760's eating alternators - Page 7 - The Combine Forum
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post #61 of 88 (permalink) Old 11-21-2018, 02:12 PM
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Originally Posted by stsdavew View Post
Out of curiosity here how does the LED fit into the circuit. Its my understanding that it is connected to the same wire that feeds the relay you guys are trouble shooting thus getting power when the alternator is charging so how does it stay off while being fed power and could this not be where the issue lies???
Yes, and this is one of the unknowns. My assumption (and most logical design) is the following:

The LED indicator is hooked to 13V, and the control wire. (Schematic does not show the 12V connection...its a "Module".)
The alternator "control wire" is pulled toward ground when the alternator is not charging.
This pulls current thru the LED indicator, illuminating it.

When charging, the alternator drives the voltage to 13V. This turns off the LED (no current drawn thru it) and turns ON the relay.

A way to test this assumption would be : Does the Charge LED come on even with the relay pulled (motor not running, key on)?? If it does, the above design is correct. If not, then the LED depends on the relay to draw current to light it.... (hope not, that would be a poor circuit design)


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post #62 of 88 (permalink) Old 11-21-2018, 08:22 PM
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Originally Posted by Jeff-C-IL View Post

The alternator "control wire" is pulled toward ground when the alternator is not charging.
This pulls current thru the LED indicator, illuminating it.
How would this be possible? Unless the wire was connected to ground as well? Then it would have to have a resistor in it to keep the voltage from shorting straight to ground yet have enough draw to turn on the led? Which i guess could create issues with keeping the relay powered as well...

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Originally Posted by Jeff-C-IL View Post
A way to test this assumption would be : Does the Charge LED come on even with the relay pulled (motor not running, key on)?? If it does, the above design is correct. If not, then the LED depends on the relay to draw current to light it.... (hope not, that would be a poor circuit design)

Maybe poor but might be better than whats happening now...

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post #63 of 88 (permalink) Old 11-21-2018, 09:30 PM
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Those charge lights should follow the same principle as automotive dash warning lights. Its been a long time since i looked at them but an internet search should pull up descriptions.



1934a - reving up an engine to start charging is not uncommon. Our 4020 with farm installed alternator does same thing, on initial start have to rev up to around 1100 rpm to get "gen" light to go out then can idle down after that all day. What i suspect is these things work the same as a self excited generator. The alternator relies on residual magnetism to start building a voltage to feed back into the the voltage regulator, to the rotor, and then build more voltage. If there is not enough magnetism you need to spin rotor a little faster to build more voltage. Once magnetized you can bring back to idle. I may be wrong but one theory to consider.
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post #64 of 88 (permalink) Old 11-21-2018, 09:55 PM
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Industrial systems would rely on a voltage relay connected directly to the source, in this case, to the output terminal of the alternator. If the voltage dropped below say 13.0v the relay would drop out.

With battery banks being common for home power solutions there are lots of options out there. Here is one

https://www.poweringthenetwork.com/lvd-wall-mount/


If the power supply of the alternator was overloaded due to poor design it should show up day 1. So i am still leary of why it goes for hundreds of hours then fails. Could be heat or mechanical vibration in the alternator causing the failure. This is my concern with using the solid state timer, we could be seeing a partial failure with the power supply that eventually leads to total failure that won't even run the solid state timer.



Just pointing out a word of caution till we know better what the insides of the alternator look like. Drawing or parts breakdown or something. Claas is likely not going to go into that detail.



So i post the idea of an actual undervoltage relay tied to the alternator, or battery or hot supply in cab. Basically, if you are under 12.5 v you are running on batteries or engine is off. Anything over 13.0v means everything is good. Its a more creative solution but may be worth toying with. I just picked one as an example that has the needed features, i don't think the timing function is too important - maybe there is a need for it but i don't have the info to say so.
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post #65 of 88 (permalink) Old 11-22-2018, 10:53 AM
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Ken: I've played with the low voltage units, and was not impressed. I used them in generator control / battery bank systems. The problem is they are not very accurate (at least the one we used). Seems like every time you tried to adjust it, the next time was different. One time it would kick out a 12, the next time 10.5, etc. Your idea is good, if the low voltage relay can be set that accurately.
I agree the timing function is minimally necessary. I just suggested those relays because they are relatively cheap, I've used them, and you can easily get them. They only come in the timer format. I also agree we don't know if his current alternator will completely fail....but I'm most concerned about the NEXT one. Using a SS relay with very little load should prevent it from failing again.

