So then, when you act like an expert, post inaccurate and misleading information, you want me to be silent?
Building a battery 12V battery charger
- Thread starter RayInMS
- Start date
Just shut up and listen to Mike. He is an qualified engineer that flies planes.
A bit cryptic at times, but I suffer from that, too.
.
you can button it too mate,You cant even wire an Led up!!
what like that pilot who flew into the Alps in France.
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Well the way of the world is through qualifications, and Mike is probably the most qualified out of all of us. I have 1/3 of an B.SC degree in information technology, but it is only one third! Plus 2-years Tafe college back in 1997 for an trade in electronics (not design)A bit cryptic at times, but I suffer from that, too.
You can't label yourself an expert. It is up to others to decide if you are an expert or not.
you can button it too mate,
Mate I have reported your PMs to the moderators. Expect a ban, especially if I put some money on the table to have you removed.
What about SgtWookie's circuit (http://forum.allaboutcircuits.com/attachments/bill-sla-float-charger-temp-compensated-png.21844/) from 2007?
Has anybody put together a better 12V float charger since that one?
Has anybody put together a better 12V float charger since that one?
I was looking at this yesterday. What is the value of R2 (the pot)? Is it 500Ω with the wiper set to about a midpoint (.42)? Is that how I should interpret the schematic?
Yes, R2 is a 500 Ohm trim pot set approximately halfway.
The circuit is OK for maintaining a floating voltage on a SLA, VRLA or AGM 12v battery.
There are multiple lead-acid charge controller ICs on the market, but I'd be more likely to design a charger using a microcontroller with a switching supply.
The circuit is OK for maintaining a floating voltage on a SLA, VRLA or AGM 12v battery.
There are multiple lead-acid charge controller ICs on the market, but I'd be more likely to design a charger using a microcontroller with a switching supply.
The laptop brick I have for a supply is 19.5 V @ 4.7 A. I'm assuming this supply would be appropriate for the circuit you posted? Its parameters are OK? Would I need to change any components?
I've been reading a lot of your old posts on this topic, and had been planning on building that circuit. But in an earlier discussion, you mentioned that this circuit was a "lowest common denominator", and that there are better options available. And now you're suggesting a different solution.
I get the impression that you absolutely know what you're talking about, and I have learned a lot just from reading some of what you have contributed; so I would like to know what your "ideal" 12v SLA float charger would be.
I have done a lot of electronics repair -- but not design. I have a slightly better than basic understanding of what's going on, but am completely lost when it comes to drawing-up a circuit from scratch. Do you find the components, and then build a circuit around them, or engineer the concept and then adjust it as you find the parts to fit?
When you say "a microcontroller with a switching supply", are you referring to a controller chip that includes a supply, or two separate items? Is there one that you would recommend? Do you have any already in use? Are there any that you know should be avoided?
I am looking to prolong the life of a 9-year-old Interstate MTP-75 12VSLA car battery that's in a 17-year-old truck that only gets driven a few times each month. This battery works perfectly most of the time, but fails to start the truck when the temp drops below about 20F. It then works again after removing the battery and charging it indoors overnight.
Ideally, I would like to find a solution that could also be used to maintain -- and resuscitate -- some other smaller 12V SLAs that are used for small UPS, alarm system, and car booster box.
Thanks for any input you may have; and thank you very much for all the great information you have already posted over the years.
-Phil
I'm in the middle of a number of projects now, so my replies won't be very rapid, as my time on here is limited.
By "lowest common denominator", I was inferring that the components shown in the schematic (like the regulator and the 2N3904 transistor) have been around for many, many years and staggering numbers of them have been made, so they are easily available everywhere on the planet. The LM317 has a rather large dropout voltage (minimum voltage difference between the input and the output) so that the power dissipation is higher than more modern regulators, but the more modern regulators may have stability issues, requiring careful selection of output capacitors.
