Battery Cabling for Parallel Bank

[Jbaffoh]

Originally Posted by goboatingnow

Nope andina is right. You can of course connect old and together. It's often not recommended mainly as a precaution, but of course it works fine and the charger just charges the bank.

Dave

I was referring to her second paragraph about mixing chemistries under one charging profile.

[Jbaffoh]

I must be dumber than I thought.

First, Andina says there is "no advantage" in charging old and new separately, and GoBoatingNow agrees, with the caveat, "It's often not recommended mainly as a precaution." To me, it seems that caveat defeats the claim there's "no advantage."

But more interesting is Andina's suggestion that there's no disadvantage in charging batteries of different types together under a single profile. If you put a flooded lead/acid battery, which wants a charge of 14.8 and a float of 13.2 on a charger set for an AGM, which wants a charge of 13.9-14.4 and a float of 13.5, will it be fully charged? Conversely, if you put that AGM on a 14.8 charge and 13.2 float, it will be happy? Really? There is no advantage to using manufacturer recommended profiles for different chemistries?

Before people chime in and say this is "tolerable," or "one can get by" or something similar. Keep in mind the operable phrase here is "no advantage." As in, manufacturer recommendations and sophisticated smart chargers with custom profiles add absolutely no benefit to battery utility or longevity.

[Wotname]

Originally Posted by Andina

<SNIP>......

While chemistry settings and charging regimens are available on modern chargers, all they do is decide how fast to charge and what the safe threshold voltage is. If you have mixed batteries in parallel you have to set the charger for the most forgiving battery type. They will still all get charged but it may take a few minutes longer if you have to use a lower setting to protect the weaker battery(ies).

Originally Posted by Jbaffoh

I was referring to her second paragraph about mixing chemistries under one charging profile.

Apart from "take a few minutes longer", I don't see anything controversial in her second paragraph. I could argue that it might take considerably longer but it would depend on the detail and we don't have that.

[Jbaffoh]

Originally Posted by Wotname

Apart from "take a few minutes longer", I don't see anything controversial in her second paragraph. I could argue that it might take considerably longer but it would depend on the detail and we don't have that.

Hmmm....

Ok, I have an old Sentry shore charger that I don't use. I don't use it because it is designed to kick in at 12.8v and shut off at 13.9v. While that is in the recommended range for AGM and Gel batteries, it does not meet the Trojan recommendation of 14.8v for my flooded batteries.

Am I to gather from the recent responses to this thread that my Sentry charger will fully charge my bank? FYI, Trojan customer support told me my bank will NEVER achieve a full state of charge under that profile. In fact, they told it it MUST reach 14.8 to be fully charged.

Who am I to believe?

[Wotname]

Originally Posted by Jbaffoh

Hmmm....

Ok, I have an old Sentry shore charger that I don't use. I don't use it because it is designed to kick in at 12.8v and shut off at 13.9v. While that is in the recommended range for AGM and Gel batteries, it does not meet the Trojan recommendation of 14.8v for my flooded batteries.

Am I to gather from the recent responses to this thread that my Sentry charger will fully charge my bank? FYI, Trojan customer support told me my bank will NEVER achieve a full state of charge under that profile. In fact, they told it it MUST reach 14.8 to be fully charged.

Who am I to believe?

Perhaps this will make it clearer

Originally Posted by Andina

.........charging regimens are available on modern chargers..........

[s/v Jedi]

Funny how all us techies just agree with Andina and the expected debate doesn't come

There is nothing else to say, all the required info is in Andina's posts

cheers,
Nick.

[Jbaffoh]

Originally Posted by Wotname

Perhaps this will make it clearer

No, not at all. You're missing the point.

Read her last two sentences. Isn't it a logical conclusion from those sentences, that a flooded battery will achieve full SOC when charged on an AGM or Gel profile? If so, then Trojan disagrees. Again, who do I believe?

My ancient charger was merely used as an example of a typical AGM bulk mode. Obviously I'm aware of modern smart chargers, and my question was why they even exist given Andina's position that the only disadvantage of charging mixed battery types under one charge profile is the charging speed.

So again, are manufacturer's recommendation a load of BS, and are the touted benefits of selectable charging profiles for different battery chemistries just marketing hype?

