Parasitic draw

[Illini Pete]

No I didn't disassemble the starter, the motor turned and ran smoothly but the Bendix was a little erratic. That turned out to be a problem. I think I've finally got the problem of parasitic draw solved and I'll give a complete report once I get the new ignition switch and starter I've ordered installed.

Thanks, Pete

 

[RevB]

No I didn't disassemble the starter, the motor turned and ran smoothly but the Bendix was a little erratic. That turned out to be a problem. I think I've finally got the problem of parasitic draw solved and I'll give a complete report once I get the new ignition switch and starter I've ordered installed.

Thanks, Pete

If you ever do decide to R&R the starter.....the brush springs are fiddly and you want to be under a sheet on a solid floor. They will fly several yards. The sheet resticts where they go. Ask me how I know . Had one that bounced off the 10 foot ceiling *tunk* and landed somewhere with a metallic *tink*....which left the open tool box lids as the likely place. Took a half hour to find the damn thing....

 

[StarTech]

I still like to know how an item connected to an open circuit, which a solenoid is open circuit when the contact are not closed, draws current. Much be by magic...

 

[Illini Pete]

I finally asked myself that question! The only way I could see the starter motor running was if the solenoid contacts were closed and the only way that could happen is if 12v were being delivered to the solenoid thru the little red wire and that could not occur - or wasn't supposed to - unless the ignition switch was in the start position. Didn't know what was going on because one of the first things I checked was the ignition switch. I had checked it for continuity when there was supposed to be continuity and no continuity when there wasn't supposed to be, using the service manual wiring diagram and switch diagrams and my multimeter, between the various contacts. Everything seemed to be OK but the proof is in the pudding. I put everything back together after cleaning and checking all the socket plugs and ground wire, turned the key to start and the starter motor whirred to life but the Bendix did not engage and the motor would not stop when I turned the key to off, in fact wouldn't stop for any key position until I disconnected the battery neg wire. This all told me I needed a new starter motor because of the non-functioning Bendix and a new ignition switch because the old one would not shut off when in the off position. I just got the new starter and new ignition switch about 10 min ago but won't have time to put then in until Monday

I hope I solved my problem with the new switch and starter. I was deceived by my half-assed checking of the ignition switch or I would have saved myself a few days of grief!

 

[slomo]

He probably had the key ON when he connected the battery cables. Little spark jumped a bit. Maybe he has headlights that come on with the key???? Or the solenoid is shorted closed slash welded from amperage strikes when the key goes to start???

OP doesn't know what a solenoid is. Probably should sell the mower and get a pro lawn crew.

 

[Illini Pete]

Slomo Thanks for your wonderful, enlightened post.

 

[Auto Doc's]

He probably had the key ON when he connected the battery cables. Little spark jumped a bit. Maybe he has headlights that come on with the key???? Or the solenoid is shorted closed slash welded from amperage strikes when the key goes to start???

OP doesn't know what a solenoid is. Probably should sell the mower and get a pro lawn crew.

Hi Slomo,

You know this, but I am sharing this with the masses who don't.

I have seen a lot of people who coin the phrase "parasitic draw" lately but have no idea what it is or how to test for it using a DVOM. Most just break out the credit card and start buying up the parts online until they give up or accidently fix the issue without really understanding how.

Ohm testing circuits is not the answer because a damaged wire with only a couple of strands will provide a "false positive" reading on the meter (DVOM).

The only way to really test is to isolate the wires and apply 12V battery power to each of them. Then check with a meter from one end to the other of the wire while current is applied, if any significant voltage reading above .1V is present on the meter, that is considered a "voltage drop" or "parasitic draw". I have corrected more bad battery cable crimps than I care to remember with that simple test. Yes, a meter will read voltage on a single wire/cable from end to end if a connection is bad or corroded while power is applied.

Since the introduction of plastic start switches years ago, it has been common for the start switch contacts to get hot and short out internally or go open circuit more than ever. This was rare on the older INDAK metal body switches, but those days have passed.

 

[StarTech]

AutoDoc you do not understand Ohm's Law....Any increase in resistance in a circuit will lower current flow as any decrease increases it.

Parasitic [leakage] current draw is where something is pulling some addition current by lowering the overall circuit resistance not increasing it. Parasitic [leakage] current draw is where an module is actually using a little current when the main function is not in use. It is called standby current usage (parasitic current draw).

