Poor Cranking? Check Your Solenoid!

The headlight is drawing maybe around 5 amps thru the sytem, a PM starter will average 200-250 amps, so this testing method is flawed.

I use a carbon pile type battery load tester to load up the system for tests like this, that way you can actually draw the full current thru the sytem. You could also disable the ignitions and do the tests but this takes a bit of precaution to avoid accidents.

Don't forget that a good ground is just as important to a good flow of electrons as the positive "feed".

Good Data Point!!

Well, V=I*R so if the headlight is drawing 15 amps, and the voltage drop is .15, then 150A > 1.5volt drop
and 300A > 3.0volt drop

From a practical standpoint, I don't know if the resistance ( .01 ohms) of the solenoid (assuming this is where the resistance occurred) will remain the same at 300 amps for the first compression, but if it does, then that is a big voltage drop.

A wound starter will produce less torque per amp than a permeant magnet starter. Think about it, you are providing power to create the stator field too. So it is necessarily less efficient for the same starting torque, i.e. it takes more amps for same torque.

I am assuming you measured voltage from the battery to the headlight. If so, that resistance is the full circuit. This means if a loose connection is in there, it could still be the culprit.

Look at it this way, a solenoid is cheaper than a starter, so if you want to replace a part, experimentally, replace the solenoid.

edit - what Walt said.

No, you did it wrong. Also, the method is not "flawed". While starter circuit is engaged you need to check voltage AT the two solenoid posts and compare the two. Not just the drop at the battery. You should do the same with the master solenoid too because you may be dropping there. If you prefer listening to other "experts", then please disregard.

aerhed said:

No, you did it wrong. Also, the method is not "flawed". While starter circuit is engaged you need to check voltage AT the two solenoid posts and compare the two. Not just the drop at the battery. You should do the same with the master solenoid too because you may be dropping there. If you prefer listening to other "experts", then please disregard.

Click to expand...

Guys, thanks for sticking around. I was a one man show trying to get these voltages and one arm short of it being easier. This is what I did:

I built 2 x 18 ga. wire, 4 ft each with alligator clips at each end. I disconnected the positive going to the starter at the starter, connected an alligator clip to the positive lead going to the starter and connected the other end to the positive of the light. I connected the negative of the light to the alligator clip of the other wire and connected the other end of that wire's alligator clip to various other grounding points (negative of the starter, engine case ground, firewall ground, negative at a/c battery). The light was next to me on the wing so that I could engage the starter with one hand and take voltages with the other. I also messed up and provided the wrong readings.

Battery Voltage with everything off - 12.2
Battery Voltage with Master on and Dynon D10A and MicroEncoder ON- 11.7
Battery Voltage with Starter engaged- 11.4
Voltage at Upstream side of Master solenoid and Starter solenoid whith starter engaged-11.4
Voltage at Starter with Starter engaged- 11.34

That would mean a 0.06V drop across the starter solenoid right?

My starter solenoid is in a very hard and awkward place to get to and by myself was not able to get a voltage drop across the solenoids while turning the key. I did manage to take a voltage on the upstream post side of the starter solenoid with starter engaged (11.4 V, same as upstream and downstream posts of Master solenoid and same as battery). I was not able to reach the 'out' post of the starter solenoid, but it is connected directly to the starter, so in my mind, in essence, the voltage at the starter (11.34) would be the same...correct?

I suppose I can determine the resistance and amp draw of the light then apply the formulas assuming a 200 to 250 amp draw from from starter to determine what the voltage drop at the starter solenoid would be seeing as that's where the drop seems to be occurring (0.06V) with the lamp hooked up. I think it's a 40W light so as someone said, about 5 amps. Seeing as 5 amps is 40 times less than 200 amps, can I assume that with a 0.06 V drop with 5 amps, the voltage drop would be 2.5V with the 200 amp starter connected. What should the voltage drop be across a good starter solenoid be?

I was drawing down to 6 or so Volts at the battery with the starter connected and engaged but that was after holding the key on for a second and the prop not being able to push through the compression stroke. Skytech says I should have at least 11V at the battery and 10V at the starter.

It is pretty cold here (-10F or so) and my battery checked in at 170 CCA which is what Odessey says it should be but maybe its not enough in my application. Maybe I should preheat the battery a bit in the winter months prior to starting.

I know it sounds logical and cheaper to change the starter solenoid but let me tell you, the builder did not take into account having to do that eventually. Although a wound starter is a more expensive fix, it would be a thousand times easier and from what I have read from others with similar 'bump and start' type symptoms, going to a wound starter made the difference. But others with those same symptoms replaced the solenoid and had success too.

What does connecting a battery booster pack to the battery for start do? The plane starts like a champ with a booster pack. Is it purely adding cranking amps?

Crank73 said:

Guys, thanks for sticking around. I was a one man show trying to get these voltages and one arm short of it being easier. This is what I did:

I built 2 x 18 ga. wire, 4 ft each with alligator clips at each end. I disconnected the positive going to the starter at the starter, connected an alligator clip to the positive lead going to the starter and connected the other end to the positive of the light. I connected the negative of the light to the alligator clip of the other wire and connected the other end of that wire's alligator clip to various other grounding points (negative of the starter, engine case ground, firewall ground, negative at a/c battery). The light was next to me on the wing so that I could engage the starter with one hand and take voltages with the other. I also messed up and provided the wrong readings.

