# SLA battery charging voltage

Discussion in 'Homework Help' started by bug13, Aug 13, 2012.

1. ### bug13 Thread Starter Well-Known Member

Feb 13, 2012
1,210
38
Hi guys

Just wondering if I connect a 13.5V DC power supply to a 12V SLA battery with a dc meter reading 12v open circuit, what would be the meter's reading?

Another question is can I charge greater than the supply voltage? say I am charging a battery with a 12V dc, can the battery be charged to over 12V?

I am asking this as I am going to work on a smart solar SLA battery charger. I got this question after read the first graph here .

I am not sure about the relationship between current and voltage of a SLA battery during charging.

Hope I am making sense here, if not, please ask me to clarify it.

Thanks

Zhuhua

Last edited: Aug 13, 2012
2. ### MrChips Moderator

Oct 2, 2009
12,622
3,451
Do you mean the battery reads 12v or the power supply reads 12v?

If the power supply is set to 13.5VDC, the voltage across the battery being charged will start at 12V and gradually increase to 13.5V. The current will start off at a high value and gradually decrease to a low value, if not zero.

(If the power supply is set to 13.5V, the power supply will hit its current limit for the first stage of charging and hopefully the voltage will drop to the battery voltage - otherwise you could damage the battery.)

13.5V is perhaps too low to fully charge the battery. I would increase it to 14V to 14.5V.
After the current drops the float charge voltage can be lowered to 13.5V.

3. ### bug13 Thread Starter Well-Known Member

Feb 13, 2012
1,210
38
I meant the battery reads 12v open circuit.

Thanks for your reply, you have answered my question

So another question, during the SLA battery getting charged, as long as I set the supply voltage to 14.5v, all I need is to monitor the charging current and I can tell the state of the charging? Is that correct?

Zhuhua

4. ### MrChips Moderator

Oct 2, 2009
12,622
3,451
I would also monitor the battery temperature and the time. If the temperature gets too high or the battery takes too long to charge I would stop charging.

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