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  • Author Author: rjena
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Workbench Wednesday 08: Affordable Hand Held Power Supply Review

 

 

 

The TENMA portable power supply (72-2660) offers bench supply capability in a backpack friendly package. The single output is capable of 45 watts with up to 30 volts and 3.75 amps out. The built-in USB ports offer an easy way to power 5 volts Arduino or Raspberry Pi projects while limiting their current. See how this portable supply performs, the things the Bald Engineer likes about it, and the points to consider before buying.

 

 

 

Bill of Materials

 

 

Product NameManufacturerQuantityBuy KitBuy Kit
Bench Portable Power Supply, Adjustable, 1 Output, 300 mV, 30 V, 0 A, 4 A (72-2660)TENMA1Buy NowBuy Now
Bench Power Supply, Linear, Adjustable, 1 Output, 0 V, 30 V, 0 A, 5 A (72-2690)TENMA1Buy NowBuy Now
Test Lead Set, Banana Plug Stackable, Banana Plug Stackable, Black, Red, 914 mmTENMA2Buy NowBuy Now
Test Lead Set, Banana Plug, Test Clip, Black, Red, 914 mmTENMA2Buy NowBuy Now

  • I just bought this power supply (branded as Axiomet AX3004H from TME), it has no fan silkscreen and the inside looks the same. However, there are no longer two capacitors as mentioned in the video, the left has already been replaced by a 1k/10k resistor (don't remember as I just closed the unit). The output voltage when turned off is below -100 mV. I haven't used a scope to see the voltage slope when turning off the power supply.

  • Definitely a good little portable piece to have in a mobile kit.

  • Good review James. I liked the mod you did to fix the "off" feature.

    A power supply like this would be great addition to a portable tool kit for many technicians.

  • Question from YouTube:

    What happens when you set a current limit of say 100mA and attach it to something like a 1 ohm resistor? will it be able to regulate down to 0.1V(since the minimum voltage is 0.3V) or would it just go over the set current limit?

    I did not cover it in the video, but when the supply cannot satify the current or voltage limits, it just shuts off the output. I could only replicate this behavior when driving large currents through my electronic load. However, my other two bench supplies did the same thing. Turns out electronic loads usually have a large capactiance associated with them. So the ripple generated from that step probably tripped some voltage protections in all of the supplies. Since it was similar with all of the supplies, I didn't mention it in the video.

     

    With that said, I tried the example conditions provided. I set the electronic load to constant resistance of 1 ohm. On the 72-2660 Tenma portable supply I set its voltage to 1 V and current to 0.1 A. Almost immediately after turning on the supply, it shuts itself off. I wasn't happy with "almost immediately," so I grabbed my scope. The yellow trace is the voltage output of the Tenma supply and the orange trace is a current probe.

     

    image

     

    It takes about 200 ms before the supply starts supplying current. It ramps to about 140 mA and then starts oscilliating. It oscillates for a bit and then just shuts off. I need to look deeper into whether or not the current is really spiking up to 500 mA. The behavior could be related to the mod I did to force the output to 0 volts. Hmm.