# What do you think.

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#### Pops

##### Well-Known Member
Log Member
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

#### haiqu

##### Well-Known Member
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.

#### FritzW

##### Well-Known Member
Log Member
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.

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#### Aerowerx

##### Well-Known Member
..... Arduino board.
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:

#### TFF

##### Well-Known Member
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.

#### Pops

##### Well-Known Member
Log Member
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:

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

#### Pops

##### Well-Known Member
Log Member
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.
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

#### Hot Wings

##### Grumpy Cynic
HBA Supporter
Log Member
Might be easier to build also, you could use an Arduino board.
Why build it? Just buy it - a fuel pump relay from any early 80's VW coupled with standard Bosch cube relay.

#### haiqu

##### Well-Known Member
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
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

#### haiqu

##### Well-Known Member
Why build it? Just buy it - a fuel pump relay from any early 80's VW coupled with standard Bosch cube relay.
I think you'd find the current used to power the relay would exceed the original requirement for dual ignition.

#### Pops

##### Well-Known Member
Log Member
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
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

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#### Dana

##### Super Moderator
Staff member
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.

#### Jan Olieslagers

##### Well-Known Member
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.

#### Pops

##### Well-Known Member
Log Member
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.
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 #### Jan Olieslagers ##### Well-Known Member But I think you are Dana NEGATIVE!!! NEGATIVE!!! NEGATIVE!!! even if I do enjoy a bit of multiple personality, it never went as far as that! #### Jan Olieslagers ##### Well-Known Member The MP sensors are$18
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.

#### Pops

##### Well-Known Member
Log Member
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.

Its not that they are expensive, but like you say, the wire is a lot cheaper I do think the better way to go is picking up a signal from the mag. No time factor and like you say cheaper than if someone had to buy the sensor, but I'm making it for myself. I got on the first production run of the sensor with a 6 month waiting time and have about 50.
Thinking about having the switch with OFF, ON and Standby. ON-- On all the time, Standby-- Comes on when the mag fails with a flashing LED. Dan