Multi-pack battery voltage monitor
in [Design]
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From: Gary Lynch on 2 Aug 2010 10:35 From: Gary Date: August 2, 2010 Subject: Re: Multi-pack battery voltage monitor On Friday, July 30, 2010 1:40 AM; Paul Keinanen" <keinanen(a)sci.fi> wrote: On Thu, 29 Jul 2010 22:17:08 -0400, "Gary Lynch" <gary.lynch(a)ieee.org> wrote: > > >I have been trying to flesh out some of the circuits > >discussed here. The following will take us beyond my > >ability to draw circuits in ASCII, so please refer to the > >graphic at > >- http://my.execpc.com/~bookworm/Projects/BattVtgMon04.gif > > > >beginning with Circuit A. > > > >I liked the idea of drawing power from the battery, only > >while the measurement is in progress, and inserted my > >circuit in series with a 7.5 V zener diode (7 V isn't that > >common). The A/D will not accept input voltages greater > >than the power to the chip, so two more resistors are needed > >to scale it down. > > My suggestion of using a 7 V zener was in place of R1. > However, a 10 V zener would be better, since it would > translate the battery voltage range 10-15 V > (charge/discharge) into the ADC input 0-5 V range. Thus a > fewer number of bits would suffice. For a larger swing, the > R1 would also be needed. > This approach has a disadvantage as the A/D built into the micro uses Vdd as a voltage reference. As the battery terminal voltage degrades with age, it will cause my A/D readings to shift as well. This will render my data worthless unless I can hold Vref steady over a wide range of battery voltages. That is why I switched to shunt regulation. > > Since you have plenty of voltage available, why not use some > series regulator power supply, which is remote controlled by > an other optoisolator, avoiding the expensive relay. > Because the divider network draws power from the battery all the time. The relay as drawn removes all load when the circuit is not in use. I am shopping around for a cheaper device. I think I can beat $3.19. ============================================================ Gary Lynch To send mail, change no$pam gary.lynch(a)no$pam.com in my domain name to ieee. ============================================================
From: ehsjr on 8 Aug 2010 15:41 Joe wrote: > On Fri, 30 Jul 2010 17:50:46 -0400, ehsjr wrote: > [snip] > >>If you've decided to use the PB1168-ND relay anyway, [snip] >> >>Maximum transfer + bounce time is 8 mS. With any relay, you want a diode >>across the coil. That delays the drop out time on the PB1168-ND relay >>for a maximum of 5 mS. So given your 42 mS spec, you can program to >>select the relay, wait 9 mS, measure the voltage for 27 ms, wait for 6 >>mS then select the next relay. A similar scheme should be used if you >>use any relay. You should adjust the timing as necessary for the >>specific relay chosen. > > [snip] > > Is that last time, 6 ms, intended for transmitting the reading > back to a controller? > No. That allows time for the relay to drop out. > If multiple relays can be on at the same time No. The design allows energizing only 1 relay at a time. Sorry I wasn't able to reply sooner, I was travelling. Ed (eg, relay drivers > controlled by bits from a SIPO shift register, not multiplexed) > one can overlap all but the readout parts of the process. > > Eg, at time 9*k ms engage relay #k; at 9+9*k, begin measuring > voltage at station #k; at time 36+9*k, begin readout #k; at > time 42+9*k, open relay #k. For 35 stations, k = 0 to 34 > and process is done at time 348 ms.
From: ehsjr on 8 Aug 2010 15:45
Joe wrote: > On Fri, 30 Jul 2010 17:50:46 -0400, ehsjr wrote: > [snip] > >>If you've decided to use the PB1168-ND relay anyway, [snip] >> >>Maximum transfer + bounce time is 8 mS. With any relay, you want a diode >>across the coil. That delays the drop out time on the PB1168-ND relay >>for a maximum of 5 mS. So given your 42 mS spec, you can program to >>select the relay, wait 9 mS, measure the voltage for 27 ms, wait for 6 >>mS then select the next relay. A similar scheme should be used if you >>use any relay. You should adjust the timing as necessary for the >>specific relay chosen. > > [snip] > > Is that last time, 6 ms, intended for transmitting the reading > back to a controller? > > If multiple relays can be on at the same time (eg, relay drivers > controlled by bits from a SIPO shift register, not multiplexed) > one can overlap all but the readout parts of the process. > > Eg, at time 9*k ms engage relay #k; at 9+9*k, begin measuring > voltage at station #k; at time 36+9*k, begin readout #k; at > time 42+9*k, open relay #k. For 35 stations, k = 0 to 34 > and process is done at time 348 ms. Ooops - regarding my previous answer, I had a different circuit in mind. The dropout time comment is valid, but he could select more than one relay at a time with the circuit he posted. Ed |