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25W*4*12h = 1200Wh
expressed in ampere-hours:
Capacity_in_Ah= 1200Wh/Voltage
You should factor in a safety margin7reserve to compensate loss og capacity due to aging and changes in temperature, e.g. nominal_capacity=1.5*calculated_capacity.
expressed in ampere-hours:
Capacity_in_Ah= 1200Wh/Voltage
You should factor in a safety margin7reserve to compensate loss og capacity due to aging and changes in temperature, e.g. nominal_capacity=1.5*calculated_capacity.
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?
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?
Very 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 per battery (240Wh total)
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 two hours 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 an 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.
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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 life
100W because there are 4 peltier cells at 25W each
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,
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...
So you get a 24V battery pack with 10Ah, or
a 12V battery pack with 20Ah
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 them
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?
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.
Assuming the surface of an organism.
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?
one thing I have seen from this thread is that you are trying to maintain a constant temp of 37... the issue is that the ambient temp is going to be -20 to +20.... peltiers don't work like this.
a peltier offer a temperature differential... so whatever one side is the other is x different. x is the watts... I have yet to figure out the equation to tell you how to calculate what the difference will be.... but on average I find about 20-30C difference. -20 to 37c is 57c... you may not get this. its trial and error. you could however piggyback them. so the cold side of 1 is -20, the hot side is therefore (lets say) 30c higher making it 10C, so the cold side of the next is 10c and its hot side will go up to 40c......
ok so with that partially explained (and I know someone is going to point out things in there a little of lol) I will also point out that you are only looking at the peltiers. what circuit are you using to control the temp? this will add to power consumption.
a good idea I saw recently was a rechargeable heat pack, plug in ad it heats a gel which holds heat longer than applying it directly to the skin. by making a sort of oven that heats a gel pack you are cutting down on a few losses. the oven itself can be solar powered, or you can find 50 other ways to power it. being insulated the gel pack will receive the majority of the heat rather than the external temps cooling it quickly, and a gel pack is easier to carry around then say an 100ah battery and wires and peltiers and microcontroller to regulate temp and power regulator.....
off course there are down sides as a gel pack will not keep at 37c for long it may go higher or much lower. but using thermal mass you could have it around that temp for ages.
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