Multi-pack battery voltage monitor
in [Design]
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From: Jan Panteltje on 24 Jul 2010 07:22 On a sunny day (Fri, 23 Jul 2010 21:16:40 -0400) it happened "Gary Lynch" <gary.lynch(a)ieee.org> wrote in <OJSdnSQxtueeotfRnZ2dnUVZ_judnZ2d(a)posted.localnet>: >8. I don't mind using opto-couplers, but 72 of them will > add up fast. > >9. PIC does make a uP with built-in A/D converter and UART > for under $1. Isolation is still unresolved. We > definitely cannot afford 72 isolated power supplies. One can use a small 1 transistor RF generator, and 72 secondary 2 turn windings or maybe even extremely small ferrite toroids with each a diode and capacitor as rectifier to make say 3.3V for each PICs. You could use optos to send the data back, or perhaps simply have each PIC, as you only need an 'alert', do a PWM output on same ringcore at a different frequency and detect that elsewhere, Or just have each PIC load the supply by switching in a low value resistor, you can then detect the amplitude variation at the oscillator that feeds them, like this: impedance matching ________________________________________________________________________________ | | osc - core0 ---wire -- core1--- core2 --- core3 --- core4 - - core72 -- detector core-- | | | | rect1 rect2 rect3 filter ----| ----| | | PIC1 | PIC2 detector | | | | | | R1 | R2 comparator |____| |____| | alarm In the same way you can send the data back if you do not like optos. I mean each PIC has an output that in case of alarm loads the supply with a specific low frequency by switching in a low value resistor (R1, R2, ... ). The current variation is seen in the chain, and that frequency filtered out and detected, and triggers the alarm. You could even have a different pattern for each PIC. Usenet patent All Rights Reserved. Copyright Jan Panteltje 2010-always, hereby donated into the public domain.
From: krw on 24 Jul 2010 11:29 On Sat, 24 Jul 2010 16:16:48 +1000, Grant <omg(a)grrr.id.au> wrote: >On Fri, 23 Jul 2010 17:37:14 -0500, "krw(a)att.bizzzzzzzzzzzz" <krw(a)att.bizzzzzzzzzzzz> wrote: > >>On Sat, 24 Jul 2010 07:25:21 +1000, Grant <omg(a)grrr.id.au> wrote: >> >>>On Fri, 23 Jul 2010 06:38:49 -0700 (PDT), whit3rd <whit3rd(a)gmail.com> wrote: >>> >>>>On Jul 22, 7:20 pm, Grant <o...(a)grrr.id.au> wrote: >>>>> On Thu, 22 Jul 2010 19:01:00 -0400, "tm" <no...(a)msc.com> wrote: >>>> >>>>> >...At least a 0.1 volt accuracy. That is non-trivial >>>>> >at 1000 volts above ground. >>>> >>>>> Non trivial? Easily enough done with opto couplers, there's 10kV and >>>>> up ones >>>> >>>>Opto couplers need circa 3V and 4 mA to drive 'em on and off. >>>>Is there a plan to make isolated power supplies for each of >>>>the seventy-two cells? Using opto couplers is not a real >>>>solution until you provide the support circuitry. You'd >>>>also want an ADC at each node, and put the digital output onto >>>>the optocoupler's drive amplifier. >>> >>>I see lots of power available there. Besides you can command the >>>things to be off most of the time, battery voltage is a fast moving >>>target ;) Two optos plus a small PIC per cell. Cheap, easy, not >>>much support components needed. >> >>Why two isolators? > >For low power option, described upthread. Sorry, don't see it and don't remember it. Got a pointer?
