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25Amp Power supply problem

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Old 08-31-2009, 11:55 AM
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Default 25Amp Power supply problem

I just bought two new 25amp 14volt power supply’s. But I am having problems with the voltage going up and down from 13.8v up to 16.6v. My charger will stop the charge once the input reaches over 16v.

Can any one give me any ideas how to fix this problem. I was thinking about adding a capacitor in the positive connection. But I don't know if this would work and what size of capacitor to use????

I am hoping to get 12-14volts at 25amps.
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Old 08-31-2009, 03:30 PM
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Default RE: 25Amp Power supply problem

Try using a very light load in parallel with your charger. For example, a couple of 12-volt lamps might draw enough current to prevent the power supply voltage from rising over 16 volts and tripping your charger. A resistor with a low enough value could accomplish the same thing. A few hundred ohms might do the trick. You would have to experiment with the values.

I would also verify if both power supplies behave the same way. Perhaps one of them is faulty and has a bad regulator circuit. If both are the same, then providing a light, constant load should prevent the voltage from spiking up as your lipos finish charging. Good luck with the trouble shooting.
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Old 08-31-2009, 09:27 PM
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Default RE: 25Amp Power supply problem

I have added a resistor which has lowed the voltage but I having problems with the high and lows in the voltage. Would a capaictor help with this????
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Old 08-31-2009, 10:13 PM
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Default RE: 25Amp Power supply problem

An honest-to-goodness regulated power supply should not do what you are describing. If the voltage is varying that much, then either it's not a regulated supply or it is defective. Most chargers require a regulated supply.

Are these power supplies originally intended for use in some piece of electronics equipment? Power supplies that are built for a particular purpose (and a particular load) sometimes don't work well as general-purpose power supplies. They only work properly with the load for which they are designed.

An example is certain types of personal computer power supplies which require a load on their 5V line in order for the 12V line to provide the proper voltage.

- Jeff
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Old 09-01-2009, 07:56 AM
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Default RE: 25Amp Power supply problem


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ORIGINAL: RC Technics

I have added a resistor which has lowed the voltage but I having problems with the high and lows in the voltage. Would a capaictor help with this????
As stated above, I agree that your power supplies don't appear to be regulating properly and may have been designed for some other purpose. One clue may be that you're getting a high voltage reading of about 16 volts which is somewhat high for a general DC supply. They are usually rated for about 13.8 volts which will drop just a bit when supplying current within it's design range. The loaded voltage should stay within a fairly tight range if the regulator circuit is working properly. These supplies usually have very large filter capacitors, so adding more is not likely to make any difference.
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Old 09-01-2009, 03:12 PM
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Default RE: 25Amp Power supply problem

If it's an unregulated supply and you are seeing ripple voltage on the output at high currents, then an additional cap will help. However, at 25A, you'll need a pretty big cap to make much of a difference. I've got a 24V 20A unregulated supply that has a filter cap the size of a soda can!

Is this a switching supply, or a transformer-rectifier-filter type supply? How are you measuring the output voltage, & seeing it vary from 13.8 to 16.6V? Are you looking at it on an oscilloscope?
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