What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Where to monitor amps?

dwilson

Well Known Member
Hi all,
I am ready to install my hall effect amp sensors for my GRT EIS 4000. I am following Bob N.'s dual alternator/dual battery setup.
Bob has a shunt amp meter on the output of each alternator, but it seems to me that I would want to monitor the battery lead more than I want to monitor the output of the alternator.

One concern I have with monitoring the battery lead is that the current flow may be a couple hundred amps for a short time during engine cranking.
Will that high current flow damage the amp sensor?

Thanks,

Duane
 
dual batteries, Dual alternators. Space shuttle?

dwilson said:
Hi all,
ready to install my hall effect amp sensors for my GRT EIS 4000....following Bob N.'s dual alternator/dual battery setup. Bob has a shunt amp meter on the output of each alternator.....seems to me I want to monitor the battery lead more.

concern monitoring the battery lead (with)........ current flow may be a couple hundred amps for a short time during engine cranking. Will that high current flow damage the amp sensor? Thanks, Duane
Duane good question? I could tell you where using Bob's book, with a system like that.

Bob says put the amp meter on the alternator, and I agree, you want the alternator, since that is where the power is coming from. :rolleyes:

My vote is put the hall effect on the main alternator out put only. If it dies you will know (zero amps). If the back-up alternator works, you know it, because the volts will be above 12.6v battery voltage. I suspect the second alterantor is for lower capacity and emergency use only? So if you had a gauge on it. it would read zero most of the time, which is kind of a waste.

WHY NOT THE BATTERY?

Look, think of it this way, the battery serves as a reservoir and to get the engnine started. After engine start and the alternator energized, the battery's job is done. All the power is from the alternator. After the battery charges back-up (less than a minute or two if in good condition), its waiting as back-up or for the next engine start. Kind of boring and no need to watch it.

The battery DOES serve a very important secondary function, a stabilizing function, handle surges, like if a high load item is switched on, e.g., landing lights or pitot heat. Once the alternator catches back-up (in seconds), the battery goes back to essentially zero current in (charge) or out (dischrage). Again boring.

THE POINT is you will get a lot more out of the AMP meter on the alternator. How much the alternator output is, 10 amps, 20 amps, 40 amps and so on, is way more important. The ampmeter on the battery reads near ZERO most of the time in flight.

What if the alternators goes dead? Voltage goes to about 12.6v and you LAND asap.

With two batteries you probably have enough juice to fly till the tanks are empty. A little electrical load shedding, turning off everything except what is absolutly needed, may be in order. Its a good idea to know what your EMERGNECY or MIN equip electical load (amps) is. You don't need a meter for that. Knowing the estimate of how long the battery will last, with the MIN equip, is a good idea.

VOLTS is a great indirect indication of battery state. Normally it should read about 12.6 volts with no alternator. It will stay there and drop off slowly. As it drains and voltage drops at a faster rate. Most radios and lightspeed electronic ignition can run down to 10 volts. Once down to 10 volts, the battery is pretty shot.

So you can live without an ampmeter on the battery.

IMPORTANT: Good battery maintenance is important. In cars we drive batteries until they don't work at all. In a plane you should CHANGE the battery OUT on a preventative schedule.


It's NOT a bad idea to have an amp meter on the battery, just given the choice of EITHER batter or alternator, the alternator is more importnat to monitor.

Some airplane manufactures and car makers, especially in the old days, had an ammeter on the battery. It usually was a CENTER needle gauge, sometime called a load meter, that deflected left or right for discharge or charge. If the needle was just right of center (no political comment) the battery was not being drained, which was its normal position. Right after start for a minute or so as the battery took some current to charge, the needle would be way right. If the needle went the other way, the battery was draining, like with the engine off and headlights on. When you where driving along and turnned the lights on, the needle would jump left for a second and than go back to just right of zero. On old cars you could get the battery to drain with the engine running because the alternator or generator could not keep up, especially at idle rpm, so the battery made the difference.


