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Old 02-16-2015, 06:45 PM   #21
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Great advice..thanks!

Since our trailer is small, perhaps I should just buy a 1000w Inverter/Charger and save the PD upgrade money. Net cost is attractive, I get the charger, and I am setup for genny/solar expansion.
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Old 02-16-2015, 06:55 PM   #22
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Lots of good info here. I'll add a couple of things:
1. WET CELL batteries can only SUPPLY 20-25% of their rated amp hours as pure current continuously. While you may design a system that can handle your amp hour needs for a day or two...make sure you can also provide for the CONTINOUS amps you may need for high loads like a microwave or coffee maker. Example: A 1500 watt microwave uses 13 AC amps. To supply this at 100% efficiency you need 125 DC amps. Figure 150 to account for inverter losses. This means that you need roughly 5 12V Group31 batteries or 6 6V 200amp batts to safely operate the microwave for extended cooking. Wire sizes need too be able to handle those loads as well and over the back/forth distance from inverter to batts.
One way around this is to get AGM's which are capable of at least twice the sustained current of a wet cell. The downside of course is a battery system that costs 2-3x more than a wet cell system without delivering more life cycles...but there are also other advantages to help justify the cost.

2. For boondocking I would ONLY go with dual 12V batteries of the largest size you can fit. If one fails in service...you still can camp. If all you have is dual 6V's...you are going home in the dark. 4 6V on the other hand will make good sense and be economical.

3. When buying an inverter...size to deliver 20% more amps than you think you'll need... and don't forget the charging side... a BIG charger can minimize generator run time and the same rules for input current covered in #1 above apply. Max input current from a charger to wet cell batts is about 20% of rate amp hours (i.e. 20 amps per 100 amp hour battery bank) ....AGM's can do twice that. More charging power above these amounts will no be used and simply be wasted money unless you plan on expanding in the future.
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Old 02-17-2015, 06:08 AM   #23
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Forget the microwave - only use it with the generator. Consider downsizing the microwave to the smallest one that meets your needs.

If you are off-gridding in an area with lots of sun, consider some solar to reduce generator time.

Recharging the battery bank to 100% takes days even on the grid. Shoot for a recharge of 85-90% to reduce generator time.

We used two Interstate 6v golf cart batteries for 4 years before downsizing. We also used a pure sine wave Xantrex SX-400 inverter (400 watt) on a single AC circuit that powered the desk area and the entertainment center. Change all lighting to LED, at least the lights you will use most. Limit use of the furnace as the fan uses around 7-8 amps. Consider a catalytic heater if doing lots of cold camping. Most older TVs are power hungry - consider a new TV and smaller screen that takes less power. (Example: our bedroom TV only takes 30 watts) Smaller TVs take less power. We also installed a battery monitoring device (Trimetric 2020 from Bogart Engineering) that reports battery status of amps in and amps out, and state of battery charge. Do not discharge batteries below 50% without risking battery life. How do you know what 50% is?? The monitor will tell you. Keep the lights off - watch the kids and guests.
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Old 02-17-2015, 03:58 PM   #24
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Forget the microwave - only use it with the generator. Consider downsizing the microwave to the smallest one that meets your needs.

If you are off-gridding in an area with lots of sun, consider some solar to reduce generator time.

Recharging the battery bank to 100% takes days even on the grid. Shoot for a recharge of 85-90% to reduce generator time.
I don't think you should be afraid to use your microwave on batteries. It may not be suited to cook an entire meal from scratch, but just for general heating (soup, leftovers, defrosting etc) or grabbing a cup of coffee, it just takes a little bit of preplanning with your inverter and proper battery bank capacity. You do have to consider the cost though and decide if MW use is worth the additional batteries and larger inverter.

I would discourage shooting for an 85-90% recharge rate. Some types of batteries you will actually be killing them pretty quickly by not providing an adequate recharge cycle.

I'm not sure what's going on that it takes days to recharge even "on grid". I would certainly be taking a closer look at my charging system if it takes that long. More than likely you're just not getting enough voltage delivered to the battery terminals to push enough amps for an adequate charge.

Solar? Can't advocate it enough! I full time with a 440ah (220ah on tap) battery bank and 540 watts of solar. I rarely turn my genny over to recharge. Part of that is learning to "live within your means", but I certainly don't suffer.

