Incandescent lamp inrush current vs. regulated power supplies

[John Nagle]

I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply. One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high. Inrush current for an incandescent
lamp is about 10x the current after warmup.

Is this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

John Nagle

 

[Phil Allison]

"John Nagle"

I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply. One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high. Inrush current for an incandescent
lamp is about 10x the current after warmup.

Is this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

** You need a regulated supply that goes into current limit, when
overloaded, to overcome the problem.

Fed with 3 amps or so the two 12W lamps will then light up slowly - in about
2 seconds.

Fraid there is no way to find out if a given SMPS does this ( or shuts down)
other than trying it.


..... Phil

 

[miso]

I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply. One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high. Inrush current for an incandescent
lamp is about 10x the current after warmup.

Is this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

John Nagle

Is this the PR-3/UL? It has some margin (like 5A momentary, with
undefined time). If inrush is really 10x, you are doing good, since that
is a 10 amp surge and the device is specd for 5 amp surge.

 

[Phil Allison]

"John Nagle"

I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply. One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high. Inrush current for an incandescent
lamp is about 10x the current after warmup.

s this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

** Errr - why are you NOT using a for of SMPS **DESIGNED** for lamp
loads ???

Halogen lamp " electronic transformers " are sold in the millions.

Dirt cheap too

Wot is your problem ???????????????


.... Phil

 

[Ecnerwal]

I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply. One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high. Inrush current for an incandescent
lamp is about 10x the current after warmup.

Is this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

John Nagle

One approach (which also leads to long life for your bulbs) is to PWM
them gradually on (the digital equivalent of the inrush current limiting
devices - I'm not over-fond of those myself without adding something to
bypass them after startup.)

We have a cheesy (110V) alarm clock that gradually ramps up an
incandescent this way - thing must be 15 years old, and the bulb has
never needed to be changed yet. The ultimate in soft-starts.

In the specific case of two or more bulbs, you could also try a setup
that ran them in series for a few seconds at turn-on to warm the
filaments, and then switched to parallel operation.

 

[Phil Allison]

"Ecnerwal" = IDIOT

One approach (which also leads to long life for your bulbs) is to PWM
them gradually on

** Absolute 100% fucking BULL SHIT !!





..... Phil

 

[[email protected]]

   I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply.  One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high.  Inrush current for an incandescent
lamp is about 10x the current after warmup.

   Is this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

                                John Nagle

You can buy LED lamps made for replacing the 12 volt auto lamps. They
are not too expensive and as a friend of mine says " works good,
lasts a long time. "


Dan

 

[Cydrome Leader]

I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply. One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high. Inrush current for an incandescent
lamp is about 10x the current after warmup.

Is this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

John Nagle

tough one. I've run into this very problem with linear power supplies.

What's happening is the cold filament looks like something close to a
short, and then the power suppply drops the output voltage to back off a
bit. It doesn't matter what voltage it's trying to output, it will never
heat the filament up enough to increase it's resistance to match the load
rating of the power supply.

You might be able to defeat the overcurrent protection which is causing
this- find the current sense resistor and slap another across it.

 

[Tim Williams]

Some switchers current limit and some "burp", namely shut down quickly
on
overload and try again later, a few times per second maybe. The latter
don't
pull up loads very well.

I've had that problem with USB 5-volt supplies, especially when driving
electronic loads that have switchers - negative impedance - loads
inside.

I find they work better. A [continuous] foldback limit is guaranteed to
get stuck forever, each and every time the load is the same. That's
boring, and dangerous besides.

Example: suppose you have a converter which draws 12V, 1A. Maybe it's a
5V buck converter or something, doesn't matter. Set your benchtop supply
to 1.5A current limit, bring it down below 8V, and just try to get it back
up without fiddling with that current limit knob.

The peak current delivered in "burp" mode is typically 1-2 times the full
load current, enough to push most loads through.

Additionally, if the heavy load is due, in part, to charging capacitance,
a few "burps" will deliver enough charge to start it up. The current
limited supply can do this, too, but if it doesn't deliver enough to cover
steady state at reduced voltage, it's still screwed.

Maybe all the "burp" supplies you've bought just suck.

Tim

 

[gregz]

I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply. One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high. Inrush current for an incandescent
lamp is about 10x the current after warmup.

Is this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

John Nagle

You need an adjustable current limit type supply. Cost more than most. A
typical supply will need, say, 10 times the current capability with a built
in shut down mode. A non regulated supply can work, as well as a variac
controlled supply.

Greg

 

[George Herold]

---
Dunno.

Are you tied to a bare single supply or can you stand some external
soft-start circuitry?

Yeah, a known voltage, load, R,C and transistor, I think I can make a
slow start.

George H.

 

[Phil Allison]

"gregz"

You need an adjustable current limit type supply.

** Why ??

A typical supply will need, say, 10 times the current capability

** Why ????

Long as the 12V supply does not shut itself down at switch on it will work
fine - providing of course it has at least 2 amps current output available.



...... Phil

 

[George Herold]

Yeah, a known voltage, load, R,C and transistor, I think I can make a
slow start.

