Hello! Sorry, I'm an Italian student (I don't speak english very well, please excuse me), and I'm creating a lead acid battery charger with the Unitrode (Texas Instruments) UC-2906. But there are some problems and questions. . .!! Can anyone help me, send me a link (not the TI datasheet, I've already downloaded, also the application notes) with a project of a battery charger with this IC? Or, if I'm writing in a wrong newsgroup, please excuse me and can anyone indicate me the correct NG?
Figure 1 on the datasheet shows a bad design for a charger using this part.
Figure 4 is a little better but they still didn't isolate the battery when the power is off. They also forgot to protect pin 2 for inverted battery polarity.
I'd say that on the whole it would be easier to design a battery charger without this chip than with it. Why are you using it?
Thank you for your prompt response :-) Well... I'm using that design!! I've added also a capacitor between PIN8 and GND to avoid the entering in float mode charge only for noise (as is wrote in the "Application Note")
Uhmmm... I've readed that the best way to charge the battery is "Dual level floatcharge,
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. . so I have choosen the project of figure 1. . . The protection against self-discharge and inverted battery polarity is important...I can modify the scheme with adding a diode, and recalculating The value of Voc, Vf, etc?
...!! I want to made an automatic battery charger, for many type of lead acid, motorbikes battery. I need a current of ,08 - 1 A max, and I must charge traditional, Pb-gel and other type of batteries, depending of bike manifacturer. Do you know another way to made one? I'm not very expert :-) , so I'm searching a simple way to made a charger..and I thinked (before your response!!) that the UC2906 was the better solutions, only changing the value of the 4 R with a multiway switch, to adapt the various tension level according with the tecnology of the battery. . . Do you think is this correct, or not? Any other solutions? Thank you! :-)
Thank you a lot! This project is quite different from the "original" project taht we can see in the application note, I think it is very complete...but also more difficult (I'm a newbye. . .!!!!)!!
One very common way is to use the LM317 or other voltage regulator and an external circuit to cause the boost in voltage to get the fast charging to happen.
As a starting point, consider this simplified circuit:
----------- A Diode Vin------! Regulator !-------->!---------To battery ! circuit ! D1 ----------- !B V Another diode --- D2 ! --GND GND ---GND
Imagine that the regulator circuit makes exactly the battery float voltage on its output. What it will really do is make this voltage appear between points "A" and "B" in the circuit.
V(A) = V(Ideal) + V(D2)
Where: V(D2) is the "diode drop" of D2 V(Ideal) is the floatc voltage for the battery
V(Battery) = V(A) - V(D1)
V(Battery) = V(Ideal) + V(D2) - V(D1)
So with this idea, if we can have two diodes with equal drops, the battery will see V(Ideal). If the power is off D1 completely isolates the circuit from the battery.
If you use two diodes of the same technology, they will match each other fairly well. D1 has a larger current in it than D2 so really what you want is to use a big diode for D1 (MUR1560) and a smaller one for D2 (1N914).
D2 also provides reversed battery protection.
You haven't said how much supply voltage we have to work with.
If I go with a wild assumption or two, I can proceed.
Look up the datasheet on the LM317. You will see that two resistors set its regulation voltage. The capacitors shown in the examples are needed to prevent oscillation. You can find the exact "float" voltages on the web. The data sheet shows how to figure the resistors.
Now we've the "float" voltage, You can set the charging current limit with a second LM317 like this:
This is usually also shown as an example on the datasheet. This circuit feeds the one above. Obviously the current out of the V(float) regulator can't be more than the current in.
The remaining issue is the "boost" or "charging" voltage for quickly charging the battery. If you check the various web sites, you will find a voltage for this and usually a current. You want to produce the "boost" voltage until the charging current drops below some level and then switch to the "float" voltage. The battery will still draw current in the "float" condition as is "topps off" the cells.
The voltage for the "Boost" mode is much more important than the current at which you switch to the "float" mode. If you switch to "float" too soon, the battery will still get charged. It just takes a very long time for the "topping off"
Remember the resistor in the current limit circuit:
This will have to have a rotary switch on it to change its value for the maximum current for each type of battery. Lucky for us, this resistor also can serve to set the end of "boost" current. The current you end boost at varies with the size of the battery in the same way as the maximum current.
To keep things easy to buy, lets use transistor or two instead of a chip for this part:
This makes two output voltages depending on the state of the switch. First, you assume the switch is open and work out the resistors for the "boost" case. Next you assume the switch is closed and work out the resistor it switches in parallel to get the "float" voltage.
No we need a way to make that switch.
Lucky for us, a small NPN transistor thinks its a switch. At this point I'm going to go cheap and just do this:
! !/c From X ----! NPN !\\e ! To D2
There is a lot I want to add, but I also want to go dig my garden. Perhaps this evening, I'll do more. Mean while others can shoot holes in my design.
Yes, I've the sheet: there is one between the pins VOUT and ADJ, and another that connect pin ADJ with GND. I can use some different resistor between those two last pins (ADJ and GND), selected by -as you suggest me- a rotative switch, to have different tension in output, according to the manifacturer's spec. Is correct....?
Just a moment...! Well, I put a second LM317, after the first...is correct? So, VOUT of first circuit is the Vin of the second LM317, used for a current regulator..? The resistor, in this case,is in series with Vout and the load (battery), or it is out between Vout and Adj pins? In the sheet there is this scheme, for a current regulator. . . But..in this case...what is the function of diode D1,...if, after the diode, there is another regulator?? The battery don't discharge in this last one? Sorry for my stupid question, remember that I'm half newbye! :-)
Well...moreover...the maximum current of LM317 is about 1A...correct?
...uhmmm....what a mess in my head!! :-)))) Well...I can use a second rotative switch to select to select some resistores values, so, for any resistor, I have an appropriare current in output. . . But, after few hours, I must select a lower current, according to "float" charge. . . or not??
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No.no....this part is a mytake for me!! Two transistor...but which ones??! Wait, you are running too fast!! :-)) My poor brain are still exploding. . .!!
Don't worry, it's not a oblige. . Thank you a lot for the time that you are spending, you are very, very courteous!!
At Vin to Vout differences of about 3V, I believe they will do a little over that.
[...]
Yes you select the resistor that gives you the maximum charging current allowed for the battery
No, the "float" condition is done by applying a fixed voltage to the battery. This voltage is just a little more than the no load voltage of a freshly charged battery.
For NPN look at 2N2222 or 2N4401 for PNP look at 2N3906
I'm only surprised that others haven't jumped in a complained about inaccuracies in my circuit .... or at least insult my gardening skills.
Uhmm..I have made a little confusion adding the parts in my text editor. . .! :-)) If you have only a minute, can you make a paint, complete. . .? thank you! :-)))
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