Author Topic: beginner bench power supply question before buying  (Read 1143 times)

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Offline ergya

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beginner bench power supply question before buying
« on: October 09, 2018, 08:50:21 pm »
Hi everyone,

First off if this is too much to answer because simple my knowledge is low on this topic can someone point me to a good read/book where I can learn more about this topic?

I'd like to buy a bench power supply. At the moment I am a complete beginner to EE things. I am sure I won't work with high current/voltage in the near future but I like high quality stuff and I don't want to limit myself if I need more power (and I especially hate when I have to buy a new something because the first one was compromised). So I am thinking of buying one of these:
  • Rigol DP832
  • AIM-TTI MX180T(P) for more power if I need in the future

As I am a beginner I need all protection I can get (shorting...) with reliable components so that I won't kill the PSU. Are there any other alternatives to consider? Is AIM-TTI regarded as a high-quality reliable PSU?


One another question, Dave talks about "floating" or "isolated" power supplies in this video (at 7.44): https://youtu.be/xaELqAo4kkQ?t=444. According to AIM-TTI MX 180T manual on page 7 here: http://resources.aimtti.com/manuals/MX180T+MX180TP_Instruction_Manual-Iss6.pdf
  • "Both are fully floating and either can be connected to ground or to a terminal of another output".
Are the 2 things (what Dave is talking about and what the manual says) the same?


Just to have better knowledge on this topic, if I compare for example R&D HMP4030 (if I am correct it is regarded as a high-end PSU) with AIM-TTI MX180T are these numbers make any big difference for a hobbyist?

Accuracy (reading):
  • R&S: < 0.05% + 5 mV and < 0.1% + 2 mA
  • MX180T: Voltage - 0.05% of reading ± 3mV; (± 30mV on 120V range) and Current - 0.3% of reading ± 3mA to 3A, 0.5% of reading ± 3mA to 10A: 0.5% of reading ± 4mA to 20A
Load regulations:
  • R&S: < 0.01 % + 2 mV and < 0.01 % + 250 μA
  • MX180T: <0.01% +5mV (CV mode) for any load change using remote sense.
Line Regulations:
  • R&S: < 0.01% + 2 mV and < 0.01% + 250 μA
  • MX180T: <0.01% +5mV (CV mode) for a 10% line voltage change.
Ripple & Noise:
  • R&S: (between 3 Hz to 100 kHz) < 250 μV (RMS), typ. <150 μV (RMS); (between 3 Hz to 20 MHz) typ. < 1.5 mV (RMS)
  • R&S: current ripple: < 1 mA (RMS)
  • MX180T: Typically <2mV rms, <15mV pk-pk, 3mV rms max. (20MHz bandwidth).; (120V range: <4mV rms, <30mV pk-pk, 6mV rms max.)
« Last Edit: October 09, 2018, 08:52:57 pm by ergya »
 

Offline Nusa

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Re: beginner bench power supply question before buying
« Reply #1 on: October 09, 2018, 09:09:47 pm »
The numbers you're comparing aren't going to matter much to a complete beginner. Or to many non-beginners for that matter, unless they have special needs. The fact one supply has remote sense capability is far more significant. A feature a complete beginner isn't likely to use for a long time.

But bottom line is either of those supplies is far better than most hobbyists start with, because either of them cost far more than beginners are usually willing to spend.
 
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Offline andyturk

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Re: beginner bench power supply question before buying
« Reply #2 on: October 09, 2018, 11:51:51 pm »
AIM TTi supplies are nice. I have a QL564T. The metering is very accurate and easy to see. The big 7-segment displays to look a bit retro, but they work. The knob is very handy. You can either grab it between your thumb and finger for precision tweaking, or spin it rapdily using the dimple. The thing is a beast though, in terms of weight.

I've only used the remote sense feature once or twice. It's a pain because you have to use the fiddly press-to-release connectors on the front panel with conductors that are entirely separate from the bananna jacks. On my supply, two channels are fully configurable, but the third is only good to 6V/3A. That's fine, and I use it to power USB devices while keeping the other two free. The ability to set/view limits in 1mV/100uA steps is super handy for the the battery operated projects I spend time on.

Is a $1k power supply in "hobbyist" territory? Depends on your hobby budget, I guess. You probably don't need a lot of "power" starting out as a hobbyist, or a lot of configurability either.

Buy what what makes you happy. If you end up spending many hours in front of it, the money will be well spent.
 
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Offline Hobby73

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Re: beginner bench power supply question before buying
« Reply #3 on: October 10, 2018, 06:26:21 am »
Look at the Korad product line for an inexpensive bench power supply that has good specs.  I have one and it works great.  It provides up to 30V and 5A DC with mV and mA precision, which makes it a good general purpose unit. 

Unless you have specific requirements, which you don't appear to, I would not overbuy at this point.  If I were to buy again, I would consider a dual power supply.  But all the other features of my single supply Korad are more than sufficient for my low power projects.
 
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Online rstofer

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Re: beginner bench power supply question before buying
« Reply #4 on: October 11, 2018, 01:59:39 pm »
If you want to do this thing just once, you should probably look at a triple output supply.  A common requirement is +-15V for analog and +5V for digital, at the same time.

I got along for decades with wall warts and batteries.  When I decided to buy a bench PS, I went with the Rigol DP832.  It is more than adequate for my needs.

Here is what is important:  A method for setting the current limit that doesn't require shorting the output and turning a knob while watching a readout.  A nice digital display that shows the voltage set point and the current limit, simultaneously, seems important.

