Products > Test Equipment
Tenma 72-8695 2 x 32v 3A + 5V @ 2A mini-review / teardown
mariush:
Tenma 72-8695
http://ro.farnell.com/tenma/72-8695/power-supply-2-x-32v-3a-5v-2a/dp/1836057
TENMA - 72-8695 - POWER SUPPLY, 2 X 32V, 3A + 5V, 2A
POWER SUPPLY, 2 X 32V, 3A + 5V, 2A
Power Supply Output Type: Adjustable
No. of Outputs: 3
Output Voltage: 32V
Output Voltage 2: 32V
Output Voltage 3: 5V
Output Current: 3A
Output Current 2: 3A
Output Current 3: 2A
Length: 380mm
Width: 600mm
Height: 245mm
Plug Type: UK / Euro
Supply Voltage Typ: 220V AC
Price: 711 RON + VAT (about 130 UK pounds + VAT)
I was planning to buy a linear power supply for a long time and even started a thread here asking what should I buy.
I finally "bit the bullet" and bought this power supply from Farnell, and I chose this one for several reasons:
* the shipping from Farnell to my country is cheap (about 5$)
* being a EU seller, I would have less problems with warranty in case it's a dud
* it's a dual output power supply at just a bit extra compared to single output power supplies
* the outputs can be joined together to get a 64V 3A output
* Last but not least, this model looks very much like the Uni-T UTP3703
Now, I have a Uni-T UT61E multimeter which I like, so I was attracted to this model because of this, but just before I bought this one, I was told by a Uni-T importer that the company decided to stop working with the factory that produced their power supplies, due to inconsistencies in the build quality.
He told me that the supplies are fine but some of the issues he noticed were that some models didn't have proper grounding, or some buttons latched as long as the buttons don't get stuck, it's properly grounded, doesn't have wobbly feet or the outputs are sometimes split.
Well, I am pleasantly surprised by this power supply.
The power supply came with both a UK style power cable and a regular EU power cable and a small 4-5 page booklet which basically is the manual that's listed on Farnell's product page.
The power supply was powered ON (power button pressed inside the package) so it was probably tested before shipped or when it was received by Tenma from the factory.
Buttons, Knobs, Front
Led digits display, bright red... not too bright to be annoying.
The ground in the front is properly connected to the ground of the mains, and by default the metal link connects the ground and + of the secondary side. With this metal link attached, (as far as I can tell, I only had a few minutes to do basic tests) it's not possible to adjust the voltage of the second output, no matter if the power supply is in tracking mode or not.
When the Tracking mode is activated (button is pushed), the second output tracks the adjustment of the first. I'm not sure (didn't test) if the current limiting works when both are linked, or which current limit is respected (I assume the first output's current output limit)
The Measure buttons switch between showing the volts or amps for each output. The output needs to be shorted out to adjust the current limit but a rough amps level can be set just by looking at the dot on the pot ... the Amps pot is not the multi turn kind.
The volts adjustment pots are 10k ten turn pots (or something like that), the Amps knobs are regular pots. The volts adjustment is pretty fine, can turn it a bit before going up or down 0.1v.
Volt Pots are made by... I don't know... there's load of them on Alibaba ... probably Vatronics : http://www.vatronics.com/Upfiles/down/201171847057.pdf
Case, Feet
Feet are screwed in with thread lock, case is thick metal with nice big openings on the side for ventilation, the strap at the top is also attached with screws.
Mains, Grounding
Transformer, front jack, back connector properly grounded.
Transformer is tied down with some nice screws, I don't see it getting loose of vibrating.
Power transformer, power board
A toroidal transformer is used - I'm not sure of it's maximum current power.
Two identical sections, each with:
* 4 diodes 1N5408 (3A max) : http://www.next.gr/components-datasheets/1N5400.pdf They're spaced pretty well so I'm not concerned they may overheat the capacitors near them
* HA17324A quad op-amp : http://documentation.renesas.com/doc/products/linear/rej03d0674_ha17324a.pdf
* L7815CV 15v linear regulator for the op-amps probably
* 3300uF / 50v 105c capacitor for each side
* BU406 epitaxial silicon transistors : http://www.fairchildsemi.com/ds/BU/BU406.pdf
* 2SC3281 NPN transistors (no-name on them) attached to the back heatsink with small to-220 heatsink in front of them (assume these are for current regulation)
* Songle SRG-24 relays (four) : http://songle.com/pdf/20085271545271000.pdf
* four adjust pots at the top for each side
There's an additional bridge rectifier on the right along with a capacitor but I'm not exactly sure what it's for... maybe it's for the front panel meters.
