Help choosing alternator 60Amp to 70Amp

[Grubi]

Hello,
I have recently got oportunity to become Mooney pilot (not owner, but guy who flies and take take care of M20J).
English is not my native language so forgive my grammar. I am from Europe(Serbia).
My Mooney has engine IO-360-A3B6D, with installed alternator HARTZELL ALY-8520 (60Amp).
I would like to replace existing alternator with stronger one(70Amp) (new one if possible). I was researching which alternator would suit her best, and got several different solutions.
ALX-85
ALX-9522
AL12-P70
Anyone has experienced alternators above?
Thanks

[N201MKTurbo]

I’m curious why you need a stronger alternator? What problem are you trying to correct? Is there something wrong with your alternator?

[Grubi]

I had problem to start the engine (after 1min stby radio, it would not crank at all), and replace new battery gill 35 for concorde rg35-axc. Than , by chance,I got information from guy who did some interventions on my Mooney, that this alternator is working on its max(due to avionics upgrade), and he propose previous owner to change alternator to 70Amp. He explain that even I replace battery, false start could repeat. That is main reason for my alternator upgrade.

[larrynimmo]

43 minutes ago, Grubi said:

I had problem to start the engine (after 1min stby radio, it would not crank at all), and replace new battery gill 35 for concorde rg35-axc. Than , by chance,I got information from guy who did some interventions on my Mooney, that this alternator is working on its max(due to avionics upgrade), and he propose previous owner to change alternator to 70Amp. He explain that even I replace battery, false start could repeat. That is main reason for my alternator upgrade.

That makes no sense....I would look to failing 60 amp alternator or a failing voltage regulator.

unless you are constantly illuminating an incandescent landing light, strobes, and pitot heat all the time.

[ArtVandelay]

What’s your voltage when engine RPM is above 1800?

I doubt your avionics is a major load, but unless you’re using pitot heat, landing lights I don’t see why alternator couldn’t keep up.

Could be the voltage regulator or broken wire, loose alternator belt, or of course a broken alternator.

[Grubi]

Guys,

Thanks a lot to you all trying to go more dip into problem, but believe me, you would help me more if you, who had expirience with alternator that I mentioned, share that information.

Thanks again

[Greg Ellis]

37 minutes ago, Grubi said:

Guys,

Thanks a lot to you all trying to go more dip into problem, but believe me, you would help me more if you, who had expirience with alternator that I mentioned, share that information.

Thanks again

I understand that you are looking for an answer to your original question.  But please keep an open mind to the fact that it may not be your alternator at all.  For instance, I have a C model with 70 Amp alternator and with all of my avionics on (Garmin 530, 300, G5, GTX 345 transponder, an ipad charger, etc...etc...), landing light, nav lights and pitot heat on I do not come anywhere close to pulling more than the alternator can handle (usually I see about 20-25 amps being pulled on the ammeter).  I cannot imagine what you must have turned on that would come close to causing an issue for a 60 amp alternator unless there is something wrong with the alternator itself (not the rating of 60 amps but something internally wrong) or something wrong elsewhere.  

You may end up spending money on a new alternator and your issue may continue because the problem may lie elsewhere.  So just keep an open mind to the answers that you receive from these very, very knowledgeable Mooney owners.  

[1964-M20E]

@Grubi

Welcome aboard.

 

When I had my E model I replaced the generator with the plane power 70A alternator due to the generator failing.  I chose not to replace the alternator breaker which was I believe 50A.  The total electrical load was less than 50A.  If you want to get the full output from a 70A alternator you will need to change the alternator circuit breaker to 70A as well and evaluate the size of the wire from the alternator to the main bus.  The front baffling on my E had to be modified to fit the new alternator.  You may not experience this since you already have an alternator.

As stated above I would try to find the real problem instead of changing parts until it is corrected.

1. A simple but very inexpensive effective first step when experiencing problems like this is to clean and reassemble every connection between the battery and the starter.
2. Would be to measure resistance across the master relay and the start relay to make sure neither of these are causing any issues.
3. You already replaced the battery so unless it is infant mortality you are good there.

Finally there are plenty of good people here that have experienced just about any problem anyone else will have and they offer plenty of free advice some is better than others but all well intentioned.

 

good luck and do not be shy about asking questions.

 

 

[philiplane]

I install a 100 amp alternator when I install electric air conditioning, because the a/c unit uses 33 amps at full load. A fully equipped panel will normally use between 20-25 amps, and then you provide for landing lights and navigation lights. I would expect your Mooney to use 35-45 amps with everything operating. So a 60 amp alternator would normally be adequate. Yes, a 70 amp alternator would give you a little extra power and should only require changing the circuit breaker to a 70 amp rating. If you go above 70 amps, you will have to install 4 gauge wire from the alternator to the main bus, in place of the 6 gauge wire that the factory used. 

Attached are the performance charts for a Plane Power 100 amp and 70 amp alternator. The curve shows how much current is supplied at each RPM. 

Your alternator runs on a 3.2 to 1 reduction, so take the chart RPM and divide by 3.2 to get the engine RPM. For example, 800 engine RPM is equal to 2560 alternator RPM.

Both of these are considered to be high output alternators at lower RPM than the factory alternator.  Even so, where this 70 amp alternator puts out 55 amps at 1500 engine RPM, the 60 amp alternator still puts out 46 amps. The 100 amp alternator is very high output at low RPM. It will put out 85 amps at only 950 engine RPM. 

