Negative Ground Conversion

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Bonwit

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Since I'm now faced with doing some re-wiring, I'm thinking it may be a good time to make the conversion to a negative ground system. I've searched the forum and the web and haven't found much in the way of specific instructions on how to go about this. I've read that I must get rid of my original rectifier and zener diode, replacing them with a PODtronics unit (I have a new one from the previous owner), and obviously my solid state ignition assimilator and my Boyer will have to be rewired according to their negative schematic . . .

Anything I need to know about re-wiring the Boyer?

What about the blue capacitor? Does it stay?

Where's a good place to mount the PODtronics box?

I've got another brick in my box of parts called a Mity Max. Is that the same thing as the PODtronics? It's much larger and heaver than the POD

Other than reversing the battery connections, is this all there is to it?

Thanks
 
Rich_j said:
Why bother?
Click to expand...
Because just about every modern electrical device's connector is assumed to be for a negative ground system. For example, on long trips I like to carry along a GPS. The wiring arrangement carries the same hazard as my battery tender, that is, a bare terminal (when removing the device at rest stops) that when touched to the frame creates a dead short. Also, I'd like to install a headlight modulator for safety reasons. Every one I've looked at specifies "negative ground only".
 
Bonwit said:
Rich_j said:
Why bother?
Click to expand...
Because just about every modern electrical device's connector is assumed to be for a negative ground system. For example, on long trips I like to carry along a GPS. The wiring arrangement carries the same hazard as my battery tender, that is, a bare terminal (when removing the device at rest stops) that when touched to the frame creates a dead short. Also, I'd like to install a headlight modulator for safety reasons. Every one I've looked at specifies "negative ground only".
Click to expand...

Not sure what you're connecting exactly but standard practice is that the fixed live stuff is a female and the removable bit male so your live side is always shrouded.
 
Running any conventional automotive accessory, such as a GPS, requires a polarity reversal that has to be treated carefully on a positive ground system. Assuming that you replace the existing power plug (the proprietary male plugs have been unavailable for years, unless you have access to Ludwig's parts stash) with something useful, like a standard 12v automotive plug, the sense of the plug must be reversed to actually use it. I've done this on my positive ground Mk3 and find it works fine, but you must always be sure that the accessory has no case ground connection, i.e., it has a floating case.

The only complication to a negative ground conversion for pre-Mk3 Commandos is the assimilator, which is hopelessly positive-ground. You can either do without it (you'll lose the charging warning light), or buy a negative-ground version. All EI systems and regulator/rectifiers come with instructions for running at either polarity. My SPARX reg/rec mounts neatly to the front of the battery case on my Mk3.

BTW, the large blue capacitor rarely survives an EI conversion, although it doesn't seem to do any harm. It sits accross the battery, so if it leaks, it'll pull your electrical system down.
 
rick in seattle said:
Running any conventional automotive accessory, such as a GPS, requires a polarity reversal that has to be treated carefully on a positive ground system. Assuming that you replace the existing power plug (the proprietary male plugs have been unavailable for years, unless you have access to Ludwig's parts stash) with something useful, like a standard 12v automotive plug, the sense of the plug must be reversed to actually use it. I've done this on my positive ground Mk3 and find it works fine, but you must always be sure that the accessory has no case ground connection, i.e., it has a floating case.

The only complication to a negative ground conversion for pre-Mk3 Commandos is the assimilator, which is hopelessly positive-ground. You can either do without it (you'll lose the charging warning light), or buy a negative-ground version. All EI systems and regulator/rectifiers come with instructions for running at either polarity. My SPARX reg/rec mounts neatly to the front of the battery case on my Mk3.

BTW, the large blue capacitor rarely survives an EI conversion, although it doesn't seem to do any harm. It sits accross the battery, so if it leaks, it'll pull your electrical system down.
Click to expand...
The GPS is a good example. The propritary connector is bare to the case grounded GPS. When you unplug the unit, if the connector touches the frame. . . sparks.

I converted my assimilator to solid state last year. Should be no problem to just reverse the connections.

So do you recommend keeping (or do you have to keep) the capacitor when switching to a PODtronics? I'm not clear exactly what the capacitor is there for.

