Ducati CDI with DC supply

[dickie]

Does anyone know if a Ducati CDI would have any problem working off 12vDC supply instead of the usual AC?

In my experience, many AC electronic devices just rectify the incoming supply and are therefore really just DC devices anyway. However, I have no knowledge of the internal components in one of these modules.

[dickie]

Someone actually posted a circuit diagram on here a few years ago which I just found http://www.ilambretta.co.uk/forum/viewtopic.php?f=7&t=4286


So I can see that DC will work. As I half expected, there's a diode on the input which acts as a half-wave rectifier.

BUT, my DC is only about 14V, and I'm pretty sure the AC from the LT coil will be much higher than that. Of course course, DC is charging the capacitor continuously, so it may be enough? But may not be enough at high RPM.

Does anyone know the voltage from the LT coil?

[Fast n Furious]

The Stator on all lambretta electronic ignitions (CDI) is designed to work on a voltage from the LT coil at around 200VAC (maximum magnetic saturation) ( around 60VAC at kick start speed) The HT coil is an integral part of the whole device.
A DC CDI gets its power from the bikes 12VDC battery via the ignition switch. Inside a DC CDI there is a DC/DC converter which is designed to transform the 12vdc to 200Vdc to charge the Capacitor.
There are some units out there which derive their power from the lighting coils. These CDI's basically are a standard DC CDI but with an additional full wave rectifier and regulator on the power input side to stabilize the voltage for the DC/DC converter circuit.
DC CDi's, fed from the battery, offer full voltage to the spark plug at any speed making for an easy starting bike that is less likley to foul the plug in rich cold conditions.

So, AC and DC CDI's are incompatible.

Unlike most ignition switches,The series 2 TV175 ignition switch has the abilty to switch power to the CDI in positions 1, 2, and 3. Failing that, with a standard AC switch just take the power from the side lights to power it (only works in position 2 and 3 so you are allways riding with some lights on)
A cheap and chearfull DC CDI often seen on GY6 derived twist and go scooters can be made to work very well. Some of these are even programmable. (Beware! These are marketed for 4 stroke machines. Very often the software has to be reinterpreted on the rpm readout!)
A separate suitable CDI coil has to be sourced because these type of CDI's dont have an integrated HT coil. They only contain the electronics.
I use the coils from reputable Outboard motor engines.(Usually Mercury) These are easily connected up and.... as they are designed to work in wet and damp condition under constant high RPM conditions they have proven to be perfectly suited for Lambrettas.

IMG_20221225_212756_871.jpg

This particular CDI uses a Yamaha pin-out standard with an RS232 programing port.

ig coil.jpg

Mercury CDi coil.

[dickie]

Thanks Pete, excellent answer.

I've tried those GY6 CDIs in the past and have found they fail pretty quickly (maybe 1000 miles ish). This only happened twice, and were bought at the same time from the same supplier, so maybe a bad batch. I've used scootronics version of the same thing with good results though. The obvious answer is to do the same again, but I just like messing about, hence the idea of using a Ducati one I have lying about. But you've put that idea to bed.

I may try one of those Mercury ones. I didn't exactly follow what you were saying; are they all programmable or only some? Is the software readily available to do this?

Thanks.

[Fast n Furious]

CDI ignition hook up.gif

They can be found in standard format (so nothing to adjust)
They can be found with a tiny pot switch to select preprogrammed curves. ( more suited to 4 strokes) These are usually used to swap out the factory unit on twist and go's to bypass the rev limiter.
Occasionally, they can be found with a serial comms port for connection to a computer (Obviously these need the matching software which comes with it) Problem with these Chinese units is that they are usually here today and gone tomorrow. So continuity of supply becomes an issue and the instructions are pathetic at best.
There is a reputable company based in the Czech republic called Ignitech. They make all sorts of ignitions for a variety of bikes and specialist applications. A bit pricey but very good. They do speak the kings and have very good after sales support.
http://www.ignitech.cz
Just a note to add........ Never use a Chinese made HT coil. Satisfactory understanding of High tension electrical insulation doesn't exist in that part of the world. It will let you down!

[Wack]

Quote-The series 2 TV175 ignition switch has the abilty to switch power to the CDI in positions 1, 2, and 3. Are the remade switches the same as original,in that they give DC power out on the 1st click ?

[Fast n Furious]

Yes Wack.
DC out in positions 1,2 and 3 is on the white wire.
So, with the ignition off and keys removed, you can isolate your ignition and any other instruments so attached to the white wire.

