Rectifier issues

[Jeff-C175 7,202]

2 hours ago, 953 nut said:

power lost in a diode the half of a cycle that is not passed by the diode, this power is converted to heat.

 

But it's not.  That half cycle which the diode does not CONDUCT results in zero added heat because at that time there is zero current flow

 

2 hours ago, 953 nut said:

isn't voltage drop as you would encounter with a resistor, The voltage rejected (not passed) by the diode would be in direct proportion to the current flow.

 

No, not like a resistor because for all intents and purposes the drop across a diode is not a proportionally linear amount as it would be with a resistor.

 

A diode's voltage drop is typically between 0.6V and sometimes as high as 1.2V.  Some diodes (Schottky for example) have less than 0.6V drop.

 

That said, the voltage drop across a diode DOES change with the magnitude of current passing through it, but it is NOT a linear relationship.  The more current that the diode is passing, the higher will be the voltage drop, but it's a SMALL amount.  If a 5 A diode showed a forward voltage drop on a multimeter of 0.6 V it might have a forward drop of 0.65 V when passing 5 A.  This can typically be neglected since it is such a small difference.

 

2 hours ago, 953 nut said:

The half cycle not being passed will produce some heat and a small electronics store 1/4 watt diode would not hold up.

 

 

That is not true.  As above, when the diode is not conducting (the negative half cycle) no heat will be created.  (Unless you want to count the MICRO AMPS of current that would flow in the reverse direction, which is essentially ZERO, and can be disregarded)  Heat in a diode is only produced when the diode is conducting in the forward direction and the power (wattage) is proportional to the current and the voltage drop across the diode.

 

Of course a dime store diode will not work.  That diode should be rated maybe 2X the voltage, and at least 5A for adequate safety margin.  I would use a diode rated for 50V and at least 5A.  This one would work perfectly.  Try and find a power rating in the specifications:

https://www.digikey.com/en/products/detail/vishay-general-semiconductor-diodes-division/P600A-E3-54/2145048

 

So let's say the drop across the diode is 0.75V, and the current is 3A.

 

0.75 X 3A = 2.25W

 

But there's more... That figure is for steady, constant, DC voltage through the diode.

 

Since we're rectifying an AC voltage,  the power would be LESS THAN 2.25W because the diode is conducting only on the positive half of the waveform, and when it is conducting on the positive half, it's half of a sine wave, not a constant DC.  Because the voltage is half a sine wave, also the current will be half a sine wave.

 

To accurately determine the power dissipation of a diode in a half wave circuit, taking the AVERAGE current and multiplying it against the forward voltage drop would give one a close enough number.  So, if that circuit has a 3 A MAXIMUM (or peak) current in the half sine wave, then the AVERAGE current would be a bit less than 1 A (I won't go into the math for this).  This means that the power dissipation of that diode in that circuit would be LESS than 1 Watt.

 

One other point I'd like to make.  You would be very hard pressed to even FIND a power dissipation rating on an epoxy encapsulated general purpose rectifier diode in their data sheets.  Because it is not important.  As long as the PIV (Peak Inverse Voltage) and the Current rating is appropriate, the wattage will be a non-issue.

 

Ask Mrs. Google if you don't believe me.  Mrs. Google knows everything.

Edited November 24, 2022 by Jeff-C175

[Snoopy11 5,714]

1 hour ago, 953 nut said:

You do know I'm a retired EE, right?          NO

 

Ummm... can'tchya' tell?

 

Don

Edited November 24, 2022 by Snoopy11

[Jeff-C175 7,202]

12 hours ago, oliver2-44 said:

Of course they said the same thing about the Mechanical guys.

 

At my place it was sorta like this:

 

   

 

Edited November 24, 2022 by Jeff-C175

[953 nut 55,324]

Edited November 25, 2022 by 953 nut

[Blasterdad 2,692]

It looks to me like you may have a bad key switch, possibly in kahoots with the PTO switch.

Check for voltage at the A terminal on the back of the key switch, ( green wire according to the wiring diagram ).

There should be no voltage with the key off.

If there is voltage, that's what's powering your light board causing your battery drain. = Bad switch.

I say this because according to earlier posts you've determined it's charging, correct?

 

[Jeff-C175 7,202]

1 hour ago, 953 nut said:

this guy named Einstein

 

has absolutely nothing to do with this.  We are not talking about the "Conservation of Energy" here.  Einstein is a 'straw man'.

