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Discussion Starter #1 (Edited)
I'm sure this has been answered before but I can't seem to find it, and I'm getting myself confused. My daily Ah draw is estimated to be around 45, conservatively I'm planning on 60Ah/day. We drive at least 30-40 minutes a day to trailheads, breweries, etc so I'm looking to maximize my charge time by getting a dedicated battery to battery smart charger. I want to keep solar open as an option for the future if I find it necessary but until then I'm looking to do a 250Ah -ish house battery, battery-battery charger, 1500-2000w inverter, and the ability to attach to shore power.

I understand an Inverter off the van battery can be used to power a 3 stage charger connected to the coach batteries but I don't think I want to go this way primarily in fear of forgetting to turn the inverter on, killing the van battery, and the 15% efficiency loss.

In researching different batteries it seems two 6V wired in series may be better then a 12v in terms of longevity and ease of finding a replacement. The batteries I'm looking at is the Rolls S6-275AGM which is rated at 250Ah. In the spec sheet from Rolls it says the recommended charge is 50amp with a max of 87.5A. The charger I'm looking at is the Sterling BB1250 which is rated at 50amp. Is the 50amp rating the number I'm trying to match to the battery spec? For example, if I went with the Rolls S6-370AGM (335Ah) which has a recommended charge rate of 77A I would need something like the Sterling BB241235 which at 12v is rated 70A?

Is the Ah rating of the battery fairly universal for what Amperage charger is required or are there 250-300Ah batteries that require a lower rated charger like 30A? What's the difference? Charge time?

Links to the batteries and chargers I'm talking about

Rolls S6-275AGM- http://rollsbattery.com/wp-content/uploads/batteries/S6-275AGM.pdf

Rolls S6-370AGM- http://rollsbattery.com/wp-content/uploads/batteries/S6-370AGM.pdf

Sterling BB1250- http://www.sterling-power-usa.com/SterlingPower12volt-12volt45ampbatterytobatterycharger.aspx

Sterling BB241235- http://www.sterling-power-usa.com/S...-12volt-dc-to-dc-batterytobatterycharger.aspx


I'm sorry if these are repetitive questions, I keep getting hung up on them though and I can't seem to find a straight answer with the search function. One last question, how do the chargers from Ctek compare to the Sterling? Are they also battery to battery? I like the idea that the sterling is automatic and that they also advertise it will charge up to 5x faster then simply using the alternator.
 

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Why would you not just use the alternator and a battery to battery interconnect device like the Battery Dr. or even better a solenoid? 2- 230 amp-hour golf cart batteries would work too either AGM or the better FLAs. Since that would work fine why “Doctor” it? Just wondering. BTW solar is a much better option, cheaper and has a mystical element better than those black boxes you are going to buy. Just say'n
 
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Why would you not just use the alternator and a battery to battery interconnect device like the Battery Dr. or even better a solenoid? 2- 230 amp-hour golf cart batteries would work too either AGM or the better FLAs. Since that would work fine why “Doctor” it? Just wondering. BTW solar is a much better option, cheaper and has a mystical element better than those black boxes you are going to buy. Just say'n
Trying to keep the roof open for white water kayaks (creek boats) and a top box. From what I understand the smart charger will charge the batteries much faster then just a basic combiner. Having no solar and driving an hour or so a day I want the most efficient charge possible. Van is being used for a mountain bike/kayak/snowboard vehicle with most trips lasting 2-4 days with a few 10 days trips throughout the year. I'm also not interested in venting the batteries, they're most likely being mounted dead center of the van. The only electrical system I've setup in the past outside of stereo installs has been a combiner so although I have a basic understanding this is mostly new to me. Surprised no one else has done something similar though? Any electronic guru's care to comment on the recommended charge rate and the charger amp rating? And why batteries like Trojan don't display a recommended charge rate on their spec sheet?
 

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Discussion Starter #5
I'm assuming meeting the recommended charge rate is not a big deal as I'm also assuming most people don't have a solar setup capable of the recommended 46A on the roof of their van... Is the difference just charge time? I will give Rolls a call tomorrow to see what they say.
 

