Hi Everyone
I have a homemade car, and it uses an Emerald k6+ engine management ecu although having a new alternator the voltage at the ecu fluctuates +_ .5 volt. My tuner suggests this could throw the AFR off target.
Is there a way I can stabilize this voltage?
My 2nd query is more of a folly I guess. My car weighs 685kg and has a smidge under 400bhp.. I am building a new engine which will have 500bhp. I thought it would be cool if there was a way to use a 12v actuator and lift a section of the boot/trunk lid at speed, and possibly use that as an air brake when i hit the brake pedal. However, my ecu is not connected to anything other than engine revs, so speed would have to be calculated using an air tube similar to an F1 car, Just guessing , but when the pressure builds builds the spoiler lifts, and when the brake lights illuminate the spoiler tips forward.
As my car is mid engined this also allows better ventilation into the engine compartment which would be a blessing
the car's website is www.thespitfire.uk
Thank you!

 

In terms of reducing the ecu voltage fluctuation I would consider adding a buck/boost converter such as this one. It is likely to have the power rating to be able to drive the ecu and has a claimed minimum input voltage of 3.8V (even under extreme engine cranking the vehicle battery voltage should not drop to anywhere near this).

As a precaution, I would also fit a bypass switch should the converter fail and leave you stranded.

https://www.ebay.co.uk/itm/39580888...nEyfCykg/bi7xvv7cg+RBX2g==|tkp:Bk9SR4a3_pDUZA

 

Are you talking the battery voltage reported by the ECU, the battery voltage measured at the ECU, or the sensor voltage?

Typically a fluctuating battery voltage shouldn't affect anything as it is a normal occurrence of any running engine and a properly designed ECU will be more than capable of dealing with it.

The sensor voltage should either be provided by the ECU (normally a 5 volt reference) or a regulator built in to the sensor itself. If the sensor voltage is fluctuating the first thing I would suspect is a weak ground. ECU grounds should go directly to the battery only and sensor grounds should only go to the ECU sensor ground connection(s). Beyond that I would say double and triple check all grounds and measure the voltage drop between the ends of each ground cable.

 

Plus or Minus one-half-Volt is very good regulation,
and will cause zero issues with the Computer or any Sensors.
Your Computer "should" function perfectly with any Voltage between ~10 and ~16-Volts.

There is one exception to this,
if the Voltage is fluctuating because of a poor-Ground-connection,
or inadequately sized Wiring,
You could have serious problems arise from these issues.

Don't mess with the Trunk-Lid rising trick,
You need to do some extensive testing to find out if it will have any effect, if any effect at all.
These types of modifications are quite often
not allowed by the rule-book that You will be required to follow, depending upon your class.
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Are you talking the battery voltage reported by the ECU, the battery voltage measured at the ECU, or the sensor voltage?

Typically a fluctuating battery voltage shouldn't affect anything as it is a normal occurrence of any running engine and a properly designed ECU will be more than capable of dealing with it.

The sensor voltage should either be provided by the ECU (normally a 5 volt reference) or a regulator built in to the sensor itself. If the sensor voltage is fluctuating the first thing I would suspect is a weak ground. ECU grounds should go directly to the battery only and sensor grounds should only go to the ECU sensor ground connection(s). Beyond that I would say double and triple check all grounds and measure the voltage drop between the ends of each ground cable.

The ecu "dashboard" provides reading like afr, rpm etc.. it also includes voltage - I have attached an mp4 of the Emerald interface. it actually fluctuates between 12.5 and 13.2volts. I was hoping for a simple voltage stabilizer to keep things steady at 12v as soon as the alternator kicks in - or volts exceed 13v

 

There is zero advantage to having any perfectly "Stabilized-Voltage".

If You are still stuck on this as being the answer to some odd problem that You may be having,
there are 2 practical solutions ............

1)
Install a much larger Battery,
or install 2 brand-new Batteries, and connect them in parallel.
( If You go with 2-Batteries, they must be exactly identical in every way )

2)
Install a much larger Alternator.
A factory-stock Alternator from a large Truck is a good bet for
keeping the Voltage "stable" for any and all conditions You may have.

3)
If You are actually experiencing a definite, identifiable, repeatable, PROBLEM ................
.....................................................................................................................................................

Double-up on ALL GROUNDING WIRING, ( or increase the size of the wiring ).

Especially, DO NOT use the Car-Body-Sheet-Metal for ANY Ground-Connections, EVER.

If You have a remote-mounted-Battery, ( more than ~2-feet, (~61cm), from the Engine-Block ),
You must install massive 2-Gauge, ( ~25/35mm squared ), Wiring between
the Negative-Battery-Terminal and the Engine-Block.

The Engine-Computer must have ALL GROUND Connections going directly to the Engine-Block.

The Main-Power-Supply -"Battery+"- wire from the Computer
must run directly to the Positive-Battery-Terminal, ( with an appropriate Fuse at the Battery ).

NO Power for anything can be taken directly from the Alternator-Output-Stud or Starter-Solenoid-Stud.
All Power must be taken from the Positive-Terminal of the Battery, AT the Positive-Battery-Terminal.
No exceptions.

The Battery must be continuously connected to a "Battery-Maintenance-Charger" at all times,
if the Car is not driven daily.
If this rule is not followed, the Life-Expectancy of the Battery WILL BE shortened,
and, every time the Engine is started,
the Alternator will be overloaded trying to charge the Battery,
which, if the Engine is not run for at least a half-hour each day,
will never completely charge the Battery.
This will reduce the Reserve-Current-Capacity of the Alternator,
which will cause Voltage fluctuations at idle-speeds, while trying to charge a depleted Battery.
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The ecu "dashboard" provides reading like afr, rpm etc.. it also includes voltage - I have attached an mp4 of the Emerald interface. it actually fluctuates between 12.5 and 13.2volts. I was hoping for a simple voltage stabilizer to keep things steady at 12v as soon as the alternator kicks in - or volts exceed 13v

My apologies, but I don't download files from people / places I don't know.

At minimum it should be showing 13.5 Volts while running and charging. Most alternators produce closer to 14 volts when running. 12.5 would mean your alternator is not charging. Do you have underdrive pulleys installed? Does the change correlate with changes in RPM?

If it is a random thing then I would check grounds, battery connections, alternator connections, and ECU connections. Do you have your power supply to the ECU through a relay or through a switched power somewhere?

There are far too many variables to consider to be able to adequately diagnose this over the internet. Long story short when running you should be able to measure 13.5 - 14.5 volts at the battery and everything else should match that. Anything less means either a faulty charging system, bad ground connection, loose connections, damaged wiring, corrosion (which I am suspecting isn't an issue yet), improper wiring, and probably a few more things I can't think of.