Heat Gun + Inverter As Dummy Load For PSU? - Page 1
Forum section: electronics / projects

author: Trurl
author_rank: Regular Contributor
timestamp: November 22, 2023, 01:45:45 pm
content: Imagine you have a 1200~1500W 12VDC server PSU you'd like to load test, mostly in the upper range of power/current output (700W+ / 50A+).Imagine the load test model with a PSU > inverter > heat gun** Heat Gun Features- 2000W 220VAC 60Hz- Triac used for heat control (ST BTA12 600B Snubberless Triac)- Heat setting variable (maximum setting would not exceed rating of PSU)The main objective of the dummy load is to load test the PSU's voltage stability at continuous high current output for extended periods(say 1 hour +), and not so much on noise response characteristics of the PSU when a load is causing noise along the test model.1. What could be the potential issue(s) or hazard(s)?2. Is there a simple solution or alternative* to resolve such "issue(s)"?* Other than non-switching resistive loads (resistors, hair dryer, heater coil etc.)The point being the use of a resistive load with TRIAC heat control.Thanks in advance...

author: Shay
author_rank: Regular Contributor
timestamp: November 22, 2023, 04:31:26 pm
content: As a crude way to load the PSU it should work.What I'd make sure is to no exceed the power supply current rating, as the inverter wont draw continuous DC current from the PSU, so you need to make sure the peaks are not too high in current. It might be a good thing as real power consumed from the PSU is dynamic, so you'll get some kind of a feedback about the loop/transiest response of the PSU.

author: zapta
author_rank: Super Contributor
timestamp: November 22, 2023, 04:38:49 pm
content: I was wondering about the problem of power dissipation from electronic loads. We do have efficient AC/DC converter that efficiently transforms mains AC to DC. Why can't we have it in the other direction, efficient electronic loads that transforms the DC to mains AC, pushing the current back to the grid.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 22, 2023, 08:53:47 pm
content: Sending AC pwer back to the grid is a bit more tricky and needs care with safety. E.g. it needs to detect if a true grid connection is lost. This is a point with the very small PV installations the try to use normal outlets instead of a dedicated wireing.The triac controlled load may have a pulsed DC current and the supply may already trip current limit from current spikes.

author: macboy
author_rank: Super Contributor
timestamp: November 22, 2023, 11:56:25 pm
content: My heat gun has digital temperature control that is quite effective, but it cycles the heater on and off in the order of seconds, rather than using phase control of the triac. This would not work for your case.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 23, 2023, 12:35:30 am
content: Quote from: Trurl on November 22, 2023, 01:45:45 pmIt depends how 'realistic' you want your test to be ?A 2kW heater dialed back to 700w+, will draw peaks above your 1200~1500W.You may be better to find an actual 1000W load, or even better, a load that is closer to how this thing actually works.I guess that's a computer power supply type load ? (rectifier + caps + maybe power factor correction ?)

author: Trurl
author_rank: Regular Contributor
timestamp: November 23, 2023, 09:13:34 am
content: Quote from: PCB.Wiz on November 23, 2023, 12:35:30 amFirst, I really appreciate ya'll chiming in.The final intended purpose would be to have the PSU's voltage output/OVP(over voltage protection) modified to accommodate say 14V(relatively easy task), then connected to a car (via engine compartment's battery charging terminals) that would have most or all of its ECUs updated(programmed) with updated firmware, a process that can take several hours.So it seems that the most pressing issue might be that the current spikes could be large enough that the PSU's OCP(over current protection) circuit could trigger and turn the PSU off.I'm having a hard time grasping how a "2kW heater dialed back to 700w+, will draw peaks above..." 1200~1500W. If you would elaborate some more on how that can be assessed I'd be grateful.I'm wondering if perhaps there is a threshold setting of sufficiently high duty cycle that would start to "tame" the current spike as the voltage/current waveform gets closer to that of non-switched resistive loads?Cheers~

author: Trurl
author_rank: Regular Contributor
timestamp: November 24, 2023, 08:56:22 am
content: Quote from: PCB.Wiz on November 23, 2023, 12:35:30 amPlease elaborate how this is expected or what technical topic to look up(recommended reading/viewing material or links would be appreciated). Thank you...

