Lower engine starting voltage?

This is a forum for discussing the development and testing of alpha MS2/Extra code. Documentation
(Runs on MS2 and Microsquirt)

Moderators: jsmcortina, muythaibxr

Post Reply
diegom6
Master MS/Extra'er
Posts: 376
Joined: Wed Jun 14, 2006 1:50 pm
Location: Lima,Peru-South America
Contact:

Lower engine starting voltage?

Post by diegom6 »

Hi there,

I think the MS it's bit sensitive with the volts that recieve to operate. I'm not so sure if a car with low battery voltage (because someone left a bulb on, etc) could start..those situations when it cranks almost and in starts before waste the last-minimum volt fo th ebattery to make it run. Can MS II fire up the engine under those circunstances?

I ask this because I had kinda low battery voltage, enought to pwer the MS and connect it to my lap top but it was weird..RPM were full ConfiG Error was ON and bunch of other odd things.

Exist any minimum required voltage to let MS II fire up the engine? If so, how much it is?

-Diego
BMW 325is Turbo E30 (m20b30) MS II Extra code X.X (13 or 14) Beta 3.0v board - 2.25MT
muythaibxr
Site Admin
Posts: 8228
Joined: Thu Oct 14, 2004 12:48 pm

Post by muythaibxr »

The voltage has to be high enough for the voltage regulator to actually regulate voltage... I think the voltage has to be around +7v for that to work.

Ken
diegom6
Master MS/Extra'er
Posts: 376
Joined: Wed Jun 14, 2006 1:50 pm
Location: Lima,Peru-South America
Contact:

Post by diegom6 »

Well, 7+ it's pretty decent number to let it work. Altough, not sure why with about 10--11 volts I got a config error once.

I will have to test in my car once it's back the MS II...with a poor charged battery and see what I get.

Thanks,

-Diego
BMW 325is Turbo E30 (m20b30) MS II Extra code X.X (13 or 14) Beta 3.0v board - 2.25MT
offtrack
Helpful MS/Extra'er
Posts: 65
Joined: Wed Jan 09, 2008 6:41 pm
Location: Puget sound, and Peru. yah 2 homes.
Contact:

min volts , "looking from pure theory, not offical MS&

Post by offtrack »

min voltage .
first not counting things you have connected externally, as they have there own specifications, eg: Ignitions modules ,Injectors? , fill in the blank?

the MS, would have 2 specs. (theory based)

1:static low voltage min. is a function of the 5v regulator,
the spec for that is at the manfuctures web site for such regulator.
LM2937ET 5v "a low drop out regulator" Designed for cars !

this regulator will hold 5v reg. when the battery has 6v applied.

called the worse case 1v minimum differential drop out spec.

that does not mean the injectors will work at 6v, ok?

this is a system and not an object, the spec of the system is another matter completely. please look at all the pieces and take scope readings.


2: the dynamic min. voltage.

now we get to the meat and potatoes of it all
while cranking the starter can still work on some cars from 7-8v.
this is a limit of the starter solenoid (it drops out mechanicaly).

Imagine that starter is spinning and that the battery is low.
way too low , in fact. (my Miata drops at 10v , other cars 9v)

it is spinning away and as each piston comes up to fire, it compresses air and fuel and the current rises directly proportional to this compression.
as the current rises , the voltgage sags. ( battery internal resistance)


the MS2 or the injectors, or the wiz bang Ignition box will drop out as some point, but the MS will drop out at 6v.

dynamically.

to see this you must have a scope, (most VM are useless for realtime data, DMMs)

observing with a scope you will see peaks and valley's , almost like a
sign wave pattern.
this voltage can be expressed as RMS , Average and many ways but on a scope it is Max and Min. (actual voltage)
when the sign wave drops below 6v the regulator will in fact drop out at this point or very close. A Digital voltmeter will lie and report Peak ,or average or RMS depending on the meter or the mode selected.
Some fancier meters can be made to report MIN DC.


the MS2V3 has one of the best regulators one can buy in the electronics business. (many others drop out at 7v)


lastly there is noise.
If you have lots of noise on the ground (poor wiring of same) then this noise adds to the 6vdc.

so, if you have 0.5v noise, then the min drop out is 6.5vdc.
the Injector drivers on the MS2v3 sink the current of the injectors right at the ground plane of the MS2v3, this means that one has to make sure the
ms2 has all the ground wires connected (non missing) with 20 guge bus wire to a heavy 14gage (approx) ground cable to the intake manifold.

that is how I keep my low impedance injectors quiet.

I hope the helps understand this topic.

related:

keep the battery charged. To 12.65 vdc (room temp)

when using a stim and an external power pack, be sure to
have close to zero ripple.
Wall warts come in many flavors.
unreguated and regulated, the unregs, have tons of ripple.
this ripple can drop too low , easy.
go for the Regulated type. 12vdc reg 500ma.



related 2:
do not confuse power problems with communication problems.
I had to buy a quality RS232 5mbps com board, PCMCIA before my DELL would ever talk to a MS2V3 MSextra. @115kbaud, A Dell problem !
"wont flash, ramdom errors with MT "
MS2V3+msextra,beta21+
DiyAutotune! < the best!
custom pnp harness done, default timings.
idles, cool, tripadation sets in, MLV soon.
2 years till retirement, then doing MS on wifes family cars. for economy $7 gallon fuel.
Post Reply