From: JosephKK on 25 Jul 2010 00:14 On Fri, 23 Jul 2010 21:16:40 -0400, "Gary Lynch" <gary.lynch(a)ieee.org> wrote: >In article <mlmd469g97a9dc08udedrjurvbviveb061(a)4ax.com>, peter2(a)hipson.net >says... >>On Wed, 21 Jul 2010 07:15:53 -0400, Gary Lynch <bookworm(a)execpc.com> >>wrote: >> >>> +------+ I am looking for an economical way to measure >> >Wow! What a turnout!! > >I apologize for my apparent disappearance. I had to change >new readers before I could reply back. This also caused me >to lose all posts between 8:00 am and 3:00 pm on July 22; so >you wrote something in that window, I fear I can't see it. > >I don't have the answer to every question, but I'll give it >my best shot. > >1. I used the word 'pack' to refer to a 6-cell, lead-acid > battery--the same type as you use to start your car. > Open-circuit voltage about 12.6 V. > > If there's an unambiguous industry term for that, I > wouldn't mind hearing it. > > A string of 72 would add up to 907 V. I have worked > with busses close to 700 V, but this may be a record, > especially if it triggers some kind of UL rule. The trip point is 600 V nominal, from 29USC1910 Subpart S. > >2. By 'offset' I presume you (PeterD) mean some kind of > voltage regulator? Cost is a factor and I should > explain the scenario. > > The appliance is a UPS. The batteries must be tested at > regular intervals. The UL spec calls for measuring the > voltage of the entire stack and warning the user when > the average voltage per cell drops below a certain > threshold. But real-world batteries don't deteriorate > uniformly and we would like to measure them individually > and sound an alarm when a single battery can not pull > its own weight. > > This happens while the unit is driving its full rated > load on the battery, so the voltage will be dropping as > we go. The shortest test lasts 30 seconds, and fitting > 72 tests into 10% of this window gives us 42 > msec/conversion (assuming they are executed > sequentially). If that proves a burden, I can also make > the test longer. I don't want it to take so long that > the last battery looks bad only because it was measured > way down the discharge curve. It may be a bit challenging to operate relays that fast. Relays with that much withstand / isolation are not known for being fast. Look for solutions running multiple converters and mux the data streams as well. > >3. I don't have a spec for accuracy, but let's say we sound > an alarm when a battery drops to 10 V. If I put 10 bit > steps between 12 & 10; that's 0.2 V. That's crude but a > starting point. I just realized I will have to account > for the accuracy of my voltage regulator if it's in > series with the A/D. Getting complicated. > > I would have to look at the curves for zener diodes. > That's obviously cheaper than a regulator, but I lose > more accuracy. And you get clobbered on temperature stability, micro and isolator per 12 V pack sounds better and better. > >4. My boss wants to use a bank of resistive dividers > enabled one at a time by relays into a single A/D, > referenced to ground (similar to a recommendation > posted here). I don't like this as the top battery > will be subject to a large common-mode voltage, > making that measurement much less accurate than the > bottom battery's. See comments for 2 and 3. > >5. I don't have to control the current or voltage of the > batteries, just want to monitor their health. OK > >6. Whatever solution I implement will be under the control > of a microprocessor. Must execute without human > intervention. OK > >7. I believe I can draw milliamps out of the batteries > during the test. The challenge is the quiescent > current, as many a customer will take delivery and stash > it in a warehouse for 6 months before trying to install > it, and the test circuit may not load it down while in > storage. Lead-acid batteries are quite notorious for high self discharge. > >8. I don't mind using opto-couplers, but 72 of them will > add up fast. Not nearly as fast as 1 kV relays. > >9. PIC does make a uP with built-in A/D converter and UART > for under $1. Isolation is still unresolved. We > definitely cannot afford 72 isolated power supplies. I would leach off the 12 V packs individually, it will be easy to get the standby current below 0.1 of self discharge. Even active current will be as much for the optos as the uC. > >Hope that gives you a better picture. >============================================================ >Gary Lynch To send mail, change no$pam >gary.lynch(a)no$pam.com in my domain name to ieee. >============================================================
From: JosephKK on 25 Jul 2010 15:08 On Sat, 24 Jul 2010 11:22:21 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Fri, 23 Jul 2010 21:16:40 -0400) it happened "Gary Lynch" ><gary.lynch(a)ieee.org> wrote in ><OJSdnSQxtueeotfRnZ2dnUVZ_judnZ2d(a)posted.localnet>: > >>8. I don't mind using opto-couplers, but 72 of them will >> add up fast. >> >>9. PIC does make a uP with built-in A/D converter and UART >> for under $1. Isolation is still unresolved. We >> definitely cannot afford 72 isolated power supplies. > >One can use a small 1 transistor RF generator, and 72 secondary 2 turn windings >or maybe even extremely small ferrite toroids with each a diode and capacitor as rectifier >to make say 3.3V for each PICs. >You could use optos to send the data back, or perhaps simply have each PIC, >as you only need an 'alert', do a PWM output on same ringcore at a different frequency and detect that elsewhere, > >Or just have each PIC load the supply by switching in a low value resistor, >you can then detect the amplitude variation at the oscillator that feeds them, like this: > > impedance matching > ________________________________________________________________________________ > | | > osc - core0 ---wire -- core1--- core2 --- core3 --- core4 - - core72 -- detector core-- > | | | | > rect1 rect2 rect3 filter > ----| ----| | > | PIC1 | PIC2 detector > | | | | | > | R1 | R2 comparator > |____| |____| | > alarm >In the same way you can send the data back if you do not like optos. >I mean each PIC has an output that in case of alarm loads the supply with a specific low frequency by >switching in a low value resistor (R1, R2, ... ). >The current variation is seen in the chain, and that frequency filtered out and detected, and triggers the alarm. >You could even have a different pattern for each PIC. > >Usenet patent All Rights Reserved. >Copyright Jan Panteltje 2010-always, hereby donated into the public domain. That is a slick idea. Add a blinking led to each PIC and pwm the led to get the modulating signal. Isolation, general alarm, and specific battery identification all with the same parts.
