Alternator Advice

[Doug Rohrer]

I am building an RV-14A, day/night VFR panel. No IFR. This is the same configuration I have in my flying -9A which I really like. I will have FlyLED Works strobe/navigation/landing lights in the wing tips. All Garmin G3X panel with one radio. I am considering going with a B&C vacuum pad drive alternator in place of the conventional belt drive unit. I will have one Odessey PC680 battery and the Garmin G5 unit will have its own standby battery. Pitot is non-heated. B&C has several rear drive alternators in the 20-40 amp range, which would be plenty for this configuration. I also like the idea of moving a little weight aft, as I understand the -14A with a CS prop can be a little nose heavy. Can anyone think of a reason the rear drive alternator idea would not be so good?

 

[Av8rRob]

If anything the -14 can be tail heavy. Never heard of a nose heavy one

 

[JET14]

Alternator

Keep in mind the alternator output is dependent on RPM and the accessory drive probably spins slower than the belt drive up front. B&C can probably advise you.

 

[rocketman1988]

Yes

The 20-40 amp vac pad came supply around 30 a at typical cruise power settings. It does spin slower than the belt drive alternators.

 

[BillL]

Sooo - - a friend has one - -check continuous output rating vs RPM with B&C compared to your operating needs. You might consider the MZ30 by Monkworz. It is a true 30 amps continuous output at cruise RPM. I like mine as a backup.

 

[dmattmul]

B&C Pad Mount

I'm assuming your 390 has the pad mount gears installed. Vans removed this option for a short time and most did not order this variant. (I know some who accidently did) Your W&B will be fine, the aft heavy rumor was a little misleading and certainly not nose heavy, after all Vans put a 360 in a 14A. Also, the 14 has more weight aft than the A model. I would not be concerned about W&B. The pad mount as mentioned does spin slower and mine below 1,400 RPM produces very little amperage. I would not purchase the new B@C pad mount rated at 35 - 50 amps as the clearance is tight with your oil filter already. As long as you don't have an energy dependent system and VFR go for it. Not needing a belt would be a plus++. (Removing the prop to change the belt a PITA)

 

[PilotjohnS]

Just me

When I bought my pad mount B&C alternator that was the lightest weight option so I went for it. I think B&C now makes a traditional belt driven alternator with the same weight as the pad mount; the advantage being that the current output is higher at low RPMs.

 

[Doug Rohrer]

Good points about lower charging rates at low RPM's, as well as checking to see if the drive gear comes with the engine. I have the non-Thunderbolt 210 HP IO-390 engine on order for delivery later this year. I will check with Matt at Van's about the drive gear. I am very happy with my belt drive B&C alternator on my -9A and could go with that.

 

[dmattmul]

Amp review

I just checked my Savoy Analysis for AMP2 vs RPM and when required getting 12 amps at 1,600 RPM and 28 amps at 2,400 RPM. Check your amp needs but doubt for a VFR platform need more than 12-14 amps in flight and 22 amps with landing, pitot heat and strobes. My pad mount alternator not really stressed as it just runs my essential bus and the primary bus feeds it when RPM's are low.

 

[dmattmul]

BC410-H B&C Alternator (20-40 amps)

Flew today from TPA to CRG (The FBO (JAX Exec Jet Service)) by the way is great to work with, use of crew car and comp barbecue lunch on Fridays. Normally I keep my batteries on a tender but wanted to test what a battery that was not fully charged would take from the pad mount alternator. From idle to 1,100 RPM the alternator's output was 0. Starting at 1,320 the output was 13 amps, 1,700 RPM the output was 19, 1,820 went to 26 amps, 2,170 was 31 amps and 2,620 RPM was 34 amps.

There is another generator out there (Monkworkz) that might provide better output at low RPM's but don't have the data available. It's certainly very light and if using a composite prop and no primary alternator suggest doing a W&B estimate before diving in.