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Ford edis with megajolt

Maybe for those with the more common larger alternator pulley a ring similar to this set up from Lightspeed could be fitted to the inside of the flywheel after having the required teeth cut in it? This would have the added benefit of mitigating some of the risk of a broken belt flying outwards and taking the reluctor and or wiring out.
I really like the ideas so for in this thread. I think you guys are onto a viable DIY ignition system here :)
 
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Maybe for those with the more common larger alternator pulley a ring similar to this set up from Lightspeed could be fitted to the inside of the flywheel after having the required teeth cut in it?

Sure. Depends on enough physical space between the nose of the engine case and the ID of the pulley for reluctor mounting. Easy to check, and as noted previously, there are lots of different reluctors available.

Here's an example from our old friend Bob Japundza. It has 60 teeth minus 1 because he intends to use an old Electroair brain box. Material is 0.125" 4130. Computer-driven waterjet and laser cutters are just grand, eh?



Lot of ways to skin this cat. For example, it would be easy to simply embed 35 solid steel dowel pins in the rear face of the aluminum flywheel, inboard of the ring gear, similar to the way other systems embed magnets. What is the OD of the belt pulley and the ID of the steel ring gear anyway?
 
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What is the OD of the belt pulley and the ID of the steel ring gear anyway?


I don't have a flywheel assembly lying around but found this on the net. Looks like 9-3/4 OD for the pulley & 10-1/4 ID for the ring gear. The shiny edge on the outer edge of the pulley is a machined edge so looks a bit deceiving at first :)


 
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Looks like 9-3/4 OD for the pulley & 10-1/4 ID for the ring gear.

Ok, so only 1/2" to work with there, and it's outside the belt, thus a belt failure might take out the reluctor(s). A toothed wheel inside the pulley makes more sense.
 
Ok, so only 1/2" to work with there, and it's outside the belt, thus a belt failure might take out the reluctor(s). A toothed wheel inside the pulley makes more sense.

I may have made a mistake there with the diameters but it makes little difference.
I think the guy that took the picture was trying to illustrate the diameter of the pulley only not the ring gear so we are probably looking at something like 10-3/4 instead for it not 10-1/4 .
There certainly seems to be more than 1/2"on some of them. The list of different part numbers is huge http://www.skytecair.com/RingGearTech.htm
 
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A toothed wheel inside the pulley makes more sense.

Here are some bolt hole dimensions for mounting an inside wheel to the larger pulley that I lifted from the Lightspeed site :)
4&6 cylinder bolt orientation in relation to the missing tooth would be 30deg. different as shown in the pic




If the wheel was made with the teeth on the OD (the same as a car) and the reluctor was mounted clock wise 90deg. from the TC mark there would be plenty of room to mount the reluctor with a bracket mounted on the 2 crankcase through bolts similar to Ross & Robert's design shown in this photo.



The ID of the wheel would just have to be bigger than the crankshaft flange to allow it to slip over in one piece. My verniers are not large enough but I think the crank flange on my engine is somewhere around 6"or so.

Getting really interested in this :D

Feel like drawing something up for us Dan? I don't have access (or the knowledge) to do a CAD drawing for it.
 
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Here are some bolt hole dimensions for mounting an inside wheel to the larger pulley that I lifted from the Lightspeed site :)
4&6 cylinder bolt orientation in relation to the missing tooth would be 30deg. different as shown in the pic

If the wheel was made with the teeth on the OD (the same as a car) and the reluctor was mounted clock wise 90deg. from the TC mark there would be plenty of room to mount the reluctor with a bracket mounted on the 2 crankcase through bolts similar to Ross & Robert's design shown in this photo.

The ID of the wheel would just have to be bigger than the crankshaft flange to allow it to slip over in one piece. My verniers are not large enough but I think the crank flange on my engine is somewhere around 6"or so.

Feel like drawing something up for us Dan? I don't have access (or the knowledge) to do a CAD drawing for it.

Sure. This would be the 4-cyl orientation, slip-over-hub style. A variation would be like Bob's 60-tooth above, a split ring with additional tooth support.

