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rtitsworth
Joined: 16 Jan 2006
Posts: 76
Location: Detroit, Mi
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 Posted: Fri Feb 16, 2007 7:05 am Post subject: 24v vs 27 volt power supplies |
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Bob, etal,
I'm building a 24v (28v) experimental aircraft power system (Z14-dual
battery-dual bus) using a "series" of 18Ah 12v RG batteries for each 24v
"battery".
I currently do not own a 24V battery charger.
Since I do not generally plan on re-charging the batteries often, I was
planning on charging them (individually or in parallel) (when necessary)
with a 12 volt charger (which I currently own).
I've also thought of purchasing one of the smaller 24v 1Amp battery tenders
for easy top off and/or 90% charging when time allows.
However, I'd like to have a 24v (28v) power source for bench testing and
hanger testing/training. Assume a required current draw rate of 10-20 Amps
for perhaps several hours at a time. Thus, I'm assuming the 1Amp rate of
the tender will be insufficient/undesirable, even if hooked to the fully
charged batteries, as the batteries could get drawn down pretty low after a
couple hours (and I don't want to abuse my new batteries).
Thus, I am considering getting a 24v (28v) benchtop power supply or (full
size) 24v battery charger.
Ideally, I'd like to use the power supply (or charger) with the plane (in
the hanger with elec equipment installed) and at home for bench testing.
I (ignorantly) envision two alternatives:
1] Get a 24v battery charger and also use it as a bench testing power
supply. (or...)
2] Get a 24v (or 27v) power supply for bench testing and also connect it to
the plane's ground power jack for in-plane electronics testing/training.
What are the ramifications of using a 24v battery charger as a 24v power
supply for bench testing aircraft avionics ((at) home without a battery)? I
realize the output will be more like 28v - but I'm assuming the avionics
will be happy with that. Will it even work? What if I used a couple of old
auto batteries at home to "quiet/buffer" the charger?
Or alternatively, if I get a benchtop power supply (10-20 amps'ish), should
I get a 24v model or 27v model? Seems the 24v model might still
abuse/exercise the airplane batteries a bit since the actual resting battery
voltage might be slightly above 24v until they are drawn down some. Seems
however that the 27v model might get a bit overloaded if the batteries
aren't fully charged when the power supply is attached as it will try and
lift (charge) the batteries to 27v (ASAP-unregulated).
Other advantages/disadvantages and considerations? Or, perhaps these are a
couple of naive thoughts (i.e. a "little" knowledge can be dangerous).
p.s. The thought crossed my mind the in lieu of a build-log I'd just submit
a sequential list of all my naive questions to this (very helpful) forum
(lol) - i.e. the FAA 51% education and recreation mandate. Seems there's no
end to the learning opportunities here, thanks all in advance.
Rick
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nuckollsr(at)cox.net
Guest
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| Posted: Fri Feb 16, 2007 8:09 am Post subject: 24v vs 27 volt power supplies |
|
|
At 10:04 AM 2/16/2007 -0500, you wrote:
| Quote: |
<rtitsworth(at)mindspring.com>
Bob, etal,
I'm building a 24v (28v) experimental aircraft power system (Z14-dual
battery-dual bus) using a "series" of 18Ah 12v RG batteries for each 24v
"battery".
|
| Quote: | I currently do not own a 24V battery charger.
|
| Quote: | Since I do not generally plan on re-charging the batteries often, I was
planning on charging them (individually or in parallel) (when necessary)
with a 12 volt charger (which I currently own).
|
You can do this. Batteries charge based on impressed terminal
voltage. In days of old, service stations and auto-parts stores
had many batteries sharing a single power supply for maintaining
many batteries in a ready to sell state. Similarly, a battery
charger of any size has no way of knowing how many batteries
are connected . . . the act of adding more individual batteries
appears no differently to the charger than if you'd simply connected
a single, larger battery.
| Quote: | I've also thought of purchasing one of the smaller 24v 1Amp battery tenders
for easy top off and/or 90% charging when time allows.
