Ammeter oddities (possible bug)

[whiic]

I've made some observations about how the ammeter on Spitfire Mk.I work. (Note: this might also apply to P-40 and P-51D.)

- Battery drainage current is measured by ammeter if electric appliances are ON while engine is OFF.
- After engine has been started and rpm is high enough for generator to function, battery charging current is added to current draw of electric appliances (until battery is fully charged).

Now, am I the only one who sees a contradiction here? Namely: think about where the ammeter is located.

If the ammeter is located between [battery] and [bus + generator], then you would see this behaviour:
- Ammeter would read battery drainage while engine OFF. (Matches simulation.)
- Engine running at high rpm: ammeter should read ZERO (or negative) because current is reversed and battery is charging. (Contradiction with the sim.)
(Or if the ammeter was designed to show absolute value, hence display both drainage and charging as positive, it should show recharge current ONLY, not current draw of appliances after generator has kicked in.)

If the ammeter is located between [generator] and [bus + battery], then ...:
- Ammeter would read ZERO while engine is OFF, regardless how high battery drainage is was. (Contradiction with the sim.)
- Engine running at high rpm: ammeter would read current draw of electric appliances + battery charge. (Matches simulation.)

If the ammeter is located between [generator + battery] and [bus], then ...:
- Ammeter would read battery drainage while engine OFF. (Matches simulation.)
- Engine running at high rpm: ammeter would read current draw of electric appliances but not battery recharge current. (Contradiction with the sim.)

___

I cannot rationalize where that ammeter could be located to produce the readings it is giving. As it is now, it functions as if there was two actual ammeters sharing a single gauge, and a switching circuit which switched between two measuring points depending on whether generator was producing current or not... but that'd be nonsensically complex for the purpose of the ammeter.

Hence: a bug. Unless I'm mistaken somewhere in my logic.

Note: the bug only affects the ammeter, not battery drainage and recharge itself. I'm not experiencing any problems with battery life. It's just the gauge what gives funny readings that doesn't seem to add up with any possible real-world location of the ammeter measurement point.

[whiteside]

Usually, you will see less than nominal battery voltage the more amp draw you'd have on the battery without engine running and generator on. So when engine running look at ammeter to see charging or discharging when not running look at battery voltage less than nominal in this case 24v.

[whiic]

Usually, you will see less than nominal battery voltage the more amp draw you'd have on the battery without engine running and generator on. So when engine running look at ammeter to see charging or discharging when not running look at battery voltage less than nominal in this case 24v.

I don't really get what you're trying to say. Or more specifically, I don't get why stuff like power cell's internal series resistance is relevant to this. I think series resistance is modeled properly, i.e the more amps you draw from the battery (when generator is OFF), the more voltage drops (but also partially recovers if the current is reduced again).

Also, early Spits had a 12 volt system, not 24 volt. But that's a technicality.

____

Originally I thought the increase of current draw wasn't even battery charge. I thought that the increase of amps was due to increase of volts due to formulas: I = U/R (current = voltage / resistance), where R can be assumed to be roughly constant (although heating can cause it to increase in most resistive components). Thus, if bus voltage is increased then current though electric devices would also increase.

...but then I noticed current draw drops to normal after some time, so the phenomenon had nothing to do with increased voltage on the bus. I was only about battery recharging current ...but as noted in opening post, the way it's displayed on the ammeter gauge just makes no sense regardless where the ammeter is located.

I know this is a very minor bug and while it may apply not just to Spitfire but also P-40 and P-51D, the buggy code probably won't affect the in-development GA planes because they usually have bi-directional ammeters that clearly show discharge / recharge rates to battery (and do not measure total power consumption at all... unless you turn off the generator). The fact that the ammeter is one-directional on the warbirds give a hint that it's not even supposed to measure recharge/discharge of the battery, but rather power consumption of the devices. It would make most sense if the ammeter was located between [generator + battery] and [bus] than the other two alternatives in the first post. If it was located between [generator + battery] and [bus], the ammeter wouldn't show battery recharge current as it does now.

EDIT: "not just to Spitfire but only P-40 and P-51D": only -> also
EDIT: "series resistance if modeled properly": if -> is

[francesco.doenz]

you can find the electrical circuits in the A.P.1565A publication, vol 1, sect 6 chapter 1.
I tried unsuccessfully to attach a jp image of this diagram to my reply....and unfortunately I am incompetent to read these diagrams....

