Amp draw

[Benbell4140]

Does anyone know how many amps the 912 series puts out? The reason I’m asking is I removed the 60 amp alternator from my o-200 to replace with a 30 amp which is shorter. I had firewall clearance issues with the 60 amp and didn’t want to modify the firewall. The 30 amp will clear with no issues. Just want to make sure 30 amp will be sufficient. Thanks


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[Eric Page]

It depends on the engine:

The 912UL and ULS have one 20A alternator.

The 912iS has an alternator with two isolated coils. The primary coil can produce 16A and is dedicated to powering the engine's electronics, while the secondary coil can produce 30A for the rest of the ship. If the primary coil or regulator fails, the ECU automatically switches the engine to the secondary coil/regulator and the rest of the ship falls back to battery power.


I'm not sure I understand how the Rotax 912 electrical system output relates to changing the alternator on your O-200. The way to be sure you have enough alternator capacity is to add up the electrical current demands of everything installed in your plane. That's a tricky process, as many avionics spec sheets list max draw (i.e. a radio while transmitting) so accurate numbers can be hard to come by.

Unless you have a multi-screen IFR panel with redundant GPS and AHRS sensors, or large incandescent landing lights, I would be very surprised if 30A weren't plenty. A typical VFR glass panel and LED wingtip lights will be hard pressed to use half of that.

[Benbell4140]

Thank you for the info Eric. I’m single display with an iPad and I’ll be using led lighting. Simple VFR


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[airlina]

Ben , On my Continental IO-240 I have the original 60 amp OEM alternator , but I purchased a plane power ER-50 (50 amp) which is waiting in the wings for installation and will save close to 6 lbs . The reason its not on yet is because as you mention, the tight clearances requires the engine to be pulled to do the job. I am waiting for winter to do this and will add my second Pmag electronic ignition at the same time ( also requires engine pulled). A few years ago , I pulled the engine to add my first P mag and kept one slick standard mag , but I have found the p mag to be very reliable and a great upgrade over standard mags so will add the second one. Bruce N199CL

[Benbell4140]

Ben , On my Continental IO-240 I have the original 60 amp OEM alternator , but I purchased a plane power ER-50 (50 amp) which is waiting in the wings for installation and will save close to 6 lbs . The reason its not on yet is because as you mention, the tight clearances requires the engine to be pulled to do the job. I am waiting for winter to do this and will add my second Pmag electronic ignition at the same time ( also requires engine pulled). A few years ago , I pulled the engine to add my first P mag and kept one slick standard mag , but I have found the p mag to be very reliable and a great upgrade over standard mags so will add the second one. Bruce N199CL

I’m also running a single p mag. I installed it before mounting the engine but looks like there is plenty of room on the o-200 to pull a mag with the engine mounted. Maybe the io240 sits a little further aft. I’m really looking forward to my first engine start!


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[PapuaPilot]

I have one P-Mag too and it has been very reliable.

30 amps should be plenty. I put a 30A B&C alternator on my IO-240 and it does the job well. I would highly recommend the B&C BC433 unit. It is actually a generator that uses permanent magnets. The only moving parts are the bearings, so there isn't anything to wear out like a tradition alternator, which has such as brushes, commutator, diode bridge, etc. It weighs about 4 lb. and I shaved about 6 lb. off of my stock alternator. Two cautions the B&C alternator. 1: the outer housing rotates, you need to keep stuff away from it. 2: it is a generator and doesn't produce a positive charge till about 1300 RPM.

[Benbell4140]

That’s the alternator that I ordered. I sent out my gear for them to install today. I didn’t realize that the outside housing rotated but that shouldn’t be a problem. I’m looking forward to installing it. Now I just need to sell my overhauled 60 amp to get some of my money back.

[Climberrn]

Sorry for the thread drift, but those of you running the P-Mags that have to pull the engine for access: How do you do the annual inspection to check the gear slop (or lack of)? I am running dual P-Mags on my RV and they have been sent back to the factory twice in 600 hours for repair. I love them, but think there is some harmonic issues with the high compression engine.

[Benbell4140]

Sorry for the thread drift, but those of you running the P-Mags that have to pull the engine for access: How do you do the annual inspection to check the gear slop (or lack of)? I am running dual P-Mags on my RV and they have been sent back to the factory twice in 600 hours for repair. I love them, but think there is some harmonic issues with the high compression engine.

The mags or p-mags are removable. It’s the bigger more common sized alternator that isn’t removable. I’m sure your RV has a lycoming with a belt driven alternator. The continental has a gear driven alternator on the accessory case.


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[Benbell4140]

After reading further up it appears that someone did have an issue removing the mags. On the O-200 it isn’t an issue though.


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[Climberrn]

Got it. Thanks.