|
Early results of experiments we're conducting right now suggest
that the line of Lilliputian chargers known as Battery Tenders,
Battery Minders, et. als. ARE capable of fully charging a battery
of any practical size . . . if you have the patience. I'll have
a better definition of this assertion in a few days.
| Quote: | However, I'd like to have a 24v (28v) power source for bench testing and
hanger testing/training. Assume a required current draw rate of 10-20 Amps
for perhaps several hours at a time. Thus, I'm assuming the 1Amp rate of
the tender will be insufficient/undesirable, even if hooked to the fully
charged batteries, as the batteries could get drawn down pretty low after a
couple hours (and I don't want to abuse my new batteries).
|
Yeah . . . I wish you hadn't bought new batteries for your
shop work . . . It was hard to stand in the booth at OSH
and watch folks walk away with brand new batteries after
having revealed that they were a year or more away from
flying. Nonetheless, it's quite possible to keep these
critters reasonably 'fresh' in anticipation of first
flight.
Your 20A requirement is pretty severe. What kind of
electrowhizzy takes that much snort? If this is a real
requirement, the options get expensive.
You might be able to find some surplus power supplies.
24v are common in outputs of up to 10A. Here's a 28V
power supply:
http://mpja.com/productview.asp?product=16033+PS
These can be paralleled so if you can find some
really cheap ones as industrial surplus, you can
parallel for more snort. This on is unusual in that
it's rated at 28V output . . . 24 is more common
but those will run your goodies just fine. Keep in
mind that your 24 v battery starts out at 25 volts
and goes down from there. 22v is 95% used up. So
your electrowhizzies should run just fine from a
24.0 volt supply.
<snip>
| Quote: | Or alternatively, if I get a benchtop power supply (10-20 amps'ish), should
I get a 24v model or 27v model? Seems the 24v model might still
abuse/exercise the airplane batteries a bit since the actual resting battery
voltage might be slightly above 24v until they are drawn down some. Seems
however that the 27v model might get a bit overloaded if the batteries
aren't fully charged when the power supply is attached as it will try and
lift (charge) the batteries to 27v (ASAP-unregulated).
|
If you get a real technician's power supply, it
will be adjustable voltage and current limit and
very quiet for use as a stand along supply.
HOWEVER . . . take care in using bench supplies
to charge batteries. For example, when deprived of
AC input power (switch turned off or power fails)
some supplies will go into ov trip (crowbar) and
put a dead short across the battery. Very smelly
smoke. Consider a surplus supply like this:
http://tinyurl.com/2lrw8e
I have several critters like this around the shop
and they're quite useful for doing ANY task. The really
neat feature is adjustable current limiting. You
can set the supply's output so that should the
unfortunate fault occur, energy delivered into
the system is not capable burning things.
| Quote: | p.s. The thought crossed my mind the in lieu of a build-log I'd just submit
a sequential list of all my naive questions to this (very helpful) forum
(lol) - i.e. the FAA 51% education and recreation mandate. Seems there's no
end to the learning opportunities here, thanks all in advance.
|
You got that right. KNOWLEDGE is essentially free,
EDUCATION is always expensive.
Bob . . .
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walter.fellows(at)GMAIL.C
Guest
|
| Posted: Fri Feb 16, 2007 10:45 am Post subject: 24v vs 27 volt power supplies |
|
|
Bob
Thanks, this comprehensive guide to power supplies is very helpful. I run into relatively high amperage surplus units from time to time but have never been quite sure of what features to look for.
