battery chargers, again
in [Design]
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From: Spehro Pefhany on 30 Sep 2009 20:38 On Tue, 29 Sep 2009 15:18:12 -0700, the renowned Rich Grise <richgrise(a)example.net> wrote: >On Tue, 29 Sep 2009 10:24:57 -0700, John Larkin wrote: >> >> 1.2 amps from a Lascar bench supply, overnight, is hardly >> overcharging. Contrary to stated theory, the car works fine now. >> >> I guess several of the posters here, if they left their lights on and >> killed their battery, will always have their car towed and the battery >> replaced. They have no need for jumper cables, and are happy buying >> chargers that only charge batteries that don't need to be charged. >> >Ouch! John, I've never heard you scathe before, but geez! This post >singed my eyebrows! > >Keep it up. >:-> It helps dispel that "leprechaun" image. ;-D > >Cheers! >Rich Something like this http://www.speff.com/jl.jpg ? Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: John Larkin on 30 Sep 2009 22:17 On Wed, 30 Sep 2009 14:40:06 -0700, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Wed, 30 Sep 2009 16:04:00 -0500, Vladimir Vassilevsky >> <nospam(a)nowhere.com> wrote: >> >>> >>> John Larkin wrote: >>> >>> >>>> I'm working on a smallish board that has four switchers in one corner >>>> and an ADC that's looking for a 1 nV spectral line in the other, >>> The 1nV over the background of how many nV/root(Hz) ? >> >> About 1. That's our target noise floor. The existing system is >> ballpark 100 nv/rtHz with huge birdies all over the place. >> >> Never let scientists design electronics. >> >>>> range >>>> of interest straddling all the switcher frequencies. >>> Synchronize the switchers away from the particular frequency of interest? >> >> The signals can be all over the place. >> >>>> I'm planning on >>>> spread-spectrum wobulating all the switchers, just in case. >>> So the dirt will be in band for sure? >> >> Yup. Operating range is audio to many MHz, all at once. We digitize at >> 64 Ms/s and FFT and see what's there. >> > >How many MHz is "many"? And how much power does the biggest of the >switchers have to deliver? 20-ish. And just a couple of watts. I need 5, 3.3, 2.5, 1.8, 1.2, and -5. All from +12. John
From: John Larkin on 30 Sep 2009 22:20 On Wed, 30 Sep 2009 14:23:38 -0700, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Wed, 30 Sep 2009 13:01:31 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> Jan Panteltje wrote: >>>> On a sunny day (Wed, 30 Sep 2009 11:17:34 -0700) it happened Joerg >>>> <invalid(a)invalid.invalid> wrote in <7ihlm2F3179urU2(a)mid.individual.net>: >>>> >>>>>> Are you referring to the loop filter? >>>>>> There is no loop filter. >>>>>> >>>>> No, to the output filter. You can't possibly let the ripple just saunter >>>>> out the banana jacks of a bench supply and pollute whatever it find >>>>> downstream. >>>> All depends, 10mV is fine with me:-) >>>> >>>> You really got to come up with some numbers, else it all makes no sense, >>>> >>> Ok, this is the number I typically need: Not being able to show the >>> ripple on a scope when set to 2mV/div. Good enough? >>> >>> Seriously, 10mV piping out would be disastrous when doing things like >>> ultrasound experiments. >> >> I'm working on a smallish board that has four switchers in one corner >> and an ADC that's looking for a 1 nV spectral line in the other, range >> of interest straddling all the switcher frequencies. I'm planning on >> spread-spectrum wobulating all the switchers, just in case. >> > >Spread spectrum just smears the noise so it looks lower (and is to some >extent but not a lot). Like throwing excess junk under the sofa and >pretending it ain't there no more. It will take a big spectral spike and make it into wide and low hump. If the psd gets below my 1 nv/rtHz noise floor, it's as good as gone. > >Since you wrote spectral line, how about rotating the switchers through >three different frequencies and have the ADC always look in the quiet bands? No, we've got to digitize in one burst and see what's there. The next shot may be different chemicals, and we need all the data. John
