Multi-pack battery voltage monitor
in [Design]
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From: whit3rd on 23 Jul 2010 09:38 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.
From: whit3rd on 23 Jul 2010 09:40 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.
From: Charlie E. on 23 Jul 2010 13:19 On Thu, 22 Jul 2010 19:01:00 -0400, "tm" <noone(a)msc.com> wrote: > >"Grant" <omg(a)grrr.id.au> wrote in message >news:74ih46p6p96hijj70n8dg1c1muij7kmttu(a)4ax.com... >> On Thu, 22 Jul 2010 23:47:16 +0300, Paul Keinanen <keinanen(a)sci.fi> wrote: >> >>>On Thu, 22 Jul 2010 15:52:53 -0400, "tm" <noone(a)msc.com> wrote: >>> >>>> >>>>"ehsjr" <ehsjr(a)nospamverizon.net> wrote in message >>>>news:i2a6cg$6cp$1(a)news.eternal-september.org... >>>>> Gary Lynch wrote: >>>>>> +------+ I am looking for an economical way to measure >>>>>> | _|_ terminal voltages of individual SLA batteries >>>>>> --- | ? | in a stack up to 72 packs high. Atmel & Linear >>>>>> = |___| Technology make products that ALMOST do >>>>>> | | this--allow direct connect to battery >>>>>> +------+ terminals to steal power, serial output with >>>>>> | level shifting so they can be cascaded, >>>>>> +------+ etc--but tout them only for Li-Ion technology. >>>>>> | _|_ It appears they cannot straddle a potential >>>>>> --- | ? | greater than 5 V. = |___| >>>>>> | | I read another post that claimed for a low-end >>>>>> +------+ appliances such as mine, it was cheaper to >>>>>> : replace the batteries every 3 years than to >>>>>> : watch for 'slackers.' +------+ >>>>>> | _|_ Any other ideas? >>>>>> --- | ? | >>>>>> = |___| Thanks. >>>>>> | | >>>>>> +------+ >>>>>> ============================================================ >>>>>> Gary Lynch To send mail, change no$pam >>>>>> gary.lynch(a)no$pam.com in my domain name to ieee. >>>>>> ============================================================ >>>>>> >>>>> >>>>> >>>>> I suspect that you really want to _monitor_ the voltage. Anyway, >>>>> until you answer the questions you've already been asked, here's >>>>> a generic solution that does not depend on those answers. >>>>> >>>>> You could use a micro & some low current telecom relays like Digikey >>>>> PB1168-ND to select the batteries individually. Conceptually, >>>>> something like this: >>>>> >>>>> / >>>>> +---o o---A >>>>> | >>>>> [Bat] Rly---------- uP port A0 >>>>> | >>>>> +---o o---B >>>>> | \ >>>>> | >>>>> | / >>>>> +---o o---A >>>>> | >>>>> [Bat] Rly---------- up port A1 >>>>> | >>>>> +---o o---B >>>>> | \ >>>>> }}} >>>>> | / >>>>> +---o o---A >>>>> | >>>>> [Bat] Rly---------- uP port B7 >>>>> | >>>>> +---o o---B >>>>> \ >>>>> >>>>> The A and B points all connect to whatever circuit you're >>>>> using to monitor the voltage. >>>>> >>>>> You could also use p and n FETs and inverters to replace >>>>> the relay contacts and save on $, at the cost of more >>>>> assembly work. (The relays cost $3.19 each in low quantity.) >>>>> >>>>> Ed >>>> >>>>The OP stated up to 72 batteries. At 14 volts each, it would be near 1000 >>>>volts >>>>on the end. >>> >>>In Europe, still within the Low Voltage Directive (1500 Vdc). >>> >>>>Some thought needs to be given to safety with whatever scheme is >>>>chosen. Of course, we never got any good follow-up on some of the >>>>questions >>>>asked. >>> >>>When working with batteries, I would be more concerned with the >>>potentially very high fault currents. >> >> Too right, but voltage sensing is easily isolated by resistors to >> control fault current. >>> >>>In the rely example above, if there is a malfunction in the relay >>>control and two relays are active simultaneously or if , say contact B >>>on a relay gets stuck and an other relay is activated, one or more >>>batteries are shorted. >>> >>>Of course, if the batteries have sufficient capacity and sufficiently >>>low source resistance, the stuck relay contact is cleared :-), with >>>the relay itself, as well as a lot of low power wiring going up in >>>smoke. Thus it is essential that any wires going from the battery >>>poles to the small signal relays are protected by suitable fuses. >>> >>>For a large number of batteries in series, it is simpler to have >>>individual electronics floating across each battery and then using >>>optoisolators for communicating the data to a processor. After all, >>>1000 V is not a problem for most optoisolators. >> >> I don't like the relay option for reliability, but they don't >> draw a standby load from batteries. >> >> V to F -> optos probably easiest? Possibly some addressable scheme >> to reduce battery loading, another opto to enable each V/F unit? >> > >If the need is to monitor 12 volt lead acid batteries, then I would think >it necessary to have at least a 0.1 volt accuracy. That is non-trivial >at 1000 volts above ground. > >tm > > > >--- news://freenews.netfront.net/ - complaints: news(a)netfront.net --- Personally, I would probably just use some little PICs with enough circuitry to handle the 12V power, and measure that power for each battery. I would then use an isolated comm channel to report the status of each battery. Maybe have one of them be a little bigger unit to monitor the comms from the others, and provide supervisory functions. Heck, if I used a PSOC, it might be even cheaper... Charlie
