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Using Arduino => General Electronics => Topic started by: calvingloster on May 27, 2014, 06:59 pm

Title: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 27, 2014, 06:59 pm
I have set up a LM317 to output 13.7v. From the output to adjust I have used a 5ohm resistor and then my R2 which is from the R1 to ground I have used a 50ohm resistor. When I put a 16v power supply on the 50ohm resistor gets smoking hot!!! Like I can even smell it! Why is this?
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: KeithRB on May 27, 2014, 07:08 pm
Use ohms law to calculate the dissipation. The current through them is 16.7/55 = 300 mA. The power in the 50 ohm resistor is .3*.3*50 = 4.6 W.

You can safely increase the resistance by 10 or even 100 times to minimize the power dissipation.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 27, 2014, 07:13 pm

Use ohms law to calculate the dissipation. The current through them is 16.7/55 = 300 mA. The power in the 50 ohm resistor is .3*.3*50 = 4.6 W.

You can safely increase the resistance by 10 or even 100 times to minimize the power dissipation.


If I increase the resistance the power dissipation barely decreases. If I use a 100ohm for R1 and a 1000ohm for R2 I get 12W of heat dissipation off R2!!!!!!!!

I can't understand this? Why do they say u can use the LM317 as a voltage regulator. It's ridiculous
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: fungus on May 27, 2014, 07:19 pm
So... you've got 55 Ohms between 13.7v and GND.

a) Can you calculate the current that's going to flow through the resistors?

b) Using the answer from (a), how much power will each resistor dissipate? (volts * amps)

c) Do the answers from (b) seem reasonable?


Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 27, 2014, 07:33 pm

So... you've got 55 Ohms between 13.7v and GND.

a) Can you calculate the current that's going to flow through the resistors?

b) Using the answer from (a), how much power will each resistor dissipate? (volts * amps)

c) Do the answers from (b) seem reasonable?





A) yes I can 250mA
B) R1 will dissipate 1.25W. R2 will dissipate 12.5W
C) No 12.5W does not seam reasonable for a 1/8W resistor

However if I increase R1 to 100ohms and R2 to 1000ohms then:

A) 0.0125A
B)R1 will dissipate 1.25W and R2 will dissipate 12.5W
C) oh look it's exactly the same BUT the R2 doesn't get hot at all unlike the first case where they burn up
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: 123Splat on May 27, 2014, 07:42 pm
E/R= I
I*I*R=P, not I*R*R
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 27, 2014, 07:47 pm

E/R= I
I*I*R=P, not I*R*R



Can you please talk in words and not letters? I don't know what you trying to say?

Heat dissipation is Amps multiplied by resistance.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: JChristensen on May 27, 2014, 07:48 pm

I can't understand this? Why do they say u can use the LM317 as a voltage regulator. It's ridiculous


Because it is a voltage regulator :D

Have a glance at the datasheet. 240? is the usual value for R1. (What would ever possess a person to use 5?.) The LM317 develops a 1.25V reference voltage across R1, resulting in 65mW power dissipation. Use 2400? for R2, this will set the output voltage to 13.87V, and 66mW dissipated by R2.  Where is the problem.

Use 1% resistors and change R2 to 2370?, this will come closer to the target voltage, 13.71?.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 27, 2014, 07:54 pm


I can't understand this? Why do they say u can use the LM317 as a voltage regulator. It's ridiculous


Because it is a voltage regulator :D

Have a glance at the datasheet. 240? is the usual value for R1. (What would ever possess a person to use 5?.) The LM317 develops a 1.25V reference voltage across R1, resulting in 65mW power dissipation. Use 2400? for R2, this will set the output voltage to 13.87V, and 66mW dissipated by R2.  Where is the problem.

Use 1% resistors and change R2 to 2370?, this will come closer to the target voltage, 13.71?.


Ok so let me ask you this, if I use a 240 ohm resister as R1 then I can supply a voltage whatever depending on R2 but my maximum current I can provide is 1.25/240 is 0.005 Amps. Now what if I need 250mA?
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: JChristensen on May 27, 2014, 07:54 pm


E/R= I
I*I*R=P, not I*R*R


Can you please talk in words and not letters? I don't know what you trying to say?


