Very first project - beginner stumped

[jayc73]

Hi All,
This is my very first project and I'm not sure if I'm heading in the right direction or not ...

What I'm trying to do is increase DC voltage.

What I'm working with;
I have a DC power supply generating aprox.15kv @ 0.5A
a power input point or destination point
an obstacle - 5k ohm resistor

In a nut shell, I have 15kv - 15kv , departure and destination if you will.
I'm aiming for 15kv - 30kv or there abouts

The problem I think I'm faced with is there is a 5k ohm resistor I can not physically work around / bypass and must remain in place as it is a noise suppressor .

In other words, all voltage supplied must pass through a 5k ohm resistor to reach the "destination point".

I'm pretty sure using a 30kv capacitor will bump the voltage up but what options do I have with the resistor ?

Thanks in advance,
Jay

 

[(*steve*)]

15kV at 500mA?!?!?!? 7500 Watts!!!!

I hope it's running from 3 phase power.

edit: and is that a 1250W resistor?

Can you confirm all of these figures and explain what you're actually trying to do.

 

[jcurrie]

wow 15,000V to 30,000V if thats is what you have be carefull my friend even at .5amps thats a dangerously high voltage.
jc

 

[jayc73]

Sorry guys, error on my behalf

Should be 15kv @ 0.05A ( 50 Miliamps).

What I'm trying to achieve is boosting the voltage a spark plug fires with . Its for a 30cc 2 stroke with CDI ignition and I'm looking to convert to methanol.
Methanol needs a bigger charge to ignite so, I need a bigger spark to ignite it.

There are other high performance CDI ignition coils out there but most don't physically fit this particular application .
A higher output ignition coil doesn't really solve the problem either as the plugs are internally fitted with a 5kΩ resistor for rfi suppression which I assume, would kill +/- 75% of the higher output ignition coil voltage.

I can't use a non resistor type plug as there's too much sensitive gear surrounding the engine and rfi shielding would be horrendous.

I have seen plenty of modifications using capacitors or diodes but all with non resistor type plugs.

 

[(*steve*)]

The energy in the spark is not really related to voltage. The voltage only rises until something causes the current to flow (hopefully a discharge across the spark plug gap).

If you need more energy, you need to get a higher current through the primary side of the ignition coil. In a traditional ignition this is done by extending the dwell time.

However this can only be done to a certain point. Eventually you'll require a "larger" coil.

The 5k resistor will drop only 250 volts at 50mA.

I'm not sure what the correct answer for you is, but it may involve a larger coil. If it doesn't fit... dunno.

 

[jpanhalt]

There may be a little confusion of terms. Voltage needed to make a spark increases with pressure. I wasn't aware that the minimum voltage increased in moving from gasoline to methanol. The model engines I have dealt with had ignitions that handled both.

Back to the problem:
1) Will the capacitor and spark coil for the ignition take a higher voltage? Capacitors used in model CDI's are usually are usually rated 400 to 600 V.

2) You may get arcing in the spark coil, if you try to get to 30KV

3) Some model CD's use a voltage doubler right at the lower voltage transformer. Is that circuit accessible? Do you have the schematic? If no schematic, can you show a picture?

4) Hobby King sells CD ignitions very cheaply. You may find something there that will cost less than the cost of modifications to what you have, particularly, if you need a new spark coil.

John

 

[jayc73]

Thanks guys , starting to become clearer to me on how these things work.

Here's a picture of the engine and ignition system. Its a magneto driven CDI

Both coils are completely sealed

Ignition coil

Source coil

Set up

John,
I'll see if I can track down schematics for both of those coils.
Electronics is an unknown territory for me .
You mentioned the use of a voltage doubler at the lower voltage transformer .
Would it be worth increasing the voltage between both coils or am I looking at this the wrong way ?

The model engines you mentioned, would they be the Nitro engines ? as they use glow plugs over spark plugs to ignite a combusted charge.

Methanol needs a bigger spark to ignite inside a spark plug combustion engine. That's due to nothing more than the volume of methanol used ( 2-3 time more) per combustion cycle when compared to petrol.
These particular engines rev to 22000 rpm and the risk of methanol extinguishing the 'standard' spark is greatly increased .

Jay.

 

[jpanhalt]

Nice boat. Have you come across the "Big Boat" site (aka Gompy)? I believe he is in the Netherlands. He specializes in racing boat ignitions. I used to have his site marked, but switched computers and OS recently and couldn't find it. Here is a link to a site that is more directed to model airplanes. Gompy has posted in it and given links to his own site there.

http://www.rcgroups.com/forums/showthread.php?t=1781959&highlight=diy+ignit&page=40

What you call ignition coil, I was calling spark coil. We are on the same page there. What you have is a fairly standard version in my area. The other device is a magneto, as you note. I do not see the typical capacitor used in CDI and am not familiar with magneto-driven CDI. The fellows in my area either seem to have straight magneto (as shown in your "set up" diagram) or CDI running off a 4.8 to 6 V battery. The rest of my comments about voltage doubler are related only to pure CDI. I have attached a schematic for a Chinese ignition that I reverse engineered a few years back. It had reliability problems. The voltage doubler is C4 plus the two diodes (For a description, see: http://en.wikipedia.org/wiki/Voltage_doubler ). The CDI capacitor is C5 (0.47 uF), which is a fairly typical size. It uses a typical Hall sensor for "points."



Sorry, I cannot be much help on the magneto ignition.

John

 

[jcurrie]

don't know if it would work but you might sub the coil for a self grounding HEI auto coil they range from 50kv to 80kv,but changing the coil is your best option might check around for high out put coils.

 

[jayc73]

John,
No problems. The help you have given so far has been great.
I'm trying to stay away from the from the dc powered CDI's for the simple reason of electricity and water doesn't mix. Trying to keep a battery, battery connections, circuitry,etc waterproof is a mission in its self.

jcurrie,
Would a HEI coil work with a magneto?
I've had a good look at HEI coils and may have found something that would physically fit.

I have found another CD ' performance' ignition coil that will physically fit but this is the only info that is given

Primary Resistance 0.47Ω
Secondary Resistance 3.6KΩ

This is all of the info I can find on both standard coils - pictured in my previous post

Source coil / magneto

Core to red wire - infinite
Core to black wire 185Ω

Ignition coil
High Tension lead to red wire 2.1kΩ
Red wire to earth/core 0.1Ω
High Tension lead to black wire 2.1kΩ



Unfortunately , this is another language for me so, I have no clue as to what the difference is

 

[jcurrie]

don't realy know if it would work if it does you wont probley get full voltage, just a quess it would have to one of the old single input can grounded typs.
jc