Measuring High Amperage

[Save Old Iron 1,563]

Ahhh yes

we hear it all too often - clickety clickety clickety of the starter solenoid as we try to start a tractor.

we hear - "gee, the starter is getting pretty hot during cranking" or " the starter seems a little slow in spinning".

Many have asked for a way to tell if the starter is drawing too little amperage (corrosion) or too much amperage. (shorted windings).

Well, here at SOI University, we don't spew guesses, we collect the facts and apply diagnostic logic to pinpoint tractor issues with laser like accuracy. A less expensive and more enjoyable tractor repair experience is your direct benefit from these beliefs.

First in a long series of diagnostic modules in our toolbox will be an ammeter capable of measuring over 100 amps with pinpoint accuracy. This device, when connected to an oscilloscope, can even measure cranking rpm's and even diagnose generator brush and commutator condition all by the display on the o'scope screen.

I can hear the shouts in the crowd now - "SOI is selling his Snake Oil again".

Well I have three words for you - High Amperage Shunt.

Here is a picture of the prototype product.

A picture of the 100AMP SHUNT

A pic of the voltmeter connections to the shunt

And finally the $1.99 meter for - you guessed it - Harbor freight.

The concept is simple. A SHUNT is placed in series with the battery negative lead.

The SHUNT is a precision calibrated resistor that will display a voltage drop of .001 volt for every amp flowing thru the SHUNT.

So, if we have a starter current of 65 amps, 65 x .001 = .065mv.

Measured on the 200 mv scale of a voltmeter, this voltage drop will show as 65.0 on the meter. So the reading is easily interpreted as 65 amps.

Easily connected to the tractor - quickly measures the current and easily disconnected from the tractor.

Now we can collect some facts to support theories (guesses) about the starter condition, battery capacity and resistance within the starter circuit.

More to come as we will investigate two real world issues. We will be putting a freebie 212-5 (knicknamed "Satan's little helper" by its previous owner) next to its bigger D200 brother and checking out some starter issues on both systems. We will also investigate some SG issues on the 857. If I can get my scope working with this setup, I should be able to take pics of the current pulses thru each and every segment of the commutator on the generator unit. The scope picture can then tell if any segments of the commutator are worn or defective. So Kool.

So stay tuned for some high current shenanigans at SOI University - Fall semester.

And for those thinking I forgot about the C160 RR autopsy post, this tool gives me the ability to put the repaired "no user serviceable parts inside" regulator thru its paces on the D tractor. Thus answering too questions about ability to repair these regulators and can regulators be interchanged among different series tractors.

Stay tuned - way more to come on this one.

[MaineDad 85]

Standing bye for more information. This will be a thread I print out and use!

[Save Old Iron 1,563]

This will be a thread I print out and use!

I could not hope for a higher compliment.

Let me know if there is anything in particular you need to know and we can stress that at the beginning of this post.

I am going into a little more theory about how this works later tonight. Mrs. SOI has the grill going and I'm outta here for a while.

[MaineDad 85]

I do not need anything specific. These type of threads have always helped me learn something new and are printed out and put in a 3 ring binder.

[racinfool40 202]

I love them not being much into electrical issues for tractors you got my attention!!! :)

[dkopp 1]

Where did you acquire the shunt and what is the typical cost of said shunt? Just in case someone may want to build one of these for their tool box.

These are some great courses SOI. Wish my college courses were more like these.

[Save Old Iron 1,563]

Dan,

thanks for the kind words. I actually had a college physics professor who made things very interesting - a big time smart ass - but everyone learned quite a bit from Mr. B.

The shunt was acquired on EBAY for approx $18

http://cgi.ebay.com/100-Amp-Shunt-100-mV-O...=item4ce944be6d

the meter was a $1.99 special from Harbor Freight.

the polyethylene cutting board was about $2.00 at Target.

the bolts that hold the shunt to the board are carriage bolts (that need to be trimmed shorter on my board) - the carriage bolts self seal into the soft plastic quite nicely.

I actually had a chance to use the tool today to diagnose a neighbor's C-120 with a no charge condition. Darn, I forgot to bring the camera, but I should have a few extra "how to use" pics this weekend.

I also think I might go to the next larger cutting board and add another additional meter to monitor battery voltage simultaneously with current flow.

Just as an additional note, a lower cost 100 amp shunt can be ordered for about $5 and will work just fine. The issue is that 100 amps flowing thru this lower cost shunt will only produce 75 millivolts - so you lose the 1 amp to 1 millivolt correlation.

On the 100a / 100mv shunt, 65 millivots = 65 amps of current flow.

On the 100a / 75 mv shunt, 65 millivolts = 87 amps of current flow.

With the 75mv shunt, you save money but need to multiply whatever you see on the voltmeter by 1.3 to get the true amp flow.

[horsefeathers 15]

Old_Iron,

I'am a poke 'n hope electrical troubleshooter!

That gets me in trouble more offten than not!

If I can pay attention long enough here I might learn something!

Where do I send the tuition check for the semester?

Did you finish your multimeter tutorial publication?

For us dummys that don't know the diffrence between,

Volts, amps, Ohms or Infinity!

(can't find my way around the "Dark side of the moon"!) HORSEFEATHERS!

"Snake Oil" that comes out of an iginition coil, right?

[Save Old Iron 1,563]

Did you finish your multimeter tutorial publication?

