Matthias Richter Posted June 21, 2012 Report Share Posted June 21, 2012 hopefully any electronic gurus around: I have a small DC/DC converter (to isolate a 12V device) that works when powered of a Li-Ion NP1 battery but doesn´t when powered of a SLA battery. converter: wide input range 9-18V, regulated 12V output, 3W load (IFB100): draws 104mA / 12V what is the difference between the NP1 and a SLA? Since the converter works from 9-18V both batteries are within the specs on paper. I have attached an Elko 10.000 mikroF / 25V to the input - no success. Any ideas? Matthias Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 21, 2012 Report Share Posted June 21, 2012 hopefully any electronic gurus around: I have a small DC/DC converter (to isolate a 12V device) that works when powered of a Li-Ion NP1 battery but doesn´t when powered of a SLA battery. converter: wide input range 9-18V, regulated 12V output, 3W load (IFB100): draws 104mA / 12V what is the difference between the NP1 and a SLA? Since the converter works from 9-18V both batteries are within the specs on paper. I have attached an Elko 10.000 mikroF / 25V to the input - no success. Any ideas? Matthias Should work. See what the SLA voltage terminal voltage is when the converter is operating. Something is wrong here. Capacitor was a good thought by the way. Best, Larry F Lectro Quote Link to comment Share on other sites More sharing options...
Matthias Richter Posted June 21, 2012 Author Report Share Posted June 21, 2012 thanks for chiming in Larry! the SLA reads 12.8V with or without the converter. output of the converter is 12.0V without load and drops to 3V with IFB100 attached. NP1 reads 16.4V when converter is working. output is 12.0V with and without load. Have called the manufactor of the converter. They have no idea. Saying it should work as long as it sees 9-18V on the input. Thanks, matthias Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 21, 2012 Report Share Posted June 21, 2012 If you can find a variable power supply, I bet you will find that the converter is failing when the input voltage gets close to the output voltage. If they spec it 9 to 18 Volts, then it isn't meeting its specs. This has nothing to do with the type of battery. The SLA is just lower voltage and making the defect obvious. My best guess. Best, Larry F Lectro Quote Link to comment Share on other sites More sharing options...
Matthias Richter Posted June 21, 2012 Author Report Share Posted June 21, 2012 feels like having Larry right here in my little workspace ;-) no variable PSU at hand but tried a standard 9V battery - and the IFB works!! Very strange. I tried different SLAs. Nothing. A friend suggested the cap because SLA is to "soft" (whatever that means). As said - nothing. Matthias Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 21, 2012 Report Share Posted June 21, 2012 feels like having Larry right here in my little workspace ;-) no variable PSU at hand but tried a standard 9V battery - and the IFB works!! Very strange. I tried different SLAs. Nothing. A friend suggested the cap because SLA is to "soft" (whatever that means). As said - nothing. Matthias Hi Matthias, What he meant by "soft" is the internal resistance of the battery. That means that the battery voltage will fall as you pull more current out of it. Think of a perfect battery that is 12 Volts with no current being pulled out and is also the same 12 Volts with a 100 Amps being pulled out of it. That would be a "hard" voltage source (and a figment of the imagination). If you put a 0.1 (tenth) Ohm resistor in series with the battery, then when you pull 10 Amps out of the battery, the voltage at the resistor output would fall by one Volt to 11 Volts. This is beginning to sound like a real battery rather than an imaginary one. So we can model a real battery by placing a perfect battery in series with a resistor so that the battery voltage falls and rises as you pull more or less current out of the combination. The imagined resistor is called the internal resistance of the battery. A motorcycle battery might have a tenth Ohm resistance. A car battery might have a hundredth of an Ohm so 400 Amps starting current might drop the voltage by only 4 Volts for a second or so. The internal resistance varies with the charge of the battery and the outside temperature as well as the construction. So a soft battery or soft voltage source means it has a relatively high internal impedance. Your friend recommended the cap so that the cap would bypass the internal resistance of your SLA and act as an instantaneous current source (short term, high current battery) to allow the voltage converter to start if it pulled high current at startup. It shouldn't be necessary but it was a good idea for a test. The voltage converter you have, can down convert high voltages ok and up convert low voltages ok. These usually require two different types of switching converters but there are special converters that will do both such as a SEPICH (sp?) converter or a flyback converter. The one you have sounds like it loses control when it is fed an input voltage equal to its nominal output voltage. It could also be a cheap linear regulator for reducing voltage in combination with a single switcher to step it up. But whatever, it sounds as if it gets lost in the middle. I'd put it on a variable power supply, if you can find one or borrow one, and see if the regulator fails with voltages in the middle around 12 Volts. I don't think it is your SLA from your tests and measurements. It would be nice if the regulator is still under warranty. Best Regards, Larry Fisher Lectro Quote Link to comment Share on other sites More sharing options...
soundslikejustin Posted June 21, 2012 Report Share Posted June 21, 2012 Brilliant, Larry. Ps. It's SEPIC. Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 22, 2012 Report Share Posted June 22, 2012 Another cheap trick, if it is out of warranty or you are in a hurry, is to take five 1n4001 diodes or equivalent and put them in series to obtain a fairly constant 3 Volt drop. Those diodes are about a dime apeice in quanttity. Put the five diodes in series with your SLA to take it down to 9 Volts. This is a waste of a small amount of power but you aren't pulling a significant amount of power anyway. That should allow your regulator to operate. If the battery is on a charger it will be about 14.1 Volts and 3 Volts might not be enough drop. But off charge the SLA will fall to 12.5 within a minute or so. Radio shack will have similar diodes at a bit more money. The 1n4001 is a 1 AMP continuous diode. You don't care about reverse voltage rating since you will be using them in the forward direction. Any silicon power diode (forward drop 0.6 to 0.7 Volts at moderate currents) will work as long as it is 200 mA or more. Five Amp diodes would also work though the drop will be a little less per diode. Remember to operate them in the forward direction, non banded end goes to the battery positive, banded end goes to the regulator positive input. Series connection is banded to unbanded on each diode. Best, Larry F Quote Link to comment Share on other sites More sharing options...
Matthias Richter Posted June 22, 2012 Author Report Share Posted June 22, 2012 went to Kortwich to try a variable PSU. It worked at 9V and 16V. Wouldn´t start at 12-13V. However when I started the IFB at 16V and dropped the voltage to 12V it continued working. And - now it get´s voodoo: after that it would even start at 12V (several times). At home with just my 3 different supplies it wouldn´t start at 12V. At first it wouldn´t even start at 16V just the 9V. Once brought to life at home it now works with 9V and 16V. More testing needed ... Matthias Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 22, 2012 Report Share Posted June 22, 2012 went to Kortwich to try a variable PSU. It worked at 9V and 16V. Wouldn´t start at 12-13V. However when I started the IFB at 16V and dropped the voltage to 12V it continued working. And - now it get´s voodoo: after that it would even start at 12V (several times). At home with just my 3 different supplies it wouldn´t start at 12V. At first it wouldn´t even start at 16V just the 9V. Once brought to life at home it now works with 9V and 16V. More testing needed ... Matthias Warranty? LEF Quote Link to comment Share on other sites More sharing options...
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