From: keithw86 on 23 Jul 2010 14:01 On Jul 23, 12:19 pm, Charlie E. <edmond...(a)ieee.org> wrote: > On Thu, 22 Jul 2010 19:01:00 -0400, "tm" <no...(a)msc.com> wrote: > > >"Grant" <o...(a)grrr.id.au> wrote in message > >news:74ih46p6p96hijj70n8dg1c1muij7kmttu(a)4ax.com... > >> On Thu, 22 Jul 2010 23:47:16 +0300, Paul Keinanen <keina...(a)sci.fi> wrote: > > >>>On Thu, 22 Jul 2010 15:52:53 -0400, "tm" <no...(a)msc.com> wrote: > > >>>>"ehsjr" <eh...(a)nospamverizon.net> wrote in message > >>>>news:i2a6cg$6cp$1(a)news.eternal-september.org... > >>>>> Gary Lynch wrote: > >>>>>> +------+ I am looking for an economical way to measure > >>>>>> | _|_ terminal voltages of individual SLA batteries > >>>>>> --- | ? | in a stack up to 72 packs high. Atmel & Linear > >>>>>> = |___| Technology make products that ALMOST do > >>>>>> | | this--allow direct connect to battery > >>>>>> +------+ terminals to steal power, serial output with > >>>>>> | level shifting so they can be cascaded, > >>>>>> +------+ etc--but tout them only for Li-Ion technology. > >>>>>> | _|_ It appears they cannot straddle a potential > >>>>>> --- | ? | greater than 5 V. = |___| > >>>>>> | | I read another post that claimed for a low-end > >>>>>> +------+ appliances such as mine, it was cheaper to > >>>>>> : replace the batteries every 3 years than to > >>>>>> : watch for 'slackers.' +------+ > >>>>>> | _|_ Any other ideas? > >>>>>> --- | ? | > >>>>>> = |___| Thanks. > >>>>>> | | > >>>>>> +------+ > >>>>>> ============================================================ > >>>>>> Gary Lynch To send mail, change no$pam > >>>>>> gary.lynch(a)no$pam.com in my domain name to ieee. > >>>>>> ============================================================ > > >>>>> I suspect that you really want to _monitor_ the voltage. Anyway, > >>>>> until you answer the questions you've already been asked, here's > >>>>> a generic solution that does not depend on those answers. > > >>>>> You could use a micro & some low current telecom relays like Digikey > >>>>> PB1168-ND to select the batteries individually. Conceptually, > >>>>> something like this: > > >>>>> / > >>>>> +---o o---A > >>>>> | > >>>>> [Bat] Rly---------- uP port A0 > >>>>> | > >>>>> +---o o---B > >>>>> | \ > >>>>> | > >>>>> | / > >>>>> +---o o---A > >>>>> | > >>>>> [Bat] Rly---------- up port A1 > >>>>> | > >>>>> +---o o---B > >>>>> | \ > >>>>> }}} > >>>>> | / > >>>>> +---o o---A > >>>>> | > >>>>> [Bat] Rly---------- uP port B7 > >>>>> | > >>>>> +---o o---B > >>>>> \ > > >>>>> The A and B points all connect to whatever circuit you're > >>>>> using to monitor the voltage. > > >>>>> You could also use p and n FETs and inverters to replace > >>>>> the relay contacts and save on $, at the cost of more > >>>>> assembly work. (The relays cost $3.19 each in low quantity.) > > >>>>> Ed > > >>>>The OP stated up to 72 batteries. At 14 volts each, it would be near 1000 > >>>>volts > >>>>on the end. > > >>>In Europe, still within the Low Voltage Directive (1500 Vdc). > > >>>>Some thought needs to be given to safety with whatever scheme is > >>>>chosen. Of course, we never got any good follow-up on some of the > >>>>questions > >>>>asked. > > >>>When working with batteries, I would be more concerned with the > >>>potentially very high fault currents. > > >> Too right, but voltage sensing is easily isolated by resistors to > >> control fault current. > > >>>In the rely example above, if there is a malfunction in the relay > >>>control and two relays are active simultaneously or if , say contact B > >>>on a relay gets stuck and an other relay is activated, one or more > >>>batteries are shorted. > > >>>Of course, if the batteries have sufficient capacity and sufficiently > >>>low source resistance, the stuck relay contact is cleared :-), with > >>>the relay itself, as well as a lot of low power wiring going up in > >>>smoke. Thus it is essential that any wires going from the battery > >>>poles to the small signal relays are protected by suitable fuses. > > >>>For a large number of batteries in series, it is simpler to have > >>>individual electronics floating across each battery and then using > >>>optoisolators for communicating the data to a processor. After all, > >>>1000 V is not a problem for most optoisolators. > > >> I don't like the relay option for reliability, but they don't > >> draw a standby load from batteries. > > >> V to F -> optos probably easiest? Possibly some addressable scheme > >> to reduce battery loading, another opto to enable each V/F unit? > > >If the need is to monitor 12 volt lead acid batteries, then I would think > >it necessary to have at least a 0.1 volt accuracy. That is non-trivial > >at 1000 volts above ground. > > >tm > > >--- news://freenews.netfront.net/ - complaints: n...(a)netfront.net --- > > Personally, I would probably just use some little PICs with enough > circuitry to handle the 12V power, and measure that power for each > battery. I would then use an isolated comm channel to report the > status of each battery. Maybe have one of them be a little bigger > unit to monitor the comms from the others, and provide supervisory > functions. > > Heck, if I used a PSOC, it might be even cheaper... If you're putting a PSoC in there, transformers are probably lower power and cheaper than Optical Isolators. Maybe even capacitors in a "ring" topology to limit voltage. The data rate isn't an issue.
From: Grant on 23 Jul 2010 17:25
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. Grant. |