Robin2 Posted August 23, 2011 Report Share Posted August 23, 2011 I never suggested they did. You were querying why AC motors were less efficient than DC and a quick Google threw that up. Tony The web page you referred to is about the efficiency of control systems ! Link to comment Share on other sites More sharing options...
smileypete Posted August 23, 2011 Report Share Posted August 23, 2011 (edited) The web page you referred to is about the efficiency of control systems ! OK... What do DC motors have that AC motors don't? What does this do? How is this provided in AC motors? What does providing the same in AC motors entail? cheers, Pete. Edited August 23, 2011 by smileypete Link to comment Share on other sites More sharing options...
Robin2 Posted August 23, 2011 Report Share Posted August 23, 2011 OK... What do DC motors have that AC motors don't? What does this do? How is this provided in AC motors? What does providing the same in AC motors entail? cheers, Pete. You are not being very helpful! Are you auditioning for the job of quizzmaster? Link to comment Share on other sites More sharing options...
WotEver Posted August 23, 2011 Report Share Posted August 23, 2011 Time to brush up on your theory Tony Link to comment Share on other sites More sharing options...
smileypete Posted August 23, 2011 Report Share Posted August 23, 2011 (edited) Time to brush up on your theory Not quite, as DC brushless motors don't have them. I was thinking of magnets. cheers, Pete. Edited August 23, 2011 by smileypete Link to comment Share on other sites More sharing options...
Robin2 Posted August 23, 2011 Report Share Posted August 23, 2011 Not quite, as DC brushless motors don't have them. I was thinking of magnets. cheers, Pete. What have magnets got to do with it? Link to comment Share on other sites More sharing options...
smileypete Posted August 23, 2011 Report Share Posted August 23, 2011 (edited) What have magnets got to do with it? How can you create a magnetic field without a permanent magnet? cheers, Pete. Edited August 23, 2011 by smileypete Link to comment Share on other sites More sharing options...
Gibbo Posted August 23, 2011 Report Share Posted August 23, 2011 What have magnets got to do with it? You're not making much progress here are you! Most low to medium power DC motors have permanent magnets. Most AC motors have electromagnets. So before you even do anything flash like making the rotor spin round, the AC motor instantly has an efficiency disadvantage because it has to use power to make some magnets. Link to comment Share on other sites More sharing options...
Robin2 Posted August 23, 2011 Report Share Posted August 23, 2011 You're not making much progress here are you! Most low to medium power DC motors have permanent magnets. Most AC motors have electromagnets. So before you even do anything flash like making the rotor spin round, the AC motor instantly has an efficiency disadvantage because it has to use power to make some magnets. I hope you are not suggesting that magnets supply energy ! Link to comment Share on other sites More sharing options...
Gibbo Posted August 23, 2011 Report Share Posted August 23, 2011 I hope you are not suggesting that magnets supply energy ! why would you think I suggested that? Link to comment Share on other sites More sharing options...
Robin2 Posted August 23, 2011 Report Share Posted August 23, 2011 why would you think I suggested that? If they don't supply energy (and they don't) how could magnets improve efficiency? Link to comment Share on other sites More sharing options...
Gibbo Posted August 23, 2011 Report Share Posted August 23, 2011 If they don't supply energy (and they don't) how could magnets improve efficiency? Jeez... A motor needs magnets to operate. The electromagnet then has something push against. That's how motors work. In most small DC motors, those magnets are permanent magnets. In terms of energy they are free, they don't use any energy. In AC motors they are electromagnets. In terms of energy they are not free, they use energy. Link to comment Share on other sites More sharing options...
Robin2 Posted August 23, 2011 Report Share Posted August 23, 2011 Jeez... A motor needs magnets to operate. The electromagnet then has something push against. That's how motors work. In most small DC motors, those magnets are permanent magnets. In terms of energy they are free, they don't use any energy. Sounds like it would be a good idea to replace the coils on the armature with permanent magnets also ! In AC motors they are electromagnets. In terms of energy they are not free, they use energy. They only consume energy due to heating losses in the coil. If you had superconductors they wouldn't use energy. If we start discussing the practical inefficiencies in different types of motor the list for DC motors will be as long as for any other type. Link to comment Share on other sites More sharing options...
Gibbo Posted August 23, 2011 Report Share Posted August 23, 2011 (edited) They only consume energy due to heating losses in the coil. Do they really? Oh, and here was silly me thinking they used energy to overcome hysteresis losses and eddy current losses in the core. Both of which I thought should be equally balanced with the resistive losses in a correctly designed motor. I also thought there were hysteresis and eddy current losses in the surrounding metalwork. But what do I know? Thank you for educating me. If you had superconductors they wouldn't use energy. Again, really? Silly old me thought you could only build a lossless superconducting electromagnet with DC. I'm learning so much from you tonight. Edited August 23, 2011 by Gibbo Link to comment Share on other sites More sharing options...
