KTM Question on Electrical Circuit - I'm Confused

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6/12/2018 1:23 PM
Edited Date/Time: 6/12/2018 2:31 PM

My 2017 KTM 450SX-F lost all electrical functions including starter, fuel pump, solenoid, etc. I'd hit the starter button and not even a "click" or cycling of the fuel pump or anything. Battery is fine. Traced it down to the ground strap off the battery to the subframe had NO continuity. The grounding strap subframe mounting plate welds had broken so there was no ground for the entire electrical system (i.e. it was an open circuit). Fixed the broken welds, reattached the battery ground and once again all is good.

What puzzles me is when the bike was stationary and troubleshooting the issue I took a voltage tester to the positive terminal on the starter and the other end of the tester to a ground (i.e., the frame). The tester lit up indicating I had 12v power going to the starter. Note this was observed without pushing the starter button or touching anything on the bike. Why/how would I have 12v hot going to the starter when the system was NOT grounded off the battery?

I'm confused why I'd have what appears to be a 12v closed circuit to the starter when the ground off the battery was not attached? I just can't understand why this wouldn't result in an open circuit to the starter?!?!?!

Rick

P.S. FWIW, the broken welds on the subframe were my fault, not a material failure or poor welds.

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6/12/2018 1:27 PM
Edited Date/Time: 6/12/2018 1:28 PM

The Negative terminal on the battery would be grounded, No....

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Riding is Freedom, Freedom is Riding!

6/12/2018 1:48 PM

You were measuring a voltage difference between the positive battery terminal (via a cable from the battery to starter) and ground (frame).

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6/12/2018 1:55 PM

fox1nz wrote:

The Negative terminal on the battery would be grounded, No....

No, that's my point. The battery's negative terminal was completely disconnected due to the grounding strap being disconnected.

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6/12/2018 2:00 PM

erik_94COBRA wrote:

You were measuring a voltage difference between the positive battery terminal (via a cable from the battery to starter) and ...more

I guess I'm not too bright. NOT challenging the help you offered I just don't understand what you're teaching me.

Shouldn't it be an open circuit from the battery's positive terminal to the starter's positive terminal unless the starter button is depressed/pushed which results in a closed circuit?

I wasn't pushing the starter button when I observed 12v directly to the starter's positive terminal.

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6/12/2018 2:08 PM

erik_94COBRA wrote:

You were measuring a voltage difference between the positive battery terminal (via a cable from the battery to starter) and ...more

rikhek wrote:

I guess I'm not too bright. NOT challenging the help you offered I just don't understand what you're teaching me.

Shouldn't ...more

No problem.

Everything connected to the positive terminal should be at 12 volts (that is 12 volts above ground). That only represents a difference in potential energy. When the starter button is pressed, it likely completes a circuit energizing the solenoid and actually making the starter start the engine. With no ground strap, then electricity cannot flow even though there is a potential difference.

https://www.quora.com/How-bike-starter-works

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6/12/2018 2:11 PM

I'm not a super electrical nerd but my guess is current flow. Even though you say the ground was disconnected there was probably a slight connection that was broken when you tried to use anything. Hitting the start button, turning on the fuel pump, heck even engaging the starter solenoid is a high current flow compared to a multimeter.

An input circuit on a meter is in the mega ohm range. Meaning if your going to measure a 12V system, the current the meter draws to do so is far less than 0.000012 amps. Probably not enough to break the small circuit still remaining and hence why the meter read the proper battery voltage.

Just my thoughts anyways.

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6/12/2018 2:15 PM

When a ground is off it does weird things. An example is on a rear blinker on a street bike not grounded properly and is turned on, the other blinker and tailight lights up dim.

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Take it to the limit, one more time!

6/12/2018 2:19 PM

erik_94COBRA wrote:

You were measuring a voltage difference between the positive battery terminal (via a cable from the battery to starter) and ...more

rikhek wrote:

I guess I'm not too bright. NOT challenging the help you offered I just don't understand what you're teaching me.

Shouldn't ...more

erik_94COBRA wrote:

No problem.

Everything connected to the positive terminal should be at 12 volts (that is 12 volts above ground). That only ...more

Ahhh. Now I get it. Thanks for taking the time to explain as it just didn't make sense to me. Been 35 years since I took Electrical Engineering 401 while getting my Petroleum Engineering degree. What you don't use, you forget...

Rick

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6/12/2018 2:47 PM

erik_94COBRA wrote:

You were measuring a voltage difference between the positive battery terminal (via a cable from the battery to starter) and ...more

rikhek wrote:

I guess I'm not too bright. NOT challenging the help you offered I just don't understand what you're teaching me.

Shouldn't ...more

erik_94COBRA wrote:

No problem.