author: magic
author_rank: Super Contributor
timestamp: November 24, 2023, 09:24:17 am
content: A 2kW heater working at 700W with triac control is a 2kW heater working at 2kW for 33% of time. It turns off when line voltage crosses zero and then the control circuit waits for 66% of line half-cycle before turning it back on. Approximately, because in real world line voltage is sinusoidal and duty cycle required for 33% power is not exactly 33%, but you get the idea.I would try a bunch of 12V light bulbs instead. A reasonably well behaved DC load working directly off the PSU. It may be necessary to connect them one by one, because cold bulbs draw some inrush current when turned on.

author: Trurl
author_rank: Regular Contributor
timestamp: November 24, 2023, 10:38:10 am
content: Quote from: magic on November 24, 2023, 09:24:17 amThank you for your input... I now understand PCB.Wiz's reasoning.But doesn't the current's amplitude through a TRIAC vary as with voltage depending on the phase?(refer to attached image below) For example, at 90 degrees the current amplitude will be max and decline to 0 at 180 degrees. If the trigger phase is say 160 degrees, the current amplitude would be lower than at 90 degrees. If I'm misunderstanding something here I'd appreciate clarification.I'd be grateful if someone would point me in the direction of a good introductory reference for transient current spikes(amplitudes, power draw etc.) in TRIACs.Thanks in advance...

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 25, 2023, 01:04:38 pm
content: Quote from: Trurl on November 23, 2023, 09:13:34 amI wouldn't expect the ECUs to use much power, certainly not enough to overload a server power supply. I would say the simplest solution would be a current limiting resistor that is bypassed with MOSFETs.

author: Trurl
author_rank: Regular Contributor
timestamp: November 25, 2023, 06:56:34 pm
content: Quote from: NiHaoMike on November 25, 2023, 01:04:38 pmI'm trying to avoid the electronic dummy load path as the cooling method would require quite a lot of attention. Hence the appeal of a ready made solution like a hair dryer.When the idea to use a heat gun came to mind, I was thinking that a heat gun's heat control would be similar to a hairdryer, but I soon realized heat guns are heat controlled by TRIACs (not simply by the coiled wires themselves). I don't have a hairdryer sittin' around so down the TRIAC rabbit hole I went... interesting indeed but not the "simple household appliance" solution I was seeking.During ECU programming sessions, a voltage regulator PSU would be loaded to about 20~30amps(13~14V must be maintained) and as high as 50+/-amps when the A/C or heating systems or other motor driven accessories kick in all at once. The 1200~1500W PSUs are of interest to meet the car manufacturer's recommended 70~100amp rating for PSU (a bit of redundant capacity there to be safe I think).I'm now thinking that it will be easier to just use a hairdryer and an inverter (both pretty cheap), or some 150W 24V halogen bulbs I already have with a switch for each bulb and increase the load one bulb at a time to prevent the OCP circuit from kickin' in.Of course I'm still open to anyone's suggestions for making a TRIAC heat controlled device work as the load if there is an easy/simple way to make it work. Thanks...

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 25, 2023, 08:34:07 pm
content: Quote from: Trurl on November 25, 2023, 06:56:34 pmThe MOSFETs would be used as switches, they'll be fully on unless the current is too high in which case they'll switch off and let the resistor into the circuit. Easily done with a comparator and small transistor for quick turn off, something like a 1k pullup for a slow turn on.QuoteYou could remove the compressor fuse or relay so it won't try to start and pull a lot of power. (But I thought that's run from the high voltage system so it would just be the control side that's powered? That's how it is in Toyotas built in the last 10 years or so.) Same goes for the radiator and HVAC fan relays/fuses, as well as headlights. The radio likely would only be at idle power unless it is playing loud bass (and I assume it would be one of the devices updated so can't just disconnect it), so I suppose switch it to aux input (and nothing plugged in except maybe a cable if it checks for one) with the volume turned down before you start the updates.

author: Trurl
author_rank: Regular Contributor
timestamp: November 25, 2023, 09:11:06 pm
content: Quote from: NiHaoMike on November 25, 2023, 08:34:07 pmAh~ I see, you were suggesting making a switch like gizmo (to counter act any current spikes that might be caused by the TRIAC), and not an electronic dummy load itself. Interesting...I git the jist of what ur sayin' but I ain't no electronics expert so I'd have to see a circuit to "really" git it through me head. If you happen to have yer schematic handy please slap it on here. : DThanks...