Trigger%20Wheel%20Small.jpg


No warranties gentlemen. You're welcome to a .dwg file, but it's your project. Check dimensions, output waveform, etc.
 
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Ok, so only 1/2" to work with there, and it's outside the belt, thus a belt failure might take out the reluctor(s). A toothed wheel inside the pulley makes more sense.

Sure. This would be the 4-cyl orientation, slip-over-hub style. A variation would be like Bob's 60-tooth above, a split ring with additional tooth support.



No warranties gentlemen. You're welcome to a .dwg file, but it's your project. Check dimensions, output waveform, etc.

You are a true Gentleman Dan. Thanks :) I would love to have a copy of the file for it.
I will send you a PM with my email address
 
All this clunky hardware bolted to the flywheel or inside the mag case to use magnetic sensors which have timing drift with rpm.

Hall Effect= elegantly simple, inexpensive, accurate and reliable.
 
Dual EDIS - one trigger wheel

You can run dual EDIS units from one timing wheel by mounting the second pickup 180 degrees (other side of engine) around the wheel. Then the spark plug leads would be swapped rear to front.
 
If finding two pickup mount locations 180 degrees apart is problematic, you can mount Ign#2 pickup 15 degrees before ign #1 pickup. Then, like most mag setups, you always start the engine on #1 ignition only. At cranking speed Ign #1 will fire near TDC, while ign #2 will fire near 15 deg BTDC.

Once running, the EDIS advances 10 degrees at around 400 rpm, resulting in 10 fixed advance for ign #1 and 25 degree fixed advance for ign#2. Megajolt can be connected to ign#1 with 0 degrees pickup alignment correction and run an appropriate advance map. Megajolt #2 can be set with a 15 degree pickup alignment offset and run the same advance map. Pickup alignment can be adjusted electronically in Megajolt up to 30 degrees either direction.
 
Kirk;
I like your thinking re; 15 degree sensor offset. Would work as a passive fixed 25 degree advanced with Megajolt failure too.
I have a Pmag on the left side. It replaced a Bendix 200 Shower of Sparks combination that was making radio noise in flight.
The other Bendix (on the right side) is running fine, but I've accumulated a pile of EDIS parts, and I like the trigger wheel inside the pulley idea presented on this thread.
FINALLY there is enough forum interest for EDIS to approach 'Critical Mass'.
Get several great minds on a project and watch it grow!
Who is having a "inside the small diameter pulley" 36-1 timing wheel made? Want to make a few and share costs?
I have a large pulley flywheel on my T-18, so I might be interested in an inside the pulley timing wheel for it, should that be my only choice...
 
Who is having a "inside the small diameter pulley" 36-1 timing wheel made? Want to make a few and share costs?
I have a large pulley flywheel on my T-18, so I might be interested in an inside the pulley timing wheel for it, should that be my only choice...

Sort of a long distance trade, but Graham ("Airtractor8", above) might be happy to swap EDIS modules for wheels. Trust me ;)
 
Kirk;
Who is having a "inside the small diameter pulley" 36-1 timing wheel made? Want to make a few and share costs?

I had an inside ring for the large pulley made yesterday at the local Water Jet shop.
It was easy with Dan's Cad drawing :D I did have them increase the OD to 8"to allow enough meat on the edge for me to countersink the holes for 8/32 screws. Made it from .125 Mild Steel. It cost me all of $37 :)
Will probably get it plated before fitting.







Here is a test fit on a flywheel I found lying around. The hole centres line up right in the middle of the flange bosses and it has just the right amount of clearance from the radius on the inside of the pulley.




As far as sourcing EDIS components are concerned, I am having a lot of trouble finding a 4 cylinder 12 pin module connector plug.
Does anyone know where I can get a new one? There seems to be plenty of the 8 cylinder type but these won't fit. The keyways are different.
I managed to get a module of ebay and it seems that the reluctor plug and coil plug are plentiful but non genuine.
I would go to the Wrecking yard for a used one but this system was not fitted to Aussie cars unfortunately :(
 
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As far as sourcing EDIS components are concerned, I am having a lot of trouble finding a 4 cylinder 12 pin module connector plug.
Does anyone know where I can get a new one? There seems to be plenty of the 8 cylinder type but these won't fit. The keyways are different.
I managed to get a module of ebay and it seems that the reluctor plug and coil plug are plentiful but non genuine.
I would go to the Wrecking yard for a used one but this system was not fitted to Aussie cars unfortunately :(

I used a 6 cylinder plug on a 4 cylinder EDIS. It has all the right pins and it clips securely in place. Just trim the key tabs from the ends of the plug. Use a little more care when assembling connector to module. Once it snaps in place it ain't going anywhere.
 
