M20J Alternator options

[Martin S.]

Morning gents,

trying to figure out the options I have to replace my ALY 8420 alternator on a 78 M20J (24-0520) with A3B6D. I'd like to go with a plane power. According to the plane power site it should be this one: AL12-P70. Can you guys confirm? Also wondering if its a direct replacement, because It seems the plane power is 70 AMP while the former Kelly is 60 AMP, can that cause any troubles?

Greets,

 

Martin

Edited March 23 by Martin S.

[ArtVandelay]

I used 10-1050-1 in particular but my engine is the A3B6 with 2 mags.

I don’t know the difference between P70 vs 70, but the AL models are designed as direct replacements with different mounting parts included in the kit, they are PMA certified replacements.

Don’t worry about excess capacity of the new alternator. As most of us have replaced our old landing/nav lights with modern LEDs, even 50 amps is excessive.

[mooneyflyfast]

I believe the Plane Power will require some wiring changes. It has a built in voltage regulator whereas yours is buried behind the instrument panel.

[ArtVandelay]

I believe the Plane Power will require some wiring changes. It has a built in voltage regulator whereas yours is buried behind the instrument panel.

Not the version I have.

[201Mooniac]

I used the AL12-P70 on my 1980 M20J and it was a simple replacement.  That alternator did not require any wiring changes and still uses the external VR (mine is the Zeftronics R15300 I believe).

[A64Pilot]

On 3/23/2024 at 5:14 AM, ArtVandelay said:

I used 10-1050-1 in particular but my engine is the A3B6 with 2 mags.

I don’t know the difference between P70 vs 70, but the AL models are designed as direct replacements with different mounting parts included in the kit, they are PMA certified replacements.

Don’t worry about excess capacity of the new alternator. As most of us have replaced our old landing/nav lights with modern LEDs, even 50 amps is excessive.

You should replace the wire to carry the potential higher amperage and replace the CB with a higher rated one, but if the original CB is left in place then it should be fine safety wise, but the possibility exists that the alternator could output more amperage than the CB could handle causing it to trip. Would it reset or just trip again? I don’t know. What would it take to max out an alternator? Maybe a dead battery?

Bottom line, you have to do whatever the STC calls for, if it says just R&R the alternator and regulator then that’s all you have to do.

Putting a Plane Power on my little C-140 the STC called for bigger wire and CB, but that was to replace a weak generator.

[Aerodon]

I can't ever remember the alternator output pegged at 60A, never mind 70.  Especially with LED instead of halogen LL's.  There might be a bump when selecting gear up or down, or after starting.

So really no benefit or problem installing a 70A alternator, and unless you reach 60A you are not going to trip the breaker.  And breakers are notoriously inaccurate anyway.

And its not like you are changing from a 40A to 70A alternator - I would look at the aircraft wire sizing chart, you may well have a big enough wire for a 70A alternator already, then go ahead and change the breaker?

 

Aerodon

 

 

 

 

 

 

 

 

[Martin S.]

10 hours ago, Aerodon said:

I can't ever remember the alternator output pegged at 60A, never mind 70.  Especially with LED instead of halogen LL's.  There might be a bump when selecting gear up or down, or after starting.

So really no benefit or problem installing a 70A alternator, and unless you reach 60A you are not going to trip the breaker.  And breakers are notoriously inaccurate anyway.

And its not like you are changing from a 40A to 70A alternator - I would look at the aircraft wire sizing chart, you may well have a big enough wire for a 70A alternator already, then go ahead and change the breaker?

 

Aerodon

 

 

 

 

 

 

 

 

Thanks guys. I got the LED lights, so it indeed shouldn’t be a big deal. Checking the circuit breaker and wires is a good point, will have a look at it.

[N201MKTurbo]

You need to do an ELA to find out if your alternator is the right size. With all the panel work done to most planes, there should be one in the maintenance record somewhere. Most of the avionics STCs require it.