# Safely replace a battery by dc power from 220v wall outlet

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#### techguy

##### New Member
I bought a vacuum-cleaner driven by battery, which lasts about 6 minutes.
I want to replace the battery in a way that I can safely use my 220v wall outlet to power the vacuum-cleaner.
The battery has 21.6 volt and 350 watt.

Is it possible to use something like this :
https://www.amazon.com/SUPERNIGHT-S...-Transformer/dp/B01LATMSGS?ref_=fsclp_pl_dp_5

I have very little knowledge of electronics but I think it is pretty cool if this is possible (safely).

#### Les Jones

##### Well-Known Member
350 watts is not a rating for a battery so do you mean 350 watt hours ? If so that will make the battery 16.2 amp hours . (350watts /21.6 volts.) That would mean that as it discharges in 6 minutes (One tenth of one hour.) the vacuum cleaner would be drawing about 160 amps. In practice it would be somewhat less than this is the Ah rating of a battery will be less than its stated value when it is discharged in such a short time. I find it difficult to believe that a vacume cleaner would draw that much current. Can you give some more information on the vacuum cleaner to see if we can come up with a more realistic figure.

Les.

#### Nigel Goodwin

##### Super Moderator
350W (consumption) at 21.6V is about 15 amps, so perfectly possible for a battery powered vacuum cleaner - which is why battery life isn't very long.

#### Les Jones

##### Well-Known Member
Hi Nigel,
That interpretation of the 350 watts being the rating of the vacuum cleaner makes far more sense than the way I interpreted it as being the rating of the battery.

Les.

#### Nigel Goodwin

##### Super Moderator
Hi Nigel,
That interpretation of the 350 watts being the rating of the vacuum cleaner makes far more sense than the way I interpreted it as being the rating of the battery.

Les.
46+ years of repairing domestic electronics makes you good at deciphering what people say

#### gophert

##### Well-Known Member
I bought a vacuum-cleaner driven by battery, which lasts about 6 minutes.
I want to replace the battery in a way that I can safely use my 220v wall outlet to power the vacuum-cleaner.
The battery has 21.6 volt and 350 watt.

Is it possible to use something like this :
https://www.amazon.com/SUPERNIGHT-S...-Transformer/dp/B01LATMSGS?ref_=fsclp_pl_dp_5

I have very little knowledge of electronics but I think it is pretty cool if this is possible (safely).
No, that type of power supply is not suitable for a rookie.
1) it is an open fram type power supply - meaning it is intended to be mounted inside of a protective chassis so the user doesn't accidentally touch the AC connections (they are only protected by some plastic flaps. An errant finger could easily touch both 220vac connectors).
2) it is only 12V output - you need 21 to 23V.
3) it is not easy to make it "safe" by simply selecting the right power supply - other techniques are needed as well. The load draws 15 amps. that can easily heat a poorly made connection or a poorly selected piece of wire (14 AWG or fatter). Proper fuse selection and proper mounting and installation of fuse holder is critical.
4) make sure any power supply is current protected (overload protected) as well
5) make sure any connectors you use can handle 15 amps or more - if you forego connectors and connect cord directly, make sure you understand cord restraints (to prevent breaking cord by pulling or repeated twisting) which can be a difficult challenge to overcome on a device that moves a lot during use (vacuum cleaner).

A proper power supply - with 21V output and 15 amps with overload protection will cost more than $100 (likely$200).

I recommend buying a simple AC powered vacuum with a CE or UL listing. At 220VAC input, it will only need 1.5 amps to get the same suction power and it will be professionally designed and covered by your homeowner's insurance policy.

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#### Nigel Goodwin

##### Super Moderator
I recommend buying a simple AC powered vacuum with a CE or UL listing. At 220VAC input, it will only need 1.5 amps to get the same suction power and it will be professionally designed and covered by your homeowner's insurance policy.
It will also be a great deal more powerful than a battery operated one.

#### schmitt trigger

##### Well-Known Member
And when the battery dies, (and it will die) you won’t have to purchase a new cleaner, because the cost of the replacement battery is very near the price of a brand new cleaner.

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