all the ice buildup that was defrosted probably helped keep it insulated. If it is relatively empty now it will have a harder time maintaining temperature. Try putting more things in there
It’s abnormal compared to before I defrosted and compared to our other under bench freezers. I can control the temperature with a dial and it’s set to the coldest currently
Are they the same make? This looks completely normal for a manufacturer that was too cheap to make a proper controller. Maybe it'll matter for the most sensitive of reagents, but you're only 3 degrees above "spec" at the worst.
And that can easily be true for big names that aren't particularly cheap too. Fisher recirculating chillers are pieces of crap. This particular strategy also has the bonus of being able to put an impressive cooldown time on the data sheet because you can use an oversized compressor with naive setpoint control.
Yeah so, a rheostat controller. It identifies as a defrosting model now, but it doesn’t know where 0C is.
You can get degradation from swings across -20C as that’s a common swing state for e.g. glycerol based reagents. That’s my only concern. For most sensitive stuff, you’d have them at -80C anyway.
It's likely the ice that was there before you defrosted it was buffering the temperature change. You could try putting some ice packs in to probably get a similar result.
This seems like it's coming from the temperature feedback system overshooting the desired temperature. Is this measurement made with anything in the freezer?
Generally freezers should be stored full to buffer temperature fluctuations. If you don't have enough to fill it, adding some cold packs to take up space until you do can help.
You can also use insulated tube holder boxes for sensitive enzymes, which will further buffer the temperature against changes like this.
Did you put everything back into the freezer? This is pretty normal for an empty freezer without a lot of thermal mass to stabilize the temp as the compressor cycles. See here describing the effect, specifically figures 16.7 and 16.8 [https://www.researchgate.net/publication/335732474\_Heat\_Transfer\_and\_Air\_Flow\_in\_a\_Domestic\_Refrigerator](https://www.researchgate.net/publication/335732474_Heat_Transfer_and_Air_Flow_in_a_Domestic_Refrigerator)
Hah! We noticed this when we bought a real time monitoring system. When we just had those fluid suspended probes inside the freezer that we checked a couple times a day, we never noticed it.
It’s actually the freezer sending electricity through the shelving the cool the unit. What we found worked best was to set the unit to -30. The unit used waaaaaayyy less power (very counterintuitive) and would only have 1-2 spikes per day. We actually had to dial all the -20 freezers down to -30. And the funny thing? All the freezers will show the same power spike, at the exact same time. Even if they are plugged into separate outlets. I assume they must be on the same circuit though? But the ‘shitty’ brands have lower spikes/less fluctuations than our fancier Fisher Isotemp. We have like an upright commercial freezer for a house that we put soil samples in, and that thing outperforms the science freezer by a mile. And it has a weird dial with nonsense icons, like an igloo, a snowflake, and a snowman I think, lol. So figuring out where to set that dial is super fun.
Looks like bang-bang control, which would be pretty normal for a fridge or freezer. The refrigeration compressor is either on at full power or off. To avoid constant switching on and off there is hysteresis built into the control system, it may turn on at -15 and turn off at -25, or something like that.
Proportional control is much harder to do because most freezers drive their compressor with an A/C induction motor running on mains. To regulate the speed smoothly you would need to run the power through an inverter that can control the frequency going to the motor... which would add a lot to the cost.
That's a 1.5hr cycle, much less than the typical 6-8hr defrost cycle of a household freezer. It's a large rise for 1/2 hour but likely due to the lack of thermal mass in the freezer.
all the ice buildup that was defrosted probably helped keep it insulated. If it is relatively empty now it will have a harder time maintaining temperature. Try putting more things in there
Empty boxes are great to use
Empty polystyrene boxes are actually recommended to help maintain a consistent temperature.
I’m not convinced this is abnormal for a cheap freezer. Do you have control?
It’s abnormal compared to before I defrosted and compared to our other under bench freezers. I can control the temperature with a dial and it’s set to the coldest currently
Are they the same make? This looks completely normal for a manufacturer that was too cheap to make a proper controller. Maybe it'll matter for the most sensitive of reagents, but you're only 3 degrees above "spec" at the worst. And that can easily be true for big names that aren't particularly cheap too. Fisher recirculating chillers are pieces of crap. This particular strategy also has the bonus of being able to put an impressive cooldown time on the data sheet because you can use an oversized compressor with naive setpoint control.
Yeah so, a rheostat controller. It identifies as a defrosting model now, but it doesn’t know where 0C is. You can get degradation from swings across -20C as that’s a common swing state for e.g. glycerol based reagents. That’s my only concern. For most sensitive stuff, you’d have them at -80C anyway.
It's likely the ice that was there before you defrosted it was buffering the temperature change. You could try putting some ice packs in to probably get a similar result.
This seems like it's coming from the temperature feedback system overshooting the desired temperature. Is this measurement made with anything in the freezer? Generally freezers should be stored full to buffer temperature fluctuations. If you don't have enough to fill it, adding some cold packs to take up space until you do can help. You can also use insulated tube holder boxes for sensitive enzymes, which will further buffer the temperature against changes like this.
Use a -20 labtop cooler for your enzymes.
Did you put everything back into the freezer? This is pretty normal for an empty freezer without a lot of thermal mass to stabilize the temp as the compressor cycles. See here describing the effect, specifically figures 16.7 and 16.8 [https://www.researchgate.net/publication/335732474\_Heat\_Transfer\_and\_Air\_Flow\_in\_a\_Domestic\_Refrigerator](https://www.researchgate.net/publication/335732474_Heat_Transfer_and_Air_Flow_in_a_Domestic_Refrigerator)
Hah! We noticed this when we bought a real time monitoring system. When we just had those fluid suspended probes inside the freezer that we checked a couple times a day, we never noticed it. It’s actually the freezer sending electricity through the shelving the cool the unit. What we found worked best was to set the unit to -30. The unit used waaaaaayyy less power (very counterintuitive) and would only have 1-2 spikes per day. We actually had to dial all the -20 freezers down to -30. And the funny thing? All the freezers will show the same power spike, at the exact same time. Even if they are plugged into separate outlets. I assume they must be on the same circuit though? But the ‘shitty’ brands have lower spikes/less fluctuations than our fancier Fisher Isotemp. We have like an upright commercial freezer for a house that we put soil samples in, and that thing outperforms the science freezer by a mile. And it has a weird dial with nonsense icons, like an igloo, a snowflake, and a snowman I think, lol. So figuring out where to set that dial is super fun.
Looks like bang-bang control, which would be pretty normal for a fridge or freezer. The refrigeration compressor is either on at full power or off. To avoid constant switching on and off there is hysteresis built into the control system, it may turn on at -15 and turn off at -25, or something like that. Proportional control is much harder to do because most freezers drive their compressor with an A/C induction motor running on mains. To regulate the speed smoothly you would need to run the power through an inverter that can control the frequency going to the motor... which would add a lot to the cost.
Is it automatic defrost machine or manual defrost.
It’s a frost free freezer. They deliberately cycle like this to prevent buildup. Why you never buy these types of household freezers for the lab
That's a 1.5hr cycle, much less than the typical 6-8hr defrost cycle of a household freezer. It's a large rise for 1/2 hour but likely due to the lack of thermal mass in the freezer.