Reducing 18 volt DC to 12 volt DC

[[email protected]]

I have a cargo trailer that the lights work only when the parking
lights are onin my truck. This is problematic seeing as we are in and
out of the trailer all day. I am a contractor that uses 18 volt
Dewalt tools and therefore I own many batteries. We broke open an 18
volt flashlight and wired 4 12 overhead lights to it and find the
lights to be very bright and in addition they burn out the battery in
less than 20 minutes.? What to do? Can I limit the volts? Will that
extend the battery life? Lower the light amps? Phone a friend?
50/50? Ahhh! I thought I was so clever. Not so much. Any help??

 

[petrus bitbyter]

I have a cargo trailer that the lights work only when the parking
lights are onin my truck. This is problematic seeing as we are in and
out of the trailer all day. I am a contractor that uses 18 volt
Dewalt tools and therefore I own many batteries. We broke open an 18
volt flashlight and wired 4 12 overhead lights to it and find the
lights to be very bright and in addition they burn out the battery in
less than 20 minutes.? What to do? Can I limit the volts? Will that
extend the battery life? Lower the light amps? Phone a friend?
50/50? Ahhh! I thought I was so clever. Not so much. Any help??

They will not only be too bright, they will only live too short. Guess you
would also do with 1.5 times overload. You'll have to bring back the voltage
to the 12V required by the bulbs or use 18V bulbs. Guess you will have 18V
bulbs when you have 18V flashlight. Bringing down the voltage is not that
difficult but the easy way spills a lot of power. That's either a series
resistor/bulb or a 12V lineair regulator. Both will produce a lot of heat,
amount depending on the wattage of the bulbs. The best way is a switching
regulator but I doubt a newbie in electronics can handle such a circuit. You
can nevertheless google on it. Lineair has a lot of examples, Micrel is
another. There are much more. If you like experimenting try the "2
transistor Black regulator."

petrus bitbyter

 

[Homer J Simpson]

I have a cargo trailer that the lights work only when the parking
lights are onin my truck. This is problematic seeing as we are in and
out of the trailer all day. I am a contractor that uses 18 volt
Dewalt tools and therefore I own many batteries. We broke open an 18
volt flashlight and wired 4 12 overhead lights to it and find the
lights to be very bright and in addition they burn out the battery in
less than 20 minutes.? What to do? Can I limit the volts? Will that
extend the battery life? Lower the light amps? Phone a friend?
50/50? Ahhh! I thought I was so clever. Not so much. Any help??

Use an auto battery to run the lights and charge it off the 18 V supply.

--
..
..
..
..
..
..
..
..

 

[[email protected]]

Thought of using 12 volt car battery. Any better way to charge? From
my truck? Cigarette lighter?

 

[Homer J Simpson]

Thought of using 12 volt car battery. Any better way to charge? From
my truck? Cigarette lighter?

Cheapest is a resistor from the supply, but ideally you would use a proper
charging circuit. This will prevent overcharging and drying out the battery.

Have you tried a truck supply store? Someone must have done this before.

--
..
..
..
..
..
..
..
..

 

[Homer J Simpson]

Thought of using 12 volt car battery. Any better way to charge? From
my truck? Cigarette lighter?

http://www.powerstream.com/CHB0644.htm is possible. Give them a call and see
what they have.

 

[Ross Herbert]

I have a cargo trailer that the lights work only when the parking
lights are onin my truck. This is problematic seeing as we are in and
out of the trailer all day. I am a contractor that uses 18 volt
Dewalt tools and therefore I own many batteries. We broke open an 18
volt flashlight and wired 4 12 overhead lights to it and find the
lights to be very bright and in addition they burn out the battery in
less than 20 minutes.? What to do? Can I limit the volts? Will that
extend the battery life? Lower the light amps? Phone a friend?
50/50? Ahhh! I thought I was so clever. Not so much. Any help??

Am I correct in assuming that what you are trying to do is to run 12V
lamps (4) from the fully charged (spare) Dewalt 18V power tool
batteries?

If I have this correct then you must use some form of voltage
step-down. Either a linear or switch mode PSU which accepts 18V dc
input and ouputs 12V dc at a suitable current determined by the total
wattage of lamps you are trying to drive.

Other than that, as long as your truck has a 12V battery which is
charged by the vehicle alternator, why not wire in a separate feed
(with fuse) just to run the lamps? That is simpler and cheaper than
any other solution.

 

[ehsjr]

I have a cargo trailer that the lights work only when the parking
lights are onin my truck. This is problematic seeing as we are in and
out of the trailer all day. I am a contractor that uses 18 volt
Dewalt tools and therefore I own many batteries. We broke open an 18
volt flashlight and wired 4 12 overhead lights to it and find the
lights to be very bright and in addition they burn out the battery in
less than 20 minutes.? What to do? Can I limit the volts? Will that
extend the battery life? Lower the light amps? Phone a friend?
50/50? Ahhh! I thought I was so clever. Not so much. Any help??

