Mike you just: . -explained your purchase, -did an "unofficial" tear-down, -Identified most of the potential concerns (both with build construction AND performance) -MODed the display! . All in 30min!! . It would have taken Dave Jones a Week to do all that! . (I still love you Dave!!!)
I like these bench power supplies alot! Also, in later (i.e. current) versions, you can actually push on the knobs to select the digit you want to adjust. That's a nice bonus so you don't accidentally scew your hand off. EDIT: Oh, and in the newer versions the set current is acutally displayed when the output is off.
@11:14 I just noticed with the light 10k load, you have it set to 3.3V but it's giving you 4V! So the overshoot is still there it just takes longer for it to settle down.
I have been looking for a new bench supply and found that this unit seemed to fit the bill but ,I was concerned about the granularity of the v/c adjustments. You have certainly answered my questions. Thank you very much!
I know this is an old post but I have the same model power supply , maybe a newer revision but im able to push in on the knob and select witch digit I want to increase or decrease. Bet they just had a bunch of complaints about it so they added the new knob. Anyway thanks for the great review!
When it goes into the unstable mode that you can hear it can blow the power transistors on the primary side as well as the fuse, some times it is just the fuse that goes. Luckily the power transistors are easily available and I have stocked up on them as I have caused them to blow several times, I even had a fuse physically explode once. I have not seen any coloration in the loads the PSU does not like.
We had something similar to this at work. I can confirm that those front dials were the first casualty when someone opened a cupboard and it fell on its front! We replaced it with a B&K 9200 series (£1000 600 watt psu, so not exactly in the same league lol). The B&K controls are low profile and protected by a rubber bumper. Much better design!
Seems that in the last couple of years, Tenma listened and fixed several of the issues.. metering is faster and the jitter has been fixed on my 20V@5A model, encoders allow setting any of the digits, set current shows whenever you tweak it's encoder (regardless of output being on or off). I think that covers all your main gripes :) I've only had mine for maybe half a year.. possibly slightly longer.. they didn't fix the binding post gripes though.
1) it only has 2 connections so is definitely an inductor. 2) Yes you are correct - I did this in a hurry & only noticed this after editing and couldn't be bothered to correct it.
I've got a rebranded 20V 5A one from maplin which has single turn pots instead of encoders, and it is the most tremendous pain. 1V is about 15 degrees turn, so it's really challenging to set the output precisely. The readout refreshes much faster too, and it is incredibly precise with much less noise and overshoot than yours. I always seem to get the extremes of good and bad...
i've rebuilt an old 60's era linear supply using modern components and voltage reference etc, i've given it 5 presets using the existing radio buttons with multiturn trimpots for setting, 6 constant current settings again using radio buttons (handy for testing most LEDs 100uA - 40 mA and i've trimmed the shunts a bit). considering its a supply i built myself its pretty good and it'll supply a few amps
I've never looked at the difference made by surfaces (but do have a Thermal imaging camera on the way...!) I would normally put some black marker on a heatsink but didn't have one to hand.
11:20 (During the 3.3V overshoot test, no load) Actually, that looks like the same overshoot as with the load, only with a slower decay and not jitter. It still seems to peak at ~4V.
For folks looking for inexpensive used gear, don't forget to consider old variable linear supplies. I have a Heathkit from the 70s, good from 0-30V @ 1A with adjustable current output, and it has great stability. All I had to do was swap out the original pot with a 10-turn bournes from ebay and it was even better for more precise work.
I've got a similar supply, the Maplin N27GG. Has the same problems but a couple aspects that better the model you have. Bit more bodgey in the build quality though, They've crammed quite a few boards and jumper wires in there. I did a little review/tear down on my blog a while back so I might go back to it and see if I can get the update running on it faster like you did.
Not seen those - there are some long ones Farnell 211-2490 and 1538516, which are long enough to hold the base to stop spinning. There are also some doubles, but the centre earth makes this less useful.
I have an issue with one of these PSU´s. My output seems to be constantly on, you can push the on/off switch an the display also indicates, that output switches, but on the output-terminals there´s always current. How is the output switched? Any ideas wich part can be faulty. besides this issue it seems to work fine, but it´s annoying not be able to switch output.
