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Old 16th Dec 2021, 11:21 am   #1
logicaluk
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Default Looking for a Bench PSU. Suggestions please.

I did electronics at collage and do a bit of auto electrics, my clean workshop isn't finished yet but not too far off, but I need to find a corner stone of the work bench the bench power supply.
I am looking for a goldilocks PSU, not expensive but good quality, something I'm not going to regret buying in a couple of years time, I would guess 30V 2A with current limiting would be a sensible baseline, but it must have a dual display.
Budget is sub 50

What would the learned members of this forum suggest to look out for or avoid?

Dan
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Old 16th Dec 2021, 11:41 am   #2
Goldieoldie
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Default Re: looking for a Bench PSU suggestions please

I have used the toward tps 2000 series for years .Very reliable .
30 v 3a .It has analogue meters which I prefer and current limiting.
Should be able to pick up one on eBay for 25 -30
They also to a twin version 4000 series ,prob about 50
Cheers
Pete
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Old 16th Dec 2021, 2:22 pm   #3
duncanlowe
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Default Re: looking for a Bench PSU suggestions please

Quote:
Originally Posted by Goldieoldie View Post
I have used the toward tps 2000 series for years

I think your autocorrect may have got at your post, as I believe the brand is Topward. Certainly my computer tried to autocorrect it too.
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Old 16th Dec 2021, 5:33 pm   #4
Vintage Engr
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Default Re: Looking for a Bench PSU suggestions please.

Also excellent quality & longevity are the later Farnell series. The later ones had a digital readout using LED devices, whilst the slightly earlier ones had analogue meters.

Often available secondhand on the web. Single & dual models were made.

I recently purchased a Thurlby-Thandar, very similar to the Farnell design & construction. Proper mains transformers, - also useful as a door-stop / heavy weight!

All those mentioned have proven very reliable & easily serviced.

David.
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Old 16th Dec 2021, 6:49 pm   #5
logicaluk
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Default Re: Looking for a Bench PSU suggestions please.

Quote:
Originally Posted by Vintage Engr View Post
Also excellent quality & longevity are the later Farnell series. The later ones had a digital readout using LED devices, whilst the slightly earlier ones had analogue meters.

Often available secondhand on the web. Single & dual models were made.

I recently purchased a Thurlby-Thandar, very similar to the Farnell design & construction. Proper mains transformers, - also useful as a door-stop / heavy weight!

All those mentioned have proven very reliable & easily serviced.

David.
the farnell ones despite looking like very nice only have a single switchable display, so not ideal. I have my eye on a Weir 4000, from the scarce info Ive found look to be a decent PSU.
Dan
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Old 16th Dec 2021, 7:35 pm   #6
SiriusHardware
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Default Re: Looking for a Bench PSU suggestions please.

We have several generations of the Thurlby-Thandar PLxxx series power supplies at work, all are quite agreeable and the current limiting works as it should, it does not ever allow the output to provide more than the set current. The only problems I ever see on them are meter faults, often caused by failure of the CMOS switch IC (4066 etc) used on the meter circuit PCBs. Also the odd failed switch

We have some modern generic 'Tenma' branded 'digital' bench power supplies and the current limit is reactive, that is, it cuts in to limit the current only when too much current is detected, so if I set the output limit to 200mA and then short the output leads together, the initial zap, at 5A out, is enough to weld the leads together before the current limiting kicks in. Completely useless. If I'm trying to troubleshoot something which I suspect might be drawing too much current I go and get one of the old Thandars.
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Old 17th Dec 2021, 9:44 am   #7
knobtwiddler
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Default Re: Looking for a Bench PSU suggestions please.

Something to bear in mind with the Weir is that it's only single-output. Many circuits will want a dual-rail supply, particularly if you are fault-finding items such as audio. You can lash up a 'rail splitter' or 'virtual ground', but it'll be a lot easier to get a dual PSU.

