EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: polemon on August 12, 2016, 11:06:36 pm
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Hello, I have a battery charger for a car lead-acid battery (it charges from a solar panel). I'd like to use simple means of display, for instance a single LED to check whether the battery is charging.
How should I do this?
The idea I came up with, is using two large diodes on the (+) terminal one in each direction and kinda putting a led in parallel with one of these large diodes. But I'm really not sure.
Thanks in advance~
--polemon
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The easiest way to do this is to connect the solar panel to the battery via a diode and connect and LED (with a suitable series resistor) on the solar panel side of the diode. The LED will illuminate when the solar cell is generating a voltage.
The disadvantage with the above solution is the solar panel may be outputting a high enough voltage to turn on an LED but not enough to charge the battery. Another solution is to use a transistor to turn on the LED when the voltage across a sense resistor exceeds 0.6V but it's late and I can't be bothered to draw it at the moment. I'll draw it tomorrow, if no one else has.
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The easiest way to do this is to connect the solar panel to the battery via a diode and connect and LED (with a suitable series resistor) on the solar panel side of the diode. The LED will illuminate when the solar cell is generating a voltage.
Not really an option. The panels is connected to a power management unit, which manages charging the battery and load balancing when a load draws enough current, so that it draws power from both the solar panel and the battery.
I want specifically the "current direction LED" on the battery side.
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Not really an option. The panels is connected to a power management unit, which manages charging the battery and load balancing when a load draws enough current, so that it draws power from both the solar panel and the battery.
I want specifically the "current direction LED" on the battery side.
The LED you want sounds like something the power management unit should have had built in. You can't be the only person looking for this, have you searched for hacks to this unit? Maybe post the model number of the unit and see if anyone here has done so or can supply a schematic for it.
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1 opamp a shunt and two leds can indicate charge discharge, I think.
Positive current, opamp clips V+, led green.
Negative current, opamp clips V-, led red.
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maybe try this... adjust R1 value so that voltage across it 0.7V at desired current flow. R2 is led current limit, you may need it you may not. ymmv.
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maybe try this... adjust R1 value so that voltage across it 0.7V at desired current flow. R2 is led current limit, you may need it you may not. ymmv.
Yes, that's what I had in mind but beware that the BJT won't be able to handle much base current and will be fried if the current exceeds 50mA or so.
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You want simple....?
How about a length of copper bar as a shunt with a centre-zero galvanometer/microammeter across it?
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The LED you want sounds like something the power management unit should have had built in. You can't be the only person looking for this, have you searched for hacks to this unit? Maybe post the model number of the unit and see if anyone here has done so or can supply a schematic for it.
Indeed it has a "charging LED", but it doesn't make sense. Even when current is drawn from both, the battery and the solar panel, the LED is lit (I've tested this with a multimeter).
It seems to me that the LED is always lit, when the solar panel generates enough voltage to charge the battery, but when the load is large enough it stays lit, even though current is drawn from both, the panel and the battery.
You should be able to use a series current sensing resistor in series with the battery line to present a differential voltage which will change polarity and magnitude depending on charge / discharge direction and magnitude.
With series current sensing resistor, do you mean shunt resistor?
You might be able to find a comparator with a low supply current (to save the battery) which could be powered by the battery voltage (assuming your battery is under 48V or so and over 4V or so, higher/lower voltages may require some special considerations).
Well, it's a standard car battery, so 10V to 15V is the basic operational range.
The right comparator would be able to sense differential millivolts level voltages at the positive supply rail level of the comparator itself. That is to say that the input common mode range for the comparator must include its positive supply voltage level, but I think some but not all parts have this feature.
Then the comparator's output would drive a LED through a resistor.
You'd have to think about what you desire in terms of having some threshold current level that must be met in order to turn on the LED, e.g. must be over 0.5A or whatever. You could bias the circuit somehow to set a threshold in conjunction with the choice of the current sensing resistor.
Yeah, I thought a max. of 100mA into the battery should trigger the LED on. Actually, anything >0A into the battery should actually turn it on, etc. but well, that's up to testing, etc.
Looks like the LTC1042 might work at up to 16V battery level, otherwise you'd have to lift its ground with a zener or something to keep the supply in that range.
http://www.linear.com/product/LTC1042 (http://www.linear.com/product/LTC1042)
You'd have to check the details, I don't have a lot of time for a few days.
Thanks, man! Nudging me into the right direction is a load of help already! I'll look into the part you linked and see if I can find more information about current sensing, etc.
Feel free to add to this thread if new ideas pop up!
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You want simple....?
How about a length of copper bar as a shunt with a centre-zero galvanometer/microammeter across it?
That is actually a good idea. Get one of those center zero NOS things on eBay (some are cheap!). At a glance, takes very little energy, and you are actually measuring a physical entity.
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What about using one of the battery wires for the shunt?
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a resistor + two back-to-back leds will do.
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What about using one of the battery wires for the shunt?
Worth investigating.
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KISS - keep it simple stupid .
http://www.stuttgartperformanceengineering.com/inductiveammater.html (http://www.stuttgartperformanceengineering.com/inductiveammater.html)
Depending on the current range , low - high tape it to wire , the needle will show the direction and the amount of current ;)
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a resistor + two back-to-back leds will do.
:palm: Think for a second. Big lead-acid battery, it's going to be 60 Ah at a minimum, so a 0.1C charge current of 6A dropped through the 1.6V that a LED is going to want to see is going to be the best part of ten watts or potentially much, much more. You've just cut the efficiency of the system by something on the close order of 15%, both during charging and discharging. Moreover, what's the charge management system doing to think of an extra 1.6V drop?
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You want simple....?
How about a length of copper bar as a shunt with a centre-zero galvanometer/microammeter across it?
That is actually a good idea. Get one of those center zero NOS things on eBay (some are cheap!). At a glance, takes very little energy, and you are actually measuring a physical entity.
Plus proper meters are cool. I recently picked up an old HP 6002A power supply and it has two big proper analogue meters on the front - even SHMBO approves of it.
Now all you need is a Jacob's Ladder or two and you're good to go. :)
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car amp meter
(http://www.clker.com/cliparts/2/b/6/7/12178622901512910749Startright_Automotive_Amp_Meter.svg.med.png)
This type uses no power setting there
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You want simple....?
How about a length of copper bar as a shunt with a centre-zero galvanometer/microammeter across it?
This is what a car amp meter is.
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a resistor + two back-to-back leds will do.
:palm:
My response was more... ???
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a resistor + two back-to-back leds will do.
I'm glad someone else said this - I was just about to post!!
Obviously Not as the current carrying element!!
Shunt it - and watch the side path current drive the LEDs
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... that would work in principle, but the voltage drop required to light up the LEDs would make it a poor solution.
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I second the battery wiring concept.
Plus two thin sensing wires.
It is a comparator circuit so the positive hysteresis is needed. And filtering.
The 100mA sensitivity should not be a problem here as long as LED indicates:
(-inf:0mA] always off
(0mA:100mA) unknown state (could be either on or off)
[100mA:inf) always on
So basically the challenge is: "offset voltage temperature drift" + same TCO of resistors used.
For 5mm2 Cu wire of 1m length we get:
R=3.3e-3 ohms
So at 0.1A that gives 330uV
Your comparator must not have the offset voltage drift higher than ~330uV/2 in whole operating range and the circuit is doable if you adjust zero to +50mA.