A good example is my external hard drive. It not operating all the time but the little LED is still drawing very small current all the time.

And while we are at it even batteries have their own parasitic [leakage] current draw which is why they need recharging every so often even not in use.

Ohm testing circuits is not the answer because a damaged wire with only a couple of strands will provide a "false positive" reading on the meter (DVOM).

This is because only a small current and voltage is applied. As those couple of strands heat up so does the resistance increases as the atoms separate farther apart. This is why you see hot spot when there are fewer strands. I have seen where two conductors laying side by side where the insulation have got damage to arc weld due to this increase resistance at the shorting point. Think of this like it is an incandescent light bulb. Look the size of the wires going to the filament. They are a lot larger then the filament. As current flows thru the filament it heats up until produces light. Quite hot which why it is made if Tungsten which has a very high melt temp in a vacuum. Now when a light bulb is first turned on there is a huge inrush of current until the filament get hot then the current drops as its resistance increases.

 

[Illini Pete]

Star Tech, thanks for your detailed post. I'll cut to the chase of where I wound up and even though I'm not sure of how, I seem to have the parasitic draw solved. I first heard the term parasitic draw to refer to a condition where a battery (automotive) lost charge because current was flowing out of the battery when everything was (seemed to be ) turned off. Not referring to my late model 911 that has umpteen computers that use current around the clock so it's always on a battery tender. I used the term to describe my situation when I got a spark when attaching the negative (ground) cable to my battery. One of the first things I suspected and checked was the ignition switch as I saw that as the main control of everything involving electricity. The wiring diagram in the Cub Cadet service manual has diagrams of the 7 post switch that show the connections between the various posts when the ignition switch is in the off, start, run1 and run 2 positions. I checked everything using my multimeter set to continuity, not ohms (resistance) for the reason you mentioned. Everything seemed to check out OK but it turned out there must have been something going on inside the switch that connected the B (battery) post to one of the other posts (possibly the starter solenoid). In any case, when I got everything together after cleaning and checking connections, I started the tractor and the starter ran but the Bendix didn't engage and I could not get the starter motor to shut off regardless of the key position until I disconnected the battery cable. That told me the switch was bad.

Now with a new starter motor and new switch installed, all is well electrically. I can get the engine to start and run with starting fluid or gas sprayed into the air cleaner openings but dies after a few seconds. I started at the line from the tank to the in-line filter, had good flow to the filter, and after the filter up to the fuel pump. Removed the fuel pump and blew through the intake and outlet, then put the pump back on and got good flow to the carb when I cranked the motor. That's where I'm at right now and today will remove, check and clean the fuel solenoid which I think is where the fuel delivery problem must be.

Comments?

Thanks,
Pete

 

[Auto Doc's]

AutoDoc you do not understand Ohm's Law....Any increase in resistance in a circuit will lower current flow as any decrease increases it.

Parasitic [leakage] current draw is where something is pulling some addition current by lowering the overall circuit resistance not increasing it. Parasitic [leakage] current draw is where an module is actually using a little current when the main function is not in use. It is called standby current usage (parasitic current draw).

A good example is my external hard drive. It not operating all the time but the little LED is still drawing very small current all the time.

And while we are at it even batteries have their own parasitic [leakage] current draw which is why they need recharging every so often even not in use.


This is because only a small current and voltage is applied. As those couple of strands heat up so does the resistance increases as the atoms separate farther apart. This is why you see hot spot when there are fewer strands. I have seen where two conductors laying side by side where the insulation have got damage to arc weld due to this increase resistance at the shorting point. Think of this like it is an incandescent light bulb. Look the size of the wires going to the filament. They are a lot larger then the filament. As current flows thru the filament it heats up until produces light. Quite hot which why it is made if Tungsten which has a very high melt temp in a vacuum. Now when a light bulb is first turned on there is a huge inrush of current until the filament get hot then the current drops as its resistance increases.

When I test for a parasitic draw, I'm not looking for resistance on a circuit, I'm looking for voltage that should not exist on an individual circuit wire. A short to a power due to a pinched wire or a melted connector would be an example.

I have had Ohm tests lead me down a wrong path many times, so no I prefer using a device called a Load Pro or a Halogen headlamp bulb to confirm a wire can actually carry a load sufficiently.

A basic Power Probe and a/or a test light can also give false positive results.