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Author Topic: Are Push Button Starter Switches Any Good?  (Read 5320 times)
Dave Siegel
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« on: April 03, 2007, 05:25:19 AM »

Hi Everyone,
      In our PD3751 (Silversides )  (12 volt neg ground) I have never had a keyed start switch. I have always used a push button rocker type switch. Over the years I have had to replace the switch several times. In the beginning my main problem was too small wires from the batteries to the starter. That was resolved. But the switch still remains a re-occuring issue.
      This weekend we were going camping with the grandkids and when I tried to start the bus I got nothing on the first push, only after several tries did it finally crank. It cranks great, with lots of power, once it gets a connection. Coming home it did the same thing, but it even took more pushes on the switch.

So here are my questions:
      Should I go to a regular keyed or push buttom style starter switch?  Should I use a relay with the switch? How and where should I put the relay? How does a relay work?  I remember in early street rodding days Chevy motors were hard to crank when they were hot, so we used to put a Ford starter relay in the line. Would something like that work? Would I put that back by the starter?
      Sorry for all the questions, but this is one of the few unsolved problems I have on this bus.

Thanks for any advice, in advance.

Dave Siegel, PD3751 Naples, Florida
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Dave & Jan Siegel    1948 GMC  "Silversides"
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larryc
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« Reply #1 on: April 03, 2007, 05:51:34 AM »

Dave

I doubt that your starter switch is tied directly between the battery and the starter.
More likely it is already used to energize a relay which in turn energizes the starter relay.
I would strongly suggest (here comes the shameless plug) that you obtain the manuals for this fine coach from

www.coachinfo.com

to see how your coach should be wired.

Q. What's the difference between a bus and a coach?
A. A coach is paid for
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kyle4501
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« Reply #2 on: April 03, 2007, 08:03:17 AM »

A relay is simply an electrically operated switch - it uses a small current to switch off-on a large current device. You can remote mount relays close to the power source to minimize the length of the large wire for the actual load. Smaller wires are run to a manual switch in a convient location to control the relay.

I'm guessing the contacts are burning up on the switch due to the actual load exceeding the switch's rating. DC is harder on switches than equal power AC.

Connect an amp meter to the power wire going to that switch. Note the amp load on the switch when starting. For your next switch, be sure the switch rating exceeds the actual load.

If you can't find a suitable rated switch, there may be some kind of condenser you can use with the switch to minimize arcing at the contactors, but that is way beyond my abilities to know what to use or even if it will work in this application.

Good luck.

PS Love your bus!

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DrivingMissLazy
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« Reply #3 on: April 03, 2007, 08:24:45 AM »

Dave, my recommendation would be to get one of the 30 amp cube relays that are available at any automotive parts house. And they are very inexpensive also.
Replace the existing starter switch you are using and use the new switch to control the cube relay. Use the cube relay to control the starter solenoid.
I did this on all my rear lights and Jake brake controls also. Sure solves lots of electrical problems.
Richard
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« Reply #4 on: April 03, 2007, 08:49:26 AM »

 Good ideas here so far. But isnt a solenoid basicly a relay? Why would you want to add another relay? This would violate the KISS principal. Unless the wires from the switch to the solenoid are undersized.
 The push botton starter switch on my MCI5C 6V71 has been in it for 7 years that I know of and from the looks of it much longer than that!!  If I were trouble shooting my bus for this issue. My first uneducated guess would be the switch does not have a high enough amp rating or is not a DC rated switch.
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Dave Siegel
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« Reply #5 on: April 03, 2007, 08:50:58 AM »

Thanks Richard and Kyle, that is the kind of information that I have been looking for. Is there as special way that I have to wire that cube relay? Should I have the relay close to the switch (at the dash) or should it be closer to the starter?

