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Old 02-07-2012, 03:00   #151
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Re: Electrical Musings

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My problem is the right and most efficient charging regime, not the amount of power consumed.
The attached table should be able to indicate to you what would be the most efficient way of recharging batteries.
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Old 02-07-2012, 08:11   #152
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Re: Electrical Musings

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I think this series/parallel debate is much ado about nothing. Keep in mind that the internal construction of a battery consists of a bunch of PARALLEL wired plates. Higher Ah capacity batteries get that higher capacity through some combination of larger plates and/or more plates in parallel.
Not really: a battery consists of cells wired in series. In each cell the negative and positive plates are placed parallel to each other, not wired in parallel. This means that all the negative plates are connected (wired) to the negative post and all the positive plates are connected (wired) to the positive post. If a plate was to be connected to both the positive and the negative then the plate will short circuit the cell. If a cell did consist of a bunch of parallel wired plates, then they would be a bunch of short circuits.
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In contrast, if your battery bank is made of two 6V batteries wired in series, the same shorted plate fault will once again drag down the bank voltage by 2.2V - same as the parallel case. Assuming the net Ah capacity of the batteries is the same, the same amount of energy will be discharged through the shorted plate creating the same risk of overheating etc. as the parallel configuration. If you are unobservant and continue to operate with the bad cell, you will ultimately ruin the remaining good battery, just like in a parallel setup.
Given that the load on a battery bank made of two 6V batteries wired in series is, for example 7A, the current in the batteries will also be 7A. That a fault develops in one of the cells of the bank, depending on what the load is made of, the 7A current is likely to increase or decrease only slightly or remain the same. Can you explain how this relatively small change in the 7A current will ultimately ruin the remaining good battery?

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but a 2.2V drop in your battery bank voltage should quickly capture the attention of all but the most unobservant owners.
Because the voltage in a parallel configuration is an average it is unlikely that the drop will be 2.2V.
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Old 02-07-2012, 08:48   #153
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Re: Electrical Musings

Taking into consideration that two 10mm square conductors can carry more current and are lighter than a 25mm square conductor it is possible that they may be more suitable for a boat. That a conductor is subject to 3.3kV or 12V the Current Carrying Capacity of that conductor remain the same.

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I accept that some have differing views
I do too.
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Old 02-07-2012, 09:01   #154
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Re: Electrical Musings

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This means that all the negative plates are connected (wired) to the negative post and all the positive plates are connected (wired) to the positive post..
You are describing a parallel connection not series.
In a 12v battery there are 6 cells ( or small batteries ). They are wired in series, so the + is connected to the - of the next cell.
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Old 02-07-2012, 09:03   #155
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Re: Electrical Musings

"Taking into consideration that two 10mm square conductors can carry more current and are lighter than a 25mm square conductor it is possible that they may be more suitable for a boat."

Chala, are you sure of that, for DC applications?

Two 10mm square bars have less than half the conductance of a single 25mm bar. They should be able to carry about 40% of the same power, perhaps 50% because of the relative increase in surface ara and heat shedding.

But AC and DC current are very different things. AC travels by a "skin effect" on the surface of conductors, while DC travels through the whole mass. All things being equal...either one should be conducted better by the 25mm bar stock, unless there's something I'm missing here?


noelex-
"In a 12v battery there are 6 cells ( or small batteries )." We all speak sloppy that way, but technically....I know you know, a battery consists of at least two cells in a group. So we have "D cells" and "AA cells" but only the "9 volt transistor" battery is really a battery, a collection of cells in that case. And very few of us will ever have industrial 2.2 volt cells bolted up on our boats to make our batteries.

Canons and electrical piles...why on earth do we use the same term for assemblies of these?
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Old 02-07-2012, 10:04   #156
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Re: Electrical Musings

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Two 10mm square bars have less than half the conductance of a single 25mm bar. They should be able to carry about 40% of the same power, perhaps 50% because of the relative increase in surface ara and heat shedding.
We have round, square, hex, and flat bar I have not see too many bars on small yachts if it is for the bar. The requirement is mostly for circular flex cable preferably tinned as per table I have some flat but they are not so easy to install or terminate. I remember installing many years ago some high frequency furnaces where the solid (not stranded) conductor was hollow and carried cooling water but this is another cup of tea. Let not confuse boaties. If they start to ask sales peoples at a boat supply shop if the cable is suitable for AC or DC they may get charged twice or the sales person may have an heart attack.
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Old 02-07-2012, 13:39   #157
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Re: Electrical Musings

You said bar, not rod. And with only one dimension, that makes it conventional square profile bar stock.

Which leaves my original question, how do you figure two 10mm bars are better than one 25mm bar in what way? For what application? Your two 10mm bars have 200sq.mm. of conductor. One 25mm bar has 625 sq.mm. of conductor, more than three times the power carrying capacity, or 1/3 the resistance and voltage drop.

