Thanks: 
Likes: We can do front pulley-driven or rear gear-driven alternator on our IO375 build. Running a fixed pitch prop for now but may go to CS in the future.
School me on negatives & benefits of rear vs front, please!
Thanks,
Johnny
We can do front pulley-driven or rear gear-driven alternator on our IO375 build. Running a fixed pitch prop for now but may go to CS in the future.
School me on negatives & benefits of rear vs front, please!
Thanks,
Johnny
I like the gear drive alternators because it eliminates the belt and brackets. You can also mill off the belt pulley from the flywheel. Be sure to measure the clearance from the vacuum pump drive to the firewall to make sure there is clearance for the alternator model you choose.
Web
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I was told by folks who know Cubs much better than me (down at Legend Aircraft) that the gear-driven alternators can be a bear to replace or remove for oil leaks, etc.
Also I recall reading somewhere about internal regulator alternators (front mount) having trouble working with EarthX batteries’ internal controls.
Fact or fiction for those points?
They go on and off just like a vacuum pump. Four nuts and then slide it off. As for problems with internal regulators, I'm very picky about which ones I use due to design issues. But no concerns here over pairing them with an EarthX.
Web
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I use a B&C 410 on the accessory case. I can remove it without swinging the mount… barely. I could probably get away with a 12 amp. Getting to the alternator bolts requires removing the RH Pmag, but that may be true with the 12a unit, too. With the B&C LR14, no problem with the EarthX.
Last edited by stewartb; 03-28-2023 at 11:44 AM.
I wish I had went with the rear mount but I measured and didnt think it would fit. Later I saw one installed just fine. I believe you can request B&C to move the lead connection on it to the side to get more clearance.
Here is a pic of the weights of the skydynamics fly wheel and another light weight one with the pully grove still attacged. Additional weight saved will be in the wires to the alternator on front of the engine, the actual belt, and a spare belt.
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I have a plane power fs1-14 30a rear mounted alternator. Got a field approval for it and "modified flywheel to remove belt pulley". Ive had it on the cub for probable 1,000 hrs and never had an issue. Works great, and takes some weight off the nose.
I run the small B&C 8amps rear alternator with an EarthX battery. Both going strong for 7+ years.
I don't know why would I install a stronger alternator, 8 amps is more than enough.
Custom homemade lightweight flywheel is a bonus
I considered the small output alternators but I like to make short flights on my Cub so want full recharge in a short time. Just something to consider.
I also had that 8 amp rear mount dynamo/alt field approved on my last cub. Replaced it once around the 800-900 hour mark due to an oil leak filling it up with oil. Ran another 8 years with no problems in the arctic on floats wheels and skis. New plane just has too many electric requirements for that one.
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What kind of avionics? We have a Garmin G3X, G5, autopilot, ADS-B, intercom, and big LED lights that run more often than not.
Originally Posted by Olibuilt
I run the small B&C 8amps rear alternator with an EarthX battery. Both going strong for 7+ years.
I don't know why would I install a stronger alternator, 8 amps is more than enough.
Custom homemade lightweight flywheel is a bonus
I don't have any..
I would compute average amperage draw and see if 7amps @ 2450rpm is enough, but I doubt in your case.
http://photos.app.goo.gl/wfcHQyxEdfTa6AuC9
FWIW, my avionics master is a 30a switch breaker. In addition the electric trim and fuel pump each have 10a breakers. The G3X components all have individual pull breakers. It’s how Garmin suggested we wire it. How does Legend wire for breakers?
Breaker size is not the same as electrical load. The breaker exists only to protect the wire it feeds. To find electrical load, the current draw for each electrical item is added up. For items such as radios use the amp spec for the usual use. I.e., the radio is normally receiving so use that spec and not the much higher spec for transmit. The goal is to have the total electrical load be no more than 80% of the alternator output. However CAR3 has no rule for that.
Web
Last edited by wireweinie; 03-29-2023 at 08:03 AM.
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Typical Legend layout. Two buses. Each Garmin piece has its own CB, as do Alt field, start switch, etc.
Last edited by JohnnyR; 03-29-2023 at 09:11 AM.
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I’m running a constant loss battery for my starter and a XP pack for my radio and gps. I’ve been thinking I’d like to get a wind driven generator. Would I need need a field approval to use that? My airplane’s never had an engine driven electric system, and I don’t want to ruin it by putting one on. I’m stealth.This dynamo from a Kubota tractor would be worth considering for a front belt driven generator. Total installed weight with the prop and regulator is 5 lbs. It produces 15 amps. The prop is attached to the front face of the pulley.
