Smart Battery Chargers

Yes, you're right Terry.
When a Smart Charger considers a battery fully charged it switches to "Float Mode" which maintains the voltage at typically 12.4 to 13.6 volts.
At this voltage the charger will only contribute current if there is any need due to battery self-discharge. The charger can remain connected to the battery indefinitely in this mode.

To be a bit picky, the charger will typically go to float when the battery is only accepting around 0.5A. Now, how full of charge that is is debatable, but I have found that by leaving my van batteries ( AGM 3 X 120 a/h ) on float for at least a day or more gives them a deeper charge than just disconnecting not long after going to float.
As an example, when 1st arriving at camp, the batts will be approx 13V ( resting ) and only running a fridge, will be down to around 12.7 (resting ) after approx 6hrs.
If the batts have been floated for a few days, that voltage will be up around 12.9 after 6hrs.
Have seen this difference many times, and while some will say 0.2V is nothing, it can make a big difference by the end of a long weekend with no solar input.

As Gronk wrote, the charger switches to float mode when the current drops to a pre determined level, when forced charged at a high voltage this is around the 97% SOC mark, they actual SOC being determined by the size of the battery and its state of health.

When the voltage reduces to the float value the surface voltage of the battery will drop a little and the battery opposition to the charging current will drop and the battery will continue to accept a charge, hence why they call it float charge.

You can see this if you monitor the charge voltage just before the charger goes to float mode, you may see 500ma flowing, disconnect the charger for a minute or so and then reconnect it and you'll see the current jump up into the amps range for a short duration.

The battery may take hours, days or longer to get to 100% charged mark, most consider it fully charged though when the charger reverts to float mode.

Personally I don't leave my batteries on permanent float, even at float voltages they still gas slightly and when charged 24/7 for weeks/months/years on end this causes loss of electrolyte. Telcos use float voltages at the lower side of the float range to reduce battery maintenance, they still have to periodically top up the batteries.

My chargers are connected to time clocks, they run for 30 minutes a day and that's enough to keep the fully charged even with the vehicles constant drain.

.
Well yes, it is being a bit "picky".
I gave Terry a simple but adequate answer.........
"When a Smart Charger considers a battery fully charged" etc. I can see no reason to lecture on precision and detail which can only confuse a layman.
'Technoprecision' is of no value to him.

Thanks Allan. Seems to be common here. People over complicate things.
Gronk so after 6 or so hours of running your fridge you disconnect your battery, wait for an hour or so and check the voltage and you keep accurate enough records to know there is a .02 difference in voltage if your battery has been on float for a few days as opposed to only hitting float that day. To put it crudely I think you might be tugging something.

To put it not crudely a difference of .2v in Gronks example implies his charger goes to float at about 80% charged. I thought that was about when the absorption phase kicked in. Perhaps the little lights or whatever are misleading.

Yes it may have been a bit technical but at least it was correct!

Simplify if you feel like it but correcting with incorrect information helps no one,
the following statement is simply not correct even ignoring the 12.4V:

"When a Smart Charger considers a battery fully charged it switches to "Float Mode" which maintains the voltage at typically 12.4 to 13.6 volts.
At this voltage the charger will only contribute current if there is any need due to battery self-discharge. The charger can remain connected to the battery indefinitely in this mode."

To quote a battery manufacturer:

"The two broad types of small, portable chargers available today are classified as either automatic or manual. Automatic chargers can be further classified as those that charge the battery up to a certain voltage and then shut off and those that charge the battery up to a certain voltage and then switch to a lower float (trickle) voltage. An example of the first type of automatic charger is one that charges a battery up to 14.7V, then immediately shuts off. An example of the second type of automatic charger would bring the battery up to 14.7V, then switches to a float (trickle) voltage of 13.6V; it will stay at that level indefinitely.

The second type of automatic charger is preferred, because the first type of charger will undercharge the battery."

Clearly the manufacturer is indicating that the battery reaches a fully charged by the trickle charge stage and if this is immediately ended the battery will be under charged. As I previously posted, this could take hours/days/weeks depending on the size of the battery.

The fact that most consider the battery to be fully charged when the charger switches to float charge doesn't make it so.

.

Sorry Leigh, that "12.4V" was a miss-type. Clearly it should have been 13.4V
I don't see that your "battery manufacturer" statement negates what I said which I maintain is simply correct in the context of the subject. And the operative word there is "SIMPLY". (the actual specific voltage is related to battery type and charger brand and you would know that)

Terry asked a simple question and got a simple and adequate answer from me but then the scholarly expressions begin which Terry acknowledged as confusing and common on this forum.

There are many on this forum who seek simple & practical answers but the thread often dissolves into responses that are peppered with un-necessary detail and precision gauged more to exhibit superior intelligence than to providing a understandable response to the enquirer. These discourses belong in the Halls of Learning, not on a forum of non-technical persons who just want things to work simply and effectively.

A couple of years back Collyn Rivers gave up and quit this forum due to the frustrations of squabbles with those seeking to challenge his practical wisdom which was adequate to form the content of his published books. His expressions were technically correct yet within the comprehension of laymen and without academic grandstanding. We are poorer without him here.

To put it simply....... can we please knock off a couple of decimal points for the benefit of the average bloke?

