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Old 11-06-2014, 18:37   #121
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Re: Mixing Battery types in 1 Bank

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Originally Posted by hellosailor View Post
Ah, LIFELINE.

Bear in mind that you cannot compare a Lifeline AGM to ANY other AGM battery. Lifeline does not make "AGM" batteries, they make military.aviation AGM batteries.

These are designed to withstand the pressure change involved with repeatedly going to 30-40,000 feet and back to sea level again, without bursting or venting the case. A conventional AGM battery, or any "sea level-to-Denver" battery would be ruined by one cycle with that big a pressure difference.

Which is probably why Lifeline AGMs can and should be equalized--which would, again, cause all conventional AGM batteries to be ruined.

Lifeline is the unicorn ranch.
No reason to put much effort into sussing out attainable charge/discharge rates for AGM's. Nobody I know with a typical cruising bank has a 1C charging capacity, let alone a 5C. Likewise with discharge capacity (our 3kW inverter can't pull 0.5C out of our relatively modest bank). So it doesn't matter in practice.

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Old 11-06-2014, 18:53   #122
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Re: Mixing Battery types in 1 Bank

Well I found a battery site that talks about mixed batteries.

From FAQ about AGM Batteries - First Start Batteries

Under mixing batteries they say:

The reasons we do not recommend wet cell and AGM Batteries together are:

1. When charging, the AGM will reach full charge before the wet cell. This means that the charge system will do one of two things. It will keep charging until the wet cell is fully charged and may over-charge the AGM or it will switch off when the AGM is fully charged which means the wet cell is only partially charged.



2. The wet cell will try to draw power from the AGM and this will reduce the life of both batteries because of under-charging then draining them will naturally damage both batteries but will kill the wet cell quickly.

If both batteries are charged separately, like in most dual battery set ups you can use the two together. With a voltage sensitive regulator or blockout diode (used in most dual battery systems) the start battery is charged first then it switches over to the 2nd or house battery.

So just FYI.
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Old 11-06-2014, 19:08   #123
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Re: Mixing Battery types in 1 Bank

Quote:
Originally Posted by sailorchic34 View Post
Well I found a battery site that talks about mixed batteries.

From FAQ about AGM Batteries - First Start Batteries

Under mixing batteries they say:

The reasons we do not recommend wet cell and AGM Batteries together are:

1. When charging, the AGM will reach full charge before the wet cell. This means that the charge system will do one of two things. It will keep charging until the wet cell is fully charged and may over-charge the AGM or it will switch off when the AGM is fully charged which means the wet cell is only partially charged.

2. The wet cell will try to draw power from the AGM and this will reduce the life of both batteries because of under-charging then draining them will naturally damage both batteries but will kill the wet cell quickly.

If both batteries are charged separately, like in most dual battery set ups you can use the two together. With a voltage sensitive regulator or blockout diode (used in most dual battery systems) the start battery is charged first then it switches over to the 2nd or house battery.

So just FYI.
And we have come full circle!

That FirstStart information was what kicked this whole thing off! You, of course, are excused from having to wade through so much density to find that earlier post!

Even the person here who seems to have a problem with my postings agreed that the FirstStart information was lacking in knowledge.

For example, look at their description of how they describe VSR and diode isolator function in the last paragraph of your posting. In your experience, do these devices charge one battery first, and then switch over to the other?

And what about that wet cell being killed quickly before the AGM during discharge? You have already agreed with Dave that the opposite is more likely…

Note that they also recommend their AGM batteries be charged at 14.1-14.2V. I would not recommend batteries of such different charging voltages as 14.1V vs. 14.4V be combined - and have stated that many times now.

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Old 11-06-2014, 19:18   #124
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Re: Mixing Battery types in 1 Bank

Quote:
Originally Posted by colemj View Post

BTW, I haven't been able to confirm SC's internal resistance numbers. They are remarkably hard to find, and few manufacturers publish them. I have found one reference in a physics paper for FLA of 20mOhm, which she also lists. For AGM's, I have found 5mOhm from PowerSonic and Century and 9mOhm from Eaton. Lifeline just gives a blanket statement that their AGM's are 5x less internal resistance than FLA's without giving any of the numbers supporting that statement.