Battery Voltage with everything off - 12.2
Battery Voltage with Master on and Dynon D10A and MicroEncoder ON- 11.7
Battery Voltage with Starter engaged- 11.4
Voltage at Upstream side of Master solenoid and Starter solenoid whith starter engaged-11.4
Voltage at Starter with Starter engaged- 11.34

That would mean a 0.06V drop across the starter solenoid right?

My starter solenoid is in a very hard and awkward place to get to and by myself was not able to get a voltage drop across the solenoids while turning the key. I did manage to take a voltage on the upstream post side of the starter solenoid with starter engaged (11.4 V, same as upstream and downstream posts of Master solenoid and same as battery). I was not able to reach the 'out' post of the starter solenoid, but it is connected directly to the starter, so in my mind, in essence, the voltage at the starter (11.34) would be the same...correct?

I suppose I can determine the resistance and amp draw of the light then apply the formulas assuming a 200 to 250 amp draw from from starter to determine what the voltage drop at the starter solenoid would be seeing as that's where the drop seems to be occurring (0.06V) with the lamp hooked up. I think it's a 40W light so as someone said, about 5 amps. Seeing as 5 amps is 40 times less than 200 amps, can I assume that with a 0.06 V drop with 5 amps, the voltage drop would be 2.5V with the 200 amp starter connected. What should the voltage drop be across a good starter solenoid be?

I was drawing down to 6 or so Volts at the battery with the starter connected and engaged but that was after holding the key on for a second and the prop not being able to push through the compression stroke. Skytech says I should have at least 11V at the battery and 10V at the starter.

It is pretty cold here (-10F or so) and my battery checked in at 170 CCA which is what Odessey says it should be but maybe its not enough in my application. Maybe I should preheat the battery a bit in the winter months prior to starting.

I know it sounds logical and cheaper to change the starter solenoid but let me tell you, the builder did not take into account having to do that eventually. Although a wound starter is a more expensive fix, it would be a thousand times easier and from what I have read from others with similar 'bump and start' type symptoms, going to a wound starter made the difference. But others with those same symptoms replaced the solenoid and had success too.

What does connecting a battery booster pack to the battery for start do? The plane starts like a champ with a booster pack. Is it purely adding cranking amps?

Click to expand...

yan,
OK, until a real expert responds . . .

1. -10F already puts your battery at a disadvantage at 60-70% of room temperature energy level. The 12.2 volts is consistent with that.

2. (key) 2.5 volts drop across the starter contractor (solenoid) would be too much. 0.2 volts seems to be the accepted standard. The problem here is that without a full 200 amp load, or more than 5 amps, this might not be an accurate projection.

3. Yes, adding a second battery (booster) acts like a constant voltage source and allows much higher voltage at the starter, so there is more torque and power for starting.

There is no hard conclusion until the contractor voltage drop is measured at a higher amperage, but you have several things going against a free spinning engine. a. cold battery, 2. cold engine, 3. possible degraded starter contactor.

No guarantees, Yan. I think if you attach the booster, then hook up for a voltage drop measurement, one good spin should tell you if the contactor (solenoid) is bad. It could still be a lead, if you are compelled to test at the starter post.

Even with a warm battery, eliminating this (possible) voltage drop, you could still have a starter issue but fixing what is broken, then moving to the next issue will ultimately bring your system to full capability. That said, I don't remember what you posted about engine preheat and oil temps for this test. Warm oil/cylinders is a must for starting at -10F ambient.

Good Luck.

Would a starter require or draw less amps without the resistance of the propeller. All of my cowls and panels are off right now while I troubleshoot so preheating will be difficult (other than a oil pan heater). What if I disconnect 'unbolt' the starter from the engine and secure it elsewhere where it won't engage anything. I am not suspecting a faulty starter as this one is brand new and starts pretty much the same as my previous starter (NAPA car starter).

Does anyone else have a wood prop setup with an Odessey PC680 battery and -10F temperatures here?

If I can generate a 200 amp load and measure the voltage drop at the starter solenoid it would point me to either the solenoid or the combination of a weak (cold) battery and a magnet type starter. If the drop would be acceptable then I would spring for a new wound type starter. If the voltage was out of limits then I would change the solenoid. As mentioned, the solenoid change will not be easy and will be awkward due to its location.

I suppose I could put it all back together....preheat, start with a battery booster pack, warm her up, then do the voltage check.

Back in the day when I lived up north I installed a second battery in my car so it would start in the morning, short of that I would have to bring the battery in the house to keep it warm or jump it.

So.. maybe you just need more juice, perhaps you should consider installing a second battery or replacing the PC680 with larger battery with more capacity?

Personally I would start with replacing the PM starter, it demands more from the battery/system which is already struggling in the cold temps.

I had some poor cranking last week, so I started searching around for a suitable replacement for my Ford style starter solenoid. There are a couple of threads where this might be helpful, but I decided I would post here, for anyone who might search for ' NAPA Solenoid ': ST81 is a good one to use, has a grounded case, so install it on the firewall, connect the leads, connect the start circuit wire to the 'S' post and you are on your way (If you are headed to some other store, just ask for a starter solenoid for a '69 Mustang, you can remember that, right? ).

Still building? Carefully consider your relay locations.

After going through a starter relay replacement, I was cursing the whole time about where I put my master and starter relays just under the battery box. (I believe it is where the plans recommended to put them) It was tough getting a wrench on anything under there.

There's a bunch of empty space on the firewall next to the battery that would be a great spot for these relays, but you need to plan ahead while building.