Boost On indicator

[RVG8tor]

I want to wire a light that tell me I have the boost pump on. The plan is to have tow wires come off the out side of the switch, on to the pump and one to the light. The pump wire is #18, do I need to run #18 to the indicator light as well or can this be a smaller wire like #20 or #22.

I am not sure what happens with a short; will the CB pop before the smaller wire melts.

Thanks

 

[Walt]

22 is fine for the light. If you have an actual short in the wire the CB will pop.

 

[jferraro17]

Mike,

I don't really have another solution for you, but doesn't this just tell you that the light is receiving power...not necessarily the pump? Flip the switch, light comes on, do you really know the pump is running?

I'm looking to do the same thing right now, and dismissed this way of wiring it as not meeting the intent of the indication.

Thinking out loud--
Joe

 

[Walt]

I have a light to remind me that the pump is on, true enough it doesn't actually tell you if the pump is working but the pressure gauge will do that for you.

I suppose if you wanted to add more "stuff" you could install a pressure switch on the pump output and wire it to a light... but seems like overkill to me

 

[AltonD]

I have a light to remind me that the pump is on. . .

I have the same thing. It works for me.

 

[jferraro17]

I was trying to think of a way to tap the light wire off of the pump power wire somewhere down line of the switch...perhaps a small terminal block near the pump? More weight/stuff.

I don't know, the light and gauge are probably good enough...airplane, not a clock and all that

 

[RVG8tor]

Reminder light

Mike,

I don't really have another solution for you, but doesn't this just tell you that the light is receiving power...not necessarily the pump? Flip the switch, light comes on, do you really know the pump is running?

I'm looking to do the same thing right now, and dismissed this way of wiring it as not meeting the intent of the indication.

Thinking out loud--
Joe

Joe,

I am want the light as a reminder that the pump is on, it is not a pump function light. I could do the same with with a lighted switch which is what I have for my Pitot heat. I went that route just because I needed a switch with a different shape (too many toggles in a hard to reach area)

As some posted the pressure gauge will tell me if the pump is working, I just want something to help remind me the switch is in the on position so I don't fly for 2 hours with the pump on.

Back to lace tying wires

 

[Greg Arehart]

I just used a lighted rocker switch.

greg

 

[Ironflight]

My light is tapped off the power switch as well, and yup - it doesn't tell me that the pump is functioning, it tells me that the switch is on. But that's what I want it for. Fuel pressure tells me the pump is working - the light reminds me to turn the pump off (cause pressure doesn't stick out on the display...)

Paul

 

[vlittle]

22 is fine for the light. If you have an actual short in the wire the CB will pop.

The size of the wire is set by the circuit breaker/fuse rating according to AC 43.13 Section 4. The purpose of this wire sizing is to prevent fires. If you have a 10A breaker for the 18 AWG pump wiring, then the wire to the light needs to be 18 AWG.

If the lamp wire is in open air (not in a bundle) it is acceptable to use one size smaller gauge. In this case it would be 20 AWG.

If you have a 7A breaker, then you could use 22 AWG in open air.

Vern

 

[jferraro17]

Fair enough. Now that I think about it, forgetting that the switch is on is really what I want the light for too...disregard all previous transmissions.

 

[Snowflake]

Wouldn't a 12 Volt indicator light rated for the same current as the pump, and wired in series with the pump make more sense? Then you know the pump has power, and you simplify the circuit. Surely the voltage drop across a light isn't that great?

 

[Ironflight]

Wouldn't a 12 Volt indicator light rated for the same current as the pump, and wired in series with the pump make more sense? Then you know the pump has power, and you simplify the circuit. Surely the voltage drop across a light isn't that great?

Ahhh...but if the light burns out, the pump is disabled - not a piece of equipment that I'd give up easily. And, of course, if you're using an LED as an indicator, the current flow through the pump might be unfriendly to the indicator.

Paul

 

[Mark Burns]

Sorry, no

Wouldn't a 12 Volt indicator light rated for the same current as the pump, and wired in series with the pump make more sense? Then you know the pump has power, and you simplify the circuit. Surely the voltage drop across a light isn't that great?

