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Using Nokia ACP-7 PSU to power other device

L

Lem

Jan 1, 1970
0
I want to match a small mains adaptor to a small hand-held whisk.

Normally the whisk is battery powered (AA x 2) and has a variable
speed. At its max I would like to run the whisk a little bit
faster than the internal batteries permit. So I figure I could
replace the two AA cells with a mains adaptor feeding approx 4V.

I came across the basic Nokia mobile phone mains adaptor (which
used to be supplied as standard with Nokia phones). It's nothing
fancy: no switched mode or high speed charging or any of that.
This is Nokia model ACP-7X (X for the UK where I am) with a spec
of 230 V, 50 Hz, 4.8 VA. Output 3.7 V, 355 mA.

HOWEVER ... when I measure the voltage across the output of the
PSU it measures about 9V with no load. Don't know a whole lot
about regulated/unregulated PSU's but I guess this is pretty
unregulated if it goes from 9V to 3.7V.

Would it be LIKELY that the voltage would come down to about 4 V
when I attach my whisk? The whisk has a resistence of about 250
ohms. When I measure the resistence of the Nokia when it's not
attached to the mains, I get infinity.

So would this ACP-7 be safe to use? Or would it deliver well
above 4v and blow the motor in my whisk?
 
P

Palindr☻me

Jan 1, 1970
0
Lem said:
I want to match a small mains adaptor to a small hand-held whisk.

Normally the whisk is battery powered (AA x 2) and has a variable
speed. At its max I would like to run the whisk a little bit
faster than the internal batteries permit. So I figure I could
replace the two AA cells with a mains adaptor feeding approx 4V.

I came across the basic Nokia mobile phone mains adaptor (which
used to be supplied as standard with Nokia phones). It's nothing
fancy: no switched mode or high speed charging or any of that.
This is Nokia model ACP-7X (X for the UK where I am) with a spec
of 230 V, 50 Hz, 4.8 VA. Output 3.7 V, 355 mA.

HOWEVER ... when I measure the voltage across the output of the
PSU it measures about 9V with no load. Don't know a whole lot
about regulated/unregulated PSU's but I guess this is pretty
unregulated if it goes from 9V to 3.7V.

Would it be LIKELY that the voltage would come down to about 4 V
when I attach my whisk? The whisk has a resistence of about 250
ohms. When I measure the resistence of the Nokia when it's not
attached to the mains, I get infinity.

So would this ACP-7 be safe to use? Or would it deliver well
above 4v and blow the motor in my whisk?


You need to make more measurements of the load that the whisk applies.
Using 2 fresh AA batteries, measure the minimum current whisking in the
empty air and the maximum current whisking something *really* stiff on
full speed.

That will tell you what the replacement supply will need to provide. It
could be that the supply needs to provide amps, not milliamps, on full
load. The nokia charger is unlikely to meet the spec.

For your proposed supply, you can substitute a resistor that draws the
same current as the whisk on minimum load and measure the load voltage.
If the voltage is higher than 5 volts is will probably blow the whisk's
electronics. It may blow it at 3 volts or even lower. You will have
picked a supply that is capable of supplying the maximum full load
current, incidently.

Having done the above, the whisk can still be damaged by the supply. It
may have been designed knowing the discharge characteristics of AA
batteries - giving it a constant, mains-derived supply, can lead to
overheating on prolonged heavy load and failure whereas, with batteries,
the batteries would go flat first. You may need to add an
over-temperature trip to the whisk's electronics.


Or, you could simply use rechargeables and a fast charger. Less chance
of wires getting tangled..
 
S

SQLit

Jan 1, 1970
0
Lem said:
I want to match a small mains adaptor to a small hand-held whisk.

Normally the whisk is battery powered (AA x 2) and has a variable
speed. At its max I would like to run the whisk a little bit
faster than the internal batteries permit. So I figure I could
replace the two AA cells with a mains adaptor feeding approx 4V.