With the DP832, there are really two current limits:  The first type of current limit is Constant Current and when the circuit reaches this current, the output voltage falls to prevent delivering more than this current.  The second type of current limit is Overcurrent and when the circuit reaches this value, the output shuts off.  Both of these help prevent damage due to mistakes.  Both are set on a digital display and the values are always shown, you don't have to go looking to find the setpoints.

I want those features.  If a PS doesn't provide them, I'm not interested.
« Last Edit: October 11, 2018, 04:11:36 pm by rstofer »
 
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Offline bd139

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Re: beginner bench power supply question before buying
« Reply #5 on: October 11, 2018, 02:40:57 pm »
Note that the AIM-TTI MX180T is a post-regulated switcher. It's going to have more noise than the DP832.

The AIM-TTi supplies are extremely good quality.  If you're a beginner though, I'd probably hit one of the less fancy supplies. You don't need a lot of power supply really. The AIM-TTi PL series ones are pretty excellent as an example, are fully linear and you can pick older fully working units up for virtually nothing these days. I have two of those which covers all of my requirements, a PL310 and a PL154. Joy with them is that when you switch the output off they display the set voltage/current. So much better interface than most of the alternative and older power supplies. Also has current damping as it's impossible to read current display on some supplies as load changes rapidly.
 
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Offline ergya

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Re: beginner bench power supply question before buying
« Reply #6 on: October 11, 2018, 06:39:29 pm »
Thanks for all the answers. About this question I had:
  • "Both are fully floating and either can be connected to ground or to a terminal of another output".
Does this mean the same thing as Dave was talking about in the video I linked? If I am correct galvanic isolation and floating "design" are 2 separate things, aren't they?
 

Offline cdev

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Re: beginner bench power supply question before buying
« Reply #7 on: October 11, 2018, 07:00:52 pm »
rstopher's suggestion to get a triple supply is spot on. As is the usefulness of having a dual +- setting thats higher and a single supply that can do lower voltages at a higher current.

Fully floating (dual or more) multiple power supplies can - if you need to do this, be used in series or parallel to give you more voltage or more current.

Really good multiple ones will also have means of using them both at the same time as a dual positive and negative supply with a center ground. Good for precision op amps.

I actually have two triple supplies now.

One is digital one is analog.

For most of what I do, I really like having the precise digital readout for low voltages and especially the current limit. (which makes a small click when it starts limiting- also an LED changes color)  It is a Sorensen "XL" series triple supply that can provide 60 watts (conservatively rated) in each section.

What I do is I look up, what is the current draw supposed to be?

Then I set the supply for exactly that plus around 20%. Sometimes when you have wired up a circuit you have made some simple - but sometimes not so obvious mistake. Without a current limit, or if it is set to high, your part may instantly become toast if you hook it up wrong.

If you limit the current you vastly reduce (if not eliminate) the chance of causing any damage to your components under the usual kinds of error conditions. The more precise you can set the limit to the better. Supplies vary in terms of their accuracy and ease of use there.

It helps that most of the things I work on take very little current - but its probably prevented problems many times.

You can get help and advice here, use it to get a deal on a better than average supply.  I would look for a quality lab supply thats being sold by a reputable dealer that has some fixable issue.  You'll likely save a lot. Older supplies rarely have parts in them you can't buy yourself. There also you can get advice here. When you see a unit being sold on ebay, look for its service manual and download and read it.

Yes, older supplies are a gamble and often they are less convenient to use - for example, mine weighs a lot, hums noticeably when its on, (but doesn't need a fan) and because of its weight, is kind of a pain to move between my two temporary work bench areas.. but that fine-grained dial in is really nice to have. And its so accurate I never need to check it.

I have and as far as I can tell, its still within spec, its accurate to four digits.

A power supply is the one thing you use pretty much all of the time.
« Last Edit: October 11, 2018, 07:18:21 pm by cdev »
"What the large print giveth, the small print taketh away."
 
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Online tautech

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Re: beginner bench power supply question before buying
« Reply #8 on: October 11, 2018, 08:00:22 pm »
Doesn't the Rigol have an issue with a shared negative rail, that means they're not a properly isolated PSU.


Yes at some stage we all want a nice clean PSU, well down into the mV ripple, preferably sub mV and plenty of grunt as at some point we're gunna want it.
If I was setting up again, I'd skip anything SMPS and first get a single rail PSU and later a 3 rail unit.
These might be of interest:
https://www.siglentamerica.com/power-supplies/spd1000x-series-programmable-dc-power-supply/
https://www.siglentamerica.com/power-supplies/spd3303x-spd3303x-e-series-programmable-dc-power-supply/

Both are smart fan cooled and you have to push them some before the fan ramps up.
Avid Rabid Hobbyist
 

Offline joeyjoejoe

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Re: beginner bench power supply question before buying
« Reply #9 on: October 11, 2018, 10:27:46 pm »
Just picked up a SPD3303X-E. Highly recommend it. It can be unlocked to SPD3303X. I was using a SMPS (Gophert), and while it was a nice little unit, I should have just listened to those who said go for linear.
 

Online rstofer

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Re: beginner bench power supply question before buying
« Reply #10 on: October 12, 2018, 03:19:02 am »
Doesn't the Rigol have an issue with a shared negative rail, that means they're not a properly isolated PSU.

There is something odd when sharing a single ground between CH2 and CH3.  Rigol has a paper on proper connections. 

http://beyondmeasure.rigoltech.com/acton/attachment/1579/f-034c/1/-/-/-/-/DP832%20Proper%20Connections.pdf
 
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