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Gee Optima lists their AGM's at 2.8 milliohms, Century lists theirs at 4.8 milliohms.

so YMMV
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Old 11-06-2014, 19:27   #125
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Re: Mixing Battery types in 1 Bank

Quote:
Originally Posted by colemj View Post
And we have come full circle!

That FirstStart information was what kicked this whole thing off! You, of course, are excused from having to wade through so much density to find that earlier post!

For example, look at their description of how they describe VSR and diode isolator function in the last paragraph of your posting. In your experience, do these devices charge one battery first, and then switch over to the other?

And what about that wet cell being killed quickly before the AGM during discharge? You have already agreed with Dave that the opposite is more likely…

Mark
Actually if the battery charger has separate branches for different banks with blocking diode's protecting the branch charge circuits then you can have different battery types in different battery banks. This thread talks about different battery types in the same bank. Which to me is a no no unless that's your only option. A expensive option in the long term.

Some battery chargers actually do charge one branch at a time. Not all.

Actually I think that both the AGM and FLA will have very short life's in a mixed bank, though for different reasons.

Yes the firststart info is lacking. But some of us understand what they are talking about.
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Old 11-06-2014, 20:43   #126
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Re: Mixing Battery types in 1 Bank

Don,

Nice try, but batteries are dynamic. What that means is that they are not liner.

What that means is Ohms law, and Kichoff's law..s are a moving target.

A battery under both is moving dependent on SOC, DOD, and current ie; Pukert.

So if you think you can model that, then you have to take each into consideration. Then your model must become dynamic to adjust for each as the dynamics change.

A battery internal resistance is fixed only in one state of time. Then it changes. The Ir of a battery follows a bell curve, based on SOC, DOD, Current, and finally heat/temp. These are all dynamic based on the change of each.

Nice try.

but it doesn't work

Lloyd



Quote:
Originally Posted by donradcliffe View Post
I wrote a little program to calculate the discharge from a 200 amp-hr battery bank where 100 amp-hrs is FLA and 100 Amp-hrs is AGM. The program uses the internal resistance provided by Sailorchic, and a linear model of internal voltage vs SOC. I started with full batteries, and held the total bank discharge rate steady at about 13 amps. The results seem pretty reasonable--the AGM starts by taking nearly all the load, but by the end of the second hour, the FLA is taking over half the load. At the end of the 10th hour, the terminal voltage is down to 12.01 and the total amp-hrs taken from the bank is 149, with 67 coming from the FLA and 82 coming from the AGM--not ideal, but not the end of the world. Next time I have some spare time, I'll do the charging scenario.

hour amps-FLA amps AGM
0 -2.5 15.2
1 5.1 8.6
2 6.8 6.7
3 7.3 7.6
4 7.5 5.8
5 7.1 6.3
6 7.2 6.8
7 7.2 5.8
8 7.0 6.4
9 7.1 6.8
10 7.1 5.9
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Old 11-06-2014, 23:36   #127
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Re: Mixing Battery types in 1 Bank

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Originally Posted by colemj View Post
I am having a hard time comprehending the rest of your statement (after the first sentence). Perhaps you could rewrite it more clearly?

Mark
High currents affects increased difference in SOC of the batteries, low current less. Charge or discharge are the same assuming batteries have been resting a while ie S
OC has been balanced. During higher loads you are saying AGM's internal resistance rises, that's true, but FLA's resistance rises too and AGM continues to deplete more. And the same with loading.
This means the SOC's could be for the AGM btw 40 to 90 and FLA btw 60 to 80. That's quite propable outcome with continous heavy loading and generator charging.
Lightly loaded bank with, lets say solar panels charging, could outcome even 50 to 95 SOC for both. These are the easy cases where a really smart charger could manage well.
In real life boat battery bank it would be something mixed with over charging and under charging time to time which is the real battery killer. No charger can know the excact state of charge of mixed battery bank and thus a nono..
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Old 12-06-2014, 06:28   #128
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Re: Mixing Battery types in 1 Bank

Quote:
Originally Posted by sailorchic34 View Post
Gee Optima lists their AGM's at 2.8 milliohms, Century lists theirs at 4.8 milliohms.

so YMMV
OK, I listed Century at 5 milliohms, but will easily agree to 4.8 milliohms. That changes the ratio for Don from 4.00 to 4.16. I couldn't find figures for Optima, so don't know why you are chiding me on that (my poor searching skills, maybe?).