 

1 hour ago, 953 nut said:

Where did the energy from the half cycle that did not pass through the diode go?

 

It didn't "go" anywhere!  A diode is NON-CONDUCTING in it's reverse state. 

 

Maybe an analogy... when you turn off a light switch, where does that energy 'go' ?  Right... it goes NOWHERE because the switch is OFF.

 

A diode in it's REVERSE BIASED, NON-CONDUCTING STATE is just like a turned OFF switch.  There is no current flow, there is no heat.

 

Why doesn't the energy behind a turned off light switch need to 'go somewhere' ?  Why aren't the wires in your walls, and all your light switches burning up?

 

1 hour ago, 953 nut said:

Did it convert to heat perhaps?

 

No, it did not.

 

Something else to think about:  VOLTAGE is POTENTIAL ENERGY. 

 

Meaning that it isn't 'really' energy at all, until it does some WORK, meaning a LOAD to drive some CURRENT into.

 

1 hour ago, 953 nut said:

If not then why do larger rectifiers have heat sinks?

 

Because larger diodes conducting MUCH MORE CURRENT in the ON, or FORWARD BIASED half of a rectifier cycle don't have enough surface area on their cases to dissipate the heat that is generated during their ON cycle.  Even a MONSTER diode, say 400 or 500 Amps, still will not generate heat in is OFF state.  All the heat generated is done so during a diodes ON, or CONDUCTING state.

 

1 hour ago, 953 nut said:

The only reason I brought up the wattage consideration was to point out that all diodes are not created equally and if someone needs a diode for their three amp system the ones from Radio Shack won't do the job.

 

Yeah, understood, but throw your WATTAGE thing out the window.  You won't find anything from Radio Shack anymore... in case you haven't noticed!  BUT... back in the day, you COULD buy an adequate diode at Radio Shack.  You needed to buy a rectifier diode rated at 50V and 6A, and Radio Shack DID carry them, and that is NOT, repeat NOT a 300 W diode!

 

1 hour ago, 953 nut said:

the US Navy

 

Respect, thank you for your service!

 

 

Edited November 24, 2022 by Jeff-C175

[Snoopy11 5,714]

Excellently put, Jeff. When it comes to electrical, sometimes analogies are necessary and helpful.

 

Correct me if I am wrong, but simply put, when a diode is in reverse biased it simply does not permit current flow much like a check valve.

 

Don

[Jeff-C175 7,202]

6 minutes ago, Snoopy11 said:

Excellently put, Jeff. When it comes to electrical, sometimes analogies are necessary and helpful.

 

Correct me if I am wrong, but simply put, when a diode is in reverse biased it simply does not permit current flow much like a check valve.

 

Don

 

Exactly.  A check valve is also an excellent analogy!

 

 

[Rick3478 428]

On 11/23/2022 at 8:48 AM, Jeff-C175 said:

 

You do know I'm a retired EE, right?

 

 

Me too.  Wow!

 

Reminds me of a young guy that worked with me for awhile.  He was tasked with designing a heat sink for a new product, and kept coming up with really weird shapes with super-thin cross-sections that obviously wouldn't work and would be hard to manufacture.  After a couple of iterations, we cornered him and asked how he was coming up with this stuff.  He showed us a bunch of differential equations and explained that he was trying to "maximize thermal flow".  You could have heard a pin drop in the silence.  Then we explained that what he really needed to do was more like "minimize thermal difference".  The look on his face as it sunk in was priceless.

 

[953 nut 55,324]

On 11/23/2022 at 8:48 AM, Jeff-C175 said:

You do know I'm a retired EE, right?

OK, I'm stupid and you are smart! Let it rest because none of this is beneficial to this post or anyone that will read it in the future.

[Jeff-C175 7,202]

6 minutes ago, 953 nut said:

OK, I'm stupid and you are smart! Let it rest because none of this is beneficial to this post or anyone that will read it in the future.

 

Sorry you got your feelings hurt.

 

I never said you were stupid, you said that.

 

Never stop learning Sir.

 

Any learning is beneficial to anyone, but they have to want to learn.

 

 

Edited November 25, 2022 by Jeff-C175

[Snoopy11 5,714]

22 minutes ago, 953 nut said:

OK, I'm stupid and you are smart! Let it rest because none of this is beneficial to this post or anyone that will read it in the future.