[Gypsy Baron]

AS I recall from beta, the electrical system was thoroughly researched and the area in question
was discussed and found to be accurate. That being the case, there is no 'buggy code'.

I'd have to dig back in the archives a couple of years to find the relevant discussions and
electrical system diagrams and I just don't have time to do that now.

Perhaps Killratio can clarify this, if he is so inclined.

[whiic]

AS I recall from beta, the electrical system was thoroughly researched and the area in question
was discussed and found to be accurate. That being the case, there is no 'buggy code'.

I trust that you've done the research properly and know where the ammeter should be.

You may even have had input from people who know how the ammeter reacts to turning generator ON/OFF. The problem is that turning the generator ON will not just start to recharge the battery but ALSO bump up the voltage and due to increased voltage make every (non-voltage-regulated) electric device consume a higher current. This could have been mistaken as battery recharge showing on the ammeter as testing the real life system would produce practically identical reactions on the ammeter.

Basically, what I'm saying is that increased amperage is expected when generator is turned ON... but the amperage should not return to a lower level when battery is fully charged. That is for most scenarios, the ammeter functions as expected but for different reasons than is in the code. Battery recharge rate cannot have anything to do with it.

[CAPFlyer]

The ammeter is working correctly. The gauge is actually a "load meter" and does not differentiate between flow in or out, only total load on the system. When all other electrical systems are off, the meter will show the charging demand by the battery (about 2 amps). As you add load, it will show the total load. This is used to ensure you are not overloading the bus and to check that individual systems do not have dead shorts that can cause your electrical system to overload. So, if you know how much each system should draw, then when you switch it on, you can take the before and after values on the ammeter to determine if that system is working, not working, or shorting.

[whiic]

The ammeter is working correctly. The gauge is actually a "load meter" and does not differentiate between flow in or out, only total load on the system.

Well, the problem is how we define "the system".

If you include battery as part of the system which "consumes", rather than which "supplies" power, then you would actually see charging current as part of "system load" (i.e load on the generator)... but the result would be that the ammeter would show exactly zero amps if you turn on devices while generator is OFF, because both the battery and the power requiring component would be connected to each other WITHOUT current ever passing through the ammeter.

[CAPFlyer]

Okay, I guess I wasn't clear. The gauge labeled "Ammeter" is *NOT* an ammeter. It is a loadmeter. Loadmeters do not measure directionality of load, only that there is one. The loadmeter is attached to the bussbar and not the battery so all load shows as POSITIVE. So, if the battery is the only thing live on the bus, the load will be 0. The moment you turn something on, then a load will be shown. If you start the engine, turn on the generator, run up the revs to get the field to engage, and turn off all other electrics, the load shown will be load demanded by the battery to charge. You determine if the generator is working by looking for a voltmeter reading of 14+. I tested the ammeter behavior today before making my reply and it is working how I described and is correct for the airplane and its DC system.

Sent from my SAMSUNG-SGH-I747 using Tapatalk 2

[newblackgold]

I may have an answer for you. I was typing up a more complex response when I stopped to think, it all depends on the type of ammeter.

Certain ammeters show the amount of current in absolute terms, but a battery ammeter only shows the net result. Some ammeters show the current on one circuit, others can show the combined current of many. You can get pretty creative with the circuitry.

A simple zero-center ammeter. It has one in and one out lead, and reads amps that travel between. It has a magnet to hold the needle at zero and electrical current deflects this needle away from center, the more current, the more deflection. This would show a charging or discharging current. You could say a traditional ammeter is "half" of this.

So, you're right in that you can only read battery output, or generator output, but not both, with this kind of ammeter.

I'd have to see the electrical diagrams to see what kind of ammeter a given plane may have, but if it has two separate in's and two separate out's, then it's an gauge that combines two signals for a net result. I know of certain cars which use such gauges.

The simulation implies a two signal ammeter. The leads would be placed in areas on the circuit that only have current of one direction under all circumstances. Reading the current on the N sides of the battery and generator separately would give this result in a traditional system.

