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Noob lead acid batt. charge controler ic

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Goatnutz

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I want to make a charger to stay in my boat i have a solar panel 12-15volt to keep the batt topped off and over winter i want to plug in some wall wart to keep it topped off. Also maybe in the future add some wind power. Did not want some big complex circuit maybe some IC that can do most of it.
 

MikeMl

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LM431 with external transistor configured as a shunt regulator is what I use. One regulator, three different power sources. Shunt regulator means no headroom above the battery float voltage is required. Ideal float voltage for flooded-cell lead acid battery is ~12.9 to 13.1V. Float voltage should be adjusted for ambient temperature, either a pot, or automatically with a thermistor.
 
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Goatnutz

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Thanks

I checked out the PDF for LM431 is one of the "typical applications" in the pdf what you are talking about? Also any good example circuits or reading you can point to?
 

MikeMl

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Yes, this one:
 

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crutschow

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And, of course, the shunt transistor has to dissipate the maximum power that any of the charging sources can generate, so will likely require a power transistor on a heat sink.
 

MikeMl

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The solar panel I am using puts out a maximum of ~250mA at 14V, so the max dissipation is ~4W, which doesn't require a very large heatsink. I found a wall wart which puts out ~300mA @ 14V, so when I want to float the batteries when I have AC available, I substitute the wall-wart for the solar panel.
 

audioguru

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The solar panel I am using puts out a maximum of ~250mA at 14V, so the max dissipation is ~4W, which doesn't require a very large heatsink. I found a wall wart which puts out ~300mA @ 14V, so when I want to float the batteries when I have AC available, I substitute the wall-wart for the solar panel.
You need a battery charger circuit and you need a solar panel and a wall-wart with enough voltage to feed it.

If you connect a DC wall-wart to a battery that needs charging then without anything to limit the current the overloaded wall-wart will blow up or catch on fire.

Your solar panel will have its max output current for only one hour per day. It might take weeks for it to charge a dead battery.
 

MikeMl

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...
If you connect a DC wall-wart to a battery that needs charging then without anything to limit the current the overloaded wall-wart will blow up or catch on fire.
No. By design, wall-warts have pretty loose coupling between the primary winding and the secondary winding (gap in the core?). As part of the UL and CSA certification they have to prove that they can be overloaded without catching fire...:D I have used the one I described for years and it doesn't get particularly hot.

Your solar panel will have its max output current for only one hour per day. It might take weeks for it to charge a dead battery.
Neither I nor the OP said anything about charging a "dead" battery. I use mine to float charge my boat batteries (one for starting, the other is a deep-cycle house battery) while the boat is in dry storage at Lake Powell.

In the summer, daily temperatures there are 100 to 110degF
(42degC), which causes a fully charged flooded-cell lead acid battery to loose ~15% of its charge per month. The average current required to keep up with the self discharge of the battery is on the order of 20 to 100mA, the latter for a battery that is long in the tooth.

The 8W panel I have is more than enough. In the summer, the panel gets 14 hours of sunlight. At winter temperatures, the self discharge rate of the batteries is much less; so less daylight on the solar panel doesn't matter. The boat sits unused for several months at a time, but since I have been using the solar float charger, my battery life has increased from an average of two years to over five.

Its output takes care of a 65 and a 120Ah battery. There is no AC power available where the boat is normally stored. If I haul the boat to my house, I use the plug-in wall-wart as a substitute for the solar panel. Works great.

Another trick I use is to use the boat alternator to "equalize" the batteries while cruising on the lake, since there is no AC power available within miles.. I added a toggle switch to the alternator voltage regulator. In one position, the VR puts out its normal 14.5V; in the other, the VR bumps the alternator output up to 15.7V, which runs the battery voltage high enough to perform an equalization charge. This stirs the acid due to small bubbles rising through the acid thereby preventing statification.
 

audioguru

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Many cheap products come with un-certified (Chinese) wall-warts that get extremely hot normally and catch on fire when shorted.

It is safer when a wall-wart is not overloaded.
 

MikeMl

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Many cheap products come with un-certified (Chinese) wall-warts that get extremely hot normally and catch on fire when shorted.

It is safer when a wall-wart is not overloaded.
I never (intentionally) short a wall-wart.:p Connecting a 12VDC wall-wart to a 12V battery is hardly shorting it. My batteries never get discharged below ~80% of their capacity, which is the use model for a starting battery. The house battery is large enough that my usage doesn't tax it very much.

So when is my wall-wart overloaded? The wall-wart I am using is rated to deliver [email protected] (6W). Its (unregulated) output current naturally falls off to ~300mA at 13V(4W), <[email protected] (0.7W), and its open-circuit voltage is ~15V.

The shunt regulator is set to 13V, so the total wall-wart current is 300mA, about 250mA of which flows to ground through the shunt regulator, the other 50mA into the battery. This is the typical 99%-of-the-time situation

Even if the battery were mostly discharged, as indicated by an open circuit voltage of ~12.0V, the wall-wart would only deliver 100% its rated output of 500mA, all of which is initially going into the battery. The shunt regulator does not begin shunting any wall-wart current to ground until the battery reaches a terminal voltage of just under 13V at which point, the wall-wart is delivering 75% of its rated output.
 
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audioguru

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I have never seen a lead-acid battery charged at only 50mA.
My tiny Ni-MH AAA cells charge slowly at 85mA.
 