Since you are using a EIS4000 engine monitor I can tell you the HALL EFFECT sensor can handle the two way current flow in or out of the battery, but the display does not show negative numbers, but there's a workaround explained in the manual. With the hall effect on the alternator "B-lead", it works better, since all readings out of the alternator are positive or in one direction.

You mention a SHUNT can not handle the start current. You are correct. The hall effect will not be damaged but it will not read that high, unless sized for that.

To explain about shunts and the starter wire draw/current, you could make it work, but you would need a BIG 400 amp shunt or a hall effect sensor. Also you need a gauge scalled for say 400 amps. Can you image reading 10 amps on a 400 amp scaled gauge? That is why we dont do it and we don't care what the starter draws.

IF you want to measure the battery wiht a shunt, put it on the smaller battery wire to the aircraft buss. The starter wire is ignored. With a HALL EFFECT, it does not matter. You can put it right on the POS BAT wire to the master relay (or contactor). When you start, the starter current will go thru the HALL EFFECT, but it does hurt it, but you will not get any useful reading on the EIS4000, for one, it usually is not ON during start. Unless the EIS4000 has its own power, the voltage drops to 8 or 9 volts during start and the EIS drops out and reboots. Some people don't turn the EIS on until after start.

With you dual dual system you could go all the way and have 4 shunts (hall effect meters) and 4 amp meters (or use more EIS4000 AUX inputs or a switch). I don't suggest you do that or need it, but you sure would have the total picture.

Can I asked what made you go to dual alternators and batteries? I mean there are 10's of thousands of single engine planes all over the world flying with one battery and one alternator. The space shuttle does not have that much stuff. :rolleyes: With an electrically dependent engine and/or panel, electical redundancy is needed and a great idea, but I think either, (1)-alternator and (2)-batteries -OR- (2)-alternators and a (1)-battery is plenty. Does Bob have any stats to justify his rocketship electial design? Just a question.
 
Last edited:
Crusade against overkill

I have no idea about any ones need for dual everything, electical wise. I am not picking on anyone. I understand some who fly with electronic ignintion, electronic fuel injection and electical panel IFR may want dual dual stuff. I just want to shed some light on this. May be I am missing something.


The following is a reality check, or at least my reality. Sure we want the safest plane possible. However these are little planes with lots of critical single point failure modes, like that one crankshaft. I am focusing more on Lyc's, but even lycs can have dual electronic ignition of the non-self-powered kind. Also the panels are going all electric and vacuum redundancy of instruments old hat and dead, at least in the experimental sector.


I noticed that more and more RV's are being equipped with very complicated electrical architecture and equip. I have to say for most, especially VFR, of the planes I have seen, its not needed in many cases.

Despite some wild stories about once in a 1000 life times, legends of danger, batteries just don't die all of a sudden or explode. They usually go bad slowly, thus may I recommendation you change it every few, years depending on condition (load) test.

Keep it simple and light weight. You are paying a price of weight and cost. Not only is there the weight of the extra alterantor and battery, there is the associated wiring, brackets, switches and all kind of things to go wrong. If you put is ALL on a scale it may shock you.

ONE big healthy alternator and one big healthy battery works for 98% of the builders with Lycs.

If VFR I would definitely only have one and one. With EFIS (and I am, Dynon) I use a little 3-5 amp backup just for that and the electronic ignition. I could have used the dynon self contained battery, but they cost too much and they have had some issues. My little AUX battery cost is low and is paralleled and diode isolated from the main system. Simple. I can buy a new one every year of two for cheap.

I also check the alternator every 200 hours or yearly (brushes, bearings, belt, connections). The main battery, even though it works fine, is replace every 2-3 years. Maintenance is key to reliability.

Don't design a super redundant dual everything system unless needed. Of course you are the one that decides if you need it. I just see a big miss match in B777 electical redundancy and a single engine plane with one pilot. You have to have a balance in design. Weight is so important in getting the most out of your RV. SYSTEM EXPERTS, like Bob are so focused on just the electical system they really don't think about the weight. This is common. I was involved in large jet design long ago. Every department wanted to make there system bigger, better and more expensive. However it takes COMPRAMISES to fly.