Magnet holds needle on zero. One lead placed near the generator N would pull the needle to the P side (since current in that direction means generator output which is always P), and the battery N would pull it to the N side (since electrons moving in this location would mean battery discharge.) The movement of the needle is only based on polarity and you can get this effect by reversing one side. The end result would be the net effect. Every electron that moves must stop somewhere. For every electron that leaves one side of the battery or generator, one must appear on the other side. By covering both N's (or P's) of a battery/generator circuit, you accomplish the intended function of the "ammeter." This is actually two ammeters within the same gauge and would appear on an electrical diagram as two ammeters.

This type of ammeter would read zero with a charged battery, regardless of load. It's not terribly useful, and only shows battery charging status, like on a car.

You can do the same thing with two positive leads or two negative with the same gauge. Where two separate circuits could pull the ammeter a certain amount in the P direction. It would show the raw amp output for all devices, as well has battery charging, and is useful for determining circuit health, since you can switch off the battery and see what happens to the electrics and the gauge.

I quickly fooled with the mark I, and it appears to be of the above type that shows the combined current output of the generator and battery. It really, really depends on the circuitry. I guess calling the gauge an "ammeter" is kind of confusing since it could technically be two ammeters, which make all sorts of wizardry possible.

But to hopefully make you feel better, yes, your logic is right, but planes are very complex machines and without knowing something as simple as what kind of ammeter it has, or even the electrical diagram, there's no way to know if the simulation is right or not.

Put it this way, from everything I've seen of A2A's accusim planes, the electrical systems appear to behave in a logical and electrically possible manner. I've never felt they were incorrect, but I'd have to see a diagram to know.

[newblackgold]

The accusim B17 is pretty complex in the battery and generator aspects compared to A2A's other offerings, and I've found it to work properly based on voltage, amps, generator voltage, and battery voltage. Just think of a "loadmeter" as a complex ammeter that reads amps from different sources and gives the total output without respect to battery charging. In this case, all output, including that for battery charging, would show as a load and thus a positive deflection of the needle.

[whiic]

you're right in that you can only read battery output, or generator output, but not both, with this kind of ammeter.

I'd have to see the electrical diagrams to see what kind of ammeter a given plane may have, but if it has two separate in's and two separate out's, then it's an gauge that combines two signals for a net result. I know of certain cars which use such gauges.

The simulation implies a two signal ammeter.

That's what I thought, but I also thought it's too complex and totally useless to have on a plane that doesn't even have a switch to disconnect batteries (at least not inside the cockpit). If you noticed something very odd with your battery (like it's shorting out), there's nothing you could do with it in a Spitfire... thus there's not reason for pilot to be aware of the increased amperage between generator and battery. (You can verify generator's proper functioning and generators capability to recharge the battery from the voltmeter.)

I thought it would make sense to connect generator and battery to each other unmetered, and put a single one signal ammeter from the [generator + battery] combo to the bus. It would basically include all load on both battery and generator powered operation EXCEPT battery recharge rate... which is totally useless thing to know for the pilot. After all, battery recharging was a regular maintenance task for the ground crew. They have a way better chance to tell if there's anything wrong with the battery.

This does not however prove my intuition right. If it indeed has a two signal "ammeter" (two ammeters sharing one gauge) then it is that way, even if I deemed it totally pointless to have such a thing installed.

The leads would be placed in areas on the circuit that only have current of one direction under all circumstances. Reading the current on the N sides of the battery and generator separately would give this result in a traditional system.

"N" as in "negative"? Because batteries sure don't have a North pole, like magnets. I think your logic fails... thinking the current is only one-directional regardless whether you discharge or recharge the battery. Obviously they are in different directions regardless whether you measure (+) or (-) terminal of the battery.

Negative currents however are not a problem with moving iron ammeters that use stationary coil and a moving iron core (rather than stationary permanent magnets and moving coil). They don't care about directionality of current. The fact that the gauge is non-linear also implies Spitfire may have a moving iron ammeter.

However, if you were to wind up several coils to move a single iron core in a moving iron ammeter, you would have to start to think about the directionality. The core would react to result magnetic field in the same way regardless of the direction but if the fields from two coils cancel each other out, the net field would be zero rather than twofold making a big difference.

I still don't know where I'd take the signals to make a good "loadmeter". If I take one from battery and one from generator, I get battery load when generator OFF, and I get generator load when generator ON... except that battery recharge rate shows up twice as high on the ammeter because the same current passes through two coils rather than one.