I have several TTI PSUs. What others have said about them is true. You can find them cheaply if you are patient. Kingshill PSUs can be found cheaply, although the ones I've seen had quite a bit of triangular corruption on the rails (not sure if this was a servicing issue or inherent). The Kingshill are made from deluxe components, Sifam meters etc.

Modern SMPS types such as Tenma ought to work well, although I've always found the TTI ones easily so haven't been tempted to try.
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Old 17th Dec 2021, 10:31 am   #8
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Default Re: Looking for a Bench PSU suggestions please.

I've got various power supplies that I use in different places and for different projects. Here are my experiences:

Farnell LT30/2 and L30/5: great general-purpose supplies, 30V 2A and 5A. Advantages: common on UK secondhand market, nice big analogue meters, coarse/fine voltage controls, effective current limiting. The 2A and 5A ones have internal protection against being connected to power sources, which is important if you ever intend to charge batteries with the power supply. The 1A versions don't have this for some reason. Disadvantages: meter shared between V and A on 1A and 2A versions. Rotary controls can wear out and get sloppy/drifty. Connectors to the PCB inside can make poor contact, resulting in strange symptoms like random current limiting.

Solartron AS1164.2: one of my favourites, dual output 30V 1A, outputs can be paralleled. Analogue ammeters with decade switches for setting voltage. Advantages: output voltage extremely stable and accurate when properly maintained. Big positive controls, no chance of accidentally knocking a setting while doing something else. Disadvantages: properly vintage (all germanium transistors, nearly 60 years old), can suffer poor switch contacts, current limiting is foldback so not really suitable for constant-current applications. Decade switches aren't so convenient if you want to sweep the voltage smoothly.

Thurlby/Thandar PL3xx series and friends: the industry standard, found everywhere in electronics companies. Common as muck on the secondhand market though people try to charge too much for them. Nice digital meters, though the LCD ones can be hard to read. Apparently the early ones have some reliability problems but documentation is readily available. I've just bought a slightly dog-eared PL320 with "K2" add-on module for one of my workshops - three outputs (2x 30V 2A and a 5V one) for about 50 seems to be the going rate for actual sales. A bit big and heavy, but otherwise hard to fault.

Maplin "80W slim" power supply, also sold as Voltcraft LSP-1403, as seen on Big Clive: every time I use this power supply I want to throw it out of the window. Fiddly controls, slow to respond, hopeless flickery digital meters which show four digits when they're really only accurate to about one digit, annoying sockets instead of binding posts. Worst of all, ridiculously easy to nudge one of the range buttons and have the voltage suddenly jump to a different value, destroying the circuit you're testing (I speak from experience). Only advantage: small and light and therefore easy to hide somewhere you won't find it.

The big boys, HP 6012B and 6031A: 1000W bench power supplies capable of 60V/50A or 20V/120A respectively. Awesome if you need the power, accurate digital metering, practically indestructible and efficient. Noisy and lack output switch.

The wildcard: Keithley 2306 battery/charger simulator. Can sometimes be picked up cheaply because nobody knows what it is. Common surplus from the mobile phone development industry. Actually a handy little (though with noisy fan) box, dual 15V/5A/60W supplies with extremely precise (about 0.01%) voltage and current setting and limiting, also works as a 3A electronic load on both channels. User interface is really designed to be computer-driven, but there are buttons and display on front panel that do everything you need though a bit fiddly. I actually use this quite a lot and want to fit a quieter fan.

Other far-eastern models, of which I've used a lot: there are some pitfalls to look out for. First, make sure it's got an output on/off switch separate from the mains switch. You'll miss it if it isn't there. Check the that controls, especially if they're digital, aren't too fiddly. Nudge buttons and cheap rotary encoders quickly get annoying. And check that it doesn't have an enormous capacitor across the output. Many of them have several thousand microfarads there, which means that if you set the current limit to a low value and then switch the output on, a huge capacitor discharges in to your load. I witness someone testing LED backlights with one of these and, in his words, it "went off like a flash bulb". Not helpful.

