8.4v Power Supply (1000+ Watts)  ??? - Page 1
Forum section: electronics / beginners

author: trilerian
author_rank: Regular Contributor
timestamp: May 09, 2023, 06:48:49 pm
content: I know I can buy an adjustable voltage bench power supply that can deliver 80-100 amps, and this would be close to my needs. But I also don't want to spend that kind of money.This is for a flywheel dyno I use to dyno my bldc motors for RC use. Currently I use a 2s lipo, since that is the power source we use in the cars, but having to charge the lipo again right after 3 runs gets quite annoying. I have a 5v 70amp power supply that I have tried out, but the lower voltage produced results that were not good for 2s application. I have thought about buying a golf cart battery and not fully charging it, but I figured I would ask if there was a way to convert an HP server 1200 watt power supply from 12v to 8.4v and keep the usable current? I have a 200 amp current sensor inline on the positive lead from the battery, so that is my current limit. Most of the motors I dyno are pulling between 70-150 amps. Since I only currently have the 1 flywheel load.What I am looking for is something consistent, there are already enough variables to examine while trying to dyno one of these motors.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 09, 2023, 07:27:00 pm
content: Sound like a really interesting project. I made a few small dynos to use as models to develop a larger one. It's posted somewhere on the internet..I have a few Meanwell supplies that would do what you are asking. They will go into current limit rather than shutdown. It's possible to gain two together so even 150A wouldn't pose a problem. You can vary the voltage with a pot or voltage input. The problem is they require 220V.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 09, 2023, 07:50:39 pm
content: Here's mine:https://www.msuk-forum.co.uk/forums/topic/81512-self-built-rc-dyno/?do=findComment&comment=1013094

author: trilerian
author_rank: Regular Contributor
timestamp: May 09, 2023, 09:07:45 pm
content: Thanks for the trip down memory lane running 27t brushed motors! I used to have a green machine.Anyway, the dyno I am using wasn't made by me. It is the MiniPRO dyno. While I do want to make my own dyno, I'll start simple, lol. Just get a good power supply for what I am currently using.Although you might be able to answer some other questions I have. I am trying to work out how to get useful info from running a motor connected to a slave that has 0.10 ohm 100 watt resistors connected to each phase and then shorted together. I know this creates a higher load for the test motor, but I am not sure how to go about measuring it for useful data.Just as an fyi, I am only getting into the theory behind this stuff. A hobbyist so to speak. So I am very green and I don't work in the industry, which means limited knowledge and understanding.Thanks

author: joeqsmith
author_rank: Super Contributor
timestamp: May 09, 2023, 10:07:15 pm
content: No worries. I have never owned any sort of RC toys and the motor you see was given to me from someone who had bought it for some non RC home project. When I started posting about the dyno, I seem to remember members assuming I was some RC car buff. I had someone write me directly who claimed they were some factory blah blah race team something or other. It was pretty funny as my only interest was like you, to learn the basics to go on to build a full scale dyno.If you follow that thread, you can see I had started out with a brush motor for a load and I think a motor out of a VCR for my test motor. The dyno works like any other using a arm with a load cell to measure the torque and sensors to measure the shaft speed. In this case, the load cell was a balance. The problem with that first one was the alignment was poor and eventually I damaged the absorber motor. The last one used 1/2" plate steel to mount the parts on with purchased blocks and ceramic bearings. The absorber was replaced with a 3 phase brushless. There is a photo of a ground shaft that was used to align it. It worked well with very little drag.Nice thing about this method is I can run the motor steady state. Not that this matters with these little motors but the plan was to construct a similar dyno for small car engines. This allowed us to use the dyno to brake them in. We could also run constant torque or constant speed. It was a pretty fun project.

author: trilerian
author_rank: Regular Contributor
timestamp: May 09, 2023, 11:25:57 pm
content: 3.2v nominal. They have a 3.65v full charge. That is a lot to get rid of through some wire. Also they are $80 for one, I would need at least 2 and then I think a golf cart battery maybe better.But really I want to make one of the HP server power supplies I have work.

author: james_s
author_rank: Super Contributor
timestamp: May 09, 2023, 11:45:04 pm
content: Get some hot swap server PSUs and modify them for lower voltage, shouldn't be too hard to do. Most of them are 12V and most RC guys try to tweak the voltage up in order to power chargers but dialing it down ought to be easier. They support current sharing and can be wired in parallel to get the current you need if you can't find one that's big enough to deliver 1kW at the voltage you need.

author: trilerian
author_rank: Regular Contributor
timestamp: May 10, 2023, 12:06:52 am
content: I have about 6 HP 1200 watt server power supplies. I already use them for my chargers. How do I go about dialing down the voltage? Remember, new to this. While I have no issues reading and learning how to do it, I am at a loss on where to start.Thanks

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2023, 01:38:43 am
content: In principal it's a matter of finding the feedback loop that monitors the output voltage and modifying it, in practice how hard that is varies tremendously but if you look around for specific models that people have modified you should be able to largely duplicate what they do. Reducing the voltage is the same process as increasing it except you don't have to worry about over-volting components like output filter caps. Somewhere I saw someone demonstrating a server PSU they modified into a variable bench supply but I don't remember where that was, some youtube video.

