The peltier device accepts pwm for temperature control and reverse current for switching from cooling to heating. A standard motor controller would do the trick, but they are only 12v 2a, and I need 12v 8a. Where do I find such a controller?
Task-specific devices are available for the purpose, and there are plenty of devices targeting motor drive applications that could be made to work. There are probably dimmable LED drivers a person could use.
Much depends on the desired control scheme. If using motor-focused devices however, an appropriate filter should be provided to reduce ripple across the device to less than 10%, with less being better.
It should be understood that while they do offer certain conveniences of size, reversibility, and ease of control, peltier devices are terrible from an efficiency standpoint. Most who try to use them for cooling without doing the necessary math end up disappointed, in my experience.
See this post on understanding the device specifications, this one on thermal modeling of related systems, and this one on related application considerations.
Thanks so much. That’s a lot of info! I’m trying to heat/cool about .25 liter of water that is in an aluminum tray (not unlike photo chemicals). The tray sits within a 1/8" thick plastic enclosure that’s about 1.5 cu.ft. of space. The ambient temperature (and therefore the starting temperature of the water in the tray) can vary from 50 degrees F to 120 degrees F. The goal of the peltier system is to bring the ambient temperature of the water to 78 degrees, from either extreme, and then maintain the 78 degrees for several hours. In most cases, the starting temperature extremes would probably be from 55 degrees F (in the winter) to 95 degrees F in the summer. While my time and ability to absorb the math and apply it accurately in one shot do not exist, after reading the links it appears the peltier project is doomed. What do you think? There are many simple heating options, but it’s the cooling requirement that’s the rub. The entire system needs to come in under $100. Any other suggestions beyond peltier?
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Compressor-based mini-fridges can be had for <$100 new, and there’s no telling what a person could find on the secondary market.
A 1.5 cubic foot “plastic” enclosure 0.13" thick could be expected to leak on the order of 100W at the 42°F max temperature difference given. Not necessarily out of reach for a peltier based solution, though a damp finger in the breeze suggests you’d have to burn around 400W of electricity to do it.
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