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This one is on an EAB airplane and the propeller is homemade.
NX1PA
I had a wind alternator on a Seaplane, certified PA 12 with a Field approval. It’s kind of expensive, but I think it’s actually approved on PA 18s we just had to get the field approval on a PA 12. I’ll probably need to do that again.
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Breaker size is approx 125% of load potebtial for the appliance, right? Pretty simple math.
Lisa, Look at this thread to see what we went through in developing this generator. https://www.supercub.org/forum/showt...t=solar+panels
If you can pull something like this off in getting a field approval using your previous experience, it could prove to be very productive.
NX1PA
The standard FX-3 Carbon Cub displays battery current but not alternator current. I added a Hall effect sensor to my alternator output lead so I log alternator and battery current.
I picked a flight at random and found peak alternator current of 25.2 A after engine start. Flight load when flying a coupled LPV approach with stobes and wig/wag landing lights (but not navigation lights) was between 14 A and 15 A. Having landing light on continuous rather than wig/wag, and adding nav lights, would add another 2-4 A. This aircraft has a 40 A belt driven alternator.
These numbers should be typical for Garmin G3X with dual servos, G5, and a Garmin GPS IFR navigator.
Last edited by frequent_flyer; 03-29-2023 at 11:03 AM.
The circuit breaker size may be dictated by the component manufacturer in the installation diagrams or it may be calculated. See the attached chart from the AC43.13. Breakers are sized to allow only enough current through a wire to produce a minimal voltage drop and to not overheat the wire. As you can see, this is a three way calculation that takes into consideration, current flow in amps, length of wire in feet, and allowable voltage drop while still maintaining circuit operation.
Keep in mind that the breaker or fuse is only there to prevent overheating of the wire. Never for protecting the component on the end of the wire.
Web
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It is certainly true that a breaker is not intended to protect the load equipment and should be sized to protect the wire. However, an alternator breaker should also be sized to protect the alternator from overload.
First find the maximum expected alternator load, then select an alternator with adequate capacity, then size the wire and select the appropriate breaker.
An alternator will not 'overload'. Put one on a test bench and bring it up to max current output. The windings will saturate and limit the output before any heat damage will occur. For example, if you put a load on a 40 amp alternator and adjust it to try to draw 50 amps, the output will just hang around the 40 amp mark and the voltage will start to collapse. This is due to the magnetic fields around the windings interfering with each other when they build up to a certain point. You can't just 'pull' current from an alternator, it has to be produced from the windings. An example of this in an aircraft is the small B&C, 8 amp alternators. After the engine starts, that battery will take MUCH more than 8 amps while recharging. But if you have the ammeter on the alternator output, you will just see an 8 amp reading until the battery starts to charge up. All the time this is happening, the alternator is self limiting to the 8 amp level, putting 8 amps through a wire that is fused for 10 amps.
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Install one of these. You get system voltage, battery amperage and alternator amperage all in one instrument.
NX1PA
Example of building a load chart for your aircraft:
Whelen 650 nav (X 2) = .4 amps
Whelen 650 strobes (X 2) average = 1.16 amps
Whelen 500 nav = .2 amps
Whelen 500 strobe average = .72 amps
GDU 470 typical = .6 amps
GEA 24 = .2 amps
GMU 11 = .25 amps
etc
etc
All specs are found in the manufacturers installation data. When you have all of the actual current specs added up, this will be your 'total load'. Specs like current draw while transmitting may be ignored for this calculation as any momentary load in excess of the alternator output will be supplied by the battery. Then the battery recharges when you are not talking. All momentary loads are treated like the engine cranking current; we don't include 100+ amps in our load analysis because it only occurs for a few seconds.
Web
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Big fan of the dual amps/volts gauges. Pilot can monitor volts during normal ops and I can use the amps to troubleshoot problems.Install one of these. You get system voltage, battery amperage and alternator amperage all in one instrument.
Web
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Benefits of a rear mount, Less Weight. No belt. CG is slightly further aft. no weight of brackets to hold alternator. Can reduce weight of the flywheel. Cost of rear mount....... Higher engine RPM required to get full output of alternator.
Benefit of Front Mount. Full Output at lower engine RPM supports battery recharge during pattern work because geraring of belt and pulley turns ALT at a higher RPM. CG is slightly Further Forward. Cost of Front Mount..... Belt driven. Heavier due to mounting hardware.
