Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
> From: Ian Finder > so just on the safe side we'll cover some Engineering for Poets (or > Programmers) ROFL! Noel
RE: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
> My favorite low tech dummy load is the one my father came up with: a couple > of > resistors (carbon composite is best, carbon film or metal film will do), 1-2 > watt size, > in a jar filled with water. Works just fine for 100 watts or so, and is > useable not just > for power supplies but for HF transmitter testing. Why am I thinking of the Heathkit Cantenna? -tony
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
On 2015-10-26 2:32 PM, Ian Finder wrote: Not sure how much of a noob you are, although you repeatedly claim to be one so just on the safe side we'll cover some Engineering for Poets (or Programmers) to reassure you ;) -- V = I * R Power (watts) = I * V You know the voltage of the monitor. You know the resistance of your resistor. So, you also know the maximum power the resistor needs to be rated to dissipate. If the spec says the single air-cooled resistor you're buying is good to dissipate X watts into ambient temperature Y, I'd just go ahead and believe it. Make sure the numbers work out and you're fine, no heavy duty HVAC needed. :-P Yes, I got that far, and I got the same figure Mike did: 7.2W. Should I put that on one (say 10W) part, or copy Brian's technique and spread over multiple resistors? Now to see about building the board... Thanks for everyone's inputs. --Toby Cheers, - Ian On Mon, Oct 26, 2015 at 10:52 AM, Toby Thain wrote: On 2015-10-26 1:23 PM, Ian Finder wrote: This thread took a turn for the absurd. Oil? Water? What a practical bunch of people. /s They make resistors with adequate cooling... Almost as if they're rated for a certain number of watts of dissipation and you can buy them based on that. They are resistors after all. And if they overheat-- oh wait, they're heavy duty resistors, not ICs. Get a couple, put them in a metal project box, put it inline with the cable, and call it a day. Damn, I already ordered a pile of HVAC gear. j/k - yeah that was what I was basically planning, Ian ... just as a noob, I'm not totally confident with what a single air cooled part can dissipate. (The thread was kind of interesting anyway!) --Toby Sent from my iPhone On Oct 26, 2015, at 09:24, simon wrote: please skip this ridicule and grab yourself a couple of headlights from a car. On 26-10-15 17:16, Dale H. Cook wrote: My recommendation of oil is based upon my decades of experience with broadband dummy loads from 60 watts to 2.5 kilowatts. The dummy loads that I have worked with for medium wave and below and from 5 kilowatts down have all been convection air cooled. Broadband dummy loads that I have used for higher powers (up to 25 kilowatts) have been forced air cooled. I prefer to stick with what I have experience with. As for water, YMMV. Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA http://plymouthcolony.net/starcityeng/index.html -- Met vriendelijke Groet, Simon Claessen drukknop.nl
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
Hi Toby, I'll try to post some photos in a week or 2. Rob has asked me to make some internal load boards for him so I can show more details while I'm at it. The bulb is the best option in my opinion and seems to work just fine without additional cooling in the cube. -- Brian On Mon, Oct 26, 2015 at 6:43 AM, Toby Thain wrote: > On 2015-10-26 1:02 AM, Brian Archer wrote: > >> Even a 10W resistor will get really hot. I embed two 5W resistors into a >> pentium class CPU cooler for a good compromise on space/thermal concerns. >> You can see a pic on my site here: >> http://asterontech.com/Asterontech/next_adb_conversion.html >> >> > Hi Brian > > I did see your mod while looking around for info. > > I'd prefer not to mod the soundbox so my options seem to be your internal > backplane load board ( > http://www.nextcomputers.org/forums/viewtopic.php?t=3616&highlight=load+board > ) or maybe a small load board inline to the monitor cable? > > It looks like ambient cooling is sufficient for the version shown here? > > Thanks very much for the excellent info you've posted so far! > > --Toby > > Internal to the cube, I've found using a 5W appliance bulb to be the >> easiest. >> >> -- >> Brian Archer >> \ >> >