I used a 6 cylinder plug on a 4 cylinder EDIS. It has all the right pins and it clips securely in place. Just trim the key tabs from the ends of the plug. Use a little more care when assembling connector to module. Once it snaps in place it ain't going anywhere.


Thanks guys. Great information.

I'm thinking at this point I will probably just get an 8 cylinder plug new from your side of the pond (half the price of UK) and cut the keys of it as Kirk suggested.

Be nice to have one that has NOT been pre wired like this one or a source for replacement female pins perhaps? Any Ideas?

 
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The pre-wired connector is not as elegant, and there is a bundle of unused wires, but if I have to use one somewhere really important, I like to solder with eutectic solder and cover with high quality glue lined heat shrink.
 
I had an inside ring for the large pulley made yesterday at the local Water Jet shop.
It was easy with Dan's Cad drawing :D I did have them increase the OD to 8"to allow enough meat on the edge for me to countersink the holes for 8/32 screws. Made it from .125 Mild Steel. It cost me all of $37 :)
Will probably get it plated before fitting.




Here is a test fit on a flywheel I found lying around. The hole centres line up right in the middle of the flange bosses and it has just the right amount of clearance from the radius on the inside of the pulley.




As far as sourcing EDIS components are concerned, I am having a lot of trouble finding a 4 cylinder 12 pin module connector plug.
Does anyone know where I can get a new one? There seems to be plenty of the 8 cylinder type but these won't fit. The keyways are different.
I managed to get a module of ebay and it seems that the reluctor plug and coil plug are plentiful but non genuine.
I would go to the Wrecking yard for a used one but this system was not fitted to Aussie cars unfortunately :(

I am curious how you are planning to center this ring. I am sure you know this, but the air gap between the sensor and the teeth generally needs to be in the .010 - .045 (varies by sensor) range for each tooth (I don't know requirement for the EDIS module). Tighter is better, but you have to leave some room for movement with worn bearings. I would be a little concerned that the flange may not be exactly centered. I would expect the tolerance for the pulley to be a tad loose and there would be no precision tolerance required for interior of the cast boss. IF that flange is machined, that's a different story, but you still don't know that tolerance. Maybe a michanest would know.

Let us know how it works out.

Larry
 
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I am curious how you are planning to center this ring. I am sure you know this, but the air gap between the sensor and the teeth generally needs to be in the .010 - .045 (varies by sensor) range for each tooth (I don't know requirement for the EDIS module). Tighter is better, but you have to leave some room for movement with worn bearings. I would be a little concerned that the flange may not be exactly centered. I would expect the tolerance for the pulley to be a tad loose and there would be no precision tolerance required for interior of the cast boss. IF that flange is machined, that's a different story, but you still don't know that tolerance. Maybe a michanest would know.

Let us know how it works out.

Larry

This from the OP in regards tolerances.

It seems to be very accurate with a timing light on the chuck and very tolerant to sensor to Wheel clearance, up to 1/4 inch no problem and no shift in timing.

Hope you like it and open to comments :)

Frank

It doesn't seem like the reluctor to pickup clearance will be a problem. Yes the mounting surface has been machined by Lycoming.

