Converting my 1965 scrambler 250 6v to 12v

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nursejim
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Location: North Wales, UK

Converting my 1965 scrambler 250 6v to 12v

Postby nursejim » Tue May 12, 2020 9:18 am

Hi all, I like many others would like to convert my bikes electrics from the factory 6v to 12v. Whilst looking around and reading various forums / articles, I found the following article. Any thoughts? Has anyone used this chaps method to convert their bikes electrics?

Regards
Jim
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ranton_rambler
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Location: Stafford UK

Re: Converting my 1965 scrambler 250 6v to 12v

Postby ranton_rambler » Tue May 12, 2020 11:52 am

There are a few different alternators. I have a 2-wire and converted to 12v by insulating the centre ground like he describes, with an Electrex reg-rec. I think you can also use a generic reg-rec.

ducwiz
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Location: near Frankfurt, Germany

Re: Converting my 1965 scrambler 250 6v to 12v

Postby ducwiz » Tue May 12, 2020 7:52 pm

This is to my knowledge the right way to convert the n/c 60Watt alternator to 12 Volt. It does not work for other versions of n/c alternators.
This figure from the workshop manual shows such device:
alt_fig.jpg
The same conversion can be done with the w/c 90 Watt type, and even much easier, because the center tap of the 2 intertwined windings is not soldered to ground, but routed outside the engine by the red wire. Anyway, you have to desolder, reconnect and insulate this "tap" as described. Imho, using a bridge rectifier without any regulation is not sufficient, will stress your battery. There are very inexpensive electronic shunt regulators from chinese scooters available on the market, in 12 Volt version. Here is one of these:
https://www.ebay.com/itm/VOLTAGE-REGULATOR-5-WIRE-HONDA-CG-125CC-150CC-200CC-250CC-ATV-DIRT-BIKE-GO-KART/111359753092?hash=item19ed8efb84:g:ShMAAOxyIPNTcSMi
There are others with different plug sizes available. You can cut them off and crimp on whatever connectors are to your needs. Example:
https://www.ebay.com/itm/5-Pin-5-Wire-Type-N-HK-D-Rectifier-Voltage-Regulator-with-Male-Pin-Connector/254276931625?hash=item3b34161029:g:WV4AAOSwHqddE77E
But it is important to choose a R-R version with 5 wires, not 4, which are also offered and look very similar. Theydo not feature the black wire. Some are deliberately offered for 12 Volt single phase operation; those are the right ones. Their wires must have the following colors:

yellow - AC input 1
pink or orange - AC input 2
black - control input (+ battery, after the keylock switch)
red - battery + (continuous)
green - battery -/chassis frame


Of course, the information given above is to my best knowledge, but without engagement.

Hans

nursejim
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Location: North Wales, UK

Re: Converting my 1965 scrambler 250 6v to 12v

Postby nursejim » Tue May 12, 2020 10:43 pm

Many thanks guys, I really appreciate your contributions.

Warmest regards
Jim

JimF
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Re: Converting my 1965 scrambler 250 6v to 12v

Postby JimF » Wed May 13, 2020 1:57 am

Hi Jim,

What are you hoping to gain with a 12-volt system that you aren’t already getting with your 6-volt system?

You could run a 12-volt ignition system, but if you are looking to operate modern 12-volt Halogen or incandescent lighting you will likely have insufficient power available.

We can talk about this more depending on your answer.

Jim

ranton_rambler
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Location: Stafford UK

Re: Converting my 1965 scrambler 250 6v to 12v

Postby ranton_rambler » Wed May 13, 2020 11:52 am

In my simple understanding, the original systems were half-wave rectified. The Electrex reg-rec is full-wave so some additional performance is gained. Also, 12v systems are more reliable with lower current flowing.
My generator was able to deal with the OE 25W headlamp bulb, but I have fitted an LED conversion to reduce demand.
Ian

Ventodue
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Re: Converting my 1965 scrambler 250 6v to 12v

Postby Ventodue » Wed May 13, 2020 1:05 pm

nursejim wrote:I found the following article. Any thoughts? Has anyone used this chap's method to convert their bikes electrics?

