nuckolls.bob(at)aeroelect
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 Posted: Sat Feb 19, 2011 6:30 am Post subject: First Start Alternator Woes |
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At 05:42 AM 2/19/2011, you wrote:
| Quote: | Thanks Bob.
This morning, I got the ALT to come on line. I connected up two
30Amp blade fuses in parallel on a fully charged battery and voila,
14.5 volts on the BUS.
Is it possible the drained battery was pulling more AMPs than the
ANL40 and 20AMP fuse could handle?
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Sure. But I'm mystified as to why the ANL40 got into
trouble. Here's the spec sheet on ANL current limiters:
http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ANL_Specs.pdf
Note that these are VERY ROBUST protective devices
intended to carry rated currents + overloads for
protracted periods of time. I.e. these are not
intended to be fast acting fuses. They're intended
to clear HARD faults in power distribution systems.
My best guess is that your 'ANL40' may have been
a poorly crafted clone that behaved more like a
fuse than a current limiter. Get a 'real' ANL of
any current rating from 40 to 60 an you'll probably
fix the problem.
If you can't find a qualified ANL, consider an
automotive in-line fuse holder for the MAX series
of plastic fuses.
http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/MAXI_Specs.pdf
http://aeroelectric.com/Pictures/Fuses/Fuse_Holders/MaxiFuse_Holder.jpg
Install a MAX70 or MAX80 fuse in the holder.
I charged of in the direction of 'failed diodes'
assuming that your 'anl' fuses were performing
to specs. But your question is right on point.
A 60A amp alternator charging a dead battery will
go flat-out and quite often will trip a 60A
breaker. My assumption was out in the weeds.
http://www.aeroelectric.com/articles/anl/anlvsjjs.html
http://www.aeroelectric.com/articles/never_again.html
The 60A breaker on the B-lead of 60A alternators
in tens of thousands of GA aircraft are DESIGNED
to nuisance trip under precisely the conditions
you hypothesized.
Get the right b-lead protection installed and I
think you're good to go. By the the way, paralleled
fuses is a useful experiment but not a permanent
fix.
Bob . . .
| Quote: | Subject: Re: Fwd: First Start Alternator Woes
At 06:34 PM 2/18/2011, you wrote:
>Dear Bob,
>
>I did a first start of my RV7 EI-EEO last weekend and the alternator
>did not come on line.
>
>I have an L-60 and LR3 regulator from B&C. Wiring diagram attached.
>
>On working through B&Cs LR3 troubleshooting all voltages looked
>good, then checked the Field connector. Connectors were pushed back.
>Great we found the problem. No joy. Then went through all the checks
>again. The ANL40 that I have installed was blown. We put a blade
>fuse holder with a 20Amp fuse in its place. Fired her up, switched
>on the Alt field (no electrics on expect for the EFIS) and the 20Amp
>fuse blew almost immediately.
>
>What are the modes that could produce this behaviour? Would a 20AMP
>fuse always blow? I see now that the ANL40 should have been a 60ANL,
>but why would the ANL40, with such low loads. If the battery was
>low, would that be the reason.
The only thing that will blow an ANL
b-lead fuse is shorted diodes in the
alternator. A normally working alternator
cannot open its own b-lead protection.
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Bob . . .
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