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Old 12-06-2014, 06:31   #129
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Re: Mixing Battery types in 1 Bank

Quote:
Originally Posted by sailorchic34 View Post
Actually if the battery charger has separate branches for different banks with blocking diode's protecting the branch charge circuits then you can have different battery types in different battery banks. This thread talks about different battery types in the same bank. Which to me is a no no unless that's your only option. A expensive option in the long term.

Some battery chargers actually do charge one branch at a time. Not all.
They are not talking about battery chargers, but rather VSR's and diode isolators. You avoided/deflected my question?

Quote:
Originally Posted by sailorchic34 View Post
Yes the firststart info is lacking. But some of us understand what they are talking about.
I agree!

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Old 12-06-2014, 06:44   #130
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Re: Mixing Battery types in 1 Bank

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Originally Posted by TeddyDiver View Post
High currents affects increased difference in SOC of the batteries, low current less. Charge or discharge are the same assuming batteries have been resting a while ie S
OC has been balanced. During higher loads you are saying AGM's internal resistance rises, that's true, but FLA's resistance rises too and AGM continues to deplete more. And the same with loading.
This means the SOC's could be for the AGM btw 40 to 90 and FLA btw 60 to 80. That's quite propable outcome with continous heavy loading and generator charging.
Lightly loaded bank with, lets say solar panels charging, could outcome even 50 to 95 SOC for both. These are the easy cases where a really smart charger could manage well.
In real life boat battery bank it would be something mixed with over charging and under charging time to time which is the real battery killer. No charger can know the excact state of charge of mixed battery bank and thus a nono..
Ask yourself this - if you put a load on a mixed bank (you pick the load), and let the load run until the bank goes dead, and have a way of measuring the SOC of each battery independently --- Do you think the AGM runs down to depletion and sits at that level for a long time before the FLA reaches depletion?

Reverse that example to describe charging. Do you think the AGM runs up to full charge hours before the FLA and sits there boiling waiting for the FLA to catch up?

You say charge/discharge SOC are the same if the batteries are allowed to stay connected for a period of time (and "resting"). Doesn't this describe a typical house bank on a boat? I know I never disconnect our paralleled batteries from each other, and while there are periods of time where I apply loads to them, there are also periods of time where no loads are applied at all.

BTW, your description above is in opposition to Don's computational analysis. Maybe Lloyd is correct and that analysis has no basis in reality. I can't comment because I don't know what Don did. Perhaps he will return and comment on it.

And no charger knows the exact SOC of a single battery or a bank of same batteries.

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Old 12-06-2014, 07:13   #131
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Re: Mixing Battery types in 1 Bank

One comment on this belief of many here that the batteries in a mixed bank will have a very short lifespan.

No one is providing any examples or even defining what they consider "short", or what they estimate (and why) the delta lifespan between a mixed bank and a non-mixed one of each type.

People are providing what they "think" happens and what they "think" the results will be, but they are avoiding answering some pretty simple direct questions I have been asking in order to understand their positions.

One cannot just say things because they "believe" them and then tell others they are wrong to question it. One also cannot just make up numbers out of thin air like "This means the SOC's could be for the AGM btw 40 to 90 and FLA btw 60 to 80." without backing that up somehow (and saying "this is probable" is not evidence).

Don actually tried to provide something real and was ignored by some and told he was wrong by others. OK, maybe. But at least he is trying and not just sitting on an unexamined and unquestionable belief.

I have no problem being wrong here. However, pointing to a highly questionable and easily picked apart marketing blurb and saying things like "some of us understand what they are talking about" while simultaneously saying that parts of it are incorrect and that it is lacking overall (!!!) isn't helping me understand the opposite argument.

Neither is agreeing with posts that support what I have been saying, while disagreeing with me about the exact same things.

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Old 12-06-2014, 07:44   #132
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Re: Mixing Battery types in 1 Bank

Let's restart this by me posting the questions I have asked various posters that have gone unanswered.

Anyone can answer, even though the questions were posed to individuals.

1. "Can two batteries combined together have different voltages?"

2. "I am really stuck on your claim that the currents accepted and discharged by an equal-sized AGM will always be higher than that of the FLA. How does this happen? There cannot magically be more "stuff" packed into the AGM."

3. "Using your example, your AGM will deliver 630 amps as it goes to 10.5V (well, not really, but let's ignore the dynamics). Your equal sized FLA will deliver 105 amps. How do you reconcile this?"

4a. "Do you really think in a combined bank the AGM will be a depleted battery many hours early while the FLA is happily pumping current into a load? Alternately (if this is your meaning), do you think it matters if the FLA delivers its current to the AGM vs. the load?"

4b. "Are you still willing to say that during discharge, an AGM will tap out hours earlier than a FLA and just sit there while the FLA powers the load? Conversely, are you still sticking to your point that during charging, the AGM races up to full charge and then sits there boiling away while the FLA pokes along at a much lower SOC?"

(edit: the above two questions are really the same, and have been asked in various form many times more without answer - I won't repeat all those others again here).

5. "After 100 full cycles of this combined bank, how many cycles do you think each battery has experienced?"

6. "Given that (equal sized batteries with identical absorption voltages), what do you think the chances are of fizzing the above AGM before the above FLA (assuming a good charger)? How long do you estimate an AGM would be at full charge waiting for a FLA to catch up? Given that we have also discussed real-life charging to less than 100%, what are the chances of fizzing ever?"

7. "If this bank were in real-life usage, being discharged to 50% and recharged to 80-90% (low fractional C for both), how much would you estimate the lifespan of the bank would be shortened over having all AGM? How about all FLA?"

8. "Let's say you do a partial discharge of this bank to 12.4V during the day and it is now time to recharge. What is the relative SOC of each battery at this point? Surely, the SOC of each battery is close to the same even before complete depletion?"

9. "The question is: will the AGM have to sit at 14.4V for such a long time waiting for the FLA to stop taking current that it will boil and gas? "

10. "In your experience, do these devices (ACR's and diode isolator's) charge one battery first, and then switch over to the other?"

11. "And what about that wet cell being killed quickly before the AGM during discharge? You have already agreed with Dave that the opposite is more likely."

12. "How many amps can a 100Ahr AGM battery deliver until it reaches 10.5V? How many can a 100Ahr FLA battery deliver until it reaches 10.5V? What is the amps/unit of voltage drop from 12.7-10.5V for both? "


To be fair, I may have missed a question posted to me. Please let me know if there are any questions anyone has asked me that I have let go unanswered.

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Old 12-06-2014, 09:21   #133
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Re: Mixing Battery types in 1 Bank

Quote:
Originally Posted by colemj View Post
Let's restart this by me posting the questions I have asked various posters that have gone unanswered.

Anyone can answer, even though the questions were posed to individuals.

1. "Can two batteries combined together have different voltages?"

You would be measuring voltage at essentially one spot in a circuit so there is no way the voltage could be different, as long as the batteries are connected. This assumes minimal resistance in the wire between the batteries. Basic physics. This however, does not mean that the batteries might be at a different state of charge with current flowing from one battery to the other and if disconnected the voltage might immediately change a lot.


2. "I am really stuck on your claim that the currents accepted and discharged by an equal-sized AGM will always be higher than that of the FLA. How does this happen? There cannot magically be more "stuff" packed into the AGM."

If you model the batteries as simple resistive circuits connected in parallel then the circuit with the lower resistance must pass more current than the one with the higher resistance. In a simplified way this is how two different batteries would appear in parallel.

3. "Using your example, your AGM will deliver 630 amps as it goes to 10.5V (well, not really, but let's ignore the dynamics). Your equal sized FLA will deliver 105 amps. How do you reconcile this?"

