I would like to include a circuit in my preamp to monitor battery voltage. with some pushing from WSJ I think I am going to try to design it myself.
I found this online and wondered if I could modify it for my purpose. my battery operating range is 38v-50v. How could I modify this to work with my voltage.
I found this online and wondered if I could modify it for my purpose. my battery operating range is 38v-50v. How could I modify this to work with my voltage.
In that circuit, the LM358 max. pwr is 32V and LM7805 max. is 35V, so the 50V requirement is too high for many IC's. The 7805 wastes 5mA quiescent current, plus 20mA LED on all the time, which might be too much. Is this a tiny battery pack? Usually a low battery LED is sufficient or do you want the window comparator?
Dropping the supply voltage with a series zener diode, say 24V 1W could work, but you will be wasting ~1/2W as heat. The resistor values (R1,R3,R2,R4) need to be changed too for the higher trip points.
I would also look at the TL431 which contains an op-amp and voltage reference (fewer parts) - but a 36V limit you can use a zener diode to drop that down. See the datasheet battery monitor circuit Fig. 26 which would need some mods to work at 50V. This chip is a bit harder to understand.
Dropping the supply voltage with a series zener diode, say 24V 1W could work, but you will be wasting ~1/2W as heat. The resistor values (R1,R3,R2,R4) need to be changed too for the higher trip points.
I would also look at the TL431 which contains an op-amp and voltage reference (fewer parts) - but a 36V limit you can use a zener diode to drop that down. See the datasheet battery monitor circuit Fig. 26 which would need some mods to work at 50V. This chip is a bit harder to understand.
Great points!! thanks
I was thinking I would have a button to active the circuit when you want to check voltage. maybe a numerical display would be easier?
There must be some IC for this voltage since golf carts use 48v.
Its a pretty large battery pack - 6ah
can you monitor just the cell that has the highest power draw? ie. is this pack made up of several batteries in series? if it is, its as simple as sending the voltage on that.
Green DC10-90V/24V/36V/48V/72V digital display LED Panel Voltage Meter Voltmeter | eBay
push a button to operate. seems cheaper and simpler to me.....
push a button to operate. seems cheaper and simpler to me.....
I've got a 30VDC digital panel meter from China, but one that runs up to 100VDC (power) is news to me. I think it uses a buck converter- which makes electrical noise and defeats the purpose of running a pre-amp on batteries.
Maybe an LCD panel meter with its own 9V battery would work.
Maybe an LCD panel meter with its own 9V battery would work.
It does not defeat the purpose if you just are pushing a button to check the voltage.
The meter is off until you press the button.
The way I used to tell when my battery powered phono stage was flat was by listeing to the sound. It would gradually start to sound not as good. I didnt need any meters to tell me it was getting flat.
The other way was that I knew it lasted about 8 hours before needing charge.
The meter is off until you press the button.
The way I used to tell when my battery powered phono stage was flat was by listeing to the sound. It would gradually start to sound not as good. I didnt need any meters to tell me it was getting flat.
The other way was that I knew it lasted about 8 hours before needing charge.
A discrete circuit can easily be tailored to the application, is simpler, cheaper and takes less quiescent power.
This example uses less than 200µA quiescent current (can be further reduced with a suitable zener) and gives a progressive indication: when the voltage passes below the ~40V limit, the LED begins to flash briefly at a rate of one every few seconds, and if the voltage goes lower, the rate increases up to 3/second.
All these parameters can be adjusted by adapting the components values.
Even when it flashes at full rate, the consumption remains low thanks to the low duty cycle.
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