Main Alt and Spline Alt Alternative?

BMC_Dave · #1 01-12-2019, 11:55 AM

After realizing I didn't need to spend exorbitant sums of money on an "aircraft" alternator, I'm wondering if there are any spline alternatives? I think the spline might just be aircraft specific so I'm probably SOL, thought I'd ask though.

Here's what I'm eyeing for my main: https://www.oreillyauto.com/detail/b.../4602545?pos=2, though I'll have to do some surgery to switch to external regulation.

Backup will be on the accessory pad and will probably cost me $$$.

I will be buying the premium external primary and standby regulators, while I could roll my own for the effort those seem like a good value.

lr172 · #2 01-12-2019, 12:08 PM

There are automotive options that are 50 amps, CC rotation and externally regulated. I forget the lester number, but have posted it in the past.

Is was going to try machining a spline adapter, but it seemed like a lot of work and ultimately skipped the second alternator.

Larry

rv7charlie · #3 01-12-2019, 01:47 PM

Rotation direction doesn't matter with virtually all current alternators; the internal fan will still cool it and the electrons don't care.

Many of the alternators for newer vehicles are set up for external regulation (the car's CPU handles that, along with door locks and toilet flushes).

Having said that, the external reg mod is typically fairly easy if you're handy with a soldering iron, but be aware that if it ain't broke...it might be after modding.

Having said *that*, I'm not enough of a machinist to do the spline drive adaptation. If you look at a spline drive alt, the entire front of the case is replaced with a casting that includes the bearing assy & nose to bolt on the engine. Perhaps one could make a pulley adapter for the spline drive, then use a belt to drive an unmodified alt (meaning you could get full output instead of compromised output), but failure after either attempt could put metal in the engine. (Ask Continental owners about gear drive starters.)

For me, doing rolling my own spline alt would be like floating sheet rock or installing blown-in insulation. :-)

Charlie

BMC_Dave · #4 01-12-2019, 02:16 PM

Yeah that's what I figured, thanks for the confirmation. The pulley conversion sounds like an interesting project when I have more time.

If anyone has a P/N for a 60A+ auto alternator that's externally regulated I'd appreciate the advice.

BMC_Dave · #5 01-13-2019, 10:36 AM

So I cam across a matronics post that suggests modifying an IR ND alternator makes it incompatible with the B&C LR3 regulator, positive switching vs. ground switching. Is this the case?

http://www.matronics.com/forums/view...f16d81dfb9931e

As much as I'd like to have a drop in replacement I can easily source I'm leaning toward modifying an ND since that's what the "aircraft" alts are and they seem to have better reliability.

lr172 · #6 01-13-2019, 12:07 PM

Quote:

Originally Posted by BMC_Dave

So I cam across a matronics post that suggests modifying an IR ND alternator makes it incompatible with the B&C LR3 regulator, positive switching vs. ground switching. Is this the case?

http://www.matronics.com/forums/view...f16d81dfb9931e

As much as I'd like to have a drop in replacement I can easily source I'm leaning toward modifying an ND since that's what the "aircraft" alts are and they seem to have better reliability.

Externally regulated alternators are pretty standard; they all use the same field polarity scheme (can't remember if it's neg or pos, but think it is POS). Internally regulated alternators are not standard (irrelevant to a stanadard installation, but relevant to a conversion process to externally regulated). The US manufacturers use one polarity and the Asian's use the other. However, when you do your surgery to make it external, you can make it whatever polarity you want it to be. However, the process is different for each polarity type and you'll need some guidance to properly wire it. The internal VR modules do not have polarity markings, so you have to figure it out by understanding the polarity of the other components it is wired to.

Do you really need 60 amps? Buying an OTS 50 amp externally regulated unit offers not only ease of installation, it allows you to easily swap the ALT away from home if it fails. They are $40 and available at any autozone.

Larry

rv7charlie · #7 01-13-2019, 01:06 PM

Larry makes good points, but since you seem to have my aversion to needlessly expensive stuff, there are alternatives.

If I were bound to the vac pad for the 2nd alt, I'd consider using B&C hardware justified by the 'floating sheet rock' metaphor. For the primary, I've used internally regulated versions for a couple of decades. The only real downside is lack of positive control. You can achieve that with one high current relay and an overvoltage protection module. Nuckolls used to detail that technique in 'the book', but pilots were 'testing' the function in flight with the alternator loaded down, and early IR alternator regulators would die when the load was 'dumped'. The solution for that is the He Haw principle: If it hurts when you do that, DON'T DO THAT. You can find the circuit for IR alternator OV protection by looking at the drawings that show the permanent magnet alternators. The 'B lead' from the PM alt's regulator feeds through a relay, and the OV module trips the circuit breaker that supplies coil voltage. So with the complication of one relay, you get $600 functionality for $60.

Charlie

BMC_Dave · #8 01-13-2019, 02:14 PM

Great info on alternator regulation, thanks Larry. My only aversion to going cheap externally regulated is that ND alts seem to have a good reliability history. I found this one: https://www.oreillyauto.com/detail/b.../4602876?pos=0 which is a Hitachi rebuild, 60A externally regulated. If I were to be less conservative on my cruise loads I could just make 50A work if the alt you're referencing is a better quality.

Charlie: By saying "early IR" do you mean it's not as much an issue anymore? I would want a way to periodically test the function of the secondary alt without hurting the primary. After much research it sounds like the main failure of alternators is the internal regulator, hence my wanting to get away from it.

rv7charlie · #9 01-13-2019, 02:55 PM

If weight (or space) is a big concern, I'd weigh that alt you just linked. Hard to tell by just looking at the pic, but it appears to be a rather old model & could be 2-5 lbs heavier and a bigger frame than some of the more recent alts. Also, the external fan can bite you (or at least your cowl) if space is tight. Ask me how I know. :-)

When I said 'earlier' it did imply that newer offerings were more robust when it comes to load dump. And most probably are; there are numerous engineering documents describing new regulators that are specifically designed for load dump immunity. Problem is, most of us homebuilders don't have access to the detailed mfgr specs that would tell us about a particular alternator. That goes triple for something that's rebuilt or overhauled; we can't know what the rebuilder stuck in the back.

The trick for avoiding load dump is to not do it with the alternator heavily loaded. Not hard, if you wait a few minutes after startup to test, to let the battery recover, and keep the high current stuff off while you test. Another (but more convoluted) trick is to have a way of monitoring both without turning one on/off, but that would require some fat Schottky diodes in the B lead paths, with voltage monitoring ahead of the diodes.

Charlie

BMC_Dave · #10 01-13-2019, 05:02 PM

Good points Charlie. Been looking for examples like you said, I think this is similar to what you suggested: https://www.bandc.aero/pdfs/505-500_rev_j.pdf

Minus the capacitor. I imagine I'd need a larger capacity relay, 60A for a 60A alt maybe, if they make those. Maybe a schematic of this with a IR alt is somewhere out there?