I couldn't see and I didn't check the actual output jacks. Other than seeing that the green jack is grounded to mains, I'm not sure if they have protection (diodes) and if they're properly soldered there.
The buttons in the front seem to be good buttons with good switches and replacing them should be easy if they latch.
There's a whole bunch of wires on that board and I didn't want to mess with it now, didn't have time to go in detail on that small board, sorry.
Front display, Meters
Plain simple meter chip with led digits output
* ICL7107CPLZ in PDIP 40 packages : http://www.intersil.com/content/dam/Intersil/documents/fn30/fn3082.pdf
Should be easy to mod if someone wants, to get it to refresh faster (sacrificing accuracy) or anything else.
5v output
The 5v 2A output is performed by two L7805CV regulators linked together and screwed down on the bottom of the metal case. There's a 470uF 16 capacitor and a diode for protection on the jacks.
Other notes
It seems like a very simple design. I particularly like that:
* the boards that I see are not bodged.. I don't see anything obvious as fix or bodge.
* all wires are soldered to the boards - I don't see connectors with glue on them, no risk of cables being detached during shipping . And they're all tied nicely at various intervals.
* all capacitors are Chang ( http://www.huaweiec.cn/index_en.asp ) - while not a brand name, they're not exactly huang lo, crap no-name or rebadged caps.... they're owned by Huawei and I've seen them in various equipment... basically it's refreshing to see they didn't just grab a bags of capacitors and threw them on the boards.
* some of the chips are brand name (or very good fakes) and they didn't bother erasing what's written on the chips.. makes it easy to fix it if something happens.
* lots of heatshrink where it should be.
* Power cables are nice, thick, and they provided both UK and EU cables.
Not liking
The only flaws/ not so nice that I see on a first look is :
* the transformer doesn't have power ratings on them
* not really a flaw, but some of the wires going into the boards have a bit too much un-insulated area. Seems like the plastic melted or shrunk due to heat when wires were soldered
Also, I'm not sure that I like that one of the NPN transistors is so close to the main power jack. It is properly insulated, with heat shrink and so on but still.
Other notes
* I would have liked to see 10 turn pots on the amps knobs
* When shorting the output, it seems the amp limit goes up to about 3.2 A
Pictures below :
If you want the hi-res (~ 3200x2500) download the pack here : http://savedonthe.net/a/tenma_72-8695.zip (if the link goes dead in the future, pm me and I'll send them to you)
(edited the post to remove the part about fuse not used, it was incorrect. It is connected/fused properly)
mariush:
Second set of pictures (exceeded 5 MB post limit with the first) :
Monkeh:
--- Quote from: mariush on September 25, 2012, 05:50:39 pm ---!!! I may be wrong, but the fuse in the power connector doesn't seem to be connected - the power supply may have been designed with the assumption that it's going to be sold in UK, and in that case the cable has its own fuse. See pictures... I'll double check when I have more time.
--- End quote ---
You're wrong. The fuse is used.
You do not use the fuse in the plug to protect the equipment. Please don't ever make that assumption.
I don't like the 5V output at all. Nasty little hack, and no option on the ground reference. But easy to improve.
mariush:
I know the fuse on the UK power cable is not to protect device, but rather the house wiring and other electric equipment.. due to how the wiring is done in UK.
Like I said, I'll double check the fuse to see if it's used - I just saw the metal contacts unused (see picture) and assumed... I have some work now and can't do it right away.
What's wrong with the 5v output? It's just to 7805 connected together for 2A. Kind of hard to screw it up...
PS. Ah, nevermind. I see it now it is fused ... looking at the picture I can see where the contact with the cable is and where the actual cable inside goes, at the other end of the fuse. It's fused.
Monkeh:
--- Quote from: mariush on September 25, 2012, 06:24:10 pm ---I know the fuse on the UK power cable is not to protect device, but rather the house wiring and other electric equipment.. due to how the wiring is done in UK.
--- End quote ---
It's to protect the cable, nothing else.
--- Quote ---What's wrong with the 5v output? It's just to 7805 connected together for 2A. Kind of hard to screw it up...
--- End quote ---
Ugly implementation, forced earth reference, and the packages are subject to stress from flexing of the chassis (which is not meant to have ICs secured to it!).
Navigation
[0] Message Index
[#] Next page
Go to full version