tag:blogger.com,1999:blog-6231841547435511043.post3854743413953308379..comments2023-06-13T01:05:30.996-07:00Comments on The Electricle™ : Bicycle Electric-Motor-Assist Project: Noise Vs HeatM.E.http://www.blogger.com/profile/15375034485988839284noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-6231841547435511043.post-74978549712511140812009-08-25T08:44:11.300-07:002009-08-25T08:44:11.300-07:00Weighing of options can be oppressive!Weighing of options can be oppressive!Joehttps://www.blogger.com/profile/10265425172888920679noreply@blogger.comtag:blogger.com,1999:blog-6231841547435511043.post-51437254632829809102009-08-25T04:20:47.533-07:002009-08-25T04:20:47.533-07:00I'm considering using the standard TO220 MOSFE...I'm considering using the standard TO220 MOSFET size that the 2QD originally ran a parallel pair of for each leg of the half-bridge, just because they'll fit right on the PCB as designed, and I can bolt the whole PCB into an aluminum ex-modem case, which is smaller and thinner by far than the plastic one I'm using now (which does not fit where I had hoped it would, by only about 1/4"). <br /><br />The capacitor would have to stick out of a hole bored in the top of the case, but that's ok. It'd get better cooling that way anyway. :)<br /><br />The MOSFETs I'm considering downgrading to from the NTY100N10s are some Fairchild 60V 80A 3.8mOhm, FDP038AN06A0, because I have several that all test ok, and they should be high enough voltage to not risk destroying them from BEMF and the like. <br /><br />At a load current of 80A (which I will not be drawing on this bike with these poor batteries!) with gate drive of 10V, the RDSon will increase from 3.5mOhm typical at ambient (25C) to 7.1mOhm at 175C (which I hope I never reach!). <br /><br />The NTY100N10 is 9mOhm typical at ambient, 10V gate drive, 50A load current, and 19mOhm same conditions at 150C, which they'll definitely never reach unless I take the heatsink off. ;) <br /><br />I guess that means that the already-in-place NTY100N10 is actually *better* for the current-sense than the other one. Hmmm. <br /><br />But the FDP038AN06A0 is lower RDSon, lower gate charge (so it can be switched faster by less of a gate driver), and easier to mount, so maybe I should use them anyway, especially since the PCB is already designed to use a pair of them in parallel for each leg of the half-bridge. I'd get theoretically 160A capability (for bursts, less for sustained operation depending on my heatsink and airflow) at an RDSon of say, 1.8mohm, about 1/5 that of the NTY100N10, thus only wasting 1/5 of the power currently being converted to heat inside the MOSFETs, in theory. <br /><br />The only real disadvantage is that the NTY100N10 has a 100V D-S limit, but the FDP038AN06A0 has only a 60V D-S limit, making it more likely that a spike somewhere in the motor noise could kill them. <br /><br />AAARGH. Decisions decisions. <br /><br />Maybe I should just carry a portable soldering iron and spare MOSFETs with me in case the worst should happen. :) <br /><br />Really, it would be better just to carry a whole spare *controller*. It'd be about as light or more so, and certainly faster and easier to deal with changing out!M.E.https://www.blogger.com/profile/15375034485988839284noreply@blogger.comtag:blogger.com,1999:blog-6231841547435511043.post-4909035135836990542009-08-24T06:21:31.651-07:002009-08-24T06:21:31.651-07:00ah, I can see you possibly considering trying weak...ah, I can see you possibly considering trying weaker MOSFETs. I devised that type current control before I knew anyone else was using it--like the 2QD uses. I have since gone to simpler method I thought of.<br /><br />I have a minor correction that the DC resistance of the motor I use is about 1 ohm, not 12 ohm.Joehttps://www.blogger.com/profile/10265425172888920679noreply@blogger.comtag:blogger.com,1999:blog-6231841547435511043.post-79895810000004121242009-08-24T02:24:33.475-07:002009-08-24T02:24:33.475-07:00Eventually I will start worrying about the conditi...Eventually I will start worrying about the condition of the motors, and how I'm treating them, but just at the moment I am going to press the system as hard as I can to see what breaks first, and how.<br /><br />Sure, I could probably calculate out what would happen, but it somehow doesn't seem as much fun. :)<br /><br />The 2QD isn't exactly a current controller, but it does do current limiting in a different way than many. It senses the voltage drop across the motor drive MOSFET in the half-bridge. That doesn't help protect the motor itself, but it does help protect the controller/MOSFET. If it heats up enough to raise the RDSon significantly, then the current limiting kicks in to help prevent it from getting any worse. <br /><br />I doubt that current limiting is even *going* to activate with the MOSFETs I have on it now, given that they barely even get warm under the loads they currently have, and that's pretty hefty load as far as the bike itself is concerned.M.E.https://www.blogger.com/profile/15375034485988839284noreply@blogger.comtag:blogger.com,1999:blog-6231841547435511043.post-38614334747421490682009-08-23T09:40:48.213-07:002009-08-23T09:40:48.213-07:00Hi Mike. One thing to keep in mind is the DC resi...Hi Mike. One thing to keep in mind is the DC resistance of the motor. My 12V motor gets up to 48V supplied to it, but only when the load on them is low enough. That is why the controller that I designed is current mode control. It would burn out my motors pretty quickly if I let the 48V go full into the 12 Ohm resistance. They are probably only about 50 watt long term power handling motors.<br /><br />So, they can handle about 7 amps. I^2R is the power dissipation. I derate that for higher voltages just to compensate for brush arcing. Yet, say 5amps times 40V means that my 50W motors can do 200W @ 40V. That is why I can hit close to 40mph if I peddle furiously in tenth gear at full throttle. --JoeAnonymousnoreply@blogger.com