I had one of those power supplys, it was the 20v 5a one, bought it in maplin for about €100. It had linear pots instead of the stepped ones in yours and i think the update speed and accuracy was better. I found out the hard way that the primary heatsink was live. Sadly it blew up while i was making hydrogen and oxygen. It was in constant current mode at 15v 5a and suddenly the current went up to 9a and 20v then after making alot of noise i saw a large flash and it stopped supplying any voltage.
thank you very much, i was always wondering if these are any good. here in germany, your unit goes as 'Manson NSP 3630' for 80€, so sadly not as cheap as you got it
I have been noticing a humming noise at times when you press the 'on' button, as I hear in many electronics, just wondering if this is something you noticed (I did only observe this after you added the resistor to increase the LCD update speed).
Mike.... been waiting patiently for your hack vid... cough. I've got three of these in the 60V variant and would love to try any of your mods. Cheers Peter
Hi mike, I've recently discovered your page. Been watching that ozzy bloke for some time. I'm a computer guy but I'm getting into working with micro-controllers etc, this meaning I'm also learning some electronics, I do have some background in the area but not in a professional way. Can you recommend a cheap option for a desktop PSU (I'm looking for something with a current limit and two isolated outputs) and a cheap option for a scope. Ive looked on ebay and people are always saying there are cheap scopes on there but I rarely see anything. I do have a comprehensive computer setup, Are there are decent USB devices that would work for my needs, I'm working with Rf or anything like that. how much was this supply? Great vids, thanks.
I could never do that, I need accuracy! the last power supply I bought had the same problem and altering the RC oscillator clock on the main IC sorted it out. you have to get it fast enough to respond with the dial but slow enough to not jitter
I had (still have) such a PSU, that accidently got drenched in ferric oxide and saltwater. Didn't even blow a fuse, and after a little while with qtips and an old toothbrush it worked fine. Btw, mine is rated for 30minutes duty, but it runs fine for a week. =P
I actually soldered on the ISP header and tried to dump the code. However the lock bits are sets, so no code download :(. May trace the PCB and see if I dare to throw out the official firmware...
A small hint: There are some revision of the PSU on the market. "old ones" do have a real potentiometer instate of this decoders. I was a little bit sad, when I ordered for a company more of does (being happy with the pots) and then got this revision with decoders...
I really enjoyed this. But I'm a bit confused: is there any *dis*advantage to the update rate change you made adding the resistors? It's not like it would have increased the cost of manufacture at all, so I'm trying to work out why Tenma don't do this themselves...
I wanted to make a couple of corrections on your video. 1). That transformer with the zip-tie on it I don't think is an APFC, I think it's some kind of choke or step-down transformer for mains AC. 2) That little transformer just below the big power one is the gate driver for the power mosfets and not for stand-by power. I think the SB transformer is that small one is the lower-left.
I have to say that the jitter would drive me to distraction, seeing it in my peripheral vision jumping about. I would probably end up duct taping a 7107 based display over the LCD haha
@donpalmera @cemailumeu I hate houses wired this way. Mine doesn't have solid wire, instead it has stranded wire and they made some messy color coding, seems like they ran out of a certain wire color many occasions. I have a good earth connection, though.
As an electronics novice, I still found this video interesting, and I watched it in its entirety... (By the by, I was sent over by Aussie50). I was surprised that the off /off indicator was such crap. Fancy crap, but still crap. I was also surprised that you blithely dismantled a brand new unit, but on the other hand, it was a thorough review and I'm a new sub to your channel. Would it have been difficult to add an on/off led? Or is that something you are doing later?
One thing to be aware of is that infrared thermometers are COMPLETELY USELESS if you need to measure most metallic surfaces (i.e heatsinks). Infrared thermometers operate at approximately 10um wavelength, and at that wavelength, most machined aluminium surfaces (and stainless, have not tested much else) are essentially mirrors, with ~80%+ reflectivity. If you look at an aluminium surface with an infrared camera, it actually behaves much like a glass mirror does at the optical wavelengths.
Ah, I see. I misunderstood you in the video, where you appeared to say that there wasn't significantly more jitter (just a faster update rate, which made the numbers appear to change more).
SuperBoobaloo Did you end up calabrating it? I have the same issue and I am about to return it if I can't figure it out. Can you please provide some assistance.
