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I don't have much experiences from designing and understanding more complex circuits. I only have basic knowledge how different components work and how to create and calculate simple transistor circuits with 4 resistors and a transistor. So I need some help from more experienced people.

I'm working on a 12VDC home automated system, and there is components in the system that needs stabile voltage ~(12V - 12.8V), as long as the generator is active, it delivers 13.8V. But the battery voltage can drop down to 10.5V when I'm not on the site.I have also limited battery capacity, and it can go a week between I'm on place and charge the battery. So I need a effective power supply that can deliver stable voltage. So I have done some search and found that Buck boost converter is what I'm looking for.

Not all equitment is powered on 24/7, but I will install such powersupply for every fuse, so every equitment has same stable voltage. And I have calculated that I need least 15A for the equitment that needs most power. So I'm looking for a buck boost converter that can least deliver 15A@12VDC.

I have done some searches for such curcuit, but the best I have found can deliver 5A@12VDC and 10A@24VDC, is it possible to change these curcuit to deliver 15A+@12VDC? Or does any body has a cicuit that can deliver such current.

The reason why I want to solder the PCB by my self is because I want to have PSU and Control unit for the home automation in the same case. The cases are going to be designed as mini-rack (10 inch).

Here is the circuits that I have found:

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  • \$\begingroup\$ This isn't a "give me the circuit" sort of site. You need to narrow the focus of your question somewhat. A 15A buck-boost circuit is certainly possible. Designing a PCB for a converter which you admit may be beyond your experience level is almost certainly a recipe for disaster. I would seek a commercial solution or hire someone to do the design for you. \$\endgroup\$
    – Adam Lawrence
    Dec 7, 2015 at 20:44
  • \$\begingroup\$ I understand that this is not a «give me the circuit» site, but I have done some reasearch, tried to acquire the necessary knowledge to change these circuits, but I have given up. I had hoped that someone could help me redesign the circuit to be able to deliver 15A+ current. I can also pay for the help, but then I need to delay it to January, when I have more money available. \$\endgroup\$
    – BufferOverflow
    Dec 7, 2015 at 21:42
  • \$\begingroup\$ Personally, I would look for an off-the-shelf component unless you are doing this as a learning exercise. There will be a lot of system design involved in this project because of thermal issues. So it is not just a matter of soldering the board together and putting it in a case. Heat sinks will probably be required, and fan cooling, also. \$\endgroup\$
    – user57037
    Dec 7, 2015 at 22:07
  • \$\begingroup\$ @mkeith: Yes I'm aware of heat problem, that's one of the reasons I would like to use buck boost converter. More effective power supply is equal with less heat. I have seen many circuits that can deliver 15A@12VDC but that is linear circuits. So much power disappear in heat. I have also consider the power problem when I designed the 10 inch rack cases, I'm planing of having 4 connectors, and a 8 inch heat sink on the back side of the case where the mosfet's are placed. However if it require a fan will time show. \$\endgroup\$
    – BufferOverflow
    Dec 7, 2015 at 22:28
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    \$\begingroup\$ My math is wrong. Sorry. 15 * 12 = 180 W. So it is not a 300 W supply. Input power would be 180/0.85 = 212 W. So only 32 extra Watts need be dissipated, assuming 85% efficiency. \$\endgroup\$
    – user57037
    Dec 8, 2015 at 4:12

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While you may be able to get a 12V@15A buck-boost supply to work, the boost portion of that power supply is the portion of the design that will be very challenging.

Linear Tech does offer the LTC7812 which would supposedly allow you to do this (bear in mind the link is a press release!). You would need to cascade multiple units together to accomplish your goal, and that solution is designed to cascade outputs together. I have not personally used this part before so I can't vouch for the viability of that part.

Linear Tech does have a good reputation, and they probably have some development kits that you can obtain from them that would allow you to play around and see if it works. Once you are past that stage, it is likely to be fairly expensive to build this from the ground up; so unless you are building a lot of units you may wish to consider a solution that is composed of off-the-shelf components.

Have you considered using 24V automotive (truck) batteries and 24V-capable battery chargers? All of these components including the 24V->12V buck converters are readily available and can be sourced from retail outlets like Amazon.com.

I love the idea of rack-mounting this. Don't forget to add some cooling fans as dissipating ~30W of heat due to loss in there is something that you will need to think about. You'll want to ensure that you have some headroom in your battery capacity if you are gone for a long time, especially if the system is going to experience environmental temperature variations as that does sometimes affect battery capacity. This varies from battery-to-battery chemistry, so do your homework on that one before you build a bunch of units.

Good luck!

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  • \$\begingroup\$ Thanks for the input. I have thought of 24VDC system, but I didn't know that the boost part was so expensive to build. I have already consider the battery capacity problem, I was thinking of adding a cut-of circuit to the design, so the powersupplies shutdown if the battery voltage drops under ex. 10V. \$\endgroup\$
    – BufferOverflow
    Dec 9, 2015 at 1:40

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