Cold mornings

[bushpilot]

Thanks for going to the trouble to dig up this info, SBF..

 

Brian - Ref your suggestion - you are pretty handy with things mechanical - so why do u think spinning it on the starter with mags off first helps? I would have thought that that would take the edge off the battery... It needs the full 12.8V to produce the 300rpm on crank, to start.

 

 

[facthunter]

Loss of starter amps. Bad earths and connections. To find them crank your engine cold for about 20 secs (don't start it) and then feel all terminals in the start circuit. Any crook ones will be warm. That includes a faulty solenoid. Most Jabs don't start well cold because there is not enough fuel getting through the choke circuit. If the jets have been opened out as per Jabiru instruction and the throttle is kept closed it should start. Nev

 

 

[Guest davidh10]

At the risk of repeating myself, It's the starter solenoid. Replace it with a quality one and be amazed.Mine starts first turn when it's -7 degrees now.

Stands to reason. If you've done all the other things, and a jump pack won't turn it well enough, then the current is going somewhere else.

 

In this case, I found it to be leaking to earth at the solenoid.

Surely you are kidding?

Even if it was only 10 amps going to earth through the solenoid, that would represent a power dissipation of at least 75 watts (assuming battery terminal voltage drops to 7.5V during cranking), or 100 watts at 10volts. The solenoid would be getting hot. A solenoid that "leaks" current to earth, other than just the actuating coil current, which should not be more than 1 or maybe 2 amps is clearly faulty.

 

The more likely issue is that the starter relay contact resistance is too high on the starter motor circuit and thus does not allow the starter motor to develop full power. This also would make the starter solenoid hot. Typical starter motor currents are hundreds of Amps. It does not take much calculation to realise that if you are to get 100s of amps at less than 12 volts, the total circuit resistance must be very very low. The battery has internal resistance, as does the solenoid, starter motor and the interconnecting wires. All these added together must be less than 0.04 ohms if the cranking terminal voltage at the battery is 8 volts and a current of 200 amps. Remember, because the battery has internal resistance, the terminal voltage will drop from 12 volts during cranking. In the days of cars having ignition coils, they were designed to run on 7.5 to 8 Volts and a series ballast resistor prevented over-current in normal operation, but was shorted out during cranking so the reduced battery voltage did not reduce the voltage available to the spark plugs.

 

 

[Jabiru Phil]

Hmmm - Winter has arrived and now our J230s dont like these cold mornings - even with all the recommended Jab factory mods - drilled choke jets (1.2mm), 19 thou plug gaps, earth wire and fully charged batteries. Even a 900 amp jump pack wont kick one on the 230s into life. Leave it til later in the day when air temp goes above 10 degrees and they both start just fine. Our J160 is fine all the time.Anyone had recent experience with overcoming 2 degree morning starts??

Chris,

 

I had the devil of a problem with my 230 for two years until I did all the mods and suggestions from these forums.

 

Change earth lead position

 

Iridium spark plugs

 

1.2 mm drill out jet

 

Different brand solenoid

 

Larger battery

 

Because I did most of these at the same time, it was impossible to tell which fixed the problem, however I think the drill out, larger battery and Iridium plugs were the main fixits.

 

Incedently I have NOT used the choke once since.

 

Phil.

 

 

[slartibartfast]

Surely you are kidding?

Actually no - I wasn't kidding (I'm sure there's a more diplomatic way to point out that I'm an idiot).

 

I was going by the symptoms.

 

The engine turned over poorly even jumping from a power pack.

 

Cold starting was very poor.

 

The earth return lead caught fire and melted.

 

Putting in a new solenoid of the same type got it going again, but still poor starting.

 

Fitting the aforementioned quality solenoid solved the starting problems completely.

 

The engine now turns over much faster and for much, much longer.

 

While turning over the engine to get oil pumping out the new hollow pushrods before completing reassambly, it probably totalled 3 minutes cranking.

 

2 weeks later without recharging the battery, it fired straight up.