Robin2 Posted August 23, 2011 Report Share Posted August 23, 2011 Do they really? Oh, and here was silly me thinking they used energy to overcome hysteresis losses and eddy current losses in the core. Both of which I thought should be equally balanced with the resistive losses in a correctly designed motor. I also thought there were hysteresis and eddy current losses in the surrounding metalwork. But what do I know? Thank you for educating me. Again, really? Silly old me thought you could only build a lossless superconducting electromagnet with DC. I'm learning so much from you tonight. I'm delighted. Let me know if I can help some more. Link to comment Share on other sites More sharing options...
14skipper Posted August 23, 2011 Author Report Share Posted August 23, 2011 Hi l expect this has been asked before but how many batteries should you need to have on a liveaboard ? Link to comment Share on other sites More sharing options...
Robbo Posted August 23, 2011 Report Share Posted August 23, 2011 Hi l expect this has been asked before but how many batteries should you need to have on a liveaboard ? You'll need to do a power audit first :-) Link to comment Share on other sites More sharing options...
blodger Posted August 23, 2011 Report Share Posted August 23, 2011 Hi l expect this has been asked before but how many batteries should you need to have on a liveaboard ? You trying to skyjack this thread? Link to comment Share on other sites More sharing options...
smileypete Posted August 23, 2011 Report Share Posted August 23, 2011 Hi l expect this has been asked before but how many batteries should you need to have on a liveaboard ? For non sealed 110Ah batts, between 3 and 8 seems reasonable. Don't forget you have to charge them well enough! (and not over discharge them too...) cheers, Pete. Link to comment Share on other sites More sharing options...
Alan Saunders Posted August 23, 2011 Report Share Posted August 23, 2011 Hi l expect this has been asked before but how many batteries should you need to have on a liveaboard ? You need none! Hand-start the engine, use heat from the engine for hot water. Use paraffin, diesel, wood, coal, gas, candles etc for cooking, heating, light, maybe an acetylene 'tunnel' lamp. If you must have electrical devices, do an audit (is there an echo here?). How long will you run the engine each day? If you go to work every day and stick to the 8am to 8pm rule you will need sufficient capacity to last between weekends. If you are retired you could run your engine for 12 hours every day. If you have a land-line connection you may be able to run everything from that. Play the game, answer the questions! Alan (~1968 - did some calculations for the first 'practical' UK superconductive motor, pump motor in a submarine. Still not practical.) Link to comment Share on other sites More sharing options...
blodger Posted August 24, 2011 Report Share Posted August 24, 2011 (edited) You need none! Hand-start the engine, use heat from the engine for hot water. Use paraffin, diesel, wood, coal, gas, candles etc for cooking, heating, light, maybe an acetylene 'tunnel' lamp. If you must have electrical devices, do an audit (is there an echo here?). How long will you run the engine each day? If you go to work every day and stick to the 8am to 8pm rule you will need sufficient capacity to last between weekends. If you are retired you could run your engine for 12 hours every day. If you have a land-line connection you may be able to run everything from that. Play the game, answer the questions! Alan (~1968 - did some calculations for the first 'practical' UK superconductive motor, pump motor in a submarine. Still not practical.) I agree with the above; The OP had all the answers it was feasible to give before the thread wandered into other territory Edited August 24, 2011 by blodger Link to comment Share on other sites More sharing options...
WotEver Posted August 24, 2011 Report Share Posted August 24, 2011 Sounds like it would be a good idea to replace the coils on the armature with permanent magnets also ! Silly designers, why ever didn't they think of that? Auto-flipping power-free permanent magnets - now there's a concept Tony Link to comment Share on other sites More sharing options...
sebrof Posted August 24, 2011 Report Share Posted August 24, 2011 ??? How would you test a fridge with a battery monitor? Tony He was joking, Tone. J O K I N G, from the verb "to joke". See also "Joke" (n) and "Jocular" (adj). Sheesh Link to comment Share on other sites More sharing options...
WotEver Posted August 24, 2011 Report Share Posted August 24, 2011 He was joking, Tone. Nope, can't be that. A joke has to have humour in it. Try again - it's good to see you exercising your brain in this way. Does it give you a headache? Tony Link to comment Share on other sites More sharing options...
sebrof Posted August 24, 2011 Report Share Posted August 24, 2011 (edited) Nope, can't be that. A joke has to have humour in it. Try again - it's good to see you exercising your brain in this way. Does it give you a headache? Tony [/quote You're right. It's a sort of mental limbo dancing, trying to get down to your level. So far I'm about twenty thousand leagues under the sea, but still have quite a long way to go. Edited August 24, 2011 by sebrof Link to comment Share on other sites More sharing options...
Featured Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now