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nuckollsr(at)cox.net
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 Posted: Thu Nov 09, 2006 5:49 am Post subject: Stacked 14v systems for 28v |
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At 05:52 PM 11/8/2006 -0700, you wrote:
| Quote: |
Well based on the response form Bob and others I revisited the Engine/Belt
driven A/C system. It turns out that with my engine and cowl combination
that there is not room enough to mount both a compressor and an
alternator. So, it looks like my options are; either to convert my
electric system to 28v (ugh!). or pursue the 'stacked' approach.
Bob:
When you say 'electrically isolated' are you saying that the "top" system
would have to NOT share a common ground with the bottom system? what other
'isolation' would be required
"This would require a special alternator for the #2 machine." I assume
you are referring to the "top" system (?) could the SD-20 perform this
function as the alternator for the #2 machine, what is the "Special"
requirement of this alternator.
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No, the SD-20 is a 20amp machine. I'm suspecting that both
of your 14 volt systems will need to be in the 60 amp class
or larger. How much power does that a/c compressor need?
The "top" system cannot be grounded to airframe. Alernators
have diode arrays that are common to the alternator case by
design. If I were crafting a floating system for stacking,
I'd bypass the built in diodes and bring all of the alternator's
field and stator wires out to be handled as needed for
the system to run 14v above ground.
| Quote: | A bottom alternator large enough to carry ship's load plus the A/C load is
not a problem.
Re: backing up the bottom with the top. When you say 'complex switching' I
infer this is more than just the cross feed contactor approach in Z14,
care to elaborate any further?
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The problem is similar to the use of two batteries
in series for starting and running them in parallel
for flying. You need to sequence contactors in the right
order to accomplish the switching . . . stuck contactors
can create potential for spectacular events (a number of
MU-2's were set on fire about 35 years ago before they
installed limiters).
| Quote: | Thanks for the information and advice so far and for any additional
insight you can provide.
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This is a MAJOR task. You'll have to fabricate a special
alternator regulator installation but is all possible.
Bob . . .
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Deems Davis
Joined: 09 Jan 2006
Posts: 925
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| Posted: Thu Nov 09, 2006 6:47 am Post subject: Stacked 14v systems for 28v |
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Thanks again Bob,
The electric A/C system consumes 45 amps at peak load. Do _both_
alternators need to be capable of carrying ship's load plus the full
load of the A/C?. If so, then that's going to put the Kabosh to this
approach because there is not room enough to mount a 2nd 60-100A alt.
(beginning to sound like an onerous task for an electric greenhorn)
I was told that there is some 'new technology' (?) that will take the
output from an externally regulated alternator and split it into 2
separate outputs, one being 12-14v and the other 24-28v. I'm trying to
track this down, just wondering if you had heard anything on this tangent.
Deems Davis # 406
Finishing - ( A Misnomer ! )
http://deemsrv10.com/
Robert L. Nuckolls, III wrote:
| Quote: |
No, the SD-20 is a 20amp machine. I'm suspecting that both
of your 14 volt systems will need to be in the 60 amp class
or larger. How much power does that a/c compressor need?
> Thanks for the information and advice so far and for any additional
> insight you can provide.
This is a MAJOR task. You'll have to fabricate a special
alternator regulator installation but is all possible.
Bob . . .
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Thu Nov 09, 2006 9:12 am Post subject: Re: Stacked 14v systems for 28v |
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Whenever this 28V from 14V subject comes up I implore the adventurous builder to get the right unit in the first place instead of trying to stuff this beast into the hole.
Viz.--Buy the right-voltage unit. If there isn't one, call the manufacturer.
Viz.--Modify the unit to run on 12V. Even this is easier than up-converting the 14 volts.
Viz.--Do the whole job another way. Put dry ice in the glovebox, move to Alaska, open a window...whatever. It's surprising how cool sitting on a seat filled with silver dollars can be.
Remember, voltage conversion is easy if the power is small. But FORGET IT when the power gets large. Find some other way.
My two cents.
"When trouble arises and things look bad,
there is always one individual who perceives
a solution and is willing to take command.
Very often, that individual is crazy."
--Dave Barry
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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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Deems Davis
Joined: 09 Jan 2006
Posts: 925
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| Posted: Thu Nov 09, 2006 10:20 am Post subject: Stacked 14v systems for 28v |
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Thanks Eric, I appreciate the input, and I'm beginning to understand
that this is a bigger task, than my limited skills/knowledge will support.