 

You're no doubt right - I bow to your knowledge on the subject. It was probably initially poor contacts, then a leak to earth which melted the lead.

 

Replacing it with an identical but new unit didn't solve the poor starting. Fitting a better solenoid did.

 

I'd like to see Chris change nothing but the solenoid. If that fixes his problem too, we have a winner.

 

 

[Guest davidh10]

Actually no - I wasn't kidding (I'm sure there's a more diplomatic way to point out that I'm an idiot).

It was a rhetorical question.

I apologise if that is what you felt I was saying. It was certainly not intended in that light. I only ever try to be helpful.

 

The earth return lead caught fire and melted.

Wow! Sounds like some metal had come adrift inside and shorted starter terminal to ground.

 

 

[slartibartfast]

All good David. I realised it was just the inadequacy of the printed word - hence my mild retort.

 

I was serious about your superior knowledge though.

 

That's why I laid out the symptoms.

 

Hopefully Chris can prove the hypothesis.

 

 

[bushpilot]

This is now a brilliantly helpful thread; thanks guys for all your thoughtful suggestions.. The only reservations I have about trying an A/M solenoid is that we cannot change from factory 'approved' items when the a/c is used for training - which is all 3 of our Jabs.

 

But what I am really interested in is DavidH10's dialogue on electrical inputs, outputs and resistance; he clearly knows more about spark making than I ever will. Yet when I talk to the local LAME about how to check that all of these things are in order in our Jabs, I get a shrug. So, David, would u be good enough to provide some insight as to how the electrical performance and condition of a Jab motor (or I guess any motor) can be tested? I mean which instrument to use on which part of the system in which order and what readings are normal.

 

That has to be a better way than trying a heap of things and never knowing what actually fixed the problem....

 

 

[airangel]

If you have a jab that is a bit difficult to start in cold weather I have found that if you spin the engine with the starter and then turn on the mags it helpsBrian

On seriously cold mornings, tip a bucket of hot water over the crankcase. Dont laugh it worked for me every time

 

 

[Guest davidh10]

Chris;

 

I have no specific knowledge about Jabs. My comments were generic, however the starter motor and solenoid arrangement are pretty much the same on most engines. Presumably Jabiru can help out with some information too and if it turns out that the starter solenoid they supply as standard equipment is of low quality or perhaps under rated then if you go back to them with evidence, perhaps you can get them to change the build and thus avoid the issue with training aircraft having to be as per the manufacturer's specs. They could simply issue a Service Bulletin allowing a swap out with another specific part.

 

Anyway, I'm getting ahead of things.

 

Please excuse me for starting with some very elementary items, as I cannot tell who may read this post and what background knowledge they may or may not possess.

 

Caution: Unfused battery power can be dangerous and due care needs to be taken when working with the wiring attached to the battery. The risk from a battery that can deliver high current is not electrocution, but rather serious burns. Risks arise when jewelery, such as a wedding ring, or metal tools come into contact with the chassis and the active battery terminal or unfused wiring, such as that to the starter solenoid and on to the starter motor. These wires can supply hundreds of amps which will turn a wedding ring into a molten metal pool in a couple of seconds. Alternately, the current can cause molten blobs of metal from a tool that shorts the circuit to splash or eject sparks.

 

Any metal jewellery should be removed or taped over before working in close proximity to unfused battery power.

 

If you have to use tools on the starter wiring, disconnect the active terminal of the battery before doing so, to render the circuit safe.

 

=========================

 

Usually a starter circuit is very simple. The battery is connected to the vehicle / aircraft metal chassis on one side. Let's call this "Ground". There may be a specific thick, high current cable joining the Ground side of the battery to the engine.

 

The active side of the battery usually has several wires connecting to it. A fusable link connects to a master relay which supplies power to the fuse panel for distribution through individual fuses to the various circuits. The master relay is operated by the ignition switch. In addition to the fusable link, a thick high current wire connects the active terminal of the battery to the starter solenoid.

