Wiring Jake Buffer Switch

ChuckMC8 · February 23, 2007, 04:08:30 PM

Well, I'm finally getting to wiring my Jake.......the buffer switch has two terminals, the one on the left in the photo below has a diode attached.
Of course, one of these terminals takes the voltage supply from the source and then the other sends it on to the selector toggle switch.
Which one's which? I would figure that the diode is on the output of the buffer switch......is it?
I cant find a schematic on the Jacobs web site. It refeers the installer to check the instructions that came with the product.

pvcces · February 23, 2007, 09:08:29 PM

Chuck, the diode is likely for arc suppression. Hooked up backwards, the switch will look like a near short, meaning the coils won't turn off when the switch opens. The other way, the coils will be de-energized when the switch opens.

For those of you that are unfamiliar with diodes placed on switches like this, whenever a current is made to flow through an inductive load, like a coil or other winding, if the current is interupted, the collapse of the magnetic field will attempt to keep the current flowing.

This can produce quite a voltage spike, more than enough to cause a bright flash as the contacts open. The diode provides a discharge path that effectively shorts it out. This means that a good setup will have the effect of almost no spark at the contacts when they open.

Try it either way. If it doesn't work the first way, reverse the connections.

I hope this helps.

Tom Caffrey

Stan · February 24, 2007, 05:10:53 AM

If you put a diode across a coil the wrong way, it will explode the instant that voltage is applied.

DrivingMissLazy · February 24, 2007, 06:55:56 AM

Chuck, here is a link that details the wiring.
http://www.jakebrake.com/service/pdf2/003879.pdf

You may want to review this post also. A good link to Jakes and is where I got the above link.

http://www.busnut.com/bbs/messages/11/16881.html?1172324225

Richard

Quote from: ChuckMC8 on February 23, 2007, 04:08:30 PM
Well, I'm finally getting to wiring my Jake.......the buffer switch has two terminals, the one on the left in the photo below has a diode attached.
Of course, one of these terminals takes the voltage supply from the source and then the other sends it on to the selector toggle switch.
Which one's which? I would figure that the diode is on the output of the buffer switch......is it?
I cant find a schematic on the Jacobs web site. It refeers the installer to check the instructions that came with the product.

ChuckMC8 · February 24, 2007, 06:21:14 PM

thanks guys- thats what I needed- chuck

pvcces · February 24, 2007, 08:30:48 PM

Stan, I think that he was referring to the buffer switch, not the coil that it drives. In any case, sizing the diode to match his overcurrent protection will avoid damaging the diode.

For what it's worth.

Tom Caffrey

Stan · February 25, 2007, 05:58:53 AM

pvcces: Diodes are put in wires as steering diodes to prevent reverse currents getting into another circuit. In a bus these diodes are used in the engine shutdown/indicator light system. When a diode is used on a coil it is for arc suppression as you said. When the voltage to a coil is switched off, the magnetic field collapses, inducing a voltage in the winding of reverse polarity. For this reason, the diode has to tied across the coil with the cathode end to the positive supply. The diode only conducts when the reverse, collapsing voltage is present. There is not much current flow, but voltage can be very high (over 600 volts on 24 volt coils). If the diode is connected with the anode to the positive supply it is forward biased and conducts the full current that is available from the supply and it explodes.

DrivingMissLazy · February 25, 2007, 06:25:52 AM

As I recall, the diode is placed in series with the buffer switch contacts to protect the contacts from the collapsing field(s) of the Jake solenoids.
I eliminated that problem by re-wiring the Jakes so that the control circuitry actuated a 12 volt cube relay with contacts rated at 30 amps. The cube relay then actually operated the Jake solenoids. The buffer switch and h--off-low Jake switch only actuated the very low current of the cube relay. Problem gone.
Richard

Quote from: Stan on February 25, 2007, 05:58:53 AM
pvcces: Diodes are put in wires as steering diodes to prevent reverse currents getting into another circuit. In a bus these diodes are used in the engine shutdown/indicator light system. When a diode is used on a coil it is for arc suppression as you said. When the voltage to a coil is switched off, the magnetic field collapses, inducing a voltage in the winding of reverse polarity. For this reason, the diode has to tied across the coil with the cathode end to the positive supply. The diode only conducts when the reverse, collapsing voltage is present. There is not much current flow, but voltage can be very high (over 600 volts on 24 volt coils). If the diode is connected with the anode to the positive supply it is forward biased and conducts the full current that is available from the supply and it explodes.

Stan · February 25, 2007, 07:26:36 AM

Richard: Putting the diode in series does no good for arc suppression. Since the collapsing field gnerates a voltage in opposite polarity to the applied voltage, the diode conduts in forward bias and the arc appears at the switch contacts. The reverse diode across the coil conducts the voltasge spike to ground.

