12 volt battery charging boondocking

[rollintent]

Hello everyone I am fairly new to the forum and I have to say this site has the most helpful and knowledgeable members of any forum I have ever spent much time on. So I am sure I will get some good advice here from people who have been there and done that.

I am trying to figure out what is the best (most efficient, reliable, economical) way to charge a 12 volt deep cycle when camping without electrical service.

I am doing a 6x12 cargo trailer conversion and am planning to start with lights, cell phone charging, stereo, computer, and maybe a fan for hot weather. I think all I want to do is just charge the battery every so often and draw off of it even if I was in campsite that had electrical hookups rather than have a converter/charger. Here are the things I have been wrestling with.

How long will it take to charge a 100-130 amp hour 12 battery back to 100% from an 80% full state with a small generator and a good automatic charger? If I can charge the battery once or twice a day with the generator running for one to maybe three hours I would be happy with that. I am also needing advice on brands, sizes, and types of chargers that have proven themselves through use with people that really rely on them.

I have considered solar and I like the idea of solar the best (quiet, low maintenance, no fuel to haul around, etc). The downsides to me are having to be parked in full sun or at least be able to get the panel in full sun most of the day and maybe cost? I haven't researched total cost enough yet compared to a small generator and a charger to know for sure. I just think most campsites tend to be in shady spots where I plan to camp and relying on solar would force me to leave the shade and force me to deal with the heat from parking in the sun and that is a big downside since I don't plan to run an AC.

I am also thinking that with the generator I could run a small AC or fridge part of the time later if I decide I need either one of those where I couldn't do that without a LARGE solar system and battery bank. I intend to try to camp mostly in sites with no hookups like national forests, BLM ground, etc. Anywhere the crowds aren't for the most part. I may stay in some RV parks for an overnight while on the road to where I am going but not more than a day or two at the most. In those cases who cares how long it takes to charge the battery with hookups available and no generator making noise.

[eamarquardt]

General rule of thumb is that you shouldn't charge a battery more than about 10% of its capacity. So your 130 amp battery shouldn't be charged at more than about 13 amps. If you wanna put 26 amp hours back into it it's gonna take two hours at 13 amps. My experience has been that it takes longer as the charge rate slows down as you get the battery topped off.

I used to run an air compressor to fill SCUBA tanks on our boat. One day, the other boaters in the anchorage CHEERED when my tanks were full and I shut it down. Generators are quieter than compressors but noisy none the less.

Given that solar is silent and prices are way down, I'd opt for solar. You have all day to put your charge back in and won't hear a thing.

I think you'll pay about the same for a quality generator or a good solar system. One is silent and maintenance free with zero operating costs, the other isn't.

Hope this helps.

Cheers,

Gus

[Socal Tom]

Assuming that you've used 20 amp-hours (20% of the 100 amp hour battery), the rule of thumb is that you need to put back 15% more than you take out ( to make up for internal resistance) so you need to put back about 23 amps. There are a couple of options for the charging. The small generators have built in charging capability, the Honda I researched does 8 amp per hour so that would be about 3 hours in this example.
However for another 40$ you can pick up a battery charger that will put out 12A (or more) and cut that time down to 2 hours or so.

Here is a link for reference
http://www.batteries-faq.com/activekb/q ... stionid=55

Tom

[Shadow Catcher]

I am with Gus on this I hate the sound of generators and went with a solar panel which works very well. One alternative is however to recharge from your tow vehicle. My Subaru uses .35 gph on idle and is quieter than any stand alone generator. I have a 6 ga jumper cable that plugs into a 150A power pole connector at the battery with conventional battery clamps on the other end ad a fuse in between. I use it if there is not enough sun (has not happened yet).

[rollintent]

I am with Gus on this I hate the sound of generators and went with a solar panel which works very well. One alternative is however to recharge from your tow vehicle. My Subaru uses .35 gph on idle and is quieter than any stand alone generator. I have a 6 ga jumper cable that plugs into a 150A power pole connector at the battery with conventional battery clamps on the other end ad a fuse in between. I use it if there is not enough sun (has not happened yet).

Maybe I don't understand how solar panels work. Are you always parking in direct sun? I would think direct sun on the panel most of the day would be required even with a 100 watt panel and low usage (30 amps or less)

How long do you estimate to charge with the tow vehicle assuming the 20% drained 130 amp hour battery with the vehicle idling? Is the voltage regulation on a vehicle good enough to properly charge a deep cycle battery on a regular basis?

Sorry if I am asking really elementary questions but electricity is one thing I don't understand very well at all.

