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JPI EDM power and breaker location


mhrivnak

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The instructions for installing a JPI EDM 900 say that its power wire must be "connected directly to the master solenoid located at the battery to avoid a line drop when
cranking. A 5 amp circuit breaker is required." For those who have one installed, where did you put the breaker?

Putting a breaker by the solenoid is inconvenient since it's in the back. It would be nice to have the opportunity to reset it while sitting in the airplane.

But if the breaker is in the breaker panel, then the line has no protection if it shorts anywhere along its route from the battery up to the breaker panel.

How is this typically handled with our Mooneys?

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1 hour ago, mhrivnak said:

But if the breaker is in the breaker panel, then the line has no protection if it shorts anywhere along its route from the battery up to the breaker panel.

This is a danger, but there is just as much (if not more) danger on the 6/4 gauge wire that comes into the cockpit to feed the breaker panel.  We routed mine as short as possible to the breaker panel so that it would be placed like the rest of the breakers.  One could put a fuse in the line near the solenoid and then a breaker in the cockpit, but I think it would be overkill.

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Something must be getting lost in translation..?

When using it for primary instrumentation... you want it to come on with the master switch...

The JPI is not using much power itself....

So...

Yes, connect it to the bus that becomes live with the master relay...

The master relay is near the battery...

But power is already coming from way back there...

Like everything else... you will want to be able to turn it off, and on, using a CB/switch...

 

Great question...

Stand by to hear how others have done this...

Get a mechanic that has installed one before... there are a lot of wires involved, some are very sensitive to RF noise... and proper routing is everything...

When it comes to routing fuel lines for FF sensors... another +1 for prior experience...

PP thoughts only, not an instrument tech...

Best regards,

-a-

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What is it that you think is being lost in translation? Yes, if connected as the instructions say to the master solenoid, it will come on with the master switch.

It's normal that when a significant load is applied to a line, the voltage on that line drops. You may have seen the lights in a room dim when a hair dryer is turned on. Likewise you might notice nav lights dim while an airplane is running the starter. That's the phenomenon JPI is trying to avoid by having a separate line run to the source (battery).

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oops... sorry.  Tried to keep it brief for the holiday... :)


The lost part for me...

If they really want you to run a wire just for that...

When the big power line is already coming from back there...

Would another line make a difference? (It might, but why experiment..?)

 

They are making a good argument, since you may want to be reading voltage while operating the starter...

And... you wouldn’t want to see an artificially low voltage reading because you didn’t follow their wiring instructions to the T... (a typical situation when having starter problems...)

 

For my plane, there is no dimming when a heavy draw occurs... because the engine gets started before anything gets turned on...

OilP, RPM, MP, Stall warning, and FF all come on with the master... The rest of the house lights and avionics come on with the avionics master... 

So... the most pure source of power is going to come from closer to the battery... right at the master relay... (there are probably a few wires with fuses on them there doing the same thing, check your maintenance manual for detailed wiring diagrams... copy their lead)

But... the main bus is pretty pure too, oversized compared to what is connected to it...

Bringing a new wire from the back is akin to adding a new single point bus bar, sort of...

Where you add fuses has been discussed around here a few times... a long wire can short out at any point... so a fuse close to the battery is a smart idea for fire protection... this would be a challenge that occurs if the wire gets damaged somehow... pinched or insulation worn off...

At the working end, most people would want to protect the device with the proper CB... placing the CB in the proper grouping of other similar CBs is a great idea... for trying to find it when you want to recycle the power for it...

Got a pic of your CB panel? Do you have any open CB positions, or do you need to add one?

Now back to the original question to see what I may be missing...  :)

(yep, I think we are saying the same thing... just where exactly is that fuse at the back, and where exactly is the CB up front...)

Let’s see if @Baker Avionics can lend some additional detailed insight...

PP thoughts only, not a mechanic...