If I chose one to battery and one to bus, I get proper amperage when generator ON, including the recharge current, but when generator OFF, I would see ALL amperage of electric devices on the bus as twice as power hungry because everything would pass through two coils rather than one.

If I chose one to generator and one to bus, I would get proper amperage when generator OFF. I would also get proper amperage for battery recharge rate... but all current from generator to bus would still be twice as high.

So I don't really see a simple "wind two coils instead of one" solution to actually solve anything. I only see it making things worse, especially around the intermediate rpm range when generator is just about to kick in. That's because in order to make battery and generator inputs to add up rather than substract, you'd have to wind them the other opposite directions: when generator is ON (current is positive), battery is recharging (current is negative). But when you have intermediate range, you may have generator supply some insufficient current, and the rest being supplied by the battery... except the opposite winding of the coils would make the currents SUBSTRACT rather than add up on this scenario.

A two signal (i.e four terminal) ammeter would produce totally erratic readings at low rpm and generator ON. At least if you want it done simple and without switching circuitry.

[newblackgold]

I thought it would make sense to connect generator and battery to each other unmetered, and put a single one signal ammeter from the [generator + battery] combo to the bus. It would basically include all load on both battery and generator powered operation EXCEPT battery recharge rate... which is totally useless thing to know for the pilot. After all, battery recharging was a regular maintenance task for the ground crew. They have a way better chance to tell if there's anything wrong with the battery.

They can suddenly go bad, or be damaged. If you were in the air (in anything) wouldn't you want to know if your battery was bad/overheating even if you could not turn it off? It would certainly effect every decision you make. Knowing the battery is charged and healthy would effect every decision all the same.

The generator may be damaged or stop working, so it would give you peace of mind to know your battery was there if you needed it for communications and whatnot. Similarly, you'd know the generator is there in case of a sudden battery problem. I don't know what kind of batteries they used but batteries are traditionally very sensitive to vibration and any G force other than down.

This does not however prove my intuition right. If it indeed has a two signal "ammeter" (two ammeters sharing one gauge) then it is that way, even if I deemed it totally pointless to have such a thing installed.

That depends on how it was built. During that era things were built with whatever was on hand, so if all you have are these expensive ammeters, why let your shortage of the cheap ones slow down production when the county is at stake?

Put it this way, is the way the meter was implemented in the spitfire ideal? I don't know. But how it is now, it fulfills all it's functions all the same regardless of the pilot's ability to do anything about what it reads or it's cost compared to simpler solutions.

"N" as in "negative"? Because batteries sure don't have a North pole, like magnets. I think your logic fails... thinking the current is only one-directional regardless whether you discharge or recharge the battery. Obviously they are in different directions regardless whether you measure (+) or (-) terminal of the battery.

You're thinking too hard. I was using N and P because personally I think it's a little easier to read when near other text, and N and P is generally how cables are marked (in cars) in addition to color or stripe.

I meant that current can be one directional depending on the circuit. Even a battery may have negative voltage and operate backwards. (poorly) All I meant was with complex systems you have to be careful of polarity skewing the needle in the incorrect direction.

I'd have to see the diagram, but I doubt the meter is actually reading the current because then the huge wire in question would have to be routed to the meter itself. So there's probably an ammeter or two somewhere producing a voltage signal, which is deflecting the needle.

You'd pick points on the diagram which do not count the same current twice.

I still think you're thinking too hard. There's wizardry that can produce all matters of results. For example, you could have several ammeters powering the same gauge, but only one is operative at a time, switched with the generator switch, or electrically with voltage, ect...


You're right in your basic thought but it's all moot without the actual diagram, and I think my point is, how the gauge is currently reading IS POSSIBLE, it's just whether or not the plane was wired that way, and honestly, could vary from plane to plane.

They seem confident it works properly, which is good enough for me. Dig out a spitfire electrical diagram and then you will have your answer.

[whiic]

I thought it would make sense to connect generator and battery to each other unmetered, and put a single one signal ammeter from the [generator + battery] combo to the bus. It would basically include all load on both battery and generator powered operation EXCEPT battery recharge rate... which is totally useless thing to know for the pilot. After all, battery recharging was a regular maintenance task for the ground crew. They have a way better chance to tell if there's anything wrong with the battery.

