[M17x R2] - Dual PSU (2 x 240W)

[StamatisX]

@imsolidstate that's correct, 15A and 19V so 285W (from the wall it must be higher, I estimate around 328W given the efficiency of the PSU is around 85%). Yeah I don't need a bridge and that's why I didn't use all the pins, just the 3 of them, but it was easier to use instead of finding and soldering separate diodes.

[refusedchaos]

Holy moly! I've been meaning to try this out but never seen how the mod actually looks like. Thank you!

[radji]

Ehh, I wouldn't trust those diode bridges to balance the load. Had one of the bigger ones in a Variable-frequency motor drive, kept having to replace the diodes since they don't balance the load, its like a see saw more than a bridge. If one side draws more than the other for too long, it will keep taking on more of the load until it reaches the overload point.

[imsolidstate]

I agree that using diodes won't balance the load. One power supply puts out slightly more voltage than the other, and it will shoulder most of the load until the voltage droops enough that the second one starts sourcing current. However as long as neither supply is driven into overload, it shouldn't be an issue. The fact that the voltage should drop as current increases means the loads won't balance, but they shouldn't go into overload either. It kind of works like an overload protection.

VFDs are a lot different, they handle large switching currents and inductive spikes, which is probably why the diodes failed. In this application it is a straight DC load so the diodes should be fine.

The only way to truly balance the loads is to build a switching circuit with a couple MOSFETs controlling the power supply inputs. Let the power supplies switch charging a capacitor that feeds the motherboard. Overkill for this though really.

[radji]

Really? I would think that a straight DC load would be harder on a diode than an AC current since it doesn't alternate the current between the two lead, leaving all heat on one side of the rectifier all the time. But then again, I'm not that savvy with DC power. I was working with 3 phase power, where the current load was distributed across 3 lines.

[imsolidstate]

Well, we were talking about diodes in a VFD. A VFD has a three-phase rectifier as it's input stage, which is passed to an RC filter to create DC. The drive then synthesizes a sine wave by rapidly cycling the DC rail to the motor windings and varying the duty cycle to create an equivalent AC voltage. The switching creates lots of noise and back EMF that is hard on the semiconductors.

In comparison DC loads are easy to calculate and design for. If the diode is rated at 15A, it will work up to 15A. In a laptop there aren't any inductive loads that will produce voltage spikes, so the diodes will be fine as long as they are rated for the current they are operating at.

[HOPELESSLYFAITHFUL]

for just an average guy i knew a good bit about power stuff but this is way over my head lol

[radji]

I'm going to shut up now. I only have a basic knowledge of VFDs, Soft Starts, etc. Just enough to be dangerous and install and troubleshoot them. imsolidstate obviously is far beyond my level...probably an electrical engineer of sorts, yes?

[imsolidstate]

Yeah, BS in electronics engineering and MS in computer science. It's okay though, I like talking about this sort of thing because you can always learn something new. I guess that's how I ended up here anyway, I was bored and needed a new project.

[radji]

Nah, I'm just a dumb diesel mechanic. Better at fabrication and mechanical stuff than electronics. This is just my hobby.

[DigitalFubar]

ok so im going to ask a dumb question... I understand load balancing.. and if this is not doing it then whats the difference between this and just wiring to psu's together? ++/- -/ signal signal wouldn't that work also? or would i now be supplying my lappy with a god awful amount of power?

now.. I want to do this with 2 m18x psu's and id like to know exactly what i would need and where to get every thing ill need..

[DigitalFubar]

all right got my second 330 watt psu in and want to give this a go... i followed some of the links for the parts and there dead.. any one got any input?

has this dual psu mod proved viable and valuable? have you been past the limit imposed by the 240 id chip.. or even past the limit of 1 power supply?

I see ive seen what 380 watts max out of a single psu right? have you been able to go past that point and get say 400watts out of the dual psu set up?

[DigitalFubar]

what about this.. for just using 2 laptop psus..

1) measure their voltages (let's say that they're 19.55V and 19.75V

2) Determine the maximum current (let's say they're 3.2A and 2.4A)

3) Place a resistor in series with each one that will drop the voltage to 0.5V less than the lowest measured voltage at the rated maximum current

OK so drop voltage to 19.05V

R1 = 0.50/3.2 = 0.15 ohms (3W)

R2 = 0.7/2.4 = 0.29 ohms (3W)

Connect the grounds together, and connect the resistors in series with the +ve output.

As long as the voltages remain fairly stable, the power supplies will share the load fairly equally. Note that the resistors need to be at least 3W (maybe go for 5W since you'll need to insulate them) and they'll get fairly warm.

Also. the voltage to your laptop will be around 0.5V lower than normal. This probably won't matter much.

If the power supplies are running without a load, one power supply can feed into the other in this arrangement. It will *probably* be safe. Placing diodes in series with the outputs will fix this, but at the cost of lower voltage to the laptop and more dissipation.

note.. this should keep us from tripping at the max value set at the id chip right ?

[Khenglish]

what about this.. for just using 2 laptop psus..

1) measure their voltages (let's say that they're 19.55V and 19.75V

2) Determine the maximum current (let's say they're 3.2A and 2.4A)

3) Place a resistor in series with each one that will drop the voltage to 0.5V less than the lowest measured voltage at the rated maximum current

OK so drop voltage to 19.05V

R1 = 0.50/3.2 = 0.15 ohms (3W)

R2 = 0.7/2.4 = 0.29 ohms (3W)

Connect the grounds together, and connect the resistors in series with the +ve output.