When the light burns out you'll have no power to the pump this way.
And the light will probably burn out in about .2 seconds


Mark

 

[Walt]

Wouldn't a 12 Volt indicator light rated for the same current as the pump, and wired in series with the pump make more sense? Then you know the pump has power, and you simplify the circuit. Surely the voltage drop across a light isn't that great?

Back to Electrons 101, it doesn't work this way...

It would take a 100 watt landing light to handle the current (that might be the worlds biggest indicator lamp) and the light might glow orange and the pump would not run at all, each device would only have a portion of the voltage drop across it so neither one would work.

 

[David-aviator]

I want to wire a light that tell me I have the boost pump on. The plan is to have tow wires come off the out side of the switch, on to the pump and one to the light. The pump wire is #18, do I need to run #18 to the indicator light as well or can this be a smaller wire like #20 or #22.

I am not sure what happens with a short; will the CB pop before the smaller wire melts.

Thanks

Mike,

I am no wire expert but did learn a few things doing the electric stuff on several homebuilts.

A basic premise is always protect the wire. What that means is the circuit protection should not exceed the wire max load. The Aero-Electric wire load chart shows #18 wire good for 10 amps, #20 wire 7 amps and #22 wire 5 amps.

If the fuel pump requires a 10 amps and there is a short at the light the #20 wire will get very hot and the 10 amp circuit protection may not trip. (theoretically)

To protect a smaller wire, you could use an inline fuse holder and since it is just for the light, go as small as 1 amp.

 

[Walt]

Mike,

The Aero-Electric wire load chart shows #18 wire good for 10 amps, #20 wire 7 amps and #22 wire 5 amps.

It also depends on length, 43.13 (which takes precedent over AE) shows a #22 good for a continuous 7 amps if 4 ft or less, it can be 8 ft long or less if used in an intermittent circuit.

So considering an indicator light wire may be a couple of feet long in an RV I think it may be safe to say it could carry 10 amps for a few seconds without excess heating. By all means though if it makes you fell better step it up to a 20.

Some folks seem to get hung on wiring shorts, if the wiring is installed correctly "shorts" are rare or non existent. Electronic components/pumps etc. do fail and short but it's rather rare for wires themselves to short if installed correctly. CB/fuses are there to protect the wiring, but that usually happens when a component fails, not the wiring itself.

 

[MCA]

Well, let's see... if you wired this with a VP-X you would:
1. wire an 18 gauge wire from the VP-X to the fuel pump and set it to 10A breaker
2. wire a 22 gauge wire from the VP-X to the light and set that circuit to 1 amp breaker
3. wire the boost pump switch to the VP-X using 22 gauge wire (it carries no load)
4. configure the light and the boost pump to turn on when the switch is on.

Very clean, simple, and more reliable than using older mechanical components. Plus, the VP-X would give you an alarm if the boost pump stopped drawing current, and you could run the boost pump from the EFIS as a backup if the switch failed.

Just sayin...

 

[Danny7]

My light is tapped off the power switch as well, and yup - it doesn't tell me that the pump is functioning, it tells me that the switch is on. But that's what I want it for. Fuel pressure tells me the pump is working - the light reminds me to turn the pump off (cause pressure doesn't stick out on the display...)

Paul

so you have a fuel pressure read out on your display? can you also say when you generally put the boost pump on?

 

[Ironflight]

so you have a fuel pressure read out on your display? can you also say when you generally put the boost pump on?

Fuel pressure is on my EFIS display, yes. I turn the pump on for take-off (during the run-up), then off at 1,000' AGL. On again at 1,000 AGL for landing, and off as I turn off the runway. That's about it.

Paul

 

[rvmills]

Only thing I would add is to consider where you put the light. When I bought my plane, the boost pump LED was a small green LED in the lower right-hand corner of the panel, right next to an identical one for the landing light. When my seller and bud was checking me out, he'd occasionally ask what why that light was on. I'd always reply with a query on why it was way the heck over there!