They can suddenly go bad, or be damaged. If you were in the air (in anything) wouldn't you want to know if your battery was bad/overheating even if you could not turn it off?

I'm not sure if I'd want to know it but I'm pretty sure it would be only harmful if I knew it. That's why many modern fighter jets deliberately hide fault status of things that either don't require immediate action or cannot be dealt with. Knowing something bad is going to happen will only increase stress level of the pilot if there's nothing he could do to rectify it. As Spitfire has no battery switch, there's absolutely nothing to be done.

So, IMO, don't meter the battery recharge rate. If your battery is boiling, pilot does not be aware of it. I'm pretty sure that the cockpit is well ventilated enough to flush out the hydrogen gases that form from a faulty battery so the risk of a hydrogen explosion within the cockpit is very small.

It would certainly effect every decision you make.

That's why pilot should not be aware of it. If he can't do anything to it but it would still affect his performance, knowing it will only do harm, preventing him from focusing on his mission.

I'd have to see the diagram, but I doubt the meter is actually reading the current because then the huge wire in question would have to be routed to the meter itself. So there's probably an ammeter or two somewhere producing a voltage signal, which is deflecting the needle.

Could just be a "resistor" between battery/generator and bus. If you have high enough a current, even thick copper wiring will have a measurable voltage loss across it's length, hence wiring much thinner signal wires to the beginning and the end of a copper wire in which all power goes through, you can direct the same voltage to the ammeter which usually has a much higher internal resistance.

You'd pick points on the diagram which do not count the same current twice.

That's basically the problem. I don't think there is two such points.
If you have battery and generator metered, recharge current passes through both.
If you have battery and bus metered, generator OFF power consumption is counted twice.
If you have generator and bus metered, generator ON power consumption is counted twice.

Any way you put it, it crashes to epic fail.

You would need a switching circuit of some sort. Diodes, solenoids, something.

I still think you're thinking too hard. There's wizardry that can produce all matters of results. For example, you could have several ammeters powering the same gauge, but only one is operative at a time, switched with the generator switch, or electrically with voltage, ect...

Yeah. Basically. The only questions would be: is it worth it, and did they do it anyway?

Because I'm kinda reluctant to accept that Brits would bother with complex electronics. They are, after all, the people who still in 70's built cars that didn't have a single f'ing fuse in it. Short-circuit ANYTHING on it and the car could set afire from it! (Yeah, I own one of those cars. One that hasn't burnt yet. Touch wood.)

...and it's probably better I don't even mention Lucas.

You're right in your basic thought but it's all moot without the actual diagram, and I think my point is, how the gauge is currently reading IS POSSIBLE, it's just whether or not the plane was wired that way, and honestly, could vary from plane to plane.

Agreed. With enough switches, it'd be possible even with old day's technology. It's a question of "did they" rather than "could they". I'd like to see comprehensive wiring diagrams of Baby Spit. I'm just not sure if I'd find one by just Googling around.

[CAPFlyer]

And you guys are both ignoring the FACTS that I have now presented twice and continue down a path of theory and assumption that is based on absolutely no actual knowledge of the plane, the system, or (from what I'm reading) any general understanding of how aircraft systems actually work, much less 12V/14V DC electrical systems in general.

1) You are ignoring that while there is not a switch to disable the battery, there are ways to disconnect it from the loop.
2) You are ignoring that the LOADMETER that is present on the Spitfire Mk.I has absolutely nothing to do with the battery charging or discharging and instead the load on the bus as a whole and the system as a whole to ensure it is not being overloaded or given components not working that can affect the ability of the aircraft to operate in certain conditions.

The system is not "complicated". It is either placed on the bus bar itself or between the generator and bus bar. It has one input and one output and simply shows the load being placed on the generator or bus by the components in use. In this way, it is a SINGLE DIRECTION system, simply showing the flow of current through the bus.

Here's a few references for you guys -

http://aviationglossary.com/loadmeter/

http://aviationglossary.com/ammeter/

http://ma3naido.blogspot.com/2007/11/ai ... ystem.html

http://www.nflite.com/ChargingSystem.html

http://www.microair.com.au/admin/upload ... ystems.pdf