Sealed lead acid batteries and voltage?
Gerard
I just took delivery of 4 12V 12AH sealed lead acid batteries which I plan to use for my child's electric go kart (which I am the process of gathering parts for).
I checked their voltages when I unpacked them and they are all around 12.7 to 12.8 volts.
I've read that a fully charged 12 volt SLA batteries should read closer to 13.8 volts.
I have chargers on order but don't expect them to arrive for 3 or 4 weeks.
So, should I be concerned and buy a charger locally to get then fully charged a.s.a.p?
Or is 12.8 volts OK to leave on the shelf for a while?
I only ask because what I've read suggests that some care goes a long way to extending the life of what is a not totally inexpensive item.
Thanks in advance for any advice.
Cheers
Gerard
Kean Maizels
Gerard,
You won’t generally see a 12V SLA near 13.8V unless it is connected to a trickle/float charger.
For a 12V SLA that has been sitting idle, an open circuit voltage of 12.7V+ is perfectly acceptable (2.12V+ per cell).
A voltage below 12.6V (approx 2.07V per cell) will lead to sulphation (which is bad!).
Typical charging voltage would be 13.7V for trickle/float charge, or 14.7V for cyclic use.
Once fully charged, and disconnected from the charger, the battery will soon drop to around 13.2V-13.4V, and over time return to about 12.7V.
The voltages above are based on 25°C ambient – slightly higher charge voltages at lower temps.
So everything is fine, and I wouldn’t rush to charge them. If you are concerned enough, you could top them up a bit through say a 4.7 ohm to 27 ohm resistor from a 15V-16V power supply for a few hours to a day. But don’t overcharge, as that is bad too.
There should be a date code stamped on the battery – typically YYMM or YYMMDD format. Ideally you don’t want to buy a new battery that has been on the shelf more than about 6 months (maybe 12 max). Even less in a hot climate/environment, as that increases the self discharge rate.
To actually test a battery is in good nick, you need to measure the internal resistance – or better, run an actual load test (after charging).
Kean
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Gerard
Thanks for that.
I bought a charger (another one, when I consider the 4 I have on order) and hooked up a battery, which very quickly (less than and hour) switched the charger to trickle mode.
The battery dropped from 13.2 ish volts to 12.75 ish after a few hours off the charger.
It's held the 12.75 volts for a day so far so guess it's OK.
I suspect my ordering of 4 1350 mA chargers was a bit of an unnecessary overkill. Such is life, anyone at the space interested in 12V 1350 mA SLA chargers?
As to trickle charging, would it be OK to keep the batteries on trickle charge permanently when they are being stored, or is that going to damage them?
Thanks for you comments.
Gerard
On Friday, August 2, 2013 6:19:10 PM UTC+10, Kean Maizels wrote:
Gerard,
You won’t generally see a 12V SLA near 13.8V unless it is connected to a trickle/float charger.
For a 12V SLA that has been sitting idle, an open circuit voltage of 12.7V+ is perfectly acceptable (2.12V+ per cell).
A voltage below 12.6V (approx 2.07V per cell) will lead to sulphation (which is bad!).
Typical charging voltage would be 13.7V for trickle/float charge, or 14.7V for cyclic use.
Once fully charged, and disconnected from the charger, the battery will soon drop to around 13.2V-13.4V, and over time return to about 12.7V.
The voltages above are based on 25°C ambient – slightly higher charge voltages at lower temps.
So everything is fine, and I wouldn’t rush to charge them. If you are concerned enough, you could top them up a bit through say a 4.7 ohm to 27 ohm resistor from a 15V-16V power supply for a few hours to a day. But don’t overcharge, as that is bad too.
There should be a date code stamped on the battery – typically YYMM or YYMMDD format. Ideally you don’t want to buy a new battery that has been on the shelf more than about 6 months (maybe 12 max). Even less in a hot climate/environment, as that increases the self discharge rate.
To actually test a battery is in good nick, you need to measure the internal resistance – or better, run an actual load test (after charging).
Kean
Kean Maizels
Depends on the specific battery and trickle current whether the charger will be a problem (i.e. overcharging). If it does switch to trickle mode, then it should be OK – just measure the voltage occasionally to ensure it is no more than about 13.8V (or less than 12.7V). Unlike some other battery technologies (especially Lithium), SLAs prefer to be kept full while in storage.
I’ve got a bunch of 5 year old SLA batteries, which I just happened to be testing last week. The ones that were in a UPS, and thus were on constant charge, are mostly still good - a few now have high internal resistances, all have lost capacity. Others that I left on the shelf and forgot to charge occasionally are now pretty much stuffed.
Kean
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