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Old 09-23-2020, 07:52 AM   #1
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Soliciting battery advice

Son-in-law just bought a big, new Keystone 5th wheel toy hauler that came reasonably well fitted, but as expected, they put cheap batteries in. It's got 3 trays, with 3 Interstate 12V lead acid 64Ah batteries (obviously) wired in parallel. He's a hunter, and spends the majority of his time boondocking so we're looking to increase the Ah capacity as high as we can. It's got 245W of solar on the deck and an MPPT controller, but 192Ah (64Ah x 3) just won't get it done with all the lights, TV, 2000W inverter, etc. Lithium is out since the batteries are in unconditioned space and temps will get too low. I was thinking 2 or 3 12V AGM batteries in the 200Ah range, but then it struck me that the genny is using the battery bank for starting, so it may require a dual purpose battery set up. Or maybe a combination of (2) 200Ah AGM deep cycle's for house and another battery dedicated to the genny starter? But then what would need to be done to keep the separated banks charged and monitored. I assume I'd need another dedicated panel and charger if I went that route?

Any input would be appreciated, we want to get this right.
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Old 09-23-2020, 08:24 AM   #2
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Your not going to find a 200 AH battery unless you look at the large, 150 lb, 4D or 8D type.

What you can use is 3, DP31, deep cycle batteries. They are rated at 100 to 105 AH.

Deep cycle batteries can easly start engines. A majority of RV generators start on house batteries.
Starting batteries don't work in deep cycle situations well.

Sam's Club or Batteries + sell Duracell Gp31, AGM, deep cycle batteries.
They also sell the same battery in a Maintance free flooded acid design, with about the same specs. They will give you the same service.
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Old 09-23-2020, 08:29 AM   #3
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You’re over thinking the generator start a bit. The engine is much smaller, and doesn’t take as much power to start as a car.
You could do something like this for 300Ah:

https://www.amazon.com/Weize-Battery...&tag=hydsma-20

I have 380W solar and 250Ah of battery. Even on cold nights where the furnace runs quite a bit, the solar array has the batteries topped off by about 9:00AM.
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Old 09-23-2020, 08:33 AM   #4
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I wouldn't be too concerned about having a "start" battery dedicated to the genset. If you're looking to expand the bank's AH capacity to triple digits, you'll have more than ample capacity for cranking a genset, even with the bank at 50% SOC.

If you're uncomfortable with that scenario, you could fit a grp 24 battery dedicated to starting the genset. If the genset has its own charging system, you needn't worry about charging that battery. If the genset doesn't have a charging system, then you'll need to provide a means to charge that dedicated start battery, which would be overkill. There's probably not going to be a situation where you would not have a tow vehicle to provide a jump start in the event that the house bank is down too far to start the genset, and if the system has an inverter, it could be fitted with an auto start to run the genset in the event the bank drops too low while away from the rig.

To demonstrate that you don't need a dedicated start battery, do some calculations to determine the actual amp hours consumed in starting the generator, then relate that to the amp hour capacity of the house bank at 50% SOC, You'll see that the starting energy is very minimal. Just don't see the need to complicate the system with an additional battery and the gear to charge and maintain it.

When configuring the bank, keep in mind that if there are limitations in footprint real estate, you may be able to gain capacity with height. AGM's afford some flexibility in that as well as charge acceptance. But don't overlook that the charging profile for AGM's may be significantly different than flooded cells, You'll want to pay close attention that your charging profile complies with the battery manufacturer's spec. Don't rely on a generic profile. They're rarely accurate. The devil's in the details.

You can kill an expensive AGM bank by improper charging. The most important part of charging is regularly floating the bank to 100%, and the solar is perfect for that. Just make sure the profile is accurate.

The main points in considering AGM's is they don't require watering, they don't gas as much, they have a higher bulk/absorb acceptance rate, they have more flexibility in location/position, but they come at a higher cost. From an AmpHour vs. cost standpoint, flooded cells win. Neither should be discharged below 50% SOC for longest life, and both should be fully charged REGULARLY. Chronic undercharging will kill any bank.
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Old 09-23-2020, 08:46 AM   #5
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To all who have replied, thanks. I just needed validation that I was in fact overthinking this.
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Old 09-23-2020, 08:56 AM   #6
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@Bsipe01, good points on the AGM's. I'm considering replacing his MPPT with a Victron SmartSolar MPPT, and adding in the Victron Smart Battery Sense. From what I gather, those 2 devices talk across Bluetooth to dynamically adjust charging profile based on better SOC data and temperature readings. Any experience on that front?
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Old 09-23-2020, 10:14 AM   #7
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Quote:
Originally Posted by Jester14 View Post
@Bsipe01, good points on the AGM's. I'm considering replacing his MPPT with a Victron SmartSolar MPPT, and adding in the Victron Smart Battery Sense. From what I gather, those 2 devices talk across Bluetooth to dynamically adjust charging profile based on better SOC data and temperature readings. Any experience on that front?
Not specifically with the Victron, but you can't go wrong with that gear. If you're charging a bank that's at ambient air most of the time, the temps become less critical than if you're charging a bank that's located in an area that's subject to temperature swings. The marine world is replete with banks located in engine rooms that regularly get to 120F or higher. (As on my own boat) The RV bank is primarily going to be in ambient air and won't have external heating influences. Although temps do come into play, there's much less variation. Still, the manufacturer will spec a temp/charge voltage chart, and the charger profile should follow that spec as well as the charge voltages, particularly the float voltage.

