Peltier coolers as diversion loads? - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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Old 07-05-2011
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Peltier coolers as diversion loads?

So once the batteries are topped up and the loads are diverted via my charge controllers would a peltier cooler work as a diversion load? I was thinking I could either source the coolers and install them in my old 'ice box' which is used basically as a pantry now that I have a fridge or get like a coolatron unit and fill it with my drinking water. In the winter perhaps I can reverse them and use them as heaters. Anyone tried doing this? Any flaws in this plan? Do the loads just have to be able to accept a high level of current ie it blows hard for several days or I leave the boat for a while and the wind/ solar has maxed out the batteries and is in diversion mode - can peltier coolers just accept as much output as they are given like a water heater element?
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Old 07-05-2011
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"can peltier coolers just accept as much output as they are given like a water heater element?"

A water heater element, a resistance heater, actually increases in resistance as it gets hotter, and will burn out like a fuse if you apply too much power to it, exceeding the wattage rating of the element by jacking up the voltage.

I'd expect the peltier device to burn out way faster. A 12v rated peltier may have a maximum voltage rating of 16V and a power rating of 80W. Exceed either, and it becomes toast. In a nominal 12v system you need to ensure it can run safely at 14.4 volts (alternator power) and that it will never see more than 16V or whatver the max rating is.

If you use solar cells with a 17-22V maximum output, you've got expensive toast. If you use a drop regulator to reduce them to under 16V output, you may be throwing out 1/3 of your power before it goes past the regulator.

Gensets use "dump regulators", conventional solar regulators are "drop" regulators, just like the 3-pin single chip 317s and 7812's sold in electronic stores. (Which typically convert excess power to heat in their heat sinks.) Alternators are entirely differently, they regulate their output by cutting back their input and actually producing less power--instead of throwing it out.
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Essentially since I live in a hot climate I would like to create a cool sink instead of a heat sink - could be used to cool water or the cabin. I understand that one side of the peltier device gets warm while the other gets cold so in order to use it constructively it would probably need to be in a coolbox of some sort say a koolatron cooler. Is there a way to safely drop the voltage of the dump and keep it below 16V so that the power can be used constructively? Am wondering what to do with the bonus diverter power and in 100 degree weather heating water is not very attractive compared to cooling it.
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So it would seem the koolatrons only use 48 watts - I would need like 10 of them to provide a safe diversion load. Perhaps I can parallel a couple of resistors such as a koolatron or series of peltiers, maybe a fan, a light and then maybe a large diversion specific resister. Is there a way to prioritize which devices would see the excess load first ie so that if I have a large diversion resistor all the power wont go to that before running through my cooler first? What about trying to make an enormous peltier device that could safely handle the diversion load? This sort of thing is fun to think about but may probe more hassle then its worth in the real world...
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Old 07-05-2011
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Despite being an engineer and thinking about all the issues hellosailor lists above, for one fleeting second I had a vision of every cupholder in the boat having a Peltier cooler at the bottom.

Quote:
Originally Posted by Mariner777 View Post
Is there a way to prioritize which devices would see the excess load first ie so that if I have a large diversion resistor all the power wont go to that before running through my cooler first?
Naval warships have systems that work exactly the opposite - load shedding circuitry drops circuits according to priority so that essential systems can continue to function as generating capacity goes off line due to damage.

There is a story about a new ship that was out for trials and had a casualty in the generator room, triggering load shedding. The story goes that the flag cabin (the quarters for an Admiral, if aboard) was in the first round of load shedding and that said officer was not amused. *grin* Don't much care if the story is true or not it is so good.

For your purposes it should be reasonably straightforward for someone with the right background to design and build a small panel with enough intelligence to bring a handful of circuits online in order. I should think it could be done with some voltage comparators and current limiters. You'd have to find someone who was into it for the fun or the price would be ridiculous.
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Old 07-06-2011
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If you have excess output from your panels the solution is easy - enlarge your battery bank.

Then you can use the amps whenever you want for something useful.
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I just did bringing me up to 710 amp hours may go up to close to a 1000 soon. Its not the solar so much as the wind generators - lets say I have some particularly sunny and windy weather and am away from the boat for a while and my batteries are maxed out and the charge controller goes into diversion - putting it into a heat generating resistor is the last thing I would want to do given the 100 degree plus temperatures - am trying to find a useful thing to do with the potential extra power such as cool me or some beverages down somehow...
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What kind of batteries do you have?
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