When I did my panel upgrade a while back, I wanted to make it fairly Bob-proof, so I stuck my annunicators right in front of my face...centered and high. Lighted rockers are very nice (and cool), but I'm not sure they'd get my attention (Bob-proofing is a big job for me! ) Here's how it turned out:

Yellow is ALT OFF (was supposed to be low ALT volts, but that got complicated and the gent helping me was getting scarce, so its just a "don't run down the battery" warning now). Green is LL On, Blue is Boost Pump On, and Red is Low Oil P. Oil P comes off the pressure switch (tapped at the Hobbs meter), but the rest are toggle position indicators, as others have mentioned. Works great for a "turn that switch off...Bob" light.

As Paul used in his lights, I'm cool lights on, hot lights off for TO and LNDG.

To show you a little OCD-ness, the light order (L-R) matches the relative position of the switches, and the colors match the switch covers I bought from Stein. All set up for cockpit flows...I know...pretty bad...maybe good too!

Have fun making your cockpit light up!

Cheers,
Bob

 

[Special Delivery]

I think I've got it!

I've been following this thread with interest, and I appreciate the exceptionally well reasoned responses. I've always wanted an indicator light for my boost pump, but wasn't sure how accomplish the task. Here's a summary of what I think I've learned:

1. Indicator location - possibly the most important part of the install. I will however use a lighted rocker just to make sure all bases are covered.

2. Don't fuse the pump with a headlamp or similar type of indicator in series... doing so adds a failure mode.

3. Install a dedicated pressure sender to confirm pump is actually making pressure. A little extra plumbing, but it may save my life.

4. The VP-X is an excellent solution to resolve the fuse and connections complexity of adding a boost pump 'idiot' light.

Thanks guys.. It took me a while, but I think I've finally got it!

 

[Walt]

3. Install a dedicated pressure sender to confirm pump is actually making pressure. A little extra plumbing, but it may save my life.

Thanks guys.. It took me a while, but I think I've finally got it!

I don't think you need "another" pressure sensor for the pump, one fuel pressure sender is enough to verify pump operation.

 

[L.Adamson]

I have a lighted switch, in addition to an annunciator light at the top of the panel. Remembering to turn off that pump,.........was one of my toughest conquests of learning to fly the Piper. Even forgot to turn it off, for a few minutes on my check ride........after review with my instructor. I just don't want to miss it, these days.

L.Adamson ---- RV6A

 

[JonJay]

Ok - here is a stupid question....

Why do you need an indicator at all?

For those using written check lists, your climb or cruise list should get it shut off...

For those who rely on a visual "scan", you should see that you left your switch on within a few minutes if you are diligent and consistent with your scan...

I thought that most of these boost pumps are continuous duty and can not be harmed by running them all the time. Now, I also understand that it would be stupid to run it all the time and if your mech. pump fails you want to know.

I dont have an indicator on my pump. I have left in on inadvertantly before, for maybe a maximum of a couple minutes, then my scan caught up.

I am not a big fan of indicators in general. I think in the auto world when steam guages gave way to indicators we called them "idiot lights". Sorry, no offense meant to anyone by that if your too young to remember. I didn't make it up.

 

[jferraro17]

Well, I can only speak for myself...

But, if your RV isn't the only plane you fly, and your habit patterns are ingrained in a a different class/type of airplane to the tune of 700-900 hours per year, "idiot light" may be appropriate/exactly what it is!

J

 

[Ironflight]

Why do you need an indicator at all?

You're right Jon - the checklist should be enough....but we're all human. The reason I like th indicator is that the fuel flow indication is biased about 1.0 gallons/hour high when the pump is on, and if I accidentally leave the pump on longer than necessary, then my totalizer value won't be accurate. Sure, it's a small error, and in the "safe" direction, but I like to get the pump off in a timely fashion.

And yes, we had literally thousands of "idiot lights" in my business for decades - and we called them that too....(now they are little digitally generated colored boxes on computer screens. Same thing though...)

 

[JonJay]

Bias?

