Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat

On 6/17/2013 8:43 AM, Pat wrote:
Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat

I've no experience w. dc-dc converters but wonder why you just didn't
tap one of the 12v batteries to run your lights, etc. while still
leaving them series connected for the boat motor.

On Mon, 17 Jun 2013 09:14:23 -0700, Bennett
wrote:

On 6/17/2013 8:43 AM, Pat wrote:
Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat

I've no experience w. dc-dc converters but wonder why you just didn't
tap one of the 12v batteries to run your lights, etc. while still
leaving them series connected for the boat motor.

I want to keep the 48V bank balanced rather than having one of them
discharged further than the others. I am currently using a 5th
(smaller) 12V battery for the lights to avoid using one of the four
from the 48V bank. Adding the DC-DC converter keeps me from having to
manually charge that 5th battery periodically.

On Mon, 17 Jun 2013 11:43:53 -0400, Pat wrote:

Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat
That behavior is normal. The DC-DC converter almost certainly has a
capacitor across the input, and certainly has a capacitor across the
output. There will be a high initial current draw when power is
applied. Aftehr that it draws enough to provide the required output
current plus a small amount for the circuitry. With no load it's
output will rise until an overvoltage clamp shuts down the control IC.

I'd use a 5A slow blow fuse in the input line with a switch to control
the lights.

PlainBill

wrote:
On Mon, 17 Jun 2013 11:43:53 -0400, Pat wrote:

[48 V to 12 V DC-DC converter]

1) It is normal for such a device to draw high current when first
connected?

That behavior is normal. The DC-DC converter almost certainly has a
capacitor across the input, and certainly has a capacitor across the
output. There will be a high initial current draw when power is
applied.

I agree with this. The input capacitor will appear as a dead short for
a little while before it starts to charge up; this is why you get the
big arc.

Really big DC-DC converters and DC-AC inverters (several hundred watts
on up) are sometimes switched on in a two-stage process. First, the
battery is connected to the converter/inverter through a smallish
resistor for a few seconds, to charge the input capacitor part way.
Then, the battery is connected directly to the converter/inverter, with
no resistor. This saves a big arc at the switch or relay contacts and
makes the switch or relay last longer.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over.

Aftehr that it draws enough to provide the required output current
plus a small amount for the circuitry. With no load it's output will
rise until an overvoltage clamp shuts down the control IC.

Also agreed. The actual minimum load to get it to put out 12.3 V all
the time is probably not very much - on the order of a few watts or so.

I'd use a 5A slow blow fuse in the input line with a switch to
control the lights.

Make sure you have a spare fuse *on the boat* if you do this.
Alternatively, use a 5 A circuit breaker.

Another suggestion along this line:

You might wire a tap to the "lowest" 12 V battery anyway. Run the nav
lights through a SPDT switch, with the lights to the common or wiper
terminal. One end of the switch goes to the output of the DC-DC
converter and the other end goes to your 12 V tap. Most of the time,
you power the nav lights from the DC-DC converter, and your propulsion
pack stays nice and balanced. But, if the DC-DC converter ever fails,
you can flip the switch and still have nav lights to get home with, at
the cost of a slightly unbalanced propulsion pack.

Matt Roberds

On 17/06/13 23:43, Pat wrote:
Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat


Apart from the inrush current to the cap which has been discussed
already, being nav lights I would be inclined to use the converter to
charge the dedicated 12v battery and keep it as a fail safe device for
the nav lighting should the converter fail.

Pat wrote in message
...
Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat

Could you not rewire the boat lighting so 4 lamps are in series, with some
sort of LED failure indicator or something to show which lamp/wiring has
failed , when it does. One for red, one green and 2 riding lights, about 4
are used together , never separately. Then for at anchor. and just one
light. then a 48V one or 2 or 4 24V or 12V smaller wattage in one housing.

On Tue, 18 Jun 2013 08:12:54 +0100, "N_Cook"
wrote:

Pat wrote in message
.. .
Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat

Could you not rewire the boat lighting so 4 lamps are in series, with some
sort of LED failure indicator or something to show which lamp/wiring has
failed , when it does. One for red, one green and 2 riding lights, about 4
are used together , never separately. Then for at anchor. and just one
light. then a 48V one or 2 or 4 24V or 12V smaller wattage in one housing.

