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Trying to understand schematic


Jack B.'s Avatar
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12-09-09, 07:16 AM   #1  
Trying to understand schematic

I've got a craftsman rider in and I'm having a little trouble understanding the schematic for it. The model number is 917.272083. The schematic diagram is at CRAFTSMAN | Model #917272083 | LAWN TRACTOR | SCHEMATIC DIAGRAM | SearsPartsDirect.com.
First of all, there seems to be an error on the drawing. I believe that on the operators presence relays #2 and #3, that terminal #88 should be connected directly to ground (battery neg). My next question is why dose relay #2 have a short across the alternator when the seat is unoccupied? Also, on relay #3, why is the output of the regulator disconnected whenever the seat is unoccupied.

 
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12-09-09, 08:58 AM   #2  
Please post the serial number of the tractor.

 
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12-09-09, 09:10 AM   #3  
I don't see a terminal 88 on those relays.

I see:

30, 85, 86, 87, 87a

I cannot seem to find a terminal 88 anywhere on the linked drawing.

my guess as to why the relay disconnects the alt when seat not occupied is it prevents the system from charging since the alt is not designed to have much output at low RPM and typically if nobody on the seat, the rpms would be at idle.

It also prevents a feed back through the system when the ign switch is on but engine not running.

engineers may have found those situations to cause a problem and that is their remedy. I can imagine problems those situations could cause.


as to the short across the alt when seat not occupied:

I have no clue on that one. maybe if a small engine guy sees this he can clue both you and me but as a guess, maybe this is part of the circuitry needed to excite the alternator.


as to the term 88, I see your concern applied to term 86 of those relays. It does appear the 86 term could go directly to ground or it could go to a switched ground. As the diagram shows, those terms are simply connected to each other.

the fact those (that) wire is also designated as a black wire, which all other black wires do connect to bat -, I would think that there is a mistake there as well.

 
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12-09-09, 09:13 AM   #4  
If you are simply trying to understand how the system works from the "schematic" you referenced, it is not going to make any sense as it is not a "complete" schematic but more of a wiring diagram as it does not provide breakdowns for each component, and if it did, likely would require an educated knowledge of electronics to understand.

If you have a specific issue, you already know you can get help here

 
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12-09-09, 10:25 AM   #5  
Sorry, the terminal number is 86.

 
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12-09-09, 10:52 AM   #6  
have you tried tracing any of this on your tractor? Does the terminal 86 in fact connect to bat - eventually?

 
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12-09-09, 01:05 PM   #7  
I'll try that, Nap, thanks for the suggestion. Not having trouble, Just trying to understand the schematic.

 
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12-09-09, 01:14 PM   #8  
Posted By: Jack B. First of all, there seems to be an error on the drawing. I believe that on the operators presence relays #2 and #3, that terminal #86 should be connected directly to ground (battery neg).
1
My next question is why dose relay #2 have a short across the alternator when the seat is unoccupied?
2
Also, on relay #3, why is the output of the regulator disconnected whenever the seat is unoccupied.
3
1 It is.
2 I'd need to see the reg. schematic to answer that.
3 See 2.

 
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12-09-09, 01:38 PM   #9  
Posted By: hesaidshesaid 1 It is.
2 I'd need to see the reg. schematic to answer that.
3 See 2.
have you not clicked on the link? The diagram is complete from Batt + to Batt - and all connections in between.


and no, terminal 86 of either relay noted is not connected to ground (batt -). they are in fact connected to each other only.

 
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12-09-09, 03:39 PM   #10  
I am guessing, relay #1 connections 86 to 30, is likely a shunt resistor and is not depicted correctly as far as circuitry on this diagram.
An example of this diagram not showing the entire electrical path is evident by looking at the regulator, which is also likely a rectifier and the diagram shows 28V AC in with an output of of 1amp DC out...

 
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12-09-09, 04:05 PM   #11  
I am guessing that 86 to 30 connection is s direct connection.

they really should have made 30 and 86 independent connections to bat- but they didn't.

why do you believe there should be resistor between those two connections? The connection to 86 is obvious and the connection to 30 if you will notice grounds the ignition unit which would shut the tractor off when rising from the seat.

and of course the regulator contains a diode. This is a diagram of the system and only contains info pertinent for that. The diode is irrelevant because there are no connections to that that make a rats butt difference to wiring the tractor.

and I have not a clue where you are getting you 28V AC IN nor the 1 amp DC output.

what you are seeing is the notation that on the input of the regulator/rectifier is the output of the alternator: 28 VAC at 3600 RPM and at the opposite end of the reglator/rectifier is a 15 amp DC output.

are you guys even looking at the same diagram I am? You keep coming up with things that are not on the diagram I am seeing when I click on the link.

