Cranking (Starter Motor) Current - PA28
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Cranking (Starter Motor) Current - PA28
I am trying to find out what the nominal current draw is for a PA28 (IO320 engine) for the starter motor, assuming it is under normal mechanical loading. I want to know this for the purpose of building up a (lightweight) battery pack for "emergencies."
A few weeks ago our a/c battery was flat, I connected a separate 12V supply (a heavy Pb-Acid battery) and was surprised how rapidly the prop rotated, suggesting the draw was much less than the 200A or so I guessed it may be. At a rough guess from this and judging by the a/c battery cable gauges it is probably nearer 100A.
Help appreciated,
Fuji
A few weeks ago our a/c battery was flat, I connected a separate 12V supply (a heavy Pb-Acid battery) and was surprised how rapidly the prop rotated, suggesting the draw was much less than the 200A or so I guessed it may be. At a rough guess from this and judging by the a/c battery cable gauges it is probably nearer 100A.
Help appreciated,
Fuji
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You need to get the data sheet for the motor.
They vary a lot. I have seen figures from 100A (traditional type) to 260A ("lightweight starter").
You can imagine the life of the starter relays is pretty variable too
They vary a lot. I have seen figures from 100A (traditional type) to 260A ("lightweight starter").
You can imagine the life of the starter relays is pretty variable too
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Fuji
Rather than waste time with starter motors try a little research in the Piper SB's.
You will find one that recomends the replacment of the old starter motor cables with copper items, the result is spectacular ! The cranking speed will almost double and end all your starting problems.
It would seem that most of your batterys electrickery is lost in the high resistance of the old aliminium cables.
You will find one that recomends the replacment of the old starter motor cables with copper items, the result is spectacular ! The cranking speed will almost double and end all your starting problems.
It would seem that most of your batterys electrickery is lost in the high resistance of the old aliminium cables.
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And as most of the current is flowing around the outer layer of cable,they could be hollow as well,a weight saver.
Sorry just checked and it's AC only,DC is throughout the cable
Should have Googled it first
Sorry just checked and it's AC only,DC is throughout the cable
Should have Googled it first
Last edited by Lister Noble; 10th Feb 2010 at 20:25.
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Stickandrudderman
There was a non mandatory Piper SB some years back to replace the factory fitted battery & starter cabels with copper items (no I can't remember the SB number! )
The effect of new cables is dramatic increasing the cranking speed by 100%
The effect of new cables is dramatic increasing the cranking speed by 100%
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Many booster units sold in the car market would work in aviation too. The type that boost, or recharge, the vehicle battery are low current and simply transfer enough charge into the main battery to get a start. For instance, the Black & Decker one is claimed to transfer 7A for 15 mins, = a bit less than 2AH. This is sufficient to start the engine if the current is 200A and cranking time less than 30 secs. Of course the 200A only flows from the aircraft's battery, not the booster unit.
Moderator
I suggest a different approach...
Presuming that you are using a properly maintained battery, specified for that aircraft, thay battery is sufficent to start that engine, in appropriate conditions, using the proper technique.
If the battery is not holding or taking the necessary charge, maintenance activity is appropriate. If the engine is hard to start, perhaps it needs a maintnenance look. If the pilot technique is not adequate, well...
If the aircraft is too cold for a normal start (cold soaked at freezing or cooler), it should be safely and effectively preheated (takes an hour minimum to do properly).
If the battery has been run flat with repeated attempts to start, you are very near to damaging the stater motor by overheating it, and a wait of at least 30 minutes (time to preheat!) will be required to allow it to cool. If you have a good battery, you can ruin a starter before you discharge the battery, by not allowing it to cool. One published start cycle for a GA engine is: 30 seconds cranking, 30 seconds cooling, 30 seconds cranking, 5 minutes cooling, 30 seconds cranking, 30 minutes cooling.
Certainly, a small start cart is nice to have around (though you'll have to source that funny Piper plug for the cable if you're making it), but you really should not need the start cart, other than for protracted operation of the aircraft electrical system on the ground.
I am guilty, in my ealier days, of wanting to fly so badly, I boosted a dead aircraft battery to get it started. Knowing what I know now, I would not do it without allowing time to cool things down. During this time, a normal battery charger would get you going. If no plug in is available, then yes, a start cart boost will be required.
Pilot DAR
Presuming that you are using a properly maintained battery, specified for that aircraft, thay battery is sufficent to start that engine, in appropriate conditions, using the proper technique.