Thanks to all for your comments and suggestions. I'll do some testing
to see what minimum load will keep the output at 12V. I may also add
a small resistor in series with the input to keep the inrush current
down a little. I realize that will lower the overall efficiency, but
I hate that snaping sound the switch makes with nothing limiting the
inrush. Regarding the suggestion of putting the lights in series, I
thought of that, too. However, the lights (4 of them total) are not
even close to being matched loads. The red and green only draw 60 mA
each. The anchor light draws 175 mA. The spot light used for docking
draws 1.75 A all by itself. (All these are LEDs with their own
internal current limiting resistors).

Anyway, thanks again for your comments.
Pat

On Tue, 18 Jun 2013 11:00:16 +0800, Rheilly Phoull
wrote:

On 17/06/13 23:43, Pat wrote:
Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat


Apart from the inrush current to the cap which has been discussed
already, being nav lights I would be inclined to use the converter to
charge the dedicated 12v battery and keep it as a fail safe device for
the nav lighting should the converter fail.
Sorry to burst your bubble, but you can't use a 12.31 supply to charge
a 12V lead-acid battery, unless you run it through ANOTHER DC-DC
converter

PlainBill

On Tue, 18 Jun 2013 10:46:29 -0400, Pat wrote:

On Tue, 18 Jun 2013 08:12:54 +0100, "N_Cook"
wrote:

Pat wrote in message
. ..
Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat

Could you not rewire the boat lighting so 4 lamps are in series, with some
sort of LED failure indicator or something to show which lamp/wiring has
failed , when it does. One for red, one green and 2 riding lights, about 4
are used together , never separately. Then for at anchor. and just one
light. then a 48V one or 2 or 4 24V or 12V smaller wattage in one housing.

Thanks to all for your comments and suggestions. I'll do some testing
to see what minimum load will keep the output at 12V. I may also add
a small resistor in series with the input to keep the inrush current
down a little. I realize that will lower the overall efficiency, but
I hate that snaping sound the switch makes with nothing limiting the
inrush. Regarding the suggestion of putting the lights in series, I
thought of that, too. However, the lights (4 of them total) are not
even close to being matched loads. The red and green only draw 60 mA
each. The anchor light draws 175 mA. The spot light used for docking
draws 1.75 A all by itself. (All these are LEDs with their own
internal current limiting resistors).

Anyway, thanks again for your comments.
Pat

Rathe than using a low valure resistor to limit inrush current, use an
ICL. Your input current into the module will be in the order of .5 -
1 amp. Cantherm's MF72-010D7 is available from Digi-key for $.36.
At no load it looks like a 10 ohm resistor, under load it looks like a
..5 ohm resistor. Digi-Key has no minimum order; specify USPS First
Class Mail and shipping would run under $3.00

PlainBill

"Pat" wrote in message
...
On Tue, 18 Jun 2013 08:12:54 +0100, "N_Cook"
wrote:

Pat wrote in message
. ..
Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

Anyone else ever buy one of these things? Is the above behavior
normal? I guess you get what you pay for and $25 isn't much. It is
nicely potted so water resistance isn't an issue. But that also means
I can't take it apart to see what's inside. The label says "TOBSUN
THJ4812C120Z 120W DC-DC CONVERTER".

Pat

Could you not rewire the boat lighting so 4 lamps are in series, with some
sort of LED failure indicator or something to show which lamp/wiring has
failed , when it does. One for red, one green and 2 riding lights, about 4
are used together , never separately. Then for at anchor. and just one
light. then a 48V one or 2 or 4 24V or 12V smaller wattage in one housing.

Thanks to all for your comments and suggestions. I'll do some testing
to see what minimum load will keep the output at 12V. I may also add
a small resistor in series with the input to keep the inrush current
down a little. I realize that will lower the overall efficiency, but
I hate that snaping sound the switch makes with nothing limiting the
inrush. Regarding the suggestion of putting the lights in series, I
thought of that, too. However, the lights (4 of them total) are not
even close to being matched loads. The red and green only draw 60 mA
each. The anchor light draws 175 mA. The spot light used for docking
draws 1.75 A all by itself. (All these are LEDs with their own
internal current limiting resistors).