[Wack]

Thanks for that,I'll try one.

[dickie]

I run full dc on my current LI, and did so on my previous 2 as well.

I don't run a battery, so there's no need to isolate it.

It does however mean slightly worse starting as you need to build up 12V and get the motor started within one kick. Using a smaller capacitor (in place of the battery makes a big difference).

It isn't "better" than using a battery, it's just different. Simpler, but harder to start and no electrics when engine isn't running.

On my current build I'm going to omit the capacitor but may get a few blown bulbs, depending on the reg/rec I use. We'll see.

[Fast n Furious]

If you do this without a battery, then the pulsed DC from the regulator could destroy the DC/DC converter in the CDI. (the voltage that you measure with your meter is an averaged value of this pulsed output) Yes... the addition of an appropriately rated capacitor will smooth out this pulsed effect to some degree. Maybe this is why your GY6 CDI's failed prematurely Rich?
With programable CDi's it is likley to corrupt the ignition map and just stop the CDi from functioning until the map has been reloaded into the memory. (seen it, done it)
Lambretta's use Shunt type regulators. These are very basic in their performance but are dead cheap to produce which is why they are used.
Series type regulators produce a much purer regulated DC output which negates this premature failure of the electronics and extends the working life of the battery. Unfortunately, such devices are not available "off the shelf" for our scoots. This is largely because the series regulator needs to handle the unloaded incoming voltage from the stator which can be as high as 150Vac on some stators. So this type of series regulator has to be custom designed and built to handle this degree of voltage reduction (No problem for a zener controlled Thyristor shunt regulator).

[dickie]

Good point Pete, I had vaguely wondered if that was the cause of failure initially, but using an outwardly identical set up from scootronics has been failure-free (so far).

The main reason that I don't use a battery is the lack of battery tray. If I'd been able to find a 12v battery that was small enough to mount on the outrigger or similar position, I'd try that. The only issue I'd have then would be mounting a switch, but that clearly isn't insurmountable.

Anyone know of such a battery? Cylindrical would suit me best, but anything very small is probably workable.

[Fast n Furious]

My TS1 uses a small 2.1A/H lead acid gell cell battery (Yuasa NP2.1-12) like you would find in a burglar alarm panel. It's been in there for over 6 years now and still functions as it should. (granted..... it is charged by a precision, ripple free, series regulator) It fits neatly under the loop where the air box used to be and is simply held there, wrapped in a bit of old innertube, with some cable ties. (other positions on the scoot are available ) These batteries can be mounted in any position except upside down. Maintenance free and will last for years if not overcharged. They also hold their standing charge for a long time when the scoot is laid up.

[dickie]

So my next idea is a 600mAh LiFePo4 battery. I reckon I can make my own from 3.7v cells and conceal in an old regulator housing.

They should normally be charged on constant current, constant voltage basis, which I'm pretty sure won't be very controlled in the constant current phase.

I don't THINK this will be an issue, but does anyone know?

This last year, I've done a lot of work with lithium batteries but it's hard getting real information as the industry is awash with salesman and you have to fight your way through all the shite to find anyone who knows their onions. I've got a vague connection to a very good guy in Belgium so I may see if he's happy to give me some advice for personal stuff.

[Fast n Furious]

Lithium ions need battery management control to charge them safely.
Some batteries have the electronics to do this within the battery itself.
Lithiums don't like the high ripple current that is inherent with shunt regulated charging systems.
I recommend that you keep it simple and just use a small lead acid accumulator.

[dickie]

Lithium ions need battery management control to charge them safely.
Some batteries have the electronics to do this within the battery itself.
Lithiums don't like the high ripple current that is inherent with shunt regulated charging systems.
I recommend that you keep it simple and just use a small lead acid accumulator.

I've found some 3.7V cells that I can fit nicely within an BECME housing I have, so if nothing else, they'll look OK.

They have protection in-built.

I hear what you're saying, and I agree, but I'm going to try it anyway, because I'm just like that. It usually works out, but sometimes I regret it

Obviously, it will be fine initially, so any feedback I give will be close to worthless for at least a few months. At the moment, I honestly don't know the type of reg/rec I have, but I'd expect it to be shunt type. If it doesn't work out, I can change to a MOSFET in future. MOSFETs are standard fitment on late CBR600s and ZX-6R; probably a whole lot more, but I don't know for sure.

