DC to DC converter for charger - Page 1
Forum section: electronics / projects

author: electros6
author_rank: Regular Contributor
timestamp: December 23, 2017, 01:08:51 pm
content: Hi guys,I would like to convert 220V dc to 110V DC to charger the 110V batteryof 200AH capacity, any converter suggestion for this application guys. I also like to wrote the charging algorithm using Dspic

author: David Hess
author_rank: Super Contributor
timestamp: December 23, 2017, 05:12:40 pm
content: A simple buck converter would operate with a 50% duty cycle with that voltage ratio which is convenient.What charging current is required? 20 amps? 200 amps?Is isolation required between the input and output?

author: electros6
author_rank: Regular Contributor
timestamp: December 24, 2017, 02:32:42 pm
content: charging current is 30A , isolation is required

author: David Hess
author_rank: Super Contributor
timestamp: December 24, 2017, 06:15:30 pm
content: So then a transformer isolated buck converter and since 30 amps at 110 volts is 3300 watts, I might even use several out of phase smaller converters in parallel. Because of the high output voltage, there is little reason to use synchronous rectification so if a two transistor push-pull input is used with a center tapped transformer primary, no level shifting is required and the switching controllers could be placed on the input side simplifying driving of the transistors. A full bridge on the input side simplifies the transformer a little bit but doubles the number of transistors and half of them then need a high side level shift in which case the controller may be placed on the output side since switching isolation via a pulse transformer would probably be used but this makes controlling the output voltage and current easier.If there is not an auxiliary low voltage DC supply to power the switching controller, then an extra winding on the transformer or buck inductor can provide one if the switching controller is self starting with a bootstrap circuit. Otherwise maybe a low power auxiliary power supply running off of the 220 volt DC input would be desirable for the smart part of your controller. If three way isolation between the input, output, and smart controller would be advantageous, then that could be done as well with the same low power auxiliary power supply. I might want that for extra safety when working with 200+ DC volts and 3000+ watts.Those more familiar with resonate ZVS/ZCS (zero voltage switching/zero current switching) designs may have better suggestions for handing this power level.

author: Zero999
author_rank: Super Contributor
timestamp: December 25, 2017, 02:04:46 pm
content: I'd consider an off the shelf solution. Get a mains charger, rated for the current and voltage you require. It should be able to work from 220V, especially if it has a universal input voltage range: 100VAC to 250VAC.110V doesn't divide evenly by 12, so it must be either individual cells or is rounded. How many cells does the battery contain?

author: ocset
author_rank: Super Contributor
timestamp: December 26, 2017, 10:21:11 am
content: Hello,The attached is a 220vdc to 110vdc LLC converter..with output of 10A….so you would need three of these in parallel…it switches at an effective switching frequency of 92.5kHz when the dead time is also taken into account.The upper resonant frequency is 75kHz, so you can see that unfortunately it is not going to be operating with the finest efficiency of an LLC converter…however, I could not operate it at the Upper resonant frequency because the load is too heavy , and doing this would have meant operating too close to the capacitive region.The penalty of not operating at URF, is that you get more switch off switching losses than you would like, but you do have zero switch-on switching losses in the FETsHowever, as you will notice, you have zero output diode switching losses, so that’s good..The attached is the LTspice sim of it, and the pdf schem.