I spoke with a machinist today about getting the holes drilled in the flywheel.
He was more worried about how accurate the holes in the wheel were and didn't see a problem with getting his part of the job done per the drawing on a CNC machine. :)
 
I have one 12 pin connector, as removed from a car. It has about 2" of wire to the cut off point. I think the connector could be disassembled and new pin sockets crimped onto my wire, then inserted into the old shell. I (like Airtractor8) ask: Does anyone know what kind and size connector?
I would have a lot more confidence with new hardware.
Here is site that shows the disassemble of the EDIS connectors:
http://www.ken555.plus.com/gtm/connectors.html
A link to Megasquirt's EDIS page:
http://www.megamanual.com/ms2/EDIS.htm
 
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Well!
I just got a chance to take the cowl cheek off my T-18, it has a small diameter pulley like my RV-8 does. There is very little room for a timing wheel or a stock Ford EDIS pickup in there.
The only choices ( 4 cylinder Lycoming) appear to be the 'outside the flywheel pulley" timing wheel or the magneto replacement pickup when equipped with the small diameter pulley flywheel.
 
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Replacement module pins

I think the connector could be disassembled and new pin sockets crimped onto my wire, then inserted into the old shell

I may have found a few sources for new module pins.
I think this is their name and part number: Ford Wedgelock Terminals E7EB-14487-AA .060" Female Diameter Pin. Available on ebay here http://www.ebay.com/itm/10-Ford-Wedgelock-Terminals-E7EB-14487-AA-060-Female-Diameter-Pin-/351655844717?vxp=mtr&hash=item51e0525b6d
The same guys have a great price on NEW 8cylinder module plugs(you will have to remove the keys to use on 4&6 cyl ) Here:
http://www.ebay.com/itm/400324998067?ssPageName=STRK%3AMEBIDX%3AIT&fromMakeTrack=true

1rt6cm.jpg
10ynqef.jpg

2eogv1l.jpg


OR these:

http://www.autoparts-factory.net/products/repair-connector-kit/connector-terminals-rubber-boot/200pcs-female-terminal-pins-fit-oxygen-o2-sensor-connector-w-oe-fuel-pump-plugs-86-09-mustang-1669.html
These are from an 86-09 Mustang Oxygen Sensor plug. They look strikingly similar and are from the same era vehicle.Only available in 200pc lots :eek:
These guys also have lots of pins. Some with dimension drawings. The TE1233 could be it?. There is others http://parts.harnessmaster.com/?category=Terminals%20and%20Lugs&pictures=


21nfudw.jpg


I can't tell you how much time I have wasted on this small Item :eek::eek: but I just HATE having to join cables on a new installation and especially an ignition system...in an aeroplane :)
 
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I took this pull from the Ranger truck enthusiast's site after airtractor8 provided the Wedgelock PN:

The .060 can be had at CARQUEST in packs of five. They have a Dorman number of 85345 (M) and 85346 (F)
links:
http://www.summitracing.com/parts/rnb-85346
http://www.summitracing.com/parts/rnb-85345?seid=srese1&gclid=CMmQ3YW2pL4CFepAMgod_FkALQ

DORMAN LINK:
http://www.dormanproducts.com/itemdetail.aspx?ProductID=8664&SEName=85346

I can run down to Carquest with the EDIS module in hand and see if they have these pin connectors.
 
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I just ordered an Electroair mag hole timing sensor;
http://www.electroair.net/experimental_ignition_timing_kits.html
My RV-8 and T-18 both have the small belt pulley flywheel, so the Electroair unit seems the best option. They were very responsive. I called and left a phone message Saturday evening, I received the return call Monday morning, clarified the Lycoming non impulse application and now it's on the way.
now to adapt a 36-1 trigger wheel.
 

For the tests done at 8500 ft, those aren't at 75% power, are they? How much affect on performance would there be if they were conducted at cruise altitude, using true 75% power rpm (2700 rpm) instead of 2300 rpm? Is that 400 rpm spread enough to significantly affect the timing advance needed?

Were these tests flown in a Rocket? If so, wouldn't the RV airframe's 'drag wall' be affecting the numbers a bit at those speeds? (I think that was mentioned somewhere else in that thread.)

Charlie
 
Running the RPM up to 2700 should increase the required advance, but how much depends largely on mixture. I picked 2300 RPM because that is my normal cruise RPM. Each airplane/engine/prop and mixture condition will dictate a specific "best" timing set.
 
Thanks; that's what I would think, but wasn't sure.

