Novice level - power pack question  - Page 1
Forum section: electronics / projects

author: Thedrunkenflea
author_rank: Contributor
timestamp: October 13, 2022, 05:32:40 am
content: Hello.I've recently started getting deeper into electronics and was wondering if you chaps could help me out.Im interested in making PEMF machines and a lot of other stuff im learning to make safely too.My question is how to calculate the right power pack for my coil.My coil is 1.2 Ohms - The power pack I have idnetefied for my needs is here:https://www.hackster.io/mircemk/simple-to-build-high-power-pemf-therapy-device-f38d46My coil and power pack set up is 1.2 ohms resistance - the one used in this set up (the link) is 0.8ohms.In the link the power pack is higher than mine 12 v 20 amps - mine is 12 v 10 amps.I've estimated it would handle my power load - but would rather be sure before i buy the parts and run safety tests.Could you guys run the numbers - or show me how to do it my self.regards

author: jwet
author_rank: Frequent Contributor
timestamp: October 14, 2022, 06:34:05 am
content: The math is pretty simple really- a DC resistance will drop a voltage of IR. It will dissipate a power of I^2R. Your power supply of 12v at 10 amps would be about right without overloading. A 10 amp current through a 1.2 ohm R would drop 12V- which is your supply voltage. The power dissipated in the coil would be 10^2 * 1.2 or 120 watts. This would generate a bit of heat. A .5 ohm coil with 10 amps would dissipate 50W. I hope this helps some.

author: Thedrunkenflea
author_rank: Contributor
timestamp: October 14, 2022, 06:56:02 pm
content: Thanks man!!!!!! this hopefully will solve an issue for me - im currently using a mechanical car flasher for the on/off pulse they are very erratic. Burn out (buffer range by 20%) So for a 12v 10amp power pack I use a flasher rated at 12v 20 amps. Even high quality ones mechanical in nature dont last all that long - you get a month out of them at 2 hours running per day at best.I used the flasher today on much smaller coil - i dont have a reading on the ohms - but anyway my flasher is fine with the 1.2ohm coil (100ft at 1.5mm) but if i put it on my other projects it hits warp 9 and Ziiiiiiiiiiiinznznznzznznzznzznznznzng, flashes away too fast.its 14 gauge wire (2.0 mm)4 meters long roughlyrunning round magnetic copper wire - basically a small Bifilar coil12v 10 amps DC applied.I think I need to apply some resistors to the flasher? on the power input prong and the loop wire (its a 3 pin flasher) then solder the power plus loop/return wire on to resistor?Am doing it right - or close?Appreciate all the help i can get -

author: tooki
author_rank: Super Contributor
timestamp: October 14, 2022, 11:36:44 pm
content: (The best advice is to not waste your time with that stuff, because there is very, very little evidence that it actually works. The studies showing positive results are of very poor experimental design.)The load is a big coil, and a coil, in the instant it’s shut off, can produce a voltage spike in the hundreds or even thousands of volts, causing damage to other parts. Dave, the guy who created and makes EEVblog, recently did a video about this. Look for the video about “back-EMF”.Anyhow, you’ll want to protect the power supply, switches/relays/MOSFETs with a diode across the coil to prevent the voltage spike.

author: jwet
author_rank: Frequent Contributor
timestamp: October 15, 2022, 01:10:45 pm
content: I won't get into the efficacy of your end use- I'll stick to the electrical problems.Flasher modules are load sensitive. As the current goes through them, a bimetal strip heats up in side and flips state from on to off. It cools in the off state and flips back. The higher the current, the faster the flash rate. This is why when you plug in a trailer, your lights flash twice as fast. There is nothing you can do to slow it down by changing the load really. You need a flasher that's designed for more current. Maybe something from a big truck or something.The other option as the last poster mentioned is an electronic flasher module. I saw some on Amazon for about $20. They have programmable on and off durations. These are the kind of things that drive the lights on police cars. Most I saw were rated for 10 amps, might be nice to find a bigger one for a little margin. What's inside these is a timer IC and big mosfet or a relay. You can likely find some plans for one- get one that looks like its been tested, etc. I would buy one I think at $20. Do be aware of the back EMF issue, this would be very real for a giant inductor like this. You need to clamp the opening spike with a zener or tranzorb clamp of some kind- watch Dave's video. Flashers are designed for resistive loads, incandescent lamps almost a perfect resistive load- running them into big coils is a torture test.Good luck.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 15, 2022, 01:52:08 pm
content: Take a look at DC motor PWM controllers, they're designed to switch inductive loads at relatively high frequency.

author: Thedrunkenflea
author_rank: Contributor
timestamp: October 15, 2022, 03:25:00 pm
content: Quote from: jwet on October 15, 2022, 01:10:45 pmI found one of those on amazon in the USA I'm from the UK, they are made by czh-labs.comWorth a punt - one hours use per day is normally the max its used for - usually a lower amount of time.You're like me - want to know whats inside it lmao - if it held its ground and i got my moneys worth I could open it up and replicate what I find. I cant just design my own pulse module im not knowledgeable enough yet, I still need to buy a bread bin and learn the basics of capacitors, diodes, switches and become competent at a basic level.Also surely i could take the PEMF machine power pack in the first link and reduce to mosfets and other stuff like the diode and relays and just bring the power pack Down - id have two power packs essentially - i just dont know how to calculate it yet.

author: jonpaul
author_rank: Super Contributor
timestamp: October 16, 2022, 05:52:51 am
content: PEMF uses 10..50 kV HV charging a low inductance pulse capacité with many joules.Triggered spark gap or SCR switch.Patient coils use #4 or thicker wire, litz.even the huge, expensive and dangerous professional PEMF machines with qualified operators, produce very sketchy proof of effectivenessThe experiment You mentioned will not workBon courageJon