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jonlaury
Joined: 06 Nov 2006
Posts: 336
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 Posted: Sat Feb 13, 2010 10:51 am Post subject: Z-13 question |
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I have an all-electric airplane and am using Z-13 with a 40a stby alt. All mandatory engine power (EFI, IGN, etc) is on the battery bus
As I understand Z-13, if the battery has a short , it takes down the battery bus, the redundant alternators notwithstanding, as there is no disconnect from the battery/batt bus. It seems that putting a DPST ON-ON switch between Batt Bus and Batt position & Alt 2 position would allow one to isolate a problematic battery and supply Alt 2 power to the Batt Bus and keeping the prop going round.
I recognize that this defeats the bonehead-proof design of a hot battery bus, but adds an option should there be a battery problem. I'm not sure if it's a benefit or not.
I would wire the two switch poles together to the batt buss, both sides of position one to the battery, both sides of position 2 to Alt 2. I think I'm buying some switch redundancy with a DPST.
What do you all think?
John
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fvalarm(at)rapidnet.net
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| Posted: Sat Feb 13, 2010 2:11 pm Post subject: Z-13 question |
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John,
I don't think it's a good idea.
I don't believe that a "short" is a failure mode for a battery that you
should be concerned with because it is too rare especially on a well
maintained battery. Perhaps you meant a single shorted cell, while also
rare but if it did happen, would still produce enough current at an
acceptable voltage to run EFI, or so I believe.
Adding switches or relays to add control of the battery bus obviously adds
failure points which I think would be orders of magnitude more likely than a
"shorted" battery.
If your main alternator (electrical energy generator) fails, the battery
(electrical energy reservoir) is a short term back up and should be sized to
power your essential loads longer than your total onboard fuel supply. You
have a second alternator, so that is your indefinite backup (in my opinion).
If your battery is always maintained and replaced regularly, I don't think
you will ever go without sufficient electrons at-the-ready.
My opinions only. Others may disagree.
Bevan
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Bob McC
Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON
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| Posted: Sat Feb 13, 2010 10:03 pm Post subject: Z-13 question |
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John;
See embedded comments. These are not intended in any way to be “smart assed” just trying to illustrate my personal opinion and understanding of the question.
[b]> --
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_________________
Bob McC
Falco #908
(just starting) |
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nuckolls.bob(at)aeroelect
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| Posted: Sun Feb 14, 2010 6:34 am Post subject: Z-13 question |
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At 12:51 PM 2/13/2010, you wrote:
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I have an all-electric airplane and am using Z-13 with a 40a stby alt.
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40A standby alternator? How big is your main alternator
and how are you mounting a driving a 40A standby machine?
How have you integrated a 40A alternator into Z-13? At
one time, there was a Z-13/20 that proved not to be an
elegant recipe for success and it was withdrawn.
| Quote: | All mandatory engine power (EFI, IGN, etc) is on the battery bus
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How much current do each of your battery-bus accessories
draw?
| Quote: | As I understand Z-13, if the battery has a short , it takes down the
battery bus, the redundant alternators notwithstanding, as there is
no disconnect from the battery/batt bus. It seems that putting a
DPST ON-ON switch between Batt Bus and Batt position & Alt 2
position would allow one to isolate a problematic battery and supply
Alt 2 power to the Batt Bus and keeping the prop going round.
I recognize that this defeats the bonehead-proof design of a hot
battery bus, but adds an option should there be a battery problem.
I'm not sure if it's a benefit or not.
|
The probability of the 'problem' you are hypothesizing
is vanishingly small especially if you worry as
strongly about maintaining the battery as you seem
to worry about it failing. In the TC aviation community,
for high performance airplanes, it is common to pull
a battery from service at about 80% capacity . . . it
is still quite capable of starting engines but no
longer meets design goals for emergency power.
Cells shorted with some regularity in the old flooded
batteries but only after they were no longer suitable
for flight.
| Quote: | I would wire the two switch poles together to the batt buss, both
sides of position one to the battery, both sides of position 2 to
Alt 2. I think I'm buying some switch redundancy with a DPST.
|
Before we address details of hardware, let's examine
details of architecture and load analysis. I'm not
sure we have a clear picture of what your proposed
system looks like.