There are quite a lot of subtleties to a good bench power supply. The old favourites (Farnell, Thurlby/Thandar and Solartron) figured out the right answers very early on, and sometimes it feels like everyone else is still catching up.

Chris
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Old 17th Dec 2021, 4:31 pm   #9
logicaluk
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Default Re: Looking for a Bench PSU suggestions please.

Thank you very much for that Chris, it should be made a sticky.

It appears, when looking at the Wier 4000 power supply on eBay, I put the opening bid on it of 30, and won it. A Google search brings up a link to this forum, with 2 pages from the manual and a promise of the rest to follow, but I can't find it.

But I think I shall keep my eyes peeled for a Thurlby at a sensible price, they're industry standard for a reason.
Dan
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Old 17th Dec 2021, 4:48 pm   #10
SiriusHardware
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Default Re: Looking for a Bench PSU suggestions please.

Oh, one minor quirk with all of the Thurlbys, they have separate power output and sense-input terminals. The purpose of this is so that if you are powering something down very long wires for some reason, you can bring the voltage at the load back along another pair of wires to the sense inputs so that the voltmeter indicates the voltage at the load. In theory this is A Good Thing and if you actually have a use for it, so it is.

But: When the load is close to hand and you don't need to remote-sense the voltage, the volts out and sense-in terminals are strapped together by a pair of drop-in shorting bars. If these are not properly in place and tight, the voltmeter reading will not reflect the actual voltage coming out of the supply terminals, it can be out by up to about 1.6V.

I find this to be such a liability and so potentially dangerous when it comes to circuits which MUST have a specific supply voltage, like 3V3 or 5V0, that I strap the terminal pairs together internally on all the ones which I personally use and draw a line between them on the outside to show that they are internally shorted. Apart from that one major annoyance, they are great power supplies.
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Old 17th Dec 2021, 6:12 pm   #11
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Default Re: Looking for a Bench PSU suggestions please.

I've got as my main 'bench' supply a PeakTech 6005D; 0-30V at 5A, with current-limiting. I think I paid about 10 for it. It's fan-cooled and has a linear regulator, with automatic tap-changing on the big toroid transformer to avoid excess dissipation in the series-pass transistor when on low-volts. Digital display of output-voltage and current.

Thr only thing 'wrong' about it is that it totally goes to pieces in the presence of local RF fields; you don't want to be using this to power a 40-Watt HF transmitter unless you make a few internal modifications to stop RF getting-into it via the output terminals.

There's a bunch of similar bench power-supplies available, often from surplus/clearance auctions online. The KORAD KD3005D is pretty much the same electronics in a differently-shaped box and with red LEDs rather than the PeakTech's green.
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Old 18th Dec 2021, 7:24 am   #12
djsbriscoe
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Default Re: Looking for a Bench PSU suggestions please.

I use a GW-INSTEK GPP-4323 power supply. It has 4 outputs. More details here

https://www.electrobob.com/gpp-4323-...supply-review/

and I use a basic Manson EP-603 for basic stuff.

I use mainly Thurlby power supplies at work.
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Old 18th Dec 2021, 9:30 am   #13
peter_scott
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Default Re: Looking for a Bench PSU suggestions please.

Supplies with adjustable current limiting are good.

Peter
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Old 18th Dec 2021, 11:50 am   #14
wireman
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Default Re: Looking for a Bench PSU suggestions please.

I have a GW Instek GPD-3303S.

I suppose one option to keep near budget is a switch-mode module like the RD RD6006 which you could feed from an existing higher voltage DC supply if you have one.

It looks like second hand is likely to be the best option.
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Old 18th Dec 2021, 10:08 pm   #15
Radio1950
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Default Re: Looking for a Bench PSU suggestions please.

