Final decision made today on batteries

[bobofthenorth]

My question is how to reconcile a 24 volt battery bank when I'm giving away half the amp hours because they are in series.

I'm sorry - I don't understand the question.  Are you saying you have a 24 volt bank with a 12 volt tap for your inverter?

[Oonrahnjay]

I'm sorry - I don't understand the question.  Are you saying you have a 24 volt bank with a 12 volt tap for your inverter? 

       Yes, I couldn't quite figure that out, either.  Amps and volts don't matter -- what does your work is watts.  Switching from 12V to 24V has effects (battery cabling, wire sizes, etc.) but when you're dealing with energy storage and work, it's the watts and it's all the same.  Scott isn't "giving up anything" in terms of watts.

[Scott & Heather]

Sorry for my muddy response. Since my coach start system and house system are technically one bank, I have to keep it set up in terms of 24 volts right? Batteries are in series which cuts my amp hours in half. I only have it this way of course for the coach 24 volt side. So if I wanted to get a 12 volt inverter and use it how do I do that while also providing 24 volts to the coach? I other words is there a magic way to have my four 12 volt batteries wired as four 12 volt batteries (105 ah each which totals to 420ah) versus 24 volt which cuts that in half. Or is this the precise reason to run two separate banks grrr


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[buswarrior]

You are using the wrong units and math.

the wattage of that collection of batteries does not change, whether you wire it up properly in 12 volt or 24 volt.

You have the same energy available, work out the math, your voltage number doubled, when your amp/hour number halved, in the equation for watts, it will work out to the same total.

I am a fan of single battery bank, busnuts haul around way too much wasted money in redundant lead.

Dead batteries are the result of carelessness, ignorance, and/or insufficient funds spent on over-seeing electronics.

Each of us can manage to regulate our breathing? Then regulate your batteries similarly?

Don't screw around, put the kids on Kraft Dinner, and go get that big Magnum 4024.

Manage available incoming power, really convenient when all that is available is a 15 amp extension cord. Use the power in the coach at will, the Magnum will just take what it is allowed from the cord, and make up the rest from the battery bank, and goes back to charging when the power consumption drops sufficiently to allow that. No more blown breakers inside that locked facility during the night... built-in superior multi-stage charger...

You buy how many hundred dollars of batteries, try to take care of them with inadequate collection of mismatched pieces, and have to prematurely spend more hundreds of dollars replacing them.... the Magnum can be readily justified as battery protection money well spent?

You will end up with one later, after pi$$ing money on inadequate solutions...

You will have to "centre-tap" the bank for your other 12 volt needs. Battery health dictates that you get a battery equalizer, Vanner is the big player here. This magical box connects to the ground, 12 volt centre and 24 volt side, and keeps the two 12 volt pieces balanced, as you drain away from the middle. Always connected.

Without a Vanner Equalizer, you will be a battery murderer with a centre tap, even a load as small as the retrofitted car stereo will start the tumble.

As you are doing, choose your own path, and tell the rest of us to sod off!

happy coaching!
buswarrior

[luvrbus]

A good thing about a small battery bank is the charging time required to bring it back to 100% and they need to be 100% or you loose the amp hrs.
We have a friend with a new Prevost he has 10-8D Lifeline AGM batteries just for the house system it take 8-10 hours of generator time to charge his system 

[windtrader]

We have a friend with a new Prevost he has 10-8D Lifeline AGM batteries just for the house system it take 8-10 hours of generator time to charge his system

That drives me nuts, running a huge generator to float/trickle charge a battery bank. I gave up trying to top mine off with the generator after installing the new house bank. Went to an RV park and plugged in for 24 hours and batteries and I are happy as can be now.

I have much to learn about flooded batteries and charging. I believe multi stage chargers minimize abusing batteries that suffer with primitive charging systems. The key learning is a 3 stage charger will quickly get the battery back to 90% of it's previous SOC not the full capacity of the battery.

For example, a battery with 80% SOC is drawn down to 40% DOD. Start the charger, it will bulk, absorb, then float the battery back to 80%. The remaining 20% DOD will be filled during the float charge cycle which can take many hours.

This is why it is critical to ensure you have your batteries topped off when you start using them as the 3 stage charger will get you back to about 95% SOC rapidly and the float then only needs to trickle that last 5%.

What happens is people don't realize this charging pattern so the battery slowly loses its capacity a few percent at a time unless letting the float cycle run to top off the bank. For those on shore, this is rarely even observed since the charger is always on. As I boondock 95%, there is a whole different set of conditions to deal with.

As in this case, there is a strong tendency to shut off the generator once it floats thinking the bank is fully charged, not knowing each cycle you are down a few %.

[niles500]

Don, think your a little confused: Bulk charging will bring the batteries to 80-90% ; Absorption brings them to full charge ; Float simply maintains the batteries at full charge HTH

[windtrader]

Niles, that is precisely the misconception most have, including me until I figured it out. That is why the battery charging cycle is 6-8 hours on golf batteries. Most of the bulk charge happens quickly, most of the time is spent topping off on float.

Here's the math. I have a 24v 210Ah bank (4x 6v 200Ah in series). The charger is set to charge at 40 amps. With a DOD of 50%, it needs to replace 100Ah. At 45 amps it's 2.0 hours to get 90% back in, the remaining time spent on float is taking care of the last 5%-10%

[Scott & Heather]

Bus warrior, I loved your post. Really actually resonated with me because we are sometimes in those exact situations needing to plug into a 15 amp outlet and setting off breakers inside a locked building. Totally my life sometimes. I am saving up $$ for that magnum...i absolutely cannot wait to own it. Will really make life easier for us! I'm still lost on the 24/12volt amp hour deal but I'll study up on it using the mighty google. Not trying to "sod off" anyone,...I just like having one bank and was just making that clear...


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[niles500]

Don I respectfully disagree, you have too be careful with the Net there's a lot of bad info out there, here is a white paper from Xantrex, a well respected company - HTH

http://www.xantrex.com/documents/Battery-Chargers/TRUECharge/MS20070308_3-stage-whitepaper.pdf

[windtrader]

Niles,

That same document, except printed by Vanner on their 3/4 stage inverter/chargers, is what had me MISdirected for some time. It is misleading.

Go back and reread it carefully. Nowhere does it state it bring the battery back to 100% SOC in x time, just that it fully charge with enough time on float. And all that stuff about 100% charge is  what the battery is capable of accepting during those bulk and absorb phases.

The literature assumes battery had a full charge before being drawn down. Then the phased charging make sense as the battery does return full again.

It does not work the same if you started drawing off a 80% SOC battery. Maybe if you set the bulk voltage to the max, lowest current for absorption, etc. to maximize charging then it would be closer to 100% SOC once it hit float. However, the faster you charge you run the risk of overheating and gassing too much.

[bobofthenorth]

I can't add much to what Ewen said but I can reinforce his advice to forget about amp hours and think in watts.  You don't lose or gain anything by connecting in series or parallel - a watt is a watt is a watt.  Get you a 24 volt inverter and life will be even better than it is already.

[Scott & Heather]

Ok good info. Thanks guys


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[luvrbus]

You guy confuse the heck out of me ? when talking to the Lifeline rep he made mention a battery will only produce so many watts in a 20 hr period according to amp hour rating on the battery what did I miss here   

[buswarrior]

luvrbus, you need to read more internet...

happy coaching!
buswarrior