On a sunny day (Sat, 18 Mar 2023 14:09:03 +1100) it happened Sylvia Else <sylvia@email.invalid> wrote in <k7koafF9mvU4@mid.individual.net>:>On 18-Mar-23 8:14 am, legg wrote: > >> Where'd the word 'dummy' originate in the spec? If it reflects >> the attitude of the buyer, I'd say 'No Bid'. I've had it with >> idiots like that. > >"Dummy load" seems a terminology common enough not to suggest anything >about the buyer. > >Sylvia.Yes, used all the time https://panteltje.nl/pub/250W_1_GHz_dummy_load_IMG_4563.JPG https://panteltje.nl/pub/SWR_bridge_on_dummy_load_IMG_5046.JPG especially for RF
load bank puzzle
Started by ●March 17, 2023
Reply by ●March 18, 20232023-03-18
Reply by ●March 18, 20232023-03-18
On Sat, 18 Mar 2023 14:09:03 +1100, Sylvia Else <sylvia@email.invalid> wrote:>On 18-Mar-23 8:14 am, legg wrote: > >> Where'd the word 'dummy' originate in the spec? If it reflects >> the attitude of the buyer, I'd say 'No Bid'. I've had it with >> idiots like that. > >"Dummy load" seems a terminology common enough not to suggest anything >about the buyer. > >Sylvia.A dummy load is usually invariable and requires no operator adjustment. A 'dummy' can screw up even simple switches or rheostats. RL
Reply by ●March 18, 20232023-03-18
On Sat, 18 Mar 2023 05:52:37 GMT, Jan Panteltje <alien@comet.invalid> wrote:>On a sunny day (Sat, 18 Mar 2023 14:09:03 +1100) it happened Sylvia Else ><sylvia@email.invalid> wrote in <k7koafF9mvU4@mid.individual.net>: > >>On 18-Mar-23 8:14 am, legg wrote: >> >>> Where'd the word 'dummy' originate in the spec? If it reflects >>> the attitude of the buyer, I'd say 'No Bid'. I've had it with >>> idiots like that. >> >>"Dummy load" seems a terminology common enough not to suggest anything >>about the buyer. >> >>Sylvia. > >Yes, used all the time > https://panteltje.nl/pub/250W_1_GHz_dummy_load_IMG_4563.JPG > https://panteltje.nl/pub/SWR_bridge_on_dummy_load_IMG_5046.JPG >especially for RF >It's dummy because it's fixed and 'foolproof'. RL
Reply by ●March 18, 20232023-03-18
On Fri, 17 Mar 2023 14:41:51 -0700, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:>On Fri, 17 Mar 2023 17:14:59 -0400, legg <legg@nospam.magma.ca> wrote: > >>On Fri, 17 Mar 2023 08:21:23 -0700, John Larkin >><jlarkin@highlandSNIPMEtechnology.com> wrote: >> >>> >>>I've been asked to design an 8-channel dummy load board. It's not very >>>challenging but somebody's got to do it. It will be used to simulate >>>small loads like solenoids or relays or torque motors. It needs some >>>inductance too, because the drivers often PWM. Maybe 10 or so watts >>>per channel. >>> >>>I could do this electronically, but it would a lot easier and more >>>rugged if I use wirewound resistors. I was thinking of making a >>>conductance DAC, namely resistors R 2R 4R etc switched in parallel >>>across the inputs with an SSR per resistor. >>> >>>But there is a history of clever load banks. When I was an EE student >>>at Tulane, two semisters of Electrical Machinery (with lab) was >>>mandatory. It was a pain but I learned a lot. We had a big load bank >>>in the machinery lab, a string of giant series resistors with a >>>3-position knife switch at each node. That made me think about using >>>series-parallel combinations to hit some target value. >>> >>>https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1 >>> >>>The upper pic is the ancient Tulane load bank as I remember it. >>> >>>I was thinking about the lower circuit for my gadget. I could use >>>wirewould resistors and kink the leads to space them maybe 3/4 inch >>>above my PCB, in the air stream. The