"Hybrid" Large Automotive Capacitors - Page 1
Forum section: electronics / projects

author: Mike Warren
author_rank: Unknown
timestamp: April 27, 2015, 10:23:05 pm
content: Does anyone have any idea what the technology behind these capacitors might be?http://www.stingerelectronics.com/productDetails.aspx?ProductId=534The 5 Farad capacitor is smaller than many 1 Farad caps, so I'm guessing this has something to do with the hybrid name.They claim an ESR of 1.5mOhms.

author: Mike Warren
author_rank: Unknown
timestamp: May 04, 2015, 01:27:15 am
content: If anyone's interested, I've just taken a 10F version apart. It's a standard 1F capacitor, paralleled with a three 50F/2.7V and three 60F/2.7V capacitors in series.That explains why the ESR is identical to their 1F capacitors.So, technically, it is 10F, but 9F of that is not going to help supply extra current to audio amplifiers.

author: ivan747
author_rank: Super Contributor
timestamp: May 04, 2015, 02:15:12 am
content: So, in terms of ESR it's a bunch of capacitors in series plus 1F in parallel, so they are useless as decoupling caps, or at least as useful as a 1F cap. I would prefer to get real caps and make my own decisions as to how much capacitance I should use for decoupling and how much for brownouts and slower power dips.

author: Mike Warren
author_rank: Unknown
timestamp: May 04, 2015, 02:27:59 am
content: Absolutely! Just to be clear, I would never buy something like this in a million years. A customer wanted one and I was asked by the sales staff to explain the magic. I suggested it was probably being faked in some way, and when it arrived I was able to supply the requested explanation. "No magic here."But the customer is always right.In this particular case I expect the 1F will solve the customer's light dimming problem.

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2015, 07:32:48 pm
content: These audio capacitors are audiophoolery really.If your amplifier is drawing that much current the headlights dim, then the cable is too thin or the battery is dead.

author: free_electron
author_rank: Super Contributor
timestamp: May 04, 2015, 07:51:54 pm
content: Quote from: Hero999 on May 04, 2015, 07:32:48 pmJust get a Tesla. 85 KWh battery capable of sourcing 2500 ampere at 408 volts. that woudl be a kickass audio system ...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2015, 07:56:29 pm
content: Now now, that's unfair. Modern supercaps have fairly low ESR (okay, maybe not the ones pictured!). If that's less than the car battery, you have a win.What's more, if it's better than the battery under cold conditions, you have further wins. I don't recall offhand what the ESR tempco of supercaps is...Tim

author: German_EE
author_rank: Super Contributor
timestamp: May 04, 2015, 08:19:34 pm
content: If the audio power amplifier is in the rear of the car and the battery is in the front then I can understand the need for a big capacitor, especially if the amplifier stack is on the large side. At a car show once I saw a car with 10Kw of amplification, this is a 725A load @ 13,8V.

author: Mike Warren
author_rank: Unknown
timestamp: May 04, 2015, 08:39:49 pm
content: The amount of current some of these amplifiers draw on peaks is enormous. The capacitors do help in some installations, although I've only ever seen 1F ones used.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2015, 08:51:06 pm
content: If the amplifiers are in the rear, the cable might be a good 10uH in series, which will support a peak 1.2A/us slew rate; that's a good ms of dropout for a 1kA surge. But the amplifiers surely have at least enough electrolytic capacitance inside them already, so this isn't very useful. (A 1ms surge at 1kA needs a total of 0.4F for 2.4V (20%) dropout at 12V, which might break down as 40mF per 1kW amplifier * 10 amplifiers.)Another point of view might be the cutoff frequency of the cable; perhaps unusually small cables are typically used, because the load is peaky and chassis wiring rules apply (or the users just don't care..)? However, higher line resistance decreases the L/R time constant, so this wouldn't seem to be it.DC drop alone is the worst case for overly thin cables, which would seem to suggest needing less than 2.4mohm (20% dropout at 12V, 1kA surge for >> 1ms), which for a modest 3 meter run requires only #4 AWG (5mm). Note that's 2.4kW dissipated by the cable, so it would get hot quite quickly under such loads, and the duty cycle will have to be kept low. If the cable is any thinner, peak loads will have to be made up by capacitance, requiring < 2.4 mohm total ESR, and capacitance proportional to the surge duration (a 100ms burst would need 40F!).Accordingly, the "1F" caps will only be good for ~2ms surges, which will take the edge off, and certainly compensate for line inductance, but won't do much for overall system capacity. To do that, you'd need a small stack of Boostcaps or something.Ed:http://www.digikey.com/product-detail/en/BMOD0500%20P016%20B01/1182-1028-ND/3079292for reference. Note the excess capacity (10 times more than required), and the modest ESR (about as high as can be tolerated in the above scenario). Don't mind the price...Tim

author: amyk
author_rank: Super Contributor
timestamp: May 05, 2015, 01:29:23 am
content: Is that 1F really 1F?This is also the first time I've heard of RECOOL branded capacitors... as I suspected, it's Chinese:http://product.pcauto.com.cn/product/20814.html

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 05, 2015, 02:39:58 am
content: Wouldn't it make more sense to bolt a 240V generator to the engine and route a relatively thin cable to the back?

author: Zero999
author_rank: Super Contributor
timestamp: May 05, 2015, 12:16:28 pm
content: Quote from: T3sl4co1l on May 04, 2015, 07:56:29 pmHow do those amplifiers drive the speakers with such insane amounts of power?There needs to be a boost converter, otherwise at 12V, the maximum power one can ever hope for with a 4 Ohm load is a pathetic 18W.A properly designed boost converter should have sufficient decoupling on both the primary and secondary sides, otherwise it will be unstable.

author: Psi
author_rank: Super Contributor
timestamp: May 05, 2015, 12:31:32 pm
content: Quote from: T3sl4co1l on May 04, 2015, 07:56:29 pmGood supercaps are much less than a car battery, by an order of magnitudeMy starter motor sounds like it's on anabolic steroids every time i start the car. Its awesome.(I'm using supercaps instead of a battery)Normal car battery is ~10mR and supercaps are ~0.3mRSo under 200A cranking current Vdrop is 2V on a car battery or 0.06V on supercap. The extra 1.94V getting to the starter makes a noticeable difference

author: DanielS
author_rank: Frequent Contributor
timestamp: May 05, 2015, 01:06:12 pm
content: Quote from: NiHaoMike on May 05, 2015, 02:39:58 amIn most cases of such monstrous sound systems, they do exactly that - add an extra alternator to run the sound system. The car/truck's stock alternator is only good for 100A or so to run the vehicle and its normal accessories, nowhere near enough to run a 10kW sound system. But most of these car audio amplifiers are only designed for 12-15V input, maybe 30V if using amplifiers intended for cars running on a 24V system, so feeding them 100+V is not an option.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 05, 2015, 07:05:41 pm
content: All power amplifiers have a DC-DC converter inside them, usually MOSFETs driving a toroid transformer in push-pull.They're usually "controlled" with a TL494 in open loop mode. No regulation, no filter chokes, no current limiting. The only reason they don't explode outright is because of the "soft start" function (which is also open loop).Presumably, the really big ones are upscale and have some thought put into them, but I don't know how much. Needless to say, you can very easily have it happen that a shorted speaker destroys the output stage, which in turn destroys the power supply; in short, by the time the input fuse finally opens, you have to replace your entire system, because a whole lot of magic smoke just farted away due to bad (cheap) design.Tim

author: Zero999
author_rank: Super Contributor
timestamp: May 05, 2015, 07:10:42 pm
content: Quote from: DanielS on May 05, 2015, 01:06:12 pmIf you're going to add a 240V alternator then you might as well use an amplifier designed for operation off the mains.

author: Fungus
author_rank: Super Contributor
timestamp: May 06, 2015, 10:30:29 am
content: Isn't it dangerous to charge low-voltage capacitors in series?

author: ivan747
author_rank: Super Contributor
timestamp: May 06, 2015, 03:20:28 pm
content: Quote from: Fungus on May 06, 2015, 10:30:29 amYou would need something that could balance the charge so that the voltage is distributed evenly, even if the leakage current is different for each capacitor.

author: DanielS
author_rank: Frequent Contributor
timestamp: May 06, 2015, 11:32:46 pm
content: Quote from: Hero999 on May 05, 2015, 07:10:42 pmThat only works if your vehicle engine runs at constant RPM and you choose the alternator accordingly or if your amplifiers have switching power supplies with inputs that do not mind operating anywhere from 40Hz to 300Hz with whatever transients from RPM or load changes combined with alternator regulator lag.