The GAMI Supplenator unfortunately doesn’t exist. But the B&C backup alternators (which have been on the market about 25 years) are similar – 12V units and de-rated slightly at 24V.
Has anyone heard of anyone converting a 12V aircraft to 24V?
Peter wrote:
The GAMI Supplenator unfortunately doesn’t exist
12/14V airplanes should install a supplemental alternator
Well, that confirms an 28V alternator is generally more powerful than its 12V counterpart.
Has anyone heard of anyone converting a 12V aircraft to 24V?
No, I can hardly imagine any situation where that would make sense. Shouldn’t be too hard, though, replacing the starter and its cabling perhaps the hardest bit. On a non-complex plane, that is. An auto-pilot (which some here seem to consider an essential part of any aircraft) might be difficult with its servo motors?
that confirms an 28V alternator is generally more powerful than its 12V counterpart.
I think perhaps a more descriptive position might be: if you put more field current into a “12V” unit, and possibly spin it a bit faster, you get better value out of the iron and copper which is already in it 
That is how e.g. B&C manage to sell the same DENSO 12V unit as 12V or 24V, just by having a different voltage regulator. Better still, the VR is the same unit but has a different ceiling on the field current (or, if the VR is pure-PWM they limit the duty cycle to 50% in a 24V system). The alternator field coil has a low enough resistance (about 4 ohms I think) to sink enough field current for either job.
The mechanical energy input of course has to match; there is no free lunch.
An auto-pilot (which some here seem to consider an essential part of any aircraft) might be difficult with its servo motors?
Sure… However I think most 12/24V autopilots use servos which work on either. The King ones I know certainly do. They have enough leeway in the motor rpm to achieve the required gain at 12V, IIRC. The tacho feedback takes care of it.
The oxyfly FAQ links to it, suggesting that for an oxyfly installation, 12/14V airplanes should install a supplemental alternator :)
Yes; very funny. Someone please sent them to EuroGA for re-edukkkation
I think Oxyfly have no clue as to what is involved in terms of paperwork to install a second alternator on a certified plane…
I have no idea why GAMI have dropped that product. Its great selling point was that they modulated the field current to take out the 3 phase ripple (a rather obvious technique but not one I have ever heard of actually being used mainstream) so they don’t need a battery connected in order to get smooth DC. However the whole company seems to have lost its direction. They do the matched injector sets (which is a great product) and AIUI make money from doing the travelling seminars.
The phrase “12/14V airplanes should install a supplemental alternator” is an irrelevance here – it refers to the Oxyfly being a 28V only unit, so 14V planes need to install a 28V alternator of some sort. The unit draws a lot of current – up to 15A. Obviously one could use an inverter too but the input of that would draw over 30A which is highly likely to be infeasible on most GA planes. Actually even 15A is quite a lot.
Somewhere along this tread I read that GA batteries are expensive, have to be expensive, and that any comparison with cheap car batteries doesn’t count, since car batteries are basically crap and unreliable, and have a short lifetime. Now … is this so ? my last car battery latest 8 years, from 2008 to 2016. And than it didn’t fail in a split second, but gradually had to be charged more often, until I decided to buy a new one – once again for 80 bucks.
How did this happen ? Responsible had been a little device, which had cost 30 Euros, lasted over 20 years and which sends small spikes of current through the battery – entirely compatible with all other electronics on board. Please don’t ask if it’s approved, TSOed, and all the rest. Of course not. But if this can be done with a cheap car battery, why can’t this be done with a Concorde or Gill ?
Basic problem for GA is lack of production volumen compared to many other industries including auto parts. With increasing production volume price per unit drops. Add to this cost of certification and lack of competition on parts in many cases. Fx compare prices on same product certified and non-certified (expimental), gives an idea about high certification cost. Money is limited for RD in GA. In the low end of ga market (piston) the quality of components is really not that great, much of the stuff used there is still 60’s and 70’s technology. Best course for GA is to use technology from other industries, mostly auto. LED lights is a good example. But things generally have to be adapted to larger temperature changes, pressure changes, vibration, g-load etc, which they where never designed for in auto applications.
@AJ you are looking at one of these. These battery conditioners apply current pulses to the battery and strip off the sulphide layer, or something like that. I have one too and it works great for my Concorde battery; I posted about it in the linked thread.
What supports high GA battery prices is lower volumes plus a belief that a battery model cannot be changed for a different one unless the new one has an STC. Sometimes that is true but usually it isn’t, especially in the FAA world where changing from e.g. a Gill to a Concorde is generally regarded as a Minor Alteration. That misbelief results in a lack of competition because it is hard to enter the marketplace.
I think it’s regulation that keeps battery prices high. If everyone could bolt in an odyssey battery into a Cessna (and many people have) straight away the cost drops by 50%
Are 24V batteries less robust that 12v ones? Ive known many aircraft where the students flattened the battery so it’s been started by prop swinging and my observations is the 24 volts seem more likely to fail shortly after.