Walter
On 2/16/07, Robert L. Nuckolls, III <nuckollsr(at)cox.net (nuckollsr(at)cox.net)> wrote:[quote] --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr(at)cox.net (nuckollsr(at)cox.net)>
At 10:04 AM 2/16/2007 -0500, you wrote:
| Quote: | --> AeroElectric-List message posted by: "rtitsworth"
<rtitsworth(at)mindspring.com (rtitsworth(at)mindspring.com)>
Bob, etal,
I'm building a 24v (28v) experimental aircraft power system (Z14-dual
battery-dual bus) using a "series" of 18Ah 12v RG batteries for each 24v
"battery".
|
| Quote: | I currently do not own a 24V battery charger.
|
| Quote: | Since I do not generally plan on re-charging the batteries often, I was
planning on charging them (individually or in parallel) (when necessary)
with a 12 volt charger (which I currently own).
|
You can do this. Batteries charge based on impressed terminal
voltage. In days of old, service stations and auto-parts stores
had many batteries sharing a single power supply for maintaining
many batteries in a ready to sell state. Similarly, a battery
charger of any size has no way of knowing how many batteries
are connected . . . the act of adding more individual batteries
appears no differently to the charger than if you'd simply connected
a single, larger battery.
| Quote: | I've also thought of purchasing one of the smaller 24v 1Amp battery tenders
for easy top off and/or 90% charging when time allows.
|
Early results of experiments we're conducting right now suggest
that the line of Lilliputian chargers known as Battery Tenders,
Battery Minders, et. als. ARE capable of fully charging a battery
of any practical size . . . if you have the patience. I'll have
a better definition of this assertion in a few days.
| Quote: | However, I'd like to have a 24v (28v) power source for bench testing and
hanger testing/training. Assume a required current draw rate of 10-20 Amps
for perhaps several hours at a time. Thus, I'm assuming the 1Amp rate of
the tender will be insufficient/undesirable, even if hooked to the fully
charged batteries, as the batteries could get drawn down pretty low after a
couple hours (and I don't want to abuse my new batteries).
|
Yeah . . . I wish you hadn't bought new batteries for your
shop work . . . It was hard to stand in the booth at OSH
and watch folks walk away with brand new batteries after
having revealed that they were a year or more away from
flying. Nonetheless, it's quite possible to keep these
critters reasonably 'fresh' in anticipation of first
flight.
Your 20A requirement is pretty severe. What kind of
electrowhizzy takes that much snort? If this is a real
requirement, the options get expensive.
You might be able to find some surplus power supplies.
24v are common in outputs of up to 10A. Here's a 28V
power supply:
http://mpja.com/productview.asp?product=16033+PS
These can be paralleled so if you can find some
really cheap ones as industrial surplus, you can
parallel for more snort. This on is unusual in that
it's rated at 28V output . . . 24 is more common
but those will run your goodies just fine. Keep in
mind that your 24 v battery starts out at 25 volts
and goes down from there. 22v is 95% used up. So
your electrowhizzies should run just fine from a
24.0 volt supply.
<snip>
| Quote: | Or alternatively, if I get a benchtop power supply (10-20 amps'ish), should
I get a 24v model or 27v model? Seems the 24v model might still
abuse/exercise the airplane batteries a bit since the actual resting battery
voltage might be slightly above 24v until they are drawn down some. Seems
however that the 27v model might get a bit overloaded if the batteries
aren't fully charged when the power supply is attached as it will try and
lift (charge) the batteries to 27v (ASAP-unregulated).
|
If you get a real technician's power supply, it
will be adjustable voltage and current limit and
very quiet for use as a stand along supply.
HOWEVER . . . take care in using bench supplies
to charge batteries. For example, when deprived of
AC input power (switch turned off or power fails)
some supplies will go into ov trip (crowbar) and
put a dead short across the battery. Very smelly
smoke. Consider a surplus supply like this:
http://tinyurl.com/2lrw8e
I have several critters like this around the shop
and they're quite useful for doing ANY task. The really
neat feature is adjustable current limiting. You
can set the supply's output so that should the
unfortunate fault occur, energy delivered into
the system is not capable burning things.
| Quote: | p.s. The thought crossed my mind the in lieu of a build-log I'd just submit
a sequential list of all my naive questions to this (very helpful) forum
(lol) - i.e. the FAA 51% education and recreation mandate. Seems there's no
end to the learning opportunities here, thanks all in advance.
|
You got that right. KNOWLEDGE is essentially free, [quote][b]
| | - 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:
http://www.matronics.com/Navigator?AeroElectric-List |
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