So what about this for an 'approach'
Use 28V alternator (100amp capacity)
28V starter
2 14V batteries connected in series to produce 28V to the A/C
Take a 12-14/v feed off of the 1st battery and use that to drive the
existing 12V electro whizzies.
?
Or should I just sweat and save some $'s
Deems Davis # 406
Finishing - ( A Misnomer ! )
http://deemsrv10.com/
Eric M. Jones wrote:
| Quote: |
Whenever this 28V from 14V subject comes up I implore the adventurous builder to get the right unit in the first place instead of trying to stuff this beast into the hole.
Viz.--Buy the right-voltage unit. If there isn't one, call the manufacturer.
Viz.--Modify the unit to run on 12V. Even this is easier than up-converting the 14 volts.
Viz.--Do the whole job another way. Put dry ice in the glovebox, move to Alaska, open a window...whatever. It's surprising how cool sitting on a seat filled with silver dollars can be.
Remember, voltage conversion is easy if the power is small. But FORGET IT when the power gets large. Find some other way.
My two cents.
"When trouble arises and things look bad,
there is always one individual who perceives
a solution and is willing to take command.
Very often, that individual is crazy."
--Dave Barry
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=73387#73387
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retasker(at)optonline.net
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| Posted: Thu Nov 09, 2006 11:24 am Post subject: Stacked 14v systems for 28v |
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Unfortunately, unless the other electrowhizzies are very low amperage,
you will be forever overcharging the second battery with this arrangement.
Depending what the amp draw of your other 12V electrowhizzies are you
might try using a 28V to 14V converter for them. Also, be aware that a
lot of the newer electrowhizzies will run from 12-28V so you could run
those off the 28V.
Depending on your mix of electronics you might be able to run the
majority off the 28V and run a few low draw units from the second
battery or from a small 28 to 14V converter.
There are certainly ways to do what you want to do, but I suspect that
you may end up sweating...
Dick Tasker
Deems Davis wrote:
| Quote: |
Thanks Eric, I appreciate the input, and I'm beginning to understand
that this is a bigger task, than my limited skills/knowledge will
support.
So what about this for an 'approach'
Use 28V alternator (100amp capacity)
28V starter
2 14V batteries connected in series to produce 28V to the A/C
Take a 12-14/v feed off of the 1st battery and use that to drive the
existing 12V electro whizzies.
?
Or should I just sweat and save some $'s
Deems Davis # 406
Finishing - ( A Misnomer ! )
http://deemsrv10.com/
Eric M. Jones wrote:
>
> <emjones(at)charter.net>
>
> Whenever this 28V from 14V subject comes up I implore the adventurous
> builder to get the right unit in the first place instead of trying to
> stuff this beast into the hole.
>
> Viz.--Buy the right-voltage unit. If there isn't one, call the
> manufacturer.
>
> Viz.--Modify the unit to run on 12V. Even this is easier than
> up-converting the 14 volts.
>
> Viz.--Do the whole job another way. Put dry ice in the glovebox, move
> to Alaska, open a window...whatever. It's surprising how cool
> sitting on a seat filled with silver dollars can be.
> Remember, voltage conversion is easy if the power is small. But
> FORGET IT when the power gets large. Find some other way.
>
> My two cents.
>
> "When trouble arises and things look bad,
> there is always one individual who perceives
> a solution and is willing to take command.
> Very often, that individual is crazy."
> --Dave Barry
>
> --------
> Eric M. Jones
> www.PerihelionDesign.com
> 113 Brentwood Drive
> Southbridge, MA 01550
> (508) 764-2072
> emjones(at)charter.net
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=73387#73387
>
>
>
>
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Thu Nov 09, 2006 1:33 pm Post subject: Re: Stacked 14v systems for 28v |
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If you Google "12 volt air conditioner" you get a boatload of hits. I'd search very hard for a 12V solution on the internet.
Consider that almost all 12V cars have air conditioners--with the compressor running off the engine. Do you need a huge electric motor to keep cool when the engine is not running? Is this a mode of operation important to you? Better an engine-driven compressor than a second alternator.
They used to use ground a/c. Could your operation do this?
I come at this question from a desire to minimize weight and complexity. My air conditioning comes from the big fan in the nose. This may not be where you are coming from.
"Nothing is too wonderful to be true."
James Clerk Maxwell, discoverer of electromagnetism
"Too much of a good thing can be wonderful."
Mae West, discoverer of personal magnetism
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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