Buck converter for 24v - 12v conversion.

[rkochis]

I am running a 24vdc solar installation that produces 26 amps. I have two 105 amp hour batteries installed.

What I am trying to accomplish is remove the 110vac inverter and run some of the electronics in the house from 12vdc directly. Electronics like the cable modem, wireless router, inkjet printer and possibly the TV cable box. The items that are powered up 24 hours a day!

I found an excel spreadsheet from Texas Instruments that provided some insight with design. Free Tool: Component Calculator for BUCK Converters - BUCK-CONVCALC - TI Tool Folder.

I can handle the electrical side (wiring, connectors, etc) but am a noob when it comes to electronics. I estimate that I will need 12v and 5 amps (60 watts) to supply all of this stuff.

Can anyone help with an actual circuit?

Thanks in advance

 

[rkochis]

Thanks anyway but a gentleman in the UK had published this PDF file and it is exactly what I am looking for (including pcb board layout). Gotta love those amatuer (ham) radio operators!

 

[ronsimpson]

24v to 12v at 5 amp

Look at the TPS5450. (ti.com)
You could make more than one. One for the printer and another for the TV.

 

[Diver300]

Thanks anyway but a gentleman in the UK had published this PDF file and it is exactly what I am looking for (including pcb board layout). Gotta love those amatuer (ham) radio operators!

Sorry to see this rather late.

That circuit is for a linear regulator. The output current will be slightly less than the input current, so converting 24 to 12 V the efficiency will be less than 50%

If you make a buck converter, it can output more current than the input current, and the efficiency can be up to 85% quite easily.

As ronsimpson says, you might be better to make several small buck converters. The voltage drop will be less if you distribute the current at 24 V instead of 12 V

 

[Oznog]

Yeah you don't want a linear reg. You need an actual buck reg- there are ICs to do this. It's somewhat difficult to design them for stability. Look at inductors carefully for efficiency, and be concerned with capacitor ESR.

You might wanna check and see how much the original transformers are drawing as no-load power from 110v. It may not be all that much. You need to measure actual difference in DC draw off the batts ideally, because a meter reading current at 110v directly doesn't take into account the phase relationship so power can be different than current * voltage.

The problem is the devices themselves may consume more than a few watts when "not doing anything" while still powered up. Eliminating the transformer will not help that at all.

OK, wait, I see you're concerned about the 110v inverter's quiescent current draw. Yes, some inverters take many watts just to stay on. I've seen cheap ones that take like an amp at 12v. Some retarded one don't put the fan on a thermostat and make the fan run all the time, for like a 50mA @12v load.

But, it varies widely. Unfortunately, mfgs often don't properly document the quiescent current, and disreputable ones don't document it ACCURATELY. I do have a 12v 2KW inverter which draws 80mA @12v which is awesome. This is really the way to go, honestly.

Be aware that a buck converter MAY draw significant quiescent current itself. Linear ones can easily be made to draw next to nothing- but, only 50% efficient. And your devices probably aren't 12v! Say you have a router that uses 200mA @ 9V. Linear regs will burn up 3.6W right there for that one device. Now if you used highly efficient buck reg to 12v, and did a simple linear reg to 9v, you'd only lose 0.6W- but it adds up.

An inverter which uses 100mA (2.7W) to stay on as quiescent current, but avoids the linear reg losses in the individual devices- may be more efficient in the end.

 

[Speakerguy]

You could use an enclosed, pre-made DC/DC converter like those made by Astrodyne, Meanwell, TKD/Lambda, etc. These are really high quality and easy to use.

Or you could go about making your own PCB with all the individual components. I think this might be a good start if you wanted to go that route:
**broken link removed**

 

[peufeu]

You could run 24V wiring (don't forget the fuses !) through your house, and use point-of-load buck switching regulators at each appliance, depending on the voltage each one needs. You can find very cheap ones like :

**broken link removed**

This chinese junk doesn't look too bad, although personally I would replace the capacitors with something better.

 

[colin55]

The simplest method is to take two lots of 12v wiring from your batteries and if you take equal wattage from each string, the batteries will charge to the same amount. Simply keep track of the wattage consumed or put a watt-hour meter on each string.

 

[RCinFLA]

You need an MPPT charge controller. A regular output voltage regulated buck switcher from 24 vdc to 12 vdc will not work if connected directly to PV panel. Solar cells are illumination based current source with an inherent shunt diode.

A PV panel designed to charge a 24 vdc battery system will typically have 72 cells in series. Maximum power point on the panel will be about 35 vdc, which is the point where the shunt diodes just barely start to conduct.

A regular output voltage regulating 24v to 12v buck switcher will oscillate with irratic output.

An MPPT charge controller is a buck switcher but the control system is very different allowing it to be driven from a current source.

The 12 v lead acid batteries need at least 13.5 vdc to charge properly and to charge completely and shortest time need 14.3 vdc for an absorb period.