Source of 24v power supply adjustable to 20v?

[Obi-dad]

I have a couple of the MJPA POTrans 24v 6.3A power supplies, cheap but adjustable down to 20.2 volts to keep my CAT4101s cool. One of them is failing, if I tap on the case it goes back on. I opened the case and removed the pc board to inspect for cold solder joints, but I don't see any, so I am guessing a component fails as it heats up. I bought a new 24v supply from a different company but it doesn't go below 22v via the adjust screw. I see MJPA has a different POTrans supply (and other makes of 24v supplies), but they do not indicate how low any of them adjusts.

Anyone know where to get an inexpensive 24v supply that will adjust down to around 20v? (all supplies have an adjust, but some do not go far enough - so I am not looking for a guess based on the supply having an adjustment screw, I am looking for someone who has actual experience on this)

 

[gbru316]

Why not just buy a 20v power supply?

The other alternative is a voltage divider for your current supply. 2 resistors in series, tap the +20v off the wire between the two.

How many CAT4101's are you driving?

 

[Obi-dad]

Why not just buy a 20v power supply?

The other alternative is a voltage divider for your current supply. 2 resistors in series, tap the +20v off the wire between the two.

How many CAT4101's are you driving?

I don't see any 20v powers supplies on mpja.com, they do have 19v supplies, but these are bricks (like for laptops), not enough amps.

Do you have a source for 20v supplies?

I do not want the heat and waste of using resistors to reduce voltage.

 

[gbru316]

You could always use a standard buck converter to drop the 24v (or 22v) down to 20.

You mention that you don't want to waste heat, so the easiest option (linear regulator) is out.

 

[ddavies564]

Check power gate llc.

 

[Obi-dad]

Check power gate llc.

thanks, they look like they might have something, but hard to tell about how low the supplies adjust.

As for using a buck convertor or linear regulator, I'm not asking to regulate a power supply, I am looking to source a replacement supply. The cheapo one I had was able to adjust down to 20v, there must be others - I am looking for someone who has experience with 24v supplies, and how low they adjust.

 

[asid61]

Add a diode in series with your leds to make the voltage drop higher. Heat shouldn't be bad if you use large diodes.

 

[ddavies564]

thanks, they look like they might have something, but hard to tell about how low the supplies adjust.

As for using a buck convertor or linear regulator, I'm not asking to regulate a power supply, I am looking to source a replacement supply. The cheapo one I had was able to adjust down to 20v, there must be others - I am looking for someone who has experience with 24v supplies, and how low they adjust.

I know what you mean power supply manufactures rate volt adjustability by a percent which is hard to pinpoint what voltage a ps will bottom out at. Especially because the percent includes the over and the under from the spec voltage.

 

[gbru316]

As for using a buck convertor or linear regulator, I'm not asking to regulate a power supply, I am looking to source a replacement supply. The cheapo one I had was able to adjust down to 20v, there must be others - I am looking for someone who has experience with 24v supplies, and how low they adjust.

I suggested it as a means to drop a replacement power supply to 20v if you're unable to find one that self-adjusts low enough.

Have you considered running two 20 Vdc, 3A power supplies in parallel? Doing so would give you the 6 amps you require. I'm not sure how many cat4101's you have, but you could also split them between two (or more) power supplies.

 

[zachts]

Could you add just One more LED to the strings?