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Leaf Jockey
10-30-2009, 08:03 PM
I'm working on a Husky ZTH 7227 that has a problem blowing the fuse for the electric clutch. Looking at the wiring diagram I see a bidirectional diode that runs between the two wires going to the clutch. What is a bidirectional diode, what does it do and can it go bad and be the cause of my problem?

Scott

madmower
10-31-2009, 02:58 AM
a diode only works one way if you conect a ohm meter to it you should get a reading one way and infinity the other way if this is not the case you have a blown diode and this is what is blowing the fuse a diode can be used as a safety device or to convert ac to dc as currant can only travel in one direction

bill

ericg
10-31-2009, 08:00 AM
There is not that much out on the web describing what a bidirectional diode is but here is what I found:

The DIAC, or diode for alternating current, is a trigger diode that conducts current only after its breakdown voltage has been exceeded momentarily. When this occurs, the resistance of the diode abruptly decreases, leading to a sharp decrease in the voltage drop across the diode and, usually, a sharp increase in current flow through the diode. The diode remains "in conduction" until the current flow through it drops below a value characteristic for the device, called the holding current. Below this value, the diode switches back to its high-resistance (non-conducting) state. This behavior is bidirectional, meaning typically the same for both directions of current flow. I attached a diagram of the diode.

Have you checked the clutch to see if the coil was grounded which could cause the fuse to blow from excessive current? If the diode was bad, it looks like you could be putting ac on a dc clutch which could cause excessive current and a blown fuse.

Eric

Leaf Jockey
10-31-2009, 09:36 AM
I know the problem isn't with the clutch because it blows the fuse with the harness unplugged from the clutch.
The machine has a harness plug at the switch console. I was able to unplug and remove the rear section of the harness. After inspection I reinstalled the harness and it worked. Now I need to pull it back out, remove the outer sheath and inspect it again. There must be a worn spot in it somewhere.
I'm trying to understand how that diode works with the clutch.

Scott

madmower
10-31-2009, 09:41 AM
sorry i did not see it was a bidrecional diode this can be used insted of a relay to switch a load posably the surge to start the clutch

ericg
10-31-2009, 09:46 AM
Leaf Jockey, the diode converts AC voltage that the the stator produces to DC for the clutch to operate. It seems as if you have found the problem. Now you have to see where the wire is grounded.

Leaf Jockey
10-31-2009, 11:22 AM
On page 37 is the wiring diagram that shows the diode in the harness going to the pto.
http://weborder.husqvarna.com/order_static/doc/usa/2003/I03000/I0303014.pdf

unkownfl
10-31-2009, 11:47 AM
A transient voltage suppression (TVS) diode is an electronic component used to protect sensitive electronics from voltage spikes induced on connected wires. It is also commonly referred to as a transorb, after the brand name TransZorb registered by General Semiconductor (now part of Vishay). STMicroelectronics sells them under the name Transil. The name Tranzil can also be seen.

The device operates by shunting excess current when the induced voltage exceeds the avalanche breakdown potential. It is a clamping device, suppressing all overvoltages above its breakdown voltage. Like all clamping devices, it automatically resets when the overvoltage goes away, but absorbs much more of the transient energy internally than a similarly rated crowbar device.

A transient voltage suppression diode may be either unidirectional or bidirectional. A unidirectional device operates as a rectifier in the forward direction like any other avalanche diode, but is made and tested to handle very large peak currents. (The popular 1.5KE series allows 1500 W of peak power, for a short time.)

A bidirectional transient voltage suppression diode can be represented by two mutually opposing avalanche diodes in series with one another and connected in parallel with the circuit to be protected. While this representation is schematically accurate, physically the devices are now manufactured as a single component.

A transient voltage suppression diode can respond to over-voltages faster than other common over-voltage protection components such as varistors or gas discharge tubes. The actual clamping occurs in roughly one picosecond, but in a practical circuit the inductance of the wires leading to the device imposes a higher limit. This makes transient voltage suppression diodes useful for protection against very fast and often damaging voltage transients. These fast over-voltage transients are present on all distribution networks and can be caused by either internal or external events, such as lightning or motor arcing.

I copied this from wiki. It is correct I read it.

ericg
10-31-2009, 11:56 AM
Unknownfl, thanks for clearing this up. So because there is so much of a voltage spike when you disconnect an electrical coil as in the pto clutch, this bi directional diode bleeds off the excess voltage spike to prevent damage to other electrical components? I can't recall seeing bidirectional diodes in other machines. Is this a common way to correct this problem or is there another way electrically to perform the same function without a diode?

