birdy Posted May 21, 2008 Share Posted May 21, 2008 Recently it has bugged me in bed, on the bus home, everywhere. Why don't manufactures use watthours as well as ampours for their lipos? Correct me if I'me wrong, but surely if they did this it would tell you the voltage stability, which would make a pack more comparible to others. Am I forgetting something or am I the first person to think of this (surely not!). birdy Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted May 21, 2008 Share Posted May 21, 2008 A watt is the unit of power.A battery provides pressure (electromotive force, emf) to force current (amps) through a circuit (potential difference) The unit of pressure (or potential difference) is one volt.ie...a battery does not produce power. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 21, 2008 Share Posted May 21, 2008 Yes and the watts that are "consumed" by the powertrain will vary with either volts or amps, so it would be impossible to predict as it were. Quote Link to comment Share on other sites More sharing options...
birdy Posted May 22, 2008 Author Share Posted May 22, 2008 I kind of get what you are saying, but surely the same principal occures with amphours? If I am right the stronger the courent on the battery then the less efficient it is, and the less amphours it produces. Wouldn't the measuring be pretty much the same, but keeping voltage in mind as well? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 23, 2008 Share Posted May 23, 2008 Yes, the more current being pulled from the cell the more likely it is that the voltage will drop somewhat, but that doesnt necessarily equate to inefficiency, and doesnt reduce the milliamphrs as such. I guess battery manufacturers would be understandbly a bit reluctant to "admit" or specify how much their cells dropped voltage by when under load. Quote Link to comment Share on other sites More sharing options...
birdy Posted May 23, 2008 Author Share Posted May 23, 2008 You'd think though that the big expensive makes would want to advertise that though!? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 23, 2008 Share Posted May 23, 2008 Ah, but you are assuming that these will perform better than the cheaper ones......and it aint so ! Quote Link to comment Share on other sites More sharing options...
Brian Lambert Posted May 23, 2008 Share Posted May 23, 2008 Am I missing something here? power (in Watts) is voltage multiplied by current, therefor just multiply the voltage of the pack by its capacity in amp-hours and you have its Watt-hours, or is that not what you need?Brian Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted May 24, 2008 Share Posted May 24, 2008 The original query was with regard to voltage stability under load and battery labelling.As the Watt is a derived unit we would be none the wiser on voltage stability, as you have just proved. Quote Link to comment Share on other sites More sharing options...
birdy Posted May 24, 2008 Author Share Posted May 24, 2008 Well that puts an end to that question... And Rusper, I think I'm the one missing something... Thank... something that won't offend anything for the forum! Quote Link to comment Share on other sites More sharing options...
Brian Lambert Posted May 24, 2008 Share Posted May 24, 2008 Birdy I think what you are looking for is probably not available, the amount of energy you can extract from a particular battery is subject to too many variables, including, required life of battery, current draw, ambient temperature, cooling available, the battery chemistry, and I am sure many others.Timbo has a good point in that the amount you pay for a battery is not any real indication of the performance you can expect.Get one that will fly the plane, if you like it get more, if not try another.Let use know how you get on.Regards Brian Quote Link to comment Share on other sites More sharing options...
Harry Breakwell Posted June 8, 2008 Share Posted June 8, 2008 Hello everybody, just to back up Rusper's point, I bought two Mystery 900 mAh 15c lipo's off ebay, as a back up for 800 mAh battery on my lama v4, thought they would improve flight time ?, no way! about 4 minutes if I dont use rudder !, of course it could be my standard charger wont fully charge the dam things and I should spend more money on a specified charger any answers would be wellcome cheers Harry. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 8, 2008 Share Posted June 8, 2008 It could just be that they are naff batteries - they do exist....especially on fleabayWe need more info before blaming the charger. Quote Link to comment Share on other sites More sharing options...
Harry Breakwell Posted June 8, 2008 Share Posted June 8, 2008 OK, Timbo, the posibilitys there, but isnt it true that lipo manufactures always insist on useing there own charger?, as a newbie i'm thinking that these batterys are put together diferent,not like a car battery ,all you need to know is it 12v or 6v , the only info, I, as a customer get is what it sayes on the package, I maybe mistaken on thinking that a charger thats made to charge a 800mAh cannot fully charge a 900mAh battery . of coarse to back up your point the 900mAh batterys shows charged in a shorter time than the 800mAh???,in the end all I wanted to do was to have longer flight times to learn to control this choper and this is supposed to be the easy one thanks Harry Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 8, 2008 Share Posted June 8, 2008 Well actually Harry it is normally perfectly possible to charge a higher capacity battery on the same charger...it just takes a little longer - if its charging at say 1000 m/a and you want to charge a 1000ma pack then expect around an hour or so...if its a 2000ma battery then double it, and so on. As stated before I / we can diagnose any more, we need information such as charger type, output charge rate, state of battery before charge ( voltage level etc etc ) Quote Link to comment Share on other sites More sharing options...
Harry Breakwell Posted June 8, 2008 Share Posted June 8, 2008 my charger is an E sky 2 & 3 cell 7.4v & 11.1v outputs at 0.8A as issued with all lama v4s, so my final question is when the green light is constant (indicating the battery is charged)is the charger still charging?,or do I need a charger with more user control.thanks Harry Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 8, 2008 Share Posted June 8, 2008 Well if it says the steady green light indicates that charging is complete, then no..its not charging anymore.Do you need a different charger - thats up to you, but there is no reason it should not charge a 900 m/a pack. Quote Link to comment Share on other sites More sharing options...
Harry Breakwell Posted June 9, 2008 Share Posted June 9, 2008 Thanks Timbo, think I'll buy a battery pack the same as the Lama and stop experymenting cheers Harry Quote Link to comment Share on other sites More sharing options...
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