A person needs to know a little algebra and common variable names to be successful in this hobby. Do the substitution yourself, E = voltage (or you can use V), I = current, R = resistance, P = power.

Quote

Heat dissipation is Amps multiplied by resistance.


No, power (heat) is volts times amps. Or: P = V * I

With a little algebra (you passed algebra?), we also have  P = I2 * R  and P = E2 / R

Very useful and essential formulas, should be memorized.  Used properly, they are guaranteed to prevent that burning smell ;)
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: JChristensen on May 27, 2014, 07:55 pm

Ok so let me ask you this, if I use a 240 ohm resister as R1 then I can supply a voltage whatever depending on R2 but my maximum current I can provide is 1.25/240 is 0.005 Amps. Now what if I need 250mA?


Incorrect.  Where in the world did you get such an idea?
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 27, 2014, 08:05 pm


Ok so let me ask you this, if I use a 240 ohm resister as R1 then I can supply a voltage whatever depending on R2 but my maximum current I can provide is 1.25/240 is 0.005 Amps. Now what if I need 250mA?


Incorrect.  Where in the world did you get such an idea?



Sorry I am abit slow I really do wish I was as clever as many of you people, please forgive me.

I see now that I made the mistake of multiplying amps and current to get power dissipation instead of squaring amps and then multiplying it by current.

I got that idea from if you put a 240ohm resistor between output and adjust pin then u get a constant current source of 0.005A. So there is no way you can get more amps from using a 240ohm resistor. I am however confused why the LM317 does not act like a current limiter if you wire it up as a voltage regulator.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: 123Splat on May 27, 2014, 08:18 pm
AMPs am CURRENT,,, It's Voltage , Resistance, and Current (in AMPs).
The 1.25 V and 50uV (not 5mV) are what is passed by the Adjust pin of the regulator. You can read the datasheet to find out how it works. But that current path is totally different from the reference loop setup by R1 and R2.  That sets the Highend voltage the regulator will pass.  with proper heat sinking, the 317 will pass a max of something like 1 AMP, as long as you source it with Vin=Vout+1.25V, or more and at least 1 AMP.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: JChristensen on May 27, 2014, 08:25 pm

Sorry I am abit slow I really do wish I was as clever as many of you people, please forgive me.


No worries, just slow down and try to understand the fundamentals like Ohm's Law. Not difficult at all and as ever, GIYF.  It's also very important to read the datasheets of the devices in the circuit.

Quote

I got that idea from if you put a 240ohm resistor between output and adjust pin then u get a constant current source of 0.005A. So there is no way you can get more amps from using a 240ohm resistor. I am however confused why the LM317 does not act like a current limiter if you wire it up as a voltage regulator.


It doesn't act as a current limiter (well, except to protect itself when current exceeds its limits, or it gets too hot) because it's a voltage regulator.  Which do you want?  If you want both, then something other than a simple LM317 will be needed.

The main current to the load flows through the LM317 from its input terminal to its output terminal.  The Adjust terminal works in conjunction with the resistors to set the desired output voltage.  The currents involved in doing this are relatively small and have nothing really to do with the output current to the load. Does that help?
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: 123Splat on May 27, 2014, 08:32 pm
The 317 can also be configured as a current regulator (for relatively Constant Currents BELOW 1A). And,, you canconfigure one 317 as a voltage regulator (for desired Vout+1.25V) and follow it with a second 317 configured as a current limiter.  It works. It kills batteries. It wastes parts.  I've done it many times and with regret, will probablly continue to do so...
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 27, 2014, 08:36 pm
Yes that does help thanx. What I am trying to make is a voltage regulated constant current source.

I thought I would use 2 LM317's wired up after eachother. The first one would be a voltage regulator feeding into a constant current source. But I thought if the voltage regulator used a 240ohm for R1 then the second LM317 would never be able to provide more than 0.005A because the first LM317 was limiting the current as well. But I am wrong and I do not understand how this LM317 works
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: 123Splat on May 27, 2014, 08:41 pm
Good luck. we learn more by out mistakes.  Think about having another go at the data sheet. it is pretty explicit.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: KeithRB on May 27, 2014, 09:06 pm
Work out the math. You can't have a voltage regulated (constant voltage) constant current source. What is your load?
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: JChristensen on May 27, 2014, 09:37 pm

What I am trying to make is a voltage regulated constant current source.


