Automotive Protection Circuit
in [Design]
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From: JosephKK on 21 Dec 2008 22:02 On Fri, 19 Dec 2008 22:15:17 +0000, John Devereux <john(a)devereux.me.uk> wrote: >Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> writes: > >> On Fri, 19 Dec 2008 21:53:33 +0000, John Devereux >> <john(a)devereux.me.uk> wrote: >> >>>Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> writes: >>> >>>> On Fri, 19 Dec 2008 18:13:09 +0000, John Devereux >>>> <john(a)devereux.me.uk> wrote: >>>[...] >>>>> >>>>>I was thinking of making a load dump simulator/generator "one day". >>>>> >>>>>There is a circuit in the datasheet for the "LDP24M" (p4). >>>>> >>>>><http://www.digchip.com/datasheets/download_datasheet.php?id=502684&part-number=LDP24> >>>>> >>>>>The energy and currents involved are huge! >>>>> >>>>>I have seen voltages specified up to ~150V. >>>>> >>>>>47,000uF charged to 150V dumped through 2 ohms is a pretty serious >>>>>pulse. I've actually gone as far as snapping up a cheap box of 200V, >>>>>1500uF electrolytics to build the capacitor bank required. >>>> >>>> A/C thermostat driving compressor clutch will do it ;-) >>> >>>I guess I am a bit too electronics orientated - because I have no idea >>>what those words mean (when put in that order)! >> >> (Automotive) Air Conditioning thermostat (mechanical/bi-metal plus >> relay) opening a _very_ inductive magnetic clutch between pulley drive >> and (Freon) compressor. > >Oh I see! Maybe... I was wondering if it was possible to store the >energy magnetically somehow but it seemed like there would not be >enough in anything reasonable. It's 500-1000J as far as I can make >out. > >Is the energy just in the inductance, or is it mechanical energy in >the movement of the clutch (or compressor rotation)? Both as i understand it. Kind of like large solenoids.
From: John Devereux on 22 Dec 2008 05:55 JosephKK <quiettechblue(a)yahoo.com> writes: > On Fri, 19 Dec 2008 22:15:17 +0000, John Devereux > <john(a)devereux.me.uk> wrote: > >>Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> writes: >> >>> On Fri, 19 Dec 2008 21:53:33 +0000, John Devereux >>> <john(a)devereux.me.uk> wrote: >>> >>>>Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> writes: >>>> >>>>> On Fri, 19 Dec 2008 18:13:09 +0000, John Devereux >>>>> <john(a)devereux.me.uk> wrote: >>>>[...] >>>>>> >>>>>>I was thinking of making a load dump simulator/generator "one day". >>>>>> >>>>>>There is a circuit in the datasheet for the "LDP24M" (p4). >>>>>> >>>>>><http://www.digchip.com/datasheets/download_datasheet.php?id=502684&part-number=LDP24> >>>>>> >>>>>>The energy and currents involved are huge! >>>>>> >>>>>>I have seen voltages specified up to ~150V. >>>>>> >>>>>>47,000uF charged to 150V dumped through 2 ohms is a pretty serious >>>>>>pulse. I've actually gone as far as snapping up a cheap box of 200V, >>>>>>1500uF electrolytics to build the capacitor bank required. >>>>> >>>>> A/C thermostat driving compressor clutch will do it ;-) >>>> >>>>I guess I am a bit too electronics orientated - because I have no idea >>>>what those words mean (when put in that order)! >>> >>> (Automotive) Air Conditioning thermostat (mechanical/bi-metal plus >>> relay) opening a _very_ inductive magnetic clutch between pulley drive >>> and (Freon) compressor. >> >>Oh I see! Maybe... I was wondering if it was possible to store the >>energy magnetically somehow but it seemed like there would not be >>enough in anything reasonable. It's 500-1000J as far as I can make >>out. >> >>Is the energy just in the inductance, or is it mechanical energy in >>the movement of the clutch (or compressor rotation)? > > Both as i understand it. Kind of like large solenoids. Cool. The "official" simulator circuit I referenced in the datasheet above contains a 12mH inductor. A simulation indicates it can see currents of >50A. 12mH, 50A inductors are a bit thin on the ground... I found a 5mH one, it's a 10 inch diameter toroid :) -- John Devereux
From: eaglecbr on 22 Dec 2008 08:41 Thanks for the help everyone. Sorry I didn't respond earlier. It is not acceptable to power down the system during a large load dump. I need an always on system. I might end up putting like a battery backup system that will switch to backup battery during long load dump pulses. I would prefer a system that I described earlier, but don't know if its possible to clamp the voltage to 30V.
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