On Sun, Nov 29, 2015 at 7:45 AM, Brent Brown wrote: > Embedded systems wrote: > > > Brent, it's not the initial moment (t=3D0). But immediately after the > turning > > on. > > Take a look please at his pictures showing the voltage across > > the current sensing resistor: > > http://orlandorobotbuilders.com/stuff/BIM2-01.jpg > > Thanks for clarifying, I see now. > > > So, on 50miliohm and about 280mV seems to be about 5.6A after turn on a= nd > > slow down to > > 1A in normal run. > > I believe the 1A is the "hold" current he is acheiving using PWM to reduc= e > power. > The initial "full power" period makes sure the solenoid/injector repsonds > as quickly > as possible. > Ok, make sense. I have suggested a different version of driving, using the injector coil resonance. Since the PWM frequency is fixed, in LC parallel resonance the current through the mosfet will be smallest. Then the flyback diode may not be necessary anymore, but...the MOSFET should be rated at higher voltage and the injector should be tested first which is the lowest current it runs= .. Check how looks the primary driving circuit in the HV transformer in a 12V old CRT monitor or TV, it's the same principle. Vasile > > > If he measured the voltage drop across drain-source in the same time, h= e > > may knew if that > > current is producing the transistor dissipation or not. > > > > > > > > > > On Thu, Nov 26, 2015 at 11:04 PM, Brent Brown > > wrote: > > > > > On 26 Nov 2015 at 20:31, embedded systems wrote: > > > > > > > Schematic looks good. > > > > I prefer a fast rectifying diode in anti-parallel on the load versu= s > your > > > > zener on the MOSFET. > > > > Maybe you should try. > > > > At turn on you have 4x nominal current on the load. > > > > Say the value of this current. > > > > > > How at turn on can you have 4x nominal current? Inductor theory tells > me > > > at t =3D 0 > > > current =3D 0. > > > > > > http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indtra.html > > > > > > Not being critical, I'm just curious where your idea (rule of thumb?) > > > comes from. It's > > > not uncommon to hear people associating "inrush current" with > inductance. > > > In AC > > > circuits it's a different ball game, assymetric currents due to phase > > > angle at switch > > > on etc. > > > > > > Brent > > > > > > > > > -- > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > > View/change your membership options at > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .