high generator load after power up

[chr]

Good day for all
just considering last time why there is a high load on generator after start up which is than decresing to it’s normal operating rate ?
After engine startup you can see gen load ex. 300 Amps , 290 , 280 etc. down to let’s say 80 Amps (normal operating rate ) but what is the reason that load is high at the begining ?
Is it trying to recharge battery quickly after huge drain for engine start or electrical system is building up some heat which causung it’s resistance go down and load decreasing ?
Any ideas ?
Regards

[Ascend Charlie]

trying to recharge battery quickly after huge drain for engine start or electrical system is building up

Yup. Plus you are turning on radios, lights, air con, surround sound system, massage seats....

[gulliBell]

..Plus you are turning on radios, lights, air con, surround sound system, massage seats....
I know all those switches except for the massage seats, I'm still looking for that one...

[Twist & Shout]

I know all those switches except for the massage seats, I'm still looking for that one...

Every machine I fly has masochistic seats. Can’t turn them off though.
:)

[fitliker]

The load meter will give you a clue as to the health of the battery , the volt drop during start on some engines can be a limit and too big a drop might indicate time to replace the battery or abort the start as it may not be enough power left in the battery to do a healthy start on some turbines .
Batteries can be expensive , but replacing them before they get too weak can save expensive wear on other parts .
Cold can kill a battery , left to long in the cold and it may need charging . Never leave a battery on a cold concrete floor , it will kill it .
Paying attention during a start can tell you a lot about what is happening to your engine and accessories .

[roscoe1]

When you start an engine smoke is released from the aircraft wiring harness through the smoke bleed valve and out the exhaust pipe. It takes a while to generate more smoke to replenish the wiring supply. It takes electrical energy to produce, thus the higher load. The smoke is necessary. In the event of a wire breach, it is released in the form of " does that smell like electrical wiring to you?" It's like the canary in the coal mine. In the old days, before capton wiring, the Lucas electrical company sold supplemental smoke for refilling wiring in British cars. I know it sounds very strange so I'm surprised your instructor pilots never explained this to you.
https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/400x300/smokekit2_bbf762ee7f81679f24e2b45d8f15f22ba8908e2e.jpg

[Thud_and_Blunder]

What a shame this website doesn't have a "Like!" button... ;)

[Self loading bear]

Great to see that British industry still support its customers with this certified aftermarket spare part supply.
I was thinking this to be fake news but it proves this spare part is readily available via various internet channels. Delivery might be a bit extended in these day running up to Christmas but definitely much shorter than spareparts from for instance Italian heli manufacturers, Schweizer etc.

Lucas is currently in the process of reverse engineering the notorious complicated Roberson Kratos screen adapter. Once successful an STC is expected within months. Dick Smith Electronics Australia is already pre-positioning a large number of dosis by deep cooled air freight.

[roscoe1]

Ok, I've had my fun and the OP has had to take some ribbing. I hope no offense. A couple of things. Yes, your load meter reads high as soon as you turn on tthe generator after a start because it is recharging the battery due to the current drain from starting. Your flight manual should probably give you a voltage reading from the volt meter that is, more or less, a threshold lower number that if it drops down to this point when you hit the starter button it would not be wise to continue with the start. No harm with piston engines as you just end up with a dead battery if it won't start but if a turbine isn't spooled up to produce high enough air flow by the starter you may get a hung, or worse hot start, if you mismanage it. Normally, you aren't turning on any radios etc., until the load meter shows the battery has recovered to some percentage. The " drop down" in voltage and the length of time it takes a battery to recover to what ever the book says is good to go does tell you some about the condition of the battery. Also, I would never turn down an external power start if it was conveniently available. My policy, not mandatory.

As for putting a battery, or rather not putting a battery, on a concrete floor.... this would be ill advised if you had a lead acid battery that was made in the 1950s or earlier when battery cases were made out of materials that included rubber, tar and who knows what else that insulated but developed small cracks and became porous, thus allowing the battery to self discharge due to external dampness. Not so with battery construction today. Since I am an old fart, even though I know this to be true, I cannot put a battery on the floor without some wood under it. Go figure. BTW, you can actually make your own replacement smoke so you don't need to call maintenance when it escapes from the wires. Under no circumstances use smoke from, for example, a Bell product in an Airbus machine. And for heavans sake never use Russian smoke. Their smoke is much thinner and is for use in unimaginably cold conditions only. Anybody have a few gallons of rotor wash ( and don't send me any of that prop wash junk)? Also in need of 300 feet of flight line.

[ShyTorque]

You might be up for a long stand.....

[Alpine Flyer]

I remember on the PT-6 or PW120 we had a limit fo the load meter to drop below the end stop before we could start the next engine.

[ivor toolbox]

And don't forget Russian smoke is treated for anti icing, and whatever you do...Chinese smoke is often a sub standard copy.

Ttfn

[Ascend Charlie]

The most expensive smoke is "Boss Smoke", only used for blowing up his @ss.

