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 > adding a second house battery bank

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pnichols

Santa Cruz Mountains

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Posted: 04/30/12 09:58pm Link  |  Print  |  Notify Moderator

Mena,

Bowing is OK so long as it doesn't conflict too much with certain observed performance.

P.S. I'm still looking for someone to provide sound engineering data showing all AGM batteries are indeed engineered the same. Mine so far have acted, long term, as I have stated when ganged with Ford's liquid acid chassis battery.


Phil, 2005 E450 Itasca 324V Spirit

mena661

Southern California

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Posted: 04/30/12 10:41pm Link  |  Print  |  Notify Moderator

pnichols wrote:

Bowing is OK so long as it doesn't conflict too much with certain observed performance.
I think a battery engineer has observed plenty of performances. You need to do some searches here on Mex's credentials. I stand by my post.


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Son of Norway

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Posted: 04/30/12 10:55pm Link  |  Print  |  Notify Moderator

Thanks to everyone. I am doing my best to understand things. Does the fact that AGM's charge faster than lead-acids mean they can't be charged from the same converter? However, even if they can't be charged together, shouldn't they be able to be discharged together as long as they are isolated from each other?

Miles

* This post was edited 04/30/12 11:11pm by Son of Norway *

westend

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Posted: 05/01/12 03:19am Link  |  Print  |  Notify Moderator

Following this closely since I may be in the same situation (using both AGM and car jars). Since there is a substantial difference in resistance between the two battery types, it may be a fool's errand because one part of the basic electrical formula becomes a variable (my initial take on it). My first assumption is that it is going to take a considerable amount of hardware and wiring to result in both types of batteries getting charged correctly. My second assumption is that if both types are connected to power the coach, there will be a unfavorable flow of current between the two types and the devices they are powering. Maybe Mex or someone that has done a similar setup can chime back in and straighten me out.
Mr Nichols experience points to the practical aspect that using the two types together can be done but may be due to the configuration of his sytem and the power use and not typical of others.


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Son of Norway

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Posted: 05/01/12 08:23am Link  |  Print  |  Notify Moderator

I just got off the phone with the AGM battery rep. He told me that the AGM's can handle the same charging voltages (bulk and float) as the golf-carts but if they are both connected to the same charger, the AGM's will grab more of the charging amperage due to their lower internal resistance. That will be bad for the AGM's because they should be charged at a slower rate.

We discussed using a relay that will isolate the AGM's when they are being charged. That way a smaller charger could be used for them. Even with a smaller charger, they will charge more quickly than the golf-carts. He said that using them together with the golf-cart batteries during discharge is OK with a battery isolator.

This will make for a considerably more complicated system, but I've already paid for the AGM batteries, so I want to get them in service.

Miles


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pnichols

Santa Cruz Mountains

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Posted: 05/01/12 10:52am Link  |  Print  |  Notify Moderator

Here's a .pdf link to information on the two AGM batteries I use in our RV - the Interstate rebadged version of C&D's DCS-100HIT:

http://www.cdtechno.com/pdf/lit/12_1061_10.pdf

Note -

1) Their very low internal impedance - this makes for faster charging at all applied voltages ... especially so if your charger can deliver very high currents without drooping of it's terminal voltages and provided that your charger AUTOMATICALLY THROTTLES BACK IT'S DELIVERED CURRENT per temperatures that it's temperature compensation circuit detects on the AGM battery case (very important for ultra high current, and fast, charging situations). For my situation, the alternator (and the RV's fixed voltage Parallax converter when camping) can never supply enough current while simultaneously maintaining high enough terminal voltages to get into the AGM battery's high temperature danger (called "thermal runaway") zone.

2) Their 50% discharge point cycle life rate (1800 cycles) is very good.

3) Their Float Charging and Cycle Service voltages are right there in the ballpark as to where converters and vehicle alternators operate.

So ... can my brand of AGM batteries and my stock Ford chassis starting battery be directly connected together in parallel without damage ... so far it has been ... YEP.

pnichols

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Posted: 05/01/12 11:28am Link  |  Print  |  Notify Moderator

Quote:

That will be bad for the AGM's because they should be charged at a slower rate.


Huh????

Not so as far as I'm aware of ... unless of course it's because CG chargers (at golf courses) are such high power that they would force an AGM battery into thermal runaway.

mena661

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Posted: 05/01/12 04:27pm Link  |  Print  |  Notify Moderator

pnichols wrote:


Huh????

Not so as far as I'm aware of ... unless of course it's because CG chargers (at golf courses) are such high power that they would force an AGM battery into thermal runaway.
Yeah, I agree here. AGM's can most certainly take high charge rates (watch that temperature). At LEAST as much as flooded anyways.

KendallP

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Posted: 05/01/12 06:10pm Link  |  Print  |  Notify Moderator

AGMs can take higher charge rates, but it requires higher voltages than our little converters are capable of to realize any performance increase in this regard. With regulated voltage, AGMs will go into absorption mode just like any FWC battery.

Put simply: There is no quick charging benefit to AGMs using a typical RV converter, be it PD, IOTA or whatever.

Now...

Someone correct me if I'm wrong, but I had thought that MrWizard was already operating AGMs alongside GC2s with no ill effect.


Cheers,
Kendall

1986 Winnebago Chieftain 22RC
Our Camper (Don't laugh...
Unlike our credit cards... she's paid for)


full_mosey

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Posted: 05/01/12 07:10pm Link  |  Print  |  Notify Moderator

Allow me to think out loud.

If AGMs have less internal resistance, then less of the charging watts will be converted to heat when compared to flooded.

This means that less total watts will be needed to charge the AGM. Now you may not notice this when charging from shore power, but you may notice the extra power needed when charging from your genny.

I would think that if both types are charged in parallel, then the AGMs would accept Amps faster and their Voltage would rise faster. I would be more concerned about the health of the flooded batteries.

Comments?
John

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