MS v3.0 power supply criticism

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baldur
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MS v3.0 power supply criticism

Post by baldur »

I've been spending some time recently diagnosing a reset problem in a car that has Megasquirt v3.0 board with a hc08 processor.
Through the whole thing I've come to the conclusion that the power supply has design flaws that I will detail here.

Polyfuse F1 is on the wrong side of the filter caps, VCC 5V rail has no filter caps directly attached except for a single 100nF bypass cap at the processor.
Same 5V rail as powers the processor also runs out of the box to power external sensors, a bad idea. Analog rail should ideally be fed off it's own regulator. 5V power sent out of the box is insufficiently filtered from power inside the box.
Vsyn (PLL analog feed) does not have much capacitance, touching a multimeter probe to the inductor can be enough to trigger a reset.
Flyback current should not be fed back on the same wire as supply voltage, it will create a measurable ripple. Flyback should have it's own +12V wire going directly to the injector loom. Telling people to attach a "car audio capacitor" to the 12V wire is not an acceptable workaround.
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Fred
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Re: MS v3.0 power supply criticism

Post by Fred »

car audio capacitor - LOL

Yeah, I've heard people complaining that the filtering to the ADC ref is not good enough. I think it was davebmw that posted about a huge improvement from that? Or maybe it was that guy on the turbo Z site? Either way, others mention it too.

That's pretty impressively bad that the lead capacitance/load of the meter was enough to destabilise it and cause a reset! I can't say I was expecting that :-/

Thanks for the write up there, it's good to get this stuff out where people can see it so they can make an informed decision before going MS.

Fred.
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jharvey
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Re: MS v3.0 power supply criticism

Post by jharvey »

Baldur sounds like I should inquire about a review of a PCB layout I've done and posted. Were waiting for software to develope more before we make a proto, so we don't know for sure if it's all predicted right, and I'd be very happy to get more input about it. Here are some links to it, and it's documentation.

Download the KICAD files, or PDF files from here.

https://sourceforge.net/project/showfil ... _id=286538

The wiki is here

http://freeems.aaronb.info/wiki/doku.php?id=freeems_1.0

And the forum thread is here

http://www.diyefi.org/forum/viewtopic.php?f=9&t=333
RandomHero
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Re: MS v3.0 power supply criticism

Post by RandomHero »

Sorry to bump and oldish thread but are the problems that serious?
I'm about buy a ms2 v3pcb. am i making a mistake? should I go with another ecu?
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darrow
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Re: MS v3.0 power supply criticism

Post by darrow »

My biggest problem is because I am running low Z injectors and I am using the flyback circuit on the V3.0 board. There is an incredible amount of electrical noise that was throwing off pretty much all of my sensors. TPS, MAP, and RPM to a little extent. The fix I did and what is suggested on the MS boards is to separate the +V12 for the injector drivers and put a car audio noise filter on the incoming power line to the MS board between where the injector drivers split off and the board.

All and all for the price I think it is a decent ECU. I am not 100% satisfied with it (which is why I am watching what is going on here). It is finicky when it comes to electrical noise. Pretty much to be safe you will want to shield every line that goes into the engine bay.

I got V3.0 board because it seemed to be the better of the two board. On the V2.2 board the flyback circuit is different.

you are now 2 cents richer.
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Fred
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Re: MS v3.0 power supply criticism

Post by Fred »

RandomHero wrote:Sorry to bump and oldish thread but are the problems that serious?
I'm about buy a ms2 v3pcb. am i making a mistake? should I go with another ecu?
Until I put out FreeEMS 1.0 (quite a while away yet) it's still your best choice.

You have two options :

Mod the board to fix it - difficult.
Run enormous OTT wire for power and ground - what I did.

Either will work well enough.

You should always make sure your grounding and wiring is well done in terms of shielding and lack of loops etc. Provided you do that and one of the above you should be OK.

IE, buy ms2 + v3 for now :-)

Fred.
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
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n00bs, do NOT PM or email tech questions! Use the forum!
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RandomHero
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Re: MS v3.0 power supply criticism

Post by RandomHero »

Thanks Fred, appreciate your input. Definitely cant wait for FreeEMS 1.0
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