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Old 01-06-2009, 20:05   #16
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That's easy. Add a bunch of silicon diodes rated to take max current expected @ 0.7 v (forward drop) each. In other words, ten of them would drop 7 volts, etc.
Of course, we're talking about cheap results, although not necessarily efficient.
PM me if you have more questions.

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Old 02-06-2009, 13:55   #17
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Charlie, but a regulated 5.2 volt adapter or build one out of an LM317T. National semiconductor's web page will design a power supply circuit for you if you put in the parameters you want. The series diodes work well if your power into them is already regulated. The problem with a boat is that voltage can vary from a low of about 11 volts on a mostly discharged battery or nearly 15 volts when the engines are running and the batteries are charging. In that case if you design for 15 volts you'll have only 1 volt when the battery is low and if you design for 11 volts you'll have 9 when charging. This may or may not be an issue depending on the sensitivity of your equipment. Also the commercial devices are likely to provide some spike protection. Boat DC is full of voltage spikes. It's not a major issue if your going through a battery first but when powering something directly they can be quite hard on the electronics. Keep in mind that while these circuits are not difficult to build, you might have an issue with the insurance company if your home made power supply shorts out and burns the boat.

Beausoleil:
If your set on building your own try the National semiconductor web site. They have several buck converters that can step up voltage from 12 to 48 and can be up to 95% efficient. I ran a design for a circuit in about 3 minutes.
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Old 02-06-2009, 15:02   #18
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Versatile Step Down Charger

I have a 12V charger that steps down voltage to anyplace you want. There is a little dial on the side of a cigarette lighter plug to select the desired voltage. It also includes many different plugs and you can switch from positive to negative in center position of plug. I use this to charge a remote computer mouse which also requires about 5 volts DC. I can't remember where I bought this, but I think Radio Shack.
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Old 02-06-2009, 15:12   #19
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If your set on building your own try the National semiconductor web site. They have several buck converters that can step up voltage from 12 to 48 and can be up to 95% efficient. I ran a design for a circuit in about 3 minutes.
Thanks, I found it last night. Pretty good info. I missed the 95% efficient one - the highest I saw was 91%. I'll check again
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Old 02-06-2009, 15:50   #20
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The stack of diodes is really kind of pathological on a boat... it turns the voltage difference into heat. If you want to be efficient with the power (especially for a load that is on much of the time, or has more than a trivial current draw), the DC-DC converter is the way to go.

The only gotcha with these is that some generate more RFI than others, as they contain oscillators and high-speed switches connected to inductors. Most of current manufacture are pretty good; I tend to use a lot of Astrodyne since they have such a huge selection. One 12-to-5 unit, in fact, is always on running my EVDO router, mounted as a quick kluge on a piece of perfboard.

Shop for 90-ish percent efficiency, test for noise with nearby radios, and add capacitors to ground and ferrites on any long leads in the unlikely event of problems.

Cheers,
Steve
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Old 02-06-2009, 16:33   #21
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efficiency

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Thanks, I found it last night. Pretty good info. I missed the 95% efficient one - the highest I saw was 91%. I'll check again
The circuits provided by the program state the worst case efficiency at maximum load. If you look at the load graphs they are a lot more efficient when operating at 50% of rated load. I personally don't like to run things at 100% rated load if I want a long life.
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Old 02-06-2009, 16:40   #22
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5v

You can get USB adapters for 12v car usage which will give you 5v dc for low cost.

regards Bill
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Old 03-06-2009, 08:52   #23
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Charlie,

Are you going to go with a single 12v-5v car adapter like bill good says?

I've got several car adapters for various USB-equipped devices lying around the boat: Garmin Nuvi, Garmin GPS76Cx, Blackberry, etc. I also have several other devices which use various DC supply voltages - an Ethernet hub/router, USB hub, various battery chargers, Creative Labs computer satellite speaker system (actually its wall p/s puts out 12Vac, not dc)

I think I'm going to just go ahead and design a multi-voltage power converter system using some LM317T and LM2586 voltage regulators, with multiple outputs in order to clean up the rat's nest we currenly have next to the nav station. I'll probably post the plans as a PDF file here - hopefully in the next couple of weeks.
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Old 03-06-2009, 10:31   #24
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Quote:
Originally Posted by Beausoleil View Post
... I think I'm going to just go ahead and design a multi-voltage power converter system using some LM317T and LM2586 voltage regulators, with multiple outputs in order to clean up the rat's nest we currenly have next to the nav station. I'll probably post the plans as a PDF file here - hopefully in the next couple of weeks.
Look forward to seeing them!
Thanks, in advance.
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Old 03-06-2009, 14:12   #25
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Charlie-
Check some more specs on your gizmo.

