# What do you think.

Discussion in 'Volkswagen' started by Pops, Aug 10, 2014.

### Help Support HomeBuiltAirplanes Forum by donating:

1. Aug 10, 2014

### Pops

#### Well-Known Member

Joined:
Jan 1, 2013
Messages:
7,230
6,120
Location:
USA.
I have been thinking, ( Yes, please stand back, way back).
I'm using the 1835 cc VW engine with a Slick mag, ( have you looked at the prices lately ? ) . Since I fly over some very rough terrain where there is no place to land except in the tree tops, I have been wanting dual ignition for the engine. But the kicker is, I don't have an electrical system and don't want the weight of one. I do use a small gell cell model airplane starting battery to power my handheld radio, elevator trim servo and oil temp gauge. So stand back, here is my idea.

Thinking about using GP's low height fixed timing secondary ignition system, ( http://www.greatplainsas.com/cat2014I1.pdf ) . Since I was thinking of just using it for take-off and landing and when over the worst of the terrain to make the battery last as long as possible and if the Slick mag went out quickly turning the secondary ignition on before the engine stopped. But since I'm an old fart and don't do anything fast, I was thinking of something else. I have some differential pressure sensors that I can use to sense the manifold pressure and make a circuit that will turn on the secondary ignition when the manifold pressure get down to a set limit, say 15". So I will have a toggle switch to turn the secondary ignition on (with a indicating LED) after start up with the mag, and if at cruising manifold and want to use the dual ignition turn it on with another toggle switch ( with another indication LED), but with this switch off the secondary ignition will come on automatically anytime the manifold pressure gets below the set amount.
What do you think?

Dan

FritzW likes this.
2. Aug 10, 2014

### haiqu

#### Well-Known Member

Joined:
Mar 29, 2011
Messages:
274
39
Location:
Australia & New Zealand
I think the engine may stop before the pressure gets to a point where it activates the pressure switch, but the idea is basically sound and it may be worth a try. You could also install a small and light (20W or so) semi-flexible solar panel to top up the battery in flight. I have one in my van to keep the battery fully charged while I'm living on my yacht, which can be a month or more at a time.

3. Aug 10, 2014

### FritzW

#### Well-Known Member

Joined:
Jan 31, 2011
Messages:
3,719
3,339
Location:
Las Cruces, NM
Would an electronic sensor respond faster than a pressure sensor? ie... If it didn't see a pulse from the mag for half a second it would light off the other system. Might be easier to build also, you could use an Arduino board.

Sent from my phone with a tiny **** keyboard

spduffee likes this.
4. Aug 10, 2014

### Aerowerx

#### Well-Known Member

Joined:
Dec 1, 2011
Messages:
5,085
1,391
Location:
Marion, Ohio
Over kill.

Why does everyone want to use a microcomputer for everything? This could probably be done with just 2 or 3 14 pin (or smaller) DIP integrated circuits.

Do they make those any more? Maybe I'm getting too old---learned my electronics in the 1970s:gig:

5. Aug 10, 2014

### TFF

#### Well-Known Member

Joined:
Apr 28, 2010
Messages:
11,729
3,321
Location:
Memphis, TN
I say go with two of the new LifePO4 batteries. One dedicated to the ignition one to the radio, and have the radio battery as backup. You can always go with different capacities if edging too
Much weight but a 400 amp battery weighs about 3 lbs although a little expensive. Good thing is it can be charged very fast if you land where there is 110.

6. Aug 10, 2014

### Pops

#### Well-Known Member

Joined:
Jan 1, 2013
Messages:
7,230
6,120
Location:
USA.

Easy to do with the sensor and a couple of LM-324 OP-Amps. Can't get any simpler.
Dan

7. Aug 10, 2014

### Pops

#### Well-Known Member

Joined:
Jan 1, 2013
Messages:
7,230
6,120
Location:
USA.
Thanks , Hadn't thought about the time factor. I have been using a solar panel to keep my battery charged for 7 years.
My hanger/ Workshop is solar powered except for the welder and air compressor.
Dan

8. Aug 10, 2014

### Hot Wings

#### Well-Known MemberHBA Supporter

Joined:
Nov 14, 2009
Messages:
6,451
2,362
Location:
Rocky Mountains
Why build it? Just buy it - a fuel pump relay from any early 80's VW coupled with standard Bosch cube relay.