Dave Siegel
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Dave & Jan Siegel    1948 GMC  "Silversides"
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« Reply #6 on: April 03, 2007, 08:59:02 AM »

Here's a PS:

Presently, I have a switch at the dash. It is a marine rocker switch thatr wa rated for 24 amps. The wire goes directly to the starter selenoid to start the bus. I have used #10 wire for that switch.  There are no other relays anywhere.

Dave
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               Naples, Florida
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« Reply #7 on: April 03, 2007, 09:26:24 AM »

Here's a PS:

Presently, I have a switch at the dash. It is a marine rocker switch thatr wa rated for 24 amps. The wire goes directly to the starter selenoid to start the bus. I have used #10 wire for that switch.  There are no other relays anywhere.

Dave

Is that an AC or DC rating?
In AC, the voltage cycles from + to - 60 times a second. It is real easy to break a circut at 0 volts.
In DC, the voltage is constant & you will have arcing at the contacts when circut is broken - just like striking an arc when welding.

I think the easiest way is to get a higher rated switch. OR just buy 2 & keep a spare on hand. (That is what we did for a Ford we had that was rough on ign switches - I could swap one out in less than a minute  Grin  )

If you go with a relay, Richard has the experience there, so I'll defer to his opinion on location & how to wire it.
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« Reply #8 on: April 03, 2007, 09:47:24 AM »

My bus is 30 years old and has one of those chrome heavy duty push buttons for the starter (it works through a solenoid in the engine compartment).  From the looks of it, it hasn't ever been changed.  Good Luck, TomC
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« Reply #9 on: April 03, 2007, 10:41:07 AM »

I am assuming there is a starter relay of some kind on your starter and it is drawing so much current in the energizing coil that it is burning up your starter switch.

The cube relay or starter solenoid should be mounted close to the starter. Yes relays and solenoids are the same or similar. Generally solenoids are rated 50 amps or above and relays are lower rated.

The cube relay will only require about 1/2 amp or less (500ma) to be drawn thru your starter switch, so it does not require a large rated switch. The relay contacts can easily handle 30 amps and the starter relay should be connected to these contacts.

In low voltage circuits, below 50 volts, most components are rated for botheDC and AC.

And contrary to some opinions, it is a good idea to install control relays in the rear of the vehicle to control items such as turn signals, brake lights, back up lights, Jake Brakes, starter solenoids and any other electrical device that uses several amps of power. It is much better to have the control wires going from the front to the rear of the coach conducting a half an amp instead of 10 or 20 amps or more.

.
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« Reply #10 on: April 03, 2007, 12:16:01 PM »

I think every bus that I have worked on had a starter relay in the rear electrical panel. That is the relay that prevents starter engagement when the safety switches (neutral switch, fuel pressure, alternatnor charging, etc.) are operated. On the MCI 5 and 7 vintage this relay then operated a solenoid switch that had heavy duty contacts that switched the actual starter solenoid. Milliamps of current are required to operate the start relay and because it has a small coil it generates a small spike when it is de-energized doing little damage to the start switch.

The starter solenoid performs two functions. It mechanically pulls the starter drive into mesh with the flywheel and also closes the switch to the starter. This is a large coil which draws significant current and then generates a large spike when de-energized. This spike of reversed voltage either has to be suppressed with a large diode or else absorbed by a heavy duty switch. If the switch is not capable of soaking up the heat it will either burn or weld the contacts.

If you are currently using the start switch to switch the starter solenoid, you should install a relay similar to a Ford starter solenoid in the engine compartment.

To answer your question on solenoid versus relay -
A solenoid is a coil with a moveable iron core that provides a pull or push mechanical function. A good example is the solenoid that pulls your transmission into reverse gear.
If the moveable core operates an electrical switch then technically it is a solenoid switch. As I noted above the starter solenoid is both.

A relay is a coil with a fixed iron core which makes it an electromagnet. When you energize the coil the electromagnet pulls a hinged armature toward the magnet. On the end of the armature is the moveable contact that touches a fixed contact when pulled to the magnet.  When the coil is de-energized a spring pulls the armature off the magnet.


