Acceptable voltage drop when cranking?

CMS said:

I do & have to measure this stuff with regularity. Low voltage at starter = lower max current. Even for in-rush a lower voltage at the starter will result in a lower peak in-rush current...

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I think you may be confusing the non-load voltage with the load voltage (both initial start up and past that).

QUOTE A starter will not draw more current with a lower voltage than it will with a higher voltage QUOTE

A starter WILL draw more amps at a lower voltage. Sometimes much more. This is the double whamy of winter starting... decreased battery voltage and thickened oil.

caltexflanc said:

I think you may be confusing the non-load voltage with the load voltage (both initial start up and past that).

Click to expand...

Just pulled out my notes from a job a few weeks ago with a complaint of slow starting and "Not enough oomph" says the owner...

House Battery Bank Start:

Bank Resting Voltage 12.74V
Peak in-rush - Fluke 376: 378A
Peak Low Voltage Measured at Starter Motor - Fluke 289: 11.492V



Start Battery Bank Start:

Bank Resting Voltage 12.71V
Peak In-Rush Fluke 376: 264A
Peak Low Voltage Measured at Starter Motor - Fluke 289: 8.234V

Same starter motor but different batteries able to deliver different voltages at the starter. A higher voltage at the starter results in higher available cranking current.

This is also why when you do nothing but replace battery cables from say a 4GA factory installation, on some 70's & 80's boats, to 1/0 or 2/0 the owner always tends to think they got a new starter motor when nothing but the battery wiring has changed. The new wire is now able to deliver a higher voltage to the starter with less voltage drop, stacked on top of battery voltage sag, thus better cranking with more "oomph"..

Perhaps tomorrow if I have time I will demonstrate this on my test bench in a video clip...

Since you did a rewire,i would review your work. Some where there is your problem.

"For a starter motor, as battery voltage drops, the max current potential that can be developed by the stater motor goes down." YES

" A starter will not draw more current with a lower voltage than it will with a higher voltage" YES

"A starter WILL draw more amps at a lower voltage. Sometimes much more. This is the double whamy of winter starting... decreased battery voltage and thickened oil. "
This is true weather its AC or DC if the motor is "universal wound" and has brushes." NO

The joy of the brushed motor is feeding it lower voltage simply makes it weaker, and does not cause it to draw more amps .

This is the reason starters have brushes , and are not wounld like air conditoners , where when the voltage drops the watts remain the same by drawing more amps , till the white smoke escapes.

At tag sales I am always on the lookout for items with brushed motors.

Things like chain saws that may be on a 400 ft extension cord don't mind a bit.

Even circular saws can be found that work without overheating on a cruddy dock, a poor inverter or a too small noisemaker.