12v accessories timer

I've got a Coleman thermoelectric cooler that has a native 12v cigarette lighter plug. I'd like to rig up a simple and cheap timer/relay that will allow me to run the cooler for a certain period of time, and then turn it off for a period of time, and repeat. For example I would want to run it for an hour every three hours. So one hour ON, two hours OFF, repeat indefinitely. I would like both duration to be adjustable, even if by some simple means like an on-chip adjustment screw. Adding in a low voltage kill to protect the battery would be nice as well. FYI the reason I am doing this is due to the cooler not having a true thermostat, which I am considering adding but I have other uses for the timer so I'd like to get that working first if possible. Any help would be much appreciated.

For a low voltage cutout, search for the MW728 (~$20). Though various timer kits exist, it's probably cheaper with a new cooler (I'm assuming it's small - under 15L etc). Others might suggest suitable relays/kits. FYI - I was rapt to by a new Peltier (thermo-electric) cooler of ~ 40 Litres for $145 - why pay $1,000 more for compressor types? (Idiots!) After testing with my 100W $750 solar array etc, I am now looking to buy a $1,300 40 Litre compressor type. I know see why I'm the Idiot and the other idiots aren't (I exclude I'mA from this instance, though not from that statement as applied elsewhere). I need at least another array and a bigger battery. It's better spending that on a fridge that AT MOST takes 1/2 the current of the Peltier, but usually far less (1/8 - 1/4), and as a bonus - does't just cool to ~20 degreesC below ambient, but to -20C in ambients of +40C (ie, instead of ambient less 35F, to -4F in 104F).

Yea I understand that the thermoelectric units are not the most efficient. For my purposes though, which is for cigar storage, I only need to keep the temp around 60 deg F so the unit will not be working very hard whether it's heating or cooling. Another benefit of using a thermoelectric unit, is that it has a much smaller effect on humidity than does a traditional fridge, and humidity is critical to proper cigar storage. The only cooler I could find with a thermostat is a Koolatron, and after adapters and accessories those units go well beyond $400 US for the size I need which is around a 40 quart.

Then I'm with you - the Peltiers are best. But get a thermostat - a timer is no way to regulate temperature. (A box in the ground would be better!) The only issue with the thermostat is reasonable on/off time (ie, good hysteresis setting) - you don't want Peltiers on & off all the time. Get one from an old AC fridge etc.

You're right, the timer is not a proper solution, but it seemed like something I could quickly and easily throw together and get the job done. I'm actually looking more seriously at just adding a thermostat now. I found a cheap mini stat kit that looks like it may fit the bill: http://www.apogeekits.com/thermostat.htm Since the Coleman Hot/Cold PowerChill unit I have can be switched from HEAT/COOL modes by simply flipping the power cord polarities, I think I could modify the thermostat to automatically switch between modes. That, in combination with a battery saver feature, would result in a robust little portable storage unit that would work in practically all environments.

As long as there is sufficient dead time between switching (for both changeover and more of the same temperature) since Peltiers dislike thermal shocks (hence their gradual turn on). But the you'd probably be better off with a lamp to heat - since they are 95% efficient), or a resistor (for 100%). And unless it's a huge volume, I assume a small Peltier to limit rate of change. (I imagine an original Peltier chiller box to be too severe.)

I will start a new thread specific to the thermostat and required mods. Thanks for the tips :)