A RV with an empty weight that keeps it from being a dual aerobatic plane or flying within the recommend Gross is not as safe as one that is of lower weight, even if you have the worlds best electical system. Lower weight = better climb, better handling, less stress on the airframe and so on. The center of the universe is not just the electical system.

Its easy to design by fear, but you really are not making your plane safer, you are just overkilling the electical system. Keep the real world of airplane accident statistics in mind. Most planes don't come down from the electical system, OK. Your prop is more likely to fall off and that is rare. Really make every pound PAY or earn its way onto the plane. KEY is an idiot light that tells you when voltage is below the normal 14.4V or what ever.

Also when you make it complex with lots of switches and emergency check list and procedures you can make pilot induced failures. Trust me I have seen it.

We fly SINGLE PILOT, SINGLE ENGINE planes. That is an emergency right there. :D
 
Duane,

The short answer first- you will not hurt the hall effect sensor with high current. I have an EIS4000 with the hall effect sensor in the negative battery lead very near the battery (if you wire it backwards on the negative lead, it works the same as it would on the + side) and it works just fine.

Now for the long answer. I'm going to respectfully disagree with George, but I will not take 1000 words to do it. ;)

I think that a battery ammeter is more important that an alternator ammeter. Most of us learned to fly in airplanes with the old "load meters" where the needle pointed at zero and moved left or right to indicate charge or discharge. This meter provides a lot of information in a quick glance. When you turn the master on, it shows a discharge on the battery, which is normal. After starting, it should quickly show a high charge, which slowly decreases back to zero, again indicating normal operation. If it continues to show a high discharge, then you know you're alternator ain't alternating (or the starter is hung, either way don't take off.) In flight, an alternator failure is immediately obvious by a large discharge indication, accompanied by a drop in voltage of 2V or so.

This EIS shows the same information, albeit digitally. And yes, it does display negative as well as positive numbers, contrary to what Geroge posted.

An alternatior ammerter shows the output of the alternator. So what? As long as the alternator is alternating, and is properly sized for the task, who cares if it is putting out 14 or 40 amps? If it fails, it will be readily apparent on either meter. In that case, shed load and think about landing sooner than later (within a couple of hours anyway.)
 
Last edited:
sprucemoose said:
Duane,

An alternatior ammerter shows the output of the alternator. So what? As long as the alternator is alternating, and is properly sized for the task, who cares if it is putting out 14 or 40 amps? If it fails, it will be readily apparent on either meter. In that case, shed load and think about landing sooner than later (within a couple of hours anyway.)

To follow such logic one step farther, why have a load meter at all? If it is connected to the battery, the only load seen will be the start up and who cares about it if the engine starts. A single volt meter will tell the pilot if the alternator is working - 14 volts its on, 12 its off. Time spent looking at an ammeter hooked to the battery would be better spent scanning the sky for enemy aircraft. :)

There is one very good reason to monitor alternator output, especially if the engine has electronic ignition and/or the machine is IFR. Alternator load becomes a norm after some experience in the airplane just like oil pressure or engine temperatures. If a problem developes in the electric system, the abnormal load will be the first indication. If the battery is dying, for example, the charge load will be different and noticed on the ammeter.

If the airplane is pure VFR, mags, and minimal avionics, I agree, who cares? All you need is a good voltmeter.

I am not familiar with the EIS 4000 hall effect sensor, but the EIS 2000 with the annunciator panel and load meter is not reliable. I have the EI volt/amp meter and it is excellent. I would not fly without it.

dd
P.S. I had a long conversation with a friend last evening after a first flight yesterday in a one of a kind all metal VariViggen with no ammeter.

