Multiple lead-acid charging

in context float charging is not appropriate for the application being discussed....this application requires the batteries being taken thro a gas phase to return the ampre hours.....were not looking for cca amps.

Yeah, when I was studying in Kozani, we visited the North Load Distribution Centre (utility) and in the battery room of the UPS, they had special switches to avoid dangerous arcs, and even a specially designed bidet (!) so that you could wash your eyes if they were contaminated with (sulphuric) acid.

You'd be surprised what you can get used to.

Try climbing on top of 128 cell battery rated for 5250 Ah at the 3-hour rate. Navy submarine batteries are huge. ;-)

daestrom (former Chief Electrician's Mate, Submarines)

Aha! So, conventional submarines were the first hybrid vessels?

| Try climbing on top of 128 cell battery rated for 5250 Ah at the 3-hour | rate. Navy submarine batteries are huge. ;-)

Lotsa fault current there :-)

| daestrom | (former Chief Electrician's Mate, Submarines)

So you're the one that has to scrape up the charred remains?

That would be a spectacular failure if something went really wrong. That's one of the things I like about power control, when something goes wrong, it's rarely dull :)

Fortuntely the design, procedures, and training are all pretty good. Bad things do happen and good people get hurt or killed but it's very rare.

And I refuse to get nostalgic about hopping gravities at the end of an equalizer! ;-)

No, I think that honor would go to DE train engines. Submarines, AIUI, aren't really hybrid, rather dual. Thinking about it for a few more seconds, I guess it depends on how you define "hybrid". Submarines have both diesels and electric motors driving the shafts and use the diesel to charge batteries. DE locomotives run D->E->motor->loco.

I did some chip designs for these guys...

...Jim Thompson

What sorts of chips?

My father worked on some DE stuff for Cat when he was in his early

Variations on my MC4024/MC4044 PLL for speed controls.

...Jim Thompson

OK, but what kind of charger should I look for?

Multiple parallel batteries would take the same voltages at the same point in the charging cycle (if I used a voltage-based charge scheme), but I would need a lot more current.

Can I simply get a single charger with a high current output? Would it charge mulitple batteries just as well as a single battery? Maybe something like this:

Don Kansas City

One with an equalisation setting would be a good start.

Once you know the type of battery (including cell construction type), terminal voltage and total AH, come back for some recommendations.

Nope. You need a charger designed to handle the type of battery and total AH. It may have a "lot more current" capability - or may not. There are all sorts of charging profiles but most start with a constant current phase - which can be many amps or a few.

A quick look indicates it doesn't have an equalisation setting. So no good. You need periodic equalisation if you are running with batteries in parallel.

-- Sue

The current rating of the charger depends primarily on how fast you want to charge the batteries, and on how much energy you have to put back in them, rather than on the total capacity of the batteries.

If you will regularly discharge the battery by 100 AH, and have a couple of days to recharge, then a 10 amp charger will be more than sufficient. If, on the other hand, you will need to charge it in a couple of hours, you'd need a 100 amp charger.

As another poster said, if you have several batteries permanently connected in parallel (or series-parallel, as you might do to get 12 volts from a group of 6 volt batteries), you can consider the group as a single large battery. Personally, for parallelled batteries, I like to have the possibility to disconnect each parallel branch so I can easily test if any branch is losing capacity (or to readily remove a branch if it develops a shorted cell) (I've had a couple of situations where one of two parallelled batteries failed, and did not notice a problem til I tried to use the bad battery alone...)

This is interesting and a little confusing at the same time.

The way I understand battery charging, at some point it is usually necessary to produce a constant charging voltage (maybe I'm misunderstanding). But as more batteries are connected in parallel, more current is required to maintain the same voltage than for one battery. It seems to me you can't control the voltage *and* the current at the same time.

If you want to only supply, say, 20 amps to a battery, you have to provide "x" amount of voltage to force this to happen. If you have multiple batteries, this voltage would be different since the total impedance would be different. I suppose a constant-current supply deals with this accordingly.

But if you want to provide exactly 13.5 volts, the batteries will pull "y" amount of current, depending on how many batteries are connected in shunt. In fact, I would think that the amount of current would be proportionate to the number of batteries, just like resistors in parallel. This would have to eventually outstrip the capacity of the charger.

How would a charger deal with this?

Don Kansas City

On a sunny day (Thu, 19 Jun 2008 13:18:33 -0700 (PDT)) it happened eromlignod wrote in :

The charger will current limit until the voltage reaches the setpoint, then usually a trickle charge is maintained.

So that means one battery maybe getting a bit more current then the the other if it was more empty, slowing down the charge process, but in the end all batteries will be at setpoint (and thus full).

A typical charger for *big* batteries will be a 3 stage charger.

Here follows a typical explanation:

Stage 1. (Bulk Charge) A soft start delay is activated on connection to the battery to prevent sparking, after which a controlled constant current of 0.6 Amps is fed into the battery to rapidly raise the terminal voltage to 2.41 volts per cell. The length of time taken to complete stage 1 will depend on capacity of the battery and depth of discharge.

Stage 2. (Controlled Over-voltage Equalising) The terminal voltage is maintained at a constant potential of 2.41 volts per cell during which time the charge current will start to decay exponentially until it reaches a preset level of approximately 10% of the chargers maximum current rating. The length of time from start of bulk charge stage 1 to this point is monitored (T1). The terminal voltage is then maintained at 2.41 volts per cell for a further time period of T1 / 2.

Stage 3. (Standby Mode) At the end of the timed period the terminal voltage is reduced to 2.28 volts per cell which is maintained until either the battery is disconnected or discharged sufficiently to switch back to stage 1. State of charge is indicated by static red LED during stage 1 and stage 2, and by static green LED for stage 3 (Charge Complete)

Note that this is from the description of a charger intended for relatively small batteries. The 0.6A in stage 1 would take a very, very long time to charge a big battery. For many intelligent chargers, this very, very long time would be flagged as a fault condition - hence it is important to get a charger rated for the AH of the batteries that are being charged.

Note that the above description relates to one particular battery technology. Different cell compositions require different charging profiles. Hence it is important to match the charger to the batteries.

Note also that your suggested "charger", IIRC, is not designed as a charger but as a constant voltage supply. These really won't do at all as chargers - the current demanded by a flat battery is likely to cause the charger to trip out on overload. The voltage output when connected to a fully charged battery, if high enough to fast charge it, is going to destroy the battery if left connected and powered up.

Charging batteries has to be done with a charger designed for the type and size of batteries being charged. Doing anything else is either not going to charge the batteries fully or greatly reduce the battery life expectancy. Or both.

-- Sue

No temperature compensation?

...Jim Thompson

"Education is a process of decreasing deception" :)

I've tried to persuade the OP to post details of what battery bank he is intending to use, so that folks here can suggest suitable chargers. He was still at the "constant voltage" state of learning and so I posted the simplest description of 3 stage charging that I could find relating to a real charger..

But, of course, you are very right. But I was leaving the effect of temperature on the selection of charging voltage until later... ;)

-- Sue