Multi-pack battery voltage monitor
in [Design]
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From: Gary Lynch on 29 Jul 2010 22:17 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. For my voltage-to-frequency converter circuit I favored one microprocessor over a fistful of analog components and MicroChip offers the PIC10F220 with an 8-bit A/D and an on-chip timer, so I can generate a variable frequency or variable duty cycle, or whatever waveform best suits the application. I can buy it from Digi-Key for $0.36 (in onesies). Finally I can shift the information down to logic levels with an opto-coupler. (An H11A1 costs $0.19.) But my micro draws up to 80 mA, so I decided to shut down the circuit when not in use, and I decided to deploy the PB1168-ND introduced by Ed. At $3.19, this costs more than the rest of the circuit combined. But closer inspection of the micro discloses that it uses Vdd as the A/D's reference voltage. Letting that swing through several volts during the test (even though the micro can apparently take it), adds too much complexity, so I have to modify the 'voltage regultor.' In Circuit B, I have moved the zener down to the circuit common and lowered the voltage to 4.7 V. This might be worth building. Almost forgot: I mis-read the spec for battery series/parallel combinations. The tallest stack contains 35 packs, so the max voltage is only 440 V. This might allow a cheaper switch than the relay. Did I miss anything? ============================================================ Gary Lynch To send mail, change no$pam gary.lynch(a)no$pam.com in my domain name to ieee. ============================================================
From: Paul Keinanen on 30 Jul 2010 01:40 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. > >For my voltage-to-frequency converter circuit I favored one >microprocessor over a fistful of analog components and >MicroChip offers the PIC10F220 with an 8-bit A/D and an >on-chip timer, so I can generate a variable frequency or >variable duty cycle, or whatever waveform best suits the >application. I can buy it from Digi-Key for $0.36 (in >onesies). If you use some kind of uP, bit banging some serial data would be as easy and avoid the inaccuracy caused of the PWM detection at the central controller. > >Finally I can shift the information down to logic levels >with an opto-coupler. (An H11A1 costs $0.19.) > >But my micro draws up to 80 mA, so I decided to shut down >the circuit when not in use, and I decided to deploy the >PB1168-ND introduced by Ed. At $3.19, this costs more than >the rest of the circuit combined. >In Circuit B, I have moved the zener down to the circuit >common and lowered the voltage to 4.7 V. This might be >worth building. 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.
From: ehsjr on 30 Jul 2010 17:50 Gary Lynch 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. > > For my voltage-to-frequency converter circuit I favored one > microprocessor over a fistful of analog components and > MicroChip offers the PIC10F220 with an 8-bit A/D and an > on-chip timer, so I can generate a variable frequency or > variable duty cycle, or whatever waveform best suits the > application. I can buy it from Digi-Key for $0.36 (in > onesies). > > Finally I can shift the information down to logic levels > with an opto-coupler. (An H11A1 costs $0.19.) > > But my micro draws up to 80 mA, so I decided to shut down > the circuit when not in use, and I decided to deploy the > PB1168-ND introduced by Ed. At $3.19, this costs more than > the rest of the circuit combined. > > But closer inspection of the micro discloses that it uses > Vdd as the A/D's reference voltage. Letting that swing > through several volts during the test (even though the micro > can apparently take it), adds too much complexity, so I have > to modify the 'voltage regultor.' > > In Circuit B, I have moved the zener down to the circuit > common and lowered the voltage to 4.7 V. This might be > worth building. > > Almost forgot: I mis-read the spec for battery > series/parallel combinations. The tallest stack contains 35 > packs, so the max voltage is only 440 V. This might allow a > cheaper switch than the relay. > > Did I miss anything? > ============================================================ > Gary Lynch To send mail, change no$pam > gary.lynch(a)no$pam.com <mailto:gary.lynch(a)no$pam.com> in my > domain name to ieee. > ============================================================ A couple of points. If you've decided to use the PB1168-ND relay anyway, as your post indicates, there is no need for all the parts in your diagram. You can just put a resistor in series between the relay contact and the battery for a high impedance connection to your single measuring/ monitoring circuit. Mounted at the battery, that solves the fuse/short circuit in the wiring/short across the battery issues that were mentioned in the thread. There was also a question or relay reliability raised in the thread. That relay is spec'd at > 10^8 mechanical operations, and 5 x 10^5 electrical operations at 125VDC at .24 amps. 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. If you go with SPST as shown in your diagrams, you can use reed relays to save money. For example, Digikey 306-1063-ND for $1.43 in qty 10, and it includes the diode across the coil. There are cheaper ones - look around. I think you can get it to less than a dollar per relay by using SMT. I'd be concerned with the labor cost of assembling and calibrating 35 of those circuits. You'd certainly want a single program replicated in each PIC10F220, which implies that any calibration would be futzing with the ADC input voltage divider. That would be cost prohibitive, so the assumption is that there will be no calibration. If you simply pass the voltage from the battery to a single PWM or measurement device, then you can calibrate it once, but that gets back to needing 2 relays or a double pole relay per battery - or a 2 fet/inverter circuit. It's easy to get "seduced" by the electronics. Just don't overlook the labor cost of whichever approach you investigate. Ed
From: JosephKK on 31 Jul 2010 08:03 On Thu, 29 Jul 2010 22:17:08 -0400, "Gary Lynch" <gary.lynch(a)ieee.org> wrote: Yo, ($%^#$*%^*) lose the html, this is usenet. >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. > >For my voltage-to-frequency converter circuit I favored one >microprocessor over a fistful of analog components and >MicroChip offers the PIC10F220 with an 8-bit A/D and an >on-chip timer, so I can generate a variable frequency or >variable duty cycle, or whatever waveform best suits the >application. I can buy it from Digi-Key for $0.36 (in >onesies). > >Finally I can shift the information down to logic levels >with an opto-coupler. (An H11A1 costs $0.19.) > >But my micro draws up to 80 mA, so I decided to shut down >the circuit when not in use, and I decided to deploy the >PB1168-ND introduced by Ed. At $3.19, this costs more than >the rest of the circuit combined. > >But closer inspection of the micro discloses that it uses >Vdd as the A/D's reference voltage. Letting that swing >through several volts during the test (even though the micro >can apparently take it), adds too much complexity, so I have >to modify the 'voltage regultor.' > >In Circuit B, I have moved the zener down to the circuit >common and lowered the voltage to 4.7 V. This might be >worth building. > >Almost forgot: I mis-read the spec for battery >series/parallel combinations. The tallest stack contains 35 >packs, so the max voltage is only 440 V. This might allow a >cheaper switch than the relay. > >Did I miss anything? >============================================================ >Gary Lynch To send mail, change no$pam >gary.lynch(a)no$pam.com in my domain name to ieee. >============================================================
From: Joe on 31 Jul 2010 12:38
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. |