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two Banks of batteries, one AGM and the other lead acid

Old 01-21-2017, 10:34 AM
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Default two Banks of batteries, one AGM and the other lead acid

Can I run the battery switch on 1&2(all) with this set up? Agm bank is a single large 1100mca and bank 2 is two 750mca dual purpose lead acids. Thanks
Old 01-21-2017, 11:53 AM
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Conventional wisdom is to never mix battery technologies on the same bank. If you go to ALL, you are doing that ...
Old 01-21-2017, 08:38 PM
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agm is lead acid.....

it's more or less fine. the switch should never be on both anyways unless emergency starting.
Old 01-22-2017, 01:44 AM
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First, you never said whether these are both engine (starter) batteries or whether this is an engine/house setup... It matters because if it's an engine/house setup I'm wondering how you're handling the charging...

Either way, the "1 & 2" (a.k.a. "Both") setting is something that should only be used in emergencies (e.g. depleted engine battery)... You should NOT use that setting on a regular basis... It defeats the purpose of having dual electrical systems!...

IOW, if you have an emergency go ahead and use that setting... Nothing bad will happen... Otherwise, you're MUCH better off keeping your electrical systems separated...

I've tried to think about WHY you would ask a question like this... I have come up with the following scenarios:
  • Single engine scenarios (implies an engine/house setup):
    • You have an engine that's set up for the charging of two battery banks... You've "lost" one of the two charging terminals on your engine's alternator and are looking to charge both banks while out on the water. The proper thing to do would be to have your engine's alternator fixed. As an alternative you can use an "add-a-battery" kit or combiner and have both battery banks get charged from a single terminal...
    • You have an engine that's NOT set up for the charging of two battery banks... You had some sort of battery combiner that allowed the independent charging of two battery banks... Your combiner has bit the dust... The proper thing to do would be to fix or replace your combiner.
  • Dual engine scenario:
    • You have "lost" the ability to charge on one of your engines... The proper thing to do would be to get the faulty alternator repaired... You could use an "add-a-battery" kit or combiner on the other engine as an alternative but I would very much advise against it... That alternator would be working twice as hard as originally planned... It will give up the ghost sooner rather then later...

Last edited by Navatech; 01-22-2017 at 01:55 AM.
Old 01-25-2017, 12:37 PM
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Single engine, 2 banks. one starter, one stereo & misc.

Reason for contemplating it is my starting batt for 300 etec is getting weak and a buddy redid his wiring and got all new batteries and gave me a 1100mca battery in great shape.

When needed i charge each bank separately with a Battery Tender charger or run the individual bank alone when out on the water. Since I'm the only one who runs the boat I think I can keep track of battery switch

Thanks for the replies and any more are welcome. Phil
Old 01-25-2017, 12:46 PM
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Originally Posted by PalmBeachMarineFuel View Post
Single engine, 2 banks. one starter, one stereo & misc.

Reason for contemplating it is my starting batt for 300 etec is getting weak and a buddy redid his wiring and got all new batteries and gave me a 1100mca battery in great shape.

When needed i charge each bank separately with a Battery Tender charger or run the individual bank alone when out on the water. Since I'm the only one who runs the boat I think I can keep track of battery switch
I like the fact that you have a separate engine and house batteries set up... Having said that, the OFF/ONE/TWO/BOTH switch you're using is old technology... I'm also going to assume that you have two of those... One for the engine circuit and one for the house circuit... The modern way to do this and to be able to "forget" about managing the charging is to get what's called a "add-a-battery" kit... The kit consists of a dual circuit main switch and an ACR (Automatic Charging Relay)...

The ACR will ensure that your engine battery will have precedence in charging and it will prevent you from discharging both batteries by mistake... I warmly recommend you, at least, consider it...
Old 01-26-2017, 05:35 AM
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Originally Posted by PalmBeachMarineFuel View Post
Can I run the battery switch on 1&2(all) with this set up? Agm bank is a single large 1100mca and bank 2 is two 750mca dual purpose lead acids. Thanks

If you have an installed onboard charger, your charger manual will include instructions about charging profiles for various types (FLAs, AGMs, gels...). The manuals for your batteries will tell you the recommended charging voltages for each. You may be able to pick a charger setting that works for both FLAs and AGMs at the same time. (I dunno what a Battery Tender is, but it's probably got a manual...)