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I'm assuming meeting the recommended charge rate is not a big deal as I'm also assuming most people don't have a solar setup capable of the recommended 46A on the roof of their van... Is the difference just charge time? I will give Rolls a call tomorrow to see what they say.
After doing some research on some of the more expensive AGMs mentioned on the forum like Rolls and Lifeline, I’d advise caution as many larger capacity batteries appear intended for residential solar and other applications with less physical limitations on the size of arrays or charging systems. In those systems it’s easier to size your array to match the recomended charge current.

I came across this link from a sailboat forum that discusses at length many pitfalls of AGMs and how you can ‘murder’ expensive batteries unless you adopt a system approach to your application. It also advocates FLA ‘starter batteries’ for beginners as they are cheaper and more forgiving when abused.

https://forums.sailboatowners.com/index.php?threads/agm-batteries-making-the-choice.124973/

P.S. It occurred to me that solar arrays and kayaks and snowboards on the roof aren’t necessarily mutually exclusive. Perhaps it’s feasible to mount kayaks and such over top of the solar arrays. Presumably you’d be riding or storing your ‘toys’ when your van is parked and that’s just the time you’d benefit most from the solar.
 

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Discussion Starter #8 (Edited)
P.S. It occurred to me that solar arrays and kayaks and snowboards on the roof aren’t necessarily mutually exclusive. Perhaps it’s feasible to mount kayaks and such over top of the solar arrays. Presumably you’d be riding or storing your ‘toys’ when your van is parked and that’s just the time you’d benefit most from the solar.
I think the solar is overkill. Moab is a great example. I make 7 or 8 trips a year, we camp on BLM land 30-45 minutes north of town. We're in town every day no matter for either food, beers, bike shops, different trailheads, etc. There seems to be a lot of talk of the Sterling B2B chargers over on the sprinter forums so they're definitely being used for this application.

I cant think of any BLM camping that's very near to where we would recreate. Worst case would be Sedona where we would most likely stay at the RV park in town since BLM camping is pretty scarce but then I would have shore power to plug in to.

The charging formula I found is from the lifeline website-

Charge Time = [(DOD/100) x Rated Capacity (Ah) ÷ Output of Charger (Amps)] + Absorb Time

It seems the batteries would be above 90% at the end of almost every day. I definitely want to keep the option of solar open, but I'd rather start the build without it initially.

I do have the HD alternator so I'm assuming a 50amp charger would not be an issue for it. I need to research what our alternators are capable of more I guess. I don't see an issue with going with the biggest charger the alternator will tolerate if the batteries accept it? I believe this is where the guy in the sailboat thread is talking about acceptance rates?

Also according to lifeline, "Lifeline does stipulate that these batteries ideally need to be charged at a minimum of 0.2C or 20% of rated Ah capacity or you will shorten the cycle life. They will not however quantify the impact of lower charge rates on cycle life. Dave V., the engineer at Lifeline, published a paper and presented it to his peers back in the 90's on current vs. cycle life. Dave's study found that AGM's do need minimum current thresholds in order to get the most cycle life. In short, higher charging currents do lead to longer cycle life with AGM batteries."

So a 250Ah batteries needs a 50amp charger. It seems a lot of guys here are running 30amp chargers with similar capacities, but it sounds like they may be shorting the life of the batteries by doing this.
 

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I for one have heard you loud and clear. You are going to do this no matter the advice we give. I think that is great! Go to it and document what you did and learned. I’ve found there are posters here who are looking for advice and use it and those who are looking for affirmation. Consider your plan affirmed. We can learn from you.
 
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Discussion Starter #10
I for one have heard you loud and clear. You are going to do this no matter the advice we give. I think that is great! Go to it and document what you did and learned. I’ve found there are posters here who are looking for advice and use it and those who are looking for affirmation. Consider your plan affirmed. We can learn from you.
You’re right, but creating a dialogue isn’t a bad thing. I’ve found with forums like these the vocal minority usually sways quite a few folks. I didn’t mean to offend anyone by not wanting solar, there’s plenty of threads started on sole to discuss that, and I’m not even permantently ruling it out. I just think for a lot of applications it’s extremely overrated when taking that money and investing in a good b2b could be more efficient.

I was specifically looking for people who are using a B2B charged instead of just the combiner route. From what I can tell this is the prefered charge method for AGM so you don’t wreck the batteries. A combiner AND solar seems like an ok route depending on battery choice but for someone not interested in solar a B2B seems like the most efficient/best practice. Please post evidence otherwise including charge times and battery specs if I’m wrong! We’re all here to learn. From what i recall you aren’t using AGM?
 

