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Jabiru 12 Pole Alternator modification / upgrade


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I have a situation that if i do 3 or 4 circuits in my Jabiru, after i land my Radio transmission to the tower is unreadable, but if i increase the RPM to 2000, the signal is fine.

 

The Battery is new, and at present the plane is outside with a Solar charger attached.

 

The problem is not there after a longer flight, so it appears that the Battery is discharging at low RPM.

 

The other day, i was unreadable to the tower on final at 1500 RPM, but as soon as i taxied off and increased the RPM, the problem went away.

 

Also, at first startup the transmissions are fine but i am noticing that by the time i've done the run ups etc, my ready call to the tower is weak.

 

Was not using landing light on final.

 

No problem in cruise.

 

Any body else had this issue?

 

 

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It sure seems like a power issue, but it may be an interference one. There could be interference spikes at low rpm due to something about the alternator or the regulator.

 

To check on the power issue, the easiest thing to do is to connect a digital voltmeter where you can see it during flight. It can be a loose meter with the connections alligator-clipped on.Clip the connections between the positive and negative feed to the radio.

 

This will show if the voltage as supplied to the radio is falling below specs.

 

It seems strange that your battery can start the engine and do this though. Let us know what you see if you do this test.

 

 

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It sure seems like a power issue, but it may be an interference one. There could be interference spikes at low rpm due to something about the alternator or the regulator.To check on the power issue, the easiest thing to do is to connect a digital voltmeter where you can see it during flight. It can be a loose meter with the connections alligator-clipped on.Clip the connections between the positive and negative feed to the radio.

This will show if the voltage as supplied to the radio is falling below specs.

 

It seems strange that your battery can start the engine and do this though. Let us know what you see if you do this test.

Thanks Bruce, will do.

 

 

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Thanks Bruce, will do.

And i took the following readings at the Alternator during a ground test

1000RPM 8.3 volts

 

1600RPM 13.3 volts

 

2000RPM 16 volts

 

 

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That 8.3 volts sure is low Roscoe. If this it the voltage the radio sees during low rpm then that would explain the problem. However if this is so, then your battery is no good because otherwise it would keep the voltage up to the radio. For example, your radio should work even with the engine not running at all, ie zero volts from the alternator. In gliders, the radios work like this all the time.

 

Try putting the voltmeter on the battery next. And have fun, solving problems like this is very satisfying.

 

 

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That 8.3 volts sure is low Roscoe. If this it the voltage the radio sees during low rpm then that would explain the problem. However if this is so, then your battery is no good because otherwise it would keep the voltage up to the radio. For example, your radio should work even with the engine not running at all, ie zero volts from the alternator. In gliders, the radios work like this all the time.Try putting the voltmeter on the battery next. And have fun, solving problems like this is very satisfying.

Battery voltage 12.8.

Have sent a pm thanks Bruce

 

 

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Battery voltage 12.8.Have sent a pm thanks Bruce

I've spent some time poking around with a multimeter on Jabs, and it's worth checking for voltage drops from the battery to the radio, to try to isolate where a loss could be. There's a few places that need checking - in particular both sides of the avionics switch and the 12v bus bar. It doesn't take much time and makes finding the problem reasonably simple. Same with earths, being a composite airframe, checking for resistance between the earth on the radio and the battery is worthwhile. I've stumbled onto 0.5-1 volt losses in places, that's enough to make the radio unworkable at low RPM.

 

The alternator putting out <12v at ~1000rpm is "normal", unless it's the high output alternator. Operationally, running the plane at 1200rpm when not explicitly testing idle speed in your pre-takeoff check, is not a bad idea :) IT might not be your reg or alternator, invest a few minutes poking around looking for drops before you go replacing expensive things!

 

 

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I've just received a Lithium Ferro Phosphate (LiFePO4) battery and ordered another one.

 

Both from Australian businesses. The first one is just a set of four big hefty cells bolted together- no battery management system. I'm told it would be damaged by charging over 13.7v and I've wasted weeks trying hunt up a solution. Even three very experienced auto electricians couldn't help.

