How do I build a 24v 8-10amp power supply?

I am trying to "repair" an old massage chair... for every movement (except vibration) it uses different engines rated 24V and 6 to 8 amps, I tested each one with and old notebook PSU (20V 12A) and they works, but they are a little slower/weaker than before because of this 20V instead of 24V.

Now I have to choose between 2 ideas:
1) bridge 2 old PSUs like in this guide
https://www.instructables.com/id/Two-ATX-PSU-One-juiced-24-V-DC-PSU/
to get 0 > +12 > +24 (that would be extremely good since the vibration engine takes just 12V) but I am not sure about the "theory" of putting PSUs in series and I am concerned about the risks of grandma (main user of the chair) being fried after failures of this configuration.

2) I have scavenged a big (and heavy) 220Vac to 12Vac and 24Vac transformer... but I am not sure how many amps I can get out of it and, with my "useful" backgroud as chemist, this time I have the theory of rectifiers but I miss practice... I don't know what I should exactly look/shop for...
(in this case it would be nice to take the 12Vdc from it too but if it gets hard/expensive I can go with a "secondary"  power adapter refurbished from a dead cellphone charger)

I would look for a 24 volt battery charger with a 10 Amp fast charge setting and use it to power your chair.

Joe

rickharris3 years ago

What happened to the original PSU?

It would normally be easier to repair then build from scratch.

Lagash (author)  rickharris3 years ago
The only electronic board inside the chair is the dead part. When powered I see the led on the control device always lit (like if a button is pressed, therefore I suspect some kind of short circuit) and, by pressing oher buttons I can hear some "clicky" sound from that board but nothing happens...

This board receive the 24Vac, a security signal, that should stop everything if the chair case is open, and the control device signals. Then it is connected with each terminal of the engines (positive and negative) feeding dc.

I tested the transformer that feeds it and it is good (but is not the salvaged one discussed above, this one gives only 24Vac), I have also called the chair manufacturer for another board but it is not in production anymore and a new one would cost me almost like a new chair :(