Hi folks,
I've made several of these for myself or made them for others too. I've never bothered to document the entire process so that somebody else can make one. since I'm making myself an 82v charger, I thought it was time to document the entire process.
These are 20v PSU's so not ideal for anything other than 20v increments. In a later post in this thread, I'll show how to adjust the Lenovo PSU's so you can set the voltage to what you need. For now, 2 PSU's=40v, 3=60v, 4=80v and so on in 20v increments...ish. Typically these 170 watt Lenovo PSU's are not dead on 20v. They tend towards 20.5 -20.7v each.
Look on ebay or at the local computer recycle center and you will find tons of these 170 watt PSU's for $13-20 each. I paid $15.50 each for 6 of them on ebay.
Dell 170 watt PSU's will work too, but they typically cost more. There's a zillion of these older Lenovo PSU's "out there" so why pay extra? I've put 6 of these PSU's in series without issues. I bet you could do 10 or 15.
NOTE: PSU's with isolated outputs in series is just like batteries in series, except it's PSU outputs. Plus from PSU 1 connects to minus on PSU 2. Plus on PSU 2 connects to minus on PSU 3 and so on.
4 big things you are looking for:
1. The outputs are 100% isolated from the AC input. Without this, STOP NOW!
2. 170 watts is 8.5 amps at 20v. Expect to get more like 9-9.5 amps.
3. These specific PSU's are over load and over temperature protected. They won't die easily.
4. Buy legit Lenovo PSU's, not the Chinese knock-off PSU's.
So then. let's build a charger that will cost you virtually nothing, fanless and will deliver about 9 amps. Later on once it's built, if the voltage isn't quite right, that's alright, I'll take one of them apart and show you what to change to adjust the voltages. If you are impatient and want to do it now, here;s a good article on the process.
https://hackaday.io/project/3469-modifying-a-notebook-power-supply
Parts needed:
1. Legit Lenovo 170 watt PSU's complete with AC chords.
2. Solder, soldering iron, wire strippers, heat shrink, zip ties, some wire or chord
3. Cheap watt meter
4. Connector for your charging port.
Here's the PSU's:
***Notice the beveled top. Notice the single corner knocked off. Notice the Lenovo label on the bottom. Don't get fooled by some Chinese clone!
https://www.ebay.com/itm/Lenovo-170W-20V-8-5A-Laptop-Charger-AC-Adapter-Power-Supply-45N0113-45N0114/382856199240?epid=1719485080&hash=item592401fc48:g:dMcAAOSwFlNceUrS
This 20A watt meter will do the job for this charger.
https://www.ebay.com/itm/Digital-Multimeter-Charge-Discharge-Battery-Tester-DC-0-90V-0-20A-Volt-Amp-Meter/292938370933?hash=item44347ccf75:g:gLwAAOSwikBcUB-T
Let's get building!
1. First off, be sure everything is unplugged from AC power.
2. I'm doing an 82v charger so you'll see 4 PSU's and so on. It's the same process for 3 PSU's are 10 PSU's.
3. Right near the laptop connector is that large plastic bulge. There's a ferox core in there and the output chord is wrapped around it several times, to reduce noise. We don't care for a charger. Lay all your PSU's stacked together, stretch out the output chords and cut them all the same length right behind that ferox core. That will leave you with something like a 3" section with a connector on one end and the plastic bulge on the other. Keep, toss, whatever...you won't use it again for the charger. I pulled all of mine tight and then cut at the length closest to the bulges. As you can see they weren't all the same length.
4. Pull off the velcro straps. You probably won't reuse but maybe one of them.
5. Strip back the outer insulation on the ends of all PSU's about 5/8". The loose strands are ground and the white wire is +20v.
6. Strip back the insulation on the inner wire about 1/4" and twist together the loose strands on all exposed wires. Repeat for all PSU's.
Note to people that want to take short cuts:
If you look at any of my threads, you will see that I pre-tin almost everything before soldering it to something else. This serves several purposes:
A. Stranded wire often times does NOT flow solder particularly well. A dip in some flux and then tinning the exposed wire end means good solder flow into all the strands.
B. Bare copper, steel and other metals that can be soldered to oxidize. Solder flux inside the solder is often times too weak to cut through the oxide layer to get down to bare metal. Prepairing bare metal in advance of soldering something to it makes the solder joint stronger and more reliable.
C. Below you will see where I solder multiple wires together. In one case 5 wires. Holding all those wires together, getting solder to flow into the many strands and NOT make a mess of things is not easy. You are likely to get poor solder flow, burnt fingers, a lumpy connection and melted insulation on the wires. Pretinning everything in advance means, touch the soldering iron to the joint, add a little solder and you are done.
D. Stranded wire is made of many thin strands. Tinning the end of the wire binds all those loose strands together.
E. Thoroughly cover bare wires and connections so that shorts can't happen. It's your build, why skimp on details that cost you reliability and safety?
OK...back to charger building...
7. Tin the ends of the wires. A container of flux is really useful so you get enough flux into the wire to get the solder to flow. All you need is the last 1/4" of each end tinned. Solder has flowed in between all the strands binding them together. Repeat for all the exposed wire ends.
8. Pull out your multi-meter. Plug in each PSU one at a time to AC and check the output voltage across the 2 wires. I'm reading around 20.5v for all of them. 20.5 x 3 is 61.5v, 20.5 x 4 = 82v. Don't let those bare wire ends short together. There's 10 amps there!
Side line: I got ahead of myself and made a mistake which I'll present here. I soldered the outputs together in series and didn't think about properly insulating the bare ground wires. This is power outputs from 4 PSU's in series. The grounds from each output must not touch each other or else they create a short across at least 2 PSU's.