If your only charging source is engine alternator, you'll maybe have less flexibility, but generally AGMs and FLAs are the same chemistry (lead-acid) and they often use more similar charging voltages (unlike gels), so generally running (and charging) both simultaneously "should" be OK. See again, your battery manuals.

-Chris
Old 01-26-2017, 05:50 AM
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Regarding AGM batteries, the term AGM relates to the construction method; the battery is still a lead-acid battery. The precise charging requirements of an AGM battery (or any battery for that matter) are specified by the manufacturer and are usually related to temperature.

To the best of my knowledge, there are no OUTBOARD engine charging systems that have any sort of battery charging output which can be modified according to the type of battery attached to the engine. The typical charging output is just a simple voltage-regulated output with the voltage typically about 14.5-Volts.

Charging current applied to any configuration of batteries in parallel will not be likely to be equally divided between the two (or more) batteries in parallel, no matter what type of batteries are involved. The charging current will only be equal if all the batteries are of the exact same type, have the exact same chemistry, begin at the exact same state of charge, and all connections involved in the circuit have the exact same resistance. That is not going to be typical.

If you charge a group of batteries in parallel for a long time, eventually they may all arrive at the same state of charge--which may not necessarily be a full state of charge; it could be a lower state of charge due to problems in one of the batteries holding down the others. For that reason I find it preferrable to charge batteries individually.
Old 01-27-2017, 05:38 PM
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As an AGM has a different charging profile than a flooded battery, and an AGM charges faster than a flooded battery, I believe one of two things will happen if the flooded battery and AGM are in parallel with a single charging source.


1. The AGM will reach full charge first, and will be overcharged as the flooded cell continues to charge.


2. The charging source will stop charging the battery bank when the AGM is fully charged leaving the flooded cells undercharged.


Jim
Old 01-27-2017, 07:02 PM
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Originally Posted by jfwireless View Post
As an AGM has a different charging profile than a flooded battery, and an AGM charges faster than a flooded battery, I believe one of two things will happen if the flooded battery and AGM are in parallel with a single charging source.


1. The AGM will reach full charge first, and will be overcharged as the flooded cell continues to charge.


2. The charging source will stop charging the battery bank when the AGM is fully charged leaving the flooded cells undercharged.


Jim
Jim is 100 percent correct. If you buy a Powermainia as an example you can charge two types of batteries and the charge will know exactly what you have hooked up. This in most cases eliminated any issues of they are not on BOTH.

Mike
Old 01-27-2017, 09:40 PM
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agm is lead acid.....

Yes, it is, but it's not the same technology as a flooded lead-acid and doesn't have the same charge profile ...
Old 01-27-2017, 09:57 PM
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I have 2 wet of different sizes and ages and an AGM that is bigger than both of the wet ones. I charge them all at once with the same charger via ACR's and in 3 years I've never had any concerns. BUT like has been mentioned, it's not a recommended practice so it's better to spend $500 to charge each individually.
Old 01-28-2017, 07:08 AM
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Originally Posted by jfwireless View Post
As an AGM has a different charging profile than a flooded battery, and an AGM charges faster than a flooded battery, I believe one of two things will happen if the flooded battery and AGM are in parallel with a single charging source.

1. The AGM will reach full charge first, and will be overcharged as the flooded cell continues to charge.

2. The charging source will stop charging the battery bank when the AGM is fully charged leaving the flooded cells undercharged.

Yes, but... Depends. Our charger individually adjusts for each of three banks. Within reason (i.e., when the banks are generally similar in capacity). The charger manual should address that.

-Chris
Old 01-28-2017, 08:05 AM
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They will both be charged fully on the AGM setting.

They are BOTH lead-acid batteries and have the same chemistry and voltage profiles. The difference is construction, one using Glass Mats the other using conventional plate dividers. With the open structure of the latter, bubbles can rise so if allowed to go significantly above 14.2 so the electrolyte is agitated to minimize density stratification. This is beneficial for battery life. However instead of liquid electrolyte the AGM has the electrolyte trapped in the Glass Mat. Stratification is no longer a problem but bubbles can displace the electrolyte and leave bubbles that may not get re-absorbed and leave gaps in the electrolyte. This is not beneficial for battery life.

So you can use the AGM setting for both types and both will be fully charged. The downsides are :
1. The lead acid battery won't get agitated, although once a month is typically all that is needed for equalizing, not every charge.
2. Since voltages will be lower to protect the AGM battery from "lead-acid voltages" it will take a little longer to fully charge but both will still be fully charged.
Old 01-28-2017, 01:18 PM
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Originally Posted by yandina View Post
...the difference is construction, one using Glass Mats the other using conventional plate dividers. With the open structure of the latter, bubbles can rise so if allowed to go significantly above 14.2 so the electrolyte is agitated to minimize density stratification. This is beneficial for battery life. However instead of liquid electrolyte the AGM has the electrolyte trapped in the Glass Mat. Stratification is no longer a problem but bubbles can displace the electrolyte and leave bubbles that may not get re-absorbed and leave gaps in the electrolyte. This is not beneficial for battery life...
Thanks for the excellent explanation for the differences in recommended charging voltage for the AGM and flooded-cell batteries. I had not heard it explained that well before.
Old 01-28-2017, 01:22 PM
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Thanks for the comments, here's a different question. I've read in a few places that it's not recommended to run on all (1&2) even if you have matching batteries. Is this true or internet bs? Thnx
Old 01-28-2017, 02:00 PM
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When you run on BOTH you make the two batteries into a single bank that act like one big battery. It makes sense that you might want to do this for charging, but you lose the redundancy of having two batteries on board. If you forge to turn the switch off when you leave the boat both batteries are dead and now you can't start your engine. If one battery is failing it will drag the other down with it. If the batteries are identical there is no harm to them when running on BOTH.

A VSR like the blue sea add a battery kit gives you the benefit of charging both but maintaining isolation and protecting you from draining both batteries should you forget to turn the switch off.

There are times when I run on BOTH to give a charge to both batteries but I try to remember to leave it on 1 or 2 to maintain redundancy. I haven't put in my Add a battery kit yet as my batteris are forward and my switch is back. Haven't had the time to snake wires.
Old 01-29-2017, 03:05 PM
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Originally Posted by yandina View Post
They will both be charged fully on the AGM setting.

They are BOTH lead-acid batteries and have the same chemistry and voltage profiles. The difference is construction, one using Glass Mats the other using conventional plate dividers. With the open structure of the latter, bubbles can rise so if allowed to go significantly above 14.2 so the electrolyte is agitated to minimize density stratification. This is beneficial for battery life. However instead of liquid electrolyte the AGM has the electrolyte trapped in the Glass Mat. Stratification is no longer a problem but bubbles can displace the electrolyte and leave bubbles that may not get re-absorbed and leave gaps in the electrolyte. This is not beneficial for battery life.

So you can use the AGM setting for both types and both will be fully charged. The downsides are :
1. The lead acid battery won't get agitated, although once a month is typically all that is needed for equalizing, not every charge.
2. Since voltages will be lower to protect the AGM battery from "lead-acid voltages" it will take a little longer to fully charge but both will still be fully charged.
So lets assume you are correct and an AGM charging setting is ok for both, you may be correct but the aggressive AGM charging profile concern's me for a flooded battery. So an intelligent house battery charger being set to AGM, but what about an outboard motor charging both batteries in parallel? My Yamaha and Suzuki outboards have no AGM setting I know of? How do they know what charge profile to use when an AGM and flooded battery are in parallel?

Jim
Old 01-29-2017, 08:21 PM
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Originally Posted by jfwireless View Post
So lets assume you are correct and an AGM charging setting is ok for both, you may be correct but the aggressive AGM charging profile concern's me for a flooded battery. So an intelligent house battery charger being set to AGM, but what about an outboard motor charging both batteries in parallel? My Yamaha and Suzuki outboards have no AGM setting I know of? How do they know what charge profile to use when an AGM and flooded battery are in parallel?

Jim
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Old 01-30-2017, 06:25 AM
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Originally Posted by jfwireless View Post

My Yamaha and Suzuki outboards have no AGM setting I know of?
How do they know what charge profile to use
when an AGM and flooded battery are in parallel?
of course, they don't know, nor do they use a "charging profile".
The regulator/rectifier regulates voltage, and shunts any "unused" power to ground (which is why the r/r is often water-cooled)

my understanding is "the aggressive AGM charging profile" is not something that the charger does -
but simply results from the internal resistance of the battery itself (lower than that of a flooded type)

in the case of the Yamaha generator, some amount of amps are "available" at a controlled voltage:

with both an AGM and a flooded connected at the same time /same voltage,

the AGM will simply "accept" more amps (hence "charge" more) than a similar size flooded battery can.


I may have this wrong.
The "hype" of some battery manufacturers, and much worse - the "smart charger" marketers - is an almost impenetrable fog.
I look forward to being corrected.

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