Adjustable 24V DC power

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sjones 19 years ago

Hi all,

I need some help here. I want to verify a voltage "trip" point on a board that operates on battery supplied 24vdc. The maximum draw is about 600MA

The board should change to "recharge required" at 22VDC

My thought is to put some sort of resistor in line on the main battery feed so I can slowly reduce the voltage to a point where it trips the recharge indicator. A voltmeter after the resistor would allow me to monitor the voltage level where the recharge indicator is activated.

I am not an electronics guru (obviously) so something "off the shelf" would be great. Maybe some type of adjustable resistor? Any ideas?

Thanks.

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DaveM 19 years ago

The easiest way to do that would be to beg or borrow an adjustable power supply. Substitute the battery with the power supply. Set the power supply to the nominal battery voltage, connect the voltmeter to the power supply output, then slowly adjust the power supply output voltage until the recharge indicator turns on.

Cheers...

Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) "In theory, there isn't any difference between theory and practice. In practice, there is." - Yogi Berra

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Zebra 19 years ago

How about using two 12V car bulb (current drain can be control by selection of watts) and connected them in series (making up a 24V load). Then connect it at the battery and wait for the voltage drop.

"DaveM" ¼¶¼g©ó¶l¥ó·s»D:LpqdnV5VeuzcCg7bnZ2dnUVZ snipped-for-privacy@comcast.com...

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sjones 19 years ago

Unfortunately, I don't have anyone to beg or borrow one from. I hoped to just add the "adjuster" set up to an extra battery pack for future testing use. Is there anything out there that i can put in line? If anyone knows the proper terminology for what I need, I can try and search for one.

Thanks again!

supply.

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Arfa Daily 19 years ago

If the draw is really around 600mA, then you're not going to do it with a pot. As Dave suggested, the best way to do it would be with a variable PSU subbed for the battery, but failing that, you could use 1 ohm resistors inserted in series with the battery. Each one added in series will cause a drop of about 0.6v (not quite true as the amount dropped depends on the current draw, and as the volts drop, the draw will probably also drop as well, but near enough to do what you want to do). Each resistor should be a

1 watt type, which will still get pretty warm. If you wanted to use a higher wattage, that's fine. If it does what you want, and you want to be able to use it again in the future, you could just wire the resistors to a single pole rotary switch. If you want to go a bit 'finer' with each step, you could use 0.47 ohm resistors to give about 0.3v per step, or 0.22 ohm for half that again. Obviously, these are all approximate figures, but right ball park for what you want, and not of any consequence how accurate anyway, if you are going to have a voltmeter slung across the test. If that sounds like what you need, and you don't know how to wire such a switch, mail me direct.

Arfa

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Franc Zabkar 19 years ago

On Tue, 10 Jul 2007 07:05:44 -0700, snipped-for-privacy@cyperceptions.com put finger to keyboard and composed:

Make up a bank of series cells, eg 14 or 15 AA alkalines, or C or D cells if you can justify the cost. Just do your testing quickly. Otherwise try to disconnect the load section of your circuit and keep the sensing section operating.

- Franc Zabkar

Please remove one 'i' from my address when replying by email.

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whit3rd 19 years ago

It's easy to run an adjustable voltage regulator (LM317) for this purpose; two fixed resistors and one adjustable resistor, the LM317, and a small capacitor (probably not required, but it's recommended) will make a 18-23V regulator. Just power the regulator from the battery, wiggle the pot 'til it measures 22VDC output, and draw a red line there. Or do it right, put a 'too low' line at 21.3V and a 'too high' line at 22.6V.

Radio Shack should have all the parts.

The regulator can be inserted between a fully charged battery and the unit-under-test. It's going to need some heatsinking on the regulator (get an aluminum box for the project, and bolt the regulator chip through the convenient hole).

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Zebra 19 years ago

I think the term is Rheostat. Please read the following link on the High power type rheostat.

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Hope it is useful.

"whit3rd" ???????: snipped-for-privacy@n2g2000hse.googlegroups.com...

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Bill Jeffrey 19 years ago

Power it up with 16 "C" or "D" batteries in series (16 x 1.5 = 24 volts), and wait for the voltage to drop. Buy the cheapie batteries (zinc carbon, often labeled "super duty" or something equally misleading), since they are less expensive and discharge quicker than alkalines.

Bill

------------------------------------------- snipped-for-privacy@cypercepti> Hi all,

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Adjustable 24V DC power

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