I plan on charging a car battery with a bench power supply with CV and CC modes.
If I set the power supply to say 14V, then short out the leads and set the current limit to _______ then connect the wires to the battery, would that be ok? I mean it won't harm the supply if it can handle the power. I was thinking of putting an inline diode and power resistor (lightbulb?) if the power supply is at risk.
I dunno what charging current to use.. If possible, I want the battery fully charged overnight. Perhaps I just use whatever max current that results from placing a
14V source across the car battery. How do I tell when the battery is charged? Check for gassing? Or stop charging when the current falls off to a certain amount?
Wow.. The $44.99 charger charges at 10 amps (probably up to 10A).
The $114.99 charger is up to 40A (rapid charge in 1-3 hour). Ha! It's got solid state circuitry with silicon diodes for optimum performance..Duh... It's supposed to have that! That might impress Grampa from the tube era. :P
I also noticed some chargers have a 2A trickle current setting.
Yes, that will work. There are different truths when it comes to the correct voltage, though. Some say 13.8, some say 14, some say 14.4, and some say even more than that. To make sure, you must check the manufacturer's data sheet for the particular battery.
Most cars charge the battery to either 13.8V or 14.4V.
It should not. And if it is short-circuit proof, it will certainly not be damaged. If you connect the battery the wrong way, though, you might cause damage. A properly designed power supply should only discharge the battery at the set current, but I have seen some where the regulating freaked out completely when reverse voltage was applied.
No need.
Again, the manufacturer's specs are the correct source of information. But overnight charge is a very gentle charge rate for a car battery, so you'll be safe either way. For a ten hour charge on a 60Ah battery, you'd theoretically need 7.2A charge current. In practice, however, it gets more complicated: The battery will not be fully discharged (car batteries are not designed for that, and will be damaged by it), and the charge current will drop towards the end of the charge cycle.
No. A car battery has extremely low internal resistance. If the battery is somewhat discharged, you could end up with a charge current of 100A or more. Your bench supply will probably not be able to deliver more than 10A or so, so in your particular case, you'd be fine. The generator in a typical small car delivers 30-60A. Most car batteries will handle that.
When the battery voltage reaches the voltage specified by the manufacturer, the battery is fully charged.
You could also check the acid density. The problem is that the acid on a freshly charged battery contains lots of gas, which makes the density reading inaccurate.
No. The battery will start gassing before it is fully charged.
Yes, that is the proper way with a lead-acid battery. When your charge voltage is properly set, the current will slowly fall off towards the battery's self-discharge rate. After a long time, you will have perfect balance between charge rate and self-discharge rate. In this state, you can leave the battery connected forever. In fact, it is the best way to store the battery. Lead-acid batteries decay the slowest when they are fully charged, so keeping them completely charged all the time is good.
In your case, I recommend 14.4V charge voltage, and about 10A current (assuming the battery is about 60Ah). That way, the battery will always be fully charged, and not overcharged in the morning. You can leave the battery connected for days or weeks without damage. If you leave it for very long, you will lose some water. Just add as needed.
For long-time stand-by charge of LA-batteries (such as emergency lights, UPS etc.), 13.8V charge voltage is better, because the water "boils" off much slower, or not at all.
Does it really? Think about how it gets charged when in your car. The alternator does all it can (upto its max current, maybe 80-100amps) to force 14.4volts across the battery terminals. That constantly goes on forever (while the engines running) with no ill effects.
In addition to the other posts: always include a diode in series with a supply when charging a battery. Some power supplies have a crow-bar protection which shorts the output when an overvoltage condition occurs. This may also be triggered when the power supply is overheating (and shuts down).
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...Jim Thompson
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The discharged battery V will be less than power supply dialed to
13.8V. So that's ok. Upon connection to the battery, the bench supply goes from V mode to I mode and the voltage will drop. I think the change from CV mode to CC mode is called 'fold-over' but I only vaguely remember that term.
But if the supply output shorts out upon overheat-shut-down...yikes! If a crowbar kicks in, it's gonna blow something.
Put a fuse in series on the output side between the supply and the battery. The crowbar may be intended to blow the supply fuse. If you diode isolate as others have mentioned, then the extra fuse is not needed. When I do it, I use the diode, set the supply to CV 14.4 with current limited to 2A.
Some worry about diode isolating because the supply can't sense the battery voltage. If that is a concern, you can use a relay to avoid that:
The pushbutton starts the charging, once connections are made. Obviously there are other ways, the above is just illustrative of one.
By the way, it is my understanding that leaving a car battery on even a trickle or float charge "forever" (months on end ?) is detrimental to the battery. Trickle charging it overnight once a month should be sufficient to replace whatever is lost through self discharge if the battery is not used, according to what I have read.
The easy way to do this is to buy (or build) a solar battery charger. Install your power supply in place of the solar cell and use the built in charge control feature to control the charge current and voltage.
One potential problem is that many solar chargers use a shunt regulator across the solar cell. The idea is to minimize the forward voltage drop. This would be a rather bad idea if fed from a bench power supply. Make sure it's a series regulator, probably a PWM modulator type.
As far as I can tell, from the Sunguard-4.5 that I've played with, and from the various docs, Morningstar does NOT use shunt regulators.
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