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Old 12-04-2016, 06:33 PM   #1
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Electrical Overview (connecting Alternator, Shore, Generator and Solar)

Hi, I'm looking for a description and diagrams for how all of the power inputs tie into a single system to charge the house batteries. If I'm connected to shore power, my solar panels are still pulling in power. If I'm boondocking, my solar is primary, but I may be running a genny on occasion. As I drive, my alternator and solar are providing power. I may even be driving a long distance in bad weather and have to run the genny to power my fridge/freezer for food safety. All of this to ensure my batteries do not drop below 50% charge or receive too much of a charge. How does al of this tie together in a design? Can someone point me in the right direction so I can figure out what I need to start with. If I build my system as I want it, it needs to support generator, shore power and alternator from day one and be able to add solar in the future. Thanks
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Old 12-04-2016, 07:02 PM   #2
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Here's a diagram that is way simplified but shows how I think all these things should tie together to form a complete 4 way charging system.... there are things I did not include that will need to be added but since this is just a very basic overview I didn't go into too much detail.



Couple of things I should mention....

1) On the AC side, make sure your inverter INPUT is coming from your main AC load center, and connect the OUTPUT to a separate subpanel. That way you prevent your inverter output from feeding back into itself, plus it ensures the charging circuit is OFF when no external AC source is connected.

2) On the DC side, make sure you turn OFF your solar charge controller when charging from the bus alternator. I'm not sure it would damage it if power is coming in from the panels with nowhere to go but better not to chance it. And also make sure the charge controller is OFF if using shore/generator power to charge them.

If I have made any gross errors I'm sure someone will call them out.
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Old 12-04-2016, 07:21 PM   #3
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DC-Side

Thanks AlleyCat67. On the DC side of things, is it possible to feed the alternator output and solar into a single charge controller to eliminate the need to the transfer switch?

As for the AC side, it seems pretty straight forward to me. 120AC is 120AC, doesn't matter if its from the generator or the shore power. For this, I just need a big frankenstein switch and have Igor throw it to switch between shore and generator. Doesn't matter if both happen to be running/connected as the switch will only allow one to feed my system.
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Old 12-05-2016, 03:00 AM   #4
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I'm not sure if they make charge controllers that can handle more than one input... if they do that would simplify things a bit as the controller/transfer switch would be combined in one unit.

On the AC side of things, yes you're mostly correct..... there IS a slight difference between shore and generator power, in that some generators put out a modified (square) sine wave where shore power is pure sine. You don't want both connected at the same time but the transfer switch prevents that, just as you said. Transfer switches come in both manual and automatic varieties, which one you go with is a purely personal choice.
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Old 12-05-2016, 07:34 AM   #5
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Thanks again. So how does the Battery Control Center figure into this...or do bus conversions have a BCC? My RV has one and I only know about it because an automatic switch failed and allowed the Chassis and Coach batteries to remain connected. This resulted in both sets of batteries dying on our last trip. Not sure if the starter killed the coach batteries or the constant drain from the coach killed the starter battery first. After a bit of research, I discovered that the BCC has a swich taht is supposed to allow both batteries to be connected only when the alternator is providing a charge. Otherwise, they are supposed to be separate.
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Old 12-05-2016, 07:52 AM   #6
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It would only have such a beast if you add it yourself. If you do decide to wire the house batteries and coach batteries together it would probably be better to install a MANUAL switch in the connecting line somewhere, so it would take a deliberate action to connect them when you start the engine (but don't forget to turn the switch OFF when you shut down).
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Old 12-05-2016, 08:35 AM   #7
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Simplified Charging System Diagram v2

So would it make sense to add a separate transfer switch before the batteries to switch between DC and AC battery charging sources? This would allow only one source of power to feed the batteries at a time. You have the Genny/Shore power switch on the AC side and the Alternator/Solar switch on the DC side. These connect to a AC / DC Transfer Switch just before the batteries. This final transfer switch would actually feed into a shunt where my battery monitoring would occur. If I'm ever not seeing voltage, chances are one of these switches needs to be flipped.
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File Type: jpg Simplified Charging System v2.jpg (45.3 KB, 69