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I want to use a power bank to charge the battery of a toy car.

I used an old USB cable, connected the power lines only to a voltage step up circuit to step up the voltage from 5V to 8V, then connected the output of the circuit to the DC adapter interface to charge the toy (made sure I can measure the 8V at the adapter interface.)

The problem is, when I connect the setup to the car, the charging lamp is on for a few seconds then it goes off, when I disconnect the cable from the power bank and connect again, the same thing happens.

What could be the problem ? Should I use the data lines as well? Does the power bank rely on them?

Update : When I connect a shunt 1K ohm resistor, before connecting the adapter jack to the toy, the power bank remains on and I can see the 8V across the resistor. When I plug in the jack, the power bank shuts off and I can only see 5.5V across the resistor (which is really weird for me as the connection is parallel) Can you please help me what can the issue be ?

naserco
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  • once happened to my toy, it turned out that the cheap Chinese toy that I had was internally just shorting the wires. It could be your case and maybe your power bank is detecting the short circuit and turning itself off. I am just speculating it, but you should check it. – Sanmveg saini Oct 08 '20 at 05:57
  • how come they are shorting the wires and yet the battery is charged ? – naserco Oct 08 '20 at 06:52
  • What is the toy? How is its battery normally charged? – Bruce Abbott Oct 08 '20 at 07:25
  • it's a mini beach buggy, normally charged through a power supply – naserco Oct 08 '20 at 07:27
  • USB negotiation failure with your step-up? What current are you expecting from he power bank? e.g. what does the usual PSU provide? –  Oct 08 '20 at 12:25
  • the usual psu provides 600 mA , the power bank peovides 1A. It's not the step up, as I tried it with a resistance and a led and it works and doesn't shut off. – naserco Oct 08 '20 at 19:16
  • This is presumably a duplicate of [Powerbank voltage drop after while](https://electronics.stackexchange.com/questions/376417/powerbank-voltage-drop-after-while) or if not, then absent any *engineering detail* of the failure it is still an off-topic *product usage question*. – Chris Stratton Oct 09 '20 at 03:18

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I agree that the power supply is probably detecting a short and shutting itself off. Another option would be the opposite, the load might not be sufficient to keep the power bank on, you could try increasing the load by adding a resistor.

Giorgio
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  • ok, will try that – naserco Oct 08 '20 at 06:52
  • I tried adding 100 ohm in series, but same issue happens – naserco Oct 08 '20 at 21:10
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    Not a short, insufficient load. You need the load resistor in *parallel*. A series resistor would make things worse, and mean you basically weren't charging at all. – Chris Stratton Oct 09 '20 at 03:17
  • @chris, yes I connected it in parallel as per the update in the body, the power bank remains on while not charging the toy, but shuts off 30 seconds after starting to charge – naserco Oct 09 '20 at 05:03