 

A starter solenoid will usually have either three or four connections. Three if the one is via the body to the chassis of the vehicle and four if insulated and a ground wire is needed:-

 

1. Battery active power in.
    
    
   
2. Switched power out to the starter motor.
    
    
   
3. Solenoid activation terminal. Depending on the way the solenoid is designed, it may need to be supplied with voltage from the active battery terminal ( more usual) or may need to be connected to ground. Either way, this is done via the starter switch, and carries only a small current (maybe 1 or 2 amps).
    
    
   
4. Grounded case or separate ground wire.
    
    
   

 

 

Picture of a typical starter motor and solenoid circuit.

 

Too high a resistance in this high current path will prevent the starter motor from developing the power it needs to spin the engine at the required cranking speed to start. The actual resistances should be very low and usually too low to measure directly, however we can find problem points by measuring voltages before and during cranking.

 

Let's assume the battery is OK for now. You can have it tested by a battery supplier, but we can do that too, albeit that we don't know what is normal. At this point it would be good to know the normal starter motor terminal voltage during cranking. If anyone tells you 12 volts, you need to ask someone who understands the question. In a car it is usual for the battery terminal voltage to drop to 7.5 to 8 volts under heavy cranking due to the high current drawn and the internal resistance of the battery.

 

You will need a multimeter that can read DC voltage with ranges giving 12 and about 2.5 volts full scale. Digital voltmeters are ok, but take longer to give a steady indication than the trusty old analogue meters.

 

It will help to prevent the engine from starting, whether that be done by disconnecting the ignition or pulling the spark plug leads or similar does not matter. , but you need to crank for a few seconds to get a voltage reading at each of the following locations:-

 

1. Between the battery positive and negative terminals. This will give you the normal battery voltage before cranking, and during cranking the voltage that it drops to is an important measurement. If it drops below 7.5 volts, there is an issue. It could be that the battery needs to be replaced or it could be excessive current draw due to a short (like Slarti described) or due to shorted turns in the starter motor field windings. This latter problem can only be determined by the starter motor manufacturer.
    
    
   
2. Between the ground terminal of the battery and the engine body. If you measure more than about 0.2 volts during cranking, then there is a bad connection somewhere between these two points, that is causing lower than normal starter current.
    
    
   
3. Between the active battery terminal and the battery supply side terminal of the starter relay. As in 2. above, ifyou measure more than about 0.2 volts during cranking, then there is a bad connection somewhere between these two points, that is causing lower than normal starter current.
    
    
   
4. Between the battery supply side terminal of the starter relay and the output terminal to the starter motor. This will read the full battery voltage until cranking and should then drop to less than 0.05V. If you are seeing a volt or more, the solenoid contacts are likely faulty.The contacts in a starter solenoid carry very high currents and if they do not contact properly may spark and eat away the terminals, as in this picture. As this happens and the terminals become pitted, there is less area of contact and a commensurate higher resistance, evidenced by the measured voltage across the contacts when cranking.
    
    
   
5. The next area is between the starter solenoid termial that connects to the starter motor and the starter motor terminal. Often the starter motor terminal is not exposed, so this measurement cannot be made.
    
    
   
6. It may also be worth measuring the voltage at the solenoid activation terminal. If that is inadequate, then the solenoid may exhibit a poor connection due to insufficient motive force to close the contacts. It should be the same as the battery terminal voltage, during cranking.
    
    
   
7. The last area to measure is between the body of the starter motor and the engine body. If the starter is bolted on with a gasket and locktight on the bolts, then it may not have a good electrical connection. Some starter motors may have a separate ground lead to avoid that issue.
    
    
   

 

 

If there is a resistance / bad connectivity issue, this process will find it, with the exception of the shorted turns possibility in the starter motor, as previously mentioned.

 

I hope this is helpful.

 

 

[bushpilot]

Hey David - This is huge help - especially in the educative sense. And I'm sure others will benefit from your summary. Thanks a lot.