Like KeithRB says, there is no such animal. Understand what a constant current source (http://en.wikipedia.org/wiki/Current_source) is: By varying the voltage, it tries to always keep the current through the load constant, even as the load varies.

Say that I had a one-amp constant current source.  If I just hook up a simple 10? resistor as a load, it will push one amp through the resistor, by increasing the voltage to 10V.  Ohm's law tells us V = IR = 1 amp * 10 ? = 10V.

Now remove the 10? resistor and connect a 50? resistor.  The constant current source will still push 1A through it, now increasing the voltage to V = IR = 1 amp * 50? = 50V.  A 2? resistor will only require 2V to push 1A through it.

Constant current sources are good for certain applications, like high-power LEDs, that like their current to be, well, constant.

So yes please clue us in on what this power supply will be powering.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: Paul__B on May 28, 2014, 12:24 am

So yes please clue us in on what this power supply will be powering.


A SLA battery charger.  See his other thread (http://forum.arduino.cc/index.php?topic=242831.0).

Unfortunately, someone has distressingly suggested using another LM317 in series as a current control, and in his proposed design, he put this after the voltage regulator, rendering it completely unusable.

I had a half-hearted attempt at contributing to that thread, but gave up because it was simply impossible on so many counts!   :smiley-eek:

His original proposal was to charge a 12V SLA from 16V which is perfectly, easy, but requires a completely different component set and design.

Perhaps someone might point him to a properly designed version of same (as against a random "instructable" or "makey") and he can learn the principles over time.   :D
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: JChristensen on May 28, 2014, 03:22 am

A SLA battery charger.  See his other thread (http://forum.arduino.cc/index.php?topic=242831.0).


Aha, thanks for that.  I do strive to know what I don't know, and I can say that I am pretty much ignorant of battery charging algorithms.  In general maybe there is a constant current phase for most of the charge but then this tapers off and/or switches to a trickle mode to keep things topped off, but details matter as does battery chemistry.  Interesting stuff actually, I should educate myself a bit sometime.  So I might look for an IC built for the purpose, although I always understand the attraction of rolling your own.

That said, I'll probably sit the rest of this one out, other than reiterating that before actually attempting to charge any batteries, the OP should Google up some tutorials and ensure they have a very solid understanding of Ohm's Law and also power relationships.  Burning up a resistor may smell bad but failure of a lead acid battery could be quite a bit less enjoyable.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 28, 2014, 05:39 am
Ok so hear me out now. I do believe it is possible to create a constant voltage constant current source. The first LM317 limits volts to 14.1v and the second one limits current to let's say 100mA. When the "device" requires 50v to draw 100mA then the constant voltage will only allow it to draw as much current as 14.1v would allow according to ohms law. So as the "device" changes it's properties like resistance, the 2 LM317's will NEVER allow it to draw more than 100mA or be subjected to more than 14.1v. And I do believe a lead acid battery could be charged this way. It might take long but will still work. Does that not make sense?
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: JChristensen on May 28, 2014, 05:49 am

Ok so hear me out now. I do believe it is possible to create a constant voltage constant current source. The first LM317 limits volts to 14.1v and the second one limits current to let's say 100mA. When the "device" requires 50v to draw 100mA then the constant voltage will only allow it to draw as much current as 14.1v would allow according to ohms law. So as the "device" changes it's properties like resistance, the 2 LM317's will NEVER allow it to draw more than 100mA or be subjected to more than 14.1v. And I do believe a lead acid battery could be charged this way. It might take long but will still work. Does that not make sense?


Not much, I'm afraid.  Sounds more like a current-limiting situation.  Do the maths.  V=IR.  If V and I are constants, so too must R be constant.  So we can only have voltage and current constant with one specific resistance, i.e. the load resistance cannot change.