[Shadow Catcher]

There are two parts to this equation current generation and current conservation. We have a 185 high voltage panel and a 140W flexible high voltage panel. All of our lights are LED and all of the other appliances, radio, TV, refrigerator, furnace, are low current consumption. When boodocking with no shore power the 185W solar panel has met all of our needs even in heavy woods with lots of shade. The other half of the conservation is that we use propane for all tasks that require heat i.e. a french press coffee maker, water heater, grill, cook top, we do not have a microwave...

[Dale M.]

Other option is a "Charge while towing" setup... Back up TV and connect up and idle motor for a bit (I know not environmentally sound)....Let "regulation" for TV control battery charge..... But you can probably charge battery off TV in about 20 minutes instead of running genny for 3-4 hours...

Also having a charge while towing setup... It fills in in a emergency when wind or solar has failed....

Dale

[rollintent]

Well, I like the idea of charging with the tow vehicle. I know what you mean about the not environmentally friendliest BUT surely it is no worse than a generator and even hook ups at camp sites pollute some if the power comes from a coal plant and solar panels require energy to manufacture so nothing is without some degree of impact. The tow vehicle would be a heck of a lot quieter and I already am paying for/own the vehicle. If the tow vehicle charging doesn't wear out batteries too quickly (due to less than ideal voltage/amperage regulation) the cost effectiveness blows solar or a generator out of the water right away. I can burn a lot of gas recharging batteries that it would take a long time to pay for the solar panels or a generator and a generator like I would be able to afford will depreciate relatively quickly as well. If I figured 5, mulitiple day, trips per year and burning even a gallon of gas to top off the battery each day it would take years and years to pay for a solar panel setup. Since I am fairly new to this too it lets me learn a little at a time without a big up front investment. That is attractive since I really am an electricity dummy. I would say I have as much or more common sense than most but technical expetise in the way of 12 volt power is far from my strong suit, so I need all the help I can get.

This stimulates more questions now. What exactly would be the output of my tow vehicle? How would I need to size the wiring and exactly where do I tap into my tow vehicles system properly? What would be any negatives as far as excessive wear and tear on my tow vehicle's electrical system components.

[eamarquardt]

.............. But you can probably charge battery off TV in about 20 minutes instead of running genny for 3-4 hours...

Dale

I'd like to hear the specifics of this technique.

Thanks,

Gus

[rollintent]

Gus,

Sounds like you are suspiscious of the 20 minute recharge time? Am i right? It sounds too good to be true but then again I haven't chased out enough info to make a good decision yet. I just found a long thread about tow vehicle charging and it has a lot of info indeed but I am very uneducated about electricity it is hard for me to envision exactly what all everyone is talking about right now. I think I am getting a pretty good idea about how to do it but I am very cautious because of my inexperience. It's like trying to tell someone in writing how to tie an overhand knot. It sounds way more complicated in writing than it is when you can see someone actually do it.

I am not sold on anything yet so if you can steer me to some better info I will appreciate it. I will keep sifting through older threads as well.

[milliejohn]

Battery Isolator and your tow vehicle is the simple set-up when you do not have a generator or solar set-up, you never run down your starter battery, the alternator supplies the proper charge, no over charging. http://en.wikipedia.org/wiki/Battery_isolator

[eamarquardt]

Gus,

Sounds like you are suspicious of the 20 minute recharge time? Am i right? It sounds too good to be true ...................

............... it is too good to be true.

Everything in life is a compromise. You can optimize the life of your battery (discharge and charge it properly), or you can remove all controls from the field winding of an alternator, install a rheostat to control the output of the alternator, and pump up your battery in 20 minutes while shortening its lifespan considerably. You can listen to your car or generator run or you can spend money and listen to the "sounds of silence". Yer right sometimes it isn't "cost effective" to do it one way but sometimes (for example the convenience of having a solar system take care of things w/o any noise, fuel, or action on your part) it is worth the money for non monetary reasons.

Me, the less I have to listen to, the better.

Cheers,

Gus

[48Rob]

Re: 12 volt battery charging boondocking

by eamarquardt » Mon May 27, 2013 3:25 am



rollintent wrote:Gus,

Sounds like you are suspicious of the 20 minute recharge time? Am i right? It sounds too good to be true ...................
............... it is too good to be true.

Gus,

Mostly so...

I have a deep cycle battery on my truck, connected to the alternator via a battery isolator, and big 1/0 cables which power a 2000 watt inverter.
This set up is for running heavy Amp draw power tools in the field; a silent generator alternative.