 

Hopefully you will have some knowledge of battery technologies as well. We have been doing some research to try and establish if we can use jump starter packs that are designed for 'normal' lead-acid batteries in cars, boats etc. on the sealed gel type used by Jabiru and other a/c. (Chargers are not an issue as there are several designed specifically for gel batteries - eg CTek. These are brilliant - tough and technically smart:

 

http://batteriesdirect.com.au/shop/product/10571/multi-xs4003.html

 

Here is one view on jump packs; you might care to comment on it:

 

Gel cells and Absorbed Glass Mat batteries are similar to conventional lead-acid batteries, except that:

 

- the acid electrolyte is in a jelly material or soaked into fibreglass mats (AGM) - this means that they can be used in any orientation, so suitable for aircraft

 

- they are "sealed" which means that in normal charging and use, any small amounts of hydrogen and oxygen which are produced via electrolysis are kept within the cell, and are able to recombine into water

 

- however they do have a safety release valve so that if the battery is charged too fast, which results in too much electrolysis hence too much hydrogen and oxygen building up, the gases can escape rather than rupture the battery

 

- if the hydrogen and oxygen escape instead of recombining, then the electrolyte dries out and eventually the battery fails

 

So the risk of using a battery booster pack is that the charging current will be unregulated, (especially jump packs with dead battery compensators - ie more punch) hence probably too high, which may cause electrolysis, hence battery damage. It might be possible to avoid such damage by only plugging the booster in for short periods while starting.

 

 

[Hildy]

On seriously cold mornings, tip a bucket of hot water over the crankcase. Dont laugh it worked for me every time

does that work for pilots too? (see cficare's post).

 

 

[skeptic36]

does that work for pilots too? (see cficare's post).

Nope it has to be cold water for pilots, ice water if you want a guaranteed result especially for instructors

 

 

[Guest davidh10]

Hey David - This is huge help - especially in the educative sense. And I'm sure others will benefit from your summary. Thanks a lot.

You are most welcome. I'm sure we are all here for mutual assistance.

 

In this new forum software, there's a "Like" link that enables readers to flag that they received good value from a post. \<unsubtle hint\>

 

Hopefully you will have some knowledge of battery technologies as well. We have been doing some research to try and establish if we can use jump starter packs that are designed for 'normal' lead-acid batteries in cars, boats etc. on the sealed gel type used by Jabiru and other a/c. (Chargers are not an issue as there are several designed specifically for gel batteries - eg CTek. These are brilliant - tough and technically smart:

http://batteriesdirect.com.au/shop/product/10571/multi-xs4003.html

 

Here is one view on jump packs; you might care to comment on it:

 

Gel cells and Absorbed Glass Mat batteries are similar to conventional lead-acid batteries, except that:

 

- the acid electrolyte is in a jelly material or soaked into fibreglass mats (AGM) - this means that they can be used in any orientation, so suitable for aircraft

 

- they are "sealed" which means that in normal charging and use, any small amounts of hydrogen and oxygen which are produced via electrolysis are kept within the cell, and are able to recombine into water

 

- however they do have a safety release valve so that if the battery is charged too fast, which results in too much electrolysis hence too much hydrogen and oxygen building up, the gases can escape rather than rupture the battery

 

- if the hydrogen and oxygen escape instead of recombining, then the electrolyte dries out and eventually the battery fails

 

So the risk of using a battery booster pack is that the charging current will be unregulated, (especially jump packs with dead battery compensators - ie more punch) hence probably too high, which may cause electrolysis, hence battery damage. It might be possible to avoid such damage by only plugging the booster in for short periods while starting.

Let's start with a general intorduction to AGM and Gel-Cel batteries that are together classed as "Valve Regulated Lead Acid". I'll let Wikipedia do that :-)

 

One advantage of the old (flooded) lead acid batteries (those in which we used to test the specific gravity of the electrolyte and top it up with distilled water), was that they were tough. You could charge them at very high rates for short periods and would only lose some electrolyte due to electrolysis of the water and loss of hydrogen and oxygen. Of course this caused a risk of explosion from sparking when the battery charger or jump pack was disconnected. If charged at too high a current for too long, you would warp the plates and ruin the battery, but generally they were pretty resilient to abuse.