I see your reasoning and I can't fault it, but as I said I'm a novice. As a general rule, I don't buy Chinese electronics unless it is a low power dc device. Being a diesel mechanic of 30 years experience I can handle mechanical issues, as a tinkerer, I can handle electrical appliances and power tools and some computer repair as well; but for me, opening a power supply like that, or very nearly any electronic device is like viewing a Chinese movie without subtitles. Interesting but...
Why would anyone NOT take a new piece of kit apart....? Seriously with all the junk coming from China, you take your life in your hands if you plug something in without first checking it has a reasonable standard of safety. I'll probably do a vid on hacks at some point.
Chassis ground is absolutely useless on switch modes, the only real centre grounds are on linear psu's and I'm not sure of most of them. I'm talking about the ability to have true + and - rails..
Mike you just:
.
-explained your purchase,
-did an "unofficial" tear-down,
-Identified most of the potential concerns (both with build construction AND performance)
-MODed the display!
.
All in 30min!!
.
It would have taken Dave Jones a Week to do all that!
.
(I still love you Dave!!!)
Another nice review Mike! I am impressed at how seemingly effortlessly
you analyze all these circuits on the fly.
I like these bench power supplies alot! Also, in later (i.e. current) versions, you can actually push on the knobs to select the digit you want to adjust. That's a nice bonus so you don't accidentally scew your hand off.
EDIT: Oh, and in the newer versions the set current is acutally displayed when the output is off.
watching your high quality videos every morning on a big screen is so much fun!
@11:14 I just noticed with the light 10k load, you have it set to 3.3V but it's giving you 4V! So the overshoot is still there it just takes longer for it to settle down.
I have been looking for a new bench supply and found that this unit seemed to fit the bill but ,I was concerned about the granularity of the v/c adjustments. You have certainly answered my questions. Thank you very much!
I know this is an old post but I have the same model power supply , maybe a newer revision but im able to push in on the knob and select witch digit I want to increase or decrease. Bet they just had a bunch of complaints about it so they added the new knob. Anyway thanks for the great review!
When it goes into the unstable mode that you can hear it can blow the power transistors on the primary side as well as the fuse, some times it is just the fuse that goes. Luckily the power transistors are easily available and I have stocked up on them as I have caused them to blow several times, I even had a fuse physically explode once. I have not seen any coloration in the loads the PSU does not like.
We had something similar to this at work. I can confirm that those front dials were the first casualty when someone opened a cupboard and it fell on its front! We replaced it with a B&K 9200 series (£1000 600 watt psu, so not exactly in the same league lol). The B&K controls are low profile and protected by a rubber bumper. Much better design!
I have the same one! Mine's branded "Mason". Glad to see that the sense wires are easily accessible - I think I'll add a local/remote switch. Thanks.
Seems that in the last couple of years, Tenma listened and fixed several of the issues.. metering is faster and the jitter has been fixed on my 20V@5A model, encoders allow setting any of the digits, set current shows whenever you tweak it's encoder (regardless of output being on or off). I think that covers all your main gripes :) I've only had mine for maybe half a year.. possibly slightly longer.. they didn't fix the binding post gripes though.
1) it only has 2 connections so is definitely an inductor.
2) Yes you are correct - I did this in a hurry & only noticed this after editing and couldn't be bothered to correct it.
It is a bit more jittery - this may be improvable using an external oscillator on the DVM chips. May also have a small effect on linearity
I've got a rebranded 20V 5A one from maplin which has single turn pots instead of encoders, and it is the most tremendous pain. 1V is about 15 degrees turn, so it's really challenging to set the output precisely.
The readout refreshes much faster too, and it is incredibly precise with much less noise and overshoot than yours.
I always seem to get the extremes of good and bad...
i've rebuilt an old 60's era linear supply using modern components and voltage reference etc, i've given it 5 presets using the existing radio buttons with multiturn trimpots for setting, 6 constant current settings again using radio buttons (handy for testing most LEDs 100uA - 40 mA and i've trimmed the shunts a bit). considering its a supply i built myself its pretty good and it'll supply a few amps
I would love to see a video about that I love vintage computers.
I've never looked at the difference made by surfaces (but do have a Thermal imaging camera on the way...!) I would normally put some black marker on a heatsink but didn't have one to hand.