-John
 
The capacitor is there to aid starting with a flat battery, no need to keep it when going over to electronic regulator etc.
 
Where is the best spot to mount the PODtronics? At first I figured I'd tie wrap it up front to the kickbrace tube. locating it further aft would make wiring easier, but I'm wondering if it will get enough airflow.

-John
 
I did some searching and found some of the locations others have chosen. Two that stand out are on top of the rear fender, just behind the battery box, and underneath the top tube above the battery box. I'm concerned about there being enough airflow here.

-John
 
Positive-ground solid-state assimilators are NOT reversible. They contain a least one transistor and two diodes and are positive-ground ONLY. A negative-ground version for a Mk3, for example, is sold by Old Britts and others, about 40 bucks. The Mk3 assimilator, BTW, is a solid-state assimilator. Les provided a schematic last year to clarify this point.

I checked my Garmin, and the case floats, along with the metal connector body. I really haven't had a problem using it on my positive ground MK3. If I change the grounding scheme, what am I going to do with all my "Norton - Positive Earth" logos and patches???
 
rick in seattle said:
If I change the grounding scheme, what am I going to do with all my "Norton - Positive Earth" logos and patches???
Click to expand...

Aren't you more worried about the tattoo?
 
Any polarity conscious device can be used in either a positive or negative ground system. You may have to insulate the body of the device from ground when using opposite polarity. Simply connect positive to positive, negative to negative. Sometimes it is impractical to use a device that has to be insulated from ground. In that case, the proper polarity device is called for.
 
rickinseattle wrote;
I checked my Garmin, and the case floats, along with the metal connector body. I really haven't had a problem using it on my positive ground MK3.
Click to expand...

Strangely enough I contacted Garmin last week about the positive ground issue, and what they told me was that it would be " OK to fit as long as the negative terminal is connected at a lower voltage than the positive terminal, and that if the power is connected backwards it won't harm the unit, but that it wont draw power"

Therefore Rick, the question is, does yours Garmin draw power whilst running, as I understand it that means recharge/ keep the battery charged, as I believed from the voicemail (above) that I received from Garmin was that it wouldn't charge the unit with a positive earth. I didn't bother ringing back for clarification about the "lower voltage reference" as it sounds too complex (meaning I don't understand how this could be) to be bothered with for the amount of use I will be using the Garmin on the Norton (or Triumph). What I intend to do now is just run it from its batterys (approx 4 hours use) and if I'm away from home touring, recharge overnight from the mains.
 
Reggie,

Your solution will work for as long as the Garmin stays charged. In my case, with the polarity reversal at the 12v plug, the Garmin sees +12v at the center terminal of the plug, with respect to the plug base (my pseudo-ground), i.e., it thinks it's in a negative-ground environment. Both the plug and the Garmin must be isolated from the Norton frame/ground.
 
Bonwit said:
rick in seattle said:
Positive-ground solid-state assimilators are NOT reversible. . .
Click to expand...
Click to expand...
My Cool Cat Express SS3AW Assimilator is. Just swap the orange and black leads.
http://coolcatcorp.com/Merchant5/mercha ... gory_Code=

-John[/quote

Negatory, my good man. Mike Frank at CoolCat sells two versions, one each for positive and negative ground systems, respectively. Reversing the polarity of the two wires forward-biases all diodes, sends any transistors into cut-off, and reverses the sense of any comparison of voltages. If it works at all under these conditions, the device is comparing voltages with respect to the "hot" battery point, and not to a common reference, or ground. It is simply not possible for an active device, especially a comparitor, to function under a reversed polarization.
 
If you swap the leads on the battery, then all polarity conscious devices needs to swap leads also. This brings you back to the same polarity you started with. In other words, you do a 360° turn. If the case of the positive ground device is a conductor and attached to ground and ground has been changed from positive to negative, then the case must be insulated from ground and normal hot lead (now being positive) is attached to the case and the negative terminal of the device attached to ground (which is now negative). Ground is nothing but a common conductor, be it positive or negative. Sometimes it's a whole lot easier to just get the correct polarity device.
 
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