While you could run the lights off 18V batteries,
I think that would prove to be unsaticfactory.
You'd be better off to use the xisting 12V auto system.
I think you have a couple of issues to address,
so here are some things to consider:
1) Wire it up to turn the trailer lights on by
a separate switch that does not require the
parking lights to be on.
2) Include a timer in the separate switch circuit
so that the lights will turn off automatically
after X amount of time.

Depending on how you use the cargo trailer, that
may be all you need to do. You can build a simple
circuit to turn the lights off say 2 minutes
after you turn them on, and you can make the
timing adjustable. I'm envisioning going into the
trailer to get something periodically, but with
a long time between entries to the trailer. So
with the lights off the vast majority of the time,
you shouldn't run the battery down.

Ed

 

[John Larkin]

I have a cargo trailer that the lights work only when the parking
lights are onin my truck. This is problematic seeing as we are in and
out of the trailer all day. I am a contractor that uses 18 volt
Dewalt tools and therefore I own many batteries. We broke open an 18
volt flashlight and wired 4 12 overhead lights to it and find the
lights to be very bright and in addition they burn out the battery in
less than 20 minutes.? What to do? Can I limit the volts? Will that
extend the battery life? Lower the light amps? Phone a friend?
50/50? Ahhh! I thought I was so clever. Not so much. Any help??

If you put pairs of lights in series, across the 18 volts, you'd get 9
volts per lamp, which might be bright enough... try it. The lower
current will extend battery life, about double what you're seeing now.

If you put two batteries in series, that's 36 volts, which is right to
power *three* 12 volt bulbs wired in series.

But little batteries like this won't last long with a heap of lights
attached. Why not use a car battery?

John

 

[Noway2]

I have a cargo trailer that the lights work only when the parking
lights are onin my truck. This is problematic seeing as we are in and
out of the trailer all day. I am a contractor that uses 18 volt
Dewalt tools and therefore I own many batteries. We broke open an 18
volt flashlight and wired 4 12 overhead lights to it and find the
lights to be very bright and in addition they burn out the battery in
less than 20 minutes.? What to do? Can I limit the volts? Will that
extend the battery life? Lower the light amps? Phone a friend?
50/50? Ahhh! I thought I was so clever. Not so much. Any help??

Just to add another thought on this subject, you may also run into an
issue with the type of battery chemistry versus the loading. Not all
batteries are created equal with regards to their discharge patterns and
the type of load they are designed to work with. Some batteries are
capable of providing a constant discharge, such as alkaline, where as
others are better at short bursts, such as lithium (think digital
camera. If you are using the wrong type of battery for an application,
you will likely find that it doesn't perform as well or as long as you
would expect for its amp-hour rating.

 

[Old Mac User]

Use the 18 v battery but put about 9 1-amp silicon diodes in series
with the light. Each diode will drop the voltage about 0.62 volts
without having to fret over a hot resistor in series.

 

[jasen]

Use the 18 v battery but put about 9 1-amp silicon diodes in series
with the light. Each diode will drop the voltage about 0.62 volts
without having to fret over a hot resistor in series.

no resistor but you're turning the same amount of energy into heat inside
the diodes,

It'd be better to use three 6V lamps (try a motorcycle spares place)

Or maybe a PWM circuit based on a 555 and a mosfet.

but really a 12V lead-acid battery is the best solution as they're cheaper
than those tool powerpacks.


Bye.
Jasen

 

[Rich Grise]

Thought of using 12 volt car battery. Any better way to charge? From
my truck? Cigarette lighter?

Don't use a CAR battery! Use a golfcart, marine, or RV battery - the
deep-cycle kind. Car batteries are designed to be on a full float
charge while the motor's running, and provide 600 amps for as long as it
takes to start the car, and that's it. If you draw a light load for a long
time, the cells deteriorate.

A deep-cycle (marine, RV, golf cart, etc) battery is almost the opposite.
You start with it fully charged, and it can supply a moderate load
seemingly forever, until it reaches "end of charge", and needs to be
recharged again - they'll do this happily for years, but don't try
to start a car engine with one.

Get a switch or plug; when you park, disconnect the trailer lights
from the truck and use the RV battery in the trailer. When you're
done, start the truck, and plug in the trailer battery to charge
alongside the truck battery - when you get back, the trailer battery
will be recharged.

Or, you could go to an RV place and get a battery isolator, so
that that would be fully automatic.

Have Fun!
Rich