Well, it's been around a long time, that article, Jim. FWIW, I've kept this additional commentary from the author, Mike Spiers, posted to the BevelHeads forum way back in 2007:

"Going from 6v to 12v does not involve considerable time, effort or expenditure. In fact, it's one of the cheapest, easiest improvements you can do. The biggest problem you're going to have is getting the flywheel off, if you don't have a puller.

Total outlay is for the following replacements:
    Battery
    Rectifier (under EUR10.00 from an electronics store)
    Set of bulbs
    Ignition coil
    Some high temperature, oil resistant heat-shrink sleeving
    A Lucas Zener diode and heat sink (if you really want to be posh) as fitted to 12v Brit. bikes of the 70s and 80s.
Everything else works fine at 12v, but the horn will require it's adjuster screw twiddling in order to avoid self destruction."

Bevel bob
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Re: Converting my 1965 scrambler 250 6v to 12v

Postby Bevel bob » Wed May 13, 2020 5:45 pm

I used that article to convert my 67 M3 Narrowcase many years ago. Worked well until recently . Think you have to be carefull not to expect it to drive a bigger HL and EI system I am suspicious that it can overload the alt somehow . Others here will put me right?.

ducwiz
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Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: Converting my 1965 scrambler 250 6v to 12v

Postby ducwiz » Wed May 13, 2020 5:52 pm

A Lucas zener diode is technology from the last millenium - OK, not very precise but can be accepted. Most of them are made for positive ground, which possibly means that you cannot use anymore addional electronic equipment which was built for negative ground on your bike. Might be a problem or not. And - the Lucas zeners are not cheap, afaik you have to spend 15$ minimum.
So I again recommend to use one of the described chinese scooter fullwave-R-Rs. You need no additional rectifier, no extra wires.

What's inside the chinese box:

Full Wave Regulator schematic 2.jpg
I suppose at least JimF can read the circuit ...

In the list of replacements the horn is missing. A 6 Volt version pulls twice the current from 12Volt, i. e. four times the electric power, so it has to stand a heavy overload. It might work (for some time), or it might not - check it out ...

And please, don't try to get the flywheel off by a non-appropriate tool. Use a puller made according to the works specification, which applies the pulling force on the flywheel's steel hub, not on the brass or aluminum flywheel.

Hans

ecurbruce
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Re: Converting my 1965 scrambler 250 6v to 12v

Postby ecurbruce » Thu May 14, 2020 10:34 am

Hi all,
If I may, I'd like to comment on a couple of things,
First, I can say from practical application that Hans is dead on with his advice, I've had a successful 12 volt system running now for quite a while, though in several different configurations...
One thing that although has been mentioned previously, doesn't get a lot of thought or attention in a successful 12 volt system, is the battery and the roll it plays. Of course, with a battery system, we take for granted that a battery is present, but not necessarily how it affects the performance of the system.
In our 12 volt systems with such a minimal output alternator, the battery has to carry the load at low RPM's, typically under 3500 RPM's. A battery with a small AH rating that can't carry the system at low RPM's will discharge while carrying the load, until the RPM's increase enough for the stator to start charging the battery again and run the rest of the system as well. At this point the regulator sees the battery as a load, right along with the other elements of the system.
If a large enough battery is used, where it doesn't discharge as much in the low RPM's, then the regulator doesn't see the battery as an additional load when the RPM's rise up to a point where the stator can support the system, without also charging the battery.
I use two sealed lead acid agm batteries rated at 5.1 ah each, configured in series, to make 10.2 ah. This battery with my alternator will carry my system successfully through the full range of RPM's.
Another element for success of my system is to always begin with a fully charged battery, so I keep a battery tender plugged into my parked bike. (unless of course I'm cranking it right back up and riding off...)

With a smaller battery, I have been limited in the size of my headlamp bulb, but with this setup I can run a halogen 65 watt headlamp successfully. My particular alternator setup also contributes to the system success, as it's the highest power configuration possible, in my opinion, for the single alternators. I use the six pole (12 coils) stator as in the wide case singles, configured in parallel, with a Kohler single phase regulator, and the 10.2 ah battery.
Bill Corey and DewCatTea Bob put a lot of research and theory into developing the best 12 volt system, it's in this forum, lots good reading...

Thanks,
Bruce


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