Providing too much V and I ( current? )

[Hextejas]

Total newbie so please be nice.
The issue came up when I was asked to furnish a 8V power supply to charge a car vacuum.
I didn't have one, I had a 12, 14, 22, etc., so I answered no. and that made me endlessly curious .
I was hoping that the circuit could handle any range of voltages and/or currents and would only draw what was needed,
I know that cant be correct but i don't know why.
Would someone please point me in the right direction ?

Forever grateful.
George

[brucehoult]

If the voltage is correct then there's no such thing as "supplying" too much current, only too little.

The DUT will use the current it needs. If it needs more than your power supply is built to deliver then either the PS will start to output a lower voltage, or it will blow up (0V is also a lower voltage)

If you supply too much voltage then a DUT with simple design (e.g. purely resistive load) will take more current in the same proportion. e.g. if you give 12V instead of 8V then it may also take 1.5x more current than normal, which multiplied together means 2.25x more power consumption and heat in the device. Some might handle this, many will fail.

Pure excess voltage can also destroy some devices, even at low current.

And of course some smarter devices will have their own active voltage regulation and/or current limiting and work just fine.

[Zero999]

If the voltage is correct then there's no such thing as "supplying" too much current, only too little.

The DUT will use the current it needs.

That's true, but 8V is very close to the full charge voltage of two lithium ion cells, so it's possible it requires a battery charger, rather than a dumb 8V power supply. If so, then it will need to limit the current, depending on the battery capacity and voltage. Connecting it to an 8V supply, which is not current limited might blow it up.

[brucehoult]

If the voltage is correct then there's no such thing as "supplying" too much current, only too little.

The DUT will use the current it needs.

That's true, but 8V is very close to the full charge voltage of two lithium ion cells, so it's possible it requires a battery charger, rather than a dumb 8V power supply. If so, then it will need to limit the current, depending on the battery capacity and voltage. Connecting it to an 8V supply, which is not current limited might blow it up.

Absolutely!  You'd be crazy to use lithium cells without a proper charge controller, either built into the pack, or in an external charger.

We don't know which is the case here.

[Zero999]

If the voltage is correct then there's no such thing as "supplying" too much current, only too little.

The DUT will use the current it needs.

That's true, but 8V is very close to the full charge voltage of two lithium ion cells, so it's possible it requires a battery charger, rather than a dumb 8V power supply. If so, then it will need to limit the current, depending on the battery capacity and voltage. Connecting it to an 8V supply, which is not current limited might blow it up.

Absolutely!  You'd be crazy to use lithium cells without a proper charge controller, either built into the pack, or in an external charger.

We don't know which is the case here.

It's possible the original poster requires something like this, but I can't be sure without more information: vacuum cleaner make/model, battery capacity etc.
https://energylightbulbs.co.uk/replacement-8-4v-car-charger-for-rechargeable-flood-lights-torches-battery?utm_source=google&utm_medium=cpc&utm_campaign=Smart+Shopping&utm_id=12775947335&gclid=CjwKCAiAlJKuBhAdEiwAnZb7lc6t1MkKP1gGx3mExrCpq1VUkL4mgZgjjn7N6F25qSuc_z_q41A9_hoC-6AQAvD_BwE