My trucks alternator will recharge the deep cycle battery pretty fast, though It no doubt impacts battery life.
I've gotten two years of life from the battery. If it dies tomorrow, I'll be happy, not because it died, but because it is/will have been worth it to not lug a generator around for the last two years...

Rob

[eamarquardt]

I've gotten two years of life from the battery. If it dies tomorrow, I'll be happy, not because it died, but because it is/will have been worth it to not lug a generator around for the last two years...

Rob

Yup, you've done your homework, compromised to meet your needs/desires, and are happy with the results. Can't argue with that!!!!!

Cheers,

Gus

[Dale M.]

.............. But you can probably charge battery off TV in about 20 minutes instead of running genny for 3-4 hours...

Dale

I'd like to hear the specifics of this technique.

Thanks,

Gus

On has to consider most flooded cell batteries in cars are generally charged in a extreme recover rate... There is no percentage regulation of charge in automobile battery charging.... Battery simply draws current from "system" till battery voltage reaches float voltage which is around 14.5 volts..... If you had ammeter on car charge system you could see this.... Older cars had ammeters and if you notices it in the first few minutes after start ammeter would PEG to charge side showing full out put of generator/alternator was being used to recover amperage/voltage reached float voltage where the chemical action in battery was satisfies it had absorbed and much energy (recharge) it was capable of.... You can see this today in systems with volt meters and voltage will swing to max of system for firs 10 minutes or so after start, then drop back ever so slowly, just a tiny bit as system and battery stabilize as it nears max recharge.... Most system today have 90-150 amp alternators, whee do you think most off the output goes when "electrical system" is below the preset regulated voltage...

http://www.batteryfaq.org/

Start reading in section 9...

9.1. What Are the Four Stages of Battery Charging?

Three stages--bulk, absorption and float are normally used for wet car and motive deep cycle batteries with an optional equalizing stage. Three stages--bulk, absorption and float are normally used for AGM (Ca/Ca) and Gel Cell (Ca/Ca) VRLA car and motive deep cycle batteries. Three stages--bulk, float and equalization are normally used for wet stationary deep cycle batteries and two stages--bulk and float are normally used for VRLA stationary deep cycle batteries with an optional equalization stage is some cases.

9.1.1. The BULK stage is where the charger current is constant and the battery voltage increases, which is normally during the first 80% of the recharge. Give the battery whatever current it will accept as long as it does not exceed 25% of the 20 hour (expressed "C/20") ampere hour (AH) capacity rating, 10% of the Reserve Capacity (RC) rating, wet batteries do not exceed 125° F (51.5° C), and VRLA batteries do not exceed 100° F (37.8° C). {under line is mine}

9.1.2. The ABSORPTION stage is where the charger voltage, depending on the battery type, is constant between 14.1 VDC and 14.8 VDC at 80° F (26.7° C) and the current decreases until the battery is fully charged, which is typically the last 20% of the recharge. For wet batteries, gassing (making a bubbling sound) usually starts at 80% to 90% of a full charge and is normal. A full charge typically occurs when the charging current drops off to 2% (C/50) or less of the AH capacity of the battery and each cell of a wet battery is moderately gassing equally. For example, end current for a 50 AH (C/20) battery is approximately 1.0 amp (1000 milliamps) or less. If the battery will not "hold" a charge, the current does not drop after the estimated recharge time, and a wet battery is hot (above 125° F (51.5° C)), then the battery may have some permanent sulfation. (Please refer to Section 16 for more information about sulfation and how to remove it.) Manual two-stage chargers that have a bulk and absorption stage must be turned off when the battery is fully charged to prevent overcharging.

9.1.3. The optional FLOAT stage is where the charge voltage, depending on the battery type, is reduced to between 13.0 VDC and 13.8 VDC at 80° F (26.7° C), held constant. It can be used indefinitely to maintain a fully charged battery to overcome the natural self-discharge of the battery. The current is reduced to approximately 1% (C/100) or less. Three-stage "smart" chargers usually have the bulk, absorption and float stages. (Please refer to Section 13 for more information about storing batteries and continuous float charging.)


The question you have to ask is what is Amp Hour rating of battery, (20 hour discharge rate) then multiply that by 25%, that is max safe charge rate....

OR what is 10% of reserve capacity....

You can observe this just by putting digital meter across you car battery.... Turn you car head lamps on for say 20 minute (to bring battery down from float charge levels), then start car and observe the voltage curve over time.... Remembering as voltage goes up current goes down.... What you are observing is the TIME from charge start to where max voltage drops back to float voltage....

Dale