Dave: The key to how that works is what kind of circuit is in the alternator. As Ken pointed out--an unknown. My theory is that the "control wire" can actually be Ground or 12V depending on if the alternator is working. When the alternator is not working, the internal circuit grounds the control wire and turns on the LED (12V to ground). When the alternator is working, the control wire is (or should be!) 12V, turning on the relay (coil hooked to ground).

The above kind of circuit (called a dual state output or high/low driver) is very common in modern control circuitry. Think of it like there are two relays inside the alternator...one to ground and one to 12V. Which one is closed depends on the charge state of the alternator.

The test I suggested above should tell us if the theory is correct or not. But it remains a theory until we get data....

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post #66 of 88 (permalink) Old 11-22-2018, 10:07 PM
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Sounds right Jeff, i only worked with one of those cheaper ones before and got the impression that getting repeatable accuracy was not likely. Never had real test equipment to prove it out though. I do agree with the solid state timer solution. The under voltage relay scheme i mention for someone who is looking to do some reinventing.

Just for the heck of it, this is the style i have seen lots of:
https://www.productsforautomation.co...-p/vmp012d.htm
Pretty much every generator transfer switch form the 1970s to 1990s had 3 to 5 of these units for 120v line sensing and as timers - same package, same base, but Potter and Brumfield or Agastat. Always accurate, reliable for decades. But a plug in base as well as the size is not good for a combine. If the 12v is as accurate as the 120v models then they would do the job. Can't speak for the manufacturer in link though.
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post #67 of 88 (permalink) Old 11-23-2018, 01:07 AM
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How about this, when the alt light comes on while the engine is running....fix the alternator!

Usually a pretty simple circuit, a diode trio provides current to the field and to turn off the indicator lamp -voltage positive.

Have you spent any time diagnosing the actual codes that come up?

Like dig into the actual straw chopper or auto luber code?
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post #68 of 88 (permalink) Old 11-26-2018, 03:25 PM Thread Starter
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I think I'm ready to order something to try.

Jeff, you think that one you linked from waytek wire would be my best bet?

https://www.waytekwire.com/item/7553...-State-Relay-/



I could do some more testing/checking on how the idiot light works, but it doesn't really matter does it?
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post #69 of 88 (permalink) Old 11-27-2018, 10:59 AM
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Either that one or this is a little cheaper: https://www.waytekwire.com/item/7553...-State-Relay-/ Work the same, just no adjustable timer (just a straight up relay)

Yes, I think checking the idiot light would be good, it should only take a minute to pull the relay and turn on the key...It would confirm my theory about the alternator. If I'm NOT right, the idiot light may depend on the relay coil for its "ground", and that would require a different approach with the relay.

You may also want one of these https://www.waytekwire.com/item/7528...lay-Connector/ and a few of these: https://www.waytekwire.com/item/3107...lay-Connector/.
The one problem with Waytek is they require a $5 min. Line Item, so the minimum qnty of some things is 10 or 20 or..... You may just want to run down to your local NAPA and buy a relay socket with wires already made up.

AS far as hooking up that relay, the 12V power, Ground, and Output are all clearly labeled and obvious.
The thing that's different is the inputs:
>Pin "87" is a "turn relay on when grounded" input.
>Pin 87A is a "turn relay on when 12V" input.
Leave 87 disconnected, connect 87A to the Alternator Control wire. Attaching the pdf
Attached Files
File Type: pdf 75532.pdf (159.3 KB, 4 views)

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post #70 of 88 (permalink) Old 11-27-2018, 01:06 PM
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Likely doesn't apply in this case but when doing a routine test of a rebuilt alternator before handing it over to me my supplier noticed a momentary drop in voltage. disassembled it and took awhile to pinpoint that it was a faulty brush holder. apparently there are ones in the system that are made in China and are prone to binding the brushes even though visually they look the same. Just something to be aware of....

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