It may not need 5.2VDC, more likely it needs 5VDC and the extra .2 is there to overcome wiring losses if a long power wire is used.

Sometimes, those gizmos can actually run at significantly higher voltages as well (i.e. 12 volts) as part of a "power over ethernet" design.

But the odds are it will run at 5VDC and there are two inexpensive ways to giving that to it. First, most cell phone car chargers (and the "miniUSB" "USB" and "MicroUSB" car chargers) put out 5VDC these days, and sometimes you cna buy one for as little as $5. $15-20 for a top brand name. Most will supply 500mA of power, which is probably more than your gizmo needs--but you'll need to check that.

If you need more than 500mA a USB charger can sometimes be found up to 1A for under $20. Or, you can buy a 5 volt "three pin regulator" chip like a 7805 or 7905 at Radio Shack and other suppliers, good for typically 1-1.5A and requiring less than five bucks worth of components (usually, the chip, two capacitors, and that's it) to make a 12-to-5 volt regulated supply all by itself. The car chargers are more efficient, the single-chip regulator dead simple and easy to build though.

No big deal either way.
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Old 03-06-2009, 18:13   #26
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Quote:
Originally Posted by Captain Bill View Post
Charlie, but a regulated 5.2 volt adapter or build one out of an LM317T. National semiconductor's web page will design a power supply circuit for you if you put in the parameters you want. The series diodes work well if your power into them is already regulated. The problem with a boat is that voltage can vary from a low of about 11 volts on a mostly discharged battery or nearly 15 volts when the engines are running and the batteries are charging. In that case if you design for 15 volts you'll have only 1 volt when the battery is low and if you design for 11 volts you'll have 9 when charging. This may or may not be an issue depending on the sensitivity of your equipment. Also the commercial devices are likely to provide some spike protection. Boat DC is full of voltage spikes. It's not a major issue if your going through a battery first but when powering something directly they can be quite hard on the electronics. Keep in mind that while these circuits are not difficult to build, you might have an issue with the insurance company if your home made power supply shorts out and burns the boat.

Beausoleil:
If your set on building your own try the National semiconductor web site. They have several buck converters that can step up voltage from 12 to 48 and can be up to 95% efficient. I ran a design for a circuit in about 3 minutes.
Good thing I ddidn't go with my memory. the transformer is actually 9V 1.5 amps.


Quote:
Originally Posted by Beausoleil View Post
Charlie,

Are you going to go with a single 12v-5v car adapter like bill good says?

I've got several car adapters for various USB-equipped devices lying around the boat: Garmin Nuvi, Garmin GPS76Cx, Blackberry, etc. I also have several other devices which use various DC supply voltages - an Ethernet hub/router, USB hub, various battery chargers, Creative Labs computer satellite speaker system (actually its wall p/s puts out 12Vac, not dc)

I think I'm going to just go ahead and design a multi-voltage power converter system using some LM317T and LM2586 voltage regulators, with multiple outputs in order to clean up the rat's nest we currenly have next to the nav station. I'll probably post the plans as a PDF file here - hopefully in the next couple of weeks.
When you PDF it i'll study it and make a change to bring it up to 9v.

Quote:
Originally Posted by hellosailor View Post
Charlie-
Check some more specs on your gizmo.

It may not need 5.2VDC, more likely it needs 5VDC and the extra .2 is there to overcome wiring losses if a long power wire is used.

Sometimes, those gizmos can actually run at significantly higher voltages as well (i.e. 12 volts) as part of a "power over ethernet" design.

But the odds are it will run at 5VDC and there are two inexpensive ways to giving that to it. First, most cell phone car chargers (and the "miniUSB" "USB" and "MicroUSB" car chargers) put out 5VDC these days, and sometimes you cna buy one for as little as $5. $15-20 for a top brand name. Most will supply 500mA of power, which is probably more than your gizmo needs--but you'll need to check that.