There are linear ICs available specifically for lead-acid battery maintenance which provide more advanced features (bulk charging and equalization in addition to topping charge and float charge) and digital versions which can result in higher efficiency at the cost of somewhat additional complexity, along with programming requirements. Switching supplies can be tough for beginners, as you really need at least an oscilloscope to troubleshoot them; and very few start off with a bench full of test equipment and know how to use them.
If your battery is 9 years old, it's survived probably twice as long as most people's car batteries. I get 6 or 7 years out of them, but after a certain point it's not worth the trouble/inconvenience caused by having a vehicle that is not reliable. I live way out in the boonies; the nearest gas station is a 20-minute drive.
Lead-acid battery capacity is affected by the internal (core) temperature; as the temperature increases, chemical activity increases, and so does battery capacity; conversely, the "fully charged voltage" decreases - that is why temperature compensation is important. Continually overcharging a lead-acid battery will shorten it's service life. However, periodic "equalization charging" will stir the electrolyte and help remove sulphation from the plates. Equalization charging is basically a brief repeat of the "bulk charge" phase, but on a periodic basis.
While increasing the core temp increases the battery capacity, it decreases the service life due to the increased chemical activity.
Here: Battery %Charge Vs Core Temperature
As you can see on the chart, when the core temp drops to about 20°F, your battery capacity is decreased by nearly 1/3 - and your battery is ancient to begin with. If you're determined to keep using that battery, then you need to figure out how to keep it warm during the cold periods, and keep it float charged.
Getting back to an "intelligent" charger...
There are a number of different possible stages of charging:
1) Pre-charge: if the cell voltage has dropped below about 1.9v (11.4v for a 12v battery) at 77°F/25°C then the battery is considered completely discharged, and should be charged at a low current until the battery voltage increases to around 12v. If the battery voltage is below 11v, the battery may have a shorted cell.
2) Bulk charge: the battery is charged at a fixed current until a threshold voltage (14.2v-14.5v) is reached.
3) Topping charge: the battery is charged at a fixed voltage (around 13.9v-14.1v) until the charge current drops below a threshold value.
4) Float charge: the battery voltage is maintained at about 13.4-13.7v
5) Equalization charge: periodically, the Bulk Charge phase is repeated to stir the electrolyte and remove plate sulphation.
The bulk charge and equalization charge phases can significantly raise the core temp of the battery; if the battery is cold to begin with, that's good. If it's warm to begin with, further increases aren't so good. Charging at C/10 or less will help to minimize the core temp increase.
There are also "desulfator" circuits, which I've used with some successes, having revived a few riding lawnmower batteries that were ready for the salvage yard. I've posted one or more of these circuits on here; Alistair Cooper (sp?) came up with the idea originally a number of years ago. The version I made used an N-channel MOSFET instead of a P-channel, still 555 timer based; and had provisions for float charging while desulfating. These desulfator circuits don't show results overnight; it took over a month to restore a heavily sulfated battery that was down to 0% specific gravity in three cells, back to normal in all cells. MikeML prefers to use the equivalent of an equalization charge to remove plate sulfation. While the equalization charge would remove the plate sulfation in a much more rapid manner, it will also increase the core temperature of the battery. A battery with the core temperature at 55°c has 1/3 the service life of a battery with a core temp of 25°c. A desulfator won't significantly change the battery core temp.
Here's an application note on a lead-acid charger using a Microchip PIC16HV785:
http://ww1.microchip.com/downloads/en/AppNotes/01015a.pdf
Digikey stocks that PIC: http://www.digikey.com/product-detail/en/PIC16HV785-I/SS/PIC16HV785-I/SS-ND/1098727
but that's in a SSOP package, which would be difficult for a new hobbyist to use. They ARE available in DIP and SOIC packages.
By "lowest common denominator", I was inferring that the components shown in the schematic (like the regulator and the 2N3904 transistor) have been around for many, many years and staggering numbers of them have been made, so they are easily available everywhere on the planet. The LM317 has a rather large dropout voltage (minimum voltage difference between the input and the output) so that the power dissipation is higher than more modern regulators, but the more modern regulators may have stability issues, requiring careful selection of output capacitors.
