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Old 08-03-2010, 11:01 PM   #1
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Two-battery converter?

We just bought a 2007 27' International and are beginning to spec out a complete solar/electrical upgrade to make it more suitable for boondocking and our unique power needs.

The trailer came with two very new (Dec 2009) Deep Cycle Marine batteries by Interstate. They are 12 volt, 100 amp-hour batteries, clearly bought at Sam's Club. I don't really know, but I suspect these aren't terribly expensive... maybe $70 each?

Today I came across the Morningstar SunSaver Duo, a converter capable of charging two batteries (that is, two separate battery banks), and it strikes me as an elegant way of being able to keep these new lead acid batteries, and also upgrade to a couple Lifeline AGM batteries (not exactly sure which ones, yet).

The plan would be to use one bank to power the 12V system, while hooking the other bank directly to an inverter to solely power our higher-voltage needs when off-the-grid (primarily an iMac & the galley TV).

So some questions:

1) Does anyone have experience with the Duo, or a similarly-featured controller, and care to review it?

2) Does this sound like a reasonable plan on its face?

3) Which bank of batteries is better matched to power the inverter? The lead-acid or AGM?

I guess I see this as a temporary-solution, just for the remaining life of the Interstate batteries, which I would replace with an additional 2 Lifeline batteries added to the main bank. This controller would just allow me to keep two separate banks of batteries, with different characteristics, in the meantime.

Thanks for any suggestions.

Josh
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Old 08-03-2010, 11:26 PM   #2
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josh

no doubt you read this and perhaps discounted it already...

get a genset.
__________

a/s used interstate batteries as oem, so why do u think those are from sams ?

are they newer than the stream?

for the price of agms u can have 6 or more deep cycle flooded cells OR go the 6v route.
___________

the agms have LESS internal resistance so they can accept a HIGHER charge/load and FILL quicker...

but that's largely irrelevant with the solar charger you linked.

having a PRIMARY charger/converter that will have capacity for 4 or more batteries means UPgrading the p-lax...

and with something in the 80amp range.

a 3 stage style charger would allow the agms to juice quicker.

the solar charger is an add-on, it doesn't typically replace the PRIMARY c/c...

so u will still need an adequately sized charger/converter that quickly funnels shore OR genset power.
__________

imacs consume 80-200+ watts depending on screen size and activity.

that much consumption will use up the battery juice quickly.

and lcd tele can be as little as 50 watts or 5 times that.

the audio/stereo will consume a LOT too.

and lights, you'll be using a LOT of light juice.

so start compiling an energy audit (all the a/s parts are documented) and production scheme.

this is really essential IF you wanna rationally spec out solar, inverter, battery needs.

i can't imagine having adequate juice with anything less than 400 watts of panels and 6 batteries.

there is some TINY benefit in running all 4 batteries in parallel at the same time (less discharge than 2 banks of 2 )
___________

but really get a genset it's the least expense and MOST versatile way to juice the batteries, have AC power...

and back up the solar setup as needed.

cheers
2air'
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Old 08-04-2010, 12:18 AM   #3
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Yeah, I'm not real crazy about getting a generator, but the idea is growing on me. I guess I can't imagine getting much more than 250 watts of solar on top of this already-crowded roof, so a genset may be in our future.

That said, I'm gonna hold off on that idea, AT LEAST until our solar is done and we're on the road. Like you say, it's a back-up, and I'll wait until it's proven necessary.

---

The Interstate batteries clearly say 12/09 and "Sam's Club Battery Warranty" on them, making them about 3 years newer than the trailer.

---

I'm really leaning towards 2 6V Lifelines to supplement as many AM Solar panels as I can cram onto our roof (like I said, I don't imagine I'll get more than 250W). I'd like to grow that to be a 4x6V bank, but if I could use this controller to bide my time (by using the 12V Interstate's full life first), then that seems like a win-win. Obviously I can't just put 2 12V Interstate's and 2 6V AGM Lifelines in the same bank.

---

I'm a little confused when you say:

Quote:
Originally Posted by 2airishuman View Post
having a PRIMARY charger/converter that will have capacity for 4 or more batteries means UPgrading the p-lax...

and with something in the 80amp range.

a 3 stage style charger would allow the agms to juice quicker.

the solar charger is an add-on, it doesn't typically replace the PRIMARY c/c...
What's "p-lax"?

I guess I didn't realize that the solar charger/converter wouldn't replace the primary c/c. Interesting. I've got a lot to learn before I try installing all this myself.

I guess your point is that the solar charger I linked would not be sufficient to replace the main charger. SHOULD that be a goal? Would that be more efficient? Are the other popular chargers capable of doing both jobs? (Morningstar's 60 Amp TriStar MPPT costs about 4x as much as this one, but would it replace the primary anyway?)


Quote:
Originally Posted by 2airishuman View Post
imacs consume 80-200+ watts depending on screen size and activity.
Mine is the 27" and Apple's specs say maximum continuous power is 365 watts (or: A LOT). I'm really nervous about the feasibility of running this off an inverter (or the generator). I'll definitely adjust my usage in accordance with the supply of power (off-loading casual web activities to the iPad/iPhone), but I had hoped on finding SOME way of eking out a bit of use when off-the-grid. Hmph.


