Rapid charging of a 400V 11000uF capacitor. - Page 1
Forum section: electronics / general

author: TheForgottenKing
author_rank: Newbie
timestamp: May 26, 2024, 05:15:51 pm
content: Hello everyone,I'm in need of some sort of charge circuit that takes a low-voltage high-current input (think something like a 6S 100C lithium battery, the kind that outputs ~25V at hundreds of amps) and uses this power input to charge a 400V 11000uF capacitor extremely quickly (i.e. under half a second). For safety I'd like to charge it to ~380 V or 800 J of energy.If my math is correct, a 4A constant-current charge that cuts off at 400 V will be enough to charge one of these in approximately half a second (1600 W into 800 J in half a second). I highly doubt there's an off-the-shelf component that can even remotely do this.For testing, I boughtthis DC-DC boost converter, but it never rises above 3A of current even though it should be able to do 20. Not sure why, either I'm doing something wrong or the listing is wrong.By the looks of it, I'm basically going to be building a DC-DC power supply, but I've never done anything like this. Is this even possible without spending thousands of dollars?For what it's worth, I'm not opposed to doing anything shady. Ideas include putting a bunch of low-voltage constant current sources in series, or using constant-current AC LED drivers with a rectifier.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: May 26, 2024, 11:47:03 pm
content: Maybe a bridge rectifier coming off mains.Use a variac if you want an adjustable final voltage.

author: TheForgottenKing
author_rank: Newbie
timestamp: May 27, 2024, 12:18:36 am
content: Quote from: HackedFridgeMagnet on May 26, 2024, 11:47:03 pmThis is meant to be portable off a DC source, but fear not, I've come up with a terrifying solution, namely reverse engineering one of the linked boost converters, simplifying the design, and then either correctly recreating one to put out 400V or just putting four of them in series.

author: ArdWar
author_rank: Frequent Contributor
timestamp: May 27, 2024, 12:51:20 am
content: Quote from: TheForgottenKing on May 26, 2024, 05:15:51 pmWith boost converter the rating and the limiting factor is usually for input current. Make sense that a "30A" device doing 25V->100V to output 3A, allowing for 50% derating for what's look like something more like aliexpress specialty crap. Just go get bigger one.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 27, 2024, 02:58:00 am
content: Take the DC/DC stage from an inverter or UPS and mod it to work in current limit mode. Would take quite a bit of electronics knowledge.What's the application? I'm thinking a really powerful photography flash or pulsed laser, except such a large flash tube would need quite a bit more than 400V.

author: jonpaul
author_rank: Super Contributor
timestamp: May 27, 2024, 07:42:18 am
content: OP beware of extreme safety risk.At 400VDC even 1 j or 1 uF can be shocking.The thought of a 400V 11miliFD is frightningJon

author: Someone
author_rank: Super Contributor
timestamp: May 27, 2024, 07:47:01 am
content: Quote from: jonpaul on May 27, 2024, 07:42:18 amSafety standards put 400V 100nF as still dangerous to life!

author: Wolfgang
author_rank: Super Contributor
timestamp: May 27, 2024, 03:06:53 pm
content: 400V/11mF is a preferred method of seriously shortening your finger if you are silly enough to touch it

author: jonpaul
author_rank: Super Contributor
timestamp: May 27, 2024, 04:05:39 pm
content: Please can the OP to state their level of experience and actual project end goal?In 1970s..1990s, we worked with flash , radar pulsers and exploding wire HV stored energy.if you crowbar a large cap can blow the tip off a large screwdriver if you crowbar a large cap.Shock caused muscle contraction leads to jump/falls and secondary damage.Besides shock and burns, those who have pacemakers are especially susceptible.Use the rules of Nikola Tesla (NOT THE CAR!!) Keep one hand in the pocket, wear thick solde rubber shoes.Add a bleeder reisistor across any HV cap or alrge lytic > 200VJon

author: jbb
author_rank: Super Contributor
timestamp: May 28, 2024, 07:41:21 am
content: At these energy levels, I also recommend safety glasses for flying debris and ear protection. Any shorts etc. will be quite violent.Also, the thought occurs that normal-rating electrolytic capacitors may not perform well (ie die early and violently) if used for pulse discharge operation.In terms of topology…- What’s your minimum expected voltage on the cap bank after firing?- I would recommend an isolated topology if possible so you don’t accidentally energise the battery pack to 400V- I suggest you have a look athttps://magna-power.com/learn/white-paper/current-fed-power-processingfor a nice rugged topology (see Figure 3)