EEVblog #30 – Jaycar Bench Lab Power Supply ReviewPosted on September 11th, 2009 26 comments
Dave checks out an el-cheapo Jaycar lab power supply. What do you get for 150 bucks?
(Something went horribly wrong with the camcorder and the end summary didn’t get recorded, oops. It gets a thumbs sideways. Would have been better if it had better resolution on the adjustments, no overshoot, and a load button)
I think my fellow fans will agree:
The post ALWAYS ends too soon.
Hey I really liked how you analyzed the product. I have only done 1 electronics course, but I was wondering what did the shunt suppose to do?
Also when it comes to power supplies what is a bleeder resistor?
The shunt resistor is used to measure the output current, that is displayed and used for current limiting.
A bleeder resistor is a resistor placed across a (usually high voltage) power supply so that when you turn the power off the charge on the filter capacitors is dischared quickly. It’s a safety thing.
Wow, that was useful. I was thinking about buying a bench supply and now I think I’ve found my match.
When watching you video I wondered about this PIC and the apparent ISP port which in my opinion would make this supply an optimal candidate for modification. What do you think? Do you have any ideas? Adding RS232 or something? Improving some aspects of performance?
Watching your teardown and commentary is very illuminating. Dave, I’m guessing that you’re correct about the two different design teams for the boards. To further that thought, I would guess that the same display/micro board is reused on other higher-end products which would allow them to produce greater quantities and keep the costs down. The supply board did seem rather low end except for those multiturn pots. Possibly their calibration procedure is that precise? Please keep these kinds of videos coming.
I love your blog, how you described the different pots is utterly hilarous!!
I only limited experience with power supplies. I saw you mentioned constant current mode. How does it work? What applications is it used for? And where can I find out more?
Thanks Mr. Jones
Constant Current mode is primarily used for protecting the circuit you are powering.
When you power up a newly designed or built board for the first time, that power supply is capable of delivering a lot of current. And if there is a fault in your circuit (SCR latchup for example) then you risk destroying components with excess current.
If you estimate your circuit is going to draw say 100mA, you would initially set the current limit to say 150 or 200mA (you do this by shorting out the supply and adjusting the current knob). If there is a fault or short then the supply will limit at 200mA and your circuit is usually safe.
The other use is for circuits or components that actually require a contsant current. LEDs are one example of this. A 1W Luxeon might need 300mA for example.
I have to agree with my predecessors, your blog is great.
I really enjoyed episodes like this one, where you take things apart and “inspect” them. I also loved videos about electronic and product design and also the two episodes about job interviews.
Can’t wait for the next video.
Yes, it is really sad to be waiting for DAAAYYYSSSS and then the blog passes too fast.
Clearly you need to purchase one of those $275 scented Monster power cables to enhance the lackluster out-of-the-box olfactory performance of this device.
I might suggest “008 toasted mica” for you for that old-school smell rather than “117 passion fruit” or “194 tahitian vanilla”. ‘Cuz frankly, all the new 100-series scents are for suckers.
FYI for cheapskates who can do with half an amp less, Dick Smith have a sale on at the moment for their 2.5A lab power supply (Q1770), its $99.
Since you just reviewed a power supply, what are your thought as using a computer psu as a bench power source?
I’ve used a computer psu as a bench before and its nice to have all the current and the current protection, yet I do not have the equipment to test for voltage overshoot and detecting voltage fluctuations.
I loved this review! It’s very informative to see what goes into a cheap power supply like this.
I myself am wondering what kind of power supply should be my first. So far, I’m using AA and 9V batteries and am running into their limits.
Should I buy something cheap like this one? Or would something even simpler be good for starters? I’d like to get one that I won’t outgrow for a while without breaking the bank.
Power Supplies are the ideal DIY project.
Look around, plenty of circuits and magazine projects out there.
Great for learning, and you can make exactly what you want.