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
> On Oct 26, 2015, at 2:49 PM, Chuck Guzis wrote: > > On 10/26/2015 10:52 AM, Toby Thain wrote: > > >> Damn, I already ordered a pile of HVAC gear. >> >> j/k - yeah that was what I was basically planning, Ian ... just as a >> noob, I'm not totally confident with what a single air cooled part >> can dissipate. > > > The talk about dummy loads brought back a memory of the Heath Cantenna--an RF > dummy load consisting of a Globar (noninductive) resistor in a gallon paint > can filled with mineral oil with an attachment to a SO-239 "UHF" connector on > top. IIRC, it was literally capable of dissipating a full "gallon". > > Kanthal Globar is still very much in business and does offer the resistors, > if anyone wants to build such a unit for old times' sake. For that matter, dummy loads that look just like that are sold currently by MFJ. paul
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
Well, we indeed know the voltage (V or E) but not the current (I) used in your formula; since I is E/R then power is simply E^2/R, so 20 Ohms at 12V has to dissipate 144/20 = 7.2 W. m - Original Message - From: "Ian Finder" To: "General Discussion: On-Topic and Off-Topic Posts" Cc: Sent: Monday, October 26, 2015 2:32 PM Subject: Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again Not sure how much of a noob you are, although you repeatedly claim to be one so just on the safe side we'll cover some Engineering for Poets (or Programmers) to reassure you ;) -- V = I * R Power (watts) = I * V You know the voltage of the monitor. You know the resistance of your resistor. So, you also know the maximum power the resistor needs to be rated to dissipate. If the spec says the single air-cooled resistor you're buying is good to dissipate X watts into ambient temperature Y, I'd just go ahead and believe it. Make sure the numbers work out and you're fine, no heavy duty HVAC needed. :-P Cheers, - Ian On Mon, Oct 26, 2015 at 10:52 AM, Toby Thain wrote: On 2015-10-26 1:23 PM, Ian Finder wrote: This thread took a turn for the absurd. Oil? Water? What a practical bunch of people. /s They make resistors with adequate cooling... Almost as if they're rated for a certain number of watts of dissipation and you can buy them based on that. They are resistors after all. And if they overheat-- oh wait, they're heavy duty resistors, not ICs. Get a couple, put them in a metal project box, put it inline with the cable, and call it a day. Damn, I already ordered a pile of HVAC gear. j/k - yeah that was what I was basically planning, Ian ... just as a noob, I'm not totally confident with what a single air cooled part can dissipate. (The thread was kind of interesting anyway!) --Toby Sent from my iPhone On Oct 26, 2015, at 09:24, simon wrote: please skip this ridicule and grab yourself a couple of headlights from a car. On 26-10-15 17:16, Dale H. Cook wrote: My recommendation of oil is based upon my decades of experience with broadband dummy loads from 60 watts to 2.5 kilowatts. The dummy loads that I have worked with for medium wave and below and from 5 kilowatts down have all been convection air cooled. Broadband dummy loads that I have used for higher powers (up to 25 kilowatts) have been forced air cooled. I prefer to stick with what I have experience with. As for water, YMMV. Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA http://plymouthcolony.net/starcityeng/index.html -- Met vriendelijke Groet, Simon Claessen drukknop.nl -- Ian Finder (206) 395-MIPS ian.fin...@gmail.com
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
On Mon, 26 Oct 2015, Chuck Guzis wrote: The talk about dummy loads brought back a memory of the Heath Cantenna--an RF dummy load consisting of a Globar (noninductive) resistor in a gallon paint can filled with mineral oil with an attachment to a SO-239 "UHF" connector on top. IIRC, it was literally capable of dissipating a full "gallon". I have one of those sitting on the floor of my office. :) g. -- Proud owner of F-15C 80-0007 http://www.f15sim.com - The only one of its kind. http://www.diy-cockpits.org/coll - Go Collimated or Go Home. Some people collect things for a hobby. Geeks collect hobbies. ScarletDME - The red hot Data Management Environment A Multi-Value database for the masses, not the classes. http://scarlet.deltasoft.com - Get it _today_!