During the flight, the gear retract system had an indication problem. At 3000' he decided to cycle the gear to see if the light problem would go away. When the gear handle went down, the engine quit. A quick scan revealed a 35 amp cb was tripped and upon resetting it, the engine (Mazda) came back to life.

Now this is a far out example of why the ammeter is usefull. His discussion center around which cb failed. I asked, how do you know a cb failed not knowing what load was on the system when the gear handle was placed down? With nav lights, strobes, a radio, an engine running and avionics, the electric motor driving a hydraulic pump may well have pushed the load over 35 amps but there is no way of knowing without an ammeter.

Again, if the aircraft is basic VFR with Lycoming and mags, all this is not necessary. But if the machine is loaded up with glass and other magic electronic gizmos, an ammeter would be nice to have, IMHO.
 
Last edited:
You guys are missing the real issue - your significant other will be more impressed if there are lots of gauges.
John
 
Dual Alt / Dual Battery

dwilson said:
I am ready to install my hall effect amp sensors for my GRT EIS 4000. I am following Bob N.'s dual alternator/dual battery setup.

We are also Dual / Dual (FADEC (electrically dependant) ignition and Glass (no vacuum)) w/ GRT. We went dual battery as we didn't want multiple 'mini-backup-batteries' for the various sub systems - just one extra standard, maintained battery.

However I keep coming back to a 'non-standard' configuration for AMP monitoring - here are my thoughts - what am I missing.....

  • The two alternators both have 'idiot' lights to tell me when they are not working.
  • Both the batteries voltages are monitored via the A / B feeds for the EFIS - 14.X for ALT running and providing current, < 12.X for non ALT running
  • Regular maintenance means I have confidence in 'minimum' capacity of the batteries

So why shouldn't we monitor the A bus load and the B bus load? This is an 'actual' used measurement rather than a 'what ALT are putting out (don't know what batteries are adding / taking) or what are the batteries charge/dis-charging (don't know about actual current load of the aircraft)'

I understand if I could only have either one voltmeter or one ammeter, no alternator monitoring and only could monitor one point for current my requirements would be different, but with dual voltage and dual alt monitoring - why not measure the bus loads and let the other measurements take care of the batteries and alt status?

Carl
 
Funny gents very good

ha ha ha ha ha ha ha ha ha ha ha. :D Good stuff and the point is there is more than one way to do it.

Jeff thanks for the polite comments, we just agree to disagree, but that is totally cool. I understand your perspective. I would only say some of us had no NO meter, amp or load in the trainer's we flew. Its NOT required by the FAR's, I don't believe. :eek:

However I agree the more gauges you have, the better to impress.

Two engines is one way to go. When giving multi engine instruction, I always told my students not to worry, if one engine fails the good one will take you to the scene of the accident. :eek:

TWIN FACTS
Did you know to certify a LIGHT TWIN, it must demonstrate a sea level rate of climb. The ROC can be NEGATIVE! All they must do is show it, but it does not have to be positive! Most I flew could got a few 100 ft/min single engine, if you feathered the prop, gear up, flaps up, banked into the good engine for zero slip, and held your mouth just right. With a best se climb speed of approx 100-120 mph (depending on twin), the climb gradiant, assuming about 2 miles a minute and 300 feet a minute (if lucky, a 160HP Apache se ROC is 180 fpm, gross), means you only will get to pattern altitude, in 3.3 min, almost 7 miles from the airport. Oh yes, this is a standard 59F day at sea level. ha ha ha. Some times it's better to pull the good engine back and take what's coming to you, especially on a hot/high day, gross weight.
 
Last edited:
Okay, I have been watching this thread, considering the wiring diagrams and circumstances around where to monitor the amps and have come to one conclusion.

This won't stop the prop. That is, unless you have some weird engine or something. Bottom line is, this is information. Some information is better than none. Make a decision and use that system to determine the health of your electrical system.

The way I see it, either way is good and whichever one you choose you will need to interpret what is happening electrically in order to maintain an uneventful and boring flight... which is what we all strive for!