[Leotech]

Lithium ions need battery management control to charge them safely.
Some batteries have the electronics to do this within the battery itself.
Lithiums don't like the high ripple current that is inherent with shunt regulated charging systems.
I recommend that you keep it simple and just use a small lead acid accumulator.

I was quite a proponent of these Li Ion batteries about 12 months ago, since then I have had 2 go up in smoke. Both allegedy had the electronics to charge with a basic system, they were advertised as for Vespa PX200 so in theory same electrics as Lambretta system. One was on my GP 22/2 and I'm so glad it didn't go up in smoke, I managed to get it ripped off. I just went back to AC for lights.


I only have one left now on my S1 and its a huge Li ion battery, about 14 amp hours. probably good for a small car. That one for some reason seems to be ok. Maybe its larger size or maybe that its charged with a Varitronic rectifier rather than the 5 pin Ducati one. Dunno, I'm no electrician.

[Fast n Furious]

The higher the Lithium battery capacity, the more capable it is for the battery mangement electronics to cope with the high levels of unwanted ripple current from the traditional simple shunt regulator.

I've warned about the fire risks associated with lithiums on this forum before.Thanks for sharing that experience Leo. Hope it didn't do too much damage.

Lithium batteries have a poor A/H capacity compared to thier Lead acid counterparts of the same physical size.
Lithium batteries have a much better cranking capacity compared to their lead acid counterparts of the same physical size.

So, Lithium batteries are a good upgrade for say something like a big arsed Harley, which pulls a massive current when trying to crank that big V-twin over. Generators on most modern motorbikes are streaks ahead of our ancient magneto's and have plenty of capacity to run all the electrics even at tickover. So, the demand for a high A/H capacity battery isn't really there.

Our lammy's are the opposite. We dont need any cranking capacity but do need our electrics to work normally at tickover. So we need the high A/H lead acid battery to make up the deficit, which is much more tolerant of the weak generator, simple half wave rectifier and the crappy shunt regulator.

[dickie]

Thanks gents.

Peter, you make a few good points there. The only reason I've gone for Lithium is the fact that I can find something that I can make look like it belongs under there (not sure why though as I have a modern carb and a CASA filter on an elbow).

The one I've gone for is 2Ah, so can deliver about 2A, so not enough for lighting etc without the generator.

I've checked with Anthony Tambs and it is indeed shunt type. I didn't ask whether it was full or half-wave rectification, but I'll bet my left gonad it's full wave.

I'm beginning to think that I'm better off just sticking with the capacitor set up. The only advantage (in my case) in using a battery is the possibility that the ripple that I possibly have, damaged my CDI.

At the moment, there's too much guesswork in this for my liking, so I'll borrow an oscilloscope from work and see just how much ripple I actually do have.

[Leotech]

The one on my GP200 was a direct replacement for the original size lead acid but 12 volt, All it worked was as a standard UK GP, It went up in smoke about about 6 months.

Other one was on SX with pathfinder lights, that one only lasted about 4 hours on a ride where the lights were mostly on al the time. Fitted on original tray.

The larger one on my S1 powers a good horn and a single spotlight. I run with the light on mostly, occasionally I test press the horn and if its not working I turn the light off for 20 miles or so until both work again. I think im kind of keeping the battery at an acceptable charge level? This one has always been ok but it is a much larger battery and located in the legshield toolbox as it wont fit on the original tray,

[Fast n Furious]

Lithium ions need battery management control to charge them safely.
Some batteries have the electronics to do this within the battery itself.
Lithiums don't like the high ripple current that is inherent with shunt regulated charging systems.
I recommend that you keep it simple and just use a small lead acid accumulator.

I've found some 3.7V cells that I can fit nicely within an BECME housing I have, so if nothing else, they'll look OK.

They have protection in-built.

I hear what you're saying, and I agree, but I'm going to try it anyway, because I'm just like that. It usually works out, but sometimes I regret it

Obviously, it will be fine initially, so any feedback I give will be close to worthless for at least a few months. At the moment, I honestly don't know the type of reg/rec I have, but I'd expect it to be shunt type. If it doesn't work out, I can change to a MOSFET in future. MOSFETs are standard fitment on late CBR600s and ZX-6R; probably a whole lot more, but I don't know for sure.

The MOSfet regulators used on these jap bikes are better than traditional Thyristor regulators but they are still a shunt regulator and ideally need a 3 phase input from the stator. Suppliers of these regulators are specific about not using them with Lithium batteries!