But don't let me discourage you.  I am perfectly willing to be convinced.  Design the circuit, build it, test it, then bring us the schematic and the V/I curves so that we can understand it and duplicate the results.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: Grumpy_Mike on May 28, 2014, 06:06 am
Quote
I am perfectly willing to be convinced.

Well I am not.
This is a classic beginners mistake thinking you can have a constant current and constant voltage at the same time.

What the OP is describing is a current limiting supply, the sort of thing you get in bench power supplies. The voltage is constant up to a certain current, then as that current is reached any further reduction of the load to try and increase the current results in a reduction in output voltage.
You can do all that with one regulator and a bit of feedback from a current sensor.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: krupski on May 28, 2014, 07:15 am

I have set up a LM317 to output 13.7v. From the output to adjust I have used a 5ohm resistor and then my R2 which is from the R1 to ground I have used a 50ohm resistor. When I put a 16v power supply on the 50ohm resistor gets smoking hot!!! Like I can even smell it! Why is this?



Read this post: http://forum.arduino.cc/index.php?topic=240371.msg1725782#msg1725782

(the LM-317 data sheet may be a help too......)   :)

Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: fungus on May 28, 2014, 09:14 am

Does that not make sense?


Yes, but from the device's point of view it won't be a constant voltage supply.  The voltage the device sees will vary (up to the maximum allowed).

Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: fungus on May 28, 2014, 09:30 am
PS: You can get pre-built, adjustable devices for doing this:

eg.  http://www.ebay.com/itm/111323886108

You can even get them with three adjusters so they turn on a LED and shut down when they reach a certain voltage:

eg. http://www.ebay.com/itm/371059092051
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: polymorph on May 28, 2014, 02:22 pm
This can be done with two LM317, but the current limiter must come first. Essentially what you are doing is building a voltage regulator, then powering it with a current regulator. The current regulator drops the voltage to the voltage regulator if the current reaches the setpoint, and so the voltage regulator's output drops because it just isn't getting enough voltage.

It can be done, but each LM317 requires a relatively large headroom. You need about 5V headroom for each one, so for 14.1V maximum output you'll need nearly 25V. Rather inefficient.

For the current regulator, all the output current flows through the resistor between Output and Adjust, so it must be a higher wattage. At 100mA output, 1.25Vx100mA = 125mW. You always at least double the rating for resistors, so a 1/2W resistor will work. But for the voltage regulator,none of the output current flows through the voltage divider that sets the output voltage, so they can be low wattage resistors.

The LM317 each require a heat sink.

However, as has been pointed out:

1. There are better ways to do this
2. The price for failure can be high (dead or exploding batteries)
3. The OP really needs to read up on the basics: Ohm's law, Kirchoff's current and voltage laws, the voltage/resistance/current/power formulas, etc.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 28, 2014, 03:36 pm
I find this very frustrating and hard to understand. Can I ask that someone answers the questions I am about to ask in a yes no fashion.


1) the Bulk charge of a lead acid battery is done by a constant current charge. For simplicity sake let's say we want to charge our battery with 100mA. Now in order for us to force 100mA into the battery we require a voltage of 20v. So now our power supply only puts out 16v. So we will not be able to push 100mA into the battery, BUT!!!! BUT BUT BUT!!! We will still be push some amount which is LESS THAN 100mA!!! So essentially our BULK charge will take longer than usual BUT it will still work and will NOT damage the battery. Yes or no?

2)Now an LM317 CAN!!!!! CAN CAN CAN!!!!!! Provide the top explained power supply. As a constant current source? YES or NO?


3) for the float charge we charge the battery with a constant voltage source? At 14.1v. Now the LM317 can also provide us with such a power supply!!!!!! Yes or no?


The LM317 can supply us with a constant voltage and a constant current source. I hear u guys are saying it cannot but I'm sure it can because all the first LM317 is doing is limiting voltage to the second one. So the second LM317 never see's any voltage higher than say for example 14.1v. Then the second LM317 regulates current to say 100mA. So the device can never see voltage above 17volts and can never see current above 10mA.