Using a relay would eliminate the problem of damage to the critically adjusted microswitch but the relay contacts would still be suseptible to damage by the arc from the coil, if no reverse diode is put across the coil. Using a relay with heavy contacts and strong spring is a good brute force method of getting long life from the components.

DrivingMissLazy · February 25, 2007, 03:16:27 PM

Stan, I am having problems finding a coil in the buffer switch assembly.
I recall something from Jake many years ago that I received indicating the diode was to prevent reverse current thru the switch contacts when the Jake solenoids opened. I suspect that it is somewhere in the Jake literature, but I really do not have any idea where. BTW, the diode is mounted to one terminal of the buffer switch contacts.
My belief is that the diode allows current to flow from the battery thru the switch contacts and the rest of the control circuitry to the Jake solenoids. The diode then prevents any current from flowing from the Jake solenoid back thru the control circuitry and th buffer switch contacts to the DC of the battery.
Richard

Quote from: Stan on February 25, 2007, 07:26:36 AM
Richard: Putting the diode in series does no good for arc suppression. Since the collapsing field gnerates a voltage in opposite polarity to the applied voltage, the diode conduts in forward bias and the arc appears at the switch contacts. The reverse diode across the coil conducts the voltasge spike to ground.

Using a relay would eliminate the problem of damage to the critically adjusted microswitch but the relay contacts would still be suseptible to damage by the arc from the coil, if no reverse diode is put across the coil. Using a relay with heavy contacts and strong spring is a good brute force method of getting long life from the components.

Stan · February 25, 2007, 05:46:06 PM

Richard: Just a difference in terminology on coil and solenoid. I use the word coil because the effect is the same whether it has a moving core (solenoid) or a fixed core (relay coil).

The Jake solenoid has one end of its coil grounded, so the only voltage is coming through the buffer microswitch (or a relay), except for the voltage generated by the collapsing magnetic field. This voltage is in opposite polarity to the applied voltage so it would go through a series diode back to the switch contacts. A diode across the coil with the cathode connected to the positive wire sends the reverse spike voltage directly to ground. The diode can also be tied across the switch contacts so that it dumps the spike voltage back into the battery. In either case the object is to prevent pitting and welding of the contacts by a high voltage spike.
This artiicle has a quite a detailed explanation of arc suppression. In particular, note the chart at the bottom of page 2 showing the negative voltages generated in a 13.5 volt automotive relay.

http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf

DrivingMissLazy · February 25, 2007, 07:03:19 PM

OK. So going to the very first post by Chuck, how does he wire the switch up? Seems like it has to be in series with the DC voltage.
Richard

JackConrad · February 26, 2007, 06:04:04 AM

Just a guess, but I think the terminal with the diode to ground would be the wire going the the Jake Solenoids. When the Jakes are de-energized, this would prevent arcing from occuring in the buffer switch when the magnetic field in the Jake solenoid collapses. Jack

Stan · February 26, 2007, 06:48:45 AM

With the information available, that is almost an impossible question. If Chuck reads the site I referenced, he will be able to figure it out. Looking at the enlarged picture of his switch, I see a component with three bands (which is not normal marking for a diode) and apparently at least one is colored, One end looks like it was removed from a screw terminal and the other end appears to go over the side of the switch and may be attached to ground. Chuck says that the Jacobs site refers him to the instructions that came with the switch. He doesn't say if he has those instructions or if this is a used component and nobody knows what he has.

If I was connecting this switch, I would make sure that I had a conventional diode rated for at least 600 volts. A 1N4005 or 1N4006 is less than a $1.00 at Radio Shack. A few months ago Gary (Boogiethecat) was giving them away. I don't like to work with unknown or untested components

The diode connects to ground from the wire terminal that goes to the Jake solenoid. The diode will be identified with a triangle pointing to a verticle line (cathode). If there are no other markings, the cathode will be identified with a broad band close to one end. The cathode connects to the switch terminal so that it doesn't conduct when supply voltage going to the solenoid and conducts the reverse spike voltage to ground before it gets to the switch contacts. It would do no harm connected to the wrong terminal but also would do no good.

It is preferable to have the diode as close to the coil (solenoid) as possible but I would avoid putting it under the valve cover and put it at the switch.

Before posting, I loked at Jack Conrad's post and he pretty much said in two lines what I have written paragraphs about

DrivingMissLazy · February 26, 2007, 10:49:39 AM

Chuck, may I make a suggestion?
Get a couple of the 30 amp cube relays that are available from any auto parts store. 12 or 24 volt coil as appropriate.
Use the Jake control circuitry to energize either or both of these relays as appropriate for Hi or Low Jake operation. One will be energized for low, both will be energized for high.
That is the way I wired up my Jakes and they operated great for 15 years. With the Jake control circuitry controlling only a control relay, you do not have to worry about the diode on the buffer switch. Just throw it away.
I also used these relays to operate all my rear lights such as brake, reverse and turn signal.
Richard