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n103md(at)yahoo.com
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 Posted: Sun Apr 29, 2007 6:57 am Post subject: 12v supply to stabilize avionics |
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Several asked for specs, so here they are...
As Bob Nuchols surmised, this is lighter weight than
a second battery -- 0.1 lbs plus wiring.
It uses an Linear LTC3780.
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1116,P10090
The spec sheet for the 12V supply is attached.
-bob mackey
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mr.gsun+rv-list(at)gmail.
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| Posted: Sun Apr 29, 2007 2:40 pm Post subject: 12v supply to stabilize avionics |
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Bob,
Got a couple left?
How much and how do I pay you? Paypal? Snail Mail?
Greg
On 4/29/07, bob mackey < n103md(at)yahoo.com (n103md(at)yahoo.com)> wrote:[quote]Several asked for specs, so here they are...
As Bob Nuchols surmised, this is lighter weight than
a second battery -- 0.1 lbs plus wiring.
It uses an Linear LTC3780.
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1116,P10090
The spec sheet for the 12V supply is attached.
-bob mackey
[b]
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Beer30?
Joined: 23 Sep 2006
Posts: 14
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| Posted: Sun Apr 29, 2007 11:04 pm Post subject: 12v supply to stabilize avionics |
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As an electrical engineer (working on consumer electronics, not on A/C systems), I would not recommend this for A/C use. I'm not sure where you come up with 14A continuous, but that amount of current would fry the package in no time at all. The spec says that the unit can take a max temp of 125 C. Lets assume that you mount this in a temp controlled environment where it sees a max of 25 C ambient. The temp rise, as specified on the data sheet is 130C/W. At 12 volts nominal voltage, if you draw 1 amp, the unit will disspate 12 W. This means that the temp rise at the part would be 12 * 130 = 1560 degrees or toast. Turning this around, if you want to keep the temp below 125 C, with an ambient temp of 25C, you can afford a temp rise of 100C. Therefore 130 C/W divided by 100 C temp rise equals 1.3 Watts, which translates to roughly 100 mA of current.
This part is designed for computers, embedded microprocessors (in cars maybe) or other low current applications. I don't want to rain on anyones parade, but if this were suitable for A/C systems, some would have thought of it long ago. You'd be better off spending your dollars on a small backup batter or a dual bus system.
Best regards,
D Dalton
On 4/29/07, bob mackey <n103md(at)yahoo.com (n103md(at)yahoo.com)> wrote:[quote] Several asked for specs, so here they are...
As Bob Nuchols surmised, this is lighter weight than
a second battery -- 0.1 lbs plus wiring.
It uses an Linear LTC3780.
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1116,P10090
The spec sheet for the 12V supply is attached.
-bob mackey
[b]
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retasker(at)optonline.net
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| Posted: Mon Apr 30, 2007 8:25 pm Post subject: 12v supply to stabilize avionics |
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The LTC3780 IC drives the pass element MOSFETs, not the load. The
package only has to dissipate the drive power while the MOSFETs
dissipate the main power losses, which at an efficiency of 95% is less
than 9W total. In fact, with synchronous rectification, the efficiency
is probably more than 95%. MOSFETs require very little current to drive
them so the IC is probably dissipating no more than a few tens of mW so
will stay very cool. The suggested power design using this part is rated
at 5A, but merely using higher capacity MOSFETs would allow it to
provide whatever amount of power the designer wanted it to do.
The data sheet recommends it for:
■ Automotive Systems
■ Telecom Systems
■ DC Power Distribution Systems
■ High Power Battery-Operated Devices
■ Industrial Control
No airplanes listed, but then again nobody ever does list airplanes for
this type product - even though it clearly could be used there.
By the way, if one were to assume that all the power were supplied by
the chip alone (not possible in this case because the chip does not
include all the parts necessary for a power supply) the way to calculate
the allowable dissipation is: 100C allowable rise divided by 130 C/W =
0.769W of allowable dissipation. Which actually has nothing to do with
the amount of current it could provide, but everything to do with the
efficiency of the part in delivering useful output. For instance, if the
efficiency of our hypothetical one-chip power supply was 95% (like the
actual power supply system design) then, since we have calculated the
chip could dissipate 0.769W, we could deliver over 15W to the load - or
almost 1.25A at 12V.
The reason that no one has "thought of it long ago" is not that it
wouldn't work, which it will, but that there is not really much
necessity for this type solution. While what the suggested use for this
is one solution the original poster's problem, adding a second battery
would eliminate all of his concerns and have the added benefit of
providing that much more standby power. On the other hand, this will
weigh a whole lot less than an extra battery so if he has plenty of
capacity in a single battery for his use, this would definitely allow
him to eliminate the power brownout problem.
Dick Tasker
David Dalton wrote:
| Quote: | As an electrical engineer (working on consumer electronics, not on A/C
systems), I would not recommend this for A/C use. I'm not sure where
you come up with 14A continuous, but that amount of current would fry
the package in no time at all. The spec says that the unit can take a
max temp of 125 C. Lets assume that you mount this in a temp
controlled environment where it sees a max of 25 C ambient. The temp
rise, as specified on the data sheet is 130C/W. At 12 volts nominal
voltage, if you draw 1 amp, the unit will disspate 12 W. This means
that the temp rise at the part would be 12 * 130 = 1560 degrees or
toast. Turning this around, if you want to keep the temp below 125 C,
with an ambient temp of 25C, you can afford a temp rise of 100C.
Therefore 130 C/W divided by 100 C temp rise equals 1.3 Watts, which
translates to roughly 100 mA of current.
This part is designed for computers, embedded microprocessors (in cars
maybe) or other low current applications. I don't want to rain on
anyones parade, but if this were suitable for A/C systems, some would
have thought of it long ago. You'd be better off spending your dollars
on a small backup batter or a dual bus system.
Best regards,
D Dalton
On 4/29/07, *bob mackey* <n103md(at)yahoo.com <mailto:n103md(at)yahoo.com>>
wrote:
Several asked for specs, so here they are...
As Bob Nuchols surmised, this is lighter weight than
a second battery -- 0.1 lbs plus wiring.
It uses an Linear LTC3780.
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1116,P10090
The spec sheet for the 12V supply is attached.
-bob mackey
*
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