RC-Monster Forums - View Single Post - What do you guys think of these power supplies?

BrianG · 03.03.2009, 01:17 PM

I too have an issue with a computer PS being at exactly 12v. Not only does this not give you much voltage leeway before it dips too far shutting off the charger, but the lower voltage will require more current to charge a specific pack than it would at say, 14v.

However, depending on the design on the PS unit, you can usually do "stuff" to boost the voltage a bit. I've seen one of three ways to do this:

1) Load down one of the other (3.3v or 5v) rails. All three supplies (12, 3.3, 5v) are all fed from a single main transformer. So, if one is loaded down, all three voltages usually drop. But, one of those rails contains a feedback circuit (usually a coil) that tries to compensate and boost the voltage back up. Unfortunately, there is no standard to which one that is, so you have to experiment and see which rail needs to be loaded.

2) Sometimes, there is a little adjustment potentiometer inside the PS where you can make fine adjustments. I've been able to squeeze out ~13.8v adjusting this. But, you can't assume that the presence of a pot does this - it might adjust something totally different. So, again, you have to experiment; put a meter on the output and make small adjustments. If the output doesn't change, set it back.

3) Some units have a smaller gauge feedback wire that attaches to the main wire it's monitoring at the very end of the main wire. The purpose of this is to detect a voltage drop along the wire (due to high currents) and boost the output until this sense wire sees the proper voltage. However, you can sometimes "trick" the sense wire with a simple voltage divider circuit or similar so that it sees ~1-2v lower than there actually is, which causes the regulator to boost the output accordingly. I've done this on an Antec TruePower 330w computer PS with very good results.

No matter what, you have to experiment. And doing so can be dangerous since there are hazardous voltages in there. Most switchers rectify 120v AC into 180vDC and then use a high speed switching circuit to get the output you want. May seem complex, but the size, weight, and efficiency are much better because of the higher frequency (instead of the low 50/60Hz).

	(#11)
BrianG RC-Monster Admin Offline Posts: 14,609 Join Date: Nov 2005 Location: Des Moines, IA	03.03.2009, 01:17 PM I too have an issue with a computer PS being at exactly 12v. Not only does this not give you much voltage leeway before it dips too far shutting off the charger, but the lower voltage will require more current to charge a specific pack than it would at say, 14v. However, depending on the design on the PS unit, you can usually do "stuff" to boost the voltage a bit. I've seen one of three ways to do this: 1) Load down one of the other (3.3v or 5v) rails. All three supplies (12, 3.3, 5v) are all fed from a single main transformer. So, if one is loaded down, all three voltages usually drop. But, one of those rails contains a feedback circuit (usually a coil) that tries to compensate and boost the voltage back up. Unfortunately, there is no standard to which one that is, so you have to experiment and see which rail needs to be loaded. 2) Sometimes, there is a little adjustment potentiometer inside the PS where you can make fine adjustments. I've been able to squeeze out ~13.8v adjusting this. But, you can't assume that the presence of a pot does this - it might adjust something totally different. So, again, you have to experiment; put a meter on the output and make small adjustments. If the output doesn't change, set it back. 3) Some units have a smaller gauge feedback wire that attaches to the main wire it's monitoring at the very end of the main wire. The purpose of this is to detect a voltage drop along the wire (due to high currents) and boost the output until this sense wire sees the proper voltage. However, you can sometimes "trick" the sense wire with a simple voltage divider circuit or similar so that it sees ~1-2v lower than there actually is, which causes the regulator to boost the output accordingly. I've done this on an Antec TruePower 330w computer PS with very good results. No matter what, you have to experiment. And doing so can be dangerous since there are hazardous voltages in there. Most switchers rectify 120v AC into 180vDC and then use a high speed switching circuit to get the output you want. May seem complex, but the size, weight, and efficiency are much better because of the higher frequency (instead of the low 50/60Hz).