From: ehsjr on 25 Jul 2010 23:11
Gary Lynch wrote: > In article <mlmd469g97a9dc08udedrjurvbviveb061(a)4ax.com>, > peter2(a)hipson.net says... > >> On Wed, 21 Jul 2010 07:15:53 -0400, Gary Lynch <bookworm(a)execpc.com> >> wrote: >> >>> +------+ I am looking for an economical way to measure >> >> > Wow! What a turnout!! > > I apologize for my apparent disappearance. I had to change > new readers before I could reply back. This also caused me > to lose all posts between 8:00 am and 3:00 pm on July 22; so > you wrote something in that window, I fear I can't see it. > > I don't have the answer to every question, but I'll give it > my best shot. > > 1. I used the word 'pack' to refer to a 6-cell, lead-acid > battery--the same type as you use to start your car. > Open-circuit voltage about 12.6 V. > > If there's an unambiguous industry term for that, I > wouldn't mind hearing it. > > A string of 72 would add up to 907 V. I have worked > with busses close to 700 V, but this may be a record, > especially if it triggers some kind of UL rule. > > 2. By 'offset' I presume you (PeterD) mean some kind of > voltage regulator? Cost is a factor and I should > explain the scenario. > > The appliance is a UPS. The batteries must be tested at > regular intervals. The UL spec calls for measuring the > voltage of the entire stack and warning the user when > the average voltage per cell drops below a certain > threshold. But real-world batteries don't deteriorate > uniformly and we would like to measure them individually > and sound an alarm when a single battery can not pull > its own weight. > > This happens while the unit is driving its full rated > load on the battery, so the voltage will be dropping as > we go. The shortest test lasts 30 seconds, and fitting > 72 tests into 10% of this window gives us 42 > msec/conversion (assuming they are executed > sequentially). If that proves a burden, I can also make > the test longer. I don't want it to take so long that > the last battery looks bad only because it was measured > way down the discharge curve. > > 3. I don't have a spec for accuracy, but let's say we sound > an alarm when a battery drops to 10 V. If I put 10 bit > steps between 12 & 10; that's 0.2 V. That's crude but a > starting point. I just realized I will have to account > for the accuracy of my voltage regulator if it's in > series with the A/D. Getting complicated. > > I would have to look at the curves for zener diodes. > That's obviously cheaper than a regulator, but I lose > more accuracy. > > 4. My boss wants to use a bank of resistive dividers > enabled one at a time by relays into a single A/D, > referenced to ground (similar to a recommendation > posted here). I don't like this as the top battery > will be subject to a large common-mode voltage, > making that measurement much less accurate than the > bottom battery's. > > 5. I don't have to control the current or voltage of the > batteries, just want to monitor their health. > > 6. Whatever solution I implement will be under the control > of a microprocessor. Must execute without human > intervention. > > 7. I believe I can draw milliamps out of the batteries > during the test. The challenge is the quiescent > current, as many a customer will take delivery and stash > it in a warehouse for 6 months before trying to install > it, and the test circuit may not load it down while in > storage. > > 8. I don't mind using opto-couplers, but 72 of them will > add up fast. > > 9. PIC does make a uP with built-in A/D converter and UART > for under $1. Isolation is still unresolved. We > definitely cannot afford 72 isolated power supplies. > > Hope that gives you a better picture. > ============================================================ > Gary Lynch To send mail, change no$pam > gary.lynch(a)no$pam.com in my domain name to ieee. > ============================================================ Ok, with 72 batteries, you'll have 144 connections to make, even if you do not use any measuring/monitoring. So, if you do decide to set it up for measuring/monitoring, it makes sense to integrate the design of the battery to battery connectors with the connections that will be needed for measuring/monitoring. You want the time taken to connect those 72 batteries to be the same whether or not measuring/monitoring will be included. In effect, the inter-battery connectors will have a "port" on them that allows easy/fast connection of the whatever measuring monitoring equipment. The cost of the measuring equipment could easily be exceeded by the cost of connecting it, if you don't plan up front. Conceptually: -------- -------- | | | | | --,______________,-- | | --' ^ '-- | | Batt 1 | | | Batt 2 | | | P | | } } } } If you do that, you could build a resistor into the port so that there is no high current path in the event the wires connected to the port short to ground or other port connected wires. The actual "port" could be nothing more than an extra wire crimped to the connector you attach to the battery, or a wire with a ring terminal (which would add a bit to assembly time) if the battery uses nut & bolt connections. There may be many variations on the theme, but bottom line you'll need 74 connections to be able to measure each battery individually and you need to consider how to make them not only effectively, but cheaply. Ed |