OK - I'm starting to wonder if I'm looking at this wrong.I was planning on solar and starting small with 1 or 2 portable panels and eventually put them (and more) on the roof but now I'm really wondering if that's unnecessary for my needs.I have (2) 6V gc batteries (230AH each), all LED lights, live in NYS so no winter camping, we have a Mr Heater heater to take the chill off in the evening and then again in the morning for spring and fall camping, so no furnace needed, "Navy" showers so pump runs minimum amount of time, fridge/water heater on propane (obviously) and a couple of Maxxair fans that might be used for short runs to cool down if needed .. but we also have a TH so I can just open the back of the rig if it get's too warm, a couple portable fans that move a fair bit of air and use rechargeable D batteries and I plug into a 30A RV outlet at home 24/7 while not using the rig so the batteries get topped off between each trip.We tend to dry camp for 3-4 day "weekends" up to 2 weeks at a time (the long ones only happen 2-3x/year)I know I need to get actual power consumption #'s at some point but with some "back of the napkin" calculations, I'm beginning to wonder if I should just add a couple more batteries and get a different battery charger to use with my (2) Champion 2000W Inverter generators (with parallel kit).The goal would be to go without recharging for 4+ days and then be able to recharge the battery bank within 3 hrs of generator run time. I have space for at least 2 more batteries.BTW: The RV came with the standard WFCO 9855PEC power center thing. I have no problems with switching that to something else or just adding a clamp on style battery charger (like you'd use at home) if it would do what I want. I'd also like to not have to fiddle with power setting on the charger too much.You thoughts please ... besides the fact that I'm nuts.

Solar isn't something that's really "needed" if you have generators. It's just very nice to not have to lug a generator, get gas, pour gas (spilling) and listen to it.For faster charging consider AGMs.

I camp in the shade most of the time, so solar was never consider. From your usage chart, looks to me the Maxair can be the biggest draw, especially if you use them for several hr a day. Still with our use, the batteries you have would last us 2-3 days and that include 1 liter of coffee every morning made on inverter power. Adding more batteries is one of the options, but they cost money to buy and money to carry and since you have good generator, just get one of those computerized battery charger to maximize generator time. Again, with our use, all I would have to do is run generator for 1 hr every other or even 3rd morning when making coffee and charging batteries at the same time.

I would first of all get some sort of instrumentation to accurately measure what your power consumption is and get some idea of where your battery states are at. Something like a trimetric is fantastic, but even just a decent voltmeter and ammeter would be a big help and is fairly inexpensive. You'll use this no matter what you end up doing.I would guess offhand that two pairs of GC2 batteries would very well get you through four days of conservative usage without becoming excessively discharged, and a large converter (80-100A) could bring them back up to 90 percent or so in three or four hours. Alternately, a single pair of batteries and sufficient solar power (maybe 200W or so?) could likely keep you going nearly indefinitely if you have reasonably open skies. I want to emphasize that these are at best very very rough guesstimates, barely better than order-of-magnitude computations.If you find you need more battery capacity than you have space for, you might want to investigate GC12 batteries. These are 12V golf cart batteries, somewhat longer and heavier than GC2s (but of a similar width and height), and a pair of GC12 batteries has about half again more energy storage than a pair of GC2s. If the shape fits your mounting space better, this could give more battery capacity...though unfortunately rather less economically, as the price per watt-hour favors the GC2s.

You should be able to get 2-4 days off of your two batteries, but for two weeks you will need to run your generator. Why do you need 2 generators? With two 160 watt solar panels I can go for ever.

I'm thinking solar might be more trouble than it's worth since we camp in the shade most of the time. I can run portable panels out to some sun but it could be a pain in the rump and maybe not efficient enough for our needs.I never said I needed 2 generators, only stating what I have on hand so people can provide educated answers.

Do I need solar or more batteries and a better charger?

64 Replies

MEXICOWANDERER
Explorer
May 09, 2016
Veebyes wrote:
If you double your battery bank capacity without doing something about increasing the charge rate of the charger you are going to double your charging time, both on the bulk & absorb charge time.

The only other thing you might consider is installing a multi bank battery switch & work between the 2 banks. The net charging time for both will be the same.

Battery bank size comes with weight too. There are choices to be made.

----------------------------------------------------------------------

Extra batteries mean more weight, higher purchase cost, and more maintenance.

But when a standard single group 27 is kicking and screaming being fed 14.8 volts at 15 amperes absorbsion, four of them will be humming at 60 amperes. There is no death penalty forcing a person to discharge flooded batteries to 50%. Look at a cycle life chart and gawk at the cycle life estimate for 40% depth of discharge - 60% remaining.

I discharge my cells a mere 30% before charging unless there's a hurricane a howling.

