Multi-pack battery voltage monitor
in [Design]
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From: whit3rd on 21 Jul 2010 16:35 On Jul 21, 4:15 am, Gary Lynch <bookw...(a)execpc.com> wrote: > +------+ I am looking for an economical way to measure > | _|_ terminal voltages of individual SLA batteries > --- | ? | in a stack OK, I'll bite. Use a d'Arsonval movement and a resistor. Connect probes to the terminals and poke 'em at the battery cells, one at a time. More useful nowadays would be a bevy of thermosensors and, as voltmeter, some kind of machine-addressable multiplexer into an ADC, though. With a single sense resistor and a bunch of simple reed relays feeding a current-frequency converter, you could get accurate and monotonic readings (but not fast; heck, battery state doesn't change fast anyhow).
From: Grant on 21 Jul 2010 18:20 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 > | _|_ 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. > | | > +------+ Please clarify 72 packs, you talking 72 cells, or 72 x 3 or 6 cells? In any case it's a high voltage, probably opto coupling would be required. Are you monitoring or wanting to perform balancing as well? Grant.
From: David Eather on 21 Jul 2010 18:39 On 21/07/2010 10:55 PM, Paul Keinanen wrote: > 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 >> | _|_ 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. >> ============================================================ > > How much can you load those batteries ? > > How about a voltage divider across each 12 V battery, producing a > voltage less than 5 V ? > > The voltage divider could consist of a 7 V zener (the upper leg) and a > resistor (the lower leg), thus the battery voltage swing would go into > the IC without attenuation.. > 13+ volts from the battery. I think that a no, but the idea would work with a higher voltage zener.
From: Robert Baer on 22 Jul 2010 03:08 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. > ============================================================ > Maybe measure each cell junction with appropriate divider to a multiplexed ADC, software set for appropriate gain and sensitivity; derive each cell voltage wit some simple math.
From: ehsjr on 22 Jul 2010 15:32
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 |