I’m building a DIY liquid chiller for personal cooling while working outdoors in the summer heat, where temperatures often reach 100°F. The idea is to create an ultra-compact heat pump that fits into a pouch or satchel and circulates liquid through a cooling garment, like a vest.

I've already found off-the-shelf components to assemble the heat pump, and the compressor I'm considering comes in both 12V and 24V versions. The unit has to be battery-powered, and ideally, I'd like to use 20V DeWalt tool batteries since I already own several. DeWalt offers a 20V battery with a 15Ah capacity, and I'm trying to figure out how to get the best runtime out of a single charge.

What I need help with is figuring out whether to go with the 12V or 24V version of the compressor. Which one would give me better efficiency and longer runtime using a 20V battery? And is it even possible or safe to run a 24V compressor directly from a 20V source? I'm also trying to get a rough idea of how long the system might run on a full 15Ah battery, just to see if the concept is practical.

 

Welcome to AAC.

To be of help, we need to know the specifics of the pump. Please include a link to the devices you're referring to.

 

What I need help with is figuring out whether to go with the 12V or 24V version of the compressor. Which one would give me better efficiency and longer runtime using a 20V battery? And is it even possible or safe to run a 24V compressor directly from a 20V source? I'm also trying to get a rough idea of how long the system might run on a full 15Ah battery, just to see if the concept is practical.

No, it is likely not a good idea to operate the 24V compressor from the 20V battery (which likely goes down to below 18V when discharged).

For best efficiency you would need a switching boost converter to operate the 24V compressor, or a buck converter to operate the 12V compressor from the 20V battery.

How long the battery will last obviously depends upon how much current the compressors take, which you haven't stated.

 

First we hear about "a circulating pump to circulate a cooling liquid". I can easily visualize that. Then suddenly the question is about COMPRESSOR voltage choices running on 20 volt power tool batteries.
Compressors are not used for circulating liquids, they are often used in refrigeration systems. Very much different in almost every aspect.
So some actual additional explanations are in order, such as the amount of cooling required, the desired run time on one battery charge, and the allowable system weight.

 

Given a 20V battery, a buck converter driving a 12V compressor is the better choice.

A heat pump has two sides, the condenser is apparently the tubing in the vest. How are you planning to get rid of the heat produced at the compressor side?

 

Looked this up. Existing cooling vests seem to all work by phase change, i.e. you melt something to absorb heat. Some use an ice pack and circulate water. Could not find any that use a heat pump. There is likely a reason why.

 

A liquid carbon dioxide system could run open loop, and discharge very small amounts into the tubes in a vest to allow the cold vapor to absorb heat. That could run for quite a few hours on just a few pounds of liquid carbon dioxide. And the control electronics and the valve would not consume much power.
By definition, a "heat pump" uses the evaporation/condensation principle to move heat energy, and mostly that requires at least one compressor, and often also a blower or fan. Both of those consume a fair amount of power and tend to be a bit heavy, at least, all of them that I am familiar with.

 

Measure the battery's voltage and make sure it is actually 20V. M18 Milwaukee batteries are actually around 20.5V fully charged and 18V discharged. I don't have any experience with DeWalt myself and just wanted to throw that out.

 

We do not have any response from the TS, (Original Poster) as to any of the details requested.
And I do not visualize the effort to carry any sort of actual portable refrigeration system as being acceptable.
I have found that carrying two water bottles while back-packing allows me to moisten a cooling headband quite adequately.