From: Jim Thompson on 1 Oct 2009 00:27 On Tue, 29 Sep 2009 15:10:06 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 29 Sep 2009 13:29:09 -0700, Joerg <invalid(a)invalid.invalid> >wrote: > >>John Larkin wrote: >>> On Mon, 28 Sep 2009 19:28:39 -0500, krw <krw(a)att.bizzzzzzzzzzz> wrote: >>> >>>> On Mon, 28 Sep 2009 09:06:34 -0700, John Larkin >>>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>>> On Mon, 28 Sep 2009 09:04:17 -0500, Tim Wescott <tim(a)seemywebsite.com> >>>>> wrote: >>>>> >>>>>> On Sun, 27 Sep 2009 21:16:46 -0700, John Larkin wrote: >>>>>> >>>>>>> Last time a car went dead in the garage, my wife's Fit, I hacked up a >>>>>>> charger from an old DSL wall-wart and a sabre saw as a series current >>>>>>> limiter. The garage geometry makes it essentially impossible for us to >>>>>>> push a car uphill to the street to jump it. Now The Brat left her Echo >>>>>>> in the garege for a month or so and it went dead, too. So I figure it's >>>>>>> time to buy a real charger. Went to Kragen Auto Parts and bought two >>>>>>> (one for here, one for Truckee) chargers. They are all "smart chargers", >>>>>>> namely switchers with electronics, these days. >>>>>>> >>>>>>> The battery is really dead, 1.8 volts. The first charger hums and >>>>>>> outputs nothing. Tried the next one: it hummed for maybe 3 seconds then >>>>>>> sparked and smoked inside. >>>>>>> >>>>>>> Went back to Kragen and traded up, two better chargers. Neither >>>>>>> charges... no current, battery steady at 1.8 volts. Both have their >>>>>>> "charging" LEDs off and "charge complete" LEDs lit. >>>>>>> >>>>>>> Back to Kragen, 3rd time, got all my money back. Passed by Bob Pease's >>>>>>> place all three trips, same collection of rusty VWs everywhere. >>>>>>> >>>>>>> A charger that puts zero amps into a dead battery does that by design, >>>>>>> and there's only one reason to do that: to convince people they need a >>>>>>> new battery. Kragen's sales pitch was exactly along those lines; "Tt >>>>>>> won't charge, so all the cells are shorted." >>>>>>> >>>>>>> So I went to work and nabbed a cute little Lascar bench power supply. It >>>>>>> current limits at 1.2 amps, so I just cranked it up. The battery went >>>>>>> instantly to 16.5 volts, then settled down to 12 or so in a few minutes, >>>>>>> and is creeping back up. >>>>>>> >>>>>>> Interesting. >>>>>>> >>>>>>> So I guess I'll buy a couple of 3 amp or so lab supplies, with nice volt >>>>>>> and amp meters, instead of battery chargers. They're handier to have >>>>>>> around anyhow, cost about the same as a "good" charger, and aren't booby >>>>>>> trapped. >>>>>>> >>>>>>> What Kragen is doing is fraud. >>>>>>> >>>>>>> John >>>>>> I've never had a battery come back from being that dead, and I've had >>>>>> numerous chances to try it (I'm stubborn that way). You'll be lucky to >>>>>> see 12V out of it with the charger disconnected, and I doubt that you'll >>>>>> see that after the first time you touch the key. If you _do_ get the car >>>>>> started it'll just be an opportunity for you daughter to get stranded >>>>>> some place. >>>>> It started OK after about 6 hours at 1.2 amps, started vigorously >>>>> after charging all night. My wife's car was zero-volts dead a couple >>>>> months ago, got rebooted from the DSL wall-wart, and it's fine. >>>>> Lead-acids will sulphate and lose capacity if they sit dead for a long >>>>> time. >>>>> >>>>>> One new battery is cheaper than one tow truck ride. Do the math. >>>>> Our insurance covers the truck ride. >>>> It's the brat's vehicle, IIRC. I wouldn't beg *any* trouble for a >>>> woman's vehicle. ...for more reasons that I can count. The brat's, >>>> never. >>> >>> She left the Echo - her high school car - in our garage because all >>> she wants to drive now is her Jeep Rubicon. Gotta get her to sell the >>> Echo so we can have our garage back. >>> >> >>Why is everyone spoiling their kids so much? Same with the daughters of >>a business friend, they got cars courtesy of daddy. Plus tuition, room >>and board at rather ritzy colleges. I had to work for my first car. Dad >>wanted to chip in to get me a somewhat decent looking used car upon >>nailing my masters but I said I should really try to pay my own way. And >>did. Couldn't possibly show up for interviews in my old Citroen but the >>TUEV had just blown it out of the water anyhow, declared it >>unroadworthy. You could see the road surface fly by when looking down. >> >> >>> http://www.rubicon-trail.com/ >>> >>> But if her car battery did go dead, she wouldn't have any trouble >>> getting a jump start. >>> >> >>Like Keith, I'd be concerned about what happens afterwards ... > > >Please select one of the following options: > > _ >/ / Drive kid to/from school, to/from softball practice, to/from > friends houses, to/from weekend activities, to/from mall > >or > > _ >/ / Buy kid a cheap Toyota. > > >John > Make it a Nissan and you've got it right ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Coming soon to the elementary school in your neighborhood... I pledge allegiance to Dear Leader Barack Hussein Obama and to the community organization for which he stands: one nation under ACORN, unchallengeable, with wealth redistribution and climate change for all.
From: Jan Panteltje on 1 Oct 2009 08:42
On a sunny day (Wed, 30 Sep 2009 15:40:50 -0700) it happened Joerg <invalid(a)invalid.invalid> wrote in <7ii53oF31ev0lU1(a)mid.individual.net>: >> You are weaseling away from the subject of 10 mV ripple on supply lines. > > >No. I said 10mV ripple on supply lines do matter in ultrasound, it's way >too much when you must listen to the wee rumbles in the aortoa of an >incredibly obese person. I've got well over 20 years in that business. > >Anyhow, if I bought a lab bench the supply that had 10mV ripple on the >output it would go back same day. This is not to diss you PIC solution, >that can very well have its place and certainly for experiments with >digital stuff. Just not with what I usually do. FYI, one of my recent >switchers (30W) has 600uV of ripple under full load. Indeed. It matters *how* you use the lab supply. Normally chips, preamps, things that need ultra low ripple have the filtering right next to it, RC for example, and you are not going to connect you bench power supply directly to those, but to the normal power input of the board. As far as radiation from the supply leads goes, well apart from the usual ferrites and small value caps to ground, I am sure there are many applications like yours that could pick it up, especially when you open the box when you are measuring something. So that would require some extra filtering in the power supply. When we talk *industrial*, you see supplies specified at any ripple value, from 5 % to some milli volts. There are zillions of different models. Often you see 24V, if it is for relays then the ripple value is insignificant. In an industrial environment there usually are very high electrical noise levels, from relays, motors, machines, what not. So it all depends what it is for, and how you use it. Some very advanced companies with top of the line ultra high speed products, their executives use the power supplies to charge their car battery. In such a case the ripple is not very important either. I dreamt up a simple circuit to add to the PIC switcher to make it a true current mode controller. It only uses 2 transistors and 3 resistors, so ultra cheap :-) +12V U out | | [ ] R0 [ ] R1 | | ------------- | | | | e e | +5V ref -- b b-------------------------| c c | | | | | [ ] R4 | | | | | | to current | | [ ]<---> comparator [ ] R2 | | | /// /// /// The way this works is that it lowers the voltage of the current limiter setpoint when the output voltage rises above it's setpoint. With 0V on the pot the current limit is at it's lowest value. The output voltage will be regulated at 5 x R2 / (R1 + R2), or you need 5V over R2 for equilibrium. R0 can be a current source too of course, or you could use an opamp. You can make it as sophisticated as you want. Have not tried this yet, maybe in a next one :-) It also frees up one more PIC pin, that input can then be used for other goodies. So, when are we going to see some circuits or code from you Joerg? |