Need help in stablizing a power supply

E

Everett X. Wang

Jan 1, 1970
0
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?

Everett

T

Terry Pinnell

Jan 1, 1970
0
Everett X. Wang said:
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?

Guessing that the converter's oscillator is being affected by feedback
from the motor. I'd try
1) Adequately rated diode in series with motor
2) The high value capacitor you suggested, plus a 10nF ceramic
3) Fresh 12V battery (existing may have highish internal resistance)
4) Choke-based filters on input and/or output of converter
5) Combinations of the above

This assumes it really is impossible to get a second 12V battery to
give you the requisite 24V, or a 12V motor!

C

CFoley1064

Jan 1, 1970
0
Subject: Need help in stablizing a power supply
From: "Everett X. Wang" [email protected]
Date: 12/5/2004 9:54 PM Central Standard Time
Message-id: <[email protected]>

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?

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
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

E

Everett X. Wang

Jan 1, 1970
0
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

C

CFoley1064

Jan 1, 1970
0
Subject: Re: Need help in stablizing a power supply
From: "Everett X. Wang" [email protected]
Date: 12/7/2004 1:41 AM Central Standard Time
Message-id: <[email protected]>

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

I wouldn't do it, but it's up to you. I would guess your peak voltage will
probably be above 25V, which will probably smoke the cap, and might smite your
converter in rage on its way to electronics heaven.

You can get a 4700µF 35V 20% Axial-Lead Electrolytic Capacitors for $5.29 USD at RadioShack (Catalog #: 272-1022). Also, you can get a couple of 0.47 Ohm/5W 5% Wirewound Resistors for$1.59 USD
each at RadioShack (Catalog #: 271-130 ). Put them in parallel to get about
0.23 ohms.

For a less money/more time/probably equal or better quality tradeoff, try
Mouser.com.

Good luck
Chris

P

peterken

Jan 1, 1970
0
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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