4a. "Do you really think in a combined bank the AGM will be a depleted battery many hours early while the FLA is happily pumping current into a load? Alternately (if this is your meaning), do you think it matters if the FLA delivers its current to the AGM vs. the load?"

4b. "Are you still willing to say that during discharge, an AGM will tap out hours earlier than a FLA and just sit there while the FLA powers the load? Conversely, are you still sticking to your point that during charging, the AGM races up to full charge and then sits there boiling away while the FLA pokes along at a much lower SOC?"

(edit: the above two questions are really the same, and have been asked in various form many times more without answer - I won't repeat all those others again here).

5. "After 100 full cycles of this combined bank, how many cycles do you think each battery has experienced?"

6. "Given that (equal sized batteries with identical absorption voltages), what do you think the chances are of fizzing the above AGM before the above FLA (assuming a good charger)? How long do you estimate an AGM would be at full charge waiting for a FLA to catch up? Given that we have also discussed real-life charging to less than 100%, what are the chances of fizzing ever?"

7. "If this bank were in real-life usage, being discharged to 50% and recharged to 80-90% (low fractional C for both), how much would you estimate the lifespan of the bank would be shortened over having all AGM? How about all FLA?"

8. "Let's say you do a partial discharge of this bank to 12.4V during the day and it is now time to recharge. What is the relative SOC of each battery at this point? Surely, the SOC of each battery is close to the same even before complete depletion?"

9. "The question is: will the AGM have to sit at 14.4V for such a long time waiting for the FLA to stop taking current that it will boil and gas? "

10. "In your experience, do these devices (ACR's and diode isolator's) charge one battery first, and then switch over to the other?"

11. "And what about that wet cell being killed quickly before the AGM during discharge? You have already agreed with Dave that the opposite is more likely."

12. "How many amps can a 100Ahr AGM battery deliver until it reaches 10.5V? How many can a 100Ahr FLA battery deliver until it reaches 10.5V? What is the amps/unit of voltage drop from 12.7-10.5V for both? "


To be fair, I may have missed a question posted to me. Please let me know if there are any questions anyone has asked me that I have let go unanswered.

Mark

Here's my take on the subject. I'm sure everyone agrees that to get maximum life from any battery it must be charged by the most appropriate voltage and current for that battery chemistry. It seems obvious that different batteries in parallel will see the same charging profile since the voltage in a parallel circuit must be the same in each circuit.

Therefore, at least one battery type will not be charged under the optimal voltage profile.

So what does that mean? Will it matter very little or will it matter a lot?
Don't know that answer but it seems obvious that it must have some impact but it might be very small.
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Old 12-06-2014, 10:19   #134
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Re: Mixing Battery types in 1 Bank

Quote:
Originally Posted by colemj View Post
Let's restart this by me posting the questions I have asked various posters that have gone unanswered.

Anyone can answer, even though the questions were posed to individuals.

1. "Can two batteries combined together have different voltages?"
[COLOR="rgb(139, 0, 0)"]No[/COLOR]

2. "I am really stuck on your claim that the currents a[COLOR="rgb(139, 0, 0)"][/COLOR]ccepted and discharged by an equal-sized AGM will always be higher than that of the FLA. How does this happen? There cannot magically be more "stuff" packed into the AGM."
[COLOR="rgb(139, 0, 0)"]Becouse of the lower resistance you use mostly AGM first, and after it has depleted enough FLA deliveres most. Same with charging[/COLOR]
3. "Using your example, your AGM will deliver 630 amps as it goes to 10.5V (well, not really, but let's ignore the dynamics). Your equal sized FLA will deliver 105 amps. How do you reconcile this?"
LET'S SAY YOU LEAVE THEM RESTING NOW. FLA WILL DEPLETE TO AGM UNTIL THEY ARE EVEN. FOR THE BATTERIES THIS MEANS DOUBLE WORK FOR 267A.
4a. "Do you really think in a combined bank the AGM will be a depleted battery many hours early while the FLA is happily pumping current into a load? Alternately (if this is your meaning), do you think it matters if the FLA delivers its current to the AGM vs. the load?"
DOBLE WORK FOR THE BATTERIES.
4b. "Are you still willing to say that during discharge, an AGM will tap out hours earlier than a FLA and just sit there while the FLA powers the load? Conversely, are you still sticking to your point that during charging, the AGM races up to full charge and then sits there boiling away while the FLA pokes along at a much lower SOC?"
HOURS OR MINUTES, DEPENDS OF MULTIPLE VARIABLES.
(edit: the above two questions are really the same, and have been asked in various form many times more without answer - I won't repeat all those others again here).

