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Very close but not quite... It depends if you want to run the Peltier Cells at the rated voltage of 15.4V.Thanks. I have a follow-up question.
In order to sustain these 4 peltier cells (Max: 25.7 W, 3A, 15.4 V): http://www.shop.customthermoelectri...moelectric-Peltier-Module-12711-5L31-03CL.htm
and use 2 batteries (12 V, 10,000mAh, LiPo Rechargeable battery pack, 13cmX7.5cmX3cm, 150g): http://sz-haosheng.en.alibaba.com/p...h_LiPo_battery_pack_1075130_rechargeable.html
Can I assume with two of these batteries that 20Ah/3A=6.66 hr battery life?
for your first calculation, then wouldnt the power be 120Wh*2=240Wh because there are 2 batteries each at 12V and 10Ah? Then 240Wh/~100W= 2.4hours of battery lifeVery close but not quite... It depends if you want to run the Peltier Cells at the rated voltage of 15.4V.
If not, your math needs a little more work anyway... You want to run Four of these cells... which means you need 4 times the voltage, or 4 times the current. (Or a combination of both.. I'll explain later)
Otherwise, here's some math you can use.
Two batteries: 12V and 10,000mAh
Power = Voltage * Current
Power = 12V * 10Ah = 120Wh
In a perfect world. the batteries will be able to store and deliver 120 Watt Hours.
You simply take this value and device it by how many watts the device is... The odd thing though... is that the ratings for the Peltier Cell don't quite add up. It 'says' 25.7Watts, but if you calculate Watts with the voltage and Current, you get 46.2Watts... so which one to use?
If we use the 'advertised' watts, we get a result of a little over an hour for 4 cells.
If we use the watts we calculated for the Peltier Cell of 46.2Watts, then we get a result of a little over a half hour for 4 cells.
Note that this would be running the peltier cell as HARD as we possibly could.
Now.. if we want to run the peltier cells a little softer, we can use 12V on them instead of 15.4V. For this to work, we would simply put all 4 peltier cells in parallel with our batteries. This would draw 4*3A (12A) total, meaning our 20Ah battery pack would only last an hour and a half.
Haha. yes, you caught me. So you can double all the times I quotedfor your first calculation, then wouldnt the power be 120Wh*2=240Wh because there are 2 batteries each at 12V and 10Ah? Then 240Wh/~100W= 2.4hours of battery life
100W because there are 4 peltier cells at 25W each
Actually, I think I did it wrong. Wouldnt it be 24V*20Ah=480Wh because there are 2 batteries ahah. So 480Wh/100W=4.8 hours?Haha. yes, you caught me. So you can double all the times I quoted
I did the math for multiple cells, but not for multiple batteries. Good catch,
Nope. one or the other, but not both...Actually, I think I did it wrong. Wouldnt it be 24V*20Ah=480Wh because there are 2 batteries ahah. So 480Wh/100W=4.8 hours?
Ok, great. Thank you! I have two more questions. I now think I will use 5 of these batteries, so 50Ah*12V=600 Wh. Then 600 Wh/100W= 6 hrs. How should I go about taking into account peltiers lack of efficiency or the safety margin? Chop off an hour? Also, are these lipo batteries the most compact or should I be looking up other battery types (that may not be well known to inexperienced people like me)? Sorry for all the questions and thank you for taking the time to answer themNope. one or the other, but not both...
So you get a 24V battery pack with 10Ah, or
a 12V battery pack with 20Ah
Thanks for your response.What is your intended use? If you are just trying to maintain a temperature they might not need to be run continuously, and more insulation is cheaper than more battery.
Bob
Hi, so I aim to keep a surface at around 37C. The ambient temperature would range from -20 to +20 (normal canadian ambient weather temp range), so the peltier would be used for heating and cooling.Why don't you describe a little better what you are doing.
What is it you are trying to keep at a constant temp? A small enclosed space, a surface or what?
What is the range of the ambient temp? Are the Peltiers used for heating, cooling or both?
Bob
Assuming the surface of an organism.Why would you need cooling to 37C if the ambient is less than this? Is something else heating the surface?
Bob
ok so the insulation can be as simple a coat right through to a thermal blanket or a $10 fire blanket(probably cheaper over there)Thanks for your response.
Yes, the purpose is to maintain a temperature of something at around 37C lets say in a variety of external temperatures. How would you estimate the increase in length of battery life if it would not always be on? Also, what insulation materials are typical with a peltier?