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
On 10/26/2015 10:52 AM, Toby Thain wrote: Damn, I already ordered a pile of HVAC gear. j/k - yeah that was what I was basically planning, Ian ... just as a noob, I'm not totally confident with what a single air cooled part can dissipate. The talk about dummy loads brought back a memory of the Heath Cantenna--an RF dummy load consisting of a Globar (noninductive) resistor in a gallon paint can filled with mineral oil with an attachment to a SO-239 "UHF" connector on top. IIRC, it was literally capable of dissipating a full "gallon". Kanthal Globar is still very much in business and does offer the resistors, if anyone wants to build such a unit for old times' sake. --Chuck
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
Not sure how much of a noob you are, although you repeatedly claim to be one so just on the safe side we'll cover some Engineering for Poets (or Programmers) to reassure you ;) -- V = I * R Power (watts) = I * V You know the voltage of the monitor. You know the resistance of your resistor. So, you also know the maximum power the resistor needs to be rated to dissipate. If the spec says the single air-cooled resistor you're buying is good to dissipate X watts into ambient temperature Y, I'd just go ahead and believe it. Make sure the numbers work out and you're fine, no heavy duty HVAC needed. :-P Cheers, - Ian On Mon, Oct 26, 2015 at 10:52 AM, Toby Thain wrote: > On 2015-10-26 1:23 PM, Ian Finder wrote: > >> This thread took a turn for the absurd. Oil? Water? What a practical >> bunch of people. /s >> >> They make resistors with adequate cooling... Almost as if they're >> rated for a certain number of watts of dissipation and you can buy >> them based on that. They are resistors after all. >> >> And if they overheat-- oh wait, they're heavy duty resistors, not >> ICs. Get a couple, put them in a metal project box, put it inline >> with the cable, and call it a day. >> > > Damn, I already ordered a pile of HVAC gear. > > j/k - yeah that was what I was basically planning, Ian ... just as a noob, > I'm not totally confident with what a single air cooled part can dissipate. > > (The thread was kind of interesting anyway!) > > --Toby > > > Sent from my iPhone >> >> On Oct 26, 2015, at 09:24, simon wrote: >>> >>> please skip this ridicule and grab yourself a couple of headlights from >>> a car. >>> >>> >>> >>> On 26-10-15 17:16, Dale H. Cook wrote: My recommendation of oil is based upon my decades of experience with broadband dummy loads from 60 watts to 2.5 kilowatts. The dummy loads that I have worked with for medium wave and below and from 5 kilowatts down have all been convection air cooled. Broadband dummy loads that I have used for higher powers (up to 25 kilowatts) have been forced air cooled. I prefer to stick with what I have experience with. As for water, YMMV. Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA http://plymouthcolony.net/starcityeng/index.html >>> >>> -- >>> Met vriendelijke Groet, >>> >>> Simon Claessen >>> drukknop.nl >>> >> >> > -- Ian Finder (206) 395-MIPS ian.fin...@gmail.com
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
On 2015-10-26 1:23 PM, Ian Finder wrote: This thread took a turn for the absurd. Oil? Water? What a practical bunch of people. /s They make resistors with adequate cooling... Almost as if they're rated for a certain number of watts of dissipation and you can buy them based on that. They are resistors after all. And if they overheat-- oh wait, they're heavy duty resistors, not ICs. Get a couple, put them in a metal project box, put it inline with the cable, and call it a day. Damn, I already ordered a pile of HVAC gear. j/k - yeah that was what I was basically planning, Ian ... just as a noob, I'm not totally confident with what a single air cooled part can dissipate. (The thread was kind of interesting anyway!) --Toby Sent from my iPhone On Oct 26, 2015, at 09:24, simon wrote: please skip this ridicule and grab yourself a couple of headlights from a car. On 26-10-15 17:16, Dale H. Cook wrote: My recommendation of oil is based upon my decades of experience with broadband dummy loads from 60 watts to 2.5 kilowatts. The dummy loads that I have worked with for medium wave and below and from 5 kilowatts down have all been convection air cooled. Broadband dummy loads that I have used for higher powers (up to 25 kilowatts) have been forced air cooled. I prefer to stick with what I have experience with. As for water, YMMV. Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA http://plymouthcolony.net/starcityeng/index.html -- Met vriendelijke Groet, Simon Claessen drukknop.nl
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