[EEngr]

The load meter will give you a clue as to the health of the battery , the volt drop during start on some engines can be a limit and too big a drop might indicate time to replace the battery or abort the start as it may not be enough power left in the battery to do a healthy start on some turbines .

I concur. The battery voltage might look OK once the generator has topped it off and it is running under normal load. But the high draw from a start can cause the voltage of an individual weak battery cell to collapse. And a low voltage battery (following a start) will draw more power from the generator until that cell (or several cells) have been brought back from near zero volts.

In addition to the battery, this condition can place added strain on the generator, having to supply a higher then normal current until the weak cells are topped off. A good mechanic should be able to load test the battery. Switching on electrical loads with no running generator and watching how fast the battery voltage drops.

[Ascend Charlie]

Some aircraft, such as the A109, had a warning against turning the GEN on when the load was still high, as you could snap the input quill to the generator.

[DuncanDoenitz]

I don't claim to know everything about batteries, but I am a recently-retired EASA Licensed (fixed wing) Aircraft Engineer. I'm not aware of a manufacturer-mandated in situ serviceability test, but I don't have Type Ratings on everything. The only way to definitively check the health of a battery is to remove it from the aircraft and perform a Capacity Check on the bench. This takes around 24 to 48 hours. If you're in any doubt about your battery's health, talk to your engineer/mechanic or your Continued Airworthiness Manager. A Capacity Check is part of all aircraft's ongoing Maintenance Schedule, but then, so is everything else that sometimes fails.

Simply checking the voltage of your battery either before or after engine start will not tell you its health. The massive current draw during engine start takes some time for the battery to recover, and the load-meter or battery-charging indicator willl corresponding show an initially very high current, falling off as the battery recovers; typically around a half-to-one-minute before the graph starts to level out. Your POH may include a minimum generator (engine) speed during this time to ensure adequate generator cooling, and should stipulate a maximum permissable charging rate (by implication, how much the battery has recovered from starting the first engine), before starting a second engine. Subsequent engine starts will further deplete your battery, and you may find that another limitation on battery charging current exists before take-off. Your POH will tell you how long you can rely on battery power after an airborne generator failure, but this assumes that the genny failed when you had a fully charged battery.

Another problem with a partially discharged battery is that engagement of electrical equipment with a high current draw may unexpectedly drop your bus-voltage below the minimum for some equipment. For instance, the DA42 had an issue where retracting the gear would cause the engine management system to drop off-line, leading to a double loss of engine power.

[ShyTorque]

I once arrived at an IFR equipped, twin engined helicopter which had a very much depleted battery due to certain unqualified people having “fiddled” with the systems for some time and subsequently not realising that plugging in an external power supply disconnects the aircraft battery from the system, rather than charging it... :ugh:

Having pointed out the situation, I was then told to fly said helicopter to a maintenance place to get the battery swapped for a good one. Bearing in mind that the engines were DECU only, with no manual backup and didn’t have their own generators and the cloud base was well below 500 feet, I made myself extremely unpopular by refusing. An engineer with a new battery had to be dispatched by road.

A double generator failure with a failed battery (or even a cooked battery due to overcharging in flight) could have found me with no flight instruments, no engine control, or a battery fire.

[212man]

Some aircraft, such as the A109, had a warning against turning the GEN on when the load was still high, as you could snap the input quill to the generator.
I'm being a bit thick. Can you elaborate? I know what the quill drive is, but don't get how the load required to recharge the battery would be so high - the high load occurs during the engine start

[Devil 49]

I once arrived at an IFR equipped, twin engined helicopter which had a very much depleted battery due to certain unqualified people having “fiddled” with the systems for some time and subsequently not realising that plugging in an external power supply disconnects the aircraft battery from the system, rather than charging it... :ugh:

Having pointed out the situation, I was then told to fly said helicopter to a maintenance place to get the battery swapped for a good one. Bearing in mind that the engines were DECU only, with no manual backup and didn’t have their own generators and the cloud base was well below 500 feet, I made myself extremely unpopular by refusing. An engineer with a new battery had to be dispatched by road.

A double generator failure with a failed battery (or even a cooked battery due to overcharging in flight) could have found me with no flight instruments, no engine control, or a battery fire.


I applaud your decision to NOT fly that aircraft under those conditions. I have read to many accident reports of aircraft flying to a maintenance facility- mechanical 'get-home-itis'.

I flew HEMS for 16 years and at one point, the SOP was to start with an external battery on dispatch to reach the patient in order 'have a fully charged battery available for the start on the patient transport segment'. The program had good maintenance and a regular battery replacement schedule.
Then, in the middle of the night at a remote improvised pickup-point, the weak battery failed, not having the amperage available to start the aircraft. There the pilot was, patient loaded, after months of 'first starts' on the battery cart and before the scheduled battery swap.
That may be the most adverse start of your shift, a cold soaked aircraft and a battery inactive for days, it may dismay the requesting agency if you've accepted dispatch and now another aircraft has to fly longer to get there- If one has a weak battery, the place to find it is at the base.