Thanks
Eric

unkownfl
10-31-2009, 12:07 PM
regulator. Leaf jockey pm jim q or something like that he is a Husqvarna engineer. Instead of taking everything apart just use a ohm meter to confirm that you have a leak. You may need to hi-pot the cables to find the leak using a megohmeter.

ricky86
10-31-2009, 12:45 PM
They were used mostly in EFI applications. Now, I would imagine, they couldn't hurt with other. I was under the impression they could not be effectively checked without elaborate testing equipment (meaning a megaohm meter and such).... Leaf Jockey, does it plug into a harness, or in hard-wired into it? The ones Toro uses are not that expensive.

unkownfl
10-31-2009, 12:54 PM
radio shack

Leaf Jockey
10-31-2009, 01:11 PM
Leaf Jockey, does it plug into a harness, or in hard-wired into it? The ones Toro uses are not that expensive.
The diode is hard wired into the harness. I think I located it but didn't pull back the sheath to confirm.
The clutch was unplugged and the fuse would blow when I pulled the clutch engagement switch. I pulled the harness and with the harness on the bench I did a quick test with the ohm meter and the hot side of the clutch harness wasn't shorted to anything else and niether was the ground wire. I reinstalled the harness and it worked like it is supposed to.

Scott

unkownfl
10-31-2009, 01:36 PM
The diode is hard wired into the harness. I think I located it but didn't pull back the sheath to confirm.
The clutch was unplugged and the fuse would blow when I pulled the clutch engagement switch. I pulled the harness and with the harness on the bench I did a quick test with the ohm meter and the hot side of the clutch harness wasn't shorted to anything else and niether was the ground wire. I reinstalled the harness and it worked like it is supposed to.

Scott

A ohm meter won't tell you **** unless it is a dead short. You need to meg it to check it. Electrons will jump with a higher voltage or amperage that checking with a regular ohm meter can't apply. It may not be humid enough or hot enough to short it. Electrical problems just don't fix them selves they hide.

Leaf Jockey
10-31-2009, 02:03 PM
Well, the fuse blew the second I pulled the switch so I assumed it was a dead short. I also have to consider the fact that it worked after doing nothing more than handling it. To be honest I had a helper and a few other repairs happening at the same time. I'm pretty sure once I give it my full attention I will figure it out.

Scott

Two Seasons
10-31-2009, 09:05 PM
Sounds to me like you disturbed some insulation and isolated the suspected ground fault...maybe only temporarily though.

fixer67
10-31-2009, 11:14 PM
Maybe this will help
http://www.statemaster.com/encyclopedia/Transorb
http://en.wikipedia.org/wiki/Transient_voltage_suppression_diode

JimQ
11-02-2009, 01:59 PM
Hey Scott, got your PM.

The voltage suppressor is added to the circuit to suppress voltage spike that are induced by the clutch. A surge is created when the magnetic field in the clutch coil collapses each time the clutch is shut down.

If the voltage suppressor fails, it usually fails as a short between the 2 wires. This will cause the fuse to blow.

Here is an easy way to check for a short.

Disconnect the PTO switch,

Disconnect the clutch

Using a multi-meter, check for continuity between both wires on the clutch end of the harness. If there is continuity, then either the voltage suppressor has failed or the 2 wires are shorted together elsewhere.

If you think the suppressor has failed, remove it from the harness and see if the fuse blows again. If it doesn't replace the suppressor.

We call out a P6KE62CA on our drawing. You might be able to find a generic replacement using that number.

Hope that helps. Let me know if you need more info.

Q

Leaf Jockey
11-02-2009, 08:29 PM
Thanks for the info. I'll look at it again when I get the chance and let everyone know what I find.

Scott

TOSLC
11-30-2009, 12:15 PM
Make sure the relay has not been changed either. Relays have a similar magnetic field that upon colapse will create a voltage spike that must also be supressed. The newer automotive relays have a resistor or diode internal, but if it's been changed with an older one, or a cheaper one, it will not have this protection.

However that is all on shut down, and should not be causing you problems when the clutch is activated. So my guess would be maybe the diode is shorting out, or the positive wire is rubbing somewhere?

Please let us know what you find.

Leaf Jockey
11-30-2009, 06:53 PM
I'll keep you posted. Its still sitting in the shop waiting for me to get around to it.

Scott

loafycleetus
11-30-2009, 11:32 PM
I had this exact same problem on a medium duty Chevy 4500. When the A/C was turned on the fuse would blow. The A/C compressor clutch on a vehicle is the same principal as a blade drive PTO. The clamping diode gives a "loop" if you will for the high voltage spike to run around and dissipate. When you charge a coil that big and the field collapses when the power is cut the voltage is impressive! AKA ignition coil.

Leaf Jockey
12-01-2009, 06:52 AM
So in your case you just replaced the diode?

Scott

loafycleetus
12-01-2009, 07:33 AM
Yes. On that application it was in the harness so I put a new harness on it and all was well.