You're right Jon - the checklist should be enough....but we're all human. The reason I like th indicator is that the fuel flow indication is biased about 1.0 gallons/hour high when the pump is on, and if I accidentally leave the pump on longer than necessary, then my totalizer value won't be accurate. Sure, it's a small error, and in the "safe" direction, but I like to get the pump off in a timely fashion.

And yes, we had literally thousands of "idiot lights" in my business for decades - and we called them that too....(now they are little digitally generated colored boxes on computer screens. Same thing though...)

Interesting. I will have to see if my indicated fuel flow is higher with it on. I have never noticed.

I like to question things when they come up to offer another point of view, or at least to look at the "why". This is not only for my own education but for those that are making decision as they build. I think it evolves into a healthy exchange of information and opinion. Oh, and I am not shy or afraid of getting flamed for it either....(not that anybody did)

 

[DanH]

Well, let's see... if you wired this with a VP-X....

So the usual wiring would compare with the "clean, simple" VP-X wiring like so?

 

[RVG8tor]

Annunciation Redundancy

Why do you need an indicator at all?

For those using written check lists, your climb or cruise list should get it shut off...

For those who rely on a visual "scan", you should see that you left your switch on within a few minutes if you are diligent and consistent with your scan...

I thought that most of these boost pumps are continuous duty and can not be harmed by running them all the time. Now, I also understand that it would be stupid to run it all the time and if your mech. pump fails you want to know.

I dont have an indicator on my pump. I have left in on inadvertantly before, for maybe a maximum of a couple minutes, then my scan caught up.

I am not a big fan of indicators in general. I think in the auto world when steam guages gave way to indicators we called them "idiot lights". Sorry, no offense meant to anyone by that if your too young to remember. I didn't make it up.

I want the light because I think I will catch it before I noticed the switch position or fuel pressure reading in my scan. Checklists are nice but my single seat experience tells me that they get in the way with normal operations. I flew single seat in the military and I don't know anyone who actually pulls out and reads the checklist for normal operations. You learn "flows" for the various phases of flight. Once it a while you can get bitten but that to me is safer than being heads down reading a checklist. Lights horns and bells make sure you catch the important stuff.

The pump on light is just one more layer to help me catch the status of the boost pump. To each his own, many use them and so will I.

 

[JonJay]

No check list here...

I want the light because I think I will catch it before I noticed the switch position or fuel pressure reading in my scan. Checklists are nice but my single seat experience tells me that they get in the way with normal operations. I flew single seat in the military and I don't know anyone who actually pulls out and reads the checklist for normal operations. You learn "flows" for the various phases of flight. Once it a while you can get bitten but that to me is safer than being heads down reading a checklist. Lights horns and bells make sure you catch the important stuff.

The pump on light is just one more layer to help me catch the status of the boost pump. To each his own, many use them and so will I.

agree totally, and dont want this simple question to become another "check list" argument drift.
Again, just trying to insure there are other points presented and learn something while I am at it.
I dont believe that a boost pump left on is a critical item for an RV, and unless someone can correct me, leaving it on inadvertantly on occasion until your scan catches it is not harmful or dangerous.
That is why I asked the "stupid" question. If it was critical, I would have an indicator, and if it is, it is never too late to add one in.

 

[CMW]

Fusible link

Mike,

Getting back to your original question. I think this is a good place for a fusible link. Wire it as Dan shows in the diagram without the VP-X and at the switch end of the wire going to the indicator, add a fusible link. The fusible link is nothing more than a short length of smaller gauge wire ( 4 GA sizes smaller i.e if your wire to the indicator is 20 GA than the fusible link should be 24 GA or smaller) soldered inline. Cover the smaller wire with a fiberglass sleeve found here: http://www.mcmaster.com/#sleeving/=a1qlmr (look under sleeving and then high temperature sleeving) and then heat shrink over the assembly. If on the remote chance you have a short in the wire between the switch and the indicator, the fusible link will protect the majority of the wire going to the indicator.


I hope this is a good way to do it, because this is the way I wired mine.

-Chris

 

[sjhurlbut]

Not sure

I had a similar setup on a previous airplane and I can say that either:

1. If the light is too dim to see well during the day, you'll be surprised of how bright it is at night
2. If you can see it great during the day, a night approach with the landing light and fuel pump light on will drive you crazy.

