Tenma 72-8345 bench power supply review

Review of a basic general-purpose cheap & cheerful bench PSU

[AureliusR]

@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.

[Nermash]

Another nice review Mike! I am impressed at how seemingly effortlessly
you analyze all these circuits on the fly.

[johnkapri]

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.

[mikeselectricstuff]

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

[mikeselectricstuff]

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.

[joshstube]

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!!!)

[TheEPROM]

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.

[randallsalyer]

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!

[figman]

watching your high quality videos every morning on a big screen is so much fun!

[mikeselectricstuff]

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.

[colt]

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!

[Gameboygenius]

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.

[mikeselectricstuff]

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.

[DanTheAppleMan]

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...

[alexwood]

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!

[williefleete]

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

[johnalexander]

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.

[compwiz]

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.

[mikeselectricstuff]

I use black marker - just didn't have one to hand

[siliconwitch]

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.