Tweet
ESC Cooling Concept- Theory and Practice
I thought a new thread may be appropriate in response to the “Cooling Brain Fart” thread to discuss a bit of theory, few facts and present one potential workable concept for cooling ESC’s for FE boats.
The Theory….
ESC’s use conduction cooling. (so do electric motors but lets focus on ESC’s) The better the conductive path, the better the cooling. For aircraft ESC’s the high velocity wind from the prop across the finned heat sink is normally sufficient. In FE boats, the normal air cooling is not adequate which is why marine ESC’s are water cooled and/or forced air cooled by using a small brushless fan similar to that cooling a computer processing chip. Excessive heat is probably one of the major causes of ESC’s burning up in FE boats.
To improve cooling in an attempt to burn out fewer ESC’s we need to improve conduction cooling. This means using better “heat sink” materials to convect the heat away, increasing the surface area of the conductive “heat sink” and reducing the inlet cooling water temperature. Getting heat out of the FET’s is the goal.
In terms of better heat sink materials one needs to look at the thermal conductivity of the material used. Thermal conductivity is the quantity of heat transmitted through a unit thickness of material due to a unit temperature differential. (The term “unit” means that we care compare apples-to-apples so to speak). Maybe a simpler definition would be the rate at which heat is transferred by conduction when a temperature gradient exists. Simply put, the higher the thermal conductivity of a material the better it cools.
Comparing thermal conductivity of different materials………..
Silver has one of the highest thermal coefficients at 429 but copper is a close second at 400, (and a lot less expensive). Aluminum is 250 and Brass is 109. Since conductive heat transfer is directly proportional to the thermal coefficient, use of copper rather than aluminum for a heat sink would provide a 38% improvement. Can you imagine running aluminum wire from your ESC to LiPo’s and brushless motor? The building code for many areas now requires use of copper wiring and not the cheaper aluminum wiring (as in my 27 year old home).
Several great threads have been submitted on adding cooling to ESC’s such as the relatively inexpensive 200 amp Mystery models. Brass tubing is integrated into the existing aluminum heat sink. But the thermal coefficient of brass is 109 compared to 400 for copper. I think you can work the math here for the best tubing material.
A proposed open loop cooling concept ……………
In a previous thread I outlined using a 35 mm film can or canister with a cooling coil inside. The canister is filled with water than put into the freezer. The inlet water passes through this prior to going to the ESC and motor. Even this simple idea decreases the film canister outlet temperature but about 20 degrees. However I only use this on very small boats in the 12-16 inch range. It certainly would not help to any degree of most of the larger FE’s that are run by members of this forum. One comment I saw in the forum recommended just using water or alcohol in the canister (or really the cooling tank). Is this good idea? All one has to do is to compare the thermal coefficients…. remember the higher the coefficient the better the cooling. Air is 0.024, water is 0.58, alcohol is 0.17 and ice wins out at 2.18. Thus the cooling with all ice is 4 times as effective as water at the same temperature. The large ice value is a result of the latent heat of melting….if that makes any sense. (I am running some tests on the liquid used in ice packs and will post the results later.)
One Concept for “Canister Cooling” that I use on my Mean Machine with a 540 XL….
For lots of cooling we need lots of copper tubing. In the pictures you can see I purchased some small Tupperware-type containers: 4 for 99cents and the……….you guessed it, the local 99-cent store. I wound 20 inches of ¼ inch diameter copper tubing around a wooden plug so it fit perfectly in my 25-cent container. If you calculate the surface area of this length of tubing it is whopping 15.7 square inches. (Compare this to the aluminum heat sink that comes on many ESC’s) The entire cooling unit weighs 3.7 oz or 104 grams and when filled with water (ice) it weighs 6.2 oz or 176 grams. The dimensions are 3” x 2.3” x 2.4” high. (pics included)
Now for a canister cooling comparison:
1. My 35 mm film can with brass tubing has an effective total cooling number of 513. (You get this by taking into account material used as well as diameter and length of tubing)
3. My 25-cent Tupperware-type container with 20 inches of copper tubing has an effective total cooling number of 6,280. Enough said on this.
How well does this really work?…………….
Good question and that is what I am determining now. I use an Eagle Tree data logger that has 3 temperature probes (thermistors). One is on the ESC, one is the inlet water (for the fresh water lake in front of my house that is about 76 degrees F now), and the third is the water temperature on exit from the cooling canister. (pics included) Stay tune for the results.
I am sorry for this thread being so long but I wanted to create a common technical base so the different ideas and cooling gadgets from forum members can be numerically compared….apples-to-apples. As a teaser I think there is a MUCH better way to provide ESC cooling that does not require canister cooling, Peltier plates, fans, pumps or giant heat sinks. I have modified an idea used by the Russians in their MIR submersibles that have gone to the bottom of the North Pole and made over 100 trips to the Titanic. Again, stay tuned for the results……..IF I can make this concept work!
