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| Can you connect laptop power supplies in series? |
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| zirconx:
I have some unused laptop power supplies like this: 19.5v 3.3A : https://d68my205fyswa.cloudfront.net/lcf/image/data/sku/A-DEL-04-G/USA/1.png I know that it's possible hook ATX computer power supplies in series to get more voltage, I believe they have to unhook the negative output from the case when they do that. Would it work to connect these laptop power supplies in series? I'm thinking about using them to feed an adjustable buck converter: Any caveats? Would it make any difference if I use laptop power supplies with or without the 3rd wire ground pin on the 120v AC side? |
| Cliff Matthews:
I would open them first to clip the Y-cap between HV and secondary sides and then series wire them with a fuse and a 6-amp rectifier between them to ensure one won't back-feed into the other on start-up or shutdown. A 2-watt 470-ohm bleeder across each may not be a bad idea either. - The usual precautions here to make sure the negative output is not connected the mains ground, stay safe if you've not done this before or don't understand it.. maybe read a few LT adapter schematics - YMMV |
| Zero999:
--- Quote from: Cliff Matthews on March 26, 2019, 11:50:56 am ---I would open them first to clip the Y-cap between HV and secondary sides and then series wire them with a fuse and a 6-amp rectifier between them to ensure one won't back-feed into the other on start-up or shutdown. A 2-watt 470-ohm bleeder across each may not be a bad idea either. - The usual precautions here to make sure the negative output is not connected the mains ground, stay safe if you've not done this before or don't understand it.. maybe read a few LT adapter schematics - YMMV --- End quote --- I'm not sure what you're saying. I wouldn't recommend modifying it, without doing some reverse engineering first. If the output of the power supplies is connected to earth, then there might not be a Y capacitor. Another possibility is the Y capacitor is connected between the output and earth, not the primary. Finally, removing the Y capacitor can cause EMC problems. --- Quote from: zirconx on March 26, 2019, 11:31:35 am ---I have some unused laptop power supplies like this: 19.5v 3.3A : https://d68my205fyswa.cloudfront.net/lcf/image/data/sku/A-DEL-04-G/USA/1.png I know that it's possible hook ATX computer power supplies in series to get more voltage, I believe they have to unhook the negative output from the case when they do that. Would it work to connect these laptop power supplies in series? I'm thinking about using them to feed an adjustable buck converter: Any caveats? Would it make any difference if I use laptop power supplies with or without the 3rd wire ground pin on the 120v AC side? --- End quote --- It depends on whether the outputs are isolated from earth. If not, then connect a diode in reverse parallel with each power supply, before connecting them in series. If the outputs are not isolated from earth, then you could in theory remove the earth connection from one of them and do the above, but it's risky. |
| Cliff Matthews:
Since this isn't the beginner's section, I guess I threw some of the usual "mains-panic" to the wind.. |
| RoGeorge:
Connecting power supplies in series is not a good idea. Sometimes it can be done, but only if the sources were designed to support series connection. A laptop power supply is not designed to work like that. It can work or it can start a fire, you will never know. Connecting series power supplies is not the same as connecting series batteries. Apart from the Y capacitor, a lot of very ugly things can happen at startup. If one power source starts faster while the load is connected, then the other power source will see a reverse polarity at its output. Some power sources can cope with this, some other might be destroyed. Same if one power source over-current protection is triggered while the other one is not. |
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