ALT-FLX or C14-100 Performance.pdf AL12-(P)70 Alternator Performance.pdf

[A64Pilot]

A way to tell what your electrical consumption is, is pretty simple, without starting the engine, turn everything on and read the amp meter, that’s your consumption. It will decrease some with the engine running as the voltage will be higher.

There is about zero chance that your alternator isn’t big enough, if your not holding 14V plus or minus .2V at flight RPM, you have another issue, dirty contacts on the alternator side of the master switch is apparently not uncommon, voltage regulator or as has already been said dirty contacts is very likely in our older aircraft.

Going to a 70 amp alternator is just going to waste money.

‘I’d have to see avionics pull 25 amps to believe it, modern avionics just don’t pull that much power.

100 amp alternators can’t supply 100 amps continuously, they will burn up from heat if they do, and even if they could, you can’t pull 100 amps from a single belt unless it’s a serpentine belt. Max amps a single belt can hold is roughly 70 to 90 amps, after that it slips, creates dust and of course breaks after awhile.

100 amps at 14V is 1400W, and that’s a shed load of power, a metric shed load.

Alternators are not DC generators, they generate AC power that’s rectified to pulsating DC via a diode bank, and diodes create a whole lot of heat, to get 100 amps continuously out of a small frame alternator, one way to do that is to remote mount the diode bank, and I don’t think any aircraft alternators do that?

[Yetti]

The TCDS is a guide to what alternators should go on the plane.   Avionics upgrades generally DECREASE the overall load.   Put in an LED headlamp which will solve many problems.

[Marauder]

I agree with the others on the 60 versus 70 amp alternator advantages. When I went to an all glass cockpit and modern navigation radios, I did a load assessment. My concern was that if I lost the alternator, what would I need to unload and how long would things continue to function operating off of the battery (let's keep the health of the battery out of the conversation). What I discovered was the load draw wasn't that much.

So unless you are trying to start with everything switched on, there should be no reason your battery can't handle even a hard start. I think you should look whether or not the battery is getting a full charge with the 60 amp alternator and more importantly, you are not dealing with some sort of current loss from the battery to the starter.

As for your original question, I have the Plane Power alternator installed (your AL12-P70 part number). I have it paired with a new Zeftronics voltage regulator. Rock solid alternator for me. Been using it for 2.5 years. 

[RobertGary1]

I bet if you put that original alternator  on the bench it would put out 100amp. 

[EricJ]

10 hours ago, Grubi said:

Guys,

Thanks a lot to you all trying to go more dip into problem, but believe me, you would help me more if you, who had expirience with alternator that I mentioned, share that information.

Thanks again

For your serial number airplane only a 60A alternator is approved.   For serial numbers starting at 24-3000 or higher, then there is a 70A alternator approved for those airplanes.   Usually the additional ten amps is used to drive a hot propeller or air conditioner or other loads not typically seen on the previous aircraft.   If your airplane is registered in the US it would require an STC or modification paperwork to upgrade to a larger alternator.

I'd add to what other folks are saying here, though, that if there is a problem it is unlikely that increasing the size of the alternator will fix the actual problem.   There haven't been a lot of people talking about their experiences with larger alternators because it is very, very seldom done.   Usually improving avionics and switching to LED landing lights, etc., reduces the current draw so that there is even more margin than usual with a 60A alternator.   If your 60A isn't keeping up, and there isn't a large additional load (like an air conditioner) to explain the difference, then a 70A alternator would not be expected to improve the situation.

You should have an ammeter on the aircraft.   What is it telling you after an hour or so of flying?   What is the unloaded battery voltage after shutting down after a flight?

 

 

[RobertGary1]

Also modern cockpits significantly reduce the power requirement vs what theee planes came with. Old high amp radios and autopilots used to draw a lot more power than modern equipment. 

[carusoam]

Nice work so far Grubi!

You are in the right place, asking the right questions...

You got some suggestions on proper wiring and circuit breakers that may be needed...

Your English is better than mine... 

Best regards,

-a-

[jlunseth]

When I first got my 231, I was out doing night landings at my home airport one night. I generally idled the engine at about 900-1000 as I had been taught in Warriors. The 231 in particular, has poor alternator output at idle, doesn’t matter what the amp rating of the alternator is, it does not generate 60 or 70 amps at idle. I managed to kill the engine right in front of the instructors’ shack and did not have enough electrical power to turn the engine over, even though it was still warm. They had to come out and help me push my new-to-me plane onto the ramp. They were good natured about it. The problem was only partly the lack of current at idle, at the time I had incandescent lights all the way around, landing, strobe, nav. They drew the battery down very fast.

Fast forward and I now have LEDs all around. Plus a GTN750Xi, 403AW, KFC 200, and several other things on the panel. The current draw of the newer electronics is tiny compared to the old tube radios and incandescent lights. For awhile, Mooney tried installing a stronger alternator than the original 70 AMP, I think it was a 100, it made no difference at all to the lack of electrical power at idle. The cure is to idle at 1100-1200. I once had a great Mooney instructor, who flies a 231 himself, ask me whether I watch the lights flash or ride the brakes, meaning do I taxi with idle so low the battery is discharging, or so fast that the brakes are needed. There is no middle. I ride the brakes.

That is where you need to make improvements, the engine will drive the alternator only so fast at low power settings, it does not matter what the max output of the alternator is. The J is a different drive system and somewhat better at low speed, but the problem is the same. Change out the incandescent lights first, then go at the avionics.