 
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12-09-09, 04:26 PM   #12  
Posted By: nap I am guessing that 86 to 30 connection is s direct connection.

they really should have made 30 and 86 independent connections to bat- but they didn't.

why do you believe there should be resistor between those two connections? The connection to 86 is obvious and the connection to 30 if you will notice grounds the ignition unit which would shut the tractor off when rising from the seat.
Mainly because I have worked on a Craftsman model number 917.272083 and actually own one similar and I know there are components that are not depicted.
Posted By: nap and of course the regulator contains a diode. This is a diagram of the system and only contains info pertinent for that. The diode is irrelevant because there are no connections to that that make a rats butt difference to wiring the tractor.
If there was a diode, I imagine it would be depicted as such and is on most diagrams that include one. If it did or does include a diode, the only reference it has is to substantiate my point that this diagram is not complete.
Posted By: nap and I have not a clue where you are getting you 28V AC IN nor the 1 amp DC output.
15 amps output my mistake not 1 amp.
Posted By: nap what you are seeing is the notation that on the input of the regulator/rectifier is the output of the alternator: 28 VAC at 3600 RPM and at the opposite end of the reglator/rectifier is a 15 amp DC output.
Input to the regulator MUST come from the alternator and the system charging OUTPUT is labeled as such.
Posted By: nap are you guys even looking at the same diagram I am? You keep coming up with things that are not on the diagram I am seeing when I click on the link.
As far as I know...I am not doing any slight of hand magic act
My point is the diagram does not provide the information needed to determine electrical path through each component.

No offense but electrical does not equate to electronics just as most general schematics do not show the internals of a transistor, you are aware of the happenings with in one...?

 
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12-09-09, 04:38 PM   #13  
yes it does. I am not going to argue with you but that contains all the info I would need to wire that tractor and why.

what is in the reg/rectifier is irrelevent as you are not attaching to any point inside the regulator specifically. You are attaching simply to a point on the regulator and you cannot check the regulator from those points. You can check the non-electronic components and this diagram provides the information need to do so.

same thing with the ignition unit. There are going to be electronic components within that unit but they are not relevant to this diagram and it's purpose.

Input to the regulator MUST come from the alternator and the system charging OUTPUT is labeled as such.
again, you must be looking at a different drawing. They DO show the output from the alternator going to the regulator/rectifier. on the opposite side of the regulator/rectifier, they show the output (of the regulator) which then goes to the ign switch and ultimately back to the battery.

what is the problem with that?

 
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12-09-09, 04:45 PM   #14  
No argument here
Of course you can wire the tractor with this diagram as that IS the purpose of it. You CAN NOT however determine electrical path and confirm by IT alone...

Get your tail out there and put a meter on a few hundred of these systems and then see if you have the same opinion...

Otherwise I hope they let you blow the whistle on that train your driving

Peace

 
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12-14-09, 12:57 PM   #15  
I would like to apologize for the tone of my reply. In retrospect I think I was being obstinate and perhaps even discouraging to the purpose of this forum and maybe to the point of this thread.

Jack B. in order to understand this system fully it may require a bit more than a general understanding of electrical circuits, however, there are tests you can perform to show how it works, or should work.

Nap, I apologize for my reply. I have little doubt you have valuable knowledge to share...hopefully I have not deterred you from participating.

 
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12-14-09, 02:57 PM   #16  
Posted By: BFHFixit
Nap, I apologize for my reply. I have little doubt you have valuable knowledge to share...hopefully I have not deterred you from participating.
deter me? Have you checked my post count?

I just backed off. As I get older, I am finding it does no good to argue whether you are right or wrong after it starts getting ugly and it does deter the thread and is no help to the OP.

So, as others have accepted my apologies for exactly the same thing with me in your position, of course I would accept such an apology. I'm not always right but I often think I am. Sometimes I'm right, sometimes not.

 
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