There are linear ICs available specifically for lead-acid battery maintenance which provide more advanced features (bulk charging and equalization in addition to topping charge and float charge) and digital versions which can result in higher efficiency at the cost of somewhat additional complexity, along with programming requirements. Switching supplies can be tough for beginners, as you really need at least an oscilloscope to troubleshoot them; and very few start off with a bench full of test equipment and know how to use them.
If your battery is 9 years old, it's survived probably twice as long as most people's car batteries. I get 6 or 7 years out of them, but after a certain point it's not worth the trouble/inconvenience caused by having a vehicle that is not reliable. I live way out in the boonies; the nearest gas station is a 20-minute drive.
Lead-acid battery capacity is affected by the internal (core) temperature; as the temperature increases, chemical activity increases, and so does battery capacity; conversely, the "fully charged voltage" decreases - that is why temperature compensation is important. Continually overcharging a lead-acid battery will shorten it's service life. However, periodic "equalization charging" will stir the electrolyte and help remove sulphation from the plates. Equalization charging is basically a brief repeat of the "bulk charge" phase, but on a periodic basis.
While increasing the core temp increases the battery capacity, it decreases the service life due to the increased chemical activity.
Here: Battery %Charge Vs Core Temperature
As you can see on the chart, when the core temp drops to about 20°F, your battery capacity is decreased by nearly 1/3 - and your battery is ancient to begin with. If you're determined to keep using that battery, then you need to figure out how to keep it warm during the cold periods, and keep it float charged.
Getting back to an "intelligent" charger...
There are a number of different possible stages of charging:
1) Pre-charge: if the cell voltage has dropped below about 1.9v (11.4v for a 12v battery) at 77°F/25°C then the battery is considered completely discharged, and should be charged at a low current until the battery voltage increases to around 12v. If the battery voltage is below 11v, the battery may have a shorted cell.
2) Bulk charge: the battery is charged at a fixed current until a threshold voltage (14.2v-14.5v) is reached.
3) Topping charge: the battery is charged at a fixed voltage (around 13.9v-14.1v) until the charge current drops below a threshold value.
4) Float charge: the battery voltage is maintained at about 13.4-13.7v
5) Equalization charge: periodically, the Bulk Charge phase is repeated to stir the electrolyte and remove plate sulphation.
The bulk charge and equalization charge phases can significantly raise the core temp of the battery; if the battery is cold to begin with, that's good. If it's warm to begin with, further increases aren't so good. Charging at C/10 or less will help to minimize the core temp increase.
There are also "desulfator" circuits, which I've used with some successes, having revived a few riding lawnmower batteries that were ready for the salvage yard. I've posted one or more of these circuits on here; Alistair Cooper (sp?) came up with the idea originally a number of years ago. The version I made used an N-channel MOSFET instead of a P-channel, still 555 timer based; and had provisions for float charging while desulfating. These desulfator circuits don't show results overnight; it took over a month to restore a heavily sulfated battery that was down to 0% specific gravity in three cells, back to normal in all cells. MikeML prefers to use the equivalent of an equalization charge to remove plate sulfation. While the equalization charge would remove the plate sulfation in a much more rapid manner, it will also increase the core temperature of the battery. A battery with the core temperature at 55°c has 1/3 the service life of a battery with a core temp of 25°c. A desulfator won't significantly change the battery core temp.
Here's an application note on a lead-acid charger using a Microchip PIC16HV785:
http://ww1.microchip.com/downloads/en/AppNotes/01015a.pdf
Digikey stocks that PIC: http://www.digikey.com/product-detail/en/PIC16HV785-I/SS/PIC16HV785-I/SS-ND/1098727
but that's in a SSOP package, which would be difficult for a new hobbyist to use. They ARE available in DIP and SOIC packages.
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Wow! That's a lot of writing (/typing) for somebody with no time.
Thank you so much for all the info. It really is very helpful.