George H.

You can keep the surge down to barely more than the normal operating
current.  Just pre-warm them with about 10% of normal.  (I did such a
thing during my investigations of ways to do the sequential turn
signals for the Ford T-bird... but I ended up using SCR's and kissing
off worrying about the surge

                                        ...Jim Thompson
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I did a slow start thing for laser diodes... where you care about the
diode.
The circuit was copied from someone else..
(Little of what I do 'original'.)

George H.

 

[ehsjr]

I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply. One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high. Inrush current for an incandescent
lamp is about 10x the current after warmup.

Is this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

John Nagle

Phil has it right.

For a less elegant approach that may work with your existing
power supply, try this:

5ohm 10W
+12 ---+---/\/\/---+---+---[Lamp]---+
| | | |
+---o o----+ +---[Lamp]---+
\ |
|
Gnd --------------------------------+

Turn the switch on to short out the resistor after a couple of
seconds warm up. If it works to your satisfaction you could
replace the switch with a delay circuit later on.

Ed

 

[Tim Williams]

Phihong and Samsung seem to make good warts. MeanWell makes good
open-frame
switching supplies.

We've had good results with MeanWell. Also one of the few manufacturers
with a 480V input unit (size 100W and up).

Tim

 

[Allan Herriman]

Some switchers current limit and some "burp", namely shut down quickly
on overload and try again later, a few times per second maybe. The
latter don't pull up loads very well.

I've had that problem with USB 5-volt supplies, especially when
driving electronic loads that have switchers - negative impedance -
loads inside.

I find they work better. A [continuous] foldback limit is guaranteed to
get stuck forever, each and every time the load is the same. That's
boring, and dangerous besides.

Switchers don't need to fold back, and I haven't seen one that does.

Some switchers do need to fold back.

Here's why: (Assuming a steady output current) at low output voltages
the duty cycle will be low. This means the synchronous rectifier fet is
carrying a much larger RMS current than it normally would at full load.

Adding foldback to reduce the output current when the output voltage is
low can save money on thermal management for the lower fet in certain
designs.

Of course, foldback can lead to all sorts of system problems and should
be used with caution.

Regards,
Allan

 

[George Herold]

I find they work better.  A [continuous] foldback limit is guaranteed to
get stuck forever, each and every time the load is the same.  That's
boring, and dangerous besides.

Switchers don't need to fold back, and I haven't seen one that does.

Example: suppose you have a converter which draws 12V, 1A.  Maybe it'sa
5V buck converter or something, doesn't matter.  Set your benchtop supply
to 1.5A current limit, bring it down below 8V, and just try to get it back
up without fiddling with that current limit knob.

The peak current delivered in "burp" mode is typically 1-2 times the full
load current, enough to push most loads through.

We evaluared a bunch of USB switchers. The 700 mA Samsungs pulled up our loads,
and some "1 amp" burpers wouldn't.

We've been careful to have our electronics soft start, to make it easier on the
wall wart switchers at startup.

Additionally, if the heavy load is due, in part, to charging capacitance,
a few "burps" will deliver enough charge to start it up.  The current
limited supply can do this, too, but if it doesn't deliver enough to cover
steady state at reduced voltage, it's still screwed.

Maybe all the "burp" supplies you've bought just suck.

Could be. There's a huge number of bad power supplies out there.

Phihong and Samsung seem to make good warts. MeanWell makes good open-frame
switching supplies.

Oh that's good to know... We've been using the Phihongs.

George H.

 

[gregz]

"gregz"



** Why ??



** Why ????

Long as the 12V supply does not shut itself down at switch on it will work
fine - providing of course it has at least 2 amps current output available.



..... Phil

As long as it does not shut itself down, would work.

Greg

 

[gregz]

I'm trying to run two 12V 12W auto lamps off a Tripp-Lite 12V 3A
linear regulated power supply. One lamp will work, but two
of them shut down the power supply, presumably because the
inrush current is too high. Inrush current for an incandescent
lamp is about 10x the current after warmup.

Is this likely to be better or worse with low-end switching power
supplies, of the type usually used to power laptops and such?
(Assuming I get power supplies with CSA, UL, or GS safety
certification?)

John Nagle

Do you need DC ?

Greg

 

[[email protected]]

message Some switchers current limit and some "burp", namely shut down quickly
on overload and try again later, a few times per second maybe. The
latter don't pull up loads very well.

I've had that problem with USB 5-volt supplies, especially when
driving electronic loads that have switchers - negative impedance -
loads inside.

I find they work better. A [continuous] foldback limit is guaranteed to
get stuck forever, each and every time the load is the same. That's
boring, and dangerous besides.

Switchers don't need to fold back, and I haven't seen one that does.

Some switchers do need to fold back.

Here's why: (Assuming a steady output current) at low output voltages
the duty cycle will be low. This means the synchronous rectifier fet is
carrying a much larger RMS current than it normally would at full load.

Adding foldback to reduce the output current when the output voltage is
low can save money on thermal management for the lower fet in certain
designs.

But foldback will further reduce output voltage (not current) putting
you right in that box.