain confused/surprised. Certainly in the case of a reasonably full fairly modern (well-insulated) freezer, the temp within the cavity should be reasonably maintained for at least "many hours" provided that the door is not opened.

I wonder if this may be partially due to what you regard as "defrosted"? Large items (e.g. joints of meat) can take many hours to thaw, even at room temperature.

I agree! A few weeks ago, I swapped out my original consumer unit, for a new larger unit. For various reasons, It turned out to be not as easy and straight forward as I had anticipated, so took longer - the entire day before power was able to be restored. I already made sure that the doors were not opened, whilst the power was off.

I have a temperature display and alarm, monitoring the main freezer internal temperature. What I noticed was the temperature increased quite quickly after the power went off. However, when checking the contents, several hours later, just as the power was restored - the actual contents were still very much deep-frozen. So temperature of the compartment, is not that representative of the temperature of the freezer contents.

 

[JohnW2]

I agree! ..... so took longer - the entire day before power was able to be restored. I already made sure that the doors were not opened, whilst the power was off. ...
I have a temperature display and alarm, monitoring the main freezer internal temperature. What I noticed was the temperature increased quite quickly after the power went off. However, when checking the contents, several hours later, just as the power was restored - the actual contents were still very much deep-frozen. So temperature of the compartment, is not that representative of the temperature of the freezer contents.

That corresponds with my experiences, and expectations.

As you say, the temp of the air within the cavity will fall much more rapidly than will the temp of ('solid') contents of the freezer - the mass of the air is negligible in comparison with the mass of the 'contents',so relatively little heat has to be acquired for the air to warm up. That's why I said that my comments related to a 'relatively full' freezer - if it's nearly empty (i.e. the cavity mainly full of air), then the temp will fall much more rapidly.

The rapid fall of air temp within the cavity has its benefits. Like you, I have over-temp alarms in all my freezers. Since they are sensing air temp, in the event of freezer failure (due to power loss or anything else), the alarm will be triggered pretty early, before the temp of the actual 'contents' has risen appreciably.

 

[Harry Bloomfield]

As you say, the temp of the air within the cavity will fall much more rapidly than will the temp of ('solid') contents of the freezer - the mass of the air is negligible in comparison with the mass of the 'contents',so relatively little heat has to be acquired for the air to warm up. That's why I said that my comments related to a 'relatively full' freezer - if it's nearly empty (i.e. the cavity mainly full of air), then the temp will fall much more rapidly.

Exactly, which is why they suggest to keep a freezer relatively full, even if the full involves filling it with empty boxes.

 

[ericmark]

On the Falklands all chest freezers and power 9 - 11 am and 6 - 10 pm only, and no problem, so yes non auto defrost no problem with a power cut for around 12 hours, and even with auto defrost items below where the air is blown out by the fan, are OK it is only stuff at the very top where the heat from the defrost heaters and reach without the fan running, however stuff at the top if it was in the defrost cycle when the power failed can defrost rather fast.

Keep an ice lolly near the top, and if that's OK then likely so is the rest, but one can't simply say an upright freezer can last x hours without power as we simply do not know when it last defrosted. Chest freezer yes, we can say likely it will last 24 hours, but not upright.

 

[JohnW2]

Exactly, which is why they suggest to keep a freezer relatively full, even if the full involves filling it with empty boxes.

indeed - or 'screwed up newspaper'.

However, things of significant mass are even better, since they increase the thermal capacity of the contents, whereas cardboard boxes and newspaper essentially just reduce the amount of free air.

 

[JohnW2]

On the Falklands all chest freezers and power 9 - 11 am and 6 - 10 pm only, and no problem, so yes non auto defrost no problem with a power cut for around 12 hours, and even with auto defrost items below where the air is blown out by the fan, are OK it is only stuff at the very top where the heat from the defrost heaters and reach without the fan running, however stuff at the top if it was in the defrost cycle when the power failed can defrost rather fast.

I knew there was a reason why I have (deliberately) never had an 'auto-defrost' freezer

Keep an ice lolly near the top, and if that's OK then likely so is the rest, but one can't simply say an upright freezer can last x hours without power as we simply do not know when it last defrosted.

Yes, there are a (very) few things, like ice lollies,whose integrity depends upon them never starting to melt. However, with everything else, a slight 'thawing' of the outermost parts is really of no consequence. When we defrost one of our large chest freezers, we usually leave the contents (other than ice lollies etc. ) lying around in the (cool, but not sub-zero) cellar for a a few hours whilst the defrosting is done - and, although the outside of the packaging will be getting 'wet' by the end of that period, it's never resulted in any problems

Chest freezer yes, we can say likely it will last 24 hours, but not upright.

If one is concerned about power cuts, then I think one should probably avoid auto-defrosting freezers. It seems common to see it suggested that the potential problem is greater with an upright freezer than a chest one, but provided that the upright one doesn't auto-defrost, I'm not sure that I understand why it should be any 'worse' than a chest freezer (provided, of course, that the door is not opened - which is disastrous with an upright one!)

 

[Harry Bloomfield]

I knew there was a reason why I have (deliberately) never had an 'auto-defrost' freezer

Our latest one, is an upright auto-defrost. From what I have gathered, the cooling elements and the defrost section, are all concentrated at the back - so it seems unlikely it would much influence the main contents of the freezer.

If one is concerned about power cuts, then I think one should probably avoid auto-defrosting freezers. It seems common to see it suggested that the potential problem is greater with an upright freezer than a chest one, but provided that the upright one doesn't auto-defrost, I'm not sure that I understand why it should be any 'worse' than a chest freezer (provided, of course, that the door is not opened - which is disastrous with an upright one!)

Having had all three types of freezer chest, upright, and now auto-defrost upright, the only difference I notice is the convenience of access, plus the lack of masses of ice forming in the base of a chest type freezer.

I would guess the defrost cycle is very brief, and so hardly makes any difference to how long it can last without power. Insulation thickness on over old chest freezer was somewhat thicker, but insulation has supposedly improved in the 50 years since we had a chest freezer.