Excellent point about a single-well thermocycler. Rarely do you want to run 1 tube at a time however. Need several tubes at a minimum, for experimental controls, redundancy, etc. OpenPCR is considered personal-pizza-size with only 16. Apple's USB-C laptop charger is rated at 29W ( 2A @ 14.5V ), for the Macbook which has no other power supply input, only USB-C -- so the supply isn't in either the 60W or 100W class. Plastic tubes are unfortunately not very thermally conductive. The liquid volumes are under 100 uL (typical synbio anyway). I didn't check your math, I do agree that static temperature baths are the cheapest solution - either move the tubes to the bath or move the bath medium to the tubes. Most of the energy goes into heating/cooling the metal mass holding the tubes, which oddly enough are machined out of large solid metal blocks -- there may be a benefit to this that I can't see, otherwise I consider it a baffling choice (no pun intended). Some thermocyclers physically halve the heater block mass (I suppose you could call this, decoupling) when ramping temperature down. Note the use cases may include incubation temperature for long periods of time (37 C typical, or up to 65C in some cases, for up to several hours total), this would result in steady state power draw, not peak power -- this is important regarding the assumption that a battery could be used instead (not sure I'd want to use a battery unless it was remote field use). Another static temperature use case is 4C for many hours, for example.
The Lava-amp micro thermocycler was under 1W (I think). Even had it worked out, I'm not sure it would have gained acceptance because it used a different form factor - didn't use "old fashioned" tubes. Although there could be real experimental differences in results if changing equipment, obviously the ideal thermocycler would increase the surface area of the liquids for maximizing energy transfer -- i.e. not use plastic tubes. That's one part of the approach the Lava-amp design took.
About this assumption:
>Now suppose I have two water baths, one at 60 degrees, and another at 90 degrees.
>I use a small motor to move the 96 tubes from one bath to the other.
>I can have a small fan that blows over the tubes when they go from the hot bath to the cold bath to speed the cooling, so that when the tubes hit the 60 degree bath they are already at 60 degrees.
Historically there are thermocyclers designs which use fans and electronically controlled vents to direct heated (or room temperature) air for assisted ramping.
Here's an example typical use case (synbio purification-ligation) to contrast to your example.
The Lava-amp micro thermocycler was under 1W (I think). Even had it worked out, I'm not sure it would have gained acceptance because it used a different form factor - didn't use "old fashioned" tubes. Although there could be real experimental differences in results if changing equipment, obviously the ideal thermocycler would increase the surface area of the liquids for maximizing energy transfer -- i.e. not use plastic tubes. That's one part of the approach the Lava-amp design took.
About this assumption:
>Now suppose I have two water baths, one at 60 degrees, and another at 90 degrees.
>I use a small motor to move the 96 tubes from one bath to the other.
>I can have a small fan that blows over the tubes when they go from the hot bath to the cold bath to speed the cooling, so that when the tubes hit the 60 degree bath they are already at 60 degrees.
Historically there are thermocyclers designs which use fans and electronically controlled vents to direct heated (or room temperature) air for assisted ramping.
Here's an example typical use case (synbio purification-ligation) to contrast to your example.
| 100 cycles | 12 °C | 60 s |
| | 22 °C | 60 s |
| | 12 °C | 60 s |
| | 22 °C | 60 s |
| | 12 °C | 60 s |
| | 22 °C | 60 s |
| | 12 °C | 60 s |
| | 22 °C | 60 s |
| Hold | 16 °C | infinite |
## Jonathan Cline ## jcline@ieee.org ## Mobile: +1-805-617-0223 ########################On 1/26/16 2:44 PM, Simon Quellen Field wrote:
Just so I understand the problem a little better (I have never used a thermal cycler before), let me ask some questions about the specs I have found for one.
The BIO-RAD C1000 Touch Thermal Cycler 96-Well Fast uses 850 watts of input power.It has a maximum ramp rate of 5 degrees Celsius per second, and an average ramp rate of 3.3 degrees C per second. It holds 96 tubes, each with 0.2 milliliters of liquid in them.
Two other specs are a little confusing to me: the Gradient range is 30-100 degrees C,and the temperature differential range is 1-24 degrees C.
So we are talking about heating and cooling 19.2 milliliters of water, and the mass of the plastic tube. From the graph on that page, it seems like a typical use case is cycling between 60 C and 90 C, at about 30 to 40 second intervals.
To be on the conservative side, I will assume that the plastic holder takes as much power to heat as the water, and I'll round up to heating and cooling 40 ml of material.
Raising 40 ml of water by 30 degrees C takes 5,020.8 joules.Doing that at a rate of 5 degrees per second takes 6 seconds.5,020.8 joules in 6 seconds is 836.8 watts.
Let's call that the brute force method.
Now suppose I have two water baths, one at 60 degrees, and another at 90 degrees.I use a small motor to move the 96 tubes from one bath to the other.I can have a small fan that blows over the tubes when they go from the hot bath to the cold bath to speed the cooling, so that when the tubes hit the 60 degree bath they are already at 60 degrees.
Now my heating problem becomes one of maintaining the 60 degree bath at 60 degrees (making up for the losses through the Styrofoam insulation, and the evaporative losses), and maintaining the 90 degrees bath at 90 degrees, making up for the losses in heating the tubes, insulation, and evaporation.
The 90 degree bath loses 5,020.8 joules every minute (cycling 30 seconds hot and 30 seconds cold). That's 83.68 watts. Plus a small amount needed to make up for evaporative and insulation losses. And a bit to run the fan. Call it 90 watts.
At 12 volts, that's 7.5 amperes. At 20 volts, it's 4.5 amperes.
The reason the USB3.1 specification calls for 20 volts at 5 amps is so it can be used to charge laptops and power monitors. I actually own a desktop computer with USB3.1 ports and Type-C connectors, so I may be able to give actual numbers, once I get a device that can charge through a Type-C port. But the manufacturer claims it can do 20 volts at 5 amps. You can get a PCIe card with a Type-C connector for less that $20 and try it out for yourself.
So, it should be just barely possible to build a thermocycler that runs off a Type-C connector. You don't even need to go the water bath route. You can put a laptop battery in it, and get the whole 850 watts while it is running, and charge it from the USB port when it is idle.
But realistically, how much more convenient is plugging it into a USB port compared to plugging it into the wall? Just use house wiring and throw power at the problem.
Having said all that, I think a cool project would be a single well cycler that heats and cools 0.2 ml of solution, powered by USB. That should be doable in 10 watts. :-)
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