DC DC inverter couple of questions

Other Hardware General Electronics
1

Hi all!

I have couple of questions regarding DC-DC converter, but first of all I would like to present you with my problem.

So thing is that i have small 2 stroke motorcycle which has CDI ignition. But problem is that it's High voltage coil is failed and new part is very expensive, so I've come up with idea to build dc dc converter which would generate that voltage(about 250-300V).

I found this schematic on internet for the complete DC CDI, but thing is that I want to use only inverter from that circuit because I want to keep my original CDI(except spark, original CDI controls power valve in exhaust)
http://www.transmic.net/DC-CDI-v20/DC-CDI-Schematic.pdf

So this is part of the schematic that I would use:
Imgur

My question are:

  1. I was thinking of adding some voltage protection because maximum voltage taht my cdi can handle is 400V( i dismantled one old cdi and found that capactior is 1uF and rated on 400V)
    I think that 300V would be enough so I added one varistor in schematic which should serve purpose, but I don't know is that enough, and what else should i put?
    2.On this shematic for inverter which is basically same: SportDevices. CDI Programmable Digital Ignition. Is staded that "The last 1N4007 diode is necessary to load the capacitor with the current provided by the transformer" I was planing to replace 1N4007 with some shottky diode which are faster. On my shematic this diode should be connected beetween CDI ignition output and ground.
  2. What is purpose of R11 resistor, is it there only for current limiting of transformer?

If you have any advice feel free to post because I'm not so competent in analog circuits and I would like to make this as reliable as possible.

Best regards and thanks in advance.

Josip

2

Schottky diodes don't really do high voltage - and they have very bad leakage at high
temperatures, high leakage isn't good for high voltage anyway.

R11 is probably as you say to limit the heating in the transformer (or elsewhere).

3

But with this DC-DC converter, you still need the High voltage coil.
look at the right side of the schematic, it connect to coil.

4

MarkT:
Schottky diodes don't really do high voltage - and they have very bad leakage at high
temperatures, high leakage isn't good for high voltage anyway.

R11 is probably as you say to limit the heating in the transformer (or elsewhere).

MarkT

Then, can I use some fast recovery rectifier diode, let's say MR856.

BillHo:
But with this DC-DC converter, you still need the High voltage coil.
look at the right side of the schematic, it connect to coil.

BillHo,

I know that, I made this new schematics, and included it into first post, but somehow it wasn't visible! Here is the ling on part of schematics that I'm planing to use:
Imgur

What should I add on this schematics to improve reliability, or varistor is enough to protect from high voltage buildup?

Thanks

5

Hi just to clarify.

The ignition coil to the spark plugs is Okay.
The transformer you are talking about is the one used in the CDI to produce the 300Vdc to switch to the Ignition Coil?

Tom...... :slight_smile:

6

TomGeorge:
Hi just to clarify.

The ignition coil to the spark plugs is Okay.
The transformer you are talking about is the one used in the CDI to produce the 300Vdc to switch to the Ignition Coil?

Tom...... :slight_smile:

Yes! :slight_smile:

Josip

7

An inverter is usually a device that creates A/C.

8

Hi, thanks that clarifies things.

The transformer output is rectified and then used to charge a capacitor, hence CDI, Capacitor Discharge Ignition.

The old transformer, how did it fail, open circuit windings, shorted windings?

Tom..... :slight_smile:

9

There is no old transformer. Instead there is small coil and magneto which is connected to crankshaft and that coil generates that HV (~250V). So, now when that coil is dead, probably because of temperature. I've come up with idea to build 12 inverter which will replace it function.

10

jocoj100:
There is no old transformer. Instead there is small coil and magneto which is connected to crankshaft and that coil generates that HV (~250V). So, now when that coil is dead, probably because of temperature. I've come up with idea to build 12 inverter which will replace it function.

How many amps does it need? You can't even start this job until you know that.

FWIW I don't think I've ever seen a 250V DC booster and I'm guessing they're very hard to make. 250V DC is a lot of power.

Ignition coils can be had for $25. How much of your/our time does that work out to?

11

fungus:

jocoj100:
There is no old transformer. Instead there is small coil and magneto which is connected to crankshaft and that coil generates that HV (~250V). So, now when that coil is dead, probably because of temperature. I've come up with idea to build 12 inverter which will replace it function.

How many amps does it need? You can't even start this job until you know that.

FWIW I don't think I've ever seen a 250V DC booster and I'm guessing they're very hard to make. 250V DC is a lot of power.

Ignition coils can be had for $25. How much of your/our time does that work out to?

ignition coil cdi dc boost for sale | eBay

You misunderstood what is my problem

My ignition coil isn't dead. Dead is HV coil that generates 250V which are then sent to ignition coil.

I posted the schematics in first post of the converter. This doesn't consumes lot's of power. Because inverter needs to charger 1uF Capacitor.

In my last post I clarified what I'm planing to do.