Most electronics hobby work does not need a large 30V 3A range for example. Simple fixed supplies of +/-3.3V, +/-5V, +/-9V etc are the most handy.
I’ve got one of these for example:
It’s one of the handiest supplies I have, and being powered from a plugpack it’s safe for beginner to build.
Circuit is here:
As Dave said, building a PSU is the ideal beginners project. Download the data-sheet for the LM317T, & build the sample circuit from the first app-note. I suggest starting with one that’ll do 1.25V to 15V or so. It’ll be pretty easy to get going, & you’ll learn a lot about construction techniques.
Nice review, but the price quoted ($150) is either a trade price or is from somewhere other than Jaycar.
Jaycar are charging $229 retail. (http://www.jaycar.com.au/productView.asp?ID=MP3086)
If they really are making 60% or more on them, I’d like to know how they justify stocking the fart machines and other junk that “keep them in business”.
Correct, $150+GST is the wholesale price from Electus (Jaycar’s wholesale division). Anyone with an ABN number can get a cash account with them.
They need to sell the fart machines because hobby electronics doesn’t bring in enough money for Gary Johnston to maintain his Ferrari and F4 Phantom fighter jet hobbies.
FYI Tricky Dicks have a 30V 2.5A supply on sale for $99 retail at the moment, Q1770.
Would have been good to review the performance of the supply (in addition to the noise and power-on spike observations that you made): ripple, voltage and constant current regulation, meter accuracy, worst-case temperature rise, etc.
For example, I have the 30V/2.5A DSE bench supply which is good value for $100, but it’s ammeter is only about 10% accurate, voltmeter is better but still not great (about 3%).
Just curious but suppose I got in there and split off the signal wires from the mains wires where they are tied together. Would that have any measurable effect on performance or noise?
Jeremy D: I’ve got one of those DIY benchtop power supplies that Dave (admin) was suggesting.
No fancy screen or current limiter, but quite a nice supply for low current hobbyist use, it’s the only power supply I have..
I bought mine as a kit from Altronics but it looks like they replaced it with a newer product (http://www.altronics.com.au/index.asp?area=item&id=K3250).
Mr. Jones, what is the purpose of the relays in the power supply??
I have the same power supply, but mine is unfortunately broken due to reciveing back emf from a tesla coil i was running.
quick question, what value is the resistor just above the last potentiometer? (R17), as this has burnt out and i just replaced it with a 1k resistor.
i cant find the problem with it, ive replaced all op-amp ic’s and the 2n3055 transistor on the back and checked all transistors. Ive asked jaycar for schematics or a repair guide but they said they cant find anything.
Jordan — tough luck on the Tesla coil killing your supply. I am part of the Tesla Orchestra in Cleveland, and we have plenty of experience with coils killing things (namely themselves).
You still working with coils?
Also in regards to bleeder resistors, super important for coils
We had one of our Jaycar MP3086 power supplies blow up on no load. We switched it on without any connections, ready for use that day and there was a bang and a burning smell. The mains input fuse had also blown.
We bought this blighter just under 2-years ago and it has survived daily use until now.
One of our technicians removed the outside cover and we could see the black mark on the power supply PCB. The mark was from a cheap looking 104 (the marking was still just visible) brown circular ceramic cap located across the relay switched low voltage AC output from the mains transformer. This cap had turned black and split in half. Looking at the physical size, it was probably only a 50 volt DC rated fellow.
As this supply does up to 30V DC output, the raw AC must be close to the rating on this ceramic cap. With switch off/on glitches from the mains transformer, it was only a matter of time before this failure happened.
I understand the reason for the cap as it is meant to be a low impedance for RF coming in/out of the mains input.
We replaced the cap with a 102, 2KV of the same physical size, replaced the fuse and Bob’s your uncle.
We then replaced the same cap in the other working MP3086 supplies in the place, just in case.
Hope this info helps other users of this model power supply.
I enjoy your videos very much.
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