Quote:
Originally Posted by 2airishuman View Post
so start compiling an energy audit (all the a/s parts are documented) and production scheme.
An energy audit is on my to-do list for this coming weekend when we finally get to see our 'stream for the second time (it's in storage at my folks' a couple hours away). I'm also going to finish the initial cleaning/waxing, freshen ALL the seals (got Sikaflex 221 and 721, as well as Acryl-R & applicator en route from Airstream), drop the belly pan & inspect the frame & floor (and put back, if it's all good news), do ALL of the things in maintenance section of the owner's manual, and take tons of pictures & measurements, so we can plan out our next visits. Probably won't get all that done, I know, but that's my goal. Anyway, I digress.

I'll do the energy audit as described in this post (and others) but I'm counting on learning that I should start spec'ing out gensets. Heh. I guess that's basically your conclusion too, when you say "anything less than 400 watts of panels and 6 batteries" cos I just don't see that happening.

Thanks. Would still love to see some comments on the primary question here, though, and that's the feasibility/wiseness of using the SunSaver Duo to charge two separate banks of dissimilar batteries, where one bank (likely the lead-acid) is dedicated to powering an inverter, when necessary.
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Old 08-04-2010, 12:36 AM   #4
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Solar, generators and your power needs.

Josh,
Power use is key to your plans. We planned on installing four 12v AGMs, 200w of AM Solar, and upgrade our Paralax single stage converter to a Power Dynamics 3 stage charger. Also planned on upgrading our smallish inverter...Anyway, we found that after installing the solar panels, our suspected failing PLax converter was upgraded with our PD unit. All the time with the basic 2x 12v batteries mounted on the stock box. To date, we are operating just fine. We've learned to manage our power. Sunny days, rainy days, our power needs are being met at present. I do want to stress, I will someday upgrade to larger AGM's outside (wiring for two interior mounted AGM's was installed years ago as a future option). Note also the different charge/use rates of batteries mounted inside vs. out, due to temp. Mind ya, we still aways carry our trusty Yamaha generator JIK....We did both our Solar and Converter installs, plenty of great guidance here on the forums on that. Power use is key...did I mention LED lighting???
Just my 2c and it works for us...for now!
Stream Safe,
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Old 08-04-2010, 12:48 AM   #5
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p'lax = paralax.

thatz the brand of AC 115v charger/converter in the stream.

oem for your model is a 73xx series i think.

u can read about 'em here or out in space.
__________

the tristar accepts solar/wind/hydro but NOT 115 v ac.

charging from a DC source is different than from an ac source.

perhaps there is a charger unit that does AC and DC but i'm not familiar with it.

ac power must be CONVERTED to dc before jamming it in the batteries.

dc fuel (from what ever source) doesn't need the conversion step.
_________

it's NOT absolutely necessary to replace the p'lax

but the oem unit is UNDER sized for 4 batteries and doesn't have true BULK and float stages.
_________

yeah i knew the 27 inch mac sucked lotz a juice but let u declare size and power needs.

a laptop is SO much easier to use boondocking...

((spare battery sources, lower consumption, NO big inverter needed and so on))

it is technically possible to combine 12v and 6 v batteries

but further complicating this stuff with those details only makes it all more complicated.

while a genset IS backup for solar, it might be wise to START with a genset...

they are easy to find used and easy to sell.

solar once installed is very hard to pass on...

it's still not clear what u will use for towing,

but it would be simple to have 2-4 additional batteries IN the truck bed

and hook them to the solar charger OR shore charger when parked...

all the batteries are 'lead acid' the difference is flooded/wet cells vs a water/acid absorbed matrix in the agms.

and WHAT about a sam's club tag suggests they actually came from sams...

those batteries could be GOOD for 4-5 years if not OVERLY discharged and properly maintained.

i'm ALL 4 solar and have it topside,

but one can buy a genset capacity for way less money.

on a HUGE moho having 6 or 8 or 10 batteries is not an issue, but the big boys all have gensets to REFILL 'em quickly.

much depends on WHERE u will be b'docking and what season.

i like parking in the shade whenever possible and going NORTH is the hotter times.

if u r planning to hang in tx/az/nm/socal the sun is easier to utilize.

it's all good.

cheers
2air'
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Old 08-04-2010, 07:32 AM   #6
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To be able to fully charge a 27 group battery you need at least 100 watts. So with 2 batts you need approx 200 watts. You also do not want to go below 50 % charge at the most to ensure long battery life. You will find that 2 batts should be plenty of power when you learn to conserve.
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Old 08-04-2010, 11:00 AM   #7
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Here's some info from Arizona Wind and Sun Electricity from the sun since 1
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Old 08-04-2010, 02:26 PM   #8
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You could also use any good 3-stage charger, run the flooded cells and AGMs in parallel, and the converter on the AGM settings.

The loss in performance of the flooded cells, because they are on an AGM program, will be negligible.
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