 

The newer technology AGM and Gel Cell batteries have been a boon for several reasons:-

 

• No maintenance.
   
   
  
• Operate over a wider temperature range.
   
   
  
• Higher energy density.
   
   
  
• Cannot spill, so can be positioned in any orientation. ( If overcharged, there is a risk of leakage of a small amount of electrolyte through the pressure relief valve).
   
   
  
• Can be charged and discharged at high currents, compared to "flooded lead acid" batteries.
   
   
  

 

 

The disadvantages are relatively few:-

 

• Cannot check specific gravity of the electrolyte, so charge status can only be estimated from terminal voltage.
   
   
  
• Cannot replace any lost electrolyte, so overcharging will result in severely reduced battery life.
   
   
  
• Overcharging can result in electrolyte leakage through the pressure release valve.
   
   
  

 

 

As you can see the longevity of the battery is largely dependent on being careful not to overcharge it.

 

We all talk about batteries having a specific voltage (per cell), and which is also characteristic of the cell technology:-

 

• Carbon or Alkaline torch batteries: 1.5 Volts.
   
   
  
• Lithium batteries: 3 Volts.
   
   
  
• Nickel Cadmium batteries: 1.25 Volts.
   
   
  
• Nickel Metal Hydride: 1.3 Volts.
   
   
  
• Lithium Polymer batteries: 3.75 volts
   
   
  
• Lead Acid batteries: 2 Volts.
   
   
  

 

 

When we look at 9 Volt or 12 Volt or 24 Volt batteries, for instance they are composed of multiple cells, usually in series to give a higher voltage, however if you remember the old Dolphin Lantern style battery, it actually had a two sets of series connected cells in parallel to give increased current capacity as well as the desired six volts, in the required package size.

 

These are nominal cell voltages. When fully charged, the open circuit terminal voltage will be a little higher and when discharged, it will be lower. What constitutes discharged varies depending on the load (how much voltage and current is required to perform the required work). A torch is usually quite dim when the batties reach a terminal voltage of 1.1 Volts. An electronic clock may keep working down to 0.9 Volts. Your car battery is considered flat when it will no longer deliver the required current to crank the engine fast enough to start it. Here's an example voltage discharge graph for a 12 Volt battery.

 

You can now see why there are different chargers or charger settings for different battery types. All batteries have an ideal charge rate that will provide the longest battery life. Here's a graph I found that depicts battery life for different discharge rates, so that too affects battery life.

 

In the older days with flooded lead acid car batteries, the charge rate was not critical, the chargers were less controlled. They usually had no settings or just had a fast and normal charge setting. These chargers often had no regulation except their internal resistance and the terminal voltage that they produced. You could tell, because charging a very flat battery made the charger very hot. The charging current started off being high and decreased as the battery cell voltage increased.

 

Because in many of these battery types the battery cells can be damaged or in the case of Lithium Polymer (LiPo) batteries, burst into flames, the charging current has to be regulated quite closely. Thus battery chargers have moved from the old style that was just a transformer and rectifier to being electronic switched mode regulators that provide either constant or shaped charge currents.

 

LiPo batteries are charged at a constant current until they reach the full charge terminal voltage, at which time the charging stops and cell voltage is monitored. If it drops below a certain value, it gets a little more charge (pulse charging) before the charging is again switched off.

 

As during any charging of AGM or GEL Cells causes some production of hydrogen and oxygen, it must be done at a rate that allows these gasses to recombine to water (a characteristic of the technology used in these cells). In Gel Cells, recombination occurs slower and thus the charging rate must be lower than for an equivalent AGM battery.

 

Now that we've covered the technologies and the basics, we can examine the question of using a "Jump Pack" with Gel Cells:

 

I haven't done any destructive testing, so this answer is theoretical. battery manufacturers are likely to have a better answer. As I don't know the internal resistance of the battery, let's make some assumptions:-

 

• The cranking current on the starter motor is 200 Amps.
   
   
  
• The cranking battery terminal voltage on the battery is 8 Volts.
   