Do a load analysis to understand how many amps are required during normal continuous operations. B&C makes several vacuum pad alternators with various Amp Output. I installed B&C SD-8 8A on my Bearhawk Patrol. Its not flow yet, but it is very easy to install and service, I doubt I will need to for they are very reliable.
Its very possible with LED lights and replacement of your classic master solenoid with a manual solenoid to have continous amp loads of less than 6A.
Generally a vacuum pad alternator needs higher RP to produce its full rated Amp Output. So if you are doing X-C mission and you have low load requirements then it might work well. But if you did an hour of pattern work it might not recharge your battery. The B&C belt driven alternator runs at higher RPM so it puts out a high load at a lower engine RPM.
Bill Rusk installed a small 8A vacuum pad alternaotr of his cub and the next year replaced it with one that had more output. I've been curious what he experienced.
If you are experimental there is a new (untested?) option that I read good reviews on called Monkworkz. Its a 30A vacuum driven unit.
https://monkworkz.com/
https://bandc.com/wp-content/uploads...8_2022_rev.pdf
QuickFacts_BC410-H_2022_rev.pdf
The G3X Touch shows volts and amps simultaneously on the EIS page.
I would expect that the behavior of an alternator at or above rated current would depend on the specifics of the alternator design. If all alternators self protect against current overload how do you explain the failure of alternator internal regulators and diodes?
Not in dispute. However, the "amps" readout depends on where the current sensor is fitted. CubCrafters uses a current sensing shunt in the battery circuit. I wanted battery and alternator current so I added an alternator current sensor.
My G3X (GDU 465) actually displays 4 currents - battery, alternator, pitot heater, and emergency ignition battery. Three more current readouts than standard.
Automotive and aircraft alternators control output by controlling the voltage. An internal failure or bypass will allow the voltage to increase beyond design. But it would take a component failure to make this happen.
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B&C 410 and 425 accessory pad alternators put out 15a at 2000 rpm and in the mid 20s at cruise rpm. I haven’t had any issues with charging.
https://bandc.com/wp-content/uploads...H_2022_rev.pdf
On the IO-375 I ordered for my Javron build, I plan on using the Monkworkz 30A alternator linked above. I've read a lot about it from people who have used it on Vans aircraft, and it seems to be a good product. The benefits that drew me towards it are less weight (no pulley on the flywheel, no belt, smaller size), less weight far out on the nose, no current needed like an alternator since it's self exciting, it produces more power at lower RPMs, and the controller does a self test at every startup and is smart with regard to overvoltage or too much amp draw. It will put out 15 amps starting at around 800-100 RPM, and will reach a full 30 amps around 1800, compared to a B&C 425H pad mounted alternator I was considering that reaches 15 amps around 1500 RPM and doesn't reach 30 amps until 2300 RPM. Note these are all crank speed, since B&C lists output compared to alternator speed, which is 1.3 times crank speed.
Thanks for everyone's input. I always appreciate the wealth of experience in this group.
We're going with rear mounted BC410-H Alternator, 20-40 Amps (Homebuilt) - B&C Specialty Products (bandc.com)
Damn, that's expensive. The Denso 40 A alternator used by CubCrafters retails as low as $130.
https://www.ase-supply.com/product_p/nd-021080-0760.htm
I'd like to put a rear-mounted alternator on my C180, run off the vacuum pump pad.
But besides approval issues, which are probably significant,
the little orange ones (8A ?) don't put out enough juice,
and the larger ones seem like too tight a fit between the accessory case & firewall.
Is anyone here running a rear alternator on a 180?
Cessna Skywagon-- accept no substitute!
Why? My rear mounted belt driven alternator doesn’t need improving, but mine is a B&C and uses their LR14 regulator.
That's your opinion, but not mine.
Kinda like IMHO my 88" Mac prop doesn't need improving...
but an awful lot of people must disagree with me,
hence the large numbers of skywagons running MT props.
Re alternators, I'm still running the original 35A generator, and it works fine.
I don't feel that converting to a 60A or 70A belt-driven alternator that probably weighs just as much (or maybe more) is an "improvement"--
esp since I don't need anywhere near that much amperage.
But IMHO a little direct-drive alternator that mounts right to the accessory case would be an improvement-- smaller, lighter, cleaner.
In all ways a more elegant solution.
IMHO of course.
Cessna Skywagon-- accept no substitute!
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