Supercapacitor charging methods from 0 V.

[drummerdimitri]

So I have a supercapacitor bank that I like to play around with for tab welding to ups/inverter testing etc...

The problem I've been having is no power supply with a short protection will charge the bank up from 0 potential since the internal resistance of the capacitors is too low and would need to draw huge amount of current so they just shutdown.

The only way I can see this working is by using a CC power supply.

I've managed to charge them up decently with a Buck converter and a high power 24V DC power supply but the buck converter is limited in terms of power and needs around 5 minutes to fully charge.

I'd rather not use a car battery to charge them up since I have no control over the rate at which they are being charged at and don't want to harm the battery by doing so.

What would be the best way to charge them up quickly?

Would a 600W power supply meant for LED's work? They work in CC mode so I believe this can work...

[ogden]

Would a 600W power supply meant for LED's work? They work in CC mode so I believe this can work...

You mean something like PS-MW-600-12 ? They are for LEDs, but still constant voltage supplies, with some short protection. In short: it will not work. Short protection will just choke supply and it will not output any power. You really need purpose-built CC hi-power supply.

[edit] Don't confuse LED supply with LED driver.

[drummerdimitri]

I was thinking something like the Meanwell HLG-600H-15 LED driver.

Works with CC and CV modes not sure if it will read a short at 0V though...

[ogden]

I was thinking something like the Meanwell HLG-600H-15 LED driver.

Works with CC and CV modes not sure if it will read a short at 0V though...

Exactly. In case of short it can act different way. Unfortunately datasheet is not that specific. Could be so that short protection differs from CC mode at nominal output voltage. We can only guess here. BTW you can try to contact MW support and simply ask them.

[drummerdimitri]

I was thinking something like the Meanwell HLG-600H-15 LED driver.

Works with CC and CV modes not sure if it will read a short at 0V though...

Exactly. In case of short it can act different way. Unfortunately datasheet is not that specific. Could be so that short protection differs from CC mode at nominal output voltage. We can only guess here. BTW you can try to contact MW support and simply ask them.

So will it work? I can always try it before I buy it...

[The Soulman]

Most cc led psu's I've came across have a fold-back current limiting below a certain load voltage so probably wont work,
but if you have the ability to try it, why not..
Just out of curiosity, what size capacitor bank are we talking about and how fast do you want to charge it and to what voltage?

[drummerdimitri]

Most cc led psu's I've came across have a fold-back current limiting below a certain load voltage so probably wont work,
but if you have the ability to try it, why not..
Just out of curiosity, what size capacitor bank are we talking about and how fast do you want to charge it and to what voltage?

I am using 6 2.7V supercapacitors of 2000F each and would like to charge them to 12-15V.

The faster the rate of charging the better of course without harming the bank (pun intended).

[ogden]

I am using 6 2.7V supercapacitors of 2000F each and would like to charge them to 12-15V.

For series supercaps you definitely need application-specific (supercap) charger/supply. They must be balanced similar way as series li-ion batteries.

[jbb]

I've managed to charge them up decently with a Buck converter and a high power 24V DC power supply but the buck converter is limited in terms of power and needs around 5 minutes to fully charge.

...

What would be the best way to charge them up quickly?

I suggest a bigger buck converter. Or several in parallel. You might be able to come up with one that has input current limiting which will make maximum use of your 24V supply.

Also, Ogden is dead right about needing some balancing between caps.

By my calculations you have some 30kJ or more on hand. That’s a lot, so be careful! Eye protection is a must, because you don’t want hot chunks of metal in your eyes. Ear protection is probably advisable as well. And gloves to protect you from hot chunks of that-used-to-be-my-good-spanner.

Finally, remember to fit some discharge resistors so that this bank will eventually reach 0V on its own (rather than wait for weeks and surprise you).

[digsys]

For our huge EV capacitor banks, we have a permanent power resistor in series, for charge and discharge. Then a settable LV circuit that switches
contactors IN/OUT. Our Tyco Kilovac / Gigovac breakers are rated up to 1000A @ 1000V, and provide safety OFF as well. They have a huge range
of smaller sizes.

[texaspyro]

The Maxwell super cap modules that I have (58F/15V, BPAK0058 E015) have 6 caps in series.  They sell two versions... the low standby discharge ones use op-amps and interconnecting cables between modules to do balancing.  The standard ones just have resistors (270 ohm?) in parallel with each cap in the modules.  They came out of wind turbines and had 20 modules (300V) in series.  Check their app notes for balancing info.

[drummerdimitri]

I forgot to mention that my bank has active balancing circuits made by Maxwell.

I have a 12V 1500W power supply and if I can add some type of resistance in series I should be able to limit the current to the max rated power output of my power supply.

Problem is finding a resistance that will handle the load and not glow red hot and melt!

[drummerdimitri]

So I tried using my 500W 0.2 Ohm resistor bank and although it worked, the charging time is still quite slow since the current draw decreases rapidly as the charge of the capacitors goes up.