Bud,

I have not forgotten or abandoned the multimeter tutorial. The tutorial seems to be very much in demand.

I have tried a few ideas on how best to present the information for using a multimeter and how to make sense out of what it shows you.

The RS forum does not allow direct posting of videos or animated screens so I decided to go one of two different routes.

The creation of the "Board of Education" may allow for a quality presentation of the multimeter training here on the RS site.

If the degree of video or animation needed to "get the point across" is not supported on this site, I may have to go to a YOUTUBE type environment, or my own website, or possibly even send DVD's out to people who request them due to DialUp only capabilities.

I'm going to try the "Board of Education" first before continuing on to investigate the other options.

Cold weather is coming, my backside will be in this chair more often and more effort will be put into the tutorial in the fall / winter this year.

Hang in there pal - help is on the way!!

[horsefeathers 15]

Thanks, No BS meter using kindly old chap that likes to play with rusty old tractors and spell words correctly!

Teachers are under apericated in this world!

HORSEFEATHERS!

[Save Old Iron 1,563]

You left out the "Mr. Smiley" part - :)

[horsefeathers 15]

A$$ you kicked Err... You kick A$$!!!!!

MR. SMILEY!

Sir!

HORSEFEATHERS!

[Save Old Iron 1,563]

your just pushing for one of those SOI University tee shirts, aren't ya?

How about taking a crack at designing a logo for the University ?

[horsefeathers 15]

Don't want everyone to think I'am the teachers pet!

SOI University Tee's I'am on it!

apple for teacher? Or acorn?

[squonk 38,936]

I've got a cheapie ($40.00) DC clampmeter that I use to ck charging issues. Can I bring that to class? Or is the supplies and materials list strict and you have to buy everything at the university book store? :wh:

[Save Old Iron 1,563]

I've got a cheapie ($40.00) DC clampmeter that I use to ck charging issues. Can I bring that to class? Or is the supplies and materials list strict and you have to buy everything at the university book store? :)

[horsefeathers 15]

I thought- how much do darn cats change in 2 years? Just operate on older ones!

SOI, Young "cats" need lovin' Too!

The last magazine Errrr... Book I saw "Cat" anatomy hasen't changed much!

The "book store" is rippin' you off! "Cat" anatomy is 6 bucks an issue!

The "Cheeseboard checker" is a good trainer for MM instruction!

This rat is hungry bring on the "cheeseboards"!

HORSEFEATHERS!

[Save Old Iron 1,563]

The "Cheeseboard checker" is a good trainer for MM instruction!

This rat is hungry bring on the "cheeseboards"!

Cheeseboard checker is already in REV 2.0

Pics to followup but I added another $1.99 to the design and incorporated another meter to display battery cranking voltage while the other displays cranking amps.

I have to replace a repaired regulator in my neighbors tractor in the next day or two.

I 'll have some live action shots of the "Cheeseboard Checker" in action.

Then we will all know how many amps a C120 draws on start up? (Cold start at 50 - 60F, all original engine, starter, etc).

Tell you what - closest guess to the actual value wins a personally autographed SOI cheeseboard checker for their very own. I'll let this post sit for a few more days so as to give more people a fighting chance at winning a checker.

Tell your friends and neighbors to chime in on this one - freebie stuff from SOI University on tap !!

[horsefeathers 15]

The boys at "Tappa- Kegga" frat house say 488CCA!

But what do we know? Were hungover and "Have Class" in the AM!

Don't tihnk 'n drive, you might hit a bump and spill your think!

HORSEFEATHERS!

[W9JAB 156]

For us dummys that don't know the diffrence between,

Volts, amps, Ohms or Infinity!

A neat analogy to help understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.

Let's say you have a tank of pressurized water connected to a hose that you are using to water the garden.

What happens if you increase the pressure in the tank? This makes more water come out of the hose. The same is true of an electrical system: Increasing the voltage will make more current flow.

Let's say you increase the diameter of the hose and all of the fittings to the tank. You probably guessed that this also makes more water come out of the hose. This is like decreasing the resistance in an electrical system, which increases the current flow.

The water analogy still applies. Take a hose and point it at a waterwheel like the ones that were used to turn grinding stones in watermills. You can increase the power generated by the waterwheel in two ways. If you increase the pressure of the water coming out of the hose, it hits the waterwheel with a lot more force and the wheel turns faster, generating more power. If you increase the flow rate, the waterwheel turns faster because of the weight of the extra water hitting it.

[horsefeathers 15]

Wow 488cca where did I get that !

I must be workin' on a plymouth!

I really do need help!

[horsefeathers 15]

So that's it I'am in the lead to win the personally autographed SOI

Cheeseboard checker???

Com'on guys I can't win on a frat house drunkin' stuper crap shoot guess!!!

This is how I fix my electrical problems!

Man, there's got to be a better way!

This ain't trouble shootin'! This is shootin' at trouble!!!

HORSEFEATHERS!

[bmuone 15]

OK I say 218cca. But I have to go back and keep reading the question. :)

[Save Old Iron 1,563]

The question is

"if you hook up the SOI Cheeseboard Checker to a stock K series 12 HP engine, what will the ampere draw be to start the tractor from a cold start?"

this is not the cold cranking reserve of the battery but the actual ampere draw thru the starter circuit.

weather is good this week and SOI is on vacation for 2 to 3 weeks.

We will have an answer in a few days.