Best regards,

-a-

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The manual says should not must.  If you connect it that way, standard practice would be to put the CB or fuse as close to the solenoid as possible. 

However, the manual also says that the same device works on 14 or 28 volt systems but doesn’t reset until it sees less than 10 volts. So, it’s not likely to reset an a 28 volt system no matter where you connect it, and it might reset on a 14 volt system if the battery were low even if you connect it to the solenoid.

It would be interesting to put a voltmeter on the main bus and measure the voltage while cranking. 

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That's a good point. I don't know if "should" vs "must" makes a practical difference to an IA in this case, but I'll ask.

I did a basic voltage drop calculation, and it's not bad at all. Assuming a 15ft run of 6-gauge copper (the real conductor looks bigger), and a 300 amp load (max rating for the solenoid, but the starter likely is closer to 125 amps), the drop would only be 3.5V. Those assumptions are substantially worse than what we can probably expect in the real world, so this seems like a non-issue for those of us with 28V systems. I'll call JPI on Monday and see what they think. I'd much prefer to not have a breaker in the back.

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  • 1 year later...

Follow-up that I forgot to post in 2020: JPI told me to just connect it to the master bus up front. The phone support guy referred me to their engineering team, who got back to me by email in a day or two.

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55 minutes ago, carusoam said:

How well is the JPI working for you?

It's great. I love having all of the data in one place and visible all the time. Uploading the data to Savvy has been very helpful in pinpointing a couple of issues. If I ever had to buy another plane (though I hope this J lasts me for life), my top upgrade priority would be installing a JPI engine monitor as primary.

I did have to get a warranty replacement of the fuel flow transducer after several months. The interaction started well; they sent me a little test device for free. Based on the results they concluded I should send them the transducer, which I did. That's when it became difficult.

Their bench test couldn't reproduce the intermittent drop-out I was seeing, even though I'd already isolated the issue to that transducer both with their test device and by re-installing the transducer that had been in my plane previously. And everyone has a story about poor communication from JPI... the person doing the test can't talk to customers, but the people who do talk to customers have no idea what the test criteria are or if that person knew any details of the problem I had with the part. After some time on the phone where I felt like I basically coached them through how to communicate with each other about my problem, eventually someone agreed to send me a new transducer, and it's been working great ever since.

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36 minutes ago, mhrivnak said:

It's great. I love having all of the data in one place and visible all the time. Uploading the data to Savvy has been very helpful in pinpointing a couple of issues. If I ever had to buy another plane (though I hope this J lasts me for life), my top upgrade priority would be installing a JPI engine monitor as primary.

I did have to get a warranty replacement of the fuel flow transducer after several months. The interaction started well; they sent me a little test device for free. Based on the results they concluded I should send them the transducer, which I did. That's when it became difficult.

Their bench test couldn't reproduce the intermittent drop-out I was seeing, even though I'd already isolated the issue to that transducer both with their test device and by re-installing the transducer that had been in my plane previously. And everyone has a story about poor communication from JPI... the person doing the test can't talk to customers, but the people who do talk to customers have no idea what the test criteria are or if that person knew any details of the problem I had with the part. After some time on the phone where I felt like I basically coached them through how to communicate with each other about my problem, eventually someone agreed to send me a new transducer, and it's been working great ever since.

That's weird -- JPI bought Flowscan awhile back. The transducers probably cost them less to make than the time they spent testing, and talking about yours.

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  • 7 months later...
On 6/4/2022 at 7:50 PM, mhrivnak said:

Follow-up that I forgot to post in 2020: JPI told me to just connect it to the master bus up front. The phone support guy referred me to their engineering team, who got back to me by email in a day or two.

Thank you for posting this.

I was also trying to figure how to connect power wire to the the battery since 900 wire harness has only 2 feet long power cable. So your update makes sense. I will just wire it to the breaker location.  

What did you use for ground? Instruction calls for ground connection directly to the engine block, but I don't think that the ground wire will reach it.

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