Protecting electronics on the XS650 from voltage spikes.


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Baraboo, WI, USA
Discussing electronic ignitions, a topic that's surfaced here and there in the past, came up. Some of the ignition components on older motorcycles have nasty electrical habits, that result in a less than pristine +12 wandering around the wiring harness. Some components we add to the bike and some stock components can be hurt by these electrical nasties. I know nothing! But I got a bit of coaching from a few of those with the technical background to make suggestions. Here's some excerpts from @Paul Sutton
I read recently that when the coil fires it produces several (tens of) thousands of volts in the secondary for the spark and a couple of hundred volts in the primary winding i.e. the 12V+ side. So the coil can pollute the 12V+ line. On an Ebay listing I read that the rectifier should be rated higher than 400V because of the voltage induced in the primary winding. I have successfully used 19V TVS Diodes to protect electronics against these spikes.

Here is a diagram showing TVS Diode charactistics:

A TVS Diode is similar to a normal diode except it becomes conductive when you exceed a preset low voltage in the negative range where as a normal diode stays non-conductive in the negative range until you exceed the diodes max voltage rating which is often several 100 to a thousand volts.

The TVS Diode conducts in reverse as you approach Vcl. Although there is a TVS Diode rated at 14V it will be conducting significantly from about 12V so no good for auto-electricals. I settled on the 18V version because my regulator stays below 14.6 volts (14.3V with headlight on).

To remove over-voltage spikes from the power supply you just connect the TVS Diode in reverse bias between the 12V+ connection and ground. This is similar to when you reverse bias a normal silicon diode across a relay to short any induced spikes to ground.

The type I used:

I hope this helps.

Simple Diagram:


The reverse bias bit is all taken care of in the labelling of the TVS Diode. As shown in the two diagrams above the Band printed on the diode connects to the +12V. I also just checked how I wired mine in the Virago low fuel circuit and it is also the Band to the +12V. In the low fuel circuit the Op Amps would last about 2 minutes but with the TVS Diode added to the circuit the Op Amp has lasted almost 1 Year now.

I used the TVS Diode because they are designed for this job.
If it is stated not to use the +12V wire from the coil then do not use it. The TVS Diode is trimming off voltage greater than approx. 16 - 18 Volts. I believe the coil produces negative voltage spikes and perhaps some ringing. On my Virago to protect against -ve spikes I also put a regular silicon diode (1N4007) in parallel with the TVS Diode.

On my XS650SH I put silicon diodes across the relays, starter solenoid and the alternator field winding. These modifications have been mentioned several times from others on this forum - it is not my idea, just useful information shared by others. I made these modifications because my onboard voltmeter blew after about 20 miles riding. The diodes solved with problem.

And from @TwoManyXS1Bs
"The coil's inductive kickback voltage is quite high at the grounding side. But that's because the current has nowhere to go.

The same kickback currents appear on the coil's positive side, but that side is connected to the bike's power, with a buncha stuff to help absorb the current spike, keeping the voltage down. There'll still be a bit of a voltage spike there, but not as bad.

A trick used on cars back in the day was to simply add a condenser (capacitor) directly to the coil's positive connector, the other condenser wire (or body) grounded. Maybe you remember seeing some of those. Some cars came with this "suppressor" factory installed. Helped reduce power-line induced radio static. So, yes, there's a history of this nastiness occurring way back then.

Another trick I've not seen would be to feed power to the coil thru a rectifier diode, like the 6-amp 6A10. This would prevent positive kickback spikes from getting back into the power system. But, there'll be a voltage drop across this diode, somewhere around 1 volt."