9. Aug 11, 2014

### haiqu

#### Well-Known Member

Joined:
Mar 29, 2011
Messages:
274
39
Location:
Australia & New Zealand
Hey Dan,

Awesome, good to meet someone else who likes free energy. I run two ferrocement yachts and a house totally off the grid. Haven't paid an electric bill for years. I'll be buying a small diesel generator for the occasional welding and machining tasks. Reconnecting power to the house would be pointless, I'm only there a few months every year.

Rob

Topaz and Pops like this.
10. Aug 11, 2014

### haiqu

#### Well-Known Member

Joined:
Mar 29, 2011
Messages:
274
39
Location:
Australia & New Zealand
I think you'd find the current used to power the relay would exceed the original requirement for dual ignition.

11. Aug 11, 2014

### Pops

#### Well-Known Member

Joined:
Jan 1, 2013
Messages:
7,230
6,120
Location:
USA.
My daughter has been off the grid for 3.5 years and my total electric bill is about $30/$35 a month for now.

Back on subject. I think I'll bread board up a system with the Sensor and see how it works. Will just have to switch a few amps on and off. As long as I can get the secondary system to come on line while the prop is still turning, and have time to relight it should work OK.

The differential pressure sensor is not just a pressure switch. I have use them on several projects. 2 to 5 volt output, 9 volt input. I can use a pot and adjust the point where the switching will occur at any Manifold pressure.
Dan

Last edited: Aug 11, 2014
haiqu likes this.
12. Aug 11, 2014

### Dana

#### Super ModeratorStaff Member

Joined:
Apr 4, 2007
Messages:
8,688
3,065
Location:
CT, USA
Like Haiqu I suspect that the rpm will drop too low to restart before the pressure bleeds down, especially if the throttle is closed... remember you'll still have suction while the engine is turning even if the ignition has failed, and you have to catch it while it's still turning. But an ignition sensor, maybe a couple of turns of wire around a spark plug lead like a Tiny Tach, could see it instantaneously.

Dana

There's two theories to arguing with a woman. Neither one works.

13. Aug 11, 2014

### Jan Olieslagers

#### Well-Known Member

Joined:
May 28, 2014
Messages:
134
19
Location:
Haacht, Belgium
MP sensor is too expensive and too complicated. As others have said: detect spark plug activity with a wire wound 10-20 times around a high tension cable, add an opamp or two and you're good to go.

14. Aug 11, 2014

### Pops

#### Well-Known Member

Joined:
Jan 1, 2013
Messages:
7,230
6,120
Location:
USA.
The MP sensors are \$18. and I have lots of them. But I think you are Dana are right about the MP. Pickup from the high tension cable is the way to go. I am using a Tiny Tack, using a Slick mag and shielded harness and drilled the 1/16" hole beside #1 on the cap of the mag and wrapped around the lead inside the cap per instructions and it works great. So I'll just use the same pickup. Need to put my Scope on it to see what I have for an output and start breadboarding from there.
Dan

15. Aug 11, 2014

### Jan Olieslagers

#### Well-Known Member

Joined:
May 28, 2014
Messages:
134
19
Location:
Haacht, Belgium
NEGATIVE!!!

NEGATIVE!!!

NEGATIVE!!!

even if I do enjoy a bit of multiple personality, it never went as far as that!

16. Aug 11, 2014

### Jan Olieslagers

#### Well-Known Member

Joined:
May 28, 2014
Messages:
134
19
Location:
Haacht, Belgium
and a length of wire around the high voltage cable is ..?
MP sensor is too expensive, by a 1000 times at least. Better offer them on ebay if you really have a bunch of them around, with no immediate good use. And better do it quick before they are superseded.

17. Aug 11, 2014

Joined:
Jan 1, 2013
Messages:
7,230