   
  

 

 

This, using Ohm's Law: E = I/R

 

E is Electromotive force in Volts. I is current in Amps. R is resistance in Ohms.

 

The internal restistance of the battery is (12 - 8) / 200 = 0.02 Ohms.

 

In my experience, Jump Packs come in several flavours:-

 

1. A small portable battery pack that has sufficient capacity to augment the resident battery, but not replace it for starting purposes.
    
    
   
2. A small battery pack that is capable of providing a low current charging source to put some charge back in a flat battery. These have to remain connected for a period of time, like 20 minutes or longer.
    
    
   
3. A big high capacity battery or pack that could be used to start the engine alone when the internal battery is completely flat.
    
    
   

 

 

Now, understanding that a Gell Cell can be damaged by being charged at a high current and also has a very low internal resistance, lets look at two situations:-

 

1. An internal battery that cannot supply enough current to the starter motor but has a reasonable terminal voltage for other purposes (11.9 Volts).
    
    
   
2. An internal battery that is "flat" and has a terminal voltage of 10 volts or less.
    
    
   

 

 

In the first case, we are wanting to attach a jump pack that is fully charged and has a terminal voltage of 12.7 Volts. The voltage difference is 1.5 Volts and using the internal resistance of the battery calculated from the assumptions above, will result in a charge current of (using Ohm's Law) 0.8 / .02 = 40 Amps.

 

How does this compare to the rate of charge from the on-board alternator? What is the maximum charge rate from the battery? These can be obtained from the relevant manufacturers. My guess is that this is a high charge rate, but that depends on the battery specifications. A Car typical battery can be charged at 50 amps for short periods of time, so damage is not likely for a short period of time. Once the starter is activated and cranking, the current draw will from the Jump Pack will cause a voltage reduction and consequent lower charge rate, but I'd remove the Jump Pack as soon as possible.

 

In the second case, the same calculation provides a resultant charge current of 3 / 0.02 = 50 Amps. My guess is that will not cause battery damage, however if the battery were very flat at a terminal voltage of 10 Volts, then the charge current would be (12.7 - 10) / 0.02 = 135 Amps, which may even be dangerous.

 

As you can see, you will need to obtain some specs from the battery and starter motor manufacturers to be able to properly assess the situation. Especially you need to obtain advice on the maximum safe charging current for the specific battery and consequences of exceeding it.

 

* My advice is in good faith, and is not warranted in any way. The reader is totally responsible for determining its efficacy, accuracy and safety.

 

 

[brilin_air]

Chris,

 

I have found that by turning on the mags when the engine is spinning helps, as the inertia from the prop is not being pushed back by the engine timing as it is trying to fire at 25 degrees before TDC,it seems to allow the engine to achieve the required rpm easier to give you a better spark for the initial start.

 

You still need to have a good battery and starting system as nothing can help if they are not in good condition.

 

Brian

 

 

[bushpilot]

Found the source of our hard starting J230 problem: A dying battery cell. Jabaru replaced under warranty, no quibbles. But to make sure, we now have battery maintainers connected to both our J230s when temps are expected to go below 5 C over night (i.e. most nights here in Bathurst at this time of the year!). We have suspended them from the hangar ceiling, so that there are no cords to trip on and they plug staight into the Jab external Anderson plugs. Works well and the bonus is they condition and extend the life of the batteries.

 

 

[Guest davidh10]

Great that you have finally tracked down the cause.

 

 

[eightyknots]

You are most welcome. I'm sure we are all here for mutual assistance.In this new forum software, there's a "Like" link that enables readers to flag that they received good value from a post. \<unsubtle hint\>

 

Let's start with a general intorduction to AGM and Gel-Cel batteries that are together classed as "Valve Regulated Lead Acid". I'll let Wikipedia do that :-)

 

...

 

...

 

* My advice is in good faith, and is not warranted in any way. The reader is totally responsible for determining its efficacy, accuracy and safety.

David, this is a great summary of batteries in general and for aviation purposes in particular!! Thanks