Ford edis with megajolt

[DanH]

Had a note today from Autosport Labs. Want a Megajolt/E controller for your EDIS-based ignition? Black Friday Sale....15% off. Coupon code ASL15OFF

https://www.autosportlabs.com/

[DanH]

Annual time, always an opportunity to catch up on some projects.

Last year I installed a voltage monitor (see a few posts back) based on a $5 board from China. It continues to work great, flashing a light and sounding a aural warning if IGN2 power falls below a preset threshold. It would let me know if the small secondary battery dedicated to IGN2 is not being charged, as the alarm threshold is set at 13V.

However, there remained the possibility that the small battery may not have very much storage capacity, or otherwise had developed a fault. After all, the whole point of installing a dedicated battery is to have some flight time on that ignition after shutting down the aircraft electrical system. Simple approach to the problem is a load test, i.e. check the battery voltage under load.

With the engine running, pressing the test button disconnects the IGN2 battery from the charging source, and sends power to a miniature panel voltmeter. The display is battery voltage under load.

This photo taken with the engine not running. It was sitting right on 12V while powering IGN2. Sorry, the button is under my index finger.

[Chkaharyer99]

Dan,

Thanks for posting your findings on your circuit.

Have you established probable cause for the diminished storage capacity of your small battery?

Your voltmeter placement and button look well placed. I like your labeling.

Thanks,

[DanH]

Originally Posted by Chkaharyer99

Have you established probable cause for the diminished storage capacity of your small battery?

I have no reason to believe it is diminished. It's a tiny little 3AH battery running with a 1 amp draw, so 12V under load sounds about right. Anyone have a reason to believe otherwise?

[Canadian_JOY]

If I'm reading this correctly, when you use the press-to-test function you are getting the ignition battery alarm (because it trips at 13V to signal loss of its charging source) AND you're able to read the instantaneous voltage on the ignition battery. If this interpretation is correct then 12.6V certainly looks normal for an instantaneous test after disconnecting the charging source.

Ingenious.

The only possible alteration which might be considered would be to have a second locking position on the press-to-test switch in which the contacts are held closed so you can more easily perform a longer-term load test on the ignition battery. I suggest a locking toggle only because it would require a very conscious effort to more permanently isolate your ignition battery from its charging source.

I really like the way this is set up, especially because it uses the disconnect relay in its Normally Open (relaxed) state for normal operations. Pretty hard to improve on this circuit.

[DanH]

Originally Posted by Canadian_JOY

If I'm reading this correctly, when you use the press-to-test function you are getting the ignition battery alarm (because it trips at 13V to signal loss of its charging source) AND you're able to read the instantaneous voltage on the ignition battery.

Correct.

The previously discussed voltage monitor board actually has a built-in voltmeter, used for setting the alarm limits. It also displays monitored voltage when not in the "set" mode, but it's awkward to make it a nice looking panel display. Besides, I wanted to be able to disconnect the IGN2 battery from the main battery for the load test.

If this interpretation is correct then 12.6V certainly looks normal for an instantaneous test after disconnecting the charging source.

That 12.6 is no-load. It's about 12.0 given a 1 amp draw.

UPDATE 2019: The little Motobatt AGM battery was ultimately deemed defective. As noted, its voltage under load was poor when disconnected from the alternator. The kicker was that over time, it started causing voltage fluctuations detectable by the voltage monitor board. I'd get random in-flight buzzer and LED indications for just a second or so. Checked all other components and connections, with nothing found, so I replaced the battery...after which there were no more odd indications. I think the battery had a cracked internal connection.

Ingenious.

Thank you.

The only possible alteration which might be considered would be to have a second locking position on the press-to-test switch in which the contacts are held closed so you can more easily perform a longer-term load test on the ignition battery.

Yeah, I was planning to see how long IGN2 would actually run on its own little battery. The RV-8's side switch console is open on the bottom, and the switch is just a ground, so for a one-time test all it takes is a jumper wire and two alligators.

[Jim Lewellyn]

Hey Dan,

Forgive my ignorance, I am not familiar with your EI....and I am sure you have already considered this..... Are the EI internal power circuits electrically isolated from each other?

[DanH]

Originally Posted by Jim Lewellyn

Hey Dan,

Forgive my ignorance, I am not familiar with your EI....and I am sure you have already considered this..... Are the EI internal power circuits electrically isolated from each other?

Two entirely separate ignition systems, independently powered from two batteries. I don't think anything short of an EMP pulse is going to shut down both.

[Jim Lewellyn]

Originally Posted by DanH

Two entirely separate ignition systems, independently powered from two batteries. I don't think anything short of an EMP pulse is going to shut down both.

Ah, OK. We will hope for no EMP's!

[lr172]

Originally Posted by DanH

I have no reason to believe it is diminished. It's a tiny little 3AH battery running with a 1 amp draw, so 12V under load sounds about right. Anyone have a reason to believe otherwise?

I wouldn't be concerned with 12.0, but I would expect mid 12's. Given that the battery just came off of a 14V float and the load is relatively light (.33AH), I would expect around 12.5 for a new battery.

Larry