5. "After 100 full cycles of this combined bank, how many cycles do you think each battery has experienced?"
125? REALLY DONT KNOW TOO MANY VARIABLES.
6. "Given that (equal sized batteries with identical absorption voltages), what do you think the chances are of fizzing the above AGM before the above FLA (assuming a good charger)? How long do you estimate an AGM would be at full charge waiting for a FLA to catch up? Given that we have also discussed real-life charging to less than 100%, what are the chances of fizzing ever?"
AS SAID EARLIER DEPENDS OF TOO MANY VARIABLES.
7. "If this bank were in real-life usage, being discharged to 50% and recharged to 80-90% (low fractional C for both), how much would you estimate the lifespan of the bank would be shortened over having all AGM? How about all FLA?"
WILD GUESS 70% AGM AND 40% FLA BUT LOOK ANSWER ABOVE
8. "Let's say you do a partial discharge of this bank to 12.4V during the day and it is now time to recharge. What is the relative SOC of each battery at this point? Surely, the SOC of each battery is close to the same even before complete depletion?"
SEE UP
9. "The question is: will the AGM have to sit at 14.4V for such a long time waiting for the FLA to stop taking current that it will boil and gas? "
LONG OR SHORT BUT BOIL IT WILL
10. "In your experience, do these devices (ACR's and diode isolator's) charge one battery first, and then switch over to the other?"

11. "And what about that wet cell being killed quickly before the AGM during discharge? You have already agreed with Dave that the opposite is more likely."
DEPENDS..
12. "How many amps can a 100Ahr AGM battery deliver until it reaches 10.5V? How many can a 100Ahr FLA battery deliver until it reaches 10.5V? What is the amps/unit of voltage drop from 12.7-10.5V for both? "

DEPENDS..
To be fair, I may have missed a question posted to me. Please let me know if there are any questions anyone has asked me that I have let go unanswered.

Mark
Sorry about capitals above but could change color with tab too much down. Exact numbers cannot be given without knowing the resistance profiles, charging characteristics and current profile. Even then the answer would be a questimate IMHO.
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Old 12-06-2014, 11:00   #135
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Re: Mixing Battery types in 1 Bank

Quote:
Originally Posted by colemj View Post
One comment on this belief of many here that the batteries in a mixed bank will have a very short lifespan.

I have no problem being wrong here. However, pointing to a highly questionable and easily picked apart marketing blurb and saying things like "some of us understand what they are talking about" while simultaneously saying that parts of it are incorrect and that it is lacking overall (!!!) isn't helping me understand the opposite argument.

Mark
Mark, Concerning the information on Firststart, I never said it was incorrect, just not complete. I actually believe the information provided is generally correct, but does not explain it in detail as most folks would not understand it anyway.

Yes mixing batteries will shorten the life of the batteries. How much. It really depends on to many variables to say how short. My guess based on 30 old years in engineering is pretty short, somewhere around 6 months in the average cruising boat. Could be 3 months, could be 9 months. That's just my thoughts, and obviously yours are completely different.

As to the VSR and blocking diodes, I take that to mean when they are part of a battery charging system, not as stand alone devices. You can use different batteries in different banks and the life of the batteries will not be effected much when blocking diodes are used. Pretty basic really.

Place AGM and FLA in a single bank and in my opinion, that will cause premature failure due to differences in internal resistance and battery chemistry. How much.... It depends on too many variables to say with certainty.

As to the rest of your list, TD covered it well enough. Too many variables to say exactly how things will go. But Voltage and SOC only balance when all batteries are the same type and really close to the same age. Even using the same battery types but of different ages, will cause less then full charge in the newer batteries.
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