11:20 (During the 3.3V overshoot test, no load) Actually, that looks like the same overshoot as with the load, only with a slower decay and not jitter. It still seems to peak at ~4V.
For folks looking for inexpensive used gear, don't forget to consider old variable linear supplies. I have a Heathkit from the 70s, good from 0-30V @ 1A with adjustable current output, and it has great stability. All I had to do was swap out the original pot with a 10-turn bournes from ebay and it was even better for more precise work.
@ 20:12
Backlight RGB Mod for output indication. ;)
Great Idea Mike! It would make a great video for you to show us how you do these mods!!!
I've got a similar supply, the Maplin N27GG. Has the same problems but a couple aspects that better the model you have. Bit more bodgey in the build quality though, They've crammed quite a few boards and jumper wires in there. I did a little review/tear down on my blog a while back so I might go back to it and see if I can get the update running on it faster like you did.
Not seen those - there are some long ones Farnell 211-2490 and 1538516, which are long enough to hold the base to stop spinning. There are also some doubles, but the centre earth makes this less useful.
i have 1 of them but branded Maplins but i dont have a instruction book and unsure of it fuse in the plug can u help plz
I have an issue with one of these PSU´s. My output seems to be constantly on, you can push the on/off switch an the display also indicates, that output switches, but on the output-terminals there´s always current. How is the output switched? Any ideas wich part can be faulty. besides this issue it seems to work fine, but it´s annoying not be able to switch output.
I had one of those power supplys, it was the 20v 5a one, bought it in maplin for about €100. It had linear pots instead of the stepped ones in yours and i think the update speed and accuracy was better. I found out the hard way that the primary heatsink was live. Sadly it blew up while i was making hydrogen and oxygen. It was in constant current mode at 15v 5a and suddenly the current went up to 9a and 20v then after making alot of noise i saw a large flash and it stopped supplying any voltage.
Oh! thats really cool!
I thin there is a minimal or none output capacitor to minimimise the 30mv output noise
I use black marker - just didn't have one to hand
Hello. Is its earth strapped to the negative?
thank you very much, i was always wondering if these are any good. here in germany, your unit goes as 'Manson NSP 3630' for 80€, so sadly not as cheap as you got it
What is that rack mount box with the floppy and tape drive on your shelf behind yopu? looks very interesting! =)
I have been noticing a humming noise at times when you press the 'on' button, as I hear in many electronics, just wondering if this is something you noticed (I did only observe this after you added the resistor to increase the LCD update speed).
Are those Su'scon caps on the output? Ugh... pulled quite a few of them from monitors and TVs.
thanks Mike
Mike.... been waiting patiently for your hack vid... cough.
I've got three of these in the 60V variant and would love to try any of your mods.
Cheers
Peter
Hi mike, I've recently discovered your page. Been watching that ozzy bloke for some time. I'm a computer guy but I'm getting into working with micro-controllers etc, this meaning I'm also learning some electronics, I do have some background in the area but not in a professional way. Can you recommend a cheap option for a desktop PSU (I'm looking for something with a current limit and two isolated outputs) and a cheap option for a scope. Ive looked on ebay and people are always saying there are cheap scopes on there but I rarely see anything. I do have a comprehensive computer setup, Are there are decent USB devices that would work for my needs, I'm working with Rf or anything like that. how much was this supply?
Great vids, thanks.
I could never do that, I need accuracy! the last power supply I bought had the same problem and altering the RC oscillator clock on the main IC sorted it out. you have to get it fast enough to respond with the dial but slow enough to not jitter
I had (still have) such a PSU, that accidently got drenched in ferric oxide and saltwater.
Didn't even blow a fuse, and after a little while with qtips and an old toothbrush it worked fine.
Btw, mine is rated for 30minutes duty, but it runs fine for a week. =P
I actually soldered on the ISP header and tried to dump the code. However the lock bits are sets, so no code download :(. May trace the PCB and see if I dare to throw out the official firmware...
Do you have Tenma 72-7245? If so, can you do a demostrations of all the functions and features of it. Thanks
Remember the cover was off - noise is pretty minimal with cover on
He i got this one and the brand is called Manson and its 1V to 20V 5amp. I use it for a Slotcar-track, any tips? Thanks, great review!
quite a compact little unit!
