Electronics > Beginners
Is there a way to safely charge a car battery with this equipment? If not, why?
Simon:
--- Quote from: Yansi on October 20, 2019, 10:19:11 am ---No, you don't understand, nor know.
Car alternator output is usually set to about 14.4V. There is no point in charging using 13.5 or 13.8V. That would take for ages to charge the battery.
You 5-10A charging current limit is just a silly talking. Alternator is like "zero fucks given" to your current limits.
--- End quote ---
why does the alternator need to charge the battery that much? the battery is only used to start the engine and if the power demand is in excess of the alternator. The alternator will have a current limit but that is not what controls the battery charging it is to protect the alternator. The charge is controlled with the voltage and hene it is NOT 14.4V, go and measure your own vehicle if you don't beleive me!
Yansi:
Why not you go first then?
Yansi:
https://www.w8ji.com/battery_and_charging_system.htm
:popcorn:
Simon:
i did! i recently measure the output of a bus! even though it has a ot to drive the alternator is set at 27V or 13.5V per battery. Same for a tank i measured the supply voltage on: 27V / 2 - 13.5V last time I measured my car: 13.5 to 13.8V.
T3sl4co1l:
FYI, last time I went through this (floating my car battery to top it up) I set it to 14.3V and went from about 20A initially down to a few 100 mA after 24 hours. This is a little high for a proper (always-on) float, but fine for this duration, and as you can see there was very little if any overcharging.
Electrolysis starts at higher voltages; you can't really charge much faster (than whatever the peak rate is, C/2 or thereabouts?) because the plates load up with bubbles, greatly increasing resistance. Dangerous, anyway (H2+O2).
OCV is around 13V and the extra voltage is required for charging, to overcome the overpotential of the electrode materials. Basically the overpotential consumes charge efficiency: you have to charge so-and-so above the electrochemical potential to make anything happen, and the difference is lost as heat.
Which is what makes lithium ion so amazing, there's essentially no overpotential and the cell voltage is entirely due to concentration of ions in the electrodes. So the charge and discharge efficiency is super high, it looks like a crummy nonlinear capacitor more than a cell.
Tim
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