Scooterotica • Mix and match DC electrics query

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Mix and match DC electrics query

Posted: Mon Mar 21, 2011 9:00 pm

by Knowledge

I got this message from a guy called Adam who had read my article in Jetset about 12V DC conversion (I think), and then bought a tool kit off me:

Hi Martin,
Just read the excellent above ref. I have a modern 12V Electronic stator & would like to run a battery as described. I have done this before with limited success using the standard one wire from the stator to a Vespa 5 pin regulator but was not convinced by the eventual wiring? Please can you advise on improvements using your method with a Vespa 5 Pin regulator? Currently I am building an LI using a Serveta frame with a rear ignition switch and wiring diagrams as per Red Sticky's p218/219 but without indicators. The wiring is to 218, but feel this will give me power without the ignition switched on so feel 219 in this area would be better? Please can you advise on a suitable wiring configuration at the rear end using the components described with a standard rear junction box? Sorry to approach cold, but your number was unobtainable this morning. Rest assured that once suitably informed I intend to purchase your crimping kit to achieve the aim! Thanks in advance Adam

Now some of these points have been raised before, but I don't wish to enter into protracted dicussion or provide a custom wiring service via ebay, so I thought I would post it on here and see what people think. I will start off with the first reply, and perhaps other will offer some further advise. I will direct Adam to this forum, and perhaps he will become a Scooterotica member.

Re: Mix and match DC electrics query

Posted: Mon Mar 21, 2011 9:01 pm

by Knowledge

The reason you may have issues with the previous attempt at the five pin regulator/rectifier is because it does not take power-in the same way as either the 3 pin Vespa unit, or even the Wassell in the article. It requires a stator that is specially wound so it is in two parts. Two coils deliver power to the 12AC circuit, regulated by the 5 pin unit. The two other lighting coils provide power to the same 5 pin unit, where they are regulated and rectified into 12V DC.

The 5 pin rectifier/regulator consumes power, even when the engine is off. That is why the Serveta switch isolates two circuits. One kills the ignition, and the other circuit cuts the power to the rectifier. If you do not isolate the rectifier, the battery will be dead when you return to the scooter after a couple of days.

Re: Mix and match DC electrics query

Posted: Mon Mar 21, 2011 9:12 pm

by coaster

I don't have Sticky's latest book yet so can't comment of the diagrams he is refering to but thought that it was normal for batery models to leave the the feeds live with the ignition switched off. I can't personally see the problem, an isolating switch in one of the battery leads would do the trick if it really bothers.

Re: Mix and match DC electrics query

Posted: Mon Mar 21, 2011 9:34 pm

by byron

I've used vespa 5 pin rectifier units on bikes that have a split AC/DC system. So the AC is used for the standard lights, and the DC from the battery [kept charged by the B+ terminal] is used for spotlamps, brake light, horn, phone charger etc.
The C on the unit can be used to stop the battery overcharging, but this does need to be isolated when the engine is not running, otherwise the battery will drain. A ScootRS ignition switch is useful here, as it has wires and connections to do this. [nod to firekdp for that tip], but sounds like the Serveta one does too.
If the C is not connected, the battery shouldn't drain... I think, as that's how I had mine til I fitted the switch.

I'd get rid of the oe junction box, and join the necessary wires properly with solder and heatshrink etc...

But of course, a better DC system is using a Wassell type unit, there are some instructions to do that on this very site :bigsm:

Re: Mix and match DC electrics query

Posted: Tue Mar 22, 2011 12:18 am

by Craig H

Shout out to the EADCM.

Re: Mix and match DC electrics query

Posted: Tue Mar 22, 2011 3:44 pm

by firekdp

He does realise that, if he is using a vespa 5 pole reg/rec, his main lights will have to be AC unlike the early serveta 6v DC system (page 218).
If so, how to wire it then depends on which loom, ignition switch etc. he has and what circuits he wants the DC for.