Typically, solar will have me back at 100% by mid day at least, and there is still a little time to use the excess of the day to play around with.
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Old 02-17-2015, 04:16 PM   #25
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Yarome asked about taking days to fully recharge. Here are some links that help answer that question. The recharge during the last day and hours can be as low as .01 amp.

Battery Management and Charging from Progressive Dynamics

from the same website: 11. How long will it take to re-charge my RV battery?
Battery recharge time is controlled by many factors, such as battery size, converter output rating the number of 12-volt lights and appliances that are “ON” during the re-charge cycle and how far the battery has been discharged. In our testing a 125-AH (Amp Hour) battery was fully discharged to 10.5-volts and then connected to a PD9160 (60-Amp) Converter/Charger set to our standard output voltage of 13.6-volts. The battery reached full charge in 70-hours.
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Old 02-17-2015, 04:40 PM   #26
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Yarome asked about taking days to fully recharge. Here are some links that help answer that question. The recharge during the last day and hours can be as low as .01 amp.

Battery Management and Charging from Progressive Dynamics
What I'm reading into that is them pointing out the inherent flaws in standard converters and how their charge wizard remedies that. "Other battery maintenance problems solved by the Charge Wizard". Albeit, they are only talking about wet cells and charging from 10.5 volts.. which no one in their right mind would discharge their battery banks that low.

Reading further, the 20-25milliamps (.02 amps) is not in the charge cycle, but the "storage mode" charge. Basically, just enough to offset normal off-gassing of wet cells (15% per 30 days).
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Old 02-18-2015, 08:37 PM   #27
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What sort of set-up would I need if I wanted to run an air conditioner, a CPAP machine, one or two lights and TV?

I use a lithium ion battery for cpap and charge during the day
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Old 02-18-2015, 09:06 PM   #28
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Once a battery falls to less than 1% of amp hour rating in the charging process...it is considered fully charged. No need to keep going.
Example...using a modern multistage charger if you had a100 amp hour batt...then when the charging amps drops below 1 amp...you're good to go. As Yarome says...anything after that is just maintaining vs. parasitic or self discharge.
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Since it nevertheless can take a LONG time to fully charge a battery bank with a genny while boondocking...Many people will go for a cycle of 50% discharge to 90% charge...saving the full charge till they can plug in again. I would never go for more than a week doing this...and sometimes would run the genny for 6-8 hours to get the batts to 100%. AGM's are particularly sensitive to this and you can lose a big investment by not bringing them to 100% regularly rather than getting in the easy 80-90%. A battery amp monitor is essential in this situation.
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Old 02-19-2015, 04:41 AM   #29
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My previous comments are based on experience with FLA batteries - Flooded Lead Acid. I've had two setups: two 6v Interstate golf cart batteries in series (12v), and a single 12v deep cycle group 27 battery. AGM and Gel batteries have different charging and performance characteristics.
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Old 02-19-2015, 06:19 AM   #30
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I think it's important to note that the main limiting factor, and subsequent long recharge times, is not so much limited by the FLA's (or any other type battery) themselves, but the charger that is being used.

Using a programmable, heat adjusted charger will dramatically reduce charge times and improve overall battery performance. Prior to the AGM's I'm using now I ran T105's that I charged at 14.6 bulk, and 13.5 saturation. I got 9 years out of that bank (full-timing and better than 95% boondocking)... and going strong... when I made the switch to AGM.

Where most baseline chargers only deliver a timed 13.5 bulk.. no wonder it takes forever. The other issue is typically that, even for stock converter/charges that deliver 14.4, it's rare that your batteries are actually getting the full charge rate due to under wiring. So called "smart chargers" greatly improve overall performance, but you're still not going to get the full potential/life out of your batteries.

Granted.. the programmable heat adjusted chargers cost quite a bit more, but they pay for themselves by keeping your batteries much healthier for much longer.

Like Cam was saying too, limiting your charge cycles to 80-90% on a regular basis is pretty harsh on your batteries. One other approach to help avoid that is increasing your battery bank so that your discharge rate never falls below 80% SOC. Your charge times will decrease and your batteries will last significantly longer.

All that being said... for most folks that camp just a few days or weeks out of the year, it's difficult to justify the additional cost of a larger battery bank and programmable charger. Even for those though, investing in a "smart charger", at least, will make a dramatic difference in terms of charge times and battery health.

* by programmable, I don't mean those chargers that allow you to select one of several pre-programmed charge profiles. Programmables allow full custom settings... (ah's, soc levels, temp comp rates, etc)
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