This thread took a turn for the absurd. Oil? Water? What a practical bunch of people. /s They make resistors with adequate cooling... Almost as if they're rated for a certain number of watts of dissipation and you can buy them based on that. They are resistors after all. And if they overheat-- oh wait, they're heavy duty resistors, not ICs. Get a couple, put them in a metal project box, put it inline with the cable, and call it a day. Sent from my iPhone > On Oct 26, 2015, at 09:24, simon wrote: > > please skip this ridicule and grab yourself a couple of headlights from a car. > > > >> On 26-10-15 17:16, Dale H. Cook wrote: >> My recommendation of oil is based upon my decades of experience with >> broadband dummy loads from 60 watts to 2.5 kilowatts. The dummy loads that I >> have worked with for medium wave and below and from 5 kilowatts down have >> all been convection air cooled. Broadband dummy loads that I have used for >> higher powers (up to 25 kilowatts) have been forced air cooled. >> >> I prefer to stick with what I have experience with. As for water, YMMV. >> >> Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA >> http://plymouthcolony.net/starcityeng/index.html > > -- > Met vriendelijke Groet, > > Simon Claessen > drukknop.nl
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
please skip this ridicule and grab yourself a couple of headlights from a car. On 26-10-15 17:16, Dale H. Cook wrote: My recommendation of oil is based upon my decades of experience with broadband dummy loads from 60 watts to 2.5 kilowatts. The dummy loads that I have worked with for medium wave and below and from 5 kilowatts down have all been convection air cooled. Broadband dummy loads that I have used for higher powers (up to 25 kilowatts) have been forced air cooled. I prefer to stick with what I have experience with. As for water, YMMV. Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA http://plymouthcolony.net/starcityeng/index.html -- Met vriendelijke Groet, Simon Claessen drukknop.nl
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
At 11:09 AM 10/26/2015, Paul Koning wrote: >... but tap water even in NYC? New York City tap water is of higher quality than the tap water available in many US cities. Dale H. Cook, Roanoke/Lynchburg, VA Osborne 1 / Kaypro 4-84 / Kaypro 1 / Amstrad PPC-640 http://plymouthcolony.net/starcity/radios/index.html
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
My recommendation of oil is based upon my decades of experience with broadband dummy loads from 60 watts to 2.5 kilowatts. The dummy loads that I have worked with for medium wave and below and from 5 kilowatts down have all been convection air cooled. Broadband dummy loads that I have used for higher powers (up to 25 kilowatts) have been forced air cooled. I prefer to stick with what I have experience with. As for water, YMMV. Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA http://plymouthcolony.net/starcityeng/index.html
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
> > OK, so a couple years back, I wanted to have some chemistry fun with the kids. > So, I got out the jump cables, clamped them onto some aluminum foil, stuffed > the foil into test tubes, filled the tubes with water, inverted both of them > in the same basin and sprinkled in a little salt, cranked up the car, and > sure enough bubbles started evolving off the foil and collecting in the > test tubes. > Just as expected, one tube was filling with gas twice as fast as the other. > Just as expected, when we held that tube over a candle, it went WHEEP and > got hot (the flame was barely visible). > > Um the OP had a 12V supply, right? How *do* you keep from electrolyzing > your coolant in this apparatus. Firstly, don't add salt. Secondly, the low resistance dummy load is going to soak up almost all of the current, leaving very little to go through the much higher resistance water resulting in very little gas production. If the minute amount of gas produced is still a problem, you could electrically insulate the dummy load from the water. However, this may also help to thermally insulate from the water it which is not what you want. > > PS. this is a cool experiment but suitable cautions apply. The most subtle > is: not too much salt, lest you start evolving chlorine gas instead of > hydrogen. Flammable to explosive gasses, 12V sparks, etc. etc be careful > if you try to replicate this. Also, beware of the danger of shorting the jump cables together, either directly or via worn jewellery etc causing a large bang, melted terminals etc and possible damage to kids, self and car. Consider using something like a current limited bench power supply instead. Regards, Peter Coglan.
