Adding amp meter to a laptop PSU

[krtech23]

Hi, from time to time I need to diagnose a laptop at home (I have a side-job as a computer technician, but I don't want to bring my personal stuff there). I don't have enough space on my desk for a huge lab power supply (nor am I willing to spend lots of money on a good quality one at this moment). However, I have a fairly decent unused LiteOn 135 W laptop charger.

I was thinking about making a little box with one of those combo volt/amp meters you can get from eBay for $3, and screw terminals or banana plugs for an universal laptop charger cable or cables from defective chargers. Perhaps I could also add some additional overvoltage/current protection. I don't really need anything other than the 19-20V most PC laptops run on.

What do you think? Could this make a halfway decent replacement for a lab psu?

[sam_sam_sam]

Put a link to the these “ combo volt/amp meters ” so we can what you have in mind
Post a picture of this LiteOn 135 W laptop charger the power supply output jack the end of it

[televizora]

There are many laptops that use 12V. The other usual voltages are 16,19, 20, 21, 24V.
So, buy universal adapter, for example Fortron For example Lenovo x220 uses 20V charger.
But IBM T41 uses 16V charger. And HP Probook 6540 series uses 19V charger.
Not only this, but many branded laptops like HP or Dell have sense pin. Some with pullup resistor,
some even have communication between the power supply and the laptop.
If the PSU cant communicate, the laptop considers it not original and wont charge, for example.

[sam_sam_sam]

Originally Posted by krtech23

I don't really need anything other than the 19-20V most PC laptops run on.

What do you think? Could this make a halfway decent replacement for a lab psu?

The problem you are going to have is not all switching power supply are created equally

Some have a charger ID input pin to the computer so this idea will not work correctly on all computers

Now if you were to take the part of the power supply that tell the computer or one of those after market switching power supply that can power supply to many different computers you just have to make sure you use the right power tip jack

[televizora]

Originally Posted by sam_sam_sam

Some have a charger ID input pin to the computer so this idea will not work correctly on all computers

Sometimes ID pin is nothing than resistor to tell the laptop what is the wattage of the PSU. But I read some examples, where there is even encrypted communication between the PSU unit and the laptop, to deter the use of not authorized PSU-s.

[krtech23]

Hi, thanks for all the suggestions.

The meter I had in mind:
https://www.ebay.com/itm/10-50-100-V...t/333778559774

Here is the PSU, I got it for free from a friend who had no use for it. The model name is PA-1131-08, the connector look like a standard 5.5x2.5 barrel jack.



From my experience (in work, I usually fix around 5-10 laptops a week), most of the PC laptops use 19.5V, with Lenovo's 20V being a relatively irrelevant exception, since all of these laptops have some tolerance and work just fine around 19-20V. (Cannot guarantee long-term, but when fixing, they aren't plugged in for long enough to cause any problems) Of course, there are some lower-end devices that use lower voltage, and some older ones (but personally, the oldest I've ever worked with were some Pentium M Lenovo IdeaPad predecessors, which already used the classic Lenovo round 20V chargers with center pin). And of course MacBooks have weird voltages, but I refuse to work with Apple devices anyway

As for the id pins - in work I use a bench PSU with an universal laptop charger cable with interchangeable connectors. Unfortunately, as I was told, these exact ones are not made anymore, but I found some similar products on ebay, for example this universal adapter set: https://www.ebay.com/itm/34-Tips-Uni...k/402349739232

The only laptops that don't work at all with the set are some newer HPs with the thin connector with center ID pin, and of course the new USB-PD devices. All of the other PC laptops work just fine, the only problem I had with some of the higher power ones was they were tripping the overcurrent protection of the 80W PSU rails (connecting two rails in parallel fixed that issue). My PSU is 135 W, which should be enough.

[sam_sam_sam]

Well it looks like you have this project plan out pretty good

Thanks for your reply

Yes this meter module will work just use it in the shared mode and you should be able to make it work correctly

Remember that it is the negative side of the meter that has the shunt wire for the current and the yellow wire is your voltage senses wire

Follow the wiring instructions that are on page 3 ( if I remember correctly) and this should work

[diif]

Originally Posted by krtech23

The only laptops that don't work at all with the set are some newer HPs with the thin connector with center ID pin, and of course the new USB-PD devices. All of the other PC laptops work just fine, the only problem I had with some of the higher power ones was they were tripping the overcurrent protection of the 80W PSU rails (connecting two rails in parallel fixed that issue). My PSU is 135 W, which should be enough.

It won't work correctly with Dell either, the centre pin talks to an IC for setting the power rating.

[krtech23]

Do you think I should add some additional protection or voltage stabilisation, when I'm already building a box for the meter? Or would it be redundant?

Originally Posted by diif

It won't work correctly with Dell either, the centre pin talks to an IC for setting the power rating.

I never had any problem with that at work, but you may be right - my old latitude didn't want to charge from time to time due to bad contact with the center pin. Do you know if the IC could be easily removed from a Dell charger and reused with my power supply? I think I read somewhere that Lenovo chargers use eeprom or flash that communicates directly with the laptop over the center id pin, is it the same with Dell?

[sam_sam_sam]

I have wondered about this if it could be done

But I do not have more than one original charge per computer so has prevented me investigating this possibly

This is my list of possible projects but not in the top 10 list

[Christian0734]

When I am with my clients I use this inexpensive product and it is very convenient. I use a generic power supply with a DC 5.5 connector then the controller and then adapters, the same ones you mentioned in a post. And it works well for the majority of computers

https://www.banggood.com/fr/MUSTOOL-...r_warehouse=CN

[sam_sam_sam]

Originally Posted by Christian0734

When I am with my clients I use this inexpensive product and it is very convenient. I use a generic power supply with a DC 5.5 connector then the controller and then adapters, the same ones you mentioned in a post. And it works well for the majority of computers

https://www.banggood.com/fr/MUSTOOL-...r_warehouse=CN

Thanks for posting this I just bought for myself

[krtech23]

Originally Posted by Christian0734

When I am with my clients I use this inexpensive product and it is very convenient. I use a generic power supply with a DC 5.5 connector then the controller and then adapters, the same ones you mentioned in a post. And it works well for the majority of computers

https://www.banggood.com/fr/MUSTOOL-...r_warehouse=CN

Thanks for the suggestion, this looks really interesting. The Chinese mobile app scares me a bit, but a quick google search showed me that someone has already reverse engineered the communication protocol: https://github.com/msillano/UD18-protocol-and-node-red

[stj]

i dont think RUIDENG would do anything underhanded with the app, they are too well known.
and they arent facebook!
it looks like theirs.

btw, here is their store.
https://rdtech.aliexpress.com/store/923042

[sam_sam_sam]

Originally Posted by sam_sam_sam

Thanks for posting this I just bought for myself

I got mine the other day but I am a little disappointed in the main screen that the print is very small and you have to look at straight on the face of the screen to see it correctly

The secondary screen is fine and easy to read and so are the other screen are easy to read

One note the USB C input is a slow to respond to its input and start charging I am not sure why this is the case in fact sometimes it does not even turn the screen on you have connect and disconnect several times to make something happen

I have another USB C tester and it kind of reluctant to work with the USB C but you do not have to connect and disconnect a bunch of times to get it to work as you the one I just bought the other day