In the Z13 diagram, there are 2 alternators. If I were to do it today and had only ONE place to audit the current flow of the plane, I would audit the battery. This would show a cumulative indication of the dual alt setup and inform me of current draw and let me determine endurance based on my wristwatch and the ammeter indication.

A PC680 has what, 12 or 17 amp hours of duration? Soooo, if the system is pulling about that much in a load shed environment I can sustain a half an hour plus reserves. Simple math at work!

IDEALLY, a set of 3 ammeters would give you all the information you need (or don't need) depending on your situation at the time. One on each alternator and another on the battery.

This setup would obviously impress the spousal unit! I dare say that it is quite a bit of information.

Answer to the question, put it on the alternator is you want to know how close you are to the alternator's limit and/or put it on the battery if you want to know how much endurance you have left, so long as you can time WHEN the system drops off line, initially.

My $0.02...

Hi George!

:) CJ
 
Fly fly

captainron said:
Vyse= Min. rate of descent, single engine!
Ya sure U betch a, I think it is best rate of climb with one engine, but you are making a joke! funny funny :p

Vyse or BLUE line is surprisingly fast on many light twins, typically 88-106kts. The C-310 is about 106 kts. If you get to Vmc (min control), something less than Vyse, the plane just yaw roll over, out of pilots control, even with full rudder, due to asymmetric thrust and lack of rudder authority. The recovery is reduce the thrust on the running engine or lower nose for more speed or both. Vmc is usually above stall, but not necessarily, depending on altitude and plane.

In large jets Vyse is called V2 or safety speed. V2 is the min speed you fly with an engine out, but usually you fly V2+20 or 25 kts. The concord V2 was typically around 220 kts!

Captain_John said:
Okay, I have been watching this thread, considering the wiring diagrams and circumstances around where to monitor the amps and have come to one conclusion.

In the Z13 diagram, there are 2 alternators. If I were to do it today and had only ONE place to audit the current flow of the plane, I would audit the battery.

IDEALLY, a set of 3 ammeters would give you all the information you need (or don't need) depending on your situation at the time. One on each alternator and another on the battery.

Answer to the question, put it on the alternator is you want to know how close you are to the alternator's limit and/or put it on the battery if you want to know how much endurance you have left, so long as you can time WHEN the system drops off line, initially.

My $0.02...

Hi George!

:) CJ
Hi CJ, This is and outrage, how can you say this, ha ha he he he. :D

I agree kind of, but follow my logic. With two alternators when are you going to loose both? If you are putting an amp meter on the battery for the worst case, you will never need it. I would put it on the aux or backup alternator, the small one so you don't over load that, which is likely because they are only what, 8 amps. If you are down to power you should know what items to turn off and how long you have, 30 min, 45 min, 60 min. Again battery voltage can give you state of charge. (click odyssey thumb nail chart)



You say, and I quote :D : "Answer to the question, put it on the....battery if you want to know how much endurance you have left."

Ya but but but, don't you know you min equip draw? Right. Why do you need an amp meter, you know you're drawing say for example 7 or 9 amps with equip XYZ on (good for 1 to 2 hours, see chart). If you are down to battery only, regardless of how many alternators you have, you're going to load shed the heated seats, microwave and coffee maker.


However your main alternator is working hard everyday. You will see NORMAL alternator load every day, which is a good indication of everything that is going on, at least for normal operations. If the DRAIN is HI or LOW that means some equipment is not working, you forgot to turn it on, some equip is drawing too much current or the alternator is not keeping up. It's nice to know how many total amps your plane is using on a normal basis. It's a good diagnostic tool, and its not just for the alternator. Having it on the battery, it usually does nothing , unless there's is no alternator.

Once you know your normal alternators amp draw, anomalies will stick out. "Why am I only drawing 12 amps not my normal 16 amps?" System voltage is also a good indication of battery state or charge. If you are down to 12.6 volts or less you are drawing from the battery.

I just think you get more out of the AMP meter on the alternator in normal operations and in flight. The only time a battery drain/charge amp meter is needed is on the ground or if both alternators go bust.