I am now convinced I need a CC power source that switches to a CV algorithm midway to get the fast charging I need.

[ahbushnell]

Why not CC all the way?

[ogden]

I am now convinced I need a CC power source that switches to a CV algorithm midway to get the fast charging I need.

You want to have supply which switches to CV *only* when nominal voltage reached - basically at the very end of the capacitor charging.

[station240]

So I tried using my 500W 0.2 Ohm resistor bank and although it worked, the charging time is still quite slow since the current draw decreases rapidly as the charge of the capacitors goes up.

I am now convinced I need a CC power source that switches to a CV algorithm midway to get the fast charging I need.

Have you tried using a contactor to bypass the charge 0.2ohm resistor once you reach a certain voltage.

[drummerdimitri]

So I tried using my 500W 0.2 Ohm resistor bank and although it worked, the charging time is still quite slow since the current draw decreases rapidly as the charge of the capacitors goes up.

I am now convinced I need a CC power source that switches to a CV algorithm midway to get the fast charging I need.

Have you tried using a contactor to bypass the charge 0.2ohm resistor once you reach a certain voltage.

No since I don't know how to make that work...

Ideally some kind of voltage regulated automatically variable high powered resistor would be perfect for this. It would start out at 0.2 Ohms of resistance and slowly decrease it's resistance in a way that more of the power supply's power can be dumped into the supercaps. Not sure if such a thing exists!

[Bendba]

Automotive light bulb in series? Relatively high resistance when high current goes through, resistance drops when it get close to charged. Just choose the wattage depending on your charging rate.

[ogden]

Ideally some kind of voltage regulated automatically variable high powered resistor would be perfect for this. It would start out at 0.2 Ohms of resistance and slowly decrease it's resistance in a way that more of the power supply's power can be dumped into the supercaps. Not sure if such a thing exists!

Simpler and much more effective solution is "generic" supercapacitor charger which is based on buck converter. Instead of inventing exotic chargers, better look at supercapacitor as high current battery with discharge voltage equal to 0V.

[drummerdimitri]

I found a 600 W power supply capable to delivering a constant 50A to the bank from 0V and starts dropping when the bank's voltage near 14V.

I am now capable of charging them in under 2 minutes!

Model is a Mean Well PSP-600-12.

[r0d3z1]

I found a 600 W power supply capable to delivering a constant 50A to the bank from 0V and starts dropping when the bank's voltage near 14V.

I am now capable of charging them in under 2 minutes!

Model is a Mean Well PSP-600-12.

thanks, this suggestion is really useful for me.
Could you confirm me that the feature "Constant current limiting" allow the SMPS to act like a CC-CV charger ? My doubt is how does the PS discern between a short-circuit and a discharge capacitor ? Are there some documentations about the short-circuit protection from meanwell ?

[digsys]

thanks, this suggestion is really useful for me.
Could you confirm me that the feature "Constant current limiting" allow the SMPS to act like a CC-CV charger ? My doubt is how does the PS discern between a short-circuit and a discharge capacitor ? Are there some documentations about the short-circuit protection from meanwell ?

I can add support that Meanwell as an excellent manufacturer, as I used to contract to a distributor and met one of the designers. BUT, that unit is not actually a constant current P/Supply ! and you can't use it as such !

105 ~ 135% rated output power
Protection type : Constant current limiting, recovers automatically after fault condition is removed

What it is saying is - the current goes above 105% and below 135%, it will limit the current and commence voltage reduction or foldback. Not sure what the V/I profile is "exactly" with that unit, but once you try to exceed 135% it will go into full shutdown ! If I can find my tech docs, I'll see if they have a "real" CC version.

[drummerdimitri]

I found a 600 W power supply capable to delivering a constant 50A to the bank from 0V and starts dropping when the bank's voltage near 14V.

I am now capable of charging them in under 2 minutes!

Model is a Mean Well PSP-600-12.

thanks, this suggestion is really useful for me.
Could you confirm me that the feature "Constant current limiting" allow the SMPS to act like a CC-CV charger ? My doubt is how does the PS discern between a short-circuit and a discharge capacitor ? Are there some documentations about the short-circuit protection from meanwell ?

There is no way you could short this unit out as by nature CC power supplies will not try to generate larger currents that what they're rated for. I tried to with a very large gauge wire and when I turned it on it would pass 60A of current through that wire at whatever voltage it comes out to be (Ohms law).

Hope this answers your question.

[Psi]

One dirty hack you can do to get past the problem of triggering short circuit protection is to put a light bulb in series with the load and also add a high amp relay across the light bulb to short it out.
Power the relay coil from the capacitor so that once the voltage gets high enough the relay automatically removes the bulb from being in series.

[Kjelt]

Check the posts of tatus1969.
For his tab welder he designed a pcb that converts some 12V server PSU's to a supercapacitor charger. He also sells them.