Adding a capacitor right at the ignition module's power line would also help. Especially if the Tytronic doesn't have one built-in. Have a look at Sleddog's TCI schematics, find where +12v power comes in, look for the first capacitor on that feedline. I'd reckon that a minimum of 10 uF, 25v rated electrolytic cap would be used there. Capacitor filtered power inputs are quite common on automotive 12v gadgets...
So there's kinda two schemes? and they are a bit overlapping, put down a door mat to keep a component with dirty feet from making an electrical mess in the harness, or putting booties on the component you wish to protect.
I kinda like the door mat and I f my extremely limited lecricical no-ledge grocs this, these components will act as general buffers whether they are located at source or destination as long as they are in the loop?
I go looking to buy say 25 of each of the components Paul suggests to make up some electrical condoms.
TVS Diode, P6KE Series, Unidirectional, 15.3 V, 25.2 V, DO-204AC, 2 Pins

1N4007 - Standard Recovery Diode, 1 kV, 1 A, Single, 2.6 V, 30 A

and get deluged with different manu's, and specs, NONE of which I understand, add to it the usual shipping tax etc mysteries. any of the sub specs make a difference I need to worry about?

OK gggGary again;
I would like to hear, see? a best practices layout of these parts, assembled into a plug n play jumper, easily added here and there as needed for the spiffiest XS650 clean 12 volt fortress we can devise.
A few questions;
How long do I leave the leads, do I have to worry about just grabbing my 250 watt iron and globbing on some 22 gauge leads, with bullets and a ground ring? Can I slap the resulting stuff inside some heat shrink, hang it from the electrical connections and call it done? Can I test to be sure this is working? what would a good set up look like?
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Interesting stuff for sure, but a bit over my head as well. Maybe the more enlightened will "dumb" it down for us some more here. I think I bought a bag of those 1N4007 diodes a few years back when 2M was talking about this stuff. Never did nothing with them though. Not sure what to do with them, lol. Yes, a little plug-in jumper we could add where needed would be ideal.
'Til Paul and or 2M chimes in; One electrical storm maker is the ignition coil. Many of us have seen big sparks created at the points when a condenser has died, couple things going on there but when the points open the coil field collapses, that field collapse creates enough voltage in the secondary to jump a large air gap but it also sends a big voltage spike back through points to ground AND the +12 lead that supplies the coil. The battery works as a "shock absorber" but it's far away as electricity travels, electronic magic near the source should helps quiet things down, basically bleed off pulses we don't want to ground, protecting other electronics from a rough ride. When I quickly destroyed a Tyronics ignition on WJL it got me thinking. Now looking for info on the best way to build some electronic shock absorbers.
As promised and several days later...

I put a TVS Diode(Big) and a Silicon Diode -1N4007(Small) in parallel on a scrap of PCB(0.6cm x 4cm):

The bands are at the +12V end with 2 red wires attached there and 2 blue wires attached at the other end. One wire in each pair is extra long. The copper tracks on the PCB are tied together at each end and both are cut under the diodes so there is not a direct short.

The long wires are turned back on themselves to give a red and blue at each end. A lump of heat shrink can be added to tidy it all up. Fittings of your own choice can be crimped on.

It does not matter which way around you wire this because both reds are tied together as are the 2 blues. I am sure you can find a hundred different ways to do this e.g. throw away the PCB and just twist and solder the wires together.
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When I was soldering the components onto the PCB there was a loud bang and all the lights went out. My faithful old soldering iron's heating element shorted out. The loud bang was part due to the 15W iron being fitted with a 13A fuse - Naughty me I guess!:hellno:
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A few thoughts
Problem because non stock electronics there ?
Is the solution then to install more non stock electronics ?
Perhaps --- But be careful so a fried component don't do a short between 12 V and Ground
Some electronic components can open or cut the feed on the wire.
When it fails.
And has been causing expensive repairs even on factory stock bikes.
An early 80 ties Suzuki had a regulator that fried and did not shut down instead gave full to the alternator that then also fried.
We are talking unknown large Voltage spikes.
And vibrations and heat.
It is an interesting subject though .fex when it comes to DIY ignitions.
Can I test to be sure this is working? what would a good set up look like?
I don't know what you're trying to protect, but the way to test the protection is just look at it before and after with a high speed oscilloscope. If what you're after is a good 12V low current supply for electronics you can try a three terminal regulator like a 7812 chip
I don't know what you're trying to protect, but the way to test the protection is just look at it before and after with a high speed oscilloscope. If what you're after is a good 12V low current supply for electronics you can try a three terminal regulator like a 7812 chip