If you need more than 500mA a USB charger can sometimes be found up to 1A for under $20. Or, you can buy a 5 volt "three pin regulator" chip like a 7805 or 7905 at Radio Shack and other suppliers, good for typically 1-1.5A and requiring less than five bucks worth of components (usually, the chip, two capacitors, and that's it) to make a 12-to-5 volt regulated supply all by itself. The car chargers are more efficient, the single-chip regulator dead simple and easy to build though.

No big deal either way.
I will send a request for info to radio labs and see what they recommend. If I could do 12 volts that would be great and easy.
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Old 03-06-2009, 20:23   #27
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After all this discussion, there remains another possibility.
The intended load may already have a regulator built in if it's designed to run off a 120 volt brick...
I can charge my cordless Sears and Rubbish soldering iron (intended for 12 v from a computer power supply (18 v).

I'd try it directly on the boat's power, but that's just me.

Steve B.
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Old 03-06-2009, 21:38   #28
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Charlie, the 317 regulator is just wasted on this. A 7809 or similar fixed 9V regulator chip will be 1/4 of the price, need fewer external parts, and be in stock on the same shelves. Pushing 1.5Amps through one will max it out, so you'll have to choose a package that supports that much (same problem with a 317) and add a good heat sink to it. Which will cost more than the chip does.<G>
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Old 03-06-2009, 22:04   #29
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Agreed on the dedicated regulator. If you don't want to pay the big bucks for a DC-DC converter, or can't have the RF noise..Just buy a 7805 chip from digikey. It will be at your house the next day and only costs a few cents. They are good down to 7v and up to 25-35 volts input. They will supply better than 2 amps.

Ignore the 5.2 nothing is so sensitive that 5.2 volts is ok, but 5 volts is not. Almost all GPS antennas operate off of 5 nominal.

With the 7805 they give you sheets with capacitors etc, but they work just find feeding in voltage on one pin, getting 5v on the other. Grounding the third of course. (Not in that order, take a look at the drawing before hooking up).

If you're ordering one, order a few for spares! They cost almost nothing and are very hardy. -40 to 140ish operating temp, etc. Safe guards against overtemp, over voltage, over current, etc. Hard to kill unless you took them up backwards (then dont touch the case ouch).

if you need any help, PM me, its easy as pie.
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Old 03-06-2009, 23:24   #30
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Quote:
Originally Posted by senormechanico View Post
After all this discussion, there remains another possibility.
The intended load may already have a regulator built in if it's designed to run off a 120 volt brick...
I can charge my cordless Sears and Rubbish soldering iron (intended for 12 v from a computer power supply (18 v).

I'd try it directly on the boat's power, but that's just me.

Steve B.
Quote:
Originally Posted by hellosailor View Post
Charlie, the 317 regulator is just wasted on this. A 7809 or similar fixed 9V regulator chip will be 1/4 of the price, need fewer external parts, and be in stock on the same shelves. Pushing 1.5Amps through one will max it out, so you'll have to choose a package that supports that much (same problem with a 317) and add a good heat sink to it. Which will cost more than the chip does.<G>
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Agreed on the dedicated regulator. If you don't want to pay the big bucks for a DC-DC converter, or can't have the RF noise..Just buy a 7805 chip from digikey. It will be at your house the next day and only costs a few cents. They are good down to 7v and up to 25-35 volts input. They will supply better than 2 amps.

Ignore the 5.2 nothing is so sensitive that 5.2 volts is ok, but 5 volts is not. Almost all GPS antennas operate off of 5 nominal.

With the 7805 they give you sheets with capacitors etc, but they work just find feeding in voltage on one pin, getting 5v on the other. Grounding the third of course. (Not in that order, take a look at the drawing before hooking up).

If you're ordering one, order a few for spares! They cost almost nothing and are very hardy. -40 to 140ish operating temp, etc. Safe guards against overtemp, over voltage, over current, etc. Hard to kill unless you took them up backwards (then dont touch the case ouch).

if you need any help, PM me, its easy as pie.
This stuff will make me think too hard. I am thinking of A) check the voltage coming out of the transformer and then b) contacting the manufacture to see if there is a range of voltages that are acceptable. From there I will PM you electrical types and see if I can figure this out.
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