[Andina Marie]

The fully charged (at rest) voltage of most batteries is about 12.8 although I've heard it is slightly higher for some special alloy batteries. The electrical equivalent circuit for analysis and calculations is typically a perfect battery and a series resistance. (Although the series resistance may not necessarily be a constant value. There is also a high resistance in parallel to represent the self discharge rate.)

So long as the charging voltage is ABOVE the at rest voltage current will flow INTO the battery. Current flowing into the battery is stored as charge. The amount of current flowing into the battery is the charger source voltage minus the voltage of the stored charge divided by the resistance of the battery plus the reisistance of the charger.

This means a charger at 13.0 volt will fully charge ALL batteries although it may take weeks.

Because we want to minimize the time it takes we increase the charger voltage. The current will then flow until the charge state reaches the same voltage so the differential voltage across the resistance is zero, causling the current drops to zero. Unfortunately if the charge state voltage gets above 14.2 volts you start to form bubbles in the electrolyte. While this is actually good for lead-acid batteries, bubbles in a gel or AGM style battery displace the electrolyte and reduce surface area available. Although bubbles can re-combine slowly the damage is often permanent.

So chargers designed for lead-acid or multiple choice chargers with a lead-acid setting can put out 15.6 volts safely on lead acid batteries and charge them quickly. They will reduce the voltage to less than 14.2 volts after bulk charge to save losing water.

The problem with charging less tolerant batteries is knowing when the charge state is reaching a dangerous level and for how long you can "push" it before creating bubbles. You can do this by checking the voltage at the charger to see when it drops due to the lower current as the voltage differential decreases due to rising voltage on the battery. It is THIS decision that allows some chemistries to push the charge rate a little longer and harder than others. Even smarter chargers will momentarily stop charging so they can read the voltage on the battery and track its state of charge.

Smart chargers will put out their maximum current during the bulk stage. Having a higher maximum rating will help considerably in reducing charging time.

However despite all the hype from charger manufacturers, the difference in charging time from the different chemistry settings (apart from lead-acid) are quite small so setting it for the voltage of the most sensitive battery in parallel makes little difference and all batteries will get fully charged even if it switches to maintenance a few minutes earlier.

[Jbaffoh]

Originally Posted by Andina

The fully charged (at rest) voltage of most batteries is about 12.8 (good stuff snipped)

Thank you, Andina. I understand your explanation, and I appreciate your time and effort to explain it to me. It makes sense to me.

I guess the source of my confusion comes from the Trojan customer support rep, who told me my batteries will "never" achieve full SOC unless they reach 14.8v. I also bought into some of the marketing hype for chargers.

What you say is corroborated by my open circuit voltage and specific gravity readings. It seems my 18-month old batteries are maintained at full SOC, despite spending 98 percent of their time on a solar controller that delivers 14.5v, then 13.6v.

[s/v Jedi]

Originally Posted by Jbaffoh

[...]the source of my confusion comes from the Trojan customer support rep, who told me[...]

Did his mouth move when he told you something? If it did, it was nonsense.

These guys at best repeat what is on the paper sheet they gave them.

cheers,
Nick.

[noelex 77]

It has has been written many times " don't mix old and new batteries in one bank"
I don't think this thread is going to re-write that old adage.
I have some sympathy thy for the view that while this law appears cast in stone the reality is different and batteries of different ages can be mixed sometime times with good results.

The main problem is the charge / voltage profile of batteries changes as they age. A new battery will have a higher resting voltage than old battery for example. Join the two batteries without a charge source, together and the newer battery will discharge into the older battery. Are the inefficiency of this discharge significant?Is the difficulty in keeping the new battery at 100% Soc significant? It depends on the battery and the degree of the problem, but old and new batteries in one bank will shorten the life of the new batteries.

If they are joined together make sure you can detect a defective cell in the old bank. This will significantly shorten the life of the new batteries.
If you do want to mix old and and new batteries my recommendation is to make them a separate bank. It is only a battery switch and a small amount of wiring. Most if not all of the problems are removed and importantly it is very easy to detect a defective cell that is unlikely to picked up by the average cruiser otherwise.

[Rustic Charm]

Originally Posted by Andina

I am an electrical engineer with 50+ years of experience, 25 of those on boats and 14 as a live-aboard.Sooner or later old batteries die and sometimes they die with a shorted cell. When that happens the bad battery will pull charge from the good ones trying to charge the bad cell but that does not do any harm to the good ones. The bad one will prevent the good ones from charging and draw your attention to the problem. Replace the bad one and you are back in business..