I look forward to your comments and suggestions
I thought a new thread may be appropriate in response to the “Cooling Brain Fart” thread to discuss a bit of theory, few facts and present one potential workable concept for cooling ESC’s for FE boats.
The Theory….
ESC’s use conduction cooling. (so do electric motors but lets focus on ESC’s) The better the conductive path, the better the cooling. For aircraft ESC’s the high velocity wind from the prop across the finned heat sink is normally sufficient. In FE boats, the normal air cooling is not adequate which is why marine ESC’s are water cooled and/or forced air cooled by using a small brushless fan similar to that cooling a computer processing chip. Excessive heat is probably one of the major causes of ESC’s burning up in FE boats.
To improve cooling in an attempt to burn out fewer ESC’s we need to improve conduction cooling. This means using better “heat sink” materials to convect the heat away, increasing the surface area of the conductive “heat sink” and reducing the inlet cooling water temperature. Getting heat out of the FET’s is the goal.
In terms of better heat sink materials one needs to look at the thermal conductivity of the material used. Thermal conductivity is the quantity of heat transmitted through a unit thickness of material due to a unit temperature differential. (The term “unit” means that we care compare apples-to-apples so to speak). Maybe a simpler definition would be the rate at which heat is transferred by conduction when a temperature gradient exists. Simply put, the higher the thermal conductivity of a material the better it cools.
Comparing thermal conductivity of different materials………..
Silver has one of the highest thermal coefficients at 429 but copper is a close second at 400, (and a lot less expensive). Aluminum is 250 and Brass is 109. Since conductive heat transfer is directly proportional to the thermal coefficient, use of copper rather than aluminum for a heat sink would provide a 38% improvement. Can you imagine running aluminum wire from your ESC to LiPo’s and brushless motor? The building code for many areas now requires use of copper wiring and not the cheaper aluminum wiring (as in my 27 year old home).
Several great threads have been submitted on adding cooling to ESC’s such as the relatively inexpensive 200 amp Mystery models. Brass tubing is integrated into the existing aluminum heat sink. But the thermal coefficient of brass is 109 compared to 400 for copper. I think you can work the math here for the best tubing material.
A proposed open loop cooling concept ……………
In a previous thread I outlined using a 35 mm film can or canister with a cooling coil inside. The canister is filled with water than put into the freezer. The inlet water passes through this prior to going to the ESC and motor. Even this simple idea decreases the film canister outlet temperature but about 20 degrees. However I only use this on very small boats in the 12-16 inch range. It certainly would not help to any degree of most of the larger FE’s that are run by members of this forum. One comment I saw in the forum recommended just using water or alcohol in the canister (or really the cooling tank). Is this good idea? All one has to do is to compare the thermal coefficients…. remember the higher the coefficient the better the cooling. Air is 0.024, water is 0.58, alcohol is 0.17 and ice wins out at 2.18. Thus the cooling with all ice is 4 times as effective as water at the same temperature. The large ice value is a result of the latent heat of melting….if that makes any sense. (I am running some tests on the liquid used in ice packs and will post the results later.)
One Concept for “Canister Cooling” that I use on my Mean Machine with a 540 XL….
For lots of cooling we need lots of copper tubing. In the pictures you can see I purchased some small Tupperware-type containers: 4 for 99cents and the……….you guessed it, the local 99-cent store. I wound 20 inches of ¼ inch diameter copper tubing around a wooden plug so it fit perfectly in my 25-cent container. If you calculate the surface area of this length of tubing it is whopping 15.7 square inches. (Compare this to the aluminum heat sink that comes on many ESC’s) The entire cooling unit weighs 3.7 oz or 104 grams and when filled with water (ice) it weighs 6.2 oz or 176 grams. The dimensions are 3” x 2.3” x 2.4” high. (pics included)
Now for a canister cooling comparison:
1. My 35 mm film can with brass tubing has an effective total cooling number of 513. (You get this by taking into account material used as well as diameter and length of tubing)
3. My 25-cent Tupperware-type container with 20 inches of copper tubing has an effective total cooling number of 6,280. Enough said on this.
How well does this really work?…………….
Good question and that is what I am determining now. I use an Eagle Tree data logger that has 3 temperature probes (thermistors). One is on the ESC, one is the inlet water (for the fresh water lake in front of my house that is about 76 degrees F now), and the third is the water temperature on exit from the cooling canister. (pics included) Stay tune for the results.
I am sorry for this thread being so long but I wanted to create a common technical base so the different ideas and cooling gadgets from forum members can be numerically compared….apples-to-apples. As a teaser I think there is a MUCH better way to provide ESC cooling that does not require canister cooling, Peltier plates, fans, pumps or giant heat sinks. I have modified an idea used by the Russians in their MIR submersibles that have gone to the bottom of the North Pole and made over 100 trips to the Titanic. Again, stay tuned for the results……..IF I can make this concept work!
I look forward to your comments and suggestions
Comment