When you previously posted about the LM317, I thought you were saying that you selected it solely because of its availability, and that there might be better options available (at least in the U.S.). I now understand that it’s not only widely available, but much easier to work with than other solutions. I used to have an o-scope and tons of other equipment at my bench when I worked in an electronics repair shop, but I’m not there anymore and no longer have quick access to them; so I guess the 317 is my best bet for a charger.
Over the years, I have found that a fresh Interstate battery (bought from a local auto repair shop) works better – and lasts considerably longer – than any other brand I’ve tried. This one has been going strong (in the North-East, U.S.) until lately, and I get the impression that a little TLC might get a few more years out of it.
Since it’s only an issue when trying to start the truck after it sits for a few days or more in the cold, but starts easily after fully charging, I think float charging it may work even outside – especially if I can desulfate it enough to increase its capacity a little first.
I initially found this site while searching for a desulfator schematic, and was planning on building the one you posted until I read some of the comments from MikeML and others, that said it was less effective – and significantly slower – than an equalization charge.
Now you have me back to thinking about the desulfator circuit that I had previously abandoned (although I’ll still need a float charger to use with it).
Yeah – that’s a little more complicated than I’m ready to deal with right now. Maybe someday….
So, basically, I’m back to planning on building your LM317 float charger and your desulfator to use together. This sounds like the safest, and simplest solution for my car battery. Is there any reason not to also use the same circuits for smaller SLAs? I have several small UPS batteries, as well as some from a home alarm system, emergency lighting, and a portable jump box that could also use some help.
Thanks again for all your valuable input – and for the time you share with us in order to help out.
And thank you for your service! This great nation would be nothing without those who volunteer to put themselves in harm’s way to protect our way of life.
-Phil
Thank you so much for all the info. It really is very helpful.
When you previously posted about the LM317, I thought you were saying that you selected it solely because of its availability, and that there might be better options available (at least in the U.S.). I now understand that it’s not only widely available, but much easier to work with than other solutions. I used to have an o-scope and tons of other equipment at my bench when I worked in an electronics repair shop, but I’m not there anymore and no longer have quick access to them; so I guess the 317 is my best bet for a charger.
Over the years, I have found that a fresh Interstate battery (bought from a local auto repair shop) works better – and lasts considerably longer – than any other brand I’ve tried. This one has been going strong (in the North-East, U.S.) until lately, and I get the impression that a little TLC might get a few more years out of it.
Since it’s only an issue when trying to start the truck after it sits for a few days or more in the cold, but starts easily after fully charging, I think float charging it may work even outside – especially if I can desulfate it enough to increase its capacity a little first.
I initially found this site while searching for a desulfator schematic, and was planning on building the one you posted until I read some of the comments from MikeML and others, that said it was less effective – and significantly slower – than an equalization charge.
Now you have me back to thinking about the desulfator circuit that I had previously abandoned (although I’ll still need a float charger to use with it).
Yeah – that’s a little more complicated than I’m ready to deal with right now. Maybe someday….
So, basically, I’m back to planning on building your LM317 float charger and your desulfator to use together. This sounds like the safest, and simplest solution for my car battery. Is there any reason not to also use the same circuits for smaller SLAs? I have several small UPS batteries, as well as some from a home alarm system, emergency lighting, and a portable jump box that could also use some help.
Thanks again for all your valuable input – and for the time you share with us in order to help out.
And thank you for your service! This great nation would be nothing without those who volunteer to put themselves in harm’s way to protect our way of life.
-Phil
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Sorry Ray. I didn't mean to interrupt. Does anybody have an answer to this question that may have been overlooked due to my posting immediately after it?
I think somewhere in the thread it was said (or maybe implied?) that laptop bricks like mine OK for this application. Suitable current range (though way more than the LM 317 can handle!), enough voltage potential to cover the LM 317's drop, and some room to spare (hence the 500 Ω trimmer pot). I'll be working on the circuit that Sgt. Wookie posted for the next couple of months (can only do it in my spare time) as well.