Even if I use one LM317 set up as a voltage regulator regulated to 14.1volts I will be able to charge the battery until it's full!!!!! This will obviously take much longer but it does not damage the battery at all and if I leave it over night then awesome!!!!!


And I know that efficiency isn't going to be great but these are the only components I have!!! I can't just buy stuff like you guys recommend. I have what I have and I want to use it to make what I need. Even if it isn't the most efficient thing on earth.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: Grumpy_Mike on May 28, 2014, 03:38 pm
Quote
Can I ask that someone answers the questions I am about to ask in a yes no fashion.

No.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 28, 2014, 03:43 pm
Typo I meant the device can never see current above 100mA
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 28, 2014, 03:47 pm
I don't know if you guys are maybe getting confused. A constant current source means that the device can never draw current above the set limit but can draw any value below the limit. So if I set an LM317 to a constant current source of 100mA the device can never draw above 100mA but can draw 5mA or 20mA or any current bellow 100mA
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: polymorph on May 28, 2014, 03:56 pm
I think the wording is getting in the way. What you want is a power supply that is voltage regulated, current limited.

A single LM317 can do this with a transistor for feedback to limit the charging current. Try this one, with a 5.6 ohm resistor in place of R1:
http://www.sentex.ca/~mec1995/circ/labc3.html

Keep in mind that that website uses 2.45V per cell. That is only good for quick charging, short term connection. For long term slow charging such as what you are doing, use 2.35V per cell.

So without a load, adjust for 6x2.35 = 14.1V as you have said. When the voltage drop across R1 reaches about 600mV, the transistor begins turning on, reducing the voltage, which decreases the charge current. That will be slightly greater than 100mA.

The charge curve: Initially, with current limited to 100mA, voltage across the battery will be less than 14.1V. As it charges, eventually voltage rises to 14.1V and charge current begins dropping.

Keep in mind that 100mA is not a float charge. If you keep it connected for long periods, it will damage a lead acid battery. Float charge is done at a constant voltage lower than the charge voltage, current should be on the order of 1/100th the Ah (amp hour) rating or less.

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: KeithRB on May 28, 2014, 03:59 pm

I don't know if you guys are maybe getting confused. A constant current source means that the device can never draw current above the set limit but can draw any value below the limit. So if I set an LM317 to a constant current source of 100mA the device can never draw above 100mA but can draw 5mA or 20mA or any current bellow 100mA


Don't teach your grandmother how to suck eggs. You are the one who is confused. A constant current source puts out a constant current. You are talking about a current limited source.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 28, 2014, 04:12 pm


I don't know if you guys are maybe getting confused. A constant current source means that the device can never draw current above the set limit but can draw any value below the limit. So if I set an LM317 to a constant current source of 100mA the device can never draw above 100mA but can draw 5mA or 20mA or any current bellow 100mA


Don't teach your grandmother how to suck eggs. You are the one who is confused. A constant current source puts out a constant current. You are talking about a current limited source.


Let's not get personal please? An LM317 wired up with one resistor between the output and the adjustment pin is a current limiting device. I can supply any amount of current as long as it's not above the set limit. Then the thing limits the current and sais " wait now I will not allow more than 100mA" a constant current source is exactly the same thing is it not?
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 28, 2014, 04:24 pm
Why can you not just charge a lead acid battery with a constant voltage of 14.1v until the battery reaches the end end of the "top up" charge. I mean, isn't a bulk charge constant current to just speed things up? I mean, u can charge at a constant voltage it will just take much longer? But who cares if it takes longer? I certainly dont?
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: KeithRB on May 28, 2014, 04:25 pm
You started "making it personal"  by declaring we were confused. You might be starving your constant-current-source LM317 for voltage so that it can't supply the current it wants to. But that is making it a current limit not a constant current.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: Grumpy_Mike on May 28, 2014, 04:33 pm
Quote
Why can you not just charge a lead acid battery with a constant voltage of 14.1v

Because it will then take too much current.

You need a current limiting source until it reaches 14.1V AND then you do not increase the voltage any more.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: JChristensen on May 28, 2014, 04:50 pm

Let's not get personal please? An LM317 wired up with one resistor between the output and the adjustment pin is a current limiting device. I can supply any amount of current as long as it's not above the set limit. Then the thing limits the current and sais " wait now I will not allow more than 100mA" a constant current source is exactly the same thing is it not?


