Hi everyone I have circuit that i have to power with two different supplies. First one is a 24V(2x12V 3A batteries ) battery and the second one is a 28VAC AC supply. Batteries are OK. No need to change anything. But if it is comes to AC supply, I will use a rectifier but 28VAC will increase to about 40V DC. I need to drive two DC motors with this circuit. So the current will be about 15A. The question is how can I turn 40V DC into 24V (with capacity about 15A) ?

 

http://www.ebay.com.au/itm/15A-Adjustable-DC-DC-Buck-Converter-8-55V-to-1-35V-Power-Supply-Converter/182619057264?rt=nc&_trkparms=aid=222007&algo=SIM.MBE&ao=2&asc=47516&meid=264b7f9fd6bb4367ae6fb692ec53a37f&pid=100005&rk=5&rkt=6&sd=162396525672&_trksid=p2047675.c100005.m1851
Or something like this. Even if you run a couple of lower current versions together.
There are quite a lot on Ebay, just check the input voltage range is high enough. I'd go to higher output current rating if you can get one.

 

15V @15A is 225W, from a 24V battery you need 20Ah batteries minimum!!!

Mains would be better using at least 10amp supply.

 

http://www.ebay.com.au/itm/15A-Adjustable-DC-DC-Buck-Converter-8-55V-to-1-35V-Power-Supply-Converter/182619057264?rt=nc&_trkparms=aid=222007&algo=SIM.MBE&ao=2&asc=47516&meid=264b7f9fd6bb4367ae6fb692ec53a37f&pid=100005&rk=5&rkt=6&sd=162396525672&_trksid=p2047675.c100005.m1851
Or something like this. Even if you run a couple of lower current versions together.
There are quite a lot on Ebay, just check the input voltage range is high enough. I'd go to higher output current rating if you can get one.

thank you very much i have seen these ones before but i want to build my own converter. what kind of regulators i should choose ? what kind of circuit is inside this circut. ? i mean regulator? what is used for the swicthing ?

 

15V @15A is 225W, from a 24V battery you need 20Ah batteries minimum!!!

Mains would be better using at least 10amp supply.

yeah, you're complitly right. i will change it but i still dont know what to do about that 40 V DC :/

 

Have a read of....
http://www.linear.com/docs/43921
And there are other guides around. Designing a switch mode regulator has a few traps so a good read of all the info you can find is well worth while. Be prepaired for smoke
Pay attention to the inductor used. Not just any one will do.

Some example design software...
http://www.linear.com/solutions/1159

https://www.poweresim.com/

 

15V @15A is 225W, from a 24V battery you need 20Ah batteries minimum!!!

Depends on the duty cycle and duration of run times. If the motors only run for <10 - 20% duty cycle and less than a few minutes at a time the 3 AH batteries are plenty adequate.

You don't need 800+ AH battery to start a vehicles engine just because the starter draws 500+ amps when it operates.