Charge 2 x 6V on 12V Charger

I was thinking of flooded batteries, but of course 6v units are often SLA. Its not hard to add a drop or 2 of distilled/deionised per cell though.

Yes it is, see below

overcharge happens on the first charge cycle only. That much doesnt dry a battery out.

usually not very practically useful

few end users are willing to.

NT

"John Fields"

... Phil

(...)

Pull the other one. :)

(...)

The series batteries are unlikely to equalize on the first charge. I don't think they would equalize at all. As Ed mentioned yesterday afternoon, one of the batteries is likely to fail. That would be the one with the lower charge.

It is risky and uneconomical, though. :)

Are these the same users that pry open an SLA to add distilled water? Just asking. :)

--Winston

Would I josh ?:-)

How does the voltage regulator in your car work? It tailors the current to match a voltage profile versus temperature.

Just make a shunt that works oppositely. ...Jim Thompson

If there's an SLA Spice model around that actually models charge and discharge characteristics I'll show you how easy it's be. ...Jim Thompson

Right. The series internal R is not linear, which you can see in the graph. What the graph does not show is that it varies with both state of charge and the discharge current used to make the internal resistance measurement. The higher the discharge current, the greater the internal R. With small enough batteries, you'll never get 120 amps. However, if you examine a fully charged car battery, you'll find it can produce *well* in excess of 120 amps, briefly.

That's probably as good an approach as any to accommodate the non-linearity of the beasts. The numbers change with state of charge, temperature, the amount of current going out (or in), electrolyte specific gravity (which itself changes with charge/discharge).

Just another way of looking at the same thing. You could even look at it as electrons repelling each other. As more and more electrons are added to a plate, they exert a greater force against the addition of even more electrons.

Yes.

Right. I guess that in a purely theoretical world two SLA's could be 100% identical and age at the exact same rate. However, my experience supports your statement - in the real world it certainly appears they age at different rates.

I've done extensive experimenting attempting to desulfate SLAs taken from the emergency lights and from UPSs. I tried adding water to only one of them. The desulfating produced some small improvement in some batteries, but not enough to justify the time invested, nor to produce a battery useful for the application. But the learning was worth the time. :-) The water experiment was only for an experiment - I would not use an SLA that had been opened. I should also note that batteries used in emergency lighting are a really poor candidate for desulfating. The very nature of the application should prevent sulfation in the first place, as these batteries are under constant charge.

I'll have to take a look at what they say in the link you provided - but I still won't use an SLA that's been opened!

Ed

It occurs to me that you don't need to know much about battery chemistry/behavior... just devise a shunt scheme that diverts all current (but say C/10) from the battery with the higher voltage until they come up equal. ...Jim Thompson

I suspect a high accuracy, sharp kneepoint, current limited zener (or equivalent, of course) would be all that you need.

Something like that, but accomplished with comparators, and other "smarts". You have to track temperature. ...Jim Thompson

"John Fields"

I am laughing at your pig ignorance.

... Phil

I certainly cba to equalise the load on 2 batteries running separate items. Can you? But I've added water to SLAs before, and much more.

few of all end users

My 1957 Jaguar XK150 had a 12V, (positive ground), electrical system. This was made up of two 6V lead-acid batteries, one under the fender of each front wheel. These were charged, (and discharged), in series with no problems. The only difficulties I experienced were in showing a AAA tow-truck driver how to hook up for a jump-start. :-)

--- Here's my post, again:

"Let's say we have two lead-acid batteries, one of which has been discharged to 12V, and the other to 10V.

Let's also say that they both have internal resistances of 0.1 ohm:

Since the batteries are in parallel, Vt will of course be the same for both batteries, but because of the internal resistances of the batteries and the difference in their internal voltages, there will be an EMF of 2 volts impressed across the sum of the internal resistances, 0.2 ohms, which will cause charge to be transferred from BA1 to BA2 at the rate of 10 coulombs per second, which is 10 amperes."

There seems to be a bone of contention here, so what do you think AE would find humerus about it?

---

--- I'll readily admit that I don't know much about pigs, but what does that have to do with conventional current flow?

-- JF

(...)

Look! A Joshasaurus! :)

I had the same idea from Jim's comment, except for the power level. I suspect the zeners would have to be rated to easily pass full alternator current with plenty of headroom in the middle of a Mojave summer. :)

The voltage regulator in my late lamented POS BSA 500 cc single was just a power zener bolted to the frame in parallel with the battery.

--Winston

(...)

You can bet the batteries had equal state of charge when they were installed. Otherwise you would have an unreliable electrical system on your hands.

No. Wait.

--Winston

(...)

Yes but you are about as normal as I am. :)

(...)

A tiny number. I concur.

--Winston