MikeMl

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I have never seen a lead-acid battery charged at only 50mA.
My tiny Ni-MH AAA cells charge slowly at 85mA.
I have float charging lead-acid batteries for years. Take my airplane. It has a flooded-cell lead-acid 12V battery. The voltage regulator/60A alternator does a great job of charging the battery (VR is set to 14.25V +- 0.1V for temperature compensation).

Upon returning from a several hour flight, the state of charge of the battery as determined by using an accurate hydrometer is 90% to 100%. The airplane is hangared and sometimes sits for up to three or four weeks before being flown again.

I use a 2A regulated float charger set to 13.10V (winter) and 12.90V (summer). The current is metered. If I plug it in after a flight, the current is zero because the battery voltage is higher than the charger voltage. There is a diode in the charger so that the battery cannot discharge into the charger. It takes ~24 hours before the battery voltage to fall off before any current flows into the battery.

Initially, the current is small, a few mA, and then over the several hours, the current asymptotically settles to a steady-state current which just matches the self-discharge current of the battery. Here is what I see:

Newish 35Ah FLA battery: 50mA
4 year old 35Ah FLA: >120mA, which means replacement soon.
newish 55Ah FLA: 70mA
4 YO 55Ah FLA: 150mA
Newish 100Ah SLA:20mA
five y.o. 100Ah SLA:75-90mA

These depend on ambient temp. The self-discharge rate of all lead batteries is much higher at 85degF than at 45degF.

In the case of the solar charger, it too is metered, and the current drawn by the floated batteries is similar.

Another data point. If I forget to plug in the float charger after a flight, and the airplane sits for say a week, and then I plug it in, here is what happens:

The battery has been self-discharging for a week, during which it has lost some small fraction of its total charge, maybe 1-2%. If I measure the open-circuit battery voltage before plugging in the charger, I would see about 12.60 to 12.65V (depends a little on ambient temp and the age of the battery). When I plug in the charger, it pegs the ammeter at 2A. It takes about 15min for the charging current to begin to taper. It takes several more hours for the current to asymptotically settle to the same steady-state float current as described above; it just approaches the asymptote from the other side.

Now, without float charging, a FLA battery will loose 3-5% of its charge (as measured with a hydrometer) in a month at 70degF. Up to 10% of its charge per month at 100degF (1-2% per month at 40degF). Before I began using a solar float charger, in three months during hot weather (Utah/Arizona border in the red rock desert), the starting battery in the boat would not crank the V8 long enough for the fuel pump to refill the carb bowl (all the fuel evaporates in three months), because it had lost so much of its charge due to self-discharge. Floating fixes that.

It also fixes another problem. If a FLA (or SLA) is allowed to sit with less than about 90% SoC, it grows a hard form of lead sulphate, which don't dissolve. This reduces plate area, and reduces the Cranking Amp Capacity of the battery. The only way to prevent hard sulphates from forming, is to maintain the battery at a SoC >90%. Floating does that because the charge that otherwise would be lost to self-discharge is replaced in real time. Before floating, I was replacing my boat batteries every two years. With the solar charger, I'm getting 4 to 5 years per battery. Note that this is comparable to what you get out of a FLA in a car that is driven daily...

btw- I have been boating on Lake Powell since 1973. I have stored a boat there (in dry storage) for >25 years. I have had various incarnations of the solar charger running there for about 15 years. There is no AC power available where the boat is stored.

ps: This is why I have been boating on Lake Powell for almost 40 years:
 

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marcbarker

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That's very interesting your experience of FLA's and how you've got great longeivity by maintaining SoC above 90% by floating, and how ambient temperature affects self-discharge rate. The length of time before tapering off is probably a neat way of measuring capacity too.

According to my freind Bill Darden who's well upon this kind of thing, there's a long period of time exists between "90 - 100% state of charge", where residual sulphation takes a long while to convert. Apparently in motor cars, it doesn't spend much time there, so the car battery gradually suphates over time. My car is worse, it's an old design (plus car alarm etc) it has a relatively high current drain while parked up, about 8 Ah per week!

You're lucky having a solar battery charger somewhere with bright sunshine. Here in UK there's not much of it here. I conned myself by the marketing hype of company selling "solar powered battery charger, works in all weather conditions" and purchased one. D-shaped black plastic, with rounded edges, about the area of an A4 /letter sheet of paper, terminated in a cigarette-lighter plug, with a flashing LED on it.

When I tried it, it was no more than a solar-powered flashing red LED, that generated all of 50 mA in bright (for UK anyway) sunlight IF I was lucky, cloudy day the flashing LED used all the power. I returned and 2 others as 'faulty' before realising I was conned. Sadly the company that sells them are still conned with a warehouse full of them, but they refuse to accept it, saying it's the same product as their competitors sell (they're right, they are). here's an example


I tackled them about whether it should be more than a "solar-powered flashing LED" and their 'expert' said that the current was "unmeasurable" when they tried it, because he was using an analogue test meter, and that the solar panel produced 'digital current' that can't be measured. It was like talking to a brick wall of brainwashed stupidity so I gave up trying to reason with them! I think it cost more carbon footprint to manufacture it than it would ever generate in its lifetime. I put it side-by-side with a postage stamp size solar cell I was given which outputs more current!!

This I suspect brings us back to the OP, I'll guess he has a similar experience.
 
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