I don't know electronics
Looking at the ratings for that component it appears to be 1.5 A and 12 V
Fuses are 10 A and 20 A on the bike and here are mentioned 400 V spikes
is that component capable / suitable for that ?
^The current rating you found wouldn't be a problem as long as what it was powering was less than a couple amps, which is a lot for typical handful of components on a board. The 400V spikes on it's input, it might not like those. Dunno. The thing to do is look at it all on a scope. No substitute for that.

Glancing at the specs, the only thing I see about input voltages is 35V max, so to use it in spec, limit it to that
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The spikes have a very short time duration so Diode and TVS Diodes do not need a high continuous current rating. The current load of the working device being protected does not flow via the Diodes, the diodes are in parallel with the device they protect.

A 1N4007 is sufficient to wire across the alternator field winding to filter out the induced spike when the ignition is turned off.
Yeah, well.
Put not thy faith entirely in magical mumbo-jumbo.
In the 80s, I discovered MOVs as surge supressors and went fitting them merrily to everything and anything in reach. Imagine my disgust when I discovered they had a finite life and were prone to shorting out. Bummer.
The following link gives data/info regarding transient voltage suppressors:

The following is part of a table from this reference comparing MOV and TVS devices:


Note how MOVs degrade as pointed out by Grimly above. For this reason they should be fused, however, TVS Diode longevity is rated as "Long".

Grimly, I need to check my MOV protected multi-plug connectors because they have been in use about 15 Years now. I never fused them so had better do something there - Thank you..
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If you're using the 1N4007 in series with something and you want it to use its high reverse voltage spec to protect something else connected to the supply in parallel with it, remember there will be a voltage drop of about 0.7 volts across any diode, so you will lose that voltage, same as if your generator was doing it.

One place you can use the 1N4007 family in the XS is to replace certain large stock diodes in the TCI and in one of the relays. The stock ones are made of thinnish hollow glass and pretty fragile. After I discovered a problem was caused by a broken one, I replaced all of those everywhere. I liked the high reverse voltage rating just in case...I don't know if the rating was necessary but it can't hurt and it's mechanically strong and easily available and the right dimensions. It's a general purpose diode.
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...So there's kinda two schemes? and they are a bit overlapping, put down a door mat to keep a component with dirty feet from making an electrical mess in the harness, or putting booties on the component you wish to protect.

... Now looking for info on the best way to build some electronic shock absorbers.

Haha, shock absorbers.
Good grasp, gggGary.

Since you enjoy reading, do a web search on "Decoupling Capacitor".
A standard electronics engineering practice.

Let's see what kind of brain juices spew.

Then, we can discuss this further...
so without going and getting a double E degree
low or no voltage drop
high frequency suppression
low frequency suppression.
If normal applies I can't have it all. but looks like a combo of a big cap and small cap placed close to the component I wish to protect is the preferred solution?
As far as cap TYPE tantalum sounds good?
Difference between Bypass and Decoupling Capacitor
When you look at the purpose they are used for, there is not much difference between the two types of capacitors. Surprisingly, most of the times the decoupling capacitors are also called as the Bypass capacitors. This is because they are shunted to the ground sometimes.

Some of the few noticeable difference between the bypass capacitor and decoupling capacitors are , the bypass capacitor is designed to shunt the noise signals where as the decoupling capacitors are designed to smoothen the signal by stabilizing the distorted signal. For shunting the signal we can just use a single electrolytic capacitor but for soothing the signal we will need two different types of capacitor.

c'mon guys y'all fight it out and the dummy just goes n buys the winner's selection. :smoke: