Charging Ultracapacitors - Page 1
Forum section: electronics / beginners

author: olsenn
author_rank: Frequent Contributor
timestamp: May 22, 2013, 03:07:21 pm
content: Can anybody tell me how to charge a Maxwell Boostcap 2.4V Ultracapacitor using a 30V/6A bench power supply? Do I just hook the +terminal of the PSU to the +terminal of the cap and -terminal to -terminal, then put out 2.4V at max current until current stops flowing?In case it matters I have heard that these things differ from regular rechargable batteries in that they appear as a short circuit at first and that they can be charges at the same rate as discharged.

author: mariush
author_rank: Super Contributor
timestamp: May 22, 2013, 03:29:38 pm
content: put the power supply on < 2.4v (2.35v should do) and if you want, put a resistor in series with the capacitor to limit current.Yes, capacitors charge fast and have very low internal resistance, when you connect it to power supply it will initially appear as short and will use up to 6A

author: ddavidebor
author_rank: Super Contributor
timestamp: May 22, 2013, 03:39:53 pm
content: IS better if you use a resistor in series and stay under the 2.4v

author: olsenn
author_rank: Frequent Contributor
timestamp: May 22, 2013, 03:54:41 pm
content: QuoteIn that case I can do a step better; I have a DC electronic load -- I can supply constant current until the voltage reaches 2.3V

author: Excavatoree
author_rank: Frequent Contributor
timestamp: May 22, 2013, 03:57:00 pm
content: If one had a power supply with a good current limiting function (ie any good lab supply), couldn't one set a safe current limit and charge the capacitor without a limiting resistor? (not that it's a great inconvenience to use one, I just want to know if there's some reason it won't work that I'm not considering.)I've charged "regular" capacitors like that.

author: Dave
author_rank: Super Contributor
timestamp: May 22, 2013, 04:38:36 pm
content: Forget the resistors, just set the voltage on your supply to just below 2,4V and set the current limit to the max. When you will connect the cap, it will go to constant current and draw those 6A until the capacitor charges up. When it's done charging, the current will drop to zero and the PS will go back to constant voltage.

author: ddavidebor
author_rank: Super Contributor
timestamp: May 22, 2013, 05:23:18 pm
content: Yeeeeeees but why stress the cap if you can do it gently?

author: Zapro
author_rank: Contributor
timestamp: May 22, 2013, 05:36:00 pm
content: Quote from: ddavidebor on May 22, 2013, 05:23:18 pmThis won't stress a Boostcap. They are made to be charge/discharged at hundreds of Amps!// Per.

author: Dave
author_rank: Super Contributor
timestamp: May 22, 2013, 05:52:01 pm
content: Quote from: ddavidebor on May 22, 2013, 05:23:18 pmThose Maxwell caps are capable of handling several hundred amperes. 6A wouldn't stress it at all.You could always set the current limit to a lower value.Also, if you kept your power supply in constant voltage mode, by limiting the current with a resistor, it would take way longer to charge. Completely unnecessary.

author: SeanB
author_rank: Super Contributor
timestamp: May 22, 2013, 06:08:50 pm
content: Not stressing the cap, rather the power supply as it may be a little unstable into such a big capacitive load.

author: ddavidebor
author_rank: Super Contributor
timestamp: May 22, 2013, 07:07:19 pm
content: Ooook, i love too much my sparky hv caps and i protect them like a childA very abused ones

author: Paul Price
author_rank: Super Contributor
timestamp: May 22, 2013, 07:33:13 pm
content: It all boils down to this, a supercap is simply a capacitor.Currents that are surge currents in excess of those rated will damage any cap.A constant current power supply is not a constant current power supply at the instant a load is connected.The constant current output filtering capacitors will deliver an unregulated surge to any connected, accepting circuit element, and this could damage some devices by this charge dump that always occurs before constant current operation commences.

author: RPBCACUEAIIBH
author_rank: Contributor
timestamp: May 23, 2013, 02:12:11 am
content: As I know, the cap won't be damaged by 6A, nor the power supply if it's well built, but if it isn't the PS can be damaged, so I advise charging with a resistor anyway... Much safer...

author: mikes
author_rank: Regular Contributor
timestamp: May 23, 2013, 02:35:47 am
content: Quote from: Paul Price on May 22, 2013, 07:33:13 pmDarn. I've gotta remember to put a resistor in series with all my bypass caps now.

author: codeboy2k
author_rank: Super Contributor
timestamp: May 23, 2013, 03:33:45 am
content: Quote from: mikes on May 23, 2013, 02:35:47 ambe safe.. put two

author: ejeffrey
author_rank: Super Contributor
timestamp: May 23, 2013, 03:47:27 am
content: Quote from: RPBCACUEAIIBH on May 23, 2013, 02:12:11 amA lab supply that can't survive shorting the inputs needs to go to the junk bin anyway. If you want to to limit the surge, just turn the voltage up from zero, but really it isn't necessary.

author: Psi
author_rank: Super Contributor
timestamp: May 23, 2013, 07:25:48 am
content: Here's the datasheet for them. If its at all useful to anyonehttps://docs.google.com/document/d/1wALtEyEAmNQTz7g-BcxNxe1f_27Eig2xj5hzyYOvY7k/edit?pli=1The max charge/discharge is 600ATo charge mine up i set the PSU to the voltage i want (2.5V multiplied by the number of cells in series, assuming all cells are at equal charge).The psu instantly goes into current limit at 3A, but that's fine. Eventually the caps reach the set voltage and the current falls to zero.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: May 24, 2013, 08:40:10 pm
content: Quote from: mikes on May 23, 2013, 02:35:47 amYou say that but for tantalums you're supposed to use a series resistor for surge protection. It's often not done though...

author: Stonent
author_rank: Super Contributor
timestamp: May 27, 2013, 06:15:33 am
content: In this video he had 6 2600F caps and at 5A it took him 21 minutes to charge.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: May 27, 2013, 10:23:20 am
content: But note that in the video he had the capacitors connected in parallel NOT in serieshttp://en.wikipedia.org/wiki/Capacitorafter you learn the specs of the cap for example lets say you have a 10 volt 1000 F cap.You can use this formulahttp://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.htmlor the calculator below to calculate the charging timeSo if you have this cap and a 10 amp power supplyyou get 10/1000=0.01 mV/s10/0.01 = 1000 seconds wich is equal to 16.6666.... minutes