Bob . . .
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jonlaury
Joined: 06 Nov 2006
Posts: 336
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| Posted: Sun Feb 14, 2010 9:09 am Post subject: Re: Z-13 question |
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"How big is your main alternator
and how are you mounting a driving a 40A standby machine?
How have you integrated a 40A alternator into Z-13? At
one time, there was a Z-13/20 that proved not to be an
elegant recipe for success and it was withdrawn. "
The main is 60A. The engine is a Franklin. When I installed EFI, the now vacant mechanical fuel pump pad provided a place to install a second alternator drive. The 40A ND alternator bolts thru it's mounting boss to the accessory case and the adjustment bracket the same.
Re Z-13/20, we had a discussion about that and you recommended /8.
I really didn't investigate /20 any further to see what differences there are from /8 and I assumed that the size of the stby alternator in /8 was irrelevant.
"How much current do each of your battery-bus accessories
draw? "
EFI 5-8 amps (duty cycle dependent), EI (both) 7amps, Fuel pump (1 of 2) 3.5amps
"The probability of the 'problem' you are hypothesizing
is vanishingly small ...snip...after they were no longer suitable
for flight."
Point taken. Not worried about it any more.
John
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nuckolls.bob(at)aeroelect
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| Posted: Sun Feb 14, 2010 11:49 am Post subject: Z-13 question |
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| Quote: | The main is 60A. The engine is a Franklin. When I installed EFI, the
now vacant mechanical fuel pump pad provided a place to install a
second alternator drive. The 40A ND alternator bolts thru it's
mounting boss to the accessory case and the adjustment bracket the same.
Re Z-13/20, we had a discussion about that and you recommended /8.
I really didn't investigate /20 any further to see what differences
there are from /8 and I assumed that the size of the stby alternator
in /8 was irrelevant.
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Is your standby alternator internally or externally
regulated?
Bob . . .
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jonlaury
Joined: 06 Nov 2006
Posts: 336
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| Posted: Sun Feb 14, 2010 12:01 pm Post subject: Re: Z-13 question |
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> Is your standby alternator internally or externally
>regulated?
ER. Was IR.
Out put is 20a (at) 2000 shaft rpm, 30a (at) 3200, 40a (at) 5000. Engine alt drive (at) 1.65 x eng rpm.
John
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nuckolls.bob(at)aeroelect
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| Posted: Sun Feb 14, 2010 1:01 pm Post subject: Z-13 question |
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At 02:01 PM 2/14/2010, you wrote:
| Quote: |
> Is your standby alternator internally or externally
>regulated?
ER. Was IR.
Out put is 20a (at) 2000 shaft rpm, 30a (at) 3200, 40a (at) 5000. Engine alt
drive (at) 1.65 x eng rpm.
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Hmmmm . . . you may not quite see 40A from this alternator
assuming red-line at 2700 . . . but it still seems quite
adequate to the task.
What's the expected loads on the battery bus?
Bob . . .
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jonlaury
Joined: 06 Nov 2006
Posts: 336
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| Posted: Sun Feb 14, 2010 8:42 pm Post subject: Re: Z-13 question |
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"Hmmmm . . . you may not quite see 40A from this alternator
assuming red-line at 2700 . . . but it still seems quite
adequate to the task.
What's the expected loads on the battery bus? "
EFI 5-8 amps (duty cycle dependent), EI (both) 7amps, Fuel pump (1 of 2) 3.5amp, E-Bus alt feed 10 amps. So all up, less than 30 amps including transmit power and full duty cycle on the injectors.
The standard pulley on the Franklin overdrives the alt by about 10% and I could change pulleys to get the alt shaft speed up more, but I think the 30 amps is plenty and I'd like to keep the stby alt speed as low as possible for bearing life. 30 amps happens at about 1940 eng rpm so at normal power settings, there would be more than 30amps available.
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