higher value resistors might be >>>2512 surface mounts. >>> >>>I think there is a tool to bend and kink resistor leads. Or we could >>>send a bunch out to a service maybe. >>> >>> >>> >> >>Active I=kV with a delay would give you an inductance. > > >A real inductor stores energy, which a synthesized inductor usually >doesn't. > >Stored energy pumps current into flyback diodes or equivalent. > >> >>Does the driver really care? > >It certainly might. > >> >>Where'd the word 'dummy' originate in the spec? If it reflects >>the attitude of the buyer, I'd say 'No Bid'. I've had it with >>idiots like that. > >Oh, they are just a biggish aerospace company. > >No bid? Is that a good business model? > >> >>RL > >https://en.wikipedia.org/wiki/Dummy_load >The minute you considered variable, multicase and especially inductive, it ceased to be idiot-proof. Use sockets and real loads, if it's that important. RL
Reply by ●March 18, 20232023-03-18
On Fri, 17 Mar 2023 14:41:51 -0700, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:>On Fri, 17 Mar 2023 17:14:59 -0400, legg <legg@nospam.magma.ca> wrote: > >>On Fri, 17 Mar 2023 08:21:23 -0700, John Larkin >><jlarkin@highlandSNIPMEtechnology.com> wrote: >> >>> >>>I've been asked to design an 8-channel dummy load board. It's not very >>>challenging but somebody's got to do it. It will be used to simulate >>>small loads like solenoids or relays or torque motors. It needs some >>>inductance too, because the drivers often PWM. Maybe 10 or so watts >>>per channel. >>> >>>I could do this electronically, but it would a lot easier and more >>>rugged if I use wirewound resistors. I was thinking of making a >>>conductance DAC, namely resistors R 2R 4R etc switched in parallel >>>across the inputs with an SSR per resistor. >>> >>>But there is a history of clever load banks. When I was an EE student >>>at Tulane, two semisters of Electrical Machinery (with lab) was >>>mandatory. It was a pain but I learned a lot. We had a big load bank >>>in the machinery lab, a string of giant series resistors with a >>>3-position knife switch at each node. That made me think about using >>>series-parallel combinations to hit some target value. >>> >>>https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1 >>> >>>The upper pic is the ancient Tulane load bank as I remember it. >>> >>>I was thinking about the lower circuit for my gadget. I could use >>>wirewould resistors and kink the leads to space them maybe 3/4 inch >>>above my PCB, in the air stream. The higher value resistors might be >>>2512 surface mounts. >>> >>>I think there is a tool to bend and kink resistor leads. Or we could >>>send a bunch out to a service maybe. >>> >>> >>> >> >>Active I=kV with a delay would give you an inductance. > > >A real inductor stores energy, which a synthesized inductor usually >doesn't. > >Stored energy pumps current into flyback diodes or equivalent. > >> >>Does the driver really care? > >It certainly might. > >> >>Where'd the word 'dummy' originate in the spec? If it reflects >>the attitude of the buyer, I'd say 'No Bid'. I've had it with >>idiots like that. > >Oh, they are just a biggish aerospace company.Then offer them burn-in hardware as well as 'dummy' loads.> >No bid? Is that a good business model? > >> >>RL > >https://en.wikipedia.org/wiki/Dummy_load >
Reply by ●March 18, 20232023-03-18
