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voltage drops

  • Thread starter Thread starter kent
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kent

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I have been a tech in the automotive field for almost 30 years, I reciently had to go to a class on electrical properties for my continued service, we had to go through ohm's laws (ugh!!!) for the thenth billionth time, and part of that class was on voltage drops, which, if you are in the industry know is very crucial to the performance of electrical devices, so I decided to have fun with my bike, and here is what I found. the starter had a drop of almost 3 volts ( my starting problem? ) I had about 1.5 volts drop to the regulator ( could have a regulator/ rectifier problem? ) so I grounded the starter and rotor case to bring the drops down to about .05 volts, which has cured most of my problems. I think ( for what it's worth ) that most of electrical problems that suzuki's suffer could be from grounding issues. my 82 gs 1100 is still working on the factory regulator. food for thought.
 
Most of us have multiple grounds and also have replaced most of the other wires with new and heavier guage. Use soldered lugs wherever possible. Scraping the paint or rust from the contact point on the frame is also a great help.

"I think ( for what it's worth ) that most of electrical problems that suzuki's suffer could be from grounding issues. my 82 gs 1100 is still working on the factory regulator. food for thought."
__________________
I think you hit the nail right on the head :)
 
Absolutely. I first got my 850 about a year ago, and it was plagued by intermitent electrical problems. The ole' fluke helped me figure out that all of my frame grounds had voltage drops of around 2- 3 ohms, as well as various connections throughout the system. Nothing several days of tedious wiring work couldn't solve, though.
Anyway, very good observation. Drop tests are one of the first things you should do when faced with an electrical problem.
 
Agreed, voltage drops in the system are a no no. On the whole, if you have gone through the wiring harness and minimized voltage drops, you will rarely have electrical problems.

Earl
 
You use a meter to measure voltage across various places in a circuit to determine how much voltage they are using.
The theory is that in any circuit loads will use up all the voltage in the system before returning to ground. Take a simple circuit with a bulb connected to a 12v battery. If you place your leads across the bulb, you will get a reading very close to 12v because the bulb is using up all of the voltage to work. If you have any patches of high resistance in the circuit (corrosion, pinched wires) they too will use voltage, taking away from whatever it is you are trying to run. If you have a corroded ground, your bulb may not light. Place your leads across the ground wire this time, and you may find a volage reading (drop) of 4v, leaving the bulb only 8v.
In the real world, every inch of wire uses a little voltage because of resistance. A good rule of thumb is a couple of tenths or so of a volt across a length of wire or a connection. Much more and you may have found your problem. Hope this makes sense. I'm sure google has many better explanations.
 
Good explanation gslim.

For that that aren't mathematically challenged v = i * r. It's a simple relationship that suggests whenever there is current flow, the voltage drop over that portion of the circuit (wire, connector, bult, etc.) is directly proportional to the resistance. For wires and connectors you want low resistance, hence a low voltage drop.

Note that voltage is also proportional to current. High current circuits (starters for instance) are influenced heavilly by added resistance in connections. This added resistance produces heat (power = i * i * r) at a square of the current. This added heat will in turn create a greater resistance and before long we have fried parts.

The sum of the voltage drops must equal the voltage source for any circuit. That's it for today. :)
 
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hungryman said:
The sum of the voltage drops must equal the voltage source for any circuit. That's it for today. :)
Click to expand...

This is known as Kirkoff's Law

http://www.omega.com/techref/das/divider.html

However,

When dealing with a motor ( like a starter) the rules change a little bit due to back EMF from the windings. Motors also generate electricity as they run. If you measure the resistance of a motor sitting on a bench you would think It would draw many times what it should. But when it is turning the magnets inside the starter create electrical energy that opposes the incoming voltage. This is known as Lenz Law and it goes hand in hand with Farrady's law that turns the motor over in the first place.

http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/farlaw.html

I'll stop now before anyone's head explodes.
 
duaneage said:
This is known as Kirkoff's Law

http://www.omega.com/techref/das/divider.html

However,

When dealing with a motor ( like a starter) the rules change a little bit due to back EMF from the windings. Motors also generate electricity as they run. If you measure the resistance of a motor sitting on a bench you would think It would draw many times what it should. But when it is turning the magnets inside the starter create electrical energy that opposes the incoming voltage. This is known as Lenz Law and it goes hand in hand with Farrady's law that turns the motor over in the first place.

http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/farlaw.html

I'll stop now before anyone's head explodes.
Click to expand...
Back EMF doesn't change Kirkoff's law - it still stands. (I'm not sure if that's what you were saying or not.)
 
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Absolutely!
However someone might measure the resistance of a starter and think it was either shorted out or was likely to cause too much of a current drain
 
duaneage said:
Absolutely!
However someone might measure the resistance of a starter and think it was either shorted out or was likely to cause too much of a current drain
Click to expand...
It would if it wasn't allowed to rotate. :cool:

That's why a bad battery is very hard on starters. There simply isn't enough current to turn the starter, so the back emf isn't generated to help oppose the current flow. (Motors are driven by current, not voltage.)

Purely resistive circuits are a snap. When capacitances and inductances are included you then get into derivatives and integrals. As my professors used to say - "It's a second order world we live in." (Note: not amusing to most.)

Should we start a class? :-D
 
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This is how you do a voltage drop test on the ground side of your starter motor circuit. The reading is only taken when the load (starter) is being used

Place volt meter neg lead on the neg battery post (not cable)
Place pos lead on the starter motor housing
Read voltage on meter as the starter is being driven
This value is your total voltage drop or voltage lost on this circuit

There are only 3 connections in this circuit. One is where the battery cable is attached to the neg post. Two is where that cable attaches to the engine and the third is the starter to engine connection. These connections are where you get your individual voltage drops. The sum of these individual voltage drops is equal to the total voltage drop in this circuit. To measure the individual drops you put your meter leads on either side of the connection and then read the voltage as the starter is being driven. For instance to check for a poor connection at the battery....One lead goes on the post, the other onto the cable.....Seems kind of silly because they are both on the neg side of the battery right next to each other.....Now hit the starter button and read the drop while its cranking....If you see 2 volts, than the starter is running with only 10 volts applied and you need to clean your batt connection... Now do a drop on the battery + side of the starter circuit....One lead to the battery positive post and the other lead to the B+ post on top of the starter. Run the starter and read the drop. This is the total voltage drop on the B+ side of the starter circuit. If you get 2 volts here and you had 2 volts on the ground side as measured above, than the starter is running on 8 volts.......These voltage drop tests are done dynamically, with current flowing and will find faults that an ohmmeter can not........Billy
 
hungryman said:
Back EMF doesn't change Kirkoff's law - it still stands. (I'm not sure if that's what you were saying or not.)
Click to expand...
I think that most starter motors are series wound motors. Some may be permanent magnet. In a series wound motor the maximum current is at zero RPM (also the maximum torque).
 
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