Tim4 ignition

[IC-man]

Anyone had problems with this circuit.
I built lots of different ignition systems over the years but just needed something simple for a converted strimmer motor so built the TIM4.
It works fine but T1 gets quite hot (too hot) I've built a couple of them with same results. Any ideas?
12vdc and standard car coil ( no ballast)
I'm also using 22 ohm 5 watt as R4.

 

[deverett]

Don't know anything about electronics, but could you fit a heat sink?

Dave
The Emerald Isle

 

[IC-man]

Good point Dave, but already has large aluminium plate attached with compound,that should be "overkill" really, but I like to be safe.
Thanks anyway.

 

[stevehuckss396]

Could it be a design flaw. Maybe that's why there is a TIM6. Have you checked into the 6? I am a big fan of the CDI's so I have not tried the 6.

 

[bluejets]

I have a distinct feeling that was meant for 6 volt supply.
TIP42c transistor for main, 2n2907A for intermediate transistor.
Ones I used had a much higher base resistor also if I remember correctly.

I have a similar circuit here somewhere that uses an MJ10012 darlington transistor ( MJ10012 designed for ignition systems)
I'll see if I can find it.

 

[IC-man]

Hi blujets,
You're right, but the comments (I believe by the designer) said he used 12vdc and standard auto coil.
I have used the MJ Darlington but only a points version not with a Hall switch.
Thanks anyway.
Circuit for MJ would be good.
Graham

 

[Charles Lamont]

I don't know how similar it is to a Tim-6, but with mine the back-EMF (or whatever it is called) from the coil (Minimag) was too much for the power transistor.

 

[IC-man]

Could it be a design flaw. Maybe that's why there is a TIM6. Have you checked into the 6? I am a big fan of the CDI's so I have not tried the 6.

Hi Steve,
Would be interested which CDI circuit you are using.
Graham

 

[IC-man]

Hi all,
Just to avoid confusion, the circuit I'm using is from the 5 bears circuits and it appears that the circuit I'm using is what people are calling Tim 6 but my printout calls it a TIM 4
TIP42C, 2N2907, etc

 

[bluejets]

Hi blujets,
You're right, but the comments (I believe by the designer) said he used 12vdc and standard auto coil.
I have used the MJ Darlington but only a points version not with a Hall switch.
Thanks anyway.
Circuit for MJ would be good.
Graham

Found one of the 12v circuits for kettering system.
Had a 6v version as well.
Also some cdi units but anyhow..........

If you get any noise problem just stick a 0.1uF cap right on the power terminals (+ and -) of the hall effect.
Usually find some small ceramic ones around in Ebay etc.

Just be aware also there is no protection against the engine stopping with power on.

 

[IC-man]

OK Blujets,
Yes, already put cap on he Hall leads.
Thanks I'll try your circuit next.
Keep safe
Graham

 

[dsage]

Anyone had problems with this circuit.
I built lots of different ignition systems over the years but just needed something simple for a converted strimmer motor so built the TIM4.
It works fine but T1 gets quite hot (too hot) I've built a couple of them with same results. Any ideas?
12vdc and standard car coil ( no ballast)
I'm also using 22 ohm 5 watt as R4.

A standard coil will have a resistance of less than an ohm. So on 12 volts you will have over 12 amps of current. Basically a dead short. (assuming the battery can keep up). That's why the transistor is getting hot. Add a ballast resistor of maybe 3 ohms (50 watts) and consider running it on 6v as well. You'll have plenty of spark on 6v and less wasted power in heat. As mentioned previously if your engine ever stops with the ignition activated you're going to let out the magic smoke. This was one of the major flaws with the TIM ignitions.

 

[IC-man]

Thanks Dsage,
I did add a ballast resistor and it did drop the temperature a bit, I think dropping the voltage to 6vdc will probably sort it.
Thanks for your help all.
Graham

 

[dsage]

Yes. Dropping the voltage will go a long way BUT even with six volts (instead of 12v) the coil is still more of less a short circuit (less that 1 ohm) so you'll still be asking the transistor to pass 6 amps at least. The only thing saving the transistor is the fact that it's a pulsed current so it has a lot of time to cool (duty cycle). Don't let the engine stop (with the circuit energized - points closed) or the transistor will go up in smoke. A ballast resistor would still be a good idea to limit the current to whatever the transistor is capable of. That said, adding the ballast resistor just transfers the wasted heat from the transistor to the resistor.
I'm not sure what engine you are running this on but it would also help to adjust the points (or the hall sensor magnet) so the circuit is energized for the minimum required time (dwell) A few milli-seconds is all that's required to fully energize the coil.

 

[IC-man]

Hi Dsage,
All points noted thanks.
BTW my coil is about 1.2 ohms.
Although some of the smaller coils (used for dirtbikes etc) are below the
1 ohm mark, so would definitely require a ballast. Resistor.

 

[stackerjack]

Anyone had problems with this circuit.

It is designed to operate on 6 volts.

Jack

 

[Harglo]

Anyone had problems with this circuit.
I built lots of different ignition systems over the years but just needed something simple for a converted strimmer motor so built the TIM4.
It works fine but T1 gets quite hot (too hot) I've built a couple of them with same results. Any ideas?
12vdc and standard car coil ( no ballast)
I'm also using 22 ohm 5 watt as R4.

If the TM-6 is from J Howell he states not to use a auto coil. I use use his TM-6 with a Makita 12v batt to a small 12v to 6v cube many many hours before recharge.
Harvey

 

[dsage]

A good power source is to use four AA NiMh batteries. That's about 6 volts. And you can get a nice holder for them. You don't need a ballast resistor because the batteries themselves are current limited. i.e even if shorted they will only produce a reasonable current. Not that I suggest shorting them. But just to say when heavily loaded they will limit the current. This is what I use in combination with one of the cheap Ford COP coils from EBay Which are a small size.
I also use one of my IGBT transistor drivers which you can find the plans for here. In post #47
https://www.homemodelenginemachinist.com/threads/a-new-ignition-circuit.20415/page-3
It's also described in Model Engine Builder magazine in a DIY build article as described here. In post 17
https://www.homemodelenginemachinist.com/threads/model-engine-cdi-easy-and-cheap.31128/#post-326774

 

[IC-man]

Hi Dsage,
Thanks so much for you input, I didn't know about the current limiting on the batteries, I have also used the COP 's but the Audi type, I think the Ford ones are a lot smaller once the extention has been removed but haven't found any for the right price (dirt cheap)
Once again thanks better get the soldering iron warmed up.
Graham

 

[dsage]

Try Ebay for the coils. The Ford coils are the simple ones with only two wires. They can come in groups of eight.
Ford 4.6L 5.4L V8 Complete Set OF 8 Ignition Coils DG508 W/ Free Grease Pack | eBay

Maybe you can share the cost with someone. They may not be prime units for use on your hot rod but they get the job done for models.
Another source would be the autowrecker. They should be cheap(er) there.