On 17/03/2023 16:58, John Larkin wrote:> On Fri, 17 Mar 2023 16:32:56 +0000, Clive Arthur > <clive@nowaytoday.co.uk> wrote: > >> On 17/03/2023 15:21, John Larkin wrote: >>> >>> I've been asked to design an 8-channel dummy load board. It's not very >>> challenging but somebody's got to do it. It will be used to simulate >>> small loads like solenoids or relays or torque motors. It needs some >>> inductance too, because the drivers often PWM. Maybe 10 or so watts >>> per channel. >> >> <snip> >> >> Plenty of power rheostats available. eBay has loads, many new. >> Inductance is a separate matter (though they will have some of course - >> get tubular rheostats and bung a ferrite rod down the centre?). > > We want 8 channels on a PC board, programmable resistance. >If your power source fits the obvious constraints, an SMPS with a fixed load resistor and a programmable output voltage could work. -- Cheers Clive
Reply by ●March 18, 20232023-03-18
On Friday, March 17, 2023 at 11:21:37 AM UTC-4, John Larkin wrote:> I've been asked to design an 8-channel dummy load board. It's not very > challenging but somebody's got to do it. It will be used to simulate > small loads like solenoids or relays or torque motors. It needs some > inductance too, because the drivers often PWM. Maybe 10 or so watts > per channel. > > I could do this electronically, but it would a lot easier and more > rugged if I use wirewound resistors. I was thinking of making a > conductance DAC, namely resistors R 2R 4R etc switched in parallel > across the inputs with an SSR per resistor. > > But there is a history of clever load banks. When I was an EE student > at Tulane, two semisters of Electrical Machinery (with lab) was > mandatory. It was a pain but I learned a lot. We had a big load bank > in the machinery lab, a string of giant series resistors with a > 3-position knife switch at each node. That made me think about using > series-parallel combinations to hit some target value. > > https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1 > > The upper pic is the ancient Tulane load bank as I remember it. > > I was thinking about the lower circuit for my gadget. I could use > wirewould resistors and kink the leads to space them maybe 3/4 inch > above my PCB, in the air stream. The higher value resistors might be > 2512 surface mounts. > > I think there is a tool to bend and kink resistor leads. Or we could > send a bunch out to a service maybe.It's called standoff lead forming. There are bunches different tools, but it looks like the handheld plier types are more universal. Low cost too. https://forum.digikey.com/t/bending-and-forming-leads/8184 How is any of this a puzzle?
Reply by ●March 18, 20232023-03-18
On Sat, 18 Mar 2023 05:43:35 GMT, Jan Panteltje <alien@comet.invalid> wrote:>On a sunny day (Fri, 17 Mar 2023 10:22:33 -0700) it happened John Larkin ><jlarkin@highlandSNIPMEtechnology.com> wrote in ><5l791i1hev1qsuei98p7t83mprc4881jhk@4ax.com>: > >>On Fri, 17 Mar 2023 16:40:09 GMT, Jan Panteltje <alien@comet.invalid> >>wrote: >> >>>On a sunny day (Fri, 17 Mar 2023 08:21:23 -0700) it happened John Larkin >>><jlarkin@highlandSNIPMEtechnology.com> wrote in >>><u6091ide59fffa8gafp93ipmmejp424r5j@4ax.com>: >>> >>>> >>>>I've been asked to design an 8-channel dummy load board. It's not very >>>>challenging but somebody's got to do it. It will be used to simulate >>>>small loads like solenoids or relays or torque motors. It needs some >>>>inductance too, because the drivers often PWM. Maybe 10 or so watts >>>>per channel. >>>> >>>>I could do this electronically, but it would a lot easier and more >>>>rugged if I use wirewound resistors. I was thinking of making a >>>>conductance DAC, namely resistors R 2R 4R etc switched in parallel >>>>across the inputs with an SSR per resistor. >>> >>>Yes