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local ground or forest of tabs for fuel pump ground?

Desert Rat

Well Known Member
I have an EFII boost pump, not that the brand matters I suppose.

What are the odds I'd hear radio interference if I take the easy way out and ground it locally rather than running a fat 16g ground wire all the way back to my forest of tabs?

Anyone care to offer up an opinion?
 
I have an EFII boost pump, not that the brand matters I suppose.

What are the odds I'd hear radio interference if I take the easy way out and ground it locally rather than running a fat 16g ground wire all the way back to my forest of tabs?

Anyone care to offer up an opinion?

I have installed the fuel pump both ways, local ground and also to the forest of tabs and have not had any RF noise as a result. The last installation it has a ground run to the forest of tab simply because it is a short run and ensures a good connection for a such important item.
 
I think you would be ok grounding locally. I assume this is on a 7, and the plans I think show the fuel pump very near the firewall, so if anything you could co-ground with your engine-firewall ground rather than back to your forest-of-tabs. Does your FoT's get it's ground from the engine ground firewall penetration?

On the latest 8 I helped with, I grounded the fuel pump locally to the firewall, about 2 or less feet over was the engine ground bolt, which I hooked up a 16g (if I remember correctly) that ran to the ground of the Dynon ACM and from there to a FoT's ground bus. The fuel pump was the only local ground in the airframe, everything else went to the FoT's grounding bug (also the rear battery ground is a local ground to a longeron using 8g or whatever it calls for). So far, everything sounds clean and tested fine, but we have yet to fly it.
 
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hey guys- yes, an RV7. But it's fuel injected, so the pump is in the tunnel near the selector. My FoT is up high on the firewall, so it's about 3' of 16g wire to get back to it vs. about 6" to ground locally.

Unless somebody tells me they absolutely had radio noise, I think I'm going install a nut plate for a ground stud nearby and give it a try.
 
I've grounded it locally.

The only other local grounds on the airplane are the pitot heat, LED landing/taxi lights, FlyLED controller, and the buzzer at the Artex ELT. Everything else runs to the FoT. If something is buzzing, it will be pretty easy to figure out.

I won't be flipping the switch until after engine install in a few months, but if it doesn't work out, I'll report back.

thanks for the input everybody.
 
Locally better

I would ground the fuel pump locally. In fact, a long ground run to the forest of tabs can introduce noise to all the stuff you want to keep quiet. And a long ground run is hard to troubleshot and less reliable. In general, noisy stuff can be grounded locally; quiet stuff, like audio, have to be very carefully grounded per the manufacturer's directions. JMHO YMMV
 
I have an EFII boost pump, not that the brand matters I suppose.

What are the odds I'd hear radio interference if I take the easy way out and ground it locally rather than running a fat 16g ground wire all the way back to my forest of tabs?

Anyone care to offer up an opinion?

Ground it locally.

AND

Put a diode across the terminals on the motor just like you do for the starter relay, master relay. Your boost pump switch will thank you :)
 
Ground it locally.

AND

Put a diode across the terminals on the motor just like you do for the starter relay, master relay. Your boost pump switch will thank you :)

Actually since the pump is a major component, I would put two diodes in series, so a single diode failure will not blow the pump fuses (or CB). And check both diodes for short/open during conditional inspection
 
Failures

John,

Do these typically fail with a direct short?

Thanks,
Mike

Diode failures tend to turn into direct shorts or opens very fast. In my experience, diodes never soft short for very long due to self heating.

Diode failures are very rare now days; it is just that if you are the one in a million that it happens too, it will be a bad day.

And most diodes used on the airplane can fail without drastic impact on continued flight (like alternator diodes), but fuel pump diode failure that pops a breaker/fuse could have an impact on continued flight. that is all i am saying.

If a contactor diode fails short, there is so much energy behind it, that it will blow open very fast and not cause a problem, so no need to double up those.
 
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flyback capture diode not required. But ref next post for a different viewpoint.

Thread drift but no flyback capture diode needed across fuel pump leads. But ref next post for a different viewpoint.

Per Bob Nuckolls:

"Rotary pumps powered by pm motors have no 'flyback' event."​

And if you're wondering about the click click pumps used on carbureted engines:

"PutPut pumps like the Facet devices have electronically driven solenoids that kock a compression spring. A cruise through the genealogy of exemplar patents for such pumps . . . http://aeroelectric.com/Mfgr_Data/Pumps/ . . . illustrates commonly applied technology for mitigating flyback energies in these devices that include resistors, diodes and capacitors as part of the designs dating back over 30 years."​
 
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Thread drift but no flyback capture diode needed across fuel pump leads.

Per Bob Nuckolls:

"Rotary pumps powered by pm motors have no 'flyback' event."​

And if you're wondering about the click click pumps used on carbureted engines:

"PutPut pumps like the Facet devices have electronically driven solenoids that kock a compression spring. A cruise through the genealogy of exemplar patents for such pumps . . . https://tinyurl.com/2e6mmzyr . . . illustrates commonly applied technology for mitigating flyback energies in these devices that include resistors, diodes and capacitors as part of the designs dating back over 30 years."​

"It Depends"

Some PM motor/pump designs include a snubber diode, some do not (just like relays, solenoids) -- it's cheap insurance to include one...
 
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