I'm not a fan of 'indicator' lights unless they're showing me something unusual such as gear position and engine malfunctions. Or at least add a dimmer to them like you did.

Only thing I would add is to consider where you put the light. When I bought my plane, the boost pump LED was a small green LED in the lower right-hand corner of the panel, right next to an identical one for the landing light. When my seller and bud was checking me out, he'd occasionally ask what why that light was on. I'd always reply with a query on why it was way the heck over there!

When I did my panel upgrade a while back, I wanted to make it fairly Bob-proof, so I stuck my annunicators right in front of my face...centered and high. Lighted rockers are very nice (and cool), but I'm not sure they'd get my attention (Bob-proofing is a big job for me! ) Here's how it turned out:

Cheers,
Bob

 

[Dynon]

With a Dynon EMS system in the plane (D120, D180, D10, or SkyView) you can wire this to a "contact" input if you want to display the boost pump status on the EMS screen. I'd imagine you can do the same with competing EMS systems too. So you may already have something in the plane that works for you without needing to add a light.

 

[N941WR]

With a Dynon EMS system in the plane (D120, D180, D10, or SkyView) you can wire this to a "contact" input if you want to display the boost pump status on the EMS screen. I'd imagine you can do the same with competing EMS systems too. So you may already have something in the plane that works for you without needing to add a light.

I'll do that when I re-build my panel, some day.

I too put a green LED above my EFIS display. It is there more to remind me to turn off the pump when I change tanks in flight than anything else.

There are a number of pilots who never turn on their boost pump when switching tanks in flight but I am one who was trained to turn it on whenever changing tanks and occasionally I'll leave it on because I was distracted shortly after changing tanks.

 

[MCA]

Dan, your drawing is incorrect. You are not showing the circuit protection required for the pump, nor are you showing the circuit protection required for the light. If you want to compare apples and apples. Your drawing also does not provide an alarm when the pump stops drawing current nor does it have a backup switch mechanism (in our case the EFIS screen can be used as a backup switch). Further, the MTBF of your system is significantly lower than that of a solid-state system. That's my view anyway.

So the usual wiring would compare with the "clean, simple" VP-X wiring like so?

 

[DanH]

Dan, your drawing is incorrect. You are not showing the circuit protection required for the pump, nor are you showing the circuit protection required for the light.

Ok.....substitute a circuit breaker (or fuse) in each drawing where it says "power".

Your drawing also does not provide an alarm when the pump stops drawing current nor does it have a backup switch mechanism (in our case the EFIS screen can be used as a backup switch).

True.....but the subject here is the "clean, simple" pump system wiring with a VP-X. It's a cool device but it doesn't cut the wire count to any significant degree, if at all.

Further, the MTBF of your system is significantly lower than that of a solid-state system.

Perhaps. Frankly, I don't know. What I do know is I can hot-wire the conventional system while far from home, with my eyes closed.

 

[Walt]

Further, the MTBF of your system is significantly lower than that of a solid-state system. That's my view anyway.

I may be missing something here but I don't understand how the MTBF of any solid state device could possibly be better than a mil spec switch and breaker in this particular case. In my avionics career I've replaced hundreds (probably thousands) of failed silicon devices and maybe a dozen failed switches/breakers.

 

[David-aviator]

What's that light for....?

I forgot what the light is for, does it say the switch is on or off?

I have 3 lights I believe are important, one is low oil pressure, one is starter engaged and the big fat red one is EIS 4000 WARNING - the cardiac warning light.

That seems to do the job. Of course you-all can have as many lights as you wish. It is Christmas time.

 

[Special Delivery]

MTBF

Until now, I haven't even considered the MTBF of the parts used in this circuit. Earlier in this thread I was convinced that I needed to purchase a VP-X to simplify the fuse and wiring complexities associated with the installation of a boost pump 'on' annunciator in my panel. The recent discussions addressing MTBF now have me a little concerned with that decision. At my age I really shouldn't be concerned with MTBF because I'm already past my expectancy, but the MTBF discussions now have me questioning the entire circuit. Installing this dang 'idiot' light is giving me a headache!