For emergency you know the normal drain, EFIS, Elect ignition, VHF comm (RX), intercom, transponder, engine monitor and Bat relay, with intermittent fuel pump, trim, flaps and (TX) VHF comm. For me that is about 4.5 amps continuous. Intermediate: flaps 1.5 amp, VHF Tx 2.0 amp, Trim 0.15 amp. Lights? Forget it, and add autopilot if needed @ 0.5 to 1.5 amps total. To save juice, transponder off (1.4 amps) and forget elect fuel pump and flaps. Bottom line, better be on the ground within 1 hour after my single alternator goes INOP. 10.2 volts is too sporty for me, so I cut the below times in half. If I was flying IFR, I'd add a second battery for more emergency capacity before a second alternator (for cost and simplicity reasons). Like I said I don't see a dual dual ALTs and BATs on a single engine plane, but what the heck. Gosh Apollo 13 got back with from the moon to the earth with 13 amps, I know because I saw it in a move with Captain Tom Hanks. If you can't live with out electrical power, than the battery power should last at least 45 minutes.

Here is a list for a Odyssey PC680 full charge to 10.2 volts at 25c:



hummmmmmm, wack wack (sound of dead horse being beaten)

Chow CJ :D

PS: My be you can tell me this, does the Z-drawing, twin alternator set-up work in parallel at the same time? They are different ALTs, one belt driven and one smaller one, driven off the vac, just for back up. I wonder how you can parallel two different kinds of alterantors with different capacity and regulators? I know its done with light twins using two like alternators, but many times they share a dual voltage regulator that controls both. Just wondering.
 
Last edited:
Dual Alt / Dual Battery control

gmcjetpilot said:
PS: My be you can tell me this, does the Z-drawing, twin alternator set-up work in parallel at the same time? They are different ALTs, one belt driven and one smaller one, driven off the vac, just for back up. I wonder how you can parallel two different kinds of alterantors with different capacity and regulators? I know its done with light twins using two like alternators, but many times they share a dual voltage regulator that controls both. Just wondering.

With our setup (broadly following Z series) the two busses are independent - the A bus has the main belt driven alt and the B bus has the SD-20 (vac pad drive). The two are completely independent unless the cross-feed is engaged - the only reason I would expect to do that is for

a) one or other alt failing -> shed load as needed and then cross feed on,
b) extra starting juice on a really cold day.

I suspect b) isn't really a problem, a well maintained PC680 and skytec is hopefully going to spin the 360 over at a fair clip without a problem :)

I still like the idea of monitoring of used AMPs, plus battery voltage and ALT idiot light....

Carl
 
Looking at the Z-13 diagram, if the Master is on and the SD8 is powered on, yes... you CAN operate them simultaneously.

Now, getting back to the original, beat up question...

Monitoring the battery will give you an indication of a few things.

If the battery is actually charging, if the alternator is working and if it were in failure. It would tell you if there was an open or it there was resistance in the battery lead. ALSO, if there was a charging system failure you could check the discharge rate and accurately calculate your endurance without considering what is theoretically drawn by each thing on at the time (should you remember them all).

The main alt is for everyday useage. The SD8 is to extend your runtime and/or make you feel more comfortable in endurance mode.

A simple and somewhat light solution would be to place a selector switch on the panel and switch between sensors if you really wanted all that information.

Placing the sensor on the alt wire WOULD give you the LOAD on the alt. Certainly a good thing to know. You cite an excellent reason for it. One which I never considered as I am not always in the same airplane all the time. That is knowing what load is "normal" and expecting that value regularly. This would serve as a reminder of equipment left off or a malfunction of some other system.

OH, and the voltmeter! Yah... definately a VERY useful tool with respect to battery health!

Cessna and Piper seem to do things in different ways here. I don't have any wiring diagrams for them handy, but I do like the way Cessna does it. I suspect they monitor the battery wire. The Pipers show increasing alt load. I am also guessing they monitor the alt wire.