Anyway, thanks again for your comments.
Pat


Given that the currents of the running lights are so low, and the one that
draws a bit more is only used for docking, I think that you are making
things needlessly complicated for yourself. The original suggestion that
someone made of just tapping the feed from one battery up the stack, is the
perfect and sensible solution. With a total current draw of less than 300 mA
(excluding the docking spotlight) this will not cause any significant
'unbalancing' of a high current-capacity lead acid stack at all. If it did,
then there would be something seriously wrong ...

Every time you add any kind of electronics to a simple wiring scheme, you
are introducing a further layer of potential unreliability. Bear in mind
also, that this is exacerbated in a marine situation by the intimate
presence of corrosive seawater. Any kind of simple electronic 'dropper' from
48 down to 12 volts, is going to dissipate significant power and run hot
unless it is a switch-mode type, in which case, it ceases to be simple,
opening the way for even lower reliability. If you really *don't* want to
use a single battery solution, then the other simple way to do it, given
that you've now told us that the nav lights are LEDs with an appropriate
internal resistor for 12 volt operation, is to hang the lights across the
full 48 volts, but quadruple the series resistor. Or if you can't easily get
to the resistor to replace it, add an external one of three times the value
in series with each light.

Arfa

On Thu, 20 Jun 2013 02:12:21 +0100, "Arfa Daily"
wrote:


If you really *don't* want to
use a single battery solution, then the other simple way to do it, given
that you've now told us that the nav lights are LEDs with an appropriate
internal resistor for 12 volt operation, is to hang the lights across the
full 48 volts, but quadruple the series resistor. Or if you can't easily get
to the resistor to replace it, add an external one of three times the value
in series with each light.

Arfa

Interesting idea. I hadn't thought of that. You are correct that I
can't easily get to the internal resistors, but adding external
resistors would be easy enough. However, If I add the appropriate
external resistors to drop the additional 36 volts, I will be creating
a lot of wasted heat. The nav light resistors would be dissipating 2
watts each while the anchor light R would be dissipating over 6 watts.
The spot light R would be dissipating 62 watts! I think I'll stick
with the (switching type) dc-dc converter. Your comments about added
complexity are well taken, though.

Pat

On Tue, 18 Jun 2013 13:36:50 -0700, wrote:

Rathe than using a low valure resistor to limit inrush current, use an
ICL. Your input current into the module will be in the order of .5 -
1 amp. Cantherm's MF72-010D7 is available from Digi-key for $.36.
At no load it looks like a 10 ohm resistor, under load it looks like a
.5 ohm resistor. Digi-Key has no minimum order; specify USPS First
Class Mail and shipping would run under $3.00

PlainBill

Another good idea. Thank you. The part you mentioned is rated at 1
Amp continuous but I see larger parts are also available from the same
family. 1 Amp is enough for my current needs, but I will probably
want to match the rating of the converter and get the 3 amp part.

Pat

"Pat" wrote in message
...
On Thu, 20 Jun 2013 02:12:21 +0100, "Arfa Daily"
wrote:


If you really *don't* want to
use a single battery solution, then the other simple way to do it, given
that you've now told us that the nav lights are LEDs with an appropriate
internal resistor for 12 volt operation, is to hang the lights across the
full 48 volts, but quadruple the series resistor. Or if you can't easily
get
to the resistor to replace it, add an external one of three times the
value
in series with each light.

Arfa

Interesting idea. I hadn't thought of that. You are correct that I
can't easily get to the internal resistors, but adding external
resistors would be easy enough. However, If I add the appropriate
external resistors to drop the additional 36 volts, I will be creating
a lot of wasted heat. The nav light resistors would be dissipating 2
watts each while the anchor light R would be dissipating over 6 watts.
The spot light R would be dissipating 62 watts! I think I'll stick
with the (switching type) dc-dc converter. Your comments about added
complexity are well taken, though.