 

What to do with it? Put it into my old booster pack, whose Pb battery long since expired. If I carefully cut off the charger at 13.7v it should last a decade.

 

After investigating several American firms who sell drop-in LiFePO4s I found a company in Sydney which sells them for cars and boats. He was interested to hear of the potential aviation market.

 

I ordered a 400 CCA unit with built-in management circuits. It weighs only 1.6kg, so I'll be rearranging the gear in my front compartment to preserve CoG.

 

For those interested:

 

Lithiumax Car, Boat and Bike Starter Batteries

 

 

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The figure of 13.7 volts is interesting to me . I have a charger ( a model plane Swallow charger) which can charge LiFePO4 and it cuts out at 14.4 volts.

 

On the Jabiru, I switch off the charge ( by turning off the master) at 14.4 volts although sometimes I forget and it goes for up to 10 mins up to about 14.8 volts.

 

In over 2 years now, there is no sign of this battery puffing up.

 

I wonder now if I should be switching it off sooner, maybe 13.7 volts. You could tell by charging to 13.7 and then discharging ( cycling ) to see if the capacity was reduced much or at all. My charger will do this discharge and report on the amp-hours before the lower critical voltage is reached.

 

Is there any more info about the 13.7 volts?

 

 

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AND in the latest Aldi catalog, there is a "batteryless capacitor jump-starter " which will ( it says) start a car with a bad battery. I guess this means a battery which will slowly charge the capacitors and then they act as a booster for amps when you try the starter. Why have I not heard of this idea before?

 

 

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The figure of 13.7 volts is interesting to me . I have a charger ( a model plane Swallow charger) which can charge LiFePO4 and it cuts out at 14.4 volts.On the Jabiru, I switch off the charge ( by turning off the master) at 14.4 volts although sometimes I forget and it goes for up to 10 mins up to about 14.8 volts.

In over 2 years now, there is no sign of this battery puffing up.

 

I wonder now if I should be switching it off sooner, maybe 13.7 volts. You could tell by charging to 13.7 and then discharging ( cycling ) to see if the capacity was reduced much or at all. My charger will do this discharge and report on the amp-hours before the lower critical voltage is reached.

 

Is there any more info about the 13.7 volts?

Bruce the seller of the LiFePO4 cells which arrived today told me 13.7v was a safe limit for charging the four cells (3.2v each). After failing to find a way of regulating the charge to 13.7v, it occurred to me that if I added a cell, I'd have five cells with combined limit of 16v, which the standard Jab regulator would charge to about 85% capacity- which should ensure a long battery life.

 

Interestingly, the unit I ordered this arvo is claimed to tolerate up to 16v, so maybe it also has five cells.

 

 

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From what I read on an electric bike site, the 13.7 figure might give more life than a higher voltage.I'll try to look this up.

 

Be careful about using 5 cells. Your logic is right about the charge voltage, but I wonder if everything else can take it. My starter motor is much more energetic with the 13.2 LiFe than with the old Odyssey. Whether or not there is any danger to the starter motor I don't know.

 

 

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From what I read on an electric bike site, the 13.7 figure might give more life than a higher voltage.I'll try to look this up.Be careful about using 5 cells. Your logic is right about the charge voltage, but I wonder if everything else can take it. My starter motor is much more energetic with the 13.2 LiFe than with the old Odyssey. Whether or not there is any danger to the starter motor I don't know.

Bruce my understanding of electronics is rudimentary at best; I can imagine water flowing, so that's the analogy I use to image how electricity works. I won't be adding a fifth cell, but putting my four new big hefty Life cells into the old booster pack. A purpose-built Life battery should arrive shortly.

The problem then, as you say, is that it will really spin that starter motor. There have already been concerns raised about how Jab starters might be stressing the flywheel bolts. It would be nice if there was a gradual way to apply the extra cranking power.

 

 

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