Is that all you've got? I was expecting an 'electrical' reply...

 

And I beg to differ, if I may.

 

I personally learned quite a bit from this thread, incorporating my (however small) personal experience with diodes and independent research that I have done over the course of this discussion. I don't regret following this thread at all... I just regret when people get in a tizzy when their logic is challenged. That is what isn't beneficial to this post.

 

I've been wrong in the past, will be wrong in the future. So will you, so will Jeff. Doesn't make you stupid...  

 

Jeff challenged your logic... he didn't challenge you. Keep that in mind.

 

Don

[aloe 24]

Thanks, all!   WOW, I got way more than I asked for, and now I feel like I am an EE!  This is great...did not expect to learn so much from so many pros!  

I think now, as Blasterdad suggests, I'll start by checking my Switch for any voltage drain.  Can anyone give me link for a new one if it's determined to be bad?

 

I hope you all had a wonderful Thanksgiving!  

[Jeff-C175 7,202]

15 minutes ago, aloe said:

Thanks, all!   WOW, I got way more than I asked for, and now I feel like I am an EE!  This is great...did not expect to learn so much from so many pros!  

I think now, as Blasterdad suggests, I'll start by checking my Switch for any voltage drain.  Can anyone give me link for a new one if it's determined to be bad?

 

I hope you all had a wonderful Thanksgiving!  

 

Have you pulled the indicator pc board yet?  Try the simple stuff first.  You may find that board is killing the battery.

 

Pull the board, charge the battery, let it sit for a day, see what happens.

 

 

[aloe 24]

I'll check that...have been in Holiday mode, but will have a look this weekend

[gwest_ca-(File Mod) 11,048]

You can unplug the idiot light board and it will not affect the rest of the tractor functions.

 

[Blasterdad 2,692]

I've bought products from this company this in the past, no issues & have an actual phone number for service. 

On 11/25/2022 at 10:56 AM, aloe said:

Can anyone give me link for a new one if it's determined to be bad?

I've bought products from this company in the past with no issues, & they have an actual phone number. 

https://theropshop.com/shop/products/ignition-switch-toro-103990

[aloe 24]

So I cleaned up the test switch board and it looks like this... However as soon as I plug it in the PTO light comes on

[Jeff-C175 7,202]

25 minutes ago, aloe said:

cleaned up the test switch board and it looks like this

 

Good job... but the corrosion around the pins and probably under the integrated circuit (IC) is not good.

 

Those ICs are sensitive to static electricity and such... it's fairly likely that the IC is NFG.

 

I wish there was a schematic for that board available.  Couldn't find one in the files section, and nobody replied to my query if one is available.

 

I  could reverse engineer it, draw a diagram, and repair it ... if it were mine and it was in my hand.  

... EDIT:  Need to do more looking, but it appears that the 54LS86 may be no longer available, or VERY high cost...

 

I found a substitute that would work, and there is still stock around, so it could be repaired.

 

 

 

 

 

Edited November 28, 2022 by Jeff-C175

[aloe 24]

No I don't think that's corrosion that's just the green silicone mat that I couldn't remove

[aloe 24]

I have a brand new battery so what I'm going to do is just see if there's any voltage drain with it sitting without the PC board plugged in

Edited November 28, 2022 by aloe

[Jeff-C175 7,202]

2 hours ago, aloe said:

don't think that's corrosion

 

Ok, good!

 

2 hours ago, aloe said:

see if there's any voltage drain with it sitting without the PC board plugged in

 

That should tell you a lot.

 

 

[Jayzauto 89]

If you invest in a DVOM, use the amps circuit, and you'll know Immediately IF there is in fact a "Draw".  You can also confirm Charging Voltage and Current.   Monitor battery Voltage while cranking for 15 seconds will simulate a "Load Test".   All these tests can be run in under 5 minutes and Will point to a deficiency in the electrical system. 

 

*NOTE: I am neither an electrical engineer, mechanical engineer, or Any type of engineer,   Nor do I play one on TV... These are simply lessons I've Learned from The School Of Hard Knocks.

 

GLuck, Jay

[aloe 24]

OK - so after the night... with the PC board unplugged, no draw down on battery.  So....that points to some fault in PC board/indicator lights being the culprit?? But why is there power to the PC board in the first place?  

 

[gwest_ca-(File Mod) 11,048]

PC board is wired directly to the battery.