Battery capacity for boondocking

[Bruce and Jenna]

Hi,

We're wending our way down to Q now, planning to spend a month boondocking in Jan. Which gets me to thinking about nighttime heating and battery capacity. I've read differing opinions, that the fan will run down the batts and that you can run the fan and recharge via generator the next day. No doubt that depends on the batteries.

I have 6v two Trojan T-105 batteries, each with 447 minutes of capacity at 25 amps.

My furnace fan is rated at 5.0 (low) and 11.2 amps (high) at 12v.

Looking at the panel for my surge protector, I see that I'm using 0 amps at 127 volts and 1 amp at 122 volts with no appliances running, i.e. background draw. How do I convert this constant draw? Is it 10 amps at 12v?

I can recharge my batts with one or two Honda 2000 generators each rated at 13.3Amps AC with an output of 1600VA.

My Progressive Converter 9260 converts 1000 watts AC to 60amps @ 13.6vdc

I could poke these numbers into a spreadsheet and hope I understand. But I'm new at this 12v and 120v stuff and don't want to make a mistake.

*Can I get by on these two batteries or should I get another set?
*How many hours must I run one or two generators to recharge for the coming night?
*Can I rely on the meter on the control panel, or should I purchase something more to monitor the batteries? I have a simple handheld multimeter too. And an old slide rule.

? Thanks much.

[Bruce and Jenna]

Hi,

We're wending our way down to Q now, planning to spend a month boondocking in Jan. Which gets me to thinking about nighttime heating and battery capacity. I've read differing opinions, that the fan will run down the batts and that you can run the fan and recharge via generator the next day. No doubt that depends on the batteries.

I have 6v two Trojan T-105 batteries, each with 447 minutes of capacity at 25 amps.

My furnace fan is rated at 5.0 (low) and 11.2 amps (high) at 12v.

Looking at the panel for my surge protector, I see that I'm using 0 amps at 127 volts and 1 amp at 122 volts with no appliances running, i.e. background draw. How do I convert this constant draw? Is it 10 amps at 12v?

I can recharge my batts with one or two Honda 2000 generators each rated at 13.3Amps AC with an output of 1600VA.

My Progressive Converter 9260 converts 1000 watts AC to 60amps @ 13.6vdc

I could poke these numbers into a spreadsheet and hope I understand. But I'm new at this 12v and 120v stuff and don't want to make a mistake.

*Can I get by on these two batteries or should I get another set?
*How many hours must I run one or two generators to recharge for the coming night?
*Can I rely on the meter on the control panel, or should I purchase something more to monitor the batteries? I have a simple handheld multimeter too. And an old slide rule.

? Thanks much.

[chicken legs]

Bruce I think you will find the answers to all your questions at this site http://www.ccis.com/home/mnemeth/12volt/12volt.htm

As for the meter question, I don't put much stock in the lights that most panels have you can buy a digital meter that plugs into any of you 12v outlets for $ 20-30 and get a much better picture of what condition your battiers are in.

[ChiefJohn]

Bruce, linked your topic to the "RV Systems & Appliances" Forum for more visibility.

[Scooter]

Bruce, your two batteries, combined, will give you your 447 AH figure. But realistically, you can only use 1/2 of that before it is time to recharge.

We have a total of six 6 volt batteries. 2 under the steps and 4 in an adjacent storage compartment along with a Freedom 2000 inverter/charger, separated from the batteries (which are vented to the outside).

[John66]

Power out = Power in (approximately, since there is loss in the conversion), so Volts out * Amps out = Volts in * Amps in (approximately).

So 1A * 122V = ?A * 12v or ?A = 122/12 = 10A (perhaps 11A or even 12A with losses)

Your AMP/HR value is 447 minutes * 25 amps * 1 hr/60 minutes or about 180. You don't want to regularly use more than half your battery capacity to maximize the life of the batteries. So that leave 90 amp/hrs. With the background draw and the average fan rating, that is about 18 amps per hour, giving you about 5 hours of 'safe' usage. You could extend this by reducing that background draw and/or forcing the fan to alway run at the lowest rating if that is possible.

If you have the room for them, another pair of batteries will probably be useful for your usage, since the ones you have will last all night only if you don't use them for anything else besides the furnace, and replace them sooner than otherwise expected.

