Recommendation for a power supply without fan (TTI) - Page 1
Forum section: electronics / testgear

author: larsdenmark
author_rank: Regular Contributor
timestamp: June 21, 2018, 01:30:03 pm
content: I think I need a new power supply. I like the idea of not having a noisy fan. Recommendations are welcome.I have found the TTI PL155 that seems to suit my needs, but I have a few questions that I hope someone can answer:1) How long time does it take to become accustomed to this coarse/fine adjustment of the voltage? I think I would prefer to be able to adjust the integer part with one knob and the remaining part with another knob, but that doesn't seem to be the case.2) If you have been using a power supply with coarse/fine tuning do to miss having a keypad for entering voltages and current?3) Can I connect a LED directly to the power supply without a resistor? (e.g. by setting and voltage to 5 V and the current limit to 30 mA). Will the power supply be fast enough to control the current such that the LED doesn't blow?Thanks

author: bd139
author_rank: Super Contributor
timestamp: June 21, 2018, 01:44:07 pm
content: Got a PL154 and PL310 here.1. Doesn't take long. Process is: (a) set the right knob to middle, (b) set the left one to near where you want, (c) trim with the right knob. Takes no effort at all.2. No. It's easy enough to set precise voltages.3. Yes but only if the output capacitor is discharged. The instantaneous current can be quite large otherwise. If you're going to do that, set the current limit, short the terminals, connect the circuit, power it up, then remove the short. There is no overshoot that I could measure. I regularly use them to drive LEDs.Best bit with these is the output switch also sets the mode. So if you set up the voltage/current while the supply is off and the display shows the set point. When on, it shows the actual output.Really though, I require a precise voltage perhaps once a month or two for what I do so I tend to just use the coarse control.Supplies are completely 100% quiet. Not even any transformer hum.

author: wraper
author_rank: Unknown
timestamp: June 21, 2018, 01:51:05 pm
content: PL series do have fan, although you won't notice it spinning unless under heavy load.QuoteDon't do that with any PSU. Even if output capacitance is very small, PSU still need some time to drop the voltage to reduce current. The only relatively safe way without a resistor is reducing the voltage below LED forward voltage before attaching or disconnecting the LED.

author: larsdenmark
author_rank: Regular Contributor
timestamp: June 21, 2018, 04:20:47 pm
content: Thanks for the info. The thing about the LEDs is just for fun. I can live without it.Now I just have to decide if I should get the PL155 or the PL303QMD.

author: bd139
author_rank: Super Contributor
timestamp: June 21, 2018, 04:30:01 pm
content: New ones have a fan.Get an older PL330QMD. They cost bugger all. Will give you 30V at 6A and silence all day every day. Entirely reliable.

author: jpb
author_rank: Super Contributor
timestamp: June 21, 2018, 05:20:42 pm
content: Quote from: bd139 on June 21, 2018, 04:30:01 pmI'd second that.I have a PL320QMD and it has been very quiet, reliable and easy to use. The meters are accurate (generally to the last digit). I have a couple of other more expensive supplies now but I still default to using the PL320QMD.The only down side is that it is quite large though in a lot of ways it is a good shape for the bench (tall and shallow).

author: wraper
author_rank: Unknown
timestamp: June 21, 2018, 06:34:27 pm
content: Quote from: jpb on June 21, 2018, 05:20:42 pmPL303QMD is generally inaudible, at high loads you can start hearing the fan. But it's still not loud. These older models lack 0.1mA current resolution, setting lock, voltage span, meter average, % tracking (for 2 ch model).

author: larsdenmark
author_rank: Regular Contributor
timestamp: June 22, 2018, 10:05:01 am
content: I thought narrowing things down to only one brand would make it easier for me to make the right choice, but no...I can't find cheap used PL330QMDs anywhere. The ones I can find are either fairly expensive, beat up or aren't shipped outside of the UK. I would be happy having an (not too) old model, bit I also like the new versions. I especially like the improved current resolution and new binding posts. Having warranty may also be nice even though my impression is that TTI power supplies are of a very good build quality.The latter is quite funny since most videos on Youtube on these power supplies are about how to fix them - giving the impression that they fail all the time. I guess most of these failing supplies are 20-30 years old?! Perhaps more people that own a TTI power supply should make videos while the supply still worksI'll be looking for a used power supply a little while longer. If I don't find anything suitable I'll get a brand new one.

author: bd139
author_rank: Super Contributor
timestamp: June 22, 2018, 12:03:26 pm
content: It’s only the old black and white or brown ones and generally ones with the crap beaten out of them that need repairing. The grey ones are all good.Worth checking Stewart of Reading. They stock lots of these usually and shipping isn’t too painful:http://www.stewart-of-reading.co.uk/Power%20Supplies.htm