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
On 2015-10-26 16:09, Paul Koning wrote: On Oct 26, 2015, at 11:02 AM, Dale H. Cook wrote: At 10:45 AM 10/26/2015, Jerry Weiss wrote: Water in the dummy load? Water cooled - sure. Water immersed? Even though I see it posted on the web, i have may doubts it would be a stable method. I concur. Tap water may have contaminants (such as chlorine) that will cause electrical leakage. Sure, but so what? A dummy load is supposed to have electrical leakage. All that water contamination would do is reduce the effective resistance of your load by a hair. If you used seawater, it might make a difference that matters, but tap water even in NYC? No. I wonder if even sea water would make much difference...? Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: b...@softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
> On Oct 26, 2015, at 11:21 AM, Tapley, Mark wrote: > > On Oct 26, 2015, at 10:09 AM, Paul Koning wrote: > >>> I concur. Tap water may have contaminants (such as chlorine) that will >>> cause electrical leakage. >> >> Sure, but so what? A dummy load is supposed to have electrical leakage. >> All that water contamination would do is reduce the effective resistance of >> your load by a hair. > > OK, so a couple years back, I wanted to have some chemistry fun with > the kids. So, I got out the jump cables, clamped them onto some aluminum > foil, stuffed the foil into test tubes, filled the tubes with water, inverted > both of them in the same basin and sprinkled in a little salt, cranked up the > car, and sure enough … bubbles started evolving off the foil and collecting > in the test tubes. > Just as expected, one tube was filling with gas twice as fast as the > other. > Just as expected, when we held that tube over a candle, it went “WHEEP” > and got hot (the flame was barely visible). > > Um… the OP had a 12V supply, right? How *do* you keep from > electrolyzing your coolant in this apparatus? Some observations. One is that I've used this scheme for ages, and the only bubbles seen were steam (after having the dummy load dissipate 100 watts for a couple of minutes). Second: if you deliberately make the water conductive by adding salt, that's a different test setup. Try this with plain water. If your water is too cruddy, use deionized water; that's still a very cheap option. paul
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
On Oct 26, 2015, at 10:09 AM, Paul Koning wrote: >> I concur. Tap water may have contaminants (such as chlorine) that will cause >> electrical leakage. > > Sure, but so what? A dummy load is supposed to have electrical leakage. All > that water contamination would do is reduce the effective resistance of your > load by a hair. OK, so a couple years back, I wanted to have some chemistry fun with the kids. So, I got out the jump cables, clamped them onto some aluminum foil, stuffed the foil into test tubes, filled the tubes with water, inverted both of them in the same basin and sprinkled in a little salt, cranked up the car, and sure enough … bubbles started evolving off the foil and collecting in the test tubes. Just as expected, one tube was filling with gas twice as fast as the other. Just as expected, when we held that tube over a candle, it went “WHEEP” and got hot (the flame was barely visible). Um… the OP had a 12V supply, right? How *do* you keep from electrolyzing your coolant in this apparatus? - Mark PS. this is a cool experiment but suitable cautions apply. The most subtle is: not too much salt, lest you start evolving chlorine gas instead of hydrogen. Flammable to explosive gasses, 12V sparks, etc. etc… be careful if you try to replicate this.
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
> On Oct 26, 2015, at 11:02 AM, Dale H. Cook wrote: > > At 10:45 AM 10/26/2015, Jerry Weiss wrote: > >> Water in the dummy load? Water cooled - sure. Water immersed? Even >> though I see it posted on the web, i have may doubts it would be a stable >> method. > > I concur. Tap water may have contaminants (such as chlorine) that will cause > electrical leakage. Sure, but so what? A dummy load is supposed to have electrical leakage. All that water contamination would do is reduce the effective resistance of your load by a hair. If you used seawater, it might make a difference that matters, but tap water even in NYC? No. paul
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
> On Oct 26, 2015, at 10:56 AM, Paul Koning wrote: > > >> On Oct 26, 2015, at 10:45 AM, Jerry Weiss wrote: >> >> Water in the dummy load? Water cooled - sure. Water immersed? ... > ... > But for low voltage dummy loads, or for medium power ham transmitters, the > voltages involved are not that high. Plain tap water is slightly conductive, > but nowhere near as much as the resistors you're using. Come to think of it, water immersed setups have shown up in the literature. There was a nice article in QST a decade or so ago describing a 1296 MHz kilowatt amplifier, built with a 3CX100A5 converted to water immersion cooling. The setup included a clever trick to monitor the conductivity of the cooling water, so you could swap it out if it got too conductive. The water there was in direct contact with the anode, at around 2 kV or so. Worked fine apparently. I never built anything like that but the appraoch seemed sensible. paul
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
Distilled water will not conduct. Its a perfect insulator. It will work fine. On 10/26/2015 7:45 AM, Jerry Weiss wrote: > Water in the dummy load? Water cooled - sure. Water immersed? Even > though I see it posted on the web, i have may doubts it would be a stable > method. > > Oil is the usual medium here. Excluding of course the pre-1980 > transformer oils that were notorious for having contaminated PCB’s within or > anything with flammability at working temperatures. > > > Jerry Weiss > WB9MRI > > >> On Oct 26, 2015, at 9:27 AM, Paul Koning wrote: >> >> >>> On Oct 26, 2015, at 9:43 AM, Toby Thain wrote: >>> >>> On 2015-10-26 1:02 AM, Brian Archer wrote: Even a 10W resistor will get really hot. I embed two 5W resistors into a pentium class CPU cooler for a good compromise on space/thermal concerns. >> My favorite low tech dummy load is the one my father came up with: a couple >> of resistors (carbon composite is best, carbon film or metal film will do), >> 1-2 watt size, in a jar filled with water. Works just fine for 100 watts or >> so, and is useable not just for power supplies but for HF transmitter >> testing. >> >> paul >> >> > -- The contents of this e-mail and any attachments are intended solely for the use of the named addressee(s) and may contain confidential and/or privileged information. Any unauthorized use, copying, disclosure, or distribution of the contents of this e-mail is strictly prohibited by the sender and may be unlawful. If you are not the intended recipient, please notify the sender immediately and delete this e-mail.