why not.. >>>'SSR' == solid state rectifier ? you mean relay? You get AC as input right? >>>oh wait you mean sold state relay.... >> >>Yes. >> >>>googling SSR gives among many things Wikipedia with "Soviet Socialist Republic" >>> >>> >>>>But there is a history of clever load banks. When I was an EE student >>>>at Tulane, two semisters of Electrical Machinery (with lab) was >>>>mandatory. It was a pain but I learned a lot. We had a big load bank >>>>in the machinery lab, a string of giant series resistors with a >>>>3-position knife switch at each node. That made me think about using >>>>series-parallel combinations to hit some target value. >>>> >>>>https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1 >>> >>>We use rectangles as resistor symbol here :-) >> >>Quaint olde world customs. >> >>> >>> >>> >>>>The upper pic is the ancient Tulane load bank as I remember it. >>>> >>>>I was thinking about the lower circuit for my gadget. I could use >>>>wirewould resistors and kink the leads to space them maybe 3/4 inch >>>>above my PCB, in the air stream. The higher value resistors might be >>>>2512 surface mounts. >>>> >>>>I think there is a tool to bend and kink resistor leads. Or we could >>>>send a bunch out to a service maybe. >>> >>>My setup: >>> https://panteltje.nl/pub/power_resistors_IMG_6291.JPG >>> uses test leads with alligator clips to switch configuration. >> >>We have a couple of Kikusui benchtop electronic load boxes, which are >>handy. They can do square wave loads, handy for checking power supply >>dynamics. >> >>I want programmable 0 to 1 zillon ohms, isolated, ac/dc, 10 or 20 >>watts, metered, overload protected, 8 loads per board, maybe 4 square >>inches per channel. >> >>I was wondering if anyone had cute ideas. I considered PWM-ing a big >>resistor, but that has complications. >> >>> >>>So as to Soviet Socialist Republic >>>Here a very funny thing happened in politics >>>We just had elections, and a new party, BBB (translated: farmers people movement) >>>wiped out all parties going from zero to more than the biggest ones. >>>Protest against all the CO2 idiots who want to close farms because cows make CO2. >>>I voted for them too :-) >>>We need farmers and their produce. >> >>Most people think eating is good. >> >>>We will see where it goes now... >>> >>> >> >>People will surely get tired of crazy prices and blackouts and food >>shortages and waiting hours to recharge their cars. > >I did a switched inductor thing many many years ago, >it was for tuning and used relays IIRC (up to a few hundred kHz). >I see electronics to simulate inductors as a possibility.That's worth discussing, but I don't think it's practical in my case, making small, fairly inexpensive dummy loads that can behave like solenoids or relay coils. They need to behave when the user PWMs them or whatever.>But what sort of users need this? >Normally you would test on the real thing >any unexpected things could exist in a real system, >parasitic capacitances, lead resistance and inductances, >unexpected couplings.. what not. >Nothing like a real test.If one is testing FADECs, for example, it might be inconvenient to have a jet engine as part of every test bench.> >Bridge rectifier with a power MOSFET in it for AC load? >Gives all sort of problems too... >A bridge ahead of some active load is an interesting idea, but it doesn't look ohmic at low voltages and can't return energy like a real inductor can. I have a mosfet-based load circuit that does look ohmic for ac or dc, all the way through zero volts, but it still doesn't store energy.