Back to the Megajolt & trigger wheels; how flexible is the software on the required number of teeth? Could it be told to run on 6-1? 4-1? In other words, does it just count teeth to set advance, or is it smart enough to measure rpm (with the missing tooth interval) and calculate an advance *time* at a given rpm? Reason for asking is that it would make a triggering system a lot simpler. I've never actually a Lightspeed system, but from what I've seen in pics, it appears to use a simpler trigger system than a full fledged many-tooth wheel.

Thanks for any info,

Charlie
 
Function of the EDIS module

I think that is a function of the ignition module not the Megajolt software.
 
Back to the Megajolt & trigger wheels; how flexible is the software on the required number of teeth?

You want a Megasquirt, not a Megajolt. Megasquirt will accept all kinds of inputs. Megajolt is a simplified system for control of a Ford EDIS ignition only...and that means 36 minus 1 trigger wheels.
 
Ah, that explains it. A friend installed a Microsquirt on a Jeep, & he told me that it could use multiple trigger methods. I was hoping the jolt would get the same flexibility.
 
If I understand this system correctly the EDIS is capable of running without the ECU/Megajolt and will fire at 10 degrees BTC. If one were to position the pickup so that corresponds with 25 degrees BTDC on our engines failure of the Megajolt in cruise is almost a non event.

One Megajolt is also capable of firing multiple EDIS units. So it is reasonable to build a dual ignition system with one Megajolt and two EDIS units? It may actually be preferable to reduce programming requirements etc.

Presumably the EDIS is a CD ignition, and would compare to the PMAG in terms of spark energy and duration?

Has anyone measured the current requirements of the system to size an appropriate backup battery?
 
If I understand this system correctly the EDIS is capable of running without the ECU/Megajolt and will fire at 10 degrees BTC. If one were to position the pickup so that corresponds with 25 degrees BTDC on our engines failure of the Megajolt in cruise is almost a non event.

One Megajolt is also capable of firing multiple EDIS units. So it is reasonable to build a dual ignition system with one Megajolt and two EDIS units? It may actually be preferable to reduce programming requirements etc.

Presumably the EDIS is a CD ignition, and would compare to the PMAG in terms of spark energy and duration?

Has anyone measured the current requirements of the system to size an appropriate backup battery?

EDIS uses standard inductive coils. However, that is not a downside for our application in my opinion. There's lot's of hype about capacitive discharge coils, but most of it doesn't directly translate to benefits for our engines. CD fires a hot spark, but it's duration is very short compared to a standard coil. CD ignition systems tend to be less reliable than inductive. These have been common in the hot rod scene for some time and lots of guys have reliability issues. Do the research on pro's and con's of each before assuming CD is better.

Larry
 
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If I understand this system correctly the EDIS is capable of running without the ECU/Megajolt and will fire at 10 degrees BTC. If one were to position the pickup so that corresponds with 25 degrees BTDC on our engines failure of the Megajolt in cruise is almost a non event.

Kirk (see earlier, this thread) is planning to install his #2 ignition without a Megajolt box, EDIS module only, thus fixed timing at 25 degrees via offsetting the pickup 15 degrees.

One Megajolt is also capable of firing multiple EDIS units. So it is reasonable to build a dual ignition system with one Megajolt and two EDIS units? It may actually be preferable to reduce programming requirements etc.

The programming requirements are nil. The ignition maps are created offline. With two maps stored on your laptop, plug in, open one at a time in the Megajolt software, and flash each with two keystrokes. For the second ignition, just move the RJ11 plug from #1 to #2 and repeat.

Presumably the EDIS is a CD ignition, and would compare to the PMAG in terms of spark energy and duration?

As Larry noted, the EDIS system is inductive, not CDI. Spark characteristics will be very similar to a P-mag, because a P-mag uses the same Ford coil. To clarify; there are two Ford coils, early and late model. The early model incorporates positive plug wire retention. The late model has a flat bottom, so mounting is simplified (like on a P-mag body), and it has taller towers. Choose your preference; there doesn't seem to be any practical difference in output or reliability. Other coils seem to work fine too. Select one without internal switching.

Energy, duration, and claims of increased HP are mostly BS.

