Adam, I added a (free) inductor by wrapping the motor wires around the core of the biggest microwave transformer that I could find. You can pick up old microwaves most days from Craigslist and the like for free. I occasionally get one, disassemble it if I can't get it to work to give to a needy friend, so I have a stash of components to fix the next one. Note that it is required to put a very thin spacer between the two core halves to avoid saturation and you need something (I used a very large hose clamp plus 1 or 2 steel wires cross-wise along the core) to keep the two halves together and aligned.
Cor van de Water Chief Scientist Proxim Wireless Corporation http://www.proxim.com Email: [email protected] Private: http://www.cvandewater.info Skype: cor_van_de_water Tel: +1 408 383 7626 -----Original Message----- From: EV [mailto:[email protected]] On Behalf Of Adam Chasen via EV Sent: Monday, August 11, 2014 2:16 PM To: [email protected] Subject: [EVDL] Protecting DC PWM Controller from low inductance/resistancemotors I recently purchased a 1980 Lectric Leopard (Renault 5 "Le Car" http://www.evalbum.com/190) with the following specifications: * original Presolite 6.7"(?) series wound DC motor (presumably advanced for higher voltages) * 16kWh LiPo NMC packs in 24s4p arrangement for 90V nominal with 150A semiconductor on each of the 4 packs * Curtis 1231C controller with PB-6 2 weeks ago I heard a loud pop as I depressed the throttle out of a rolling stop/turn and my voltmeter read 0. Seemed like my semiconductor fuses did the job and all 4 were popped ($100 worth of fuses mind you). Unfortunately in my distressed mindset I bypassed the fuse on one pack and the car lurched a few inches as soon as I flipped my breaker and then stopped (I know, bad call). I disassembled the Curtis controller and discovered 2 "gently" blown mosfets and 1 "catastrophic" mosfet failure. I ordered replacement mosfets IXTH50N20. One trace on the power board looks like it overheated and there appears to be some damage (a resistor?) on the control board. There is possibly damage to a trace in an internal layer, but not sure if it is a 2 layer board and some surface heating caused some damage. I have since swapped the Curtis out for a 750A Logisystems which I am aware are plagued with (similar?) issues. These failures appear to be due to low resistance/low inductance motors causing a overcurrent condition. The logisystems doesn't provide for a 1.5kHz during startup. That is a bit concerning as that was the "workaround" for the Curtis. I have since measured the motor side of the controller with an inrush current sensor and measured 645A max even with being very careful to slowly depress the throttle. My concern centers around this happening again, especially on my larger 1989 BWM 535i with a directly coupled FB1-4001a motor. There are a few proposed solutions I read about and a few I came up with on my own which I am soliciting opinions on. A big unknown to me is how much resistance or inductance needs to be introduced to prevent this kind of inrush/runaway. One solution is to use the clutch in the Leopard to ensure there is no starting load on the motor. I still measured inrushes of >300A with no load! That will not work for my directly coupled 1989 BMW. I am curious if Lee Hart (with his Leopard) and others with series wound DC motors drive using the clutch. I have since modified my shifting behavior to much higher RPMs after reading some about his driving style. Another is to control the current with a large inductor. There was a lot of talk, but no pictures of these inductors. I am not sure how much inductance is necessary to help, but haven't done much research into this. There was some mention of using surplus transformers with insulated layers, but wasn't able to get a good picture in my head of size and process. Someone mentioned a 30 lbs choke on an older PMC, but that also doesn't provide me a good picture in my head other than it will likely be bigger than any non-power system transformer I have ever seen. Where can I get one (or the materials for) of these inductors and how much will the cost? There are two other passive electronic components which can control current I didn't see mentioned. * Resistors * Thermistor I am not sure about the practicality of using a thermistor for this purpose. It would appear the PTC thermistor would effectively be a self-resetting fuse. Ideally I could find a thermistor which would only increase in resistance to the point where the motor still received current, but provided some restriction. It appears they are mostly sold as "switches" due to their non-linear response. I am also unsure if the response time will be of any use. I would much prefer something more linear. Using an NTC thermistor (or bank of them) would provide a tiny resistance to start with but would "close" very quickly. My guess is that it would not provide the necessary protection. Introducing a fixed resistor would introduce a loss in the system which is not desirable, but it could be as simple as just the resistance of the feed wire. The thought would be to reduce the size of the cable (or a portion of the cable) to the point where it begins acting as a resistor (i.e. heating element) as high currents pass through it. I am not an EE, so I don't understand exactly the nuances of high currents through wire. It would seem cables do not have a linear resistance. Once again, I am unsure of how practical this is or what resistance is necessary. There is also an option for a combination of these two passive components which would slow down the NTC. The motor could be connected to the controller with two connections, one which adds a resistance and the other which is limited by a few large NTC inrush preventers. The current would prefer the resistance path until the NTCs "close." This may provide additional time to make the NTCs useful. One active method is to use the overcurrent protection mechanism in the Open Revolt controller and prevent/take over the mosfet gate signal if a hall sensor detects current that is too high: http://ecomodder.com/forum/showthread.php/paul-sabrinas-cheap-diy-144v-m otor-controller-6404-161.html#post108442 While I would prefer to use a passive process, I am leaning toward the active method. Thanks for all of the good information on this list, especially to Lee Hart for this issue in particular. Adam -------------- next part -------------- An HTML attachment was scrubbed... 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