[ShyTorque]

I'm being a bit thick. Can you elaborate? I know what the quill drive is, but don't get how the load required to recharge the battery would be so high - the high load occurs during the engine start

Yes, but when starting the first engine it's generator isn't immediately online - the first high load is taken by the battery. As soon as the first engine's generator comes on line it will try to replenish the battery. If the second engine is then set to crank, the first generator may get overloaded because it's replenishing the battery and supplying a load to crank the engine.

The earlier Squirrels reputedly had a delicate quill drive to their starter/gennies. The generator switch wasn't selected on until after engine start was complete because in starter mode the quill drive is driving the engine. In generator mode the quill drive has a reverse load, i.e. the engine is driving the generator. The critical part was the sudden reverse load/torsion, caused by driving to being driven.

[212man]

Yes, but when starting the first engine it's generator isn't immediately online - the first high load is taken by the battery. As soon as the first engine's generator comes on line it will try to replenish the battery. If the second engine is then set to crank, the first generator may get overloaded because it's replenishing the battery and supplying a load to crank the engine.

The earlier Squirrels reputedly had a delicate quill drive to their starter/gennies. The generator switch wasn't selected on until after engine start was complete because in starter mode the quill drive is driving the engine. In generator mode the quill drive has a reverse load, i.e. the engine is driving the generator. The critical part was the sudden reverse load/torsion, caused by driving to being driven.

Normally the first engine started generator is brought online after the start sequence is complete, and there is a maximum current allowable before the second engine can be started (if using the first generator, rather than external power) stated in the RFM, e.g. "AMPS 1 Indicator ............check at or below 150 amps". I think this is what you were actually saying, but is not what Ascend described.

The second scenario is also accurate and is one reason why the GEN Switches are checked as being OFF in the prestart checks. Obviously all of the above only relevant for those types with a combined starter/genny - big aircraft typically use MGB driven AC Gennies and may also use pneumatic starters.

[ShyTorque]

212, As always, it's important not to over-generalise and to refer to the appropriate RFM. The RFM for the A109 requires the generator switches to be selected ON prior to engine start.
As for the other types, yes, I'm aware having flown an aircraft with only AC gennys for over ten years and another with an APU/air starters for four years.

[212man]

212, As always, it's important not to over-generalise and to refer to the appropriate RFM. The RFM for the A109 requires the generator switches to be selected ON prior to engine start.
As for the other types, yes, I'm aware having flown an aircraft with only AC gennys for over ten years and another with an APU/air starters for four years.

indeed, I’m aware of your experience and I was making my later comments to a wider less knowledgeable audience. However, your knowledge of the 109 procedures makes Ascend’s comment even more puzzling - if the switches are on during start, why is there a warning about turning them on after start? Plus, if the load is high, the gen must be on anyway, by definition (which is what prompted my question).

[Ascend Charlie]

It's 20 years since I flew the A109, perhaps the brain has turned to porridge?

[ShyTorque]

212, Yes, and if I've got the right bloke, I'm likewise aware of your past experience; however I was unsure when it seemed that you were telling me about other system types ;).

Having thought more about this, Ascend might actually be referring to the earlier 109's, i.e. A to C models, which are quite different animals with Allison engines as per the earlier Squirrel models (and those models fit into a different aircraft group these days; so I'm not qualified to talk about them). I'm inclined to think this because the max generator load on the later models (P&W engines), before cranking the second engine, is actually 160 Amps, rather than the stated 150 and that limit only appears in the "Quick Engine Start" checklist, which wouldn't normally be used on the first start of the day when everything is cold. Also, I've got an A109S RFM in front of me right now and I can't find any warning about turning the generators on after engine start.

[212man]

It's 20 years since I flew the A109, perhaps the brain has turned to porridge?

mine did ages ago!

[John Eacott]

Ascend Charlie is quite right: the earlier (Allison powered) A109s had a 1 minute period between starting the engine and turning on the Generator, for the reasons discussed :ok:

[212man]

Ascend Charlie is quite right: the earlier (Allison powered) A109s had a 1 minute period between starting the engine and turning on the Generator, for the reasons discussed :ok:
I guess in the absence of an ammeter?

[RVDT]

Older "classic" A250 powered aircraft had no current limiters apart from full "welly" from the Starter / Gen.

The battery would recover after a minute a so and the demand would be acceptable. VR only knows about V after all and they were for the most part analog.

I think from memory 355 F1's onward had current limiters for cross-gen start and earlier ones you could juice up the battery a bit but turn OFF the GEN for start of the second one.

Had one customer with an F who shall remain nameless that would forget on average about every 3 months - ping!

Modern ships have current transformers all over the place and electronic control.

[Ascend Charlie]

Ours was an A109A Mk II Plus Widebody, heavy as all 5h1t, lots of cast-iron instruments and such, and the C20R engines. And yes, we did have to wait before bunging on the generators. Both engines had to be started off the battery, couldn't bring one gen on line after the first to start the second.

[ShyTorque]

Ascend, thankfully technology has moved on. There aren’t many Allison powered 109s in common use in U.K. now but the “E” models and later are very abundant.