Voltage Drop Help

[another69]

At times, only while cranking, my battery voltage will dip below 9 volts for a split second. This only affects my Aeromotive fuel pump Speed Controller, which goes into a fault and shuts down when the signal wire dips below 9 volts. This signal wire really doesn't have any real amp draw. Wondering if I can add some sort of a capacitor or diode to help with this? Any suggestions?

[andrewb70]

At times, only while cranking, my battery voltage will dip below 9 volts for a split second. This only affects my Aeromotive fuel pump Speed Controller, which goes into a fault and shuts down when the signal wire dips below 9 volts. This signal wire really doesn't have any real amp draw. Wondering if I can add some sort of a capacitor or diode to help with this? Any suggestions?

I'd say you have a ground problem or your battery is toast. While cranking a proper system should stay above 10 volts.

Andrew

[AU Doc]

What battery are you using? How old is the battery?

[another69]

I'm using a small Braille 3121 battery. Old one was doing the same thing and tested low. Replaced it with the same 3121 battery that is brand new & fully charged. Things are fine most of the time with the new battery, but once in a while voltage still dips. I spoke with Aeromotive and they are familiar with the issue. They suggested momentarily breaking power to the speed controller, which would work. I was just hoping for some sort of tiny capacitor that would supply 12vdc even if supply power (while cranking) dips below 9vdc for that moment. This is the only electrical issue I am having.

[andrewb70]

....Things are fine most of the time with the new battery, but once in a while voltage still dips.....

The fact that it is an intermittent problem leads me to think that something is wrong...In other words, you do have an electrical issue, somewhere...While adding a capacitor may work, this seems like a crutch to mask the real problem.

Andrew

[AU Doc]

A cap might help, but it would probably need to be pretty big. Unless you add a set of diodes to the circuit the cap is going to try to prop up the voltage of entire circtuit during the start cycle. So unless you’ve got a hefty cap, it’s goong to discharge quickly.

I’m not familiar with the ratings on that battery (pulse cranking amps is not the standard rating for an automotive battery, I’m pretty sure cold cranking amps is the norm), but 30 AH seems to be on the low end.

So I’d say you may need to optimize your starting circuit if you’re going to use a light (lower capacity) battery. You need to minimize voltage drop to your starter (both in the + and - legs) and do your best to keep the starting cycle short.

[another69]

By intermittent I mean that the issue only happens while cranking and not given enough time to charge in between starts. Cranks over great, you would never know there was an issue except for the pump controller being so sensitive. The voltage drop is at the battery, so I am ruling out wiring and starter pulls about 300 amps which is below the rated 750CA of the battery. The only way I cought the voltage drop is with the Holley data logger & the min setting on my multimeter. It happens so fast that you don't see it just watching the meter.

I guess it is due to the locked rotor amp draw of the starter. Much like when the AC kicks on at my house. Even though I have 200 amps of service, the voltage drops enough for a split second to dim The lights. The pump controller is just too sensitive, and I don't want a bigger battery. Braille suggested their lithium battery that is over $2000!!!!

I looked online and found several small electronic voltage regulators that may work, what do you guys think?

[GoodysGotaCuda]

I suppose I ask what the issue is with the controller? Does it drop out and the engine won't start? Is there a boot-up time that is causing the issue?

I'd be tempted to put a "crank only" 12v wire to the fuel pump directly if there is much of an issue...

Is your voltage measurement directly at the battery, or are you reading this voltage somewhere else?

[another69]

Voltage Drop is at the battery, so no other 12v source unless I add another battery. The controller goes into fault under 9v. All led lights flash and it stops the pump. If you cycle the signal wire to it again it will reset and run the pump normally

[nokones]

I have the same problem with the split second voltage drops. My Holley HP EFI ECM data logger also caught the voltage drops and I can see it in my voltage gauge on the dash. I have two grounds directly from the battery, one to the chassis and one to the engine block and my battery is located behind the passenger seat down in the radio module compartment. I'm using an optima red top battery and it is almost 3 years old. I have checked and checked the grounds. I have even wire brushed the surfaces at contact points and made sure that the battery clamp is tight.

I probably going to have JCG Restoration and Customs rewire the car. Over the years there been many bandaids affixed to the electrical system and various things have been popping up that have been electrical related. Just this past September, JCG had to rewire the two fuel pump relays because the 30 amp fuse for the relays kept popping. I think it is time to just doing everything at once. The car is almost 30 years old.

At first I thought it was a compression issue and was getting kick back because of the timing. This problem has been present with two different type of starters, one with a Tilton reverse mount starter and now with a Powermaster Gear Reduction Starter. So, it can't be the starter. One thought is it might be the circuit/wire from the ignition switch to the starter solenoid.

[dhutton]

Try installing something like this in the power line for the pump controller. It should help depending on the width of the glitch.

https://www.ebay.com/itm/DC-12V-Auto....c100508.m3226

Don

[AU Doc]

9 Volts is low. The fact that it's short duration doesn't matter.

At any rate, a regulator may work. You'll just have to make sure it's rated to supply the controller.

[dhutton]

9 Volts is low. The fact that it's short duration doesn't matter.

At any rate, a regulator may work. You'll just have to make sure it's rated to supply the controller.

A conventional linear regulator can only regulate to a voltage higher than its input so it won’t help here imho. A filter with some significant bulk storage capacitance should help.

Don

[AU Doc]

A conventional linear regulator can only regulate to a voltage higher than its input so it won’t help here imho. A filter with some significant bulk storage capacitance should help.

Don

I'll admit these electrical parts are much smaller than I work with normally, so I'm outside my realm of expertise. That said, I know Pololu makes some step-up/step-down regulators specifically for battery powered applications where the voltage starts above the regulated voltage and ends below it. I have no idea what sort of power levels we're talking about here for the controller, though.

[dhutton]

I'll admit these electrical parts are much smaller than I work with normally, so I'm outside my realm of expertise. That said, I know Pololu makes some step-up/step-down regulators specifically for battery powered applications where the voltage starts above the regulated voltage and ends below it. I have no idea what sort of power levels we're talking about here for the controller, though.

That is a switching (as opposed to a linear) regulator and a pretty extreme fix for a glitch imho. A decent filter should suffice.

Don

[andrewb70]

Kenny,

Double check the cranking timing in your Holley tune. You might have the timing set too high while cranking, which is hard on the starter.

Andrew

[TheJDMan]

If the voltage drop is truly at the battery as you say then I would suspect the battery simply has insufficient CCA capacity for the cranking load.

[GoodysGotaCuda]

If the voltage drop is truly at the battery as you say then I would suspect the battery simply has insufficient CCA capacity for the cranking load.

Yep.

[AU Doc]

If the voltage drop is truly at the battery as you say then I would suspect the battery simply has insufficient CCA capacity for the cranking load.

^^^ this - x2

[oleyeller]

Or, Too much resistance in the starting circuit. Every connection, every terminal, every length of wire ad to the circuit resistance. Have you ever checked for heat in the wiring following a start?