Everything connected to the positive terminal should be at 12 volts (that is 12 volts above ground). That only ...more

The cable that goes to the starter from the starter relay won't be energized until the starter relay is grounded making an electric magnet that connects it to the battery. That is the click you hear when it is working. If he was getting current to the starter, it had to be back feed from not having the ground connected properly.

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Take it to the limit, one more time!

6/12/2018 3:46 PM

Everything electrical is wizardry....basically voodoo. In order to understand and master this black art requires meeting a bad dude at a crossroads at midnight. Just look at history....Genghis Kahn, Hitler, Walt Disney, Madonna....all with uncanny power to control the evil energy. Don't go down this path brother...stay dumb.

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If it ain't yer's don't take it, If it ain't the truth dont say it, If it ain't right don't do it...Marcus Aurelius

6/12/2018 4:02 PM

plowboy wrote:

Everything electrical is wizardry....basically voodoo. In order to understand and master this black art requires meeting a bad ...more

ROTFLMAO. Nice.

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6/12/2018 4:34 PM

Not sure with that bike but almost all starters on all types of vehicles have a cable that runs from the positive to the solenoid which is usually attached to the starter. Its is a fat cable. The ignition circuit is a tiny wire that simply closes a solenoid providing power to the starter motor. If your ignition switch was on the same circuit it would be the same fat wire. Now as for the open ground i am puzzled as there must be continuity back to the negative terminal through the frame. Maybe at the time you tested it there was contact due to leaning on seat, or something like that.

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sponsored by zip tie, JB weld and peanut butter and jelly

6/12/2018 7:07 PM

plowboy wrote:

Everything electrical is wizardry....basically voodoo. In order to understand and master this black art requires meeting a bad ...more

rikhek wrote:

ROTFLMAO. Nice.

A Tulsa boy. I'm headed to Washington Irving this weekend to camp/fish. Bastards sold our traditional summer spot at Salt Creek north to the corporate machine.

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If it ain't yer's don't take it, If it ain't the truth dont say it, If it ain't right don't do it...Marcus Aurelius

6/12/2018 9:05 PM
Edited Date/Time: 6/12/2018 9:18 PM

resetjet wrote:

Not sure with that bike but almost all starters on all types of vehicles have a cable that runs from the positive to the ...more

I can assure you with 100% certainty there was NO contact or continuity at all to the battery's negative terminal. I was so puzzled I even ensured the bonding strap was inches equidistant away from any potential grounding source and not possible to arc across. Battery was encased in the rubber/plastic battery holder.

I was not touching the bike...

These facts are what had me puzzled as my thoughts were just as yours.

The post provided above by eric94COBRA explains what I was observing. As Eric states I was measuring the voltage differential/potential.

The post that follows was offered in a different thread and also does a great job of explaining what I observed.

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6/12/2018 9:18 PM
Edited Date/Time: 6/12/2018 9:24 PM

PROVIDED BY Trail Digger:



The meter will only read a difference in potential energy. You'll have 12V to anything not connected to the negative. If you got another battery and connected them in series lets say, you would read 24V between the positive and metal.

In order for the starter to work, the (-) side of the starter needs to in some way return back to the negative lead in order to get 12V flowing. The 12V needs to return back to the power source, otherwise it won't work.

Pretty much all vehicles achieve this by grounding to the frame or other metal parts as well as the negative terminal grounding to the frame. Since the ground plate welds are broken, then there is no way for anything to work since it has no path back to the power source. Electrical circuits need to be complete and return to where they came. If not, it's open.

Every circuit is connected back to neutral or (-) in DC circuits. If not, it's an open hot condition and in the instance of AC power, it can lead to damaged equipment if you lose a neutral.

In DC circuits, equipment won't be damaged; it just won't work since it has no where to go.

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6/13/2018 6:02 AM

WoodsRacer wrote:

I'm not a super electrical nerd but my guess is current flow. Even though you say the ground was disconnected there was ...more

This is is exactly correct. Some meters have a low Z function (very well low resistance as opposed to very high) for this exact purpose. Draw high(er) current and the voltage drops to zero.

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6/13/2018 6:03 AM
Edited Date/Time: 6/13/2018 6:10 AM

The low Z function is an ac setting. For DC I have put a 1k ohm resistor in parallel with the meter leads and same effect, voltage drops to zero

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6/14/2018 5:05 AM

Amp x volts =watts Much ty

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If I'm healthy enough to complain. I shouldn't be complaining.

11/14/2018 10:17 AM
Edited Date/Time: 11/21/2018 12:43 PM

Hi... you say the ground was disconnected there was probably a slight connection that was broken when you tried to use anything. Hitting the start button, turning on the fuel pump, heck even engaging the starter solenoid is a high current flow compared to a multimeter.

turnkey pcb

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