Thanks Andina, always good to see your input.

Is it obvious when one battery has died? or when one battery is pulling a charge from others? How does this problem 'draw your attention to the problem'.

Ted

[Andina Marie]

Originally Posted by tedsherrin

Thanks Andina, always good to see your input.

Is it obvious when one battery has died? or when one battery is pulling a charge from others? How does this problem 'draw your attention to the problem'.

Ted

1. The battery with the faulty cell will get hot, even start to steam on a big bank. You can easily determine which cell is bad, the battery will be hotter at that spot.

2. All the charger output will be going into the bad cell trying to bring the voltage up. Since the voltage is not rising no current is going into the good batteries so you will notice the low voltage the first time you try to use power or a low voltage alarm will go off in one of your instruments..

Once you remove the bad battery the good ones will recharge with no damage other than being discharged quite deeply by dumping current into the dead cell.

Even with matched batteries, sooner or later this can happen. The only difference with matched batteries is they all die about the same time so you're without the battery bank until they are all replaced.

What is much harder to detect is a battery that has gone Open Circuit in one cell. Now the only symptom is reduced capacity and you need to separate them to test which it is. Fortunately batteries going open circuit is rare in comparison to a shorted cell.

[Wotname]

Originally Posted by Andina

The fully charged (at rest) voltage of most batteries is about 12.8 although I've heard it is slightly higher for some special alloy batteries. The electrical equivalent circuit for analysis and calculations is typically a perfect battery and a series resistance. (Although the series resistance may not necessarily be a constant value. There is also a high resistance in parallel to represent the self discharge rate.)

So long as the charging voltage is ABOVE the at rest voltage current will flow INTO the battery. Current flowing into the battery is stored as charge. The amount of current flowing into the battery is the charger source voltage minus the voltage of the stored charge divided by the resistance of the battery plus the reisistance of the charger.

This means a charger at 13.0 volt will fully charge ALL batteries although it may take weeks.

Because we want to minimize the time it takes we increase the charger voltage. The current will then flow until the charge state reaches the same voltage so the differential voltage across the resistance is zero, causling the current drops to zero. Unfortunately if the charge state voltage gets above 14.2 volts you start to form bubbles in the electrolyte. While this is actually good for lead-acid batteries, bubbles in a gel or AGM style battery displace the electrolyte and reduce surface area available. Although bubbles can re-combine slowly the damage is often permanent.

So chargers designed for lead-acid or multiple choice chargers with a lead-acid setting can put out 15.6 volts safely on lead acid batteries and charge them quickly. They will reduce the voltage to less than 14.2 volts after bulk charge to save losing water.

The problem with charging less tolerant batteries is knowing when the charge state is reaching a dangerous level and for how long you can "push" it before creating bubbles. You can do this by checking the voltage at the charger to see when it drops due to the lower current as the voltage differential decreases due to rising voltage on the battery. It is THIS decision that allows some chemistries to push the charge rate a little longer and harder than others. Even smarter chargers will momentarily stop charging so they can read the voltage on the battery and track its state of charge.

Smart chargers will put out their maximum current during the bulk stage. Having a higher maximum rating will help considerably in reducing charging time.

However despite all the hype from charger manufacturers, the difference in charging time from the different chemistry settings (apart from lead-acid) are quite small so setting it for the voltage of the most sensitive battery in parallel makes little difference and all batteries will get fully charged even if it switches to maintenance a few minutes earlier.

Andina
Thanks for taking the time and effort to write clearly and with logic and facts regarding electrical circuits. These posts should help those with less electrical knowledge to grasp the fundamentals of electricity.

Really all that is needed is knowing Ohms Law and a good understanding of how to reduce any system to its equivalent resistive circuit and power (voltage) source. However many have not had the opportunity to learn this and rely on hearsay, scuttlebutt and salesman. Note I exempt most (not all) manufacturers as they usually try to present the facts, at least their design and technical sections do.

Thanks for making this easier for those of us (myself partially included) who can't do this.

Now can I get you into the lightning threads... (as there is a lot of hearsay and mystic going on there!!!) It is battle to present cogent facts in that climate.