电池耗尽的情况下，即使接入外接电源，树莓派也无法开机

[njbinbin]

按理说，作为UPS边充边放，接外接电源后应该优先保证设备供电的同时，再给电池充电，电池耗尽时，接外部电源也开不了机，只能将树莓派与UPS板分离单独供电和充电，等电池有电了再重新关机连接板子，作为UPS的意义就下降了呀。要么就只能关闭电源等待充电到一定程度再开机，这段时间无法使用树莓派。。。

[njbinbin]

又做了些测试，发现只要是在电池耗尽状态，再接入外部电源，电池也充不进电，树莓派也开不了机，放几个小时都是这个状态。把开关关掉至少充五分钟电再开，才能进入边充边放状态顺利开机。我不懂硬件，但感觉这里的逻辑应该是这样的：外部电源供电时，稳压后直供负载，同时给电池充电（正规UPS应该都是这样工作的，否则也不会标注0延时切换）。而这块板子给人的感觉是外部电源先给电池充电，再通过电池给负载供电（不存在切换过程），而耗尽电的电池电压不足，无法提供负载开机而白白消耗，如果是这个原理，应该读取电池电压，达到一定阈值时才对外供电。看过一块专业的UPS板是这么介绍的，但是价格太贵了。。。

[njbinbin]

大家都关注自动关机，通电以后的自动开机就没人关心吗？

[njbinbin]

用了个折衷的办法，外部电源接UPS板的同时，再同时接树莓派的电源输入口，这样树莓派同时从排针接到UPS电源，和从USB接入电源。测试了一块板子，似乎可以工作，但另一块板子就没那么幸运了，固定排针的热熔胶全化了，电池烫到快爆炸了。。。还好发现的早。然后，它就罢工了，RPI UPSPack字下面带散热片的芯片一插电就发烧，没有输出了

[njbinbin]

I gave up it...No matter how I tried it, even the battery with protective circuit, as long as the external power was cut off for a long time, the battery would be exhausted. Even the power supply was connected again, three led were flashing, and the pi could not be started. Only way is: turn off the switch, disconnect the pi and wait...I have put it and pi in a DIY box, which means they must be disassembled

[njbinbin]

One conclusion is that this UPS is not suitable for unattended use, even if an API interface is available to prompt and actively shut down the battery before it runs out, it also means that it will not be able to turn on again without going to the field - Raspberry pi does not have the ability to turn on remotely unless it designs the switch to be electronic and flashes off the load once the battery voltage reaches a threshold

[JokerQyou]

@rcdrones Care to explain possible reason? I've had the same concern bu don't have the time to test it. Maybe you can provide some kind of workaround?

[JokerQyou]

And, please note that newer versions of raspberrypi (3 & 3B family and newer) have the ability to boot from a GPIO pull-up signal, so theoretically it is possible to remotely boot them. Of course it would require designing an additional circuit (to act as the electronic switch) and would not be easy.

[njbinbin]

Thanks for the information of booting from GPIO pull-up signal~~~