openinverter forum

Hi guys
Here is a dumb question but I'll ask anyway.
Has anyone tried building a charger by connecting the output of multiple laptop chargers in series?
I know it would be low power but I have access to many HP chargers which are 135W 19.5V and today I tried connecting three of them in series. The result was 59V and no issues.
So for a 400V system I would need 20 or more of them but I have loads so that is no issue. I'm not sure I would want to mount them in the car but for a quick (or not so quick at 2.6kW) and dirty method of getting power into the pack it would be possible.

Any thoughts?

Alibro wrote: ↑Sat Oct 09, 2021 5:21 pm Hi guys
Here is a dumb question but I'll ask anyway.
Has anyone tried building a charger by connecting the output of multiple laptop chargers in series?
I know it would be low power but I have access to many HP chargers which are 135W 19.5V and today I tried connecting three of them in series. The result was 59V and no issues.
So for a 400V system I would need 20 or more of them but I have loads so that is no issue. I'm not sure I would want to mount them in the car but for a quick (or not so quick at 2.6kW) and dirty method of getting power into the pack it would be possible.

Any thoughts?

I would recommend you examine if there is a diode on every charger output, if not you need to add that so your charger doesnt fold in the middle if one of the modules fail. Otherwise if they are isolated outputs it should work.
You could also make a big casing and put all those module PCBs together in it. Would save space and provide uniform cooling.

I tried turning on different ones first and the voltage across all three was correct for the number turned on. This was without any load though so I'd need to do a bit more testing before deciding if it's worth persisting with it.

Laptop "chargers" are constant voltage power supplies. They shut down if too much current flows at their target voltage or the voltage sags too much. If you connect let's say a 19.5V laptop PSU to a 19.5V maximum voltage battery, which just happens to be at let's say 14V, the PSU would try to output 19.5V, detect an overcurrent event and shut down for a moment. Then it would try again with the same result.

That's why they probably are useless in this application, unless you add some kind of a current limiter between the PSU stack and the battery, or modify them to make them limit their current instead of shutting down in case of excess current.

That being said, there might be some laptop PSUs that will behave nicely. Most will not. Test them before planning too much.

arber333's comment about diodes is spot on also. I'd use a reverse diode in parallel with the output of each PSU.

Also take into account that the most of the heavier laptop PSU's have a PE-connection on the mains for the internal mains filter. Those filters have Y-capacitors from L/N to PE for filtering purposes but that also leads to some leakage current to PE (0,5...2mA). If connecting a lot of them in parallel, leakage current can get that big that the residual current breaker (RCCB) at home (usually 0,03A/30mA here) will switch off.