Need help in stablizing a power supply

  • Thread starter Everett X. Wang
  • Start date
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Everett X. Wang

Guest
Hi All,

I am working on a home project that needs to supply a 24V power to a
brushless motor controller. The motor draws 24V with current less then 3.0A
and my 12 to 24V DC to DC power supply is rated 700W. But when I connect the
things together, the power supply will shut it down. My guess is the motor
controller draws a high current at a very short time that overwhelmed the
power supply, since my current meter indicated only 3 A from the 12V side.

Can anyone give me a suggestion how to make my power supply work? Can I add
a large capacitor at the power supply output? I also tried an other DC 2 DC
(rated 4.5A output) power supply. The result is even worse. (It worked for a
few seconds vs. minutes). My application is a mobile one and I can't use a
desktop power supply. The power source is from 12V lead acid battery. Any
solution to my problem?

Thanks in advance.

Everett
 
Subject: Need help in stablizing a power supply
From: "Everett X. Wang" everteq@sbcglobal.net
Date: 12/5/2004 9:54 PM Central Standard Time
Message-id: <kKQsd.29248$zx1.21098@newssvr13.news.prodigy.com

Hi All,

I am working on a home project that needs to supply a 24V power to a
brushless motor controller. The motor draws 24V with current less then 3.0A
and my 12 to 24V DC to DC power supply is rated 700W. But when I connect the
things together, the power supply will shut it down. My guess is the motor
controller draws a high current at a very short time that overwhelmed the
power supply, since my current meter indicated only 3 A from the 12V side.

Can anyone give me a suggestion how to make my power supply work? Can I add
a large capacitor at the power supply output? I also tried an other DC 2 DC
(rated 4.5A output) power supply. The result is even worse. (It worked for a
few seconds vs. minutes). My application is a mobile one and I can't use a
desktop power supply. The power source is from 12V lead acid battery. Any
solution to my problem?

Thanks in advance.

Everett
Click to expand...
Hi, Everett. I'm assuming you're using one of those automotive 12V-to-24V
DC-to-DC converters here.

First, you should look carefully at the difference between peak power rating
and steady-state power rating. Your second DC-DC converter limited out, and
that sounds like something one of those converters would do. But even if your
first supply is only rated for 700 watts peak, it would probably be able to
handle 3A.

You might want to put an 0.22 ohm power resistor in series with the +, and then
put your "mongo cap" across the output (I'd go with at least 4700uF, 35V for
the cap rating). That will help with charge storage and help to even things
out. Automotive doublers are made to handle a capacitive surge at turn-on, but
the 0.22 ohm resistor should help. Then put a voltmeter across the 0.22 ohm
resistor and measure voltage drop when your motor is on. By Ohm's Law, you
should get 0.22V per amp of current. You can then measure the steady state
current and see if it's really 3A (V = I * R = 3A * 0.22 ohm, somewhere around
0.66V across the resistor). If it's too high, there may be something wrong
with the motor or the driver circuit.

.---------------. 0.22 ohm
| 12V-to-24V | ___
.------o+ +o----|___|--o-----
| | | |
+|Batt | | +|
--- |12V 24V| 4700uF ---
- | | ---
| | | |
'------o- -o-----------o-----
| |
'---------------'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Good luck
Chris
 
Thanks for the suggestion. I got a 38,000 uF cap. But voltage is rated 25V .
Should it be OK for 24V application? I don't think I will go over 25V.

Thanks.

Everett

"CFoley1064" <cfoley1064@aol.com> wrote in message
news:20041206091910.21623.00001383@mb-m12.aol.com...
Subject: Need help in stablizing a power supply
From: "Everett X. Wang" everteq@sbcglobal.net
Date: 12/5/2004 9:54 PM Central Standard Time
Message-id: <kKQsd.29248$zx1.21098@newssvr13.news.prodigy.com

Hi All,

I am working on a home project that needs to supply a 24V power to a
brushless motor controller. The motor draws 24V with current less then
3.0A
and my 12 to 24V DC to DC power supply is rated 700W. But when I connect
the
things together, the power supply will shut it down. My guess is the motor
controller draws a high current at a very short time that overwhelmed the
power supply, since my current meter indicated only 3 A from the 12V side.

Can anyone give me a suggestion how to make my power supply work? Can I
add
a large capacitor at the power supply output? I also tried an other DC 2
DC
(rated 4.5A output) power supply. The result is even worse. (It worked for
a
few seconds vs. minutes). My application is a mobile one and I can't use a
desktop power supply. The power source is from 12V lead acid battery. Any
solution to my problem?

Thanks in advance.

Everett

Hi, Everett. I'm assuming you're using one of those automotive 12V-to-24V
DC-to-DC converters here.

First, you should look carefully at the difference between peak power
rating
and steady-state power rating. Your second DC-DC converter limited out,
and
that sounds like something one of those converters would do. But even if
your
first supply is only rated for 700 watts peak, it would probably be able
to
handle 3A.

You might want to put an 0.22 ohm power resistor in series with the +, and
then
put your "mongo cap" across the output (I'd go with at least 4700uF, 35V
for
the cap rating). That will help with charge storage and help to even
things
out. Automotive doublers are made to handle a capacitive surge at
turn-on, but
the 0.22 ohm resistor should help. Then put a voltmeter across the 0.22
ohm
resistor and measure voltage drop when your motor is on. By Ohm's Law,
you
should get 0.22V per amp of current. You can then measure the steady
state
current and see if it's really 3A (V = I * R = 3A * 0.22 ohm, somewhere
around
0.66V across the resistor). If it's too high, there may be something
wrong
with the motor or the driver circuit.

.---------------. 0.22 ohm
| 12V-to-24V | ___
.------o+ +o----|___|--o-----
| | | |
+|Batt | | +|
--- |12V 24V| 4700uF ---
- | | ---
| | | |
'------o- -o-----------o-----
| |
'---------------'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Good luck
Chris
Click to expand...
 
"CFoley1064" <cfoley1064@aol.com> wrote in message
news:20041206091910.21623.00001383@mb-m12.aol.com...
Subject: Need help in stablizing a power supply
From: "Everett X. Wang" everteq@sbcglobal.net
Date: 12/5/2004 9:54 PM Central Standard Time
Message-id: <kKQsd.29248$zx1.21098@newssvr13.news.prodigy.com

Hi All,

I am working on a home project that needs to supply a 24V power to a
brushless motor controller. The motor draws 24V with current less then
3.0A
and my 12 to 24V DC to DC power supply is rated 700W. But when I connect
the
things together, the power supply will shut it down. My guess is the
motor
controller draws a high current at a very short time that overwhelmed the
power supply, since my current meter indicated only 3 A from the 12V
side.

Can anyone give me a suggestion how to make my power supply work? Can I
add
a large capacitor at the power supply output? I also tried an other DC 2
DC
(rated 4.5A output) power supply. The result is even worse. (It worked
for a
few seconds vs. minutes). My application is a mobile one and I can't use
a
desktop power supply. The power source is from 12V lead acid battery. Any
solution to my problem?

Thanks in advance.

Everett
Click to expand...
Might consider using an inrush current limiter
it limits the current at startup to a value depending on it's startup
resistance, and (after it heats) acts *almost* as a wire
I'd consider using a cold value of say 12Ohm limiting startup to 2amps, and
with an operational value of say 0.5Ohms
Just search the net, lots of them out there
Only thing to keep in mind is it's operational current so the operational
resistance stays low enough
 
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