Accepting that a wet cell battery will need the electrolyte topped up at certain intervals if left connected to a trickle or "smart" charger permanently i.e. months or perhaps years.
How about an AGM or even a gel cell battery? Is there any advantage or disadvantage or preferred method?
Assuming a battery is in good condition and only loses charge to normal inherent discharge, is there any reason some form of trickle, say 0.5v or thereabouts, charging should be disconnected periodically or just left connected.

In simple terms are you shortening your battery life by using either method as opposed to the other??

Cheers
Pop

neapop2jocem

I already expressed my feelings regarding this above, trickle charging or float charging is just what it states, a slow charge. The battery needs to sit on float charge for sometime to reach a fully charged state if that is what's desired. Once the battery approaches fully charged it will gas, the degree of gassing being determined by battery construction, temperature and the charging current etc.

I have found small sealed lead acid batteries being constant float charged seldom last more than a couple of years. Many moons ago I tried using flooded motor cycle batteries but found after a couple of years the electrolyte had all but disappeared.

The problem with sealed batteries ie recombination batteries is they can only recombine during a charge discharge cycle, if you leave them float charging for long periods of time they will gas. Battery manufactures generally state that charge voltages aren't a big issue with AGM's being able to tolerate normal charge voltages for up to 24 hours and more once fully charged. However they all also indicate that float charge voltages become critical when the batteries are float charged 24/7 and even minor deviations form recommended float voltages can have a severe impact on battery life yet how many consumer chargers have an adjustable float setting?

I have found that having my charger/s on a time clock that run for around 30 minutes a day works well for me where the batteries aren't being used apart form supplying the parasitic loads of a modern vehicle.

Thanks HKB,

Just as a matter of interest my "Smart Charger" does have selectable float voltages.

13.2v 13.5v and 13.8v

This 30 amp charger is connected to a pair of 105 AH DC AGMs and seems to have kept signs of life in both for some 7 years. A test I did recently showed that they have around 75 to 80% of useful charge carrying ability left. I thought that after 7 years that wasn't too bad. I have used the regime of switching the charger off and on as required, however I wasn't sure if this was the optimum method to keep them going a bit longer.

Cheers
Pop

Thanks Allan. Seems to be common here. People over complicate things.
Gronk so after 6 or so hours of running your fridge you disconnect your battery, wait for an hour or so and check the voltage and you keep accurate enough records to know there is a .02 difference in voltage if your battery has been on float for a few days as opposed to only hitting float that day. To put it crudely I think you might be tugging something.

You obviously didn't read what I wrote. What you explained above is nothing like what I wrote, but seeing as you are an expert , I'll refrain from answering again.

A couple of years back Collyn Rivers gave up and quit this forum due to the frustrations of squabbles with those seeking to challenge his practical wisdom which was adequate to form the content of his published books


It appears as though someone wants to think his "wisdom" shouldn't be questioned either ??
I didn't disagree with you, I just pointed out that when a charger goes to float, the battery isn't fully charged !
Now, 95% is good enough for some, but I'll leave it at that !

Pop,

80% after seven years is pretty good, I wouldn't change anything.

Some of you grizzlers need to settle down a bit, if it upsets you that much skip the post!

I learnt something and that is to charge with my smart chargers for 30 minutes a day, makes sense now I've heard it.

Thanks HKB.

Yes its an auxiliary battery, in the Alko box. Supposedly charging while driving. It did charge last year when I picked up the van. Did two 600 km drives and it charged up.
Only gone flat these last few months sitting in the carport.

I've found that with the roadworks on the North Coast, sitting in traffic with the footbrake on fairly often, that seems to draining the battery.

The smart charger did light up the fully charge button after a few more hours of float, so my question may have been answered.

Won't see my lecky for a couple of months so will have to monitor it closely.

Thanks for the help

bill

Quote: "I've found that with the roadworks on the North Coast, sitting in traffic with the footbrake on fairly often, that seems to draining the battery." Unquote.

This statement has REALLY got me confused????

The only logical reason I can think of for that to happen is that you are referring to a caravan-mounted battery pack which has the caravan brakes attached to it. Of course, that shouldn't be the case....electric caravan brakes are (should be!!) powered from the vehicle's main battery/ies and should have no effect on the caravan "house" power. Another possibility is that is being asked to supply power to a 3-way fridge.

I think we need more info from the OP to be able to answer this riddle fully and succinctly. I'm not going to get into the relative merits of chargers and SOC etc....that has been more than covered in full already.

However, for what it's worth, I always leave my C-Tek 25amp smart charger ON all the time whenever there is 240v available (for the batteries in the Chevy) and often do the same for the 4x 100amp batteries in the caravan too....but there are also 4 solar panels which do tend to keep the van batteries fully charged. In short, don't feel that you MUST turn the smart charger off when "float" level is achieved.....it is quite okay to leave the charger ON all the time.

Roachie

Can only back up what Roachie has said. I have two 120 amp full river batteries in my ute continually charged through a cheap mppt regulator.They run two trailblazer fridges when we camp etc. I replaced them at 10 years old and put the old ones in our van. I removed one of them in the van for our latest trip north and after 9 weeks sitting in the shed it reads 12.9 volts. The single battery in the van still reads between 12.6 and 12.8 in the morning before the sun is up on the panels after running the lights and dvd player the night before. Cant ask for more than that. Both the reg in the ute and in the van float at 13.8 and are never disconnected. The newer batteries in the ute rarely get below 12.7 running both fridges overnight with one used as a freezer. Both draw around 5 amps running but have very efficient run times.
cheers Graeme.