I came across the basic Nokia mobile phone mains adaptor (which
used to be supplied as standard with Nokia phones). It's nothing
fancy: no switched mode or high speed charging or any of that.
This is Nokia model ACP-7X (X for the UK where I am) with a spec
of 230 V, 50 Hz, 4.8 VA. Output 3.7 V, 355 mA.

HOWEVER ... when I measure the voltage across the output of the
PSU it measures about 9V with no load. Don't know a whole lot
about regulated/unregulated PSU's but I guess this is pretty
unregulated if it goes from 9V to 3.7V.

Would it be LIKELY that the voltage would come down to about 4 V
when I attach my whisk? The whisk has a resistence of about 250
ohms. When I measure the resistence of the Nokia when it's not
attached to the mains, I get infinity.

So would this ACP-7 be safe to use? Or would it deliver well
above 4v and blow the motor in my whisk?


Raising the voltage does not automatically increase the speed. At least
not where I am from.
Raising the voltage will lower the amount of current needed for the motor.
Until you burn it out.
If you want it to go faster then your going to have to (probably) get a
bigger motor and change the gearing. Just changing the gearing will probably
result in a motor failure, very soon.
 
E

ehsjr

Jan 1, 1970
0
Lem said:
I want to match a small mains adaptor to a small hand-held whisk.

Normally the whisk is battery powered (AA x 2) and has a variable
speed. At its max I would like to run the whisk a little bit
faster than the internal batteries permit. So I figure I could
replace the two AA cells with a mains adaptor feeding approx 4V.

I came across the basic Nokia mobile phone mains adaptor (which
used to be supplied as standard with Nokia phones). It's nothing
fancy: no switched mode or high speed charging or any of that.
This is Nokia model ACP-7X (X for the UK where I am) with a spec
of 230 V, 50 Hz, 4.8 VA. Output 3.7 V, 355 mA.

HOWEVER ... when I measure the voltage across the output of the
PSU it measures about 9V with no load. Don't know a whole lot
about regulated/unregulated PSU's but I guess this is pretty
unregulated if it goes from 9V to 3.7V.

Would it be LIKELY that the voltage would come down to about 4 V
when I attach my whisk? The whisk has a resistence of about 250
ohms. When I measure the resistence of the Nokia when it's not
attached to the mains, I get infinity.

So would this ACP-7 be safe to use? Or would it deliver well
above 4v and blow the motor in my whisk?

Hooking the Nokia up to the whisk has three possible
outcomes, or combinations of them:
1) The whisk works ok with no ill effects
2) The whisk burns out
3) The Nokia charger burns out

Below is a circuit (4 resistors, a switch and an LM317
voltage regulator chip) that will work with a 9 or 12 volt
DC wallwart to provide the voltage you need. And it
will work with the Nokia charger, too. What is unknown
(with all three) is how much current the whisk draws.



From wall
wart or
Charger
-------
+ ------in| LM317 |out---+---> to whisk +
------- |
Adj [240R]
| |
+----------+
| |
[180R] o
| / Switch open Vout = 4.01
+----------o Switch closed Vout = 3.07
|
[20R]
|
[330R]
|
- ------------+---------------- To whisk -

You can connect your Nokia charger and try it, first at
3 volts out with the switch closed. Measure the current
that the whisk draws - if it is > 355 mA when the whisk
is heavily loaded, the Nokia charger won't be good for you.
However, the circuit will work with a DC supply that
provides at least 7 volts under load, so something like
a 9 volt or 12 volt wall wart will work, if it can provide
the current the whisk needs - up to 1.5 amps. You will want
to mount the LM317 on a good heat sink if the whisk draws
enough current to make the LM317 hot.

Understand that if you run the whisk at 4 volts, you are
inviting it to fail prematurly.

Ed
 
J

jim.gm4dhj

Jan 1, 1970
0
Using 2 fresh AA batteries, measure the minimum current whisking in the
empty air and the maximum current whisking something *really* stiff on
full speed.

I tried that and it hurt........
 
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