See those exposed ground wires even AFTER heat shrinking? This is a short waiting to happen!
9. Cut 3/4" lengths of heat shrink that will slide over the outer insulation of each PSU wire. You will use them later. Slide them on for now.
NOTE: I use heat shrink. It is highly reliable, easy to use and cheap. This could be done with electrical tape to get the same results, but I'm not fond of tape for things like this and it gets gummy after a while. Yuck! Heat shrink is better in every way.
10. Slide heat shrink over the bare ground wires as far down as you can get it. Leave a little less than 1/4" exposed end. As you can see there is still some exposed wire here that could short to the other exposed wires.
11. Solder your wires together like this to make the series connections between PSUs. Now slide that heat shrink over the exposed ends and shrink it in place. This should have been 2 steps, but I forgot to take a picture before shrinking over the bases of the wires. AS you can see, those bits of exposed ground wires seen in step 10 are now covered and there is no chance of a short happening.
12. Put more lengths of heat shrink over the exposed solder connections.
13. Pull them all together and put a zip tie around everything so the connections can't move. This zip tie will get cut off later. It's here to hold everything together until later on so the heat shrink doesn't get stretched or solder connections stressed.
14. Your PSU's came with AC chords. However many PSU's you have in series, you need that many AC chords and that many AC outlets. I need 4 of each. We are about to test out our charger for the first time. Grab your multi-meter and a set of alligator clip test leads. Clamp them on the 2 wire ends and set your DMM to the correct setting. ***Make sure those bare ends do NOT touch.*** Plug in any 1 PSU and you should read 20v, plug in another and you'll read 40v, plug in a third and read 60v and so on. If you don't have alligator clip leads, just plug in all the PSU's and check the output voltage. You should see something like 20v x the number of PSU's. In my case, 82.3 volts...close enough to 82v to not bother with.
15. Unplug all AC chords from the PSU's and the AC outlets. Time to make a single AC chord.
16. It doesn't really matter which end of each chord you line up, just use the same end on all your chords. As you can see I have chords of various lengths.
17. Line up all the connectors that plug into the PSU's. If yours are like mine, that's various lengths. You want to cut off all 4 wall plugs leaving a long length of chord with a PSU connector on each end. You also want to leave a fairly long pigtail so all 4 chords can be soldered to it. My longest chord was 8" longer than the shortest one. The 4 chords with a PSU connector on them are all the length of the shortest chord right at the wall plug...aka all the same length or about 18" long. That left me with a single 8" long AC plug "pigtail" and 3 shorter ones.
18. Strip back 1/2" of insulation from all the wires and twist their strands together.
19. For ungrounded chords like these, it doesn't matter, but I'll do it anyway. On your 5 pieces of chord you will notice one conductor has a ribbed insulator and the other does not.
20. Take all 4 chords with PSU connectors on them, find the 4 wires with ribbed insulation. Twist them together and put a zip tie around them. Repeat for the 4 un-ribbed wires. Those zip ties will get cut off in a minute, but for now they are making your life easy by holding all 8 of those wires together in 2 sets.
21. Tin the 2 bundles of wires.
22. This is the end of my 8" pigtail with an outlet plug on it. I've tinned the ends of those wires too and then cut them a bit shorter.
23. Cut 3 sections of heat shrink. The 2 smaller ones just fit over the 4 wires from step 21. THey extend over both sides of each connection by about 1/2". The larger section looks like it will fit over top of all 8 wires plus added heat shrink. It extends beyond the inner heat shrink by at least 1/2" over each end.
24. This is the pigtail with the 3 sections of heat shrink on it BEFORE soldering the pigtail to the wire bundles. Slide the big piece on first over both wires and then the smaller sections over one wire each on the 8" pigtail.
25. Solder the AC outlet pigtail to the 2 bundles of 4 wires each. The pigtail wires are smooth and ribbed. I soldered the ribbed wire to the ribbed bundle and the smooth wire to the smooth bundle. There is no need to do more for this connection since the joints won't see vibration or much stress like an EV would see. A decent amount of solder bonding the 5 wires together is sufficient for many years of use. You can remove those 2 zip ties now. They were holding your wires together until this step was done. Trust me...soldering 5 wires together while holding all of them together is MUCH harder than wasting 2 zip ties! Pre-tinning everything before trying to solder them together makes these solder connections much easier too.
26. Slide the heat shrink over the solder connections and shrink it in place. As you can see, the solder connection has a good bit of heat shrink on either side of it. I wish this was 3X shrink so it closed up around the pigtail wires better.
27. Slide that larger section of heat shrink over all 8 wires and shrink it. You want this piece to completely cover the underlying heat shrink on both ends.
28. Zip tie all 8 wires together to keep them from stretching the heat shrink later. This joint will not fail easily and getting shocked here by 110v AC is not likely. The 4 chords going to the PSU's can't pull apart easily thanks to the zip tie. This is pretty secure!
29. Congrats, you have just made a 4 way AC chord. I've made several of these for the laptop PSU chargers I've done. This chord will work for a very long time and not overheat. At most it sees is maybe 10 amps.
30. I doubt it happened, but just for kicks. lets test that 4 way chord. Without it plugged in, put your multimeter on ohms and the test leads across the wall plug prongs. If you measure anything other than infinite resistance, you did something wrong.
31. Now plug in your 4 way chord into all your PSU's and then into the wall. You should measure 20v x the PSU number.
More to come later! My watt meter is on order and won't get here for a few weeks. I'll finish up this charger when that happens.
