Yes, I know it is not a good idea but let's try:
I have so many extra Dells (65 and 90) and IBMs that we can fry some to test.
Some might have a sensing circuit so that might be a problem.
I think we will need a rectifier on each to make sure that if one is turned on before the other, it doesn't reverse the voltage but:
Which ones on ebay to buy (voltage and amps?)
I know very little about how to wire electronic circuits so I need help.
I bet there are a lot of people who would like to double their voltage or 2x their amps for so many projects.
Thanks

 

Not recommended in either configuration.
You cannot connect them in series because the supplies are on common ground.
You cannot connect them in parallel because they will be fighting against each other.

 

I use old laptop power packs like this all the time when I am in a pinch and don't have a proper sized power source near by. No big deal with anything so far.

Sensing circuit wise typically one power pack will put out a tiny bit more no load voltage but as the load current goes it it will exhibit a voltage drop allowing for the other pack to help out. Add in wiring losses with their associated cords and in parallel operation they tend to balance each other out just fine.

In series unless both have one lead of the DC side tied to a solid dedicated earth ground on the primary (three wire Vs two wire AC cord) they also have no real issues. However if they do have a dedicated earthing connection all tyou need to do is cut that connection on the power packs circuit board.

 

Now I don't know what to do - two conflicting views.
Can others weigh in on this - have others tried it and it worked or did it fail?
Tcmtech - Did you use both series and parallel? Do you think a rectifier on both are needed? What if they don't come on at the same time?

 

How many volts, how many amps do you really need?
Most PC power supplies can deliver in excess of 350W.

 

These are switching laptop power supplies- anywhere from 16 volts 2.5 amps to 20 volts 6 amps.

 

Now I don't know what to do - two conflicting views.

That's the difference between purists and realists views of electronics.
For purists if everything's not theoretically perfect they think it can't and thusly shouldn't be done whereas for us realists we just hook things up and see how they work and if they work don't worry about anything else until it actually becomes a problem.

Now I don't know what to do - two conflicting views.
Can others weigh in on this - have others tried it and it worked or did it fail?
Tcmtech - Did you use both series and parallel? Do you think a rectifier on both are needed? What if they don't come on at the same time?

I just connect them as is. Everything they need to work is already in place internally so unless they have a three wire AC side power cored you can treat them just like batteries and connect them whichever way you need.

Either they work or they overload and need to be reset by unplugging them for 10 - 30 seconds.

 

They all have a three wire AC side power cord - I didn't know that was a problem otherwise I would have mentioned it. So is that a deal breaker or is there away around it?
thanks

 

There is no difference in the mains leads whether it is two pin or three pin cables, it's the output voltage and current limit that makes the difference, you can connect them in parallel, but one will be taking over first, ideally use a larger current capacity single psu.

 

They all have a three wire AC side power cord - I didn't know that was a problem otherwise I would have mentioned it. So is that a deal breaker or is there away around it?
thanks

It depends on whether they have a solid connection between the ground line of the cord and the DC side or not. If not no big deal but if so for series operation one or both power packs would need to have that ground connection broken.

On many of those types of power packs the DC side cord has three wires in it. Two are the power and the third one is a continuation of the ground lead from the main side power. Others however have that mains side ground tied to the DC side negative line and need to have that connection inside the power pack broken first.

AsI said before, until you hook them up and see what happens you wont know what you are working with and we are just guessing here. However at minimal thy should work fine paralleled for higher current.

 

Since I have so many, I will try several in parallel but before I do, would it help to use a cheater plug (no third ground contact) on the AC side of one or both of them? Also, from your previous statement, am I interrupting you correctly::: if I find two of the same make and type with no third AC ground, then those would be the better ones to try and can be either parallel or series?
Thanks

 

Since I have so many, I will try several in parallel but before I do, would it help to use a cheater plug (no third ground contact) on the AC side of one or both of them? Also, from your previous statement, am I interrupting you correctly::: if I find two of the same make and type with no third AC ground, then those would be the better ones to try and can be either parallel or series?
Thanks

What tcmtech said about common ground will be an issue since I tried two days back to desulfate an old lead acid battery after refilling to pump in a large current and voltage 39V approx at 6.5Amps with two hp laptop adaptors from the same outlet and they had the earth pins too. the moment i connected the output pins in series one adapter always shuts down and doesnt allow me to get series voltage.The only way I could make it work was by either adding another SLA battery in series between or by using and adapter without the earth pin(2 pin plug).

 

Since I have so many, I will try several in parallel but before I do, would it help to use a cheater plug (no third ground contact) on the AC side of one or both of them? Also, from your previous statement, am I interrupting you correctly::: if I find two of the same make and type with no third AC ground, then those would be the better ones to try and can be either parallel or series?
Thanks

Yep the cheater plug on one to remove the possible solid earth connection between the two would work just fine.

Same as for the basic two prong ones. They by design typically have no earthing connection between the AC and DC sides or at least nothing that of any concern.