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« Reply #11 on: April 03, 2007, 12:50:16 PM »

About 10 years ago, I had trouble with my 4106, starting. Sometimes it would start, and sometimes it would not.
I installed a remote relay, (Ford starter relay) in the engine compartment. The low volt side of the relay is controlled with the switch in the insturment panel, and the high voltage is wired, from the starter solenoid, to the + terminal on the starter.
This has cured the problem, for 10 years.
My 2 Cents
Steve
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« Reply #12 on: April 03, 2007, 07:24:47 PM »

Most likely what is happening with these older busses is that the inductive kickback from the starter solenoid coil is trashing the starter button's contacts.  Only in maybe the last 10 years did the industry start including a "catch diode" internally with relays and some starter solenoids to eliminate the problem.
  Whenever a coil is de-energized, the magnetic field in that coil collapses causing a voltage to appear across the coil that will rise higher and higher until it finds somewhere to go.  This usually manifests itself as a contact-eating spark across the switch contacts that control it, but it can actually get up into the hundreds of volts (only for a few tenths of a millisecond though) but even as quick in time as it is, it can do a lot of damage to contacts, electronic stuff (speedometers etc) and entertainment equipment as it dissipates.
  For ones that don't have it, all it takes is a simple Radio-shack 1n4001 (or 1n4002,3, or 4) hooked across the coil of the solenoid with the cathode (the line painted on the diode) pointing at the (+) terminal and the anode (the other wire) grounded.  It should be installed right on the solenoid to be most effective.   I put one on every solenoid in the bus. Then the inductive spike gets shunted thru the diode and right back into the coil, and is converted harmlessly to an almost unmeasurable amount of heat.  No more bad switches, no more worries.
« Last Edit: April 04, 2007, 08:42:29 AM by boogiethecat » Logged

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« Reply #13 on: April 03, 2007, 08:09:24 PM »

Dave,

The 4104 starter system has both a relay and a solenoid and I assume the 3751 is the same.

The relay is a remote electric switch that allows low current to be used by the panel starter switch. In my 4104 it is a momentary on toggle switch. I've never had any problems with this switch. A relay switches high current to the starter motor and solenoid via very large cables. The starter solenoid works the same as a relay except it is much heavier duty and actually moves the gear which engages the starter motor to the flywheel gear. As posted already, it is very much like the reverse solenoid in size and power.

It sounds as if your system has no relay and the starter button can't handle the high current.

Try replacing the button with a momentarily on switch from a marine supply store since that was probably the original type switch. Also trace down the wiring diagram and find out where the relay is located. I think the 4104 is in the rear electrical panel but can't remember for sure. My manual is outside in the bus. It could well be that your relay has failed and has been bypassed. I've found a bunch of things bypassed on my 4104 and have gradually replaced the relays with the ones mentioned earlier which are easy to find.
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« Reply #14 on: April 03, 2007, 09:23:28 PM »


Dave…All in-line DD 6 cylinders already has solenoid which is the very high current relay & solenoid combination on your Delco-Remy starter. If your starter switch is burn out too soon…is because it not design to take solenoid’s current. So get a heavier duty type like the 40s to 50s Ford car push-button which is 6v but it will work or get one being use in transit or intercity bus from charter’s bus repair shop or NAPA can get it for you.

What Richard suggested (12v horn relay cube) will work is available at any auto parts store and replace that burn out for same new rocker switch that you like. Install “cube relay” very near to starter solenoid is to your advantage.

No need to worry for feed back arc it too small to be the cause of your problem. So forget the diode……or capacitor….it only for added life to vibrator points or cut noise in radio.

So your answer is either to go for a heavy duty push button or regular switch with horn relay cube.

Very rare for Ford chrome or black push button to burn-out….been there in 40s & done that.

Keep It Simple!

PS...I rode in GM-3751 every other weeks in late 40s.....good memories.

FWIW

Sojourn for Christ, Jerry
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