Discharger build-Will this work.?

[missgoofy]

I want to build a discharger by using a micro usb charging pcb It will use a standard USB to Micro USB cord. So in theory the device to be discharged is connected with cable to the micro pcb board (mounted in an enclosure of course) and the +/- outputs of the board are either connected to really anything that will accept the power dump. I also think it might be a good idea to add a low voltage alarm of some sort. Ok, so hit me with questions and suggestions. (be nice )

 

[MikeMl]

Where does the heat go. I would expect you need a big heatsink.

I built a battery discharger ( for aircraft batteries) that included a 1200W resistor bank that glowed dull red, and got hot...

 

[missgoofy]

Oh, no I'm not trying to discharge that much at all. At most 3.7v to 5v lipo device. I could use 5v 20w bulbs and keep a fan on it to keep it cool. I'm just spit-balling right now.

 

[Tony Stewart]

A better description of your reasons to validate your assumptions is a good idea.

Is this to exercise the battery or overload the interface?

 

[missgoofy]

Exercise the battery, and I just don't have many devices that take micro usb to be charged. Doe that make sense.?

 

[upand_at_them]

Oh, no I'm not trying to discharge that much at all. At most 3.7v to 5v lipo device. I could use 5v 20w bulbs and keep a fan on it to keep it cool. I'm just spit-balling right now.

Power dissipated is V x I. Or I^2 x R. 5V at 1mA is very little heat. 5V at 500mA could destroy low power components. It all depends on how fast you want to discharge the battery.

 

[missgoofy]

Would an hour be fast.?

 

[Tony Stewart]

Have you confirmed the batteries will have a memory effect?

The ideal long term resting voltage is 50% SoC for LiPo minimum ageing.
Only Lenovo use this fact in their laptop charger design. AFAIK
Most Mfg ship cells ar 50% SoC

A 500mA load on 5V is 10Ω.

When using a halogen or tungsten bulb as a dummy load and you can't find the right R. Measure a few to future reference and keep in mind cold resistance is ~10% of hot.

e.g. a 300W 120V Halogen tube , Req= 48Ω ; R cold ~ 5Ω ( your mileage may vary )

Don't exceed the rated current of the contacts.

 

[missgoofy]

Wow, I just wanted to build something to discharge my power bank charger being that I don't have enough devices to just charge in order to discharge the battery bank. I just wanted to know if I could repurpose that micro usb board to do that. Apparently the short answer is no, so I'll just stop trying. Thanks.