Don't overlook the charge line from a tow vehicle, if that's configured. The tow vehicle is unlikely to have a smart charger, so that line could charge at 14.X volts and not reduce. Actually a whole separate issue that would probably be best to avoid.
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Old 09-23-2020, 11:12 AM   #8
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My Artic Fox 22G batteries were on the trailer front tongue when we bought it. I replaced them with LiFePO4 batteries mounted inside in the heated/cooled trailer. My batteries are between my sit and sleep sofa and the front pass through storage area serving as part of the queen size bed platform.

I installed a Vicron Energy Cerbo GX and put in 3 temperature probes. One is in the center of the batteries, One is in the pass through storage area near the VE Multiplus 3000VA inverter/charger and one under the trailer to track outside temperatures.

I find my batteries stay about 10 degrees warmer than night time cool temperatures and about 10 degrees cooler than the highs. This is with the windows open and the fan running all the time when the trailer is stored at my home. In the colder weather the windows/vents would be closed an furnace heat would be on when camping.

Here is 3 graphs showing Battery|Pass-Through|Outside temperatures for the last couple of months. The battery temperature extremes are much less than the outside temperatures.

The BMS on the batteries will prevent charging if the batteries are below 25 degrees. It doesn't prevent discharging at lower temperatures. Keeping the batteries inside helps limit the exposure to temperature extremes. Many people put them under the bed.
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Old 09-23-2020, 12:00 PM   #9
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Again, thanks guys. Here in AZ, we get some pretty unbelievable temp swings. It can be 100 in Phoenix, then 60 at elevation on the same day. Winter is equally dramatic, easily going negative.

Jeff - I honestly hadn't considered relocating the batteries altogether as you suggest. There's no reason to believe it couldn't be done. Heading over there today to review and discuss alternatives.

Nice setup you have BTW. Love the Victron gear, and the MP3000 is in my sights for my trailer. Relocating the batteries from the tongue on it, similar to what you did, opens up all kinds of opportunities for improvements. Someday maybe.

Bob
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Old 09-23-2020, 12:10 PM   #10
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Quote:
Originally Posted by Jester14 View Post
Again, thanks guys. Here in AZ, we get some pretty unbelievable temp swings. It can be 100 in Phoenix, then 60 at elevation on the same day. Winter is equally dramatic, easily going negative.

Jeff - I honestly hadn't considered relocating the batteries altogether as you suggest. There's no reason to believe it couldn't be done. Heading over there today to review and discuss alternatives.

Nice setup you have BTW. Love the Victron gear, and the MP3000 is in my sights for my trailer. Relocating the batteries from the tongue on it, similar to what you did, opens up all kinds of opportunities for improvements. Someday maybe.

Bob
Another nod for locating them in the the passthrough storage area. I didn't chime in originally because I doubted you would be amenable to that. This is how mine are arranged:

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Old 09-23-2020, 12:21 PM   #11
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Good God! 3KW of solar!! Surprised you have that much real estate to mount! That's full tilt right there, nicely done.
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Old 09-23-2020, 12:22 PM   #12
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Good God! 3KW of solar!! Surprised you have that much real estate to mount! That's full tilt right there, nicely done.
Ha, we're planning to add another 975W soon. Figured out where to put them, but need to make some custom mounts before it can happen. You can see there is still plenty of room (325W panels, currently 3 strings of 3).

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Highs here have been ranging from 95-105F this week, and we're running the air conditioning on thermostat to keep our rig a constant 72F (66F at night, because we like to sleep cool).

Due to the haze and other factors, and our other utilization, we're having to run the generator an hour or two per day to break even with consumption. Consumption has been 20-22kWh/day, and our solar is only collecting 14-15kWh (which is still on par with most expectations of 2925W * 5 solar hours or 14,625Wh, but less than what we usually observe). Adding another 975W will get us closer to not having to run the genset at all, even in these conditions. Generally speaking, we avoid the heat and rarely run the generator, though.

Thanks.
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Old 09-23-2020, 12:51 PM   #13
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Off topic, but I read your profile regarding "using water as we wish". That's an interesting concept, but all of your tanks have limits... Details?
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Old 09-23-2020, 12:53 PM   #14
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Off topic, but I read your profile regarding "using water as we wish". That's an interesting concept, but all of your tanks have limits... Details?

We've made some incremental improvements, but here is a post about it from a few months ago.

https://www.irv2.com/forums/f54/boon...on-488825.html

Essentially, we have a 95 gallon potable water bladder and a 165 gallon waste water bladder, that are designed to sit in the bed of the truck when the ball (we use a Reese Goosebox V2) is pulled.

We have a permanently attached macerator pump and permanently attached hose with quick connect fittings, that allows us to quickly and easily transfer waste into the bladder in the back of the truck. Then, we just have to take the truck to the dump station, leaving the RV in place. It makes it a whole lot easier.

My freshwater pump says it moves around 8GPM, but I think it's more like 5GPM.

Since swapping out all the fittings you see in that post with 1-1/2" ID fittings that are reduced to 3/4" ID at the port to the bag, it takes less than ten minutes to move 160 gallons of waste from the RV to truck. We usually do so in smaller increments, though, driven more by convenience than requirement.

A typical errand day is now going to town, getting groceries or whatever, and swinging by a dump station on the way home to fill potable water and dump whatever is in the waste bladder.


--

With 160 gallons of on board waste tanks and 165 additional gallons of storage in the bladder, we've never ran into a situation where we had to actively conserve water.

Same with having 66 gallons of freshwater on board and 95 gallons in the bladder, and an additional 45 gallon bladder we occasionally fill if the spigots are fast enough not to have to wait very long.

We do laundry a couple times a week, take "normal" daily showers, etc.
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