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Advice vs affirmation. Well said, RD. Both are valid.

Streetdoctor, you remind me of myself. I had even more valid reasons than you for eschewing solar. These patient guys tried for two years to talk some sense into me, but I resisted. Alas, I resisted until my ceiling, walls and trim were all nice and finished. Now that I have it, it works beautifully. It's one leg of a 3-legged stool: alternator, shore power, solar. With the three, charging essentially becomes a non-issue.

You 90% charge is not good enough for long term battery health. AGM's require a long slow tail with a push (I liken it to stuffing) at the end. This is where solar shines. Quite often, we will have driven for several hours and the alternator has charged the house batteries into the 90's. Maybe when we park, it's cloudy or we have some shade and the solar isn't putting out squat. But it's more than enough to massage those batteries slowly but surely up to their beloved 100%. Your daily trip into town just isn't going to do that.

Edit: Maybe I've already addressed, but I will re-emphasize. Proper charging of AGM's is a lengthy process. No matter how speedy your bulk charge or how fancy your B2B, stuffing that last bit takes time, and there's no speeding it up. On average, it takes my 200Ah Trojans 3-4 hours to go that last 10%. Before solar, they simply never made it unless we plugged in. If they don't get that final stuffing, they will lose that capacity.

The other reason for solar is simply peace of mind. It is cheap in the scheme of the whole build. It is painless. It just works. You are in sun country.
 

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My input...

I have a Battery Doctor combiner with (2) AGM batteries (heading into year 3). They provide power for everything I need. Lights, radios, tv, microwave, USB charging, etc.

They charge when I drive. When plugged in, I have an RV converter/charger that keeps things topped off.

Your van battery/alternator will provide a certain amount of power (volts & amps). It seems to me that no matter how you B2B it, there is only so much energy available to charge your aux batteries. A B2B doesn't "make" energy, so I'm not sure how the additional cost can make a big difference in the amount of energy that get from the van to the aux batteries.

Just my thoughts.... others have done the B2B thing, I hope they will respond too.
 

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So a 250Ah batteries needs a 50amp charger. It seems a lot of guys here are running 30amp chargers with similar capacities, but it sounds like they may be shorting the life of the batteries by doing this.
2 questions

When they say we're shortening the life of our batteries, what would the standard life be and what is the shortened life? 10 years down to 5?

Can someone tell me the bad practices that would wreck expensive batteries?



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No offense for sure! I use FLA because I am convinced they are the BEST battery for this application. I use solar almost exclusively because it works. Efficiency is an interesting term and I don't think we agree on its meaning. I ascribe to the KISS principal. If it is right for the job, works without failure or mystery, does this for 10 years or so, costs less than more esoteric solutions and returns real value for the money, I call that efficient. Solar and super rugged golf cart lead batteries do that. I can’t think of a reason to adopt a more complex, less user repairable or testable black box that is unnecessary. I did read your responses, I paid attention to your plan. I am sure what you are thinking about will work great. More efficient? Not in my book. I have yet to be convinced the alternator can’t do what you want. You could go that route and if it doesn’t work for you plop the B2B in then. I’d appreciate feedback if you try that and find it does or doesn’t work.
 

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......... When they say we're shortening the life of our batteries, what would the standard life be and what is the shortened life? 10 years down to 5?
Can someone tell me the bad practices that would wreck expensive batteries?
I have mostly experience and only bit of research on this. My opinion for FLA batteries is they last >10 years (perhaps much more) in applications where they are discharged to 60% and recharged at .1C (10% of their capacity in amps) 20% is recommended and an occasional higher charge rate seems to help a bit. Our batteries should be rated as storage not starter batteries. I lived 10 years off grid with 19- 6 volt deep cycle marine batteries and a 3KW windplant. I sold those batteries to another off grid user and he used them for lots of additional years. My last RV battery lasted 8 years and was still good. Pairing the battery to solar allows the charge rate to be managed. 200 amp hours of battery needs 200 watts of solar and 300 would be a bit better but will have almost no effect on life IMHO. Discharge is death for lead batteries and left discharged is the fastest death. Our alternators are designed to charge a starter battery and will be OK for our storage batteries but a solar controller is better. A battery left dead for a month might as well be discarded at any age. AGM are lead and most of the same applies. They will not put out quite as much current and maintain voltage, they will not last as long and require a different charging protocol. I have researched that not experienced it although I do have several AGM batteries for several uses. YMMV
 