If the battery is not holding or taking the necessary charge, maintenance activity is appropriate. If the engine is hard to start, perhaps it needs a maintnenance look. If the pilot technique is not adequate, well...
If the aircraft is too cold for a normal start (cold soaked at freezing or cooler), it should be safely and effectively preheated (takes an hour minimum to do properly).
If the battery has been run flat with repeated attempts to start, you are very near to damaging the stater motor by overheating it, and a wait of at least 30 minutes (time to preheat!) will be required to allow it to cool. If you have a good battery, you can ruin a starter before you discharge the battery, by not allowing it to cool. One published start cycle for a GA engine is: 30 seconds cranking, 30 seconds cooling, 30 seconds cranking, 5 minutes cooling, 30 seconds cranking, 30 minutes cooling.
Certainly, a small start cart is nice to have around (though you'll have to source that funny Piper plug for the cable if you're making it), but you really should not need the start cart, other than for protracted operation of the aircraft electrical system on the ground.
I am guilty, in my ealier days, of wanting to fly so badly, I boosted a dead aircraft battery to get it started. Knowing what I know now, I would not do it without allowing time to cool things down. During this time, a normal battery charger would get you going. If no plug in is available, then yes, a start cart boost will be required.
Pilot DAR
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Thanks for all the replies. I think the reason that the battery was flat was because the a/c had been used for an infrequent number of (short) flights over several months. The battery would therefore have become depleted and then been left like this over this timeframe. I think there were a few occasions where the engine was cranked for longer than usual due to inadequate priming - it fires pretty quickly if its given about 6 "squirts but is difficult otherwise. So even, say a 2 hr flight following a protracted start which had depleted significant charge, would not return it to a fully charged state. Of course once a Pb-Acid battery is in a low state of charge and then left like that, it will permanently degrade quite quickly - that's the nature of this type of battery. I need to confirm though that the alternator is regulating at the correct voltage necessary for charging, ie about 14V, if it is less than about 13V or so then it will take virtually no charge current (even if flat) but the avionics etc will work perfectly thus disguising the source of the problem.
My backup battery was attached to the a/c battery - the starter was then able to crank the engine perfectly (in fact surprisingly fast) so this proves the link from the a/c battery to the starter is good.
The desire to have a portable "emergency" backup stemmed from some of my flying holidays where the a/c had been parked up for several days, for "peace of mind" reasons. The problems I had recently, reiterated the usefulness of having a relatively lightweight portable supply of power if for some reason one was greeted by a flat a/c battery when needing to return from somewhere. I already carry a couple of Li batteries which I normally use to power other equipment (my Zaon XRX, GPS moving map PC and a few other bits), these are rated at 80A each for 3 minutes use (4 x 3.6V cells) and weigh about 700 grammes per pack. Their voltage can easily exceed 15V off load (too high for a 12V system) but it is not difficult with modern power electronic semiconductors to build up a small converter to drop this to a regulated 12V at a few hundred's of amps (I specialise in power electronics!).
Pilot DAR, I know what you mean about overheating starter motors! In my earlier days I tried to get my old car the last hundred or so metres to home, up a slight incline using the starter, following a breakdown. The soldered connections to the brushes in the motor failed.
Rich
My backup battery was attached to the a/c battery - the starter was then able to crank the engine perfectly (in fact surprisingly fast) so this proves the link from the a/c battery to the starter is good.
The desire to have a portable "emergency" backup stemmed from some of my flying holidays where the a/c had been parked up for several days, for "peace of mind" reasons. The problems I had recently, reiterated the usefulness of having a relatively lightweight portable supply of power if for some reason one was greeted by a flat a/c battery when needing to return from somewhere. I already carry a couple of Li batteries which I normally use to power other equipment (my Zaon XRX, GPS moving map PC and a few other bits), these are rated at 80A each for 3 minutes use (4 x 3.6V cells) and weigh about 700 grammes per pack. Their voltage can easily exceed 15V off load (too high for a 12V system) but it is not difficult with modern power electronic semiconductors to build up a small converter to drop this to a regulated 12V at a few hundred's of amps (I specialise in power electronics!).
Pilot DAR, I know what you mean about overheating starter motors! In my earlier days I tried to get my old car the last hundred or so metres to home, up a slight incline using the starter, following a breakdown. The soldered connections to the brushes in the motor failed.
