Charging 24v battery with 12v source. CV CC Boost converters in parallel - Page 1
Forum section: electronics / projects

author: StokesPen
author_rank: Newbie
timestamp: June 25, 2017, 02:21:15 pm
content: You can buy boost converters quite cheap capable of around 10 amps.Can I use several boost converters in parallel which crucially I must say are CC and CV, set the voltage to 28V and current limit to less than the rated value, say 7 amps on a 10 amp converter. Is there any problem with this? If they weren't constant current then clearly it wouldn't work as one would try and take all the load killing itself but regulated to 7 amps it can't. With 3 of these set at 7 amps I could charge at 250w without having to spend a lot more on a more powerful unit.In my mind I see no reason why not but having heard of words like back feed and timings etc that I don't understand I thought I'd ask.

author: Paul Price
author_rank: Super Contributor
timestamp: June 26, 2017, 11:39:18 am
content: How do you get "250W" with 28V and 7A ea. x 3 ?

author: tszaboo
author_rank: Super Contributor
timestamp: June 26, 2017, 11:45:31 am
content: Boost converters typically have a diode pointing to the output. But. Without knowing the exact type with schematic, we cannot tell you. Also, there is the usual: Things are working fine, until something happen (you disconnect something, something overheats after a while), and then everything is on fire suddenly.

author: MagicSmoker
author_rank: Super Contributor
timestamp: June 26, 2017, 12:18:53 pm
content: Quote from: StokesPen on June 25, 2017, 02:21:15 pmFixed that for you.Note that cheap Chinese boost converters might be capable of half their rated current, and that this rating probably (should, anyway) applies to theinputcurrent; it doesn't make much sense to give an output current rating for a boost converter since output current is always less than or equal to the input current.For example, to boost 12V to 28V and 10A the converter needs to draw at least 23.3A of input current (ignoring losses, which otherwise should not be ignored).However, any converter operating with a constant current control loop* can automatically be operated in parallel with other CC power supplies and the total current will be the sum of the individual converters, even if they have wildly different current ratings. It is the analogous situation to wiring multiple CV power supplies in series.* - or which uses some form of current mode control, regardless of whether the output voltage or current is ultimately regulated.

author: Fungus
author_rank: Super Contributor
timestamp: June 26, 2017, 12:33:25 pm
content: I can't think of any theoretical reason why not. In practice you never know what the failure modes of those boosters are.At the very least look up the chips on them and read the datasheets. Add some extra fuses, just in case.nb. I wouldn't run anything 'eBay' at maximum power for long periods. Always derate by 50%.

author: StokesPen
author_rank: Newbie
timestamp: June 26, 2017, 02:30:24 pm
content: Quote from: Paul Price on June 26, 2017, 11:39:18 amI think I've got the theory partly right here going with 250w, using the rating of max 10 amps, it would reach that on the input first due to the lower voltage, so 12V x 7amps x 3 converters = 252WBut I made the mistake of saying I'd set the current regulator to 7 amps which would be on the output, resulting in 588w but this would exceed the current rating on the input side. I'd need to set the output to 3amps at 28v to keep the input side within current limits.I haven't chosen any specific unit but hearing that there isn't a big red flag over the idea is good to hear so thanks. And yes i'll go with your suggestions of 50% rating of whatever they claim the units are capable of.