The two 10mm. bars have 80 linear mm. of surface area for cooling, the 25mm bar has 100 linear mm. of surface area for cooling. Again...how do the tens win? At what?
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Old 02-07-2012, 17:39   #158
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Re: Electrical Musings

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Not really: a battery consists of cells wired in series. In each cell the negative and positive plates are placed parallel to each other, not wired in parallel. This means that all the negative plates are connected (wired) to the negative post and all the positive plates are connected (wired) to the positive post. If a plate was to be connected to both the positive and the negative then the plate will short circuit the cell. If a cell did consist of a bunch of parallel wired plates, then they would be a bunch of short circuits.
I'm not following your English, as you seem to be talking in circles here. Let me elaborate further on what I mean.

A "Cell" in a battery (let's stay with flooded lead acid for now) consists of a minimum of two plates, one positive and one negative, separated from each other, and immersed in acid. Chemistry creates a nominal 2.2V potential across the two plates, and an Ah capacity of C.

If you take such a minimalistic cell, and wire a second one to it in parallel, you now have two 2.2V batteries wired in parallel. The voltage remains 2.2V, but the capacity is now 2C. This is the offending configuration that you have eluded to.

Now, going back to the minimalistic cell consisting of just a single positive and single negative plate, instead use 2 positive plates wired together, and two negative plates wired together. These plate pairs, wired in PARALLEL inside a single cell, still create 2.2V, but have 2C capacity. This is how the cells in modern batteries are constructed; multiple plate pairs wired in PARALLEL.

So back to my point, I argue that multiple parallel-wired plate pairs inside a single cell has all the same properties (good and bad) of two parallel wired cells. As such, we all live with the effects of parallel wired batteries every day of our lives no matter how we wire up our batteries.

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Given that the load on a battery bank made of two 6V batteries wired in series is, for example 7A, the current in the batteries will also be 7A. That a fault develops in one of the cells of the bank, depending on what the load is made of, the 7A current is likely to increase or decrease only slightly or remain the same. Can you explain how this relatively small change in the 7A current will ultimately ruin the remaining good battery?
Sure, the damage occurs in the subsequent charge cycles. If a cell fails as a short circuit (which is the only way the battery will continue to work at all), then you now have a 10V battery bank instead of 12V. But your charger will be trying to charge it based on 12V nominal. All cells will be charged at a higher voltage than normal. If this is let go long enough, you will damage the other cells.

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Because the voltage in a parallel configuration is an average it is unlikely that the drop will be 2.2V.
The voltage isn't an average, and I think this may be where you are getting thrown off. Let's assume two identical 12V batteries wired in parallel, and one cell in one battery fails as a short circuit. For a period of time, current will flow between the batteries, discharging the good battery and over charging the surviving cells in the bad battery. In time this will reach equilibrium at some voltage between 10V (the failed batteries nominal voltage) and 12V (the good batteries nominal voltage). Note that a lot of current can be flowing during this process and can result in overheating of batteries, cables etc. This is why proper fusing is a good practice. Once this equilibrium is reached, no further current will flow between the batteries.

In this case, the damage to the good battery also occurs as a result of charging. The 12V charge voltages will be correct for the good battery, but will result in overcharging of the bad battery. Also, more charge current will be absorbed by the bad battery, wasting available charge current and possibly preventing the good batery from reaching full charge. On discharge, since the bad battery will be of little use proving current at the battery bank voltage, the vast majority of load will be taken by the bad battery and bank voltage will drop more rapidly that if both batteries were good.

I actually think the damage potential to the surviving good battery is lower in a parallel configuration since the surviving good cells are not being constantly overcharged the way they are on a series configuration.
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Old 02-07-2012, 23:05   #159
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Re: Electrical Musings

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You said bar, not rod.
Great effort let try again.
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Taking into consideration that two 10mm square conductors
This refer to the attached table 10mm2 conductors (not bar). My impression was that superscript did not Paste on the reply. May be it should have been 10 square mm conductors. Here we have round bar, a rod is something else.
Hope that help.
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Old 03-07-2012, 01:51   #160
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Re: Electrical Musings

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These plate pairs, wired in PARALLEL inside a single cell, still create 2.2V, but have 2C capacity. This is how the cells in modern batteries are constructed; multiple plate pairs wired in PARALLEL.
Thank you for the clarification on
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a bunch of PARALLEL wired plates.
I would not use the term wired in parallel because it implies a parallel circuit. In fact it is even said that the negative plates are in series with the positive plates.

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So back to my point, I argue that multiple parallel-wired plate pairs inside a single cell has all the same properties (good and bad) of two parallel wired cells. As such, we all live with the effects of parallel wired batteries every day of our lives no matter how we wire up our batteries.
With the only difference that a cell developing a fault in a battery needs only to dissipate the energy of that cell. When connected in parallel with other batteries it has to dissipate in addition all the energy provided by the other batteries.