Rich
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Just to try and add to this already well-informed discussion,
Some 40 years ago, the UK electricity generators were experimenting with alloy cables. The major problem was the layer of oxide which forms immediately in contact with air (yes! even freshly-polished metal has a layer) Resistance built up rapidly in mechanical joints and even a good, mechanically-sound crimped connection would go high-resistance due to differential expansionand soft-alloy deformation.
Many automotive starters tried alloy field-windings ,fairly successfully - there are now soldering-fluxes which make it easy to affix the copper-braids for brushes and brass terminal posts to the alloy.
I'm sure the Piper wiring would have benefitted from soldering at all mechanical-joints.
Lead-acid batteries are liable to a rise in internal-resistance...this restricts the current and hence you get a "lazy" starter.....a blow-through with an airline can revive a well-used starter by removing the layer of copper-impregnated carbon-dust which tends to coat the innards and , i suspect,track some current to earth.
A standard Lead Acid 12V battery needs 14.2 V regulation from the alty....any more and the acid would boil and at a minimum, frequent topping-up would be required. (Aircraft alloy and sulphuric acid fumes are not good bed-fellows! ).....unfortunately, at this voltage, a deep-charge is only just starting,- any battery that's had a heavy discharge should be externally charged as soon as practicable....a battery that's KEPT fully-charged will last a lot longer......typical GA scenario of lying idle to self-discharge (they all have internal leakage) then a bashing at the weekend (heavy discharge followed by the alty banging in a heavy surface-charge) to be followed by another week of inactivity, is a sure recipe for sulphation, reduced-capacity and short-life.
Of necessity I've left a lot out...agreed, copper-cables are a good, quick fix. all connections should be scrupulously cleaned to BRIGHT metal and a smear of petroleum jelly before remaking the joints will ensure the metal-to metal contact remains sound.
Average starter lock-draw (at the point where the prop stops dead at TDC...would be ~ 180 amps...the average ,~half to 2/3 that.
hope someone finds some of this informative/useful.
Some 40 years ago, the UK electricity generators were experimenting with alloy cables. The major problem was the layer of oxide which forms immediately in contact with air (yes! even freshly-polished metal has a layer) Resistance built up rapidly in mechanical joints and even a good, mechanically-sound crimped connection would go high-resistance due to differential expansionand soft-alloy deformation.
Many automotive starters tried alloy field-windings ,fairly successfully - there are now soldering-fluxes which make it easy to affix the copper-braids for brushes and brass terminal posts to the alloy.
I'm sure the Piper wiring would have benefitted from soldering at all mechanical-joints.
Lead-acid batteries are liable to a rise in internal-resistance...this restricts the current and hence you get a "lazy" starter.....a blow-through with an airline can revive a well-used starter by removing the layer of copper-impregnated carbon-dust which tends to coat the innards and , i suspect,track some current to earth.
A standard Lead Acid 12V battery needs 14.2 V regulation from the alty....any more and the acid would boil and at a minimum, frequent topping-up would be required. (Aircraft alloy and sulphuric acid fumes are not good bed-fellows! ).....unfortunately, at this voltage, a deep-charge is only just starting,- any battery that's had a heavy discharge should be externally charged as soon as practicable....a battery that's KEPT fully-charged will last a lot longer......typical GA scenario of lying idle to self-discharge (they all have internal leakage) then a bashing at the weekend (heavy discharge followed by the alty banging in a heavy surface-charge) to be followed by another week of inactivity, is a sure recipe for sulphation, reduced-capacity and short-life.
Of necessity I've left a lot out...agreed, copper-cables are a good, quick fix. all connections should be scrupulously cleaned to BRIGHT metal and a smear of petroleum jelly before remaking the joints will ensure the metal-to metal contact remains sound.
Average starter lock-draw (at the point where the prop stops dead at TDC...would be ~ 180 amps...the average ,~half to 2/3 that.
hope someone finds some of this informative/useful.
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Its difficult to measure the current but the B&C link earlier shows what voltage you should find at different places and is the best way to diagnose the system. At least 10V at the battery while turning the starter and at least 9V at the starter terminal.
The best aircraft battery chargers are the Optimate type as they charge the battery and then drop the voltage to a maintain level so can be left in place all the time you are not flying. They also can cope with sealed batteries which some aircraft (and motorcycles have).
ZA
The best aircraft battery chargers are the Optimate type as they charge the battery and then drop the voltage to a maintain level so can be left in place all the time you are not flying. They also can cope with sealed batteries which some aircraft (and motorcycles have).
ZA
