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stube40

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  1. I've managed to find a really nice hall-effect type linear current sensor package from Honeywell Sensing and Control. Its the CS series and has the hall-effect sensor embedded into a ring-concentrator, all in a nice package. Trouble is - I'm having trouble finding anywhere that can get me one. Digikey have one model from the range for $21 - the CSLA2CD, but unfortunately it's not the CSLA2EN one I'm after. They have none available anyway. RAMELEC can't get me any for 3 weeks and they want a whopping $190 each!! If I am prepared to wait 10 weeks and order 50 then I can have them for a more reasonable $31 each. Thanks for nothing RAMELEC! Does anyone have any tips on where else I might try?
  2. I'm trying to interface an Allegro A1360 half-effect sensor to a TI MSP430 CPU. The A1360 is a 5V device whilst the MSP430 operates from a 1.8V to 3.6V supply. The MSP430 has onboard ADC, but the analog input pins have an absolute max rating of VCC + 0.3V. I have both 3.3V and 5V regulators on my PCB design and I'm assuming that I'll need some opamps or something to interface between the MSP430 CPU and the A1360 sensor. I'm still fairly new to electronics design and I'm looking for advice as to a good way to interface these two devices.
  3. Wow, thanks for that - 600A!!! Fantastic.
  4. Can anyone recommend a DAC with SPI. 10 or 12 bit would be good. It will be driven by a 3.3V TI CPU. Analog output would be 5V min, but up to 10V would be good. Also, if it has an evaluation PCB option that would be a good bonus. Thanks.
  5. Anyone know of anywhere I might get hold of a DC circuit breaker rated higher than 63A? We are currently using the Teresaki 4500 series C63 but want to go higher. Yes, I know it's a high current but those of you who know me will know why!!!
  6. By "load" I meant the entire load that the PSU sees. The coil itself is made of Type 2 Sumitomo superconducting tape which zero resistance. However, the copper surround and interconnects have small resistances associated with them. Sorry, but my resistance estimate of 0.1 Ohm missed a zero and you are correct that V = IR breaks down with 0.1Ohm. We are using 4G power cable (7x7x34x0.12mm) which has a resistance of 0.97mOhm per metre. The copper interconnects are a fraction of this. If we used 10 metres of this stuff then the overall resistance would still be around 0.01Ohm.
  7. We've been looking for a low-voltage high-current power supply for our lab to put between 200A and 1000A through a superconducting coil with inductance of 50mH. Total resistance of the load will be around 0.1 Ohm. The only thing I've been able to find so far is an electro-plating rectifier. Although it's called a rectifier, as far as I can see it's actually a low-voltage high-current PSU. The manual (attached) is not very informative. It is a 3-phase input. Switchable DC output from 0-15V and 0-1000Amps. It is based on IGBTs. Power factor of 0.95, 2% ripple. It has either constant current or constant voltage operation. It's very expensive ($12500!!!) and I'm worried about buying it and then it not doing what we require (or, even worse, we break it because we're mis-using it). Can anyone shed any light on whether we're going doing the wrong track or not? Op_Manual_161150_3000-6_15V1000A1.pdf
  8. I see - thanks for the clarification. So, if I want to protect the diode against reverse current I'm guessing I should use an external diode across drain and source, possibly a schottky? My other thought was maybe to use a 2nd MOSFET connected in parralel to the 1st and in reverse, then sequence the gates of the two MOSFETs so that neither of them ever see reverse current (assuming I know when the reverse current will happen). Saying that, i prefer the idea of an external diode if that would work.
  9. Alot of MOSFETs come with a built-in diode across the source and drain. The attached diagram outlines what I mean. I would like to confirm that the purpose of this diode is to allow the MOSFET to handle reverse current to flow. I know this question might sound really dumb, but I'm not an electronics expert. Further, if this is indeed the case, is it possible to exploit this diode to enable the MOSFET to allow reverse current in an application where we expect regular reverse currents? Finally, which particular parameters in the data sheet for a MOSFET describe the diode's maximum reverse current and how long it can maintain this current for?
  10. Thanks, and sorry for wasting your time with the double-thread. I'm now starting to lean towards the 2V LA battery solution now as a real possibility. The reason I didn't jump straight into to this solution in the first place is two fold: 1) It leads to a pseudo fixed-voltage solution that is only adjustable in large steps (ie 2V). Whereas, it may be that I need to fine-tune the power source to 1.8V or 2.V in the future - clearly this solution can't be used in this fashion. 2) I have a array of good 12V batteries already in my possession However, it's becoming clear that a suitable step down DC-DC that will give the low voltage, high current output from a 12V source is a non-trivial project, especially for someone like me that's non an expert in the area of switched mode PSUs. I think this assumption is reinforced by the lack of suggestions from the forum regarding off-the-shelf solutions, such as the TPS40180EVM sync buck controller evaluation module. If high-current 12V-2V step down converters were readily available then I'm sure there would have been some alternative solutions suggested. Thanks, Stuart.
  11. I'm trying to drop the voltage of a 12V to approx 2V but allow many 100s of amps to be drawn, in order to provide power to an experimental DC motor. I've considered many options, of which the TPS40180EVM module is my favourite so far. However, I'm playing around with another option of turning the DC battery output into AC using a H-bridge to create a -12V / + 12V square wave then feeding this into a step-down transformer, then using rectification and filtering to create a 2V DC output (we can handle a bit of ripple in the motor). The advantage of this method is being able to handle the high currents with suitable choice of power transformer, rectification and filtering components. I just wondered if anyone had any thoughts on this idea, or if anyone had any better ideas?
  12. Homopolar motors offer some advantages in certain environments, particularly where low RPM, high torque is desirable. Also, they are so simple that they can be made to be extremely quiet (hence the reason they are often used in submarines). Our experiment is to explore new and novel homopolar engines, particularly with respect to the materials used. In this instance, the actual power supply is secondary to the main aim. However, that's not to say that the PSU isn't important............
  13. Hello, sorry if I antagonised you - that was not my intention. I'm here because I would like to be helped and upsetting people was certainly not on the agenda (and not a good way of going about getting help). Clearly I have misjudged the amount of information I would need to provide in order to get the ball rolling - for that, I appologise. I have attached a basic diagram showing the layout of the system. I have also attached 2 scope traces that show voltage (yellow) and current (blue) measured across the brushes when the PSU is set to 2.0V and 3.0V. I hope this is enough information now. To be honest, I'm not sure what other information I can provide right now. If there's something missing then please feel free to ask more questions and I'll do my best to answer. Thanks, Stuart.
  14. The desgin is a bit different from textbook homopolar turbines, so that may be confusing. I have a working prototype of the motor here. Using a heavy duty Lab DC PSU, when we apply 2.0V to the motor it draws 100A at rotates at approx 2000rpm. At 3.5V it draws 180A and rotates at around 3000rpm. I need to hook up a torque transducer to the output to equate this to power (still trying to beg/borrow/steal one at the moment). The main thing for me at the moment is to replace the Lab DC PSU with my own design.
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