author: trilerian
author_rank: Regular Contributor
timestamp: May 12, 2023, 02:24:00 pm
content: I found a write up about converting a lower wattage HP server supply.http://www.npnzone.com/2020/01/28/high-current-bench-supply-project-part-1-of-2/I guess I am going to try to make this into a project then. Should be fun. Looking at the specs of my PS, it will do max 900 watts off 110v for the big 12v rail. That will give me over 100 amps at 8.4v. Which since this power supply is regulated, I may make the voltage lower. The voltage under load from my batteries get down to the mid 7s.

author: trilerian
author_rank: Regular Contributor
timestamp: May 12, 2023, 05:06:02 pm
content: So here is a thread on here for making the power supply I have increase voltage and get around the over voltage protection.https://www.eevblog.com/forum/projects/hp-hstns-pl11-over-voltage-protection-voltage-increase/That thread has schematics of the board. So if someone can help me determine what I need to change to get less voltage, that would be great! Also other models have a low voltage cutoff, so I may have to deal with that as well.Thanks

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2023, 09:58:59 pm
content: To get less voltage you change the same thing that you change to get more voltage, except in the opposite direction. I haven't read that whole thread but it's probably just a single resistor. You shouldn't have to make any other modifications as may be necessary to tolerate higher voltage.

author: eblc1388
author_rank: Frequent Contributor
timestamp: May 13, 2023, 06:12:30 am
content: Quote from: trilerian on May 12, 2023, 05:06:02 pmI have never tried to lower the output voltage before but it is definitely doable. However, the original 100 Ohm voltage adjustment VR on the control board only allows for +/- 0.5V changes on the nominal output 12V, which leads to even smaller range when the output voltage is reduced to 7 to 9V. You can't adjust between 7~9V using the existing VR unless several parts are changed or the VR is replaced. So I think we'll keep it as a fine voltage adjustment once the output voltage is set.I don't see any low voltage shutdown implemented in hardware but it is possible it is done in software inside the PIC chip. Since I have the 1200W HSTNS-PL11 in my collection, I will try out the modification and tell you exactly what to do if I'm successful. It could be a while though.

author: Psi
author_rank: Super Contributor
timestamp: May 13, 2023, 06:51:32 am
content: Might be able to hack a 1kW ATX computer power supply so the +12V rail produces 8.4V by messing with the feedback.Also, check ebay for any TDK-Lambda powersupplys that can do what you want.

author: eblc1388
author_rank: Frequent Contributor
timestamp: May 13, 2023, 11:02:53 am
content: Quote from: trilerian on May 12, 2023, 05:06:02 pmI am happy to report that the HSTNS-PL11 1200W supply does not have low voltage cut off, tested down to 6.2V.Disclaimer: Switching power supply has dangerous line voltages inside and will cause electrocution. The following steps are for reference and should be carried out by competent personal only. You've been warned.1. Open case cover and locate long vertical circuit board. Locate the variable resistor right next to IC MC33274ADG2. Without any output loading connected, adjust output voltage to exactly 12.000V3. Remove all ac power and wait one minute(for the high voltage capacitor inside to discharge)4. Locate a bare copper test pad between two smd resistors. (see image)5. Carefully cut off the copper to isolate them. Confirm the cut is now open circuit with an DVM on ohm range6. Prepare and solder two wires to a 1K5 resistor in series with a 1K variable resistor7. Solder the other ends of the wires to the on board adjustment VR and a capacitor below(red dots, see image)8. Adjust the 1K variable resistor to about middle position9. Power On the unit and check that the output voltage is about 8V10. Verify the output voltage can be adjusted from below 7V to over 9.5V via the 1K VRThe modification was carried out and I can pull about 80A(limited by my load) at 7.0V output. The voltage drop is about 0.2V measured at the output of the power supply.@trilerian: Please report back result of the modification for the benefit of others.

author: trilerian
author_rank: Regular Contributor
timestamp: May 15, 2023, 12:02:56 pm
content: Thank you very much! I have ordered components for the basic design. Hopefully I will be able to make the modification this weekend.

author: trilerian
author_rank: Regular Contributor
timestamp: May 17, 2023, 12:18:10 am
content: I am happy to say that the modification worked! Although I had to deviate slightly. First I ordered the wrong resistor, let’s just call that being new. But I did have a 1k and a 330 ohm I wired in series, so close enough. Second I removed the 01b resistor instead of cutting the trace. Cutting the trace proved difficult.After the mod I was able to get roughly 7.2v to 10.5v on the 1k variable resistor. I’m thinking of changing the design to using a 1k resistor with a 10k vr. I think that would allow for a full range of 0-13v.Next project is to design and print a 3d front to hold the potentiometer and the mini voltage display.I verified it worked with my dyno as well.Thanks again!

author: james_s
author_rank: Super Contributor
timestamp: May 17, 2023, 12:39:33 am
content: Nice job. I might have to try modifying one of those into a variable supply, there are some applications where having a ridiculous amount of power available would be nice.How are they as far as noise? My favorite power supplies are some 675W IBM units I have that are extremely quiet, but they are a tad too small to run both of my main chargers at once at full power.

author: trilerian
author_rank: Regular Contributor
timestamp: May 17, 2023, 12:10:42 pm
content: I would say that noise is only a concern if you get a fan that has issues. But also I am used to it, I have network switches and routers at my desk running constantly everyday.

author: james_s
author_rank: Super Contributor
timestamp: May 18, 2023, 04:09:50 am
content: I'm pretty sensitive to fan noise, to the point that I've installed Noctua fans in most of my test equipment. When I'm charging outside I don't care, but if I'm charging in the house the fans on a lot of hot swap supplies is pretty obnoxious. The IBM ones are super quiet though.