Has anyone measured the current requirements of the system to size an appropriate backup battery?

An English builder did so as part of his LAA approval, and reported 1.05 amps at 14.4 supply voltage at 2750 rpm. You can read about his work in the August 2011 LAA magazine. Kirk and I made local measurements on the lathe, but I seem to have misplaced the notes.

I've flown one EDIS paired with a Slick for a year. It has been trouble-free, so now I'm installing a second EDIS. The battery for #2 is a Motobatt MB3U AGM rated at 3.8Ah, charged via a Schottky. Both the PC925 main and the little MB3U are located in the cool space behind the baggage compartment. Power feeds are battery direct via fusible links for circuit protection, independent of the aircraft system. KIS is good.

Diagram (updated 2018):

Ignition%20Power%20Supply.jpg


So far, the only potential issue I've seen has to do with timing at cranking speeds. The system fires before TDC, so users with low inertia propellers could conceivably get kickback. It doesn't seem to be a problem with a metal Hartzell. Exactly how far before TDC may depend on EDIS module part number. We've measured as little at 2 degrees at very low RPM, and nobody has ever reported more than 10. It ramps up as RPM rises, transitioning to the mapped values at about 500 RPM.

Early P-mags had the same problem, since corrected with software. The EDIS doesn't seem to offer a software-based approach to retarding the spark at cranking speeds (no Megajolt control below 500 RPM), so the only way to do it is with a mechanical offset, which I flew most of last year. To fire ATDC during cranking with the EDIS, I retarded the trigger wheel 10 degrees, and uploaded a map with all values advanced 10 degrees. The result is a very soft start, almost like a turbine spooling up, in particular hot starts using the "slowly advance the mixture knob" method.
 
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Dan,

This thread seems to be mixing MegaJolt>EDIS and EDIS-only setups. In your last post, I assume that you're speaking of programming your MegaJolt, right?

Thanks,

Charlie
 
Kevin
Nice, easy to follow, wiring diagram, and simple is the operative word. For the backup battery the diagram shows it connected directly to the main battery negative post.
If the shared positive connection at the master solenoid fails, you have that 3.8ah left to get you on the ground, but it something should happened to the main ground connection, or the main battery itself, you could potentially lose both systems. I think it would be possible to ground that second battery to separate ground, eliminating a single point ground failure? This might cause a ground loop problem for your radios but at that point you are just trying to get on the ground.
 
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Dan, This thread seems to be mixing MegaJolt>EDIS and EDIS-only setups. In your last post, I assume that you're speaking of programming your MegaJolt, right?

Yes.

When I say Megajolt, I'm referring to the aftermarket Megajolt/E box produced by Autosport Labs: https://www.autosportlabs.com/product-category/megajolt-ignition/

When I say EDIS module, I mean the Ford Motorcraft OEM part, which comes in 4 cyl, 6 cyl, and 8 cyl versions. As noted, the EDIS module (combined with a coil and pickup) will function just fine as a fixed timing ignition, without the Megajolt box. The MJ is only needed for variable timing.

Megajolt boxes and Ford EDIS modules:

Megajolt%20and%20Modules%20Installed.jpg
 
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Sorry Tom, missed your post. My bad.

If the shared positive connection at the master solenoid fails, you have that 3.8ah left to get you on the ground....

Should have both batteries and two ignitions...unless the solenoid end of that positive cable breaks off and shorts to the airframe, discharging the big battery (and probably melting some aluminum). That particular failure mode is a possibility with any airplane, so we go with robust terminals and good wire fixation. I make mine from welding cable and lugs, because I like the flexibility.

.... but it something should happened to the main ground connection, or the main battery itself, you could potentially lose both systems.

That's a real risk, although again, we're talking about robust components. The EDIS/Megajolt grounds run to the adjacent single point fast-on panel inside the firewall, which is linked to the rear batteries with a #2 welding cable. Baring terminal breakage (again HD welding lugs) the disconect risk is one of nuts or bolts unwinding, one at the single point ground, one at the main battery negative terminal. Not too concerned with the 5/16 stud up front. I might drill the heads of the battery bolts and wire 'em. Right now they're 6mm with split washers.