Pat


2 Watts is nothing. A 4 or 5 watt wirewound resistor would barely get warm
at 2 watts dissipation, and could be easily encased in a bit of heatshrink
tube in line with the feed cable. Similarly, you could use three equal value
resistors of 4 watts each, all in series and again in heatshrink tubing, for
the higher demand anchor light. With a couple of watts being dissipated in
each resistor, again there would be no issue with excess heat. The 'parking'
spotlight is in use for only a short time, and I would not even bother
trying to do anything with that one. I would just run that from the battery
at the bottom of the stack for the relatively brief period that it was
needed. Try as I might, I really can't come up with a 'practical' reason not
to do that. Even with it pulling a couple of amps, it is not going to have
any significant effect on the performance of the battery stack overall, or
drain that bottom battery by any amount that wouldn't be equivalent to
acceptable variations in battery performance anyway. What is the capacity of
these batteries ? 100 AH apiece ? More ? Even running that light for an hour
would not represent consuming more than say 1.5% of the battery's fully
charged capacity, and if the system cannot cope with that, then I would be
worried anyway, as once those batteries are more than about six months old,
the variation in their capacities - and thus their potential to be
'unbalanced' - will probably exceed that figure anyway ...

Arfa

On Fri, 21 Jun 2013 00:01:26 +0100, "Arfa Daily"
wrote:



"Pat" wrote in message
.. .
On Thu, 20 Jun 2013 02:12:21 +0100, "Arfa Daily"
wrote:


If you really *don't* want to
use a single battery solution, then the other simple way to do it, given
that you've now told us that the nav lights are LEDs with an appropriate
internal resistor for 12 volt operation, is to hang the lights across the
full 48 volts, but quadruple the series resistor. Or if you can't easily
get
to the resistor to replace it, add an external one of three times the
value
in series with each light.

Arfa

Interesting idea. I hadn't thought of that. You are correct that I
can't easily get to the internal resistors, but adding external
resistors would be easy enough. However, If I add the appropriate
external resistors to drop the additional 36 volts, I will be creating
a lot of wasted heat. The nav light resistors would be dissipating 2
watts each while the anchor light R would be dissipating over 6 watts.
The spot light R would be dissipating 62 watts! I think I'll stick
with the (switching type) dc-dc converter. Your comments about added
complexity are well taken, though.

Pat


2 Watts is nothing. A 4 or 5 watt wirewound resistor would barely get warm
at 2 watts dissipation, and could be easily encased in a bit of heatshrink
tube in line with the feed cable. Similarly, you could use three equal value
resistors of 4 watts each, all in series and again in heatshrink tubing, for
the higher demand anchor light. With a couple of watts being dissipated in
each resistor, again there would be no issue with excess heat. The 'parking'
spotlight is in use for only a short time, and I would not even bother
trying to do anything with that one. I would just run that from the battery
at the bottom of the stack for the relatively brief period that it was
needed. Try as I might, I really can't come up with a 'practical' reason not
to do that. Even with it pulling a couple of amps, it is not going to have
any significant effect on the performance of the battery stack overall, or
drain that bottom battery by any amount that wouldn't be equivalent to
acceptable variations in battery performance anyway. What is the capacity of
these batteries ? 100 AH apiece ? More ? Even running that light for an hour
would not represent consuming more than say 1.5% of the battery's fully
charged capacity, and if the system cannot cope with that, then I would be
worried anyway, as once those batteries are more than about six months old,
the variation in their capacities - and thus their potential to be
'unbalanced' - will probably exceed that figure anyway ...

Arfa
If it was me I'd try to figure out a way to place the resistors
someplace where any heat they generate could keep something dry. I
wonder, do DC-DC converters emit much RF? I'm really surprised that
the original poster doesn't want to go with the most simple and robust
solution. Especially on a boat. And it would be much easier to carry
and wire in spare resistors than a spare DC-DC converter.
ERS

On Thu, 20 Jun 2013 18:45:20 -0700, wrote:

On Fri, 21 Jun 2013 00:01:26 +0100, "Arfa Daily"
wrote:



"Pat" wrote in message
. ..
On Thu, 20 Jun 2013 02:12:21 +0100, "Arfa Daily"
wrote:


If you really *don't* want to
use a single battery solution, then the other simple way to do it, given
that you've now told us that the nav lights are LEDs with an appropriate
internal resistor for 12 volt operation, is to hang the lights across the
full 48 volts, but quadruple the series resistor. Or if you can't easily
get
to the resistor to replace it, add an external one of three times the
value
in series with each light.

Arfa

Interesting idea. I hadn't thought of that. You are correct that I
can't easily get to the internal resistors, but adding external
resistors would be easy enough. However, If I add the appropriate
external resistors to drop the additional 36 volts, I will be creating
a lot of wasted heat. The nav light resistors would be dissipating 2
watts each while the anchor light R would be dissipating over 6 watts.
The spot light R would be dissipating 62 watts! I think I'll stick
with the (switching type) dc-dc converter. Your comments about added
complexity are well taken, though.