Loved the video. Keep up the excellent quality. Me? I'd rather have a two output differential supply. Yes, it cost a bit more.
A small hint: There are some revision of the PSU on the market. "old ones" do have a real potentiometer instate of this decoders. I was a little bit sad, when I ordered for a company more of does (being happy with the pots) and then got this revision with decoders...
A re-cased Acorn A540
I really enjoyed this. But I'm a bit confused: is there any *dis*advantage to the update rate change you made adding the resistors? It's not like it would have increased the cost of manufacture at all, so I'm trying to work out why Tenma don't do this themselves...
I wanted to make a couple of corrections on your video. 1). That transformer with the zip-tie on it I don't think is an APFC, I think it's some kind of choke or step-down transformer for mains AC. 2) That little transformer just below the big power one is the gate driver for the power mosfets and not for stand-by power. I think the SB transformer is that small one is the lower-left.
you should bring the sense wires to the front.. with a connector....
Most scopes have ethernet these days, which has largely replaced GPIB and RS232 on test equipment
from memeory about 0.8v
I have to say that the jitter would drive me to distraction, seeing it in my peripheral vision jumping about. I would probably end up duct taping a 7107 based display over the LCD haha
Something perhaps went into thermal runaway?
@donpalmera @cemailumeu I hate houses wired this way. Mine doesn't have solid wire, instead it has stranded wire and they made some messy color coding, seems like they ran out of a certain wire color many occasions. I have a good earth connection, though.
Why a switching power supply if u need just 3 amps max?
Wouldn't a linear psu be a better choice?
+Nox665 He says why at 1:04.
i put black tape on heatsink when i mesure temperature
Cool!
That is a
BIG resistor !!
As an electronics novice, I still found this video interesting, and I watched it in its entirety... (By the by, I was sent over by Aussie50). I was surprised that the off /off indicator was such crap. Fancy crap, but still crap. I was also surprised that you blithely dismantled a brand new unit, but on the other hand, it was a thorough review and I'm a new sub to your channel. Would it have been difficult to add an on/off led? Or is that something you are doing later?
Do you still have the supply? Maybe it's repairable... PM me, I might be interested in it.
One thing to be aware of is that infrared thermometers are COMPLETELY USELESS if you need to measure most metallic surfaces (i.e heatsinks).
Infrared thermometers operate at approximately 10um wavelength, and at that wavelength, most machined aluminium surfaces (and stainless, have not tested much else) are essentially mirrors, with ~80%+ reflectivity.
If you look at an aluminium surface with an infrared camera, it actually behaves much like a glass mirror does at the optical wavelengths.
Ah, I see. I misunderstood you in the video, where you appeared to say that there wasn't significantly more jitter (just a faster update rate, which made the numbers appear to change more).
hah! Binding post adapter is genius! :)
You could start that youtube show, "Pimp my power supply" xD
I bought one of these but the output voltage seems to overshoot the set voltage by about 0.33 V. Has anyone else experienced this?
Oops. Didn't calibrate it. Hope it turns out to be the source of my woes...
SuperBoobaloo Did you end up calabrating it? I have the same issue and I am about to return it if I can't figure it out. Can you please provide some assistance.
Nah dont have it anymore, tried replacing the mosfets and various other power transistors with no luck.
To be clear, I meant no disrespect.
I see your reasoning and I can't fault it, but as I said I'm a novice. As a general rule, I don't buy Chinese electronics unless it is a low power dc device. Being a diesel mechanic of 30 years experience I can handle mechanical issues, as a tinkerer, I can handle electrical appliances and power tools and some computer repair as well; but for me, opening a power supply like that, or very nearly any electronic device is like viewing a Chinese movie without subtitles. Interesting but...
Why would anyone NOT take a new piece of kit apart....?
Seriously with all the junk coming from China, you take your life in your hands if you plug something in without first checking it has a reasonable standard of safety. I'll probably do a vid on hacks at some point.
Chassis ground is absolutely useless on switch modes, the only real centre grounds are on linear psu's and I'm not sure of most of them.
I'm talking about the ability to have true + and - rails..
/me only has one socket with an earth terminal in the whole house :/
So you want it to be as good as a more expensive one really? lol