I think it would be possible to ground that second battery to separate ground, eliminating a single point ground failure? This might cause a ground loop problem for your radios but at that point you are just trying to get on the ground.

One possibility might be locating the little battery in the front, near the modules, for a easy direct connection. Or I could run an individual ground wire back through the airframe for each ignition. Here I've elected to rely on the big cable, which raises the classic "single point of possible failure" question; how robust must it be to consider it safe enough?
 
Hi Dan,

On the single ground issue, perhaps he meant that as drawn, the battery negatives are tied together and then a single wire goes from a negative terminal to ground. If each battery has its negative tied to the chassis, then losing one ground leaves the other battery still active. That might be how it's actually wired, but it's not drawn that way in the image.

FWIW...
 
On the single ground issue, perhaps he meant that as drawn, the battery negatives are tied together and then a single wire goes from a negative terminal to ground. If each battery has its negative tied to the chassis, then losing one ground leaves the other battery still active. That might be how it's actually wired, but it's not drawn that way in the image.FWIW...

No airframe grounds. It's a single point ground system, nice and quiet. Both ignitions ground to a standard "forest of tabs" ground point on the firewall, which is linked to the batteries via a #2 cable. Thus the classic debate...is a single high quality cable, with bolted connections at the ends (the red dots), robust enough to assume a very low probability of failure?

If you think not, the simple cure is an additional ground wire from IGN2 directly to the little battery's negative terminal. You won't get any argument from me. Might even talk me into it.
 
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This may help (or maybe not).



No airframe grounds. It's a single point ground system, nice and quiet. Both ignitions ground to a standard "forest of tabs" ground point on the firewall, which is linked to the batteries via a #2 cable. Thus the classic debate...is a single high quality cable, with bolted connections at the ends (the red dots), robust enough to assume a very low probability of failure?

If you think not, the simple cure is an additional ground wire from IGN2 directly to the little battery's negative terminal. You won't get any argument from me. Might even talk me into it.



Dan, I would highly encourage you to think of adding a second ground. And on top of that, check the battery connections regularly. It always seems like the corrosion starts on the negative terminal.

Vic
 
When I said 'airframe', I was referring to your forest of tabs location. Surely the forest of tabs is bonded to the airframe. What I was trying to describe is moving the 'white' battery negative from the 'green' battery negative terminal to the forest of tabs. If both batteries are in the rear fuselage, and the forest of tabs is at the firewall, I can see the difficulty in implementing that change.

I'm *not* saying what you've got in the drawing is unreliable. Just that if the negative connection to the airframe is near the batteries, it would be simple to make both battery negatives connect directly to airframe ground, and would achieve operational redundancy. If the 'white' battery doesn't participate in starting, perhaps running a smaller gauge negative wire to the forest of tabs would be feasible to get that redundancy.

Something that comes up all the time on the Aeroelectric List is not designing for reliability (which should be a given), but for redundancy. If you think about it, a modern battery is extremely reliable. If maintained properly, it's probably the most 'reliable' component in the plane. So why are there two?

Charlie
 
If you think about it, a modern battery is extremely reliable. If maintained properly, it's probably the most 'reliable' component in the plane. So why are there two?

Charlie

Batteries have been known to take an unexpected dump, especially some lithium ones. With a battery dependent ignition system, you lose a single battery, the engine stops. That's a good reason for a second one in my view. I have personal experience in this regard...

We never recommend anyone running two EIs in an aircraft to use a single battery.
 
...check the battery connections regularly. It always seems like the corrosion starts on the negative terminal.

Now there's a good point. Corrosion could be a problem.

Lord knows, I've seen a few corroded battery terminals in my day. Never on an Odyssey however. Vic, anybody, you're seen 'em do it?
 
We never recommend anyone running two EIs in an aircraft to use a single battery.

Even with two alternators? I have a Plane Power and an SD8.

Lord knows, I've seen a few corroded battery terminals in my day. Never on an Odyssey however. Vic, anybody, you're seen 'em do it?

Yep, I have cleaned the negative terminal of corrosion (green) on my Odyssey PC680.
 
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