squarewave

Re: Design Idea: USB > 30V Battery Power Supply
« Reply #20 on: November 21, 2020, 07:00:59 PM »
I made a little board to explore this idea and I learned a few things:

First, the DETN01L-15 SMPS does not put out +-15V at 34mA. It's more like 13.2V-ish and I saw it do 38mA without output protection kicking in. It's 15V at ~13mA and below that even higher. But that's not a show stopper for charging batteries (unless maybe the voltage goes too high in which case I'll definitely need to switch to using a PIC sooner than later). The switching noise is actually ~154kHz and not 100kHz stated in the datasheet. It's very full-wave rectifier looking and ~20mVpp.

Unfortunately I didn't know that you can't solder NiMH batteries so I was unable to test my circuit further. The pack looked ok at first running a load for hours (but did fall short of the 400mAH rating by quite a bit). But now it won't hold a charge. Battery voltage goes from say 10V to over 14.4V within only 15 minutes or so. So the internal resistance must be high. The pack is toast.

Apparently you MUST spot weld the nickel strips to the battery terminals. I'll need one of those little spot welding thingies on Ebay for $50. And a new set of batteries to make a new pack.


 

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