Electrical System Reality Check

[Binxie]

I'm getting ready to build my van, and I've been crunching the numbers on my devices and intended usage. But even after Bob's wonderful articles that have made electrical systems clearer to me than they ever have been before, I'm still a little confused. (And yet I've been doing my own taxes all my life with no problem!) Can some of you knowledgeable people give me a reality check on this system? My goal here is to have enough battery capacity for one very generous day of usage, plus recharge capacity with a portable generator. I'm also thinking about solar.

Requirements (converted to 12v)

Fan-Tastic Vent Model 2250 (24 hours @ 12v x 2.6A full speed = 62Ah per day)
LED cargo ceiling light (8 hours @ 3W/0.25A = 2Ah per day)
Chromebook (Lasts 8.25 hours off 37Wh battery, so 12 hours = (37*1.5)/12 = 56 Wh = 5Ah daily recharge)
Jetpack® MiFi® 6620L (4Ah for up to 20 hours = <4Ah daily recharge)
Wilson Sleek 4G Signal Booster and Antenna (12 hours @ 5.5V DC, 2.5 A = 14Ah)
Maximum Daily Usage = 87 Ah

House Battery

2 Trojan 6v 200 AH Deep Cycle AGM Sealed Batteries  (in series for 12v)

Generator (House Battery Recharge & Occasional High-Draw Device Usage)

Yamaha EF2000iS 2,000 Watt 79cc OHV 4-Stroke Gas Powered Portable Inverter Generator
    (1600 watt rated AC output, 2000 watt maximum AC output, 13.3/16.7 amps @ 120V)

Questions

1. Do my numbers add up? Am I doing the calculations correctly?
   
2. About how long will the generator take to recharge my batteries when they're half down (100 Ah)? I'm thinking about 45 minutes (1600W / 12 v = 133.33A = about 45 minutes)
   
3. If I did a 200W solar system (with maybe trickle charge off the engine), that should cover my daily usage most of the time, shouldn't it? I'm thinking the solar would produce conservatively 77Ah a day.

Thanks,
Alan

 

[SternWake]

The generator will need to power a charger or a converter to recharge the batteries.  Although it might have a 12v DC output function these are neither fast or regulated.

AGM batteries are a bit less forgiving regarding getting them to 100% charged, compared to flooded batteries.  Meaning it is more important to get them to 100% as often as possible.

I despise the term trickle regarding battery charging.  Generally it is a holdover from grandpa's antiquated ideas of battery charging, which is that low and slow is always a good thing, when in this lifestyle it is much more important to get the batteries as full as possible before the next discharge cycle begins.

Also since the alternator can be a huge charging source, if properly wired and the batteries are under 80% charged, to call it a 'trickle charging' source is unwise indeed.

AGm batteries also do not like the low and slow recharging method.  'Tickling them to death' is quite possible with low charging currents.  When you buy a plug in charging source, go no less than 20 amps, and do not fear going as high as 80 amps or even higher, for minimal generator run times.

Regarding a grid powered battery charger, one wants to find a charging source that meets the battery manufacturer recommendations as best as possible.  Both in terms of Absorption voltage(maximum allowed charging voltages) and minimum bulk current.

Generally Automatic  'smart' chargers will not be able to power loads while charging the battery.

RV converters like Progressive Dynamics, Iota, and Powermax are all designed to power loads while 3 stage charging, but none of them are ideal for fully charging a battery as fast as possible via a generator as none will hold absorption voltage for long enough.

Solar is great, get as much as you can afford and which can fit on your roof and your batteries will be much happier for longer.

Your Solar calculations of AH returned are too generous unless you are tilting the panels and following the Sun.  Panels only do about 85% of their rated output and only right around noon.

With a well wired alternator, your generator, and 200 watts of solar you can easily keep a pair of 6v AGM batteries happy.  however the Solar alone is not enough.  Every so many cycles the AGMs should be blasted with high amperages from grid powered charging source or well wired alternator, and then the Solar can finish the task.  But if 200 watts of solar is enough to restore the AH used, it is too slow a charging rate to make AGMs happy.  This is really too slow for 200AH of flooded battery too when deeply cycled daily.

large amp blasts in the morning from generator powered source or alternator, followed by Solar to do the 80% to 100% thing while solar also negates loading on the batteries in the afternoon, will yield happy long lived batteries.

Less than ideal= less than ideal battery life, so one must choose how much battery life one finds to be acceptable.

One can set it up to be generous to the batteries and not have to worry about them for quite some time, or less than generous and find that the batteries 'no longer take a charge' much earlier than expected.

Often it is cheaper to be generous  towards batteries initially, than it is to improve inadequate systems later.  

 

[akrvbob]

I think you have a very good plan. The 200 watts should meet your needs and the alternator and generator are the gaurantee.

I think that will work very well for you. It's not perfect and can be improved on, but at a high cost in time and learning. It should serve you very, very well just the way it is. 

You do need a battery charger to use the generator. This is the one I used and recommend to you:
http://www.amazon.com/Schumacher-SC-10030A-SpeedCharge-Automatic-Maintainer/dp/B001MYWBF0/

It's not perfect but it will get the job done for you with a 30 amp fast charge. 

Bob

 

[Binxie]

Thanks, Stern:

If I understand you correctly, I could summarize strategy as:

1. Keep the AGM batteries as fully charged as possible.
2. Charge them up at high Amperage whenever I can.

With that strategy in mind, the tactics are:

1. Use the batteries conservatively.
2. Definitely charge from the alternator when driving to high-Amp charge.
3. Plenty of solar is a good idea to help keep them topped up passively.
4. Get them near to topped up daily via my generator, but through a 3-stage charger.
5. Whenever I get the chance, quick charge from grid power at my charger's maximum Amperage.

Sound about right?

You didn't say much about the capacity of the house battery vs. requirements, so maybe I'm pretty reasonable there?

 

[Binxie]

Thanks, Bob. I just replied to SternWake's message. Am I getting this down, in your opinion?

I'll keep the link for the charger, too.

 

[akrvbob]

Yes, I think you've got it under control!
Bob

 

[VanLifeCrisis]

I basically have a similar setup and usage now, and the 200w in panels charge me up even on a cloudy day. I think it will be good to go.

 

[SternWake]

When batteries are 80% or above, the amps they can accept decline rapidly, So actually getting them to 100% Via a generator simply wastes gas.  Most people who use a generator to charge stop at 80 to 90% charged as getting those final AH shoehorned in takes ~4 hours no matter the charging source.

At higher states of charge, the solar can take over the task quietly and efficiently.

AGMs do benefit from higher recharge rates, more so than flooded.  Some AGM like Odyssey require huge rates like 0.4c, or 40 amps for a 100 AH battery.

Lifeline AGM says minimum of 20 amps per 100 AH battery.  Some lesser Asian AGM's say no more than 30amps per 100AH capacity, and all of them list slightly different absorption voltages.

Everyday charging can stray from Ideal, but occasionally, every so many cycles, and more often the deeper the average  cycles, a true 100% recharge is required, and Solar in combo with other sources can complete the task that each individual source does not excel at on its own.

getting depleted batteries upto 80% charged is simple.  It is that last 20% where they fight, and AGMs tend to suffer more at partial state of charge cycling.  So getting your moneys worth from them requires a bit more. More initial amps when depleted, and a charger whose absorption voltage comes closer to the manufacturer recommendations

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