Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Positive ground 45???

Positive ground 45???

Post Sat Nov 03, 2012 4:03 pm

Posts: 222
Location: Virginia

So my buddy recently took me to look at a 45 solo that he ended up buying. It had a dead battery, but we brought it to my place and hooked a battery charger up to it and got it running.
The positive battery terminal was on the right side and went to the frame ground post. I actually hooked the battery charger negative to the grounded post(which was actually the Pos. Post). Again this got it started.

I got him a NEW battery, charged it normally and he hooked it up correctly,NEG to ground, and got nothing. When he reversed the battery and put POS to ground, he got horn, lights and a running bike.
I haven't run across this before, so what's up with this scenerio, and what does he need to do to correct it? This is a normal 47 era WL Flathead.

Post Sat Nov 03, 2012 4:48 pm

Posts: 251
Location: Hudson, Florida
Steve, I am glad you asked this question as I have wondered about this myself. I owned a 1940 Cadillac LaSalle coupe, American made and it too was a positive ground. Forty years ago I and my friends played with Triumphs and BSA's and most were bought because of electrical problems from hooking them up backwards, there was a zenor diode I believe it was called on the rear fender and the wire would seperate from hooking it up wrong, push the wire back and she would start right up. I remember asking a brit mechanic back then and he tried to explain it but just confused me with words like earth used for ground and never let the smoke out of the wires as it was very hard to replace. I don't think it matters unless you hook it up backwards.

Post Sat Nov 03, 2012 6:34 pm

Posts: 159
Any generator system will work either way. Just repolarize, and change the ammeter connections.

Post Sun Nov 04, 2012 1:03 am

Posts: 1654
I've occasionally seen old British bikes with reversed polarities on the dynamos ( generators ). It's just a historic fluke that results from incorrect reassembly procedures at some time in the past. Ammeters were usually the first part of the system to give up and few riders bothered with them on dynamo equipped bikes once broken, you knew if your dynamo wasn't charging because the lights would fade after an hour or so. The usual mag plus dynamo, or magdyno system meant that the bike would run quite happily with a flat battery or no battery at all.

Manuals would often contain this sort of thing .. it matters more for cars because the starter motor has to run "right way round" whereas a bike system will run quite happily on either polarity. Negative earth ( ground ) systems were generally considered more reliable but whether that is actually true, I don't really know. The main thing was to know which it was!

You don't see them these days because the days when running bikes were flogged into the ground, stuck in sheds, forgotten and dragged out again years later are long gone; pretty much any bike with that sort of electrical system will have been rebuilt at least once and problems of that sort eliminated.

Zener diodes, or the flat-plate rectifiers which preceded them, relate to the later alternator systems. Dynamo equipped bikes would have a contact-breaker type voltage regulator much like the H-D one, usually mounted on the rear mudguard somewhere under the saddle.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun Nov 04, 2012 8:17 am

Posts: 251
Location: Hudson, Florida
Thanks 45 Brit, I believe I've been calling the flat plate rectifier a zenor diode for many a year. The one I am refereing to was like a stack of washers with a small wire connecting the plates.

Post Sun Nov 04, 2012 1:30 pm

Posts: 1654
the flat plate rectifiers are usually 6v items. There are various sorts, sometimes they look like a series of 5 or 6 circular plates ( usually painted black ) and some look like a stack of square plates, usually painted grey. They are usually mounted under the seat.

6v alternator systems often have no voltage control and rely on the battery to perform that function.

Zener diodes are usually associated with 12v systems and combine rectification ( AC to DC ) plus voltage control. They have, or need heat sinks which mean they have aluminium fins in various configurations. They can often be seen mounted under the lower yoke ( triple tree ) to get the benefit of the airflow
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun Nov 04, 2012 1:51 pm

Posts: 391
A battery can also be backwards! If a battery is fully discharged and then hooked up backwards and charged, it will accept it , but nothing will work correctly even though it reads correct voltage unless it is then hooked up backwards, in which case it all will work. Had that happen in a work pickup. Lights were left on, battery went dead. I sent a young laborer to hook up a charger which he did backwards. Battery read fully charged but when connected was a dead short. Took a while to figure out! Discharged it again with an accessory light, re-charged correctly, and all was well!

