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Starter health exam needed

W

wawrzynskivp

Well Known Member
Hello All

I have been using an Earth-X 680C in the NV Sierras and with an engine heater and pulling the prop through prior to cranking this has worked fine.

The batt was 3.5 years old and gave me a wonky start. The cranking system worked but just barely. I am aware of the battery warm up needs.

Installed a new 680C and saw the same slow performance and large IR drop, engine wouldn't start on first crank and the battery BMS took the battery offline on the second attempt. Hard internal fail, battery light still on three days later.

So: Battery problem or excessive current on starter? Right now it's two to one against the starter, but those things are pretty basic and very reliable.

Does anyone know of an in-situ field test for proper resistance on a SkyTec NL?
 
Freemasm said:
Apply Occam’s razor and this guide.


https://skytec.aero/aircraft-starter-performance-issues/

Vegas odds are a contractor based on what you’ve stated so far. Good luck.
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Too few Amps isn't the suspected problem, it is the possibility of too many.

I see max Ohms, but what I am looking for is too few Ohms indicating an internal short that pulls current without providing torque and trips overcurrent protection on Batt's BMS.
 
wawrzynskivp said:
Too few Amps isn't the suspected problem, it is the possibility of too many.

I see max Ohms, but what I am looking for is too few Ohms indicating an internal short that pulls current without providing torque and trips overcurrent protection on Batt's BMS.
Click to expand...

That would also be my guess. HOWEVER, I would not expect an over current scenario would create in internal fault that doesn't reset. I can see the BMS designer putting in a max current limiter to avoid runaway, but sure hope it would self-reset and not create a permanent fault. I struggle to see a reason why a current limiter trip should condemn a battery, unless they used a fuse. I don't think that you can completely rule out the battery given the symptoms even thoiugh the odds don't point there. Further, too little resistance should over spin the engine and not show as sluggish performance. It is very possible that the fault was an under voltage (due to too much resistance) and not an over current. Pretty sure that the BMS takes the battery offline when volts drop below a minimum and maybe with all the current involved it can't tell the difference between the output volttage vs the cell voltage (would seem to be difficult if not impossible to distinguish). This would better explain the symptoms, especially the sluggish performance. Did you put a charger on it to see if the fault goes away?

I always thought that a starter had around .1 ohms, so not really sure how you could get much less resistance than this other than a dead short at 0 ohms. I suppose that a failure of the insulation on the windings could create a dead short and prevent a proper magnetic field from being produced, as could conducting debris populating the spaces between the pads on a the commutator. Put a meter probe on the case and the other on the copper tab sticking out of the starter and see what it reads. Be sure to also spin it while measuring, looking for spikes in resistance, indicating a brush issue. The only things creating resistance in a starter are the brush commutator interface and the resistance due to the length of the wire on the windings and these are pretty thick and not that long.

A more definitive test would be to measure the voltage drop at the battery while cranking. That will identify any resistance issues (high or low) anywhere in the starting circuit, but won't rule out a defective battery. A defective battery can read correct voltage with no load but drop significantly with a load. A good old fashioned carbon pile tester will rule that in or out for the battery.
 
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wawrzynskivp said:
Too few Amps isn't the suspected problem, it is the possibility of too many.

I see max Ohms, but what I am looking for is too few Ohms indicating an internal short that pulls current without providing torque and trips overcurrent protection on Batt's BMS.
Click to expand...

Yep. Sorry. I don’t read but detail like I should. VAF is my bio break reading material. I can only be efficient in any one single phase.

If your theory is a possibility, the only thing I can think of is: measure the current and watch the starter motor skin temps while turning under ~ no load (take the plugs out). The amps have to go somewhere/manifest as some type of energy.
 
A little more data

Using Earth-X's 10 A charger the battery was 'fully charged' before the failure. Attaching the charger after the fault light lit made it look like the battery was nearly fully charged and a normal finishing charge cycle ensued. This did not clear the fault light and while the battery appeared fully charged and was able to power the displays, it was unable to crank the engine a second time. Of course the fault light was still illuminated so I cannot even guess what the BMS was doing at that point.

I agree that it is probably the battery and a warranty battery is on the way. Earth-X feels confident that they had load tested the battery before they shipped it and there is a high probability that the engine and electrical is at fault.

Poor connectivity to either the starter or solenoids would account for poor cranking, but would not challenge the battery in a way to cause the BMS to trip either on voltage or amperage if the BMS were working properly.

So I was looking to rule out excessive amperage. I have an inductive handheld ammeter that purportedly can display up to 400 Amps. When I get the next battery I can crank the motor while decowled and watch the draw. I just wanted to see if anyone knew how to rule out the starter internal short so I don't blow another BMS to severe amperage if that's what's going on.
 
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wawrzynskivp said:
I have an inductive handheld ammeter that purportedly can display up to 400 Amps. When I get the next battery I can crank the motor while decowled and watch the draw.
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Most of those only work on AC. The versions that also do it for DC are quite expensive.
 
Could it be your starter?

I had similar symptoms you’re describing and swapped out batteries, cables and a solenoid on the firewall. All to no avail. However once I changed the starter’s solenoid (in the starter itself) everything worked as it should. If you have the light weight Plane Power starter it is quite common for these solenoids to fail the way you have described.

Pull your starter and replace the solenoid with a ford starter solenoid. I wish I could remember the part number but they’re available at most auto parts stores.
 
Tankerpilot75 said:
............Pull your starter and replace the solenoid with a ford starter solenoid. I wish I could remember the part number but they’re available at most auto parts stores.
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OP said he has a SkyTec NL. Those don't have the Ford solenoid.

And for others wondering which Ford solenoid (for the SkyTec LS model), it's for a 2000 Crown Victoria.
 
Closing the Loop

SkyTec offered that they do not provide diagnostic numbers for testing, rather they described they 'performance test.' So I was left assuming the starter was okay, turns out it was.

Replacement battery from Earth-X arrived and behaved normally.

Observed 220A max in rush current and roughly 190 Amps sustained. Voltage drop at the battery was as low as 10.3 V. Three ten second cranks each separated by two minutes. Cranking response was strong.

So the lesson learned here is that with our modern batteries a new battery is not a sure thing until you see it perform the way you expect.
 
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