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The Water Cooler
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Have a geeky question here and if someone does electronics they may be able to help.
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<blockquote data-quote="tyromeo55" data-source="post: 3307314" data-attributes="member: 1719"><p>Forgive me i'm going to try to do my best here</p><p></p><p>Most vehicles do not use any real amount of energy to crank the engine. Like 2 watt hours. Do the math. figure 200 AMPS (average over the entire start cycle. I know initial is more) for 3 seconds or so. 200A X 12.5V = 2.5KW/HOURS to go from hours to minutes divide 2500Wh / 60min = 41.666 , divide again by 20 to get to 3 seconds crank time. 41.666/20 = 2.083 Wh consumed to start the engine Lots of factors going on with the battery but a couple ones at the top of my head are.... </p><p></p><p>chemistry - A 8Ah 12V SLA pony battery can easily come up with a ton of power for a fraction of a second. Pull a spec on one. I know that it won't list what we are wanting to know but it will show the theory. It can come up with a ton of current for a short period of time... The longer the duration of time the lower the amount of current you can expect. This is a good read look at page 9 for a chart <a href="https://www.power-sonic.com/wp-content/uploads/2018/12/Technical-Manual.pdf" target="_blank">https://www.power-sonic.com/wp-content/uploads/2018/12/Technical-Manual.pdf</a>. I think 20C is not too unreasonable for a couple seconds </p><p></p><p>Internal impedance of the battery and hookup wires - The impedance of the battery and connecting wires will have a definite affect on the amount of current the caps will be allowed to take from the pony battery.</p><p></p><p>Here is a fun one. an AA battery has about 4.5 Wh of power. You could charge a good super capacitor bank with one and start a car.</p><p></p><p></p><p>If you do try to get a couple super capacitors and try it out I would caution how you initially balance them to the pony battery. In my car stereo days I had a small incandescent 12v lamp that I soldered some leads and banana clips onto. Used it in series to recharge the cap bank. When current is flowing the lamp with light up and dim as it equalizes out.</p><p></p><p> </p><p></p><p></p><p>Ummmm. yea..... That is a complete 180 from your original post. </p><p></p><p></p><p>T?he Supercap idea is pretty cool and all but it would not work in my application and for less money I can more flexible. A AGM Odyssey battery and nothing else to worry about (at least for what I do).</p></blockquote><p></p>
[QUOTE="tyromeo55, post: 3307314, member: 1719"] Forgive me i'm going to try to do my best here Most vehicles do not use any real amount of energy to crank the engine. Like 2 watt hours. Do the math. figure 200 AMPS (average over the entire start cycle. I know initial is more) for 3 seconds or so. 200A X 12.5V = 2.5KW/HOURS to go from hours to minutes divide 2500Wh / 60min = 41.666 , divide again by 20 to get to 3 seconds crank time. 41.666/20 = 2.083 Wh consumed to start the engine Lots of factors going on with the battery but a couple ones at the top of my head are.... chemistry - A 8Ah 12V SLA pony battery can easily come up with a ton of power for a fraction of a second. Pull a spec on one. I know that it won't list what we are wanting to know but it will show the theory. It can come up with a ton of current for a short period of time... The longer the duration of time the lower the amount of current you can expect. This is a good read look at page 9 for a chart [URL]https://www.power-sonic.com/wp-content/uploads/2018/12/Technical-Manual.pdf[/URL]. I think 20C is not too unreasonable for a couple seconds Internal impedance of the battery and hookup wires - The impedance of the battery and connecting wires will have a definite affect on the amount of current the caps will be allowed to take from the pony battery. Here is a fun one. an AA battery has about 4.5 Wh of power. You could charge a good super capacitor bank with one and start a car. If you do try to get a couple super capacitors and try it out I would caution how you initially balance them to the pony battery. In my car stereo days I had a small incandescent 12v lamp that I soldered some leads and banana clips onto. Used it in series to recharge the cap bank. When current is flowing the lamp with light up and dim as it equalizes out. Ummmm. yea..... That is a complete 180 from your original post. T?he Supercap idea is pretty cool and all but it would not work in my application and for less money I can more flexible. A AGM Odyssey battery and nothing else to worry about (at least for what I do). [/QUOTE]
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