Incorrect.  An LM317 with a resistor between the output and adjustment terminals is a (constant) current source.  That is not the same thing as a current limiter.  Words mean things and these terms have precise meanings in the field.

Since you apparently won't read the datasheet, and continue to argue against what very knowledgeable people here are telling you, try Wikipedia.  In particular, note Figure 8 in the first link:

http://en.wikipedia.org/wiki/Current_source
http://en.wikipedia.org/wiki/Current_limiter

Have an open mind and try to learn the applicable theories.  Rather than continuing to be obtuse and getting all hot under the collar, redirect that energy to the challenge I gave earlier: Design, build and test the thing, then bring it back and bask in the glory of proving us all fools.  The proof is in the pudding, so go make some pudding.
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on May 28, 2014, 05:03 pm

Quote
Why can you not just charge a lead acid battery with a constant voltage of 14.1v

Because it will then take too much current.

You need a current limiting source until it reaches 14.1V AND then you do not increase the voltage any more.


Ok I get what your saying. But if I have a power supply that is 14.1v and supplies a maximum current of 100mA then it will be fine provided the 100mA is not more than 20% of the battery capacity? The charger might just get hot because it's working at its maximum rated capicity?
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: polymorph on May 28, 2014, 08:38 pm
Regular low pressure lead acid cells cannot be charged by simply connecting them to a constant voltage, unlimited current charge.

I answered your questions about using an LM317 as a constant voltage, current limited charger. Including a link to a website that tells you all about charging lead acid cells. Please study it.
http://forum.arduino.cc/index.php?topic=243044.msg1742390#msg1742390
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: cjdelphi on May 29, 2014, 06:22 am


Quote
Why can you not just charge a lead acid battery with a constant voltage of 14.1v

Because it will then take too much current.

You need a current limiting source until it reaches 14.1V AND then you do not increase the voltage any more.


Ok I get what your saying. But if I have a power supply that is 14.1v and supplies a maximum current of 100mA then it will be fine provided the 100mA is not more than 20% of the battery capacity? The charger might just get hot because it's working at its maximum rated capicity?


It's not a great idea maxing out the power supply all the time but as the battwey voltage rises, the current will drop as it approaches 14.2v, if you have a 100ma supply and the battery is rated 1000mah it will take 10 hours constant current, 11 or higher hours at constant voltage...  (as current deceeases nearer to it's charge voltage 14 v)
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: JimboZA on May 29, 2014, 09:08 am

Not difficult at all and as ever, GIYF.


How ironic.... I had to Google what that meant.

Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: fungus on May 29, 2014, 09:48 am


GIYF.


How ironic.... I had to Google what that meant.


That's the idea....

Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: fungus on Jun 01, 2014, 01:33 pm

And I know that efficiency isn't going to be great but these are the only components I have!!! I can't just buy stuff like you guys recommend. I have what I have and I want to use it to make what I need. Even if it isn't the most efficient thing on earth.


My suggestion: Instead of devoting hour and hours of your energy to something that's never going to work very well, devote that time to finding a way to get stuff from eBay.

You must know somebody who can help...
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: calvingloster on Jun 01, 2014, 01:54 pm


And I know that efficiency isn't going to be great but these are the only components I have!!! I can't just buy stuff like you guys recommend. I have what I have and I want to use it to make what I need. Even if it isn't the most efficient thing on earth.


My suggestion: Instead of devoting hour and hours of your energy to something that's never going to work very well, devote that time to finding a way to get stuff from eBay.

You must know somebody who can help...



Dude this is not about stuff! I will spend countless hours on this thing cause the whole point is to learn. I have a battery charger I don't need one, I'm trying to make one so I can learn stuff
Title: Re: LM317 voltage regulator R2 is getting very hot? why?
Post by: polymorph on Jun 01, 2014, 08:57 pm
I've tried to help, using the parts you have. You jumped down my throat and called me Mr Grumpy.

Good luck.