I'm giving up... It's been fun and entertaining!

 

[MCA]

Sorry Dan I don't agree with any of your comments as I don't feel they are accurate (but I do agree with your choice of using an IO-390 ). If you are more comfortable with older steam gauges, vacuum pumps, and mechanical breakers that's fine with me. We each have to build the plane we want.

A typical mechanical circuit breaker has a mean time between failure (MTBF) of 17,000 hours. A single electronic circuit breaker and associated components has an MTBF of about 1,000,000 hours. Further, a mechanical switch is rated for about 30,000 - 100,000 cycles. ECBs are rated for about 2 billion cycles. That's as objective as I can get.

Is it such a big deal on this specific circuit? I don't think so. But if you look at the ever increasing complexity of electrical systems in our small aircraft it does make a difference, IMO.

 

[Ironflight]

I'm giving up... It's been fun and entertaining!

"Never Surrender...Never Give Up!!"

Fly on over this weekend Ernie, and you'll fly out with a pump indicator light....

Paul

 

[Walt]

A typical mechanical circuit breaker has a mean time between failure (MTBF) of 17,000 hours. A single electronic circuit breaker and associated components has an MTBF of about 1,000,000 hours. Further, a mechanical switch is rated for about 30,000 - 100,000 cycles. ECBs are rated for about 2 billion cycles. That's as objective as I can get.

Marc,
Don't get me wrong, I think you have a great system.

However, if you go by just the numbers that would mean our electronic equipment should basically never fail but we all know that it just not the case. Maybe I'm just old school but when it comes to flying I like to take "experimental" out of building airplanes as much as possible

 

[Special Delivery]

"Never Surrender...Never Give Up!!"

Fly on over this weekend Ernie, and you'll fly out with a pump indicator light....

Paul

Thanks Paul! I'm indeed fortunate to have a NASA engineer as a dear friend.

 

[flybye]

Keep it simple!

Dan, your drawing is incorrect. You are not showing the circuit protection required for the pump, nor are you showing the circuit protection required for the light. If you want to compare apples and apples. Your drawing also does not provide an alarm when the pump stops drawing current nor does it have a backup switch mechanism (in our case the EFIS screen can be used as a backup switch). Further, the MTBF of your system is significantly lower than that of a solid-state system. That's my view anyway.

Are you proposing that lights deserve their own circuit protection? Isn't a lamp a close approximation to a fuse? The VP_X may offer this function but is it really necessary? Simplicity typically aids fault finding and extends MTBF.

 

[MCA]

Are you proposing that lights deserve their own circuit protection? Isn't a lamp a close approximation to a fuse? The VP_X may offer this function but is it really necessary? Simplicity typically aids fault finding and extends MTBF.

No, it's standard practice that wires have their own circuit protection. Lamps are not circuit protection, nor are they located in the right place on the circuit. If you have multiple wires protected by a single CB, then the CB needs to be sized to protect the smallest wire in that circuit. We see (quite often actually) that builders want to add small wires to circuits that are protected by a breaker that is too large for that wire. This is common when wiring the nav lights for example. Three smaller wires split off from a main wire which comes from the power source/breaker. The smaller wires are too small for the breaker, but the breaker is appropriately sized for the total load of the three nav lights. This can be solved very simply by running larger-than-needed wires for each nav light. Then a short anywhere in the circuit is appropriately protected by the breaker.

In the case we're talking about here, if the wire to the light is sized for the breaker then all is well (the result is that the wire to the light is larger than necesary to power the light but the right size for the larger breaker that is needed by the boost pump). The extra weight of the larger wire is insignificant and this is an easy way to solve the problem. The one downside is that if there is a short on the wire to the light you will also lose the boost pump. So by separating the circuit protection for the pump and the light you don't have this failure mode. Is that a critical distiction? Good arguments can be made either way.

Anyway, I gotta get back to shipping units out the door. Paul - you're a better writer than me, perhaps you can translate this to english! Hope that helps.