As long as the voltages remain fairly stable, the power supplies will share the load fairly equally. Note that the resistors need to be at least 3W (maybe go for 5W since you'll need to insulate them) and they'll get fairly warm.

Also. the voltage to your laptop will be around 0.5V lower than normal. This probably won't matter much.

If the power supplies are running without a load, one power supply can feed into the other in this arrangement. It will *probably* be safe. Placing diodes in series with the outputs will fix this, but at the cost of lower voltage to the laptop and more dissipation.

note.. this should keep us from tripping at the max value set at the id chip right ?

Combining a 330W m18x PSU and a 240W m17x PSU resulted in the 330W PSU having a resistor getting so hot that it melted its own solder. The PSU wasn't damaged and did run like this, but obviously this is not ideal or acceptable. The 330W PSU had a higher unloaded voltage too, so I am surprised that this happened. The PSU would not shut down early as if massive amounts of current was flowing into the 240W PSU instead of the laptop. People have combined 240W PSUs for the SLI m17x R1, so the 240W seems OK with being combined, but not the 330W.

For your case I would only bother with adding a resistor to the higher unloaded voltage PSU. If you don't do that then the lower voltage PSU will never get loaded. Diode use is likely not required.

[Guest]

@imsolidstate - I am also wanting to do a dual 330W AC adapter mod for the M18x and have both of them. I sent an email to you a few days ago asking for input. As DigitalFubar has asked the same in this thread, any input. Will simply connecting the two together work correctly? Do you have any suggestions on how we should approach this?

[Guest]

I figured it out. It has to be wired in parallel, not series. Wiring it in parallel maintains the same voltage as one AC adapter while (hopefully) delivering higher power output. I need to test the power output to see what it's actually doing, but the dual 330W mod functions with no errors in detection, charging, etc. Basically followed the wiring diagram of what StamatisX did with the dual 240W units, except that I did not purchase meters and I have the AC adapter signal wire from both adapters connected. My heat sink is mounted to the exterior of the box with a metal cover plate sandwiched between the rectifier and heat sink. After I confirm the power output, I'll post a thread with photos in the M18x sub-forum. A teaser photo is provided below. It looks promising, as I am able to run 3DMark11 with the CPU and GPU heavily overclocked without manipulating CPU clock speeds using TactX profiles with ThrottleStop. I ran all the way through the benchmark at 4.6GHz on CPU and GPU core OC above 1.1GHz across all 3DMark11 tests without a shutdown. That wasn't possible before.

@DigitalFubar - if you need any assistance let me know.

[TBoneSan]

Lol you Champion Mr Fox. I can't wait to see the insanity that will soon follow

[juliant]

I think you are better in using a 800W desktop PSU if you will be able to get same output and a better amperage. Then you can overclock to the sky and bring up again your 'mobile' AC to overcome heating issues.

[imsolidstate]

@imsolidstate - I am also wanting to do a dual 330W AC adapter mod for the M18x and have both of them. I sent an email to you a few days ago asking for input. As DigitalFubar has asked the same in this thread, any input. Will simply connecting the two together work correctly? Do you have any suggestions on how we should approach this?

Sorry Mr. Fox, I was busy.

As you found out, connecting the supplies in parallel with a diode for each will work, but there will be no load balancing. There will be a lot of current on one side, so make sure the diodes can handle the current. Since the original mod was to use a rectifier, you could parallel the diodes for better current handling. Good luck.

[Guest]

Sorry Mr. Fox, I was busy.

As you found out, connecting the supplies in parallel with a diode for each will work, but there will be no load balancing. There will be a lot of current on one side, so make sure the diodes can handle the current. Since the original mod was to use a rectifier, you could parallel the diodes for better current handling. Good luck.

@imsolidstate - Thank you for the reply! If you could provide a link to the type of parallel diodes you would recommend along with a suggestion of the wiring arrangement, I would be most appreciative.

[Khenglish]

@Mr. Fox have you opened up either PSU to see how the resistor I mentioned in the other thread was doing? This resistor is visible with just taking the plastic covering off, and is near the AC in side of the PSU. I noticed there was a problem when glue that was partially covering it started to burn.

[Guest]

No I have not. If I remember correctly, you paired the 330W and 240W? I wonder if that may have had some bearing on it.

It feels like the two halves of the plastic housing may be simply snapped together. Since you have opened yours already, have you discovered if there a simple way to separate them without breaking or marring them? I thought about opening them up just to have a look. I wondered if there are screws under the rubber feet, but did not want to pry them off only to find nothing there.

[Khenglish]

No I have not. If I remember correctly, you paired the 330W and 240W? I wonder if that may have had some bearing on it.

It feels like the two halves of the plastic housing may be simply snapped together. Since you have opened yours already, have you discovered if there a simple way to separate them without breaking or marring them? I thought about opening them up just to have a look. I wondered if there are screws under the rubber feet, but did not want to pry them off only to find nothing there.

[StamatisX]

A warning to those who consider combining two PSUs without the use of a diode.

Our PSUs are Switched-mode Power Supply Units (SMPS) and unless you have two of them with the exact same voltage output, then you gonna end up messing with the duty cycle of the PSU with the lower voltage output and eventually burn it.

Please proceed with caution and at your own risk.

More info about SMPS here:

https://en.wikipedia.org/wiki/Switched-mode_power_supply

[imsolidstate]

Sorry Mr. Fox. I just tried to draw the circuit and it won't work with the bridge rectifier, my mistake. You can only use half of the bridge in this configuration so you would need two bridge rectifiers to go parallel. Just check the rectifier you have to make sure it can take the current, each diode has to handle about 22A of continuous current at max load.