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chris Sinfield
Joined: 28 Nov 2006
Posts: 270
Location: Sydney Australia
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 Posted: Sun Feb 14, 2010 1:47 am Post subject: Larger alternator 30 Amp |
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Hi
has anyone fitted a 30/40amp alternator on a Jab3300? Someone once showed me a picture of one on the vacum pump drive but did not say if it was successful. I am doing my elec loads and so far over 30 amps needed.
Chris.
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Larzfromarz
Joined: 18 Oct 2006
Posts: 11
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| Posted: Sun Feb 14, 2010 8:02 am Post subject: Re: Larger alternator 30 Amp |
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Chris -
I'd be curious as the list of equipment (and thus loads).
With a 20% margin (results in 24 amp load- continuous) it would seem difficult to reach that limit with most modern electrical equip, especially with a fixed gear aircraft with no air-conditioning.
Just curious as many folks ignore the process of summing the electrical loads and I am happy to see that you are. Don't forget to classify loads as intermittent and continuous.
Thanks,
Larry
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craig(at)craigandjean.com
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| Posted: Sun Feb 14, 2010 10:09 am Post subject: Larger alternator 30 Amp |
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I recall asking about running an alternator off of the vacuum pump drive a
while ago. One comment was that the (direct) drive didn't turn fast enough
to produce adequate current. In a conventional setup with a pulley the
smaller pulley on the alternator makes it turn faster than the crank. Check
the specs of the alternator before you dive in.
If you have purchased your electrical gear yet it may be simpler, more
reliable and cheaper for find electronics and lighting that draws less. Some
of the LED lighting, radios and EFIS draw less than their predecessors.
-- Craig
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matronics(at)rtist.nl
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Jaba-who
Joined: 17 Feb 2010
Posts: 4
Location: Cairns, Australia
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| Posted: Wed Feb 17, 2010 2:53 pm Post subject: Re: Larger alternator 30 Amp |
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I haven't fitted it yet but I have done a lot of research and purchased a smaller B & C Specialty Products alternator (SD- 8 ) that fits on the vacuum pump pad.
B & C make a larger model ?SD- 20 I think (maybe I have the number wrong) and the smaller SD - 8. They produce the amps defined by the number in the name. (At about 3500 RPM)
They give a table of Output:RPM which says at Jabiru cruise RPMs of say 2700 the SD - 8 will output about 5.5 Amps.
SD-8 Sydney University Aviation engineering department have fitted the larger model to a Jabiru and it works well BUT.....(always a BUT)..it generates a very strong magnetic field that disrupted the compass when mounted in the usual position on the dash. I spoke to the head engineer who did the work and he said the SD-20 used different system than the SD-8 which he thought would generate less magnetic field. Though he was only theorizing as he hadn't actually tried it.
I have a few amps shortfall due to addition of extra electronics, extra radio, flight computer etc and definitely know the Jabiru alternator is not always outputting the specified 18 Amps at cruise. I have twice lost all electrical power on longer flights when the battery ran down with everything on. And that's with a load calculation of 14 AMps.
No big disaster then because the system shut down, charged up the battery to the voltage cutoff level and everything came back on after about two minutes (except the flight computer which was the big drawer) and all continued happily. Fortunately it was at a time when I didn't need either radio or transponder.
Our aeroclub had a Jabiru and they had to have a rule of landing lights off as soon as no longer required for same reason.
I have been flying without the fancy flight computer till I get some bigger alternator system added.
Just as an aside the rumour is that Jabiru factory are currently looking at a bigger alternator (or possibly stacking a second one on the existing one) so all this may be a mute point soon.
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chris Sinfield
Joined: 28 Nov 2006
Posts: 270
Location: Sydney Australia
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| Posted: Fri Feb 19, 2010 2:13 am Post subject: Re: Larger alternator 30 Amp |
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thanks for the update..
I have a mate going to do the JAB dealer engine maint week long course at Bundy. I will ask him to ask about the new Alt..
chris
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