# Simple DiY 40a PSU / Ac-Dc converter

#### bigjoncoop

Joined Feb 1, 2019
129
Hey guys,

I need to get anywhere between 12v to 24v DC @ ~40amps. All the power supplies I can find are $100+ .... I need this to power a large 1500w CC/CV boost converter to charge a large lithium ion battery pack which will be going thru its BMS. I've been keeping my eyes open for even a used server power supply etc... But again haven't found anything under$100 but normally a lot more.

I don't know how clean the DC needs to be going into the boost converter but...

I wasn't sure if it would be as simple as going through a transformer or bridge rectifier then into a large coil and some capacitors and what not. Or maybe modding a smaller psu to handle the current

Just trying to save money on this project since I'm already got too much into it.

Thanks

#### Irving

Joined Jan 30, 2016
1,018
There are plenty of Dell/HP server PSU @ 500 - 700W each on ebay.com for around $30 each. You're honestly not going to do it cheaper if you want 1200 - 1500W @ 24v. There's a listing there now for HP 750W @$20ea

#### bigjoncoop

Joined Feb 1, 2019
129
@Irving
@SamR

Oh sh*t. Thank you. Exactly what I was looking for @SamR

I've searched a few times and only found cheap options from China on ebay.

That's what I need. Thanks again guys

Just found this mamajama...
AMAZON HAS HP 750w for $17!!! #### Attachments • 318.5 KB Views: 6 Last edited: #### Irving Joined Jan 30, 2016 1,018 Thread Starter #### bigjoncoop Joined Feb 1, 2019 129 @Irving @SamR Just found a HP 506821-001 750Watt on Amazon Prine for$17!!! "Used like new"

Idk why these didn't come up before

#### SamR

Joined Mar 19, 2019
2,590
SMPSs get a bad rap but every critical computer runs on one. Maybe not as suitable for a research-grade electronics lab when looking for a mV or uV supply but I use them to supply my HF XCVRs and Amps. Suitable and value-priced depending on use. Plus there is a LOT of them available surplus for a very good price.

#### Irving

Joined Jan 30, 2016
1,018
SMPSs get a bad rap but every critical computer runs on one. Maybe not as suitable for a research-grade electronics lab when looking for a mV or uV supply but I use them to supply my HF XCVRs and Amps. Suitable and value-priced depending on use. Plus there is a LOT of them available surplus for a very good price.
I use a modified SMPS for a variable 0-50v, 25A bench 'lab' supply. It is a little noisy on the output but the 80 - 120kHz switching is easy to clean up with an LC filter (much easier than if it were 100Hz hum from a linear regulator).

#### SamR

Joined Mar 19, 2019
2,590
Yup, I just ran into a situation where I needed a 3rd PSU and thinking I might just have to do a conversion job on one of the junk computer SMPSs I have to fill the bill. But I also have a couple of dish tubs full of wall warts to chose from. LOL

#### Irving

Joined Jan 30, 2016
1,018
You can never have too many PSU! I picked up a useful 4-channel linear bench supply on eBay for £90 (\$120) (Instek PS4303) - used and ch2 voltmeter is a little flakey (probably a dry joint, it is 20y old after all!).