Does anyone know for sure?

Bottom line, I suppose it doesn't matter. If I were to do it today I would put it on the battery wire. This way if I were in main alt failure and the SD8 were kicking in, I would know certainly if the SD8 were satisfying the demand. If not, I could shed some more and re-evaluate my flight requirements and options.

:) CJ
 
Oh, and Carl...

The second alt wouldn't give additional power for starting. It just isn't spinning fast enough to make electricity when starting the engine. Starts are dependent on battery power alone.

I haven't studied the SD20 setup. I seem to recall that as Z13-20? The one I plan on using is Z13/8.

:) CJ
 
Oh I see

Captain_John said:
Monitoring the battery will give you an indication of a few things.

Cessna and Piper seem to do things in different ways here. I don't have any wiring diagrams for them handy, but I do like the way Cessna does it. I suspect they monitor the battery wire. The Pipers show increasing alt load. I am also guessing they monitor the alt wire.

Does anyone know for sure? :) CJ
I think that is right, the way cessna's and piper's work. Pipers are better. :D

Hey you make a sound argument and I understand it and appreciate it, it just happens to be wrong. :rolleyes: :D I AM KIDDING.

Bottom LINE, wire it either WAY, but know what it's telling you, ie know how your electrical system works. All the gauges will not help if you don't understand them. Clearly everyone here has great points and superior electical system knowledge. Home builders RULE!

No disrespect to the "average private pilot" renting a piper or cessna, but they just don't understand their planes as well as home builders do. Its all good, as long as you know when you're dow to battery power and follow the correct procedures.

I learned a lot for this discussion, I am 100% correct and Piper's are better than Cessna's. :eek: ha ha ha ha ha.

Really I can see with dual alts and one amp meter, the battery is a fine place to measure current. I still think a "normal system", one ALT and one BAT, measuring the alternators output has the edge in my opinion, my very correct opinion. :p
 
Last edited:
Hi John,

Agreed - second alt isn't for starting (second battery via cross feed just for starting on a cold day).

I also agree that knowing what the Alt is generating is 'interesting - but not important' (assuming idiot lights). However, why is knowing battery charge / discharge current better than knowing system load and battery voltage. Wouldn't the battery voltage by < 14V if the ALT weren't keeping up with the load?

Carl
 
This IS a great discussion! One from which I have learned much as well!

It is why they make chocolate and vanilla, for sure!

Carl, and the world...

My point of view for knowing the rate of charge/discharge is important to me for the following reasons:

1) In a glance you will see total discharge in an alt failure. If you see 17 amps and you have a 17 amp hour battery, you will be reasonably certain that in an hour you will be DOA. Change the draw and you can extend run time. Load shed environment at work. Start your timer and work your plan.

2) If you have a bad battery connection, it will be instantly apparent.

3) You can check both charging systems (in a double alt system) with one meter.

These things you will never know if the ammeter is placed on the alt wire.

During normal operation, you will see a positive indication only when the battery is recuperating from a big hit (like starting) or when the charging system is NOT keeping up with demand (which I suppose isn't normal).

Benefits of monitoring the alt wire:

1) Preicisely knowing what demands are being placed upon your alternator. Obviously, your CB will trip if properly sized. That is it's job. I choose to let the CB watch that instead of me.

2) You will know if you forgot to turn on something. By remembering the "normal" load, a low indication will serve as a reminder that something is off or failed.

3) George will stop writing 10,000 word essays on this subject and I won't stay up nights thinking about things like!

During normal operation you will see actual load being supplied by the alternator. If the alternator can't keep up, the power will come from the battery.

How is that for a summary?

:D CJ
 
The third option?

Hi John,

I understand both the battery and alt sensing options - and they make sense if limited instrumentation is planned (eg. single AMP sensor).

With multiple sensors (2 Hall Effect, 2 Voltage, 2 Idiot lights) I'm still trying to find the reason why I shouldn't do it my way.....

