Laptop chargers for Sure amplifier boards in series?

[OscarS]

So I have a pair of these Focal powered computer speakers that I was using outdoors near my welding equipment.

The high-frequency start of my plasma cutter affected something on the built-in amplifier and it now shuts off randomly, so I'm looking to use a Sure Amplifier Board as an external replacement. I have access to dozens of 19V/5A laptop chargers, so I figured I could use one to power up a Sure amp board to drive these.

I was also thinking of using a separate Sure amp mono board to drive a 10" subwoofer that I already have.

Is it possible to series two (19V) laptop chargers to obtain a single 38V/5A power source to drive the Sure amp board going to the subwoofer to get a bit more output?

 

[FauxFrench]

In principle, yes. These will form stacked supplies. The design of each 19V charger is such that the output is "floating" and therefore you can stack the voltages.
Then, for the dynamic behavior: it is not guaranteed that the stacked regulators will not interfere with one another and create oscillations. You need to try in practice. But, in order to reduce mutual interference I would put a 10000uF capacitor at the output of each 19V charger AND a diode (5A) across each 10000uF capacitor (cathode to "+" and anode to "-") in order to avoid reverse polarization.

 

[OscarS]

Thank you

 

[Pano]

Or you might be able to find a 32V or 36V supply. I've had a few as "line lumps" that came from eBay.

 

[OscarS]

Or you might be able to find a 32V or 36V supply. I've had a few as "line lumps" that came from eBay.

True, but I can get the laptop chargers for pennies on the dollar.

 

[Francisdumas]

I would put a 10000uF capacitor at the output of each 19V charger AND a diode (5A) across each 10000uF capacitor (cathode to "+" and anode to "-") in order to avoid reverse polarization.

Hi FF, the diode confuses me a little. Could you elaborate please? And would it look something like this?

Thanks and best regards.

 

[russc]

The design of each 19V charger is such that the output is "floating"

That's not my experience.
If supply has a 3 pin 'cloverleaf' input, output -ve is often earthed.

 

[john65b]

I don't believe Oscar is looking for a dual rail power supply... looking to connect in series for a 19v + 19v = 38v single rail power supply

I have used two laptop power supplies for a dual rail amp (First Watt F5) as you show (no cap or diode) and works fine as long as your DC ground on both supplies are not grounded to mains ground...

 

[Francisdumas]

Thanks John65b,
I'm sorry for answering SO late.
I assembled it without the caps and the diodes and it worked fine.
Then I removed them from their plastic casing (forced them out with a hammer and a flat screwdriver) so they could fit in the chassis. One exploded when I turned on the power. The other one did not explode but is not working anymore. I reviewed my wiring and I did not see any mistake. I guess I created a short with the chasis since the units were not insulated anymore by the plastic case. Not a big loss in any case. The units came from the flea market for less than $5 each. Now I got a transformer from an un-usable TEAC subwoofer from the same flea market for $10. I will keep on learning from my mistakes.

 

[Mark Tillotson]

That's not my experience.
If supply has a 3 pin 'cloverleaf' input, output -ve is often earthed.

Laptop supplies have a lot of switch-frequency breakthrough if not the earthed sort, this may cause interference.


A floating 2-prong supply could be stacked on a 3-prong earthed one. Don't forget the back-power prevent diodes as mentioned already.

 

[Kay Pirinha]

If we disconnect the negative output terminal from PE, it is advisable to reconnect it via a ceramic capacitor of, say, 100 nF to get rid of the RFI issue.
Best regards!