high amp DC-DC converter - Page 1
Forum section: electronics / projects

author: jtroutt19
author_rank: Newbie
timestamp: March 22, 2017, 03:58:49 am
content: Hey guys! nice forum you got here. I work in the electronic repair industry, do not know much theory enough to get me in trouble. I am in way over my head here and need some help accomplishing what I am trying to do.One of my hobbies is RC Helicopters, and I am looking for a way to add some redundancy to my power system. I am needing what they call A battery eliminator circuit that will accept a 2 cell lipo batteries voltage and give a constant 8.4 volts and be able to provide 10a max. There are companies that sell these but at over $100 bucks a pop it's a bit overpriced to me.I remember seeing something like this on mouser or digi-key but can no longer find them. So now I am looking at building my own. I have done simple circuits in the past, designed, printed and etched my own board before. So the knowledge of how to assembly everything is there.What I am hoping you guys can help me with is the design of it and component selection. Thank you in advanced for any assistance.

author: mmagin
author_rank: Frequent Contributor
timestamp: March 22, 2017, 04:15:49 am
content: What needs up to 10 amps? It seems odd that you would want to run the motors driving the props off anything but the unregulated battery, and most of the electronics (receiver, FPV transmitter, IMU/autopilot, etc) should use a lot less current than that I think.

author: jtroutt19
author_rank: Newbie
timestamp: March 22, 2017, 04:36:39 am
content: Let me describe my setup right quick. I have my main battery pack that powers my Esc and my motor. 80-100a pull there.then I have a secondary battery for my Electronics servo's included. I have power hungry servos. 10a BEC is recommended. That being said I run unregulated power currently my 2s lipo plugs directly into my receiver which powers everything else. So my voltage level to all my electronics fluctuate depending on charge level of the battery. I can use a 3s lipo which would give an input of 1012.6 max. Is it better to buck than boost?That being said if it would be easier I could tap off of one of my 6 cell batteries if need be. Would rather not but the option is there.I understand most of that blueskull...lol. But I am still going to go read. I always enjoy learning things!

author: Siwastaja
author_rank: Super Contributor
timestamp: March 22, 2017, 07:00:52 am
content: Designing a switch mode converter is not trivial, especially high current, but it is an interesting learning process. You can use tools such as TI's WEBENCH that spit out a complete design, but they are not silver bullets, the designs may not work as is, and doing the PCB layout always requires some real understanding, mostly about handling parasitic inductances.

author: jtroutt19
author_rank: Newbie
timestamp: March 22, 2017, 07:33:38 am
content: I would have to do some reading on parasitic inductance. I've heard the term before but do not know much about it. I am up for the adventure as long as I got some help along the way.I will check out that program you mention thank you!

author: Marco
author_rank: Super Contributor
timestamp: March 22, 2017, 01:23:48 pm
content: Quote from: blueskull on March 22, 2017, 04:16:13 amThere's one on Aliexpress with a 15A input fuse which they say can do 12A output. Maybe with a little prop airflow it would survive?https://www.aliexpress.com/item/LTC3780-High-Power-Automatic-Voltage-Module-Vehicle-Computer-Power-Supply/1701712496.html

author: hayatepilot
author_rank: Frequent Contributor
timestamp: March 22, 2017, 02:04:06 pm
content: @jtroutt19Hobbyking has a converter that would suit your needs at only 14$ :https://hobbyking.com/en_us/hobbyking-yep-20a-hv-2-12s-sbec-w-selectable-voltage-output.htmlIt doesn't have 8.4V out but 7 and 9V. Probably it is hackable to 8.4V.This is a step down converter so you would have to connect it directly to your main battery if you always want to get 8.4V.Greetings

author: dmills
author_rank: Super Contributor
timestamp: March 22, 2017, 02:16:23 pm
content: My instinctive reaction is that given the mission critical nature of supplying power to the radios and servos (Even more so then the main rotor!), I would be very cautious about putting more switched mode doings in there, especially a switcher not very carefully thought out...Personally if I was going here, I would probably use an 'ideal diode controller' to implement two power feeds, together with status monitoring and then use a pair of smaller lithium packs to provide the control power (Or even a small lithium pack for normal op, failing over to a tap on the main battery, worst case you have to get back on the ground before the bottom of the main battery stack undervolts and lets the smoke out).It is simple, electrically quiet (Which a boost converter often is not, less then ideal in an avionics bay with the radios), and should not have any highly stressed components.There is actually something to be said for a simple small battery with undervoltage monitoring tripping an alarm input to the telemetry transmitter, minimum electronics to fail that way, and lithium voltage collapse is gentle enough to get you a few tens of seconds to get back on the ground if you set the alarm trip threshold suitably.Regards, Dan.

author: jtroutt19
author_rank: Newbie
timestamp: March 23, 2017, 06:30:06 am
content: I have telemetry to monitor my batteries all three of them on my large heli. And alarms and notifications at the flip of the switch should anything happen. Also have failsafes set up.