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Sure, the damage occurs in the subsequent charge cycles.
Damage can occur at any time, when charging, on standby or discharging.

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The voltage isn't an average,
Four batteries connected in parallel, the voltmeter reads 12.68V. One battery develops a fault. Assuming that all four batteries had equal voltage, the voltage on the faulty battery drops from 12.68V to 10.48V. What would the voltmeter reading be at that instant?

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I actually think the damage potential to the surviving good battery is lower in a parallel configuration since the surviving good cells are not being constantly overcharged the way they are on a series configuration.
Why charging a faulty battery?
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Old 03-07-2012, 04:36   #161
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Re: Electrical Musings

Well, as is most often the case, the problem here is all about communications - or in this case the lack of good communications

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I would not use the term wired in parallel because it implies a parallel circuit. In fact it is even said that the negative plates are in series with the positive plates.
If you look at how the positive and negative plates are physically attached together inside a cell, the positive plates are wired together to a common positive terminal, and the negative plates are wired together to a common negative terminal. On this planet, that's parallel wiring.

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With the only difference that a cell developing a fault in a battery needs only to dissipate the energy of that cell. When connected in parallel with other batteries it has to dissipate in addition all the energy provided by the other batteries.
Agreed, and I acknowledged this in my post. Proper fusing will protect against this becoming dangerous, just as it protects against short circuits that might develop anywhere else in the circuit.

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Damage can occur at any time, when charging, on standby or discharging.
I was talking about the ongoing damage that surviving batteries will experience when left connected to a failed cell and continued to be used as normal. I don't know what you are talking about now, but I think it's something else.

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Four batteries connected in parallel, the voltmeter reads 12.68V. One battery develops a fault. Assuming that all four batteries had equal voltage, the voltage on the faulty battery drops from 12.68V to 10.48V. What would the voltmeter reading be at that instant?
Again, I was talking about something else. I described qualitatively what happens from the occurrence of the fault until the battery cells reach a new charge equilibrium. You are now talking about the instantaneous voltage after the fault. It's not the average of the open circuit voltages as you describe. Why don't you put together a Spice Model to calculate it and get back to us with the answer. It should reflect the battery chemistry, internal connectivity, battery to battery interconnect cables, and load at the time of the fault. And of course the state of charge of each cell in the battery bank. It would be interesting to see the I-V curve from the instant of the fault until the cells reach their new equilibrium.

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Why charging a faulty battery?
Again we are just not communicating. I don't think you are following the basic scenario that I'm describing. Or there is more context to your question that I am missing. Either way, this is becoming exhausting.
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Old 03-07-2012, 04:38   #162
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Re: Electrical Musings

Anyway, Dockhead, any report back on what you found?
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Old 03-07-2012, 05:29   #163
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Re: Electrical Musings

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Again, I was talking about something else. I described qualitatively what happens from the occurrence of the fault until the battery cells reach a new charge equilibrium. You are now talking about the instantaneous voltage after the fault. It's not the average of the open circuit voltages as you describe. Why don't you put together a Spice Model to calculate it and get back to us with the answer. It should reflect the battery chemistry, internal connectivity, battery to battery interconnect cables, and load at the time of the fault. And of course the state of charge of each cell in the battery bank. It would be interesting to see the I-V curve from the instant of the fault until the cells reach their new equilibrium.
Do you really need a Spice Model to calculate an average?
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Old 04-07-2012, 02:07   #164
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Re: Electrical Musings

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Anyway, Dockhead, any report back on what you found?
I already forgot what the question was, but all of the discussion is in the spirit of the thread title.

I did go around with a clamp meter and did discover that my shunt is incorrectly wired so that my battery monitor sees only half or so of any given current.

I am now cruising with people aboard, and the batteries are not holding a charge as well as I thought. It looks like about 100 amp/hours of consumption take the batts from 100% down to 55%, not too good for a 420 amp/hour bank, although it might not be really 100% considering how I charge them. I spent $2000 on new batteries six months ago But I am not done with them. I'll do a bunch of equalization when I get to shore power, then maybe try Nick's trick of running them all the way down.

Meanwhile, thank God, my genset is working, so I simply run it often to keep a charge on. I bought a Honda suitcase gen which will be just the thing for putting a long finishing charge on, and for equalizing on my mooring.
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Old 04-07-2012, 08:09   #165
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Re: Electrical Musings

<digression> I find my Honda gen very economical to run but the sound travels through the decks. I've discovered that it's quieter below if I put it over a bulkhead. The forepeak works best on my boat, gives me some damping and separation. I don't use the cockpit since with a full bimini the fumes are a problem. </digression>
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