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Your best setup would be:

1) Have as many watts of solar as you have amps of batteries. So if you have 250Ah of batteries, get 300W of solar
2) Also charge through the alternator via one of those ACR dealios

As Ms.Nomer said, the alternator will get the batteries from XX% to 90+% really quickly, and then the solar will bulk charge and then float up to 100%. Also, you'll find that when the van is parked and not being used, the solar will nicely float the batteries (and the van battery too), and runs the fridge, so that never gets turned off. Lastly, you get another 25-30Ah (actually usable) from the van battery when everything is hooked via ACR. Cause when the batteries are > 12.8V, the ACR ties everything together, so you'll have an extra 100Ah battery hooked up until it dips under 12.8V, at which point it unhooks to make sure the van starts.

I did the above (300Ah of batteries, which turns in 400Ah when everything is nice and charged) and it works great. The only thing I have is only 200W of solar, as I just haven't installed my 3rd panel yet. I honestly have been just fine with 200W of solar in Colorado since the sun is more intense here. I'll be installing the 3rd, just cause I already have everything, just been busy. That powers all the lights, fans, fridge, heater, usb outlets via DC, and the 2000W Xantrex inverter charges a laptop, and runs the toaster oven and electric kettle. I use a butane stove for cooking, but have been noodling with converting to an invection one, but haven't found the need to yet. IF I decide to do a electric water heater, I'll be upping the batteries to 450Ah (550 when the van battery is hooked up).

Lastly, I do have a shore power plug that is underneath the van attached to the rail. That plug just has a 3 way outlet on it. Into that is plugged in a 20Ah charger that is hooked to the batteries, and I can unplug the van plug from my inverter and plug it into that, so the AC outlets in the van become full hot and the DC stuff runs off batteries that are fully charged. If I had to do it again, I would NOT bother with all that, as I haven't used it even once. Once you have a van, you don't stay at places that have plugs anymore. There is too much awesome nature to explore :)
 

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I have mostly experience and only bit of research on this. My opinion for FLA batteries is they last >10 years (perhaps much more) in applications where they are discharged to 60% and recharged at .1C (10% of their capacity in amps) 20% is recommended and an occasional higher charge rate seems to help a bit. Our batteries should be rated as storage not starter batteries. I lived 10 years off grid with 19- 6 volt deep cycle marine batteries and a 3KW windplant. I sold those batteries to another off grid user and he used them for lots of additional years. My last RV battery lasted 8 years and was still good. Pairing the battery to solar allows the charge rate to be managed. 200 amp hours of battery needs 200 watts of solar and 300 would be a bit better but will have almost no effect on life IMHO. Discharge is death for lead batteries and left discharged is the fastest death. Our alternators are designed to charge a starter battery and will be OK for our storage batteries but a solar controller is better. A battery left dead for a month might as well be discarded at any age. AGM are lead and most of the same applies. They will not put out quite as much current and maintain voltage, they will not last as long and require a different charging protocol. I have researched that not experienced it although I do have several AGM batteries for several uses. YMMV
So basically since my solar is constantly keeping my batteries charged or close to 100% my batteries are OK? That has been my assumption anyway. I really haven't used anything other than lights and fridge. Some usb charging for my phones. I plan to get a victron battery monitor but have some other things to buy before I do that.



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You know Josh you probably can skip the victron. It is neat, I have a watt meter, it is a number on the wall. Since I cycle each day it is normally irrelevant. if the sun doesn't shine for a few days I need to run the van, I don’t really NEED a meter to tell me that. Buy the good stuff you want first.
 

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You know Josh you probably can skip the victron. It is neat, I have a watt meter, it is a number on the wall. Since I cycle each day it is normally irrelevant. if the sun doesn't shine for a few days I need to run the van, I don’t really NEED a meter to tell me that. Buy the good stuff you want first.
That's why it's down on the list. Once I install the battery doctor there will be less need for it.

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