Multi-pack battery voltage monitor
in [Design]
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From: tm on 22 Jul 2010 15:52 "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. 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. tm --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: Paul Keinanen on 22 Jul 2010 16:47 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. 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.
From: Grant on 22 Jul 2010 18:42 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? Grant.
From: tm on 22 Jul 2010 19:01 "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 ---
From: Grant on 22 Jul 2010 22:20
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. Non trivial? Easily enough done with opto couplers, there's 10kV and up ones with a LED one end and a phototransistor other end of a fairly long plastic tube. If they're not made any more, one could make their own. Grant. |