As for how long you need to run the generator(s) to recharge, you would need to find how long the batteries take to charge at various currents. Or you could just experiment, run them down to 50% (or less if you stick with the current setup) and then time how long it takes to get them fully charged. 1 Honda 2000 should provide about 1600 watts to the converter long term (2000 peak, but not rated to do that for more than a few minutes at a time)

[Bruce and Jenna]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by chicken legs:
you can buy a digital meter that plugs into any of you 12v outlets for $ 20-30 and get a much better picture of what condition your battiers are in. </div></BLOCKQUOTE>

Dear Mr. Legs.

Where do you get such a gizmo? CW doesn't show it on their website. A Google search finds battery chargers and juveniile monitoring devices.

[Workshop]

Not to answer the question for Mr. Legs, but this is the METER that I use to check my batteries. I purchased it from WalMart for about $15.00. Checked it againt a digital meter and was accurate.

You mentioned having the 9260 Progressive converter, have you checked their Web page for information on the Charge Wizard. Your unit comes with it, but could give you some information on your recharge time as you will be charging initally at 14.4v. Their "Service Department" button will provide some addition info on batteries.

[Jim & Bona]

I did a Google search for "plug in voltage meter" and came up with this site, quickly, http://www.cetsolar.com/cigplugs.htm

You will find a couple of meters here. A little more work might yield more choices. Good luck!

[Bruce and Jenna]

Thanks to all who answered. Looks like I'm OK for overnight heating, since I can force the fan to low speed, and it will only run part of the time. I still need to figure the recharging time. I'm reading thru the lengthy info that Mr. Chicken showed me. Thanks Workshop for showing me the higher taper charge feature of my Progressive system.

I (finally) found that 12v meter on the Camping World site that you all mentioned, after searching for it thru Google. $12...I'll buy one on Sunday durig my monthly CW pilgramige. The CW web site Search function is worthless. (I remember mentioning this at a CW presentation at LOW last July. Three others in the audience loudly agreed. The CW rep said, "Oh, I didn't know that." Then she moved on. )

[chicken legs]

Yep got mine at CW. Hey be sure to look at the second page of the web site I sent if you, Thats were you will find all the load info. It's easy to miss I think it's called part 2. I have also added two more 6V to my set up and have them on a 1500w inverter. I need power for a CPAP at night and find I can go several days without recharge if I make sure to load shed the un needed coach draws. Happy boondocking !!!

[HB Phil]

When we winter boondocked with our last rig which had two Group 27 batteries (about 200 amp hours combined), we conserved by turning down the thermostat to about 55 when we slept. We also used common sense conservation measures like turning off lights, etc. But nothing drastic.

Anyway we used about 50 Amp Hours per day/night. So you should be fine with 400 AH's capacity. I would top them off everyday to keep them above 70% with about 1.5-to-2 hours generator time per day, getting them up to 90% charge.

If you let them get down to 50% charge then it will take longer to give them a full charge later on.

I would give them a full charge once a week. That last 10% charge may take a few more hours. This is all just educated guesswork based on about 50-70 AH/day consumption. This is entirely different if you have an inverter and run heavy loads, 150-250 AH's per day. Then I would suggest two more batteries. Otherwise you are golden with 400 AH's.

Nothing beats a good amps-in/amps-out meter or a battery hydromteter. However, you can us simple volmeters but must dial-in some Kentucky windage.

For example, the battery manufacturers state that voltage readings should be taken with the batteries "at rest" with no loads for up to 24 hours. This is impractical. But if you understand that, with minor loads, the reading will be lower than at rest, and conversely, that just after charging (with a high "surface charge") the readings will be higher than "at rest," you can get a general feel for the true State of Charge (SoC) of your batteries. This "ballpark" feel should be fine if, in the end, you stick to the golden rules: stay above 50% discharge, and completely charge them as frequently as possible - some recommend once a week. Others go much longer just staying between 50% and 80% charged with no problem.

Your Charge Wizard will take very good care of your batteries.

[RamWilderness]

Battery Minder

[KU9L]

When I go back to read Bruce's original post I only see two Trojan T-105's listed, so he only has about 230 amp-hours at 12 volts nominal available. So he has about 1/2 the 400 amp-hour storage needed to follow Phil's example which either means running the generator more often or adding another couple T-105's.

Dave