There's nothing as sad as seeing someone forced to recharge a 50% battery every day and absolutely needing to squeeze in every last amp hour they can to last the night.

When my bank reverts to float, it then takes 14-amperes at 26.1 volts.

Yeah, right. A four thousand dollars generator consuming $2.80/gal gas to power a $250 charger to recharge a battery sucking the wattage of a 5-cell flashlight. Not very bright. Oh wait! I know what's coming! Please, oh please point me in the direction of solar panels that work in deep shade. Not everyone lives in a climate where a heatwave means 10c or more.
full_mosey
Explorer
May 09, 2016
johnm1 wrote:

...
BTW: what do "C/8" and "C/5" mean?

Thanks all,

C is the 20Hour AH rating of the battery.

With a 100AH battery, C/8 = 12.5A.

HTH;
John
pianotuna
Nomad III
May 09, 2016
C = capacity in amp-hours (usually the 20 hour rate)

C/8 = charging at 12.5 amps on a 100 amp-hour battery
red31
Explorer
May 09, 2016
C/5 ah/h

C is 20 hr ah capacity

230 Ah / 5 h = 46A = 0.2C = 1/5 C
johnm1
Explorer
May 09, 2016
So I wasn't dreaming (on that one) - thanks!

I ordered the "drop in" Powermax Boondocker 75amp converter/charger (PM4B-75 MBA) from Bestconverter.

The rig came with 6awg wire from the battery(s) to the factory WFCO converter/charger and I'll replace the plain old standard crimped on ring terminals with proper crimped battery lugs.

Hopefully I can find time this week to get to the power audit so I see what draws what. I don't want to pull my "recessed" factory LED's out of the ceiling to check the label for the amp draw and it's very easy to just clamp on a meter and look at it. I can then make a fairly educated estimate as to what our daily draw will (might) be with this info.

Most likely this will tell me if I "need" to get more storage (aka - batteries). And yes, with more batteries I'm sure the usage will go up a little but it won't be anywhere close to double (still not going to turn on the TV).

BTW: what do "C/8" and "C/5" mean?

Thanks all,
Almot
Explorer III
May 07, 2016
The way I understand it (being sheltered from pains of incomplete charging, so no real experience in this) - going from 2*6V to 4*6V it will charge faster to 85% if you keep daily energy draw at the same level as before, or at least don't draw twice as much as before. Charger must be able to deliver C/5 i.e. 90A.

Cycle would also improve then.
pianotuna
Nomad III
May 07, 2016
Hi johnm1,

That depends on the charge acceptance rate of the battery bank and the capacity of the charging device.

When you double the battery bank by twinning the jars, the resistance is much lower, and so charging happens faster provided that there is a capable charger. Obviously a 2 amp charger is not going to charge twice as fast with such a doubling of capacity. But a 125 amp charger certainly would.

Generally at about 85% state of charge, a 100 amp-hour battery may only accept 12.5 amps (c/8). So if there are 200 amp-hours the acceptance rate would double to 25 amps, 400 would be 50 and so on. But the overall charge rate is still c/8 (again assuming a capable charging source).

AGM's may charge faster to say 93% capacity, and some LI formats can do c/1.

johnm1 wrote:
If I go the more batteries route ... have I read correctly that the battery bank will charge faster, at least up to the 80-90(ish)% range, or am I dreaming that?
Almot
Explorer III
May 06, 2016
Veebyes wrote:
If you double your battery bank capacity without doing something about increasing the charge rate of the charger you are going to double your charging time, both on the bulk & absorb charge time.

This is assuming they will also double their daily energy use.
Almot
Explorer III
May 06, 2016
OP, ammeter measures "amperes". Daily energy use is measured in "amper-hours", and for this you need AH meter.

You can put clamp-on ammeter on when you're running your fan at slow, med and high speed, and it will read 1, 2, and 3A respectively. You can get these numbers from specs, not much need to measure, right? What you don't know is how many hours a day you run it on slow, med and high. The same with TV - you know it's current but don't know how many hours you or somebody else is going to use it, and there can be other devices running simultaneously with TV that you haven't mentioned yet - sat receiver, DVD, videogames etc etc.

It's hard to estimate daily energy use until you list all your devices with their currents and hours of run. With more than one person in trailer this estimate won't be too accurate. You need to actually measure energy use for a few days in varying weather, to get a better picture.
Veebyes
Explorer II
May 06, 2016
If you double your battery bank capacity without doing something about increasing the charge rate of the charger you are going to double your charging time, both on the bulk & absorb charge time.

The only other thing you might consider is installing a multi bank battery switch & work between the 2 banks. The net charging time for both will be the same.

Battery bank size comes with weight too. There are choices to be made.