Electronics > Beginners
Is there a way to safely charge a car battery with this equipment? If not, why?
Simon:
Yea, and all a battery does these days is start an engine which takes less than 50Wh and is quikly replenished.
Nusa:
--- Quote from: Simon on October 20, 2019, 06:47:28 pm ---Yea, and all a battery does these days is start an engine which takes less than 50Wh and is quikly replenished.
--- End quote ---
Under ideal conditions, perhaps. It also has to be able to start a cold engine in adverse conditions. Try it at -18C. 60% of the battery capacity is gone because it's cold. The oil in the engine is a cold thick fluid, so every moving part takes way more energy to move. In fact, that's so important that those are the conditions car batteries are rated under. The CCA (cold cranking amps) is how much current a very cold charged battery should be able to deliver for up to 30 seconds. When it's new.
Now try it at -40C. Yes, I've really had to start vehicles at those temperatures. Better to stay inside if it's not important, to tell the truth. People who deal with such climates regularly have engine and battery heaters. And replace batteries much sooner than those in warm climates.
T3sl4co1l:
Heh, speaking of low car batteries and even lower temperatures -- last year we got some -20 days, one of which I had to go to work on. Well, car wouldn't start the night before anyway, so I took the battery inside and floated it. Next morning put it back in, I guarantee you my room temperature, fully charged battery gave me the easiest start of anyone in the whole city that morning. It didn't seem to bog down from the cold oil at all. ;D
Tim
Simon:
--- Quote from: Nusa on October 20, 2019, 11:27:33 pm ---
--- Quote from: Simon on October 20, 2019, 06:47:28 pm ---Yea, and all a battery does these days is start an engine which takes less than 50Wh and is quikly replenished.
--- End quote ---
Under ideal conditions, perhaps. It also has to be able to start a cold engine in adverse conditions. Try it at -18C. 60% of the battery capacity is gone because it's cold. The oil in the engine is a cold thick fluid, so every moving part takes way more energy to move. In fact, that's so important that those are the conditions car batteries are rated under. The CCA (cold cranking amps) is how much current a very cold charged battery should be able to deliver for up to 30 seconds. When it's new.
Now try it at -40C. Yes, I've really had to start vehicles at those temperatures. Better to stay inside if it's not important, to tell the truth. People who deal with such climates regularly have engine and battery heaters. And replace batteries much sooner than those in warm climates.
--- End quote ---
In which case as Tim mentioned above the battery still charges at less than 14V. I think if a military vehicle can use 27-27.6V (13.5V-13.8V) despite having fuel fired battery and engine heaters for when it's really cold then that's about good enough.
tautech:
Simon, you overlook a couple of things, automotive charging systems have been regulated to 13.8 - 14.2 since forever for FLA 12V batteries and the max voltage any charging system can deliver is also current regulated.
These 2 things control what a charge system can deliver and it's also governed by the SOC of the battery.
All that has changed in recent years is the battery chemistry and the max is more likely 14.4 - 14.5 V these days.
Still, any checks on auto charge systems need be done with a battery with a high SOC so that the charge system is NOT current limiting and then the charge cutoff can be accurately measured.
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