Difference between revisions of "Open Biotech/PCR"
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I've been looking at the specs of some Peltier chips (see https://docs.google.com/file/d/1u2m--LONYCOyvcp76spoAP3wN3nWroROwfTtoJx9TpeeeMYY1WVNb1-KCXOk/edit?usp=sharing ) and on some of them, they seem to be designed for lower temperature operation and the lifetime of the device will be significantly reduced if you operate them at a high temperature (the limits of the device in the attached spec device, for example, is 80C.) At 95C, the hot side quickly ramps up from the cold side temp, which is starting at 95C, I've heard as much as 4x the rate of the cold side. By the time you got to 80C on the cold side, you could easily exceed 150C if your heat sink isn't able to pump that much heat that quickly. I think to ensure against damage or reduced life, you have to carefully control the amount of volatge/current applied. A feedback loop to limit applied voltage based on temp of hot side seems to be a sensible addition. I'm still trying to figure this out for a temperature controlled minielectrophoresis unit that I am designing (to be open source). [[User:Hbergeronx|Hbergeronx]]. | I've been looking at the specs of some Peltier chips (see https://docs.google.com/file/d/1u2m--LONYCOyvcp76spoAP3wN3nWroROwfTtoJx9TpeeeMYY1WVNb1-KCXOk/edit?usp=sharing ) and on some of them, they seem to be designed for lower temperature operation and the lifetime of the device will be significantly reduced if you operate them at a high temperature (the limits of the device in the attached spec device, for example, is 80C.) At 95C, the hot side quickly ramps up from the cold side temp, which is starting at 95C, I've heard as much as 4x the rate of the cold side. By the time you got to 80C on the cold side, you could easily exceed 150C if your heat sink isn't able to pump that much heat that quickly. I think to ensure against damage or reduced life, you have to carefully control the amount of volatge/current applied. A feedback loop to limit applied voltage based on temp of hot side seems to be a sensible addition. I'm still trying to figure this out for a temperature controlled minielectrophoresis unit that I am designing (to be open source). [[User:Hbergeronx|Hbergeronx]]. | ||
: | :Yeah. The temperature sensor + MOSFET + microcontroller allows us this dynamic control :-) (also, please put three tilde characters to tag comments with your name) - [[User:Juul|Juul]] | ||
::A cheap unit becomes not so cheap if after a handful of runs, you have to fix it: not trying to imply that you haven't thought of this or to be a downer, but just raising awareness of something that only recently came to my attention. [[User:Hbergeronx|Hbergeronx]] | |||
:::My apologies for the brief comment before. I was in a hurry. Interesting information indeed! One solution would be to just not switch them on at the higher temperatures. We can see how much of an effect the peltier will have above 80 C. My guess is that it will be fairly small. Another solution is to either PWM control the MOSFET, perhaps through a capacitor, or even better, to use the analog output of the microcontroller and a non-charge-pumped MOSFET to gradually control the peltier based on the temperature. We may want to do this with the heating element as well. [[User:Juul|Juul]] | |||
= Heating = | = Heating = | ||