Laptop charger as input for Ryden power supply DPH3205 - Good Option ? - Page 1
Forum section: electronics / projects

author: jayfree
author_rank: Newbie
timestamp: May 14, 2020, 08:07:02 am
content: Hello All,I would like to use a laptop charger(Lenovo 170W laptop charger) to power up the Ryden DPH3205. I can see used laptop chargers for cheap price.laptop charger (link updated)-https://www.amazon.com/Lenovo-170W-Replacement-Slim-Adapter/dp/B078XJPY49RD DPH 3205 -https://www.aliexpress.com/item/32762131242.html?spm=a2g0o.detail.1000023.30.6d7469f3zUltEODoes anyone has built such a power supply using laptop charger ? My concern is that will this laptop charger burn after sometime? Their cases are completely closed without any air circulation.My main need it to power small circuits (like arduino). Maximum I will run 12V DC motors. For sure, I wont be loading them for continuous 1 hour at its max power.Please share your feedback.

author: tunk
author_rank: Super Contributor
timestamp: May 14, 2020, 09:28:29 am
content: I guess it will work fine, but remember that the specs of many Chineseproducts are a bit optimistic, so I wouldn't run it at e.g. more than 3A.Do you have that Lenovo charger or will you buy it for that price?If the latter, for 150$ you can get reasonable bench PSU.

author: Ian.M
author_rank: Super Contributor
timestamp: May 14, 2020, 10:42:08 am
content: Its very unlikely to be satisfactory, as the laptop PSU you linked to has a two pin mains input, but as it isn't a medical grade PSU, will have a significant Y capacitor leakage current. In most countries, regulations limit the leakage current to 0.75mA, and the typical leakage current is usually over 1/3 of that. The result will be a line frequency common mode voltage on your PSU output of approximately half your mains supply voltage, with approximately half a mA 'drive' behind it, which is more than enough to almost instantly destroy MOSFETs and other highly ESD sensitive devices, simply by touching their gate terminal with a grounded soldering iron bit without either fully disconnecting the PSU from your circuit, or the PSU from the wall socket.A three pin input grounded output laptop charger wouldn't have the Y capacitor leakage current problem, but a bench PSU with a grounded output is a PITA, and if interconnected with high current loads and an Arduino with USB connection to a PC, you can easily end up with significant ground loop currents, risking a blown PC motherboard.Its possible to mod a floating output open frame PSU, replacing the Y capacitor with two in series with the intermediate node grounded via a choke, to virtually eliminate line frequency leakage current without significantly degrading its EMI performance, but obviously that's not an option for a sealed laptop charger with a two pin input.Other options are a floating output medical grade (low leakage current) PSU, which will usually use a grounded inter-winding screen to eliminate leakage current without the need for a Y capacitor, or an 'old-skool' line frequency transformer + bridge rectifier + resevoir capacitor PSU. You'll need a 22V 300VA transformer with 10% or better regulation to get full output from the DPH3205, which wont be particularly cheap. A lower voltage or lower VA transformer either wont be able to deliver full output or will overheat on sustained full output. A higher voltage or worse regulation transformer will over-voltage (and possibly destroy) the DPH3205 during low load operation if the mains supply rises towards the upper end of its tolerance range.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 14, 2020, 01:05:14 pm
content: Easiest way to shunt out the leakage without directly connecting the output to ground is to connect the ground via a series RC network, something like 1uF (nonpolar) and 100 ohms would be a good start. Then a 1M across the capacitor can discharge any charge that does build up.Then there's hacking the power supply to connect the Y capacitors to neutral, so there would only be the tiny leakage from stray capacitance. It's also possible to power the supply from a half wave rectifier so that the power supply doesn't see AC at all.

author: jayfree
author_rank: Newbie
timestamp: May 14, 2020, 01:32:18 pm
content: I have updated the charger link. Actually I wanted to use 3 pin plug(I mean with ground).What I mainly wanted to know is that if the charger will catch fire after continuous usage as it doesn't have any air circulation an d laptops might not consume 170w all the time(it stops after the battery is charged)

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 15, 2020, 01:43:52 am
content: Have you considered using a 24V 3D printer power supply?

author: jayfree
author_rank: Newbie
timestamp: May 15, 2020, 05:41:11 am
content: As it is bulky, I wanted to avoid it. Laptop chargers are small

author: wizard69
author_rank: Super Contributor
timestamp: May 19, 2020, 03:27:12 am
content: Quote from: jayfree on May 15, 2020, 05:41:11 amYou want to replicate a commercial power supply so the size will remain the same more or less for a given power. Given that constraint why not consider a commercial power supply common in industrial applications, and mount it in a box with a suitable fan. An example of such a supply with a 24 VDC output:https://solahevidutysales.com/silver_line_series_single_multi_output_linears.htm.Open frame supplies have to be enclosed obviously but you need to do that anyways for the Ryden. Often these sorts of supplies can be had with a separate 5VDC output, for example:https://www.meanwell.com/Upload/PDF/PID-250/PID-250-SPEC.PDF.Now I'm not recommend either of these, rather they are just examples of supplies that could easily be used to power a bench supply with a fixed 5VDC output. What you need to look for is a supply with proper line isolation for a bench supply, suitable power for the way you want to run the Ryden and any other features you may value.The Ryden requires an enclosure so all you need to do is go a bit bigger for one of these. Also a fan is more or less required for the Ryden so that needs to be considered. DigiKey for example lists over 10,000 open frame power supplies on its web site and 500 of those a dual channel and chassis mount. That is just digikey and frankly most of those supplies are probably cheaper than a laptop supply and probably more robust. At the same time these supplies can often be salvaged from printers and other electronics. I just don't see a good reason to go with a laptop supply.