Captain_John said:
(battery charge/discharge sensing )

1) In a glance you will see total discharge in an alt failure. If you see 17 amps and you have a 17 amp hour battery, you will be reasonably certain that in an hour you will be DOA. Change the draw and you can extend run time. Load shed environment at work. Start your timer and work your plan.

2) If you have a bad battery connection, it will be instantly apparent.

1) Sensing system load will tell you total discharge, battery voltage (<14V) will tell you battery 'health', idiot light will tell me ALT off-line
2) Engine won't start / voltage will be "zero"

Captain_John said:
(alt current supply sensing)
1) Preicisely knowing what demands are being placed upon your alternator. Obviously, your CB will trip if properly sized. That is it's job. I choose to let the CB watch that instead of me.

2) You will know if you forgot to turn on something. By remembering the "normal" load, a low indication will serve as a reminder that something is off or failed.

1) Granted, I wouldn't know total ALT current load (battery might be increasing / supplementing my sensed load - but voltage will tell me if it isn't providing 'enough' - and CB will deal with too much supplied
2) Idiot light will remind me.... Although for our configuration pullable CB on the field is also the 'switch', so forgetting it is less likely.

It is one of the those - I know Piper / Cessna don't do it like this - why am I 'special' - really I just can't understand the problem.... ;)

Cheers,

Carl

PS: Thanks for your kind words about the website - it is a mill around the neck sometimes - but the photos are easy to do - the words take more time / effort. Flying to the USA would be great, but would require wings to be removed, and shipped I think - not high on my list of enjoyable things :p
 
Last edited:
Carl, You seem to be planning dual sensors on each battery lead. That's cool. If I were dual batts, I would do that too! Install a selector switch and/or another indicator (might be provided in the EFIS, dunno).

Also, I am not sure if a volt meter will give you "health" while the system is charging. In fact, without testing it I would bet NO! I would expect the higher charging voltage of the alt to keep voltage high regardless of battery condition. When the alt is offline, you would likely get a "true" voltage reading of the battery.

I think you are on the right track.

...unless I am misunderstanding you? You want to measure amp flow on both batts, right?

:) CJ
 
Captain_John said:
Carl, You seem to be planning dual sensors on each battery lead. That's cool. If I were dual batts, I would do that too! Install a selector switch and/or another indicator (might be provided in the EFIS, dunno).

Yes, the EFIS (GRT) will monitor the 2 bus voltages, the EIS will monitor 2 seperate HallEffect / Amp loops. Currently we are planning on using the HE on the 'inbound' feeds through the firewall going to the fuses / distribution CBs - the theory being we can monitor / measure 'used AMPs' (Excluding starting and battery charging) on each of the busses.

Captain_John said:
Also, I am not sure if a volt meter will give you "health" while the system is charging. In fact, without testing it I would bet NO! I would expect the higher charging voltage of the alt to keep voltage high regardless of battery condition.

OK - that is useful information to know - the Alt voltage will bring the battery 'float' up to 14V even if the battery is 'dead'? Goes to add weight to Bob's principle of planned maintenance / replacement of batteries.

Captain_John said:
When the alt is offline, you would likely get a "true" voltage reading of the battery.

Yep, and the stop watch will be going along with George's charts from above (thanks), shortly follwed by landing at a maintenance location ;-) (and not continuing across the atlantic to find one :rolleyes: )

Captain_John said:
You want to measure amp flow on both batts, right?

Yes, sorta - more amp flow on each of the busses.

Thanks for the thoughts,

Carl

PS: As per George's comments - One really good thing about this whole process of building - I now have some idea of the lack of knowledge I used to have when renting (I was definitely in the "average private pilot" catergory), the continuous learning side really is rewarding.
 
Sounds like we are on the same page now!

Re: learning...

What I always say is, "I don't know the stuff I don't know"!

This is all part of being a teacher for me. It keeps me in touch with my students.

We should never stop learning!

:D CJ
 
Back
Top