On Mon, 20 Mar 2023 05:49:46 -0000 (UTC), Jasen Betts <usenet@revmaps.no-ip.org> wrote:>On 2023-03-19, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >> On Sun, 19 Mar 2023 17:28:35 +0000, piglet <erichpwagner@hotmail.com> >> wrote: >> >>>On 19/03/2023 15:24, John Larkin wrote: >>>> >>>> There are some very cool 2 and 3-channel isolated ADCs intended for >>>> use in electric meters. Cheap but not super fast; good for average >>>> measurements but not for closing fast control loops. >>>> >>> >>>So use the cool ADCs for metrology and do the control loop with op-amp? >>> >>>piglet >>> >>> >> >> Simulating a resistor needs multiplication. That could be done with an >> MDAC but gets complicated. > >Could be done with a digital pot, ah yeah, that's a type of MDAC I >guess.Dpots are usually terrible MDACs, intended for audio use mostly. There are good 12 and 16-bit fast 4Q MDACs around, but a multiply in an FPGA is better and cheaper.
load bank puzzle
Started by ●March 17, 2023
Reply by ●March 20, 20232023-03-20
Reply by ●March 20, 20232023-03-20
On Sat, 18 Mar 2023 08:11:29 -0700, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:>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. >> >>RL > >The 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. >In my experience the biggest issue with the versatility of even the simplest load is connecting to the DUT. Every sodding device uses a different connector. RL
Reply by ●March 20, 20232023-03-20
On Mon, 20 Mar 2023 10:39:12 -0400, legg <legg@nospam.magma.ca> wrote:>On Sat, 18 Mar 2023 08:11:29 -0700, John Larkin ><jlarkin@highlandSNIPMEtechnology.com> wrote: > >>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. >>> >>>RL >> >>The 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. >> > >In my experience the biggest issue with the versatility >of even the simplest load is connecting to the DUT. > >Every sodding device uses a different connector. > >RLYes. If we do a D25, we will also offer a small termination board, D25 to barrier strip. My big single-channel load board will use a Phoenix connector where the male has wire screws. https://www.digikey.com/en/products/detail/phoenix-contact/1861263/9349684
Reply by ●March 20, 20232023-03-20
On 2023-03-20 10:31, John Larkin wrote:> On Mon, 20 Mar 2023 05:49:46 -0000 (UTC), Jasen Betts > <usenet@revmaps.no-ip.org> wrote: > >> On 2023-03-19, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote: >>> On Sun, 19 Mar 2023 17:28:35 +0000, piglet <erichpwagner@hotmail.com> >>> wrote: >>> >>>> On 19/03/2023 15:24, John Larkin wrote: >>>>> >>>>> There are some very cool 2 and 3-channel isolated ADCs intended for >>>>> use in electric meters. Cheap but not super fast; good for average >>>>> measurements but not for closing fast control loops. >>>>> >>>> >>>> So use the cool ADCs for metrology and do the control loop with op-amp? >>>> >>>> piglet >>>> >>>> >>> >>> Simulating a resistor needs multiplication. That could be done with an >>> MDAC but gets complicated. >> >> Could be done with a digital pot, ah yeah, that's a type of MDAC I >> guess. > > Dpots are usually terrible MDACs, intended for audio use mostly. There > are good 12 and 16-bit fast 4Q MDACs around, but a multiply in an FPGA > is better and cheaper.Yup. Dpots are mostly good for fairly coarse tweaks. There are some reasonably quick ones (~6 MHz), but only in the lowest resistance range (1k). They also make really bad rheostats, on account of the 20% - 30% resistance tolerance. (Monolithic matching makes them quite a lot better as voltage dividers, as long as you don't pull too much current out of the wiper. The other main problem with both dpots and MDACs is the strong dependence of bandwidth on the digital code. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●April 1, 20232023-04-01
In article <c1c9c270-f6f6-4518-97c8-2c141b4e12f4n@googlegroups.com>, whit3rd <whit3rd@gmail.com> wrote:>On Friday, March 17, 2023 at 8:21:37 AM UTC-7, 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 ... > >So far, a Variac and big resistor on the output is a possibility. >Or, a few paint cans full of oil, with rotary switch and immersed lower-watt >resistors (Cantenna style), could work. > >But, 'load' for even just a battery test can be anything from 1 ohm to hundreds, >just for the batteries in my household; the only easy way to make the load >you want, is to specify it first, then build one. That means the 'load board' is >a connector plenum, and the loads would be plugins to that, plucked from >a bucket of prebuilt options. > >Eight-channel is easy: design one, build eight, and strap 'em together.For car batteries light bulbs are convenient. They can be constantly on. I have several emergency kits around for old cars, with wattage ranging from 5 Watt to more than a 100 Watts. Groetjes Albert -- Don't praise the day before the evening. One swallow doesn't make spring. You must not say "hey" before you have crossed the bridge. Don't sell the hide of the bear until you shot it. Better one bird in the hand than ten in the air. First gain is a cat spinning. - the Wise from Antrim -
