Can I damage my linear PSU - Page 1
Forum section: electronics / beginners

author: gb243
author_rank: Contributor
timestamp: November 12, 2021, 10:29:34 pm
content: We are told to use linear PSUs for RF projects due to their inherent low noise. Yep that is logical. The problem is I have a CW transceiver. Key down is 2.5 Amps. Key up 250mA. The rig itself (Elecraft K2) is designed to cope with the CW. My PSU (Aim TTi) switches transformer secondaries when the current peaks and then back as it drops. In other words keying CW hammers the PSU. I have other PSUs (Rigol etc) and they all do the same. Will I kill off the PSU with all the switching?

author: bob91343
author_rank: Super Contributor
timestamp: November 12, 2021, 10:57:50 pm
content: I think so. At what current does it switch? You might be able to add a dummy load to keep it in high power mode.That of course is not only wasteful of power but might not leave enough current to run the rig.Get an old fashioned power supply like an Astron RS-25 or build one. I have a couple extra ones if I should need to do that. I already use an old Alinco power supply to run my TS-440S 100W rig and it loafs along no matter how much I run CW.

author: gb243
author_rank: Contributor
timestamp: November 13, 2021, 11:39:12 am
content: The K2 spec is 9->15v input. I try and run 10W max not the 15W it is capable of. Maybe home brew with 15v unregulated taken down to 12v. Then if the pass transistor fails short the rig will still survive and I can arrange a simple crowbar at 14.9v which does not have to be particularly fast. Having just finished building my K2 I really do not want to blow it up. Call me fussy but.....

author: HB9EVI
author_rank: Frequent Contributor
timestamp: November 13, 2021, 11:43:03 am
content: Quote from: gb243 on November 12, 2021, 10:29:34 pmI cannot confirm that from the Rigol DP-832. If I set the current limit to 3A and I run my FT-817 in CW key down (drain about 2.5A), the supply delivers stable 13,8V @ 2,5A without any issues.

author: wizard69
author_rank: Super Contributor
timestamp: November 13, 2021, 07:21:18 pm
content: Quote from: gb243 on November 12, 2021, 10:29:34 pmWould that not depend how the switching is done?Frankly I'm not sure why a supply with such a limited current range would be designed that way. All you really need is a supply just large enough to handle the max current and ideally has over voltage and short circuit protection. There are literally dozens and dozens of supplies that could fit the use case.

author: tkamiya
author_rank: Super Contributor
timestamp: November 26, 2021, 03:23:15 am
content: I wouldn't use such a power supply with rigs.... I don't know what happens in transition from Low to High. I don't know how reliable that switching is when repeatedly done few time a second. 12V linear supply module (open frame type) in 3A range is 20 to 30 dollars or so on eBay. These power supplies are very similar to Astron in construction. 723 for regulator and a couple of pass transistors for current handling. I'd go with them instead.

author: tooki
author_rank: Super Contributor
timestamp: November 26, 2021, 07:44:51 am
content: Quote from: gb243 on November 12, 2021, 10:29:34 pmTransformer tap switching is normally to account for voltage change, not current.Are you sure you’re not actually just going into current limiting, causing the voltage to plummet? That shouldn’t be how your load operates.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 26, 2021, 07:57:47 am
content: The tap switching with relays in linear power supplies is usually not made to be switching very often / fast in a squence. The relay contacts see quite some load as there is some filter capacitance to charge. This may cause wear and if in fast sequence also possible sticky contacts from overheating.If just at the edge, the additional load can be enough to let the raw voltage drop enough to make the supply switch taps. Nomally the hysteresis in the control should be large enough that this should not happen. The supply going to limiting mode and than with a lower voltage going to the lower tap could also be possible. One could test the hysteresis of the tap switching (e.g. without load), maybe it is a bit on the low side.

author: ledtester
author_rank: Super Contributor
timestamp: November 27, 2021, 02:36:26 am
content: Quote from: gb243 on November 12, 2021, 10:29:34 pmWhat other power supplies does this happen with? Perhaps pressing the key creates a large current transient before stabilizing at 2.5A and the power supplies are kicking into current limiting and thus a lower voltage as others have suggested. Capturing the current draw with a scope could be helpful.

author: radiolistener
author_rank: Super Contributor
timestamp: November 27, 2021, 11:14:58 pm
content: Quote from: HB9EVI on November 13, 2021, 11:43:03 amThe same with PSU HY1505D

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 28, 2021, 12:10:02 am
content: A way to damage any PS is to connect it to higher volts and feed current back into it.Don't do what I have done.

author: BlackICE
author_rank: Regular Contributor
timestamp: November 28, 2021, 04:01:04 am
content: If you don't mind the bulk and are worried about it, why not use a nominal 12v lead acid battery, or 3S - 18650 battery pack with BMS with a low current charger attached to it.