Most of the posts I've seen that describe using a diode (Schottky or otherwise) when installing a small Sealed Lead Acid (SLA) avionics backup-battery never mention using a resistor to control the SLA charge current. Is it because the diode is going to limit the current (or fry) and not harm the battery or is there some other reason?
By way of example with some simplified assumptions and a 7.5 Ah battery...
Assume charging voltage or 14V (ignoring voltage drop across diode )
Battery voltage down to about 12V
Desired charging current 1.5A (that's 20% of 7.5)
E=IR => 2v / 1.5A = 1.3 Ohms
P=EI => 2v * 1.5A = 3 Watts
So, right around a 1 ohms / 3 watt resistor would be called for.
Of course, the math changes somewhat if the SLA is more discharged.
What am I missing / misunderstanding?
Thanks in advance,
Rob
RV-7A
N706DR
By way of example with some simplified assumptions and a 7.5 Ah battery...
Assume charging voltage or 14V (ignoring voltage drop across diode )
Battery voltage down to about 12V
Desired charging current 1.5A (that's 20% of 7.5)
E=IR => 2v / 1.5A = 1.3 Ohms
P=EI => 2v * 1.5A = 3 Watts
So, right around a 1 ohms / 3 watt resistor would be called for.
Of course, the math changes somewhat if the SLA is more discharged.
What am I missing / misunderstanding?
Thanks in advance,
Rob
RV-7A
N706DR