Need Schematic Help for Eltek power Supply - Page 1
Forum section: electronics / projects

author: DRBuck
author_rank: Contributor
timestamp: May 18, 2020, 07:38:49 pm
content: K3SKK3SKHam MemberQRZ PageI am in need of a schematic , or as a minimum the detailed circuit layout for the cooling fan circuit in an Eltek ValereFlatpack2 48v3000w P/N 241119.905A HE. I am trying to eliminate RF noise created by the power supply's PWM circuit that controls the cooling fan.I use these power supplies to power a couple solid-state KW amplifiers for ham radio. When first keyed down there is no issue. After a short time as the power supply load increases and the cooling fan in the supply speeds up I start hearing a low frequency buzzing/pulsing on my transmitted signals. I'm 99% sure the PWM circuit is my problem. When unkeying and the PS fan slows down, the noise disappears. I've added half a dozen ferrite beads on the DC supply lines to the amplifier that reduced the noise somewhat, but receiving stations still report to me that there is noise. One guy even described it a sounding like a helicopter flying outside my window. This noise is identical on all of these Eltek 3000 watt power supplies I've tried.

author: trobbins
author_rank: Frequent Contributor
timestamp: May 19, 2020, 07:11:31 am
content: Perhaps find an Eltek distributor who has a service department, as they are likely to have schematics, or can ask Eltek directly - at least for a schematic of section you are interested in as they may restrict circulation depending on how recent the model is.

author: DRBuck
author_rank: Contributor
timestamp: May 20, 2020, 09:57:19 pm
content: Quote from: trobbins on May 19, 2020, 07:11:31 amThey claim proprietary and won't release me any info.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 20, 2020, 10:10:14 pm
content: Thats sums it up, if its propriettary you wont get a schematic unless it was leaked on the web ... or reverse engineeredor try another time with an signed non disclosure agreement ?

author: trobbins
author_rank: Frequent Contributor
timestamp: May 21, 2020, 01:05:29 am
content: Have you thought about reverse engineering? At least to get the fan model and see what PWM control it has and whether it has any design notes on noise/EMI reduction for speed control applications.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 21, 2020, 03:06:51 am
content: Have you tried disconnected the fan (faking the feedback signal if necessary) and powering it from a separate supply? I suspect the problem is the fan current path is perturbing the feedback circuit and modulating the output voltage.

author: DRBuck
author_rank: Contributor
timestamp: May 21, 2020, 03:44:40 am
content: Quote from: trobbins on May 21, 2020, 01:05:29 amQuote from: NiHaoMike on May 21, 2020, 03:06:51 amI've poked around on the circuit a little, but with surface mounted components it's tough to "reverse engineer" the circuit. The fan has 4 wires connected to it and it has a connector where it plugs into the main board. I 'll try and pull a part number off the fan and see if I can figure out which wires do what. This is my first time messing with PWM circuits.

author: trobbins
author_rank: Frequent Contributor
timestamp: May 21, 2020, 06:19:10 am
content: Yes well worth confirming the fan details, and also if the fan can be removed, or the wires to the fan accessed. Suppressing emi at the source is the best bet. It may be as simple as adding in a local bypass RC or LC in line with the supply rail at the fan, or as close as possible, if that can localise any switching current pulses generated within the fan. If a PWM control line uses very fast switching pulse edges (for no good reason) then those edges may be worth slowing down (again as close to the source as possible, so back in the power supply or where the lead comes off a pcb).You may also want to look at the wiring of the total system, and see if there are any earth/ground loops from multiple mains supply connections. Is the output DC of the Eltek floating, and so is one output polarity effectively being grounded at your transmitter? If so then switching hash can circulate via capacitive coupling through the Eltek back to the mains protective earth, and loop around through your transmitter.

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 21, 2020, 03:53:47 pm
content: You could backprobe the fan's connector to look at each pin on an oscilloscope.