Pat


2 Watts is nothing. A 4 or 5 watt wirewound resistor would barely get warm
at 2 watts dissipation, and could be easily encased in a bit of heatshrink
tube in line with the feed cable. Similarly, you could use three equal value
resistors of 4 watts each, all in series and again in heatshrink tubing, for
the higher demand anchor light. With a couple of watts being dissipated in
each resistor, again there would be no issue with excess heat. The 'parking'
spotlight is in use for only a short time, and I would not even bother
trying to do anything with that one. I would just run that from the battery
at the bottom of the stack for the relatively brief period that it was
needed. Try as I might, I really can't come up with a 'practical' reason not
to do that. Even with it pulling a couple of amps, it is not going to have
any significant effect on the performance of the battery stack overall, or
drain that bottom battery by any amount that wouldn't be equivalent to
acceptable variations in battery performance anyway. What is the capacity of
these batteries ? 100 AH apiece ? More ? Even running that light for an hour
would not represent consuming more than say 1.5% of the battery's fully
charged capacity, and if the system cannot cope with that, then I would be
worried anyway, as once those batteries are more than about six months old,
the variation in their capacities - and thus their potential to be
'unbalanced' - will probably exceed that figure anyway ...

Arfa
If it was me I'd try to figure out a way to place the resistors
someplace where any heat they generate could keep something dry. I
wonder, do DC-DC converters emit much RF? I'm really surprised that
the original poster doesn't want to go with the most simple and robust
solution. Especially on a boat. And it would be much easier to carry
and wire in spare resistors than a spare DC-DC converter.
ERS

This is my last post on this subject as we have drifted off topic. My
original post was asking if the experience I had with my cheap $25
dc-dc converter (already purchased) was normal. That question was
very quickly answered as "yes". We have since drifted to how easy it
would be to repair the system out on the water in the dark. In that
situation, I would just jumper the 12 V lights to one of the traction
batteries as Arfa suggested. By the way, the boat is used on a small
inland lake and I could easily return to the dock without any lights
at all by carefully avoiding the one or two fishermen out on the lake
at night. Thanks to everyone who responded. ****End of Thread***

snip

ERS

This is my last post on this subject as we have drifted off topic.

Such is the nature of usenet ...


more snipping


****End of Thread***


Oooooohh ! :-)

Arfa

Pat wrote:

Does anyone here have any experience with dc to dc converters? I need
a unit that takes approximately 48 volts input (Four 12V Lead-Acid
batteries in series) and provides 12 volts out at a few amps. This
will be used on a pontoon boat to supply 12V for navigation lights
from the 48 V battery bank that drives the electric motor.

I found a module on the Internet that can handle 10 A output at 12
volts and only costs $25 (USD). Many no-name websites offer it
anywhere from $22 to $40. All use the same exact picture. I picked a
site that seems less scary than others and ordered one. It arrived
very quickly.

At first, it seemed defective, but after playing around a little, I
think I figured it out.

Now to my questions:
1) It is normal for such a device to draw high current when first
connected? It draws quite an arc when the 48V line is connected but
then only draws 31 mA with no load. Removing power for just a second
starts that process over - ie, draws an arc with a loud snap when
connecting it. I was using a switch when I first tried it and heard
the snap from inside the switch. I then changed to a jumper wire and
could see the arc.

2) Do these things normally have a minimum load spec? With no load,
the voltage starts at 12.34 V and then drops to 4.7 V or so over a
period of 30 to 40 seconds. It then jumps back to 12.34 and starts
the process over. The instructions don't mention a minimum load, but
I tried adding a lamp that draws a few amps. The output was then
steady at 12.31 Volts. I don't have a scope, so I have no idea what's
going on over timeframes shorter than a second or so.

This sounds perfectly normal. I presume it is a switching power supply,
and needs capacitors to buffer the switching pulses. So, the capacitor
draws a large current at turn-on. You may need a high current relay
to handle the turn-on surge without damage. Yes, your unit apparently
needs a small load to continue regulating properly. Definitely
put a fuse in the 48 V input to it.

Jon