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
At 10:45 AM 10/26/2015, Jerry Weiss wrote: >Water in the dummy load? Water cooled - sure. Water immersed? Even >though I see it posted on the web, i have may doubts it would be a stable >method. I concur. Tap water may have contaminants (such as chlorine) that will cause electrical leakage. >Oil is the usual medium here. Current non-PCB transformer oil is the preferred oil, but for relatively low power levels (say, 1 kilowatt dissipation or less) USP-grade mineral oil (available at your pharmacy) is a very viable substitute. Dale H. Cook, Roanoke/Lynchburg, VA Osborne 1 / Kaypro 4-84 / Kaypro 1 / Amstrad PPC-640 http://plymouthcolony.net/starcity/radios/index.html
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
> On Oct 26, 2015, at 10:45 AM, Jerry Weiss wrote: > > Water in the dummy load? Water cooled - sure. Water immersed? Even > though I see it posted on the web, i have may doubts it would be a stable > method. How stable do you need? > > Oil is the usual medium here. Transformer oil is a nice dielectric, so for high voltage transformers that's what you want. But for low voltage dummy loads, or for medium power ham transmitters, the voltages involved are not that high. Plain tap water is slightly conductive, but nowhere near as much as the resistors you're using. And water is a MUCH better coolant than oil. This is why machine tools typically use water as the coolant, or more precisely, water with a small amount of "soluble oil" mixed into it. It's true that resistors are not designed to sit in water indefinitely. But that means that, after a year or so, they may have been damaged. Hours or days of immersion doesn't bother them at all. If you want a good UHF dummy load, or one with 1% accuracy, this is probably not the best answer. If it needs to dissipate multiple kW, or last for a decade, ditto. But for a basic solution at near-zero cost, it works great. If you're not confident the load is still good 6 months from now, just spend 50 cents making another. Or lift the resistors out of the water-filled jar when done with the day's testing. paul, ni1d
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
Water in the dummy load? Water cooled - sure. Water immersed? Even though I see it posted on the web, i have may doubts it would be a stable method. Oil is the usual medium here. Excluding of course the pre-1980 transformer oils that were notorious for having contaminated PCB’s within or anything with flammability at working temperatures. Jerry Weiss WB9MRI > On Oct 26, 2015, at 9:27 AM, Paul Koning wrote: > > >> On Oct 26, 2015, at 9:43 AM, Toby Thain wrote: >> >> On 2015-10-26 1:02 AM, Brian Archer wrote: >>> Even a 10W resistor will get really hot. I embed two 5W resistors into a >>> pentium class CPU cooler for a good compromise on space/thermal concerns. > > My favorite low tech dummy load is the one my father came up with: a couple > of resistors (carbon composite is best, carbon film or metal film will do), > 1-2 watt size, in a jar filled with water. Works just fine for 100 watts or > so, and is useable not just for power supplies but for HF transmitter testing. > > paul > >
Re: Model 152 PSU dummy loads - Re: NeXT Cube - powers on briefly then off again
> On Oct 26, 2015, at 9:43 AM, Toby Thain wrote: > > On 2015-10-26 1:02 AM, Brian Archer wrote: >> Even a 10W resistor will get really hot. I embed two 5W resistors into a >> pentium class CPU cooler for a good compromise on space/thermal concerns. My favorite low tech dummy load is the one my father came up with: a couple of resistors (carbon composite is best, carbon film or metal film will do), 1-2 watt size, in a jar filled with water. Works just fine for 100 watts or so, and is useable not just for power supplies but for HF transmitter testing. paul