To the original question -

.front panel ON/OFF switch
.front panel bright "ON" indicator.
.DC terminals which have screw down and 4mm sockets.
.separate voltage and current meters
.adj current limiting
.full rated current at high volts
.short circuit protection.
.reverse current protection.
.voltage settable down to 1.5 V
.output NEG floating above mains earth, but with link to couple it to mains earth if required.
.no fan

0-30V is OK
0-2A is OK

Good luck

Last edited by Radio1950; 18th Dec 2021 at 10:18 pm.
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Old 18th Dec 2021, 11:10 pm   #16
calicobramble
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Default Re: Looking for a Bench PSU suggestions please.

I'll defer to wider knowledge - of course - but I would expect to see the power and sense terminals of a four terminal supply (Kelvin loop) tied together with a low value resistance - say 100 ohms or so. That way if the link between sense and power gets detached the PSU output voltage is still controlled and doesn't go whanging off where it didn't orter.

Seasons greetings all

Simon
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Old 20th Dec 2021, 11:21 am   #17
SiriusHardware
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Default Re: Looking for a Bench PSU suggestions please.

Almost correct, in the Thurlby - Thandars they are tied together with silicon diodes so that the PSU out and sense-in terminals can never be more than 0.6V different when they are not connected together by any other means, but for mission critical supply voltages even that much disparity between the actual output and the indicated output could be too much.

The sense-in terminals aren't used as part of the voltage regulation loop in these Thurlby-Thandar power supplies, it would be more accurate to think of them as voltmeter-input terminals.

The PSU output voltage is under control regardless of whether the output and sense-in terminals are strapped together - it's only the meter reading which goes offset, but if you then adjust the output voltage control so that the meter indicates the desired voltage - as you would - then the actual output voltage is not what the meter says it is.

That is why, as I said, I strap the output and sense-in terminals together internally on all the ones that I personally use.
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Old 20th Dec 2021, 1:32 pm   #18
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Default Re: Looking for a Bench PSU suggestions please.

Quote:
Originally Posted by SiriusHardware View Post
The sense-in terminals aren't used as part of the voltage regulation loop in these Thurlby-Thandar power supplies
Double-checking the schematics, I'm pretty sure that's not correct.

The negative sense terminal is connected straight to the two voltage adjust pots as well as the metering.

The positive sense terminal is connected to the control circuit ground, which is where everything is referenced from.

The simplified diagrams earlier in the manual confirm this.

I agree that adding a pair of resistors to join the force and sense terminals is a good plan, and might well go as low as 10 ohms.

I also checked this is true for the later PIC-based version. In that model, they've done away with the diodes between force and sense, and replaced them with 2k2 resistors. Seems high, but the sense current is much reduced with this version.
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Old 20th Dec 2021, 10:35 pm   #19
SiriusHardware
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Default Re: Looking for a Bench PSU suggestions please.

Quote:
Double-checking the schematics, I'm pretty sure that's not correct.
It was an assumption based on the fact that the output remains under control and regulated even when there is no intentional connection between the output terminals and the sense-in terminals but of course the diodes provide a backup connection, so I'm sure you are probably right.
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Old 21st Dec 2021, 8:52 am   #20
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Default Re: Looking for a Bench PSU suggestions please.

Quote:
Originally Posted by Radio1950 View Post
To the original question -

.front panel ON/OFF switch
.front panel bright "ON" indicator.
.DC terminals which have screw down and 4mm sockets.
.separate voltage and current meters
.adj current limiting
.full rated current at high volts
.short circuit protection.
.reverse current protection.
.voltage settable down to 1.5 V
.output NEG floating above mains earth, but with link to couple it to mains earth if required.
.no fan

0-30V is OK
0-2A is OK

Good luck
A very good 'tick list' to which I would add:

* Linear in preference to SMPS
* Separate output switch as a nice-to-have.

The former to minimise the horrendous hash and interference you can get from an SMPS, and the latter as it is nice to be able to set outputs before 'enabling' them.
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