[SOLVED] Voltage drop when starting car

[yoannes]

Hi everyone.
I tried to look everywhere and couldn't find a way to fix my problem.

I am using a microcontroller in my car's battery I use a voltage regulator (**broken link removed**) to get my 5V, everything works fine. But when I start the car the voltage drops and turn my microcontroller off..

What can I do to keep the 5V? Its ok for me to make a small circuit to prevent that.

Thanks

 

[dick_freebird]

You could diode-block the supply feed and add enough supply
capacitance to ride out the sag, perhaps. Raw voltage would
still be over 12V running, plenty of headroom.

But maybe it's your car that wants fixed. Cranking voltage
should stay over 8-10V in good condition, but bad grounds,
weak battery, corrosion etc. all can detract.

If the load is modest, for this gizmo, you might even consider
using (4) NiMH batteries and designing yourself a charge
controller instead that only tries, when IGN is on. Which
might be as simple as a diode-blocked, resistor limited to
C/10 or so, feed. If C/10 exceeds your average current
draw then you're good.

 

[yoannes]

You could diode-block the supply feed and add enough supply
capacitance to ride out the sag, perhaps. Raw voltage would
still be over 12V running, plenty of headroom.

But maybe it's your car that wants fixed. Cranking voltage
should stay over 8-10V in good condition, but bad grounds,
weak battery, corrosion etc. all can detract.

If the load is modest, for this gizmo, you might even consider
using (4) NiMH batteries and designing yourself a charge
controller instead that only tries, when IGN is on. Which
might be as simple as a diode-blocked, resistor limited to
C/10 or so, feed. If C/10 exceeds your average current
draw then you're good.

Hi,

Thanks for your reply. I will try to make the diode to block with caps. I will find a diode that can hold 2A and try.. :lol:

B. Regards,

 

[schmitt trigger]

Or you may try a super-capacitor at the output, isolated from the regulator with a Schottky diode.
That could give you a backup of several seconds seconds.
You may want to adjust the regulator's output voltage something like 0.2 volt higher.

 

[yoannes]

If used a NiMH battery, do I need to make a charge controller? or I can just use the car's controller?

My problem for capacitor is the current I need, the cap will need to be very big for just a few seconds

 

[Audioguru]

If used a NiMH battery, do I need to make a charge controller? or I can just use the car's controller?

OF COURSE a Ni-MH battery needs to have its own charger circuit.

 

[yoannes]

Hi, I've been looking for a CI charger controller and still couldnt decide on what to use.. Can you advise witch is best to work with?
I was thinking to use a 7.4V 800mAh lithium battery

 

[Audioguru]

A Lithium battery needs to have a Lithium battery charger circuit with its maximum current set to the requirement of the battery. Or the battery might explode or catch on fire.
The "7.4V" Lithium battery also needs a circuit that detects its voltage dropping to 6.4V then disconnecting its load.
A 2-cell Lithium battery should not be stored fully charged at 8.4V. It lasts much longer if it is stored at about 7.0V then charged before use.

 

[andre_luis]

You could diode-block the supply feed and add enough supply
capacitance

I performed the same approach on a design for an alarm system for vehicles and worked fine.

 

[yoannes]

Using a diode worked, but to get the capacitance is the problem, 5V 1A took me over 3000uF cap and couldnt keep the board on

 

[D.A.(Tony)Stewart]

Perhaps 3 AA cells with Schottky power diode will keep supply output going for sags in Car start. Smaller than Cap. If using rechargeable AA, then using another diode with high resistance for float charge.

Then final solution is 3 diodes. 3 AA batteries with Diode OR for 5V or 4.3 then reverse diode to float charge 4.7V, setting regulator to 5.3 or just high enough to get 5 V nominal..

 

[yoannes]

Hi,

I want to thank all of you.. I could finish my project.
Here super capacitors are hard to find, so I had to use AA rechargeable batteries