Bipolar supply with 2 laptop supplies?

Thread Starter

pdavis68

Joined Nov 27, 2013
42
I have 2 laptop power adapters (Dell) that are 19V @ ~3A. I'm curious, if I connect the + output of one to the - output of the other, will that generate a +/-19V supply (with the center/virtual ground being where the outputs connect)?

Both adapters have 2 prong plugs and the 2-pin figure 8 connectors so there's no earth connection.

My hope was to run then this into an LM317 and an LM337 regulators to generate +/- 15V power sources.

Just wondering if this is doable.
 

dl324

Joined Mar 30, 2015
13,307
Both adapters have 2 prong plugs and the 2-pin figure 8 connectors so there's no earth connection.
All of those adapters are switching regulators these days and don't use transformers for isolation from line voltage.

Do a resistance check from +/- terminals to both prongs on the plugs. If they're isolated, you're good to go.
 

Deleted member 115935

Joined Dec 31, 1969
0
All good supplies should be isolated,
and Dell are a good make,
but it is known for "grey " parts to be connected to the neutral of the mains.

Once had a TV , with an external supply, it had 110 V on its SCART plug, till the SCART was plugged into an earther VCR )
 

AlbertHall

Joined Jun 4, 2014
11,529
If you measure the voltage between one of the output pins and ground of an isolated SMPS with a high impedance voltmeter it will typically read a high AC voltage. This due to the capacitance between the primary and secondary sides of the supply but as the capacitance is small the available current is very small. Enough to show on the voltmeter but not enough to harm you.
 

upand_at_them

Joined May 15, 2010
766
In case you're interested: There is a recent thread in this section by SamR about this construction of a dual tracking supply, which I think contains the schematic he used.
 
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