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  #1  
Old 05-30-2022, 08:06 AM
togaflyer togaflyer is offline
 
Join Date: Apr 2013
Location: Fl/Ga
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Default EI back up power (concept)

So this was a discussion I had with a buddy over breakfast regarding back up power for an electronic ignition. Off the shelf TCW has their backup battery, so this is about an inexpensive alternative. So the concept is:

Purchase a Dewalt 12 volt power station dock.

Wire it to a two position toggle switch so you can select normal power (also wired to the switch) or emergency power (comes from a Dewalt 12 volt 5 ah battery).

Mount the battery docking station in an accessible location for easy access so you can remove to recharge or check on the charge level (since the battery has a built in indicator).

TCW has a 3ah backup for 260 dollars. You could install a 5ah Dewalt backup for under 100 dollars. And since it is accessible and removable you could carry an extra battery and swap it out with a fresh one.

Really couldnít come up with a negative issue other then forgetting the battery is there and not checking the charge level. In some ways I think it provides even more redundancy since, theoretically, you could maintain a power source to the EI by replacing the system with a spare fully charged Dewalt battery.
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  #2  
Old 05-30-2022, 08:52 AM
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Toobuilder Toobuilder is offline
 
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I have measured the total system draw of a single SDS CPI system at 1.69 amps. Thats at 2700 RPM and 6 cylinders. Thats a pretty modest load, and there is a vast selection of low cost, lightweight industrial batteries that will supply spark for far longer than the fuel holds out. Easiest "emergency" power source is the existing ships battery. Just have a switch that is wired to hot in case you need to shut down the master in flight. Now if you think you are going to loose an alternator AND your battery in the same flight (besides having a very, very bad flying day), there are second battery options available that are simpler, lower cost and more robust than the Dewalt scheme. There is also the very light weight Monkworks pad mounted generator if you really need a robust way to keep the engine running indefinately.
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  #3  
Old 05-30-2022, 10:24 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Toobuilder View Post
Easiest "emergency" power source is the existing ships battery. Just have a switch that is wired to hot in case you need to shut down the master in flight.
Even better, don't power an ignition via the main bus. Wire it battery direct.

Quote:
...there are second battery options available that are simpler, lower cost and more robust than the Dewalt scheme.
Agree. Power draw is very small, as Mike illustrates. The EDIS-based system on my 4-cyl only pulls 1.08 amp at 2700. So, exceeding fuel capacity driving one ignition, even with the main battery and alternator both offline, only requires 4, maybe 5ah. That's just a small bike battery or similar. And it can be wired to remain charged without remembering anything, with a charge warning, and a push-to-test voltage indication under load.
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  #4  
Old 05-30-2022, 10:35 AM
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Quote:
Originally Posted by DanH View Post
Even better, don't power an ignition via the main bus. Wire it battery direct.



Agree. Power draw is very small, as Mike illustrates. The EDIS-based system on my 4-cyl only pulls 1.08 amp at 2700. So, exceeding fuel capacity driving one ignition, even with the main battery and alternator both offline, only requires 4, maybe 5ah. That's just a small bike battery or similar. And it can be wired to remain charged without remembering anything, with a charge warning, and a push-to-test voltage indication under load.
.
My friend's RV-10 has dual Lightspeeds powered by independent circuits wired directly to the main batteries (one on each battery). There are two circuit breakers in the back by the battery in case of a short in one of the wires, but other than that, the ignitions are always hot. Well, not technically hot, but always have power.

Last edited by 1001001 : 05-30-2022 at 10:47 AM.
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  #5  
Old 06-01-2022, 11:45 AM
togaflyer togaflyer is offline
 
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If it’s a new build I can see that configuration. But on a single battery set up on a flying plane, just kicking around a keep it simple set up.
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  #6  
Old 06-01-2022, 12:30 PM
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hgerhardt hgerhardt is offline
 
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EarthX has a nice backup battery purpose-built for this kind of application: https://earthxbatteries.com/product/...ck-up-battery/
I installed one in my -6 a year ago.
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  #7  
Old 06-01-2022, 04:44 PM
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Quote:
Originally Posted by togaflyer View Post
If itís a new build I can see that configuration. But on a single battery set up on a flying plane, just kicking around a keep it simple set up.
The illustrated second battery system for IGN#2 was in fact added to an already flying airplane when it was converted from Slicks.
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  #8  
Old 06-01-2022, 07:09 PM
sailvi767 sailvi767 is offline
 
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Quote:
Originally Posted by hgerhardt View Post
EarthX has a nice backup battery purpose-built for this kind of application: https://earthxbatteries.com/product/...ck-up-battery/
I installed one in my -6 a year ago.
I agree, the EarthX battery was purpose built for this use and not all that expensive.
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  #9  
Old 06-03-2022, 09:46 AM
togaflyer togaflyer is offline
 
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Other than the BMS, what does it have over a 60 dollar 5ah Dewalt 12 volt battery?
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  #10  
Old 06-03-2022, 02:07 PM
sailvi767 sailvi767 is offline
 
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Quote:
Originally Posted by togaflyer View Post
Other than the BMS, what does it have over a 60 dollar 5ah Dewalt 12 volt battery?

I suspect the battery portion is manufactured with a higher quality margin. All Lithium batteries are not the same. It also can self regulate charging input and will provide cautions if there is a malfunction.
One thing that should be mentioned is other EarthX batteries due not regulate charging input and need to be sized to the alternator.
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