Post Sun Nov 04, 2012 2:35 pm

Posts: 251
Location: Hudson, Florida
Wow, its a wonder I was so confused pretty confusing electrical systems. One of these days I am going to drag my pre-unit chopper out of the boxes it is in and attempt to sort out the do's and don'ts of it all. I always liked the sound of a good running Triumph.

Post Mon Nov 05, 2012 2:09 am

Posts: 1654
I've never seen the battery thing, but the dynamo polarity reversal can be done in a moment without even noticing it, at least until you connect the battery. A mate of mine had an ex-WD M20 which had reversed its polarity, combined with a dead battery he was none the wiser and rode it like that for quite a while. The lights ran off the dynamo, the ignition ran off the mag and the battery just sat there....
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Mon Nov 05, 2012 8:53 am

Posts: 176
Location: Carmarthen, Wales, UK
I've no idea if similar happened in the USA, but positive ground systems were outlawed over here in the UK, I think in about the mid 1950's, I presume for safety reasons.

My old 1951 Land-Rover was positive ground.
72 Ironhead, goes better than it stops!



2005 XL1200R.... well ya gotta have a rat-bike!

Post Mon Nov 05, 2012 8:55 pm

Posts: 767
Location: Pa. , USA
Had a '31 Model A Ford P/up that was positive ground, not sure when Henry switched to neg. ground..
Vintage roadracing, Class C, AHRMA # 335

Post Wed Nov 07, 2012 7:51 am

Posts: 1654
Kev UK wrote:
I've no idea if similar happened in the USA, but positive ground systems were outlawed over here in the UK, I think in about the mid 1950's, I presume for safety reasons.

My old 1951 Land-Rover was positive ground.

MGs certainly had positive earth systems as new until 1967 and there are various references to Minis having positive earth into the early 1970s. I've also seen a number of references to corrosion effects, specifically that a positive earth terminal will corrode much more rapidly than a negative earth terminal. There certainly seems to have been a general changeover to negative earth in the 1960s but I can't find any reference to it being legal or illegal - if positive earth was illegal then a car so fitted would not pass its MoT ( annual inspection ) and that is not listed in the checklist.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Wed Nov 07, 2012 9:27 pm

Posts: 1676
Location: Interlaken, NY USA

Just to clear up a couple of details, The Zener diode is/was used to regulate the voltage in the system, clamping the voltage in the system to "12" volts by becoming a short to ground above that voltage. The Brit bike units were designed for positive ground. The Rectifier, that stack of round or square plates separated by small spacers were selenium rectifiers, used to change the ac from the alternator to DC. selenium being a predecessor to silicon in its use as a rectifier.
As for positive or negative ground, their pluses and minuses, (sorry couldn't help it), heard lots of speculation or reasoned theories as to the benefits for one or the other. Never could see the great difference between one or the other in function in a motor vehicle isolated from "earth" by rubber wheels. I guess the pits and spikes on your points change direction, but spark plugs seem to erode at the nose vs the grounding electrode no matter the polarity of vehicle ground.
As for making a grounding system illegal, that missed the target, should have revoked Joe Luca's business license instead. :D Or maybe applied truth in advertising laws to his business and allowed him to sell "darkness systems" instead of lighting systems.

Post Thu Nov 08, 2012 4:25 am

Posts: 1654
Joe Lucas, Prince of Darkness.... quite so.

The various configurations and precise functions of zener diode, rectifier etc were pretty much a mystery to contemporary British riders and largely remain so to that generation; the main thing to know was that they would probably break down sooner rather than later.

12v alternator systems with zener diodes were indeed, positive earth ... (1969-1970) Matchlessclueless has a good overview of the various 6v systems ... ng-system/ as does Real Classics Magazine ... c_regs.pdf while early 6v alternator systems like the C15 ( introduced 1957 ) also has positive earth ... wiring.htm

Frankly, I'd forgotten most of this, having long since abandoned the attempt to make any of them work for any useful length of time..... the first thing I did with my C15 grass bike was discard the alternator-powered "energy transfer" bump-and-go electrics....
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Thu Nov 08, 2012 11:39 am

Posts: 391
You mean "lethargy transfer", right?

Post Fri Nov 09, 2012 1:05 pm

Posts: 1654
RUBONE wrote:
You mean "lethargy transfer", right?

haven't heard that said in years :) there are quite a few around in the grasstrack and trials scenes but I don't know a single one still using the original electrics....
Shoot, a man could have a good weekend in Dallas with all that stuff...

Return to 45 Flatties