Reply by ●March 18, 20232023-03-18
On Sat, 18 Mar 2023 07:13:33 -0400, legg <legg@nospam.magma.ca> wrote:>On Fri, 17 Mar 2023 14:41:51 -0700, John Larkin ><jlarkin@highlandSNIPMEtechnology.com> wrote: > >>On Fri, 17 Mar 2023 17:14:59 -0400, legg <legg@nospam.magma.ca> wrote: >> >>>On Fri, 17 Mar 2023 08:21:23 -0700, John Larkin >>><jlarkin@highlandSNIPMEtechnology.com> wrote: >>> >>>> >>>>I've been asked to design an 8-channel dummy load board. It's not very >>>>challenging but somebody's got to do it. It will be used to simulate >>>>small loads like solenoids or relays or torque motors. It needs some >>>>inductance too, because the drivers often PWM. Maybe 10 or so watts >>>>per channel. >>>> >>>>I could do this electronically, but it would a lot easier and more >>>>rugged if I use wirewound resistors. I was thinking of making a >>>>conductance DAC, namely resistors R 2R 4R etc switched in parallel >>>>across the inputs with an SSR per resistor. >>>> >>>>But there is a history of clever load banks. When I was an EE student >>>>at Tulane, two semisters of Electrical Machinery (with lab) was >>>>mandatory. It was a pain but I learned a lot. We had a big load bank >>>>in the machinery lab, a string of giant series resistors with a >>>>3-position knife switch at each node. That made me think about using >>>>series-parallel combinations to hit some target value. >>>> >>>>https://www.dropbox.com/s/x3e7xxi13n6wd1o/Load_Banks_1.jpg?raw=1 >>>> >>>>The upper pic is the ancient Tulane load bank as I remember it. >>>> >>>>I was thinking about the lower circuit for my gadget. I could use >>>>wirewould resistors and kink the leads to space them maybe 3/4 inch >>>>above my PCB, in the air stream. The higher value resistors might be >>>>2512 surface mounts. >>>> >>>>I think there is a tool to bend and kink resistor leads. Or we could >>>>send a bunch out to a service maybe. >>>> >>>> >>>> >>> >>>Active I=kV with a delay would give you an inductance. >> >> >>A real inductor stores energy, which a synthesized inductor usually >>doesn't. >> >>Stored energy pumps current into flyback diodes or equivalent. >> >>> >>>Does the driver really care? >> >>It certainly might. >> >>> >>>Where'd the word 'dummy' originate in the spec? If it reflects >>>the attitude of the buyer, I'd say 'No Bid'. I've had it with >>>idiots like that. >> >>Oh, they are just a biggish aerospace company. >> >>No bid? Is that a good business model? >> >>> >>>RL >> >>https://en.wikipedia.org/wiki/Dummy_load >> > >The minute you considered variable, multicase and >especially inductive, it ceased to be idiot-proof. > >Use sockets and real loads, if it's that important. > >RLThe customer has an existing design where they select and solder a selected set of resistors and inductors per channel, unique to each unit. We don't want to be in the business of doing that for them, with every unit having its own dash number and BOM and test limits. I'd like to design a programmable dummy load board that we can manufacture and stock and ship when we get an order. It's looking like a straight conductance DAC is the way to go: parallel N resistors (R, 2R, etc) with a solid-state switch per. Given a binary control code K, net conductance is proportional to K so resistance goes as 1/K. N=5 maybe; we're not simulating RTDs. That's nice and simple and adds an open-circuit case for free. Two more SSRs can add short and ground fault cases, selling points. I like to add little goodies to products when it's not hard and doesn't interfere with the base function. You never know if something will appeal to someone and tip a basically emotional buy decision, as in "That thingie might be useful some day, let's buy theirs." Colors matter too.
Reply by ●March 18, 20232023-03-18
On Sat, 18 Mar 2023 07:08:29 -0400, legg <legg@nospam.magma.ca> wrote:>On Sat, 18 Mar 2023 14:09:03 +1100, Sylvia Else <sylvia@email.invalid> >wrote: > >>On 18-Mar-23 8:14 am, legg wrote: >> >>> Where'd the word 'dummy' originate in the spec? If it reflects >>> the attitude of the buyer, I'd say 'No Bid'. I've had it with >>> idiots like that. >> >>"Dummy load" seems a terminology common enough not to suggest anything >>about the buyer. >> >>Sylvia. > >A dummy load is usually invariable and requires no >operator adjustment.Why? A programmable dummy load can be very useful.> >A 'dummy' can screw up even simple switches or rheostats.They could wire anything wrong. A good dummy load includes measurements and waveform acquisition and overload protections. If you see 17 volts and ask for 130 ohms and don't get 130 mA, you should know that something's wrong. The load is a dummy but my customers aren't. You trust your life to them fairly often.
