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Resolved: 24V to 12V

Added by LittleJim about 5 years ago

I want to use led nodes on a boat that has a 24V system. I’ve tried a variety of 24V to 12V converters, such as this one (http://www.ebay.com/itm/221036125254) but they all get very hot and, as they are to be in an enclosed space, dangerously so. Does anyone have ideas how to reliably step down from 24V to12V to drive about a 20 ft LED strip.

thx


Replies (7)

24V to 12V - Added by martynj about 5 years ago

@LittleJim,

If you can arrange to operate pairs of 12v single-colour strips in series, there is no need to convert the 24v.  This trick is not possible with the Tri-colour strips since they have a common terminal just where you don’t want it.   The FET’s on the LedNode can handle this higher apparent string voltage.

RE: 24V to 12V - Added by LittleJim about 5 years ago

thanks but they have to be RGB, there isn’t the room to put multiple strips in.

RE: 24V to 12V - Added by martynj about 5 years ago

@LittleJim,

If you have a hot running 24-12V convertor, I doubt it is a true switching buck convertor - they can run at >85% efficiency, so need to shed a few watts. With a good thermal design and clamped to a solid metal bulkhead (or a largish steel plate if this is a fibreglass vessel) they can run fine warm, not hot, indefinitely.

Can’t you avoid the problem by going directly to 24V strings? Unusual, but they do exist.  Frustrating since it is exactly the same LED chips, but with a slight difference in the series/parallel arrangement of tracks buried in the plastic covering.

If you have purchased 12V strips already, then either a non-“China special” buck converter, or find 12V another way.  Most marine electrics, similar to trucks, run at 24V to reduce the voltage drop in the cable runs.  But the basic storage is still the familiar heavy duty, 12V nominal lead-acid battery - often two, matching batteries in series, or integrated into the same housing, but with individual cell straps accessible.

This provides simple access to nominal 12V - place the load across only one of the two series batteries.
To be kind to the charging system, presumably a 24V alternator somewhere, it is best to keep the system balanced by splitting the 12V load into two independent sections and wire one across the “lower” battery and the other across the “higher”.  Basically a single, fused, heavy gauge wire from the centre-tap of the batteries to bring to where your standard batt -ve, batt +ve connection point is located.
So two controllers, pairs of strips and some clever code that integrates the upper and lower section amps over time and attempts to keep the two integrals roughly in balance.  The charging system will cope with minor imbalance.

RE: 24V to 12V - Added by LittleJim about 5 years ago

Thanks! That’s a greatly detailed answer. I can’t access the batteries directly, but I could go directly to 24V strips. Pity, cause I already bought a whole bunch of 12V ones :-(. I’m a programmer more than a hardware gone, but it appears to me that I can’t use the LED node within a 24V system either.

RE: 24V to 12V - Added by martynj about 5 years ago

Nay good sir - we design for the general case as far as possible…

JeeLabs Shop LED Node entry:

> With the minor modification described in the Wiki, even 24v strips are supported.

IIRC, the max voltage that the FET’s can tolerate is ~30V - a comfortable margin for a 24V regulated power supply feed, but NOT for floating battery-based systems without taking precautions. The problem is that nominal 24V can easily be 27V on charge and load dump transients can spike to ~60V. The solution is to strap a stud-mount crowbar zener (anode to negative, cathode to positive) in series with a low ohm, 5W ceramic resistor directly across the supply terminals at your connection point. For short transients, the Zener will just eat them, for longer, the fuse in that feed line will blow - in either case, protecting the downstream circuits from the over voltage.
There is no need to put the zener on a heat sink - in normal operation, it is passing only a small leakage current with negligible heating effect. The reason to use an oversize zener and fat limit resistor is simply to cope with the surge current when it occurs.
Many modern marine charging systems already incorporate such crowbar protection for the more delicate loads (radios, GPS, fish-finder etc) but you would need to confirm that before dispensing with this local crowbar protection.

So the choice is either find a professional 24-12V buck converter and recycle the existing strips, or buy new 24V strips and do a little wiring….

RE: 24V to 12V - Added by LittleJim about 5 years ago

Yeah, I saw the wiki after I posted :-). Good info about the zener, I can use the existing strips as well as new 24V ones.

Thx, this has been a really informative thread

RE: 24V to 12V - Added by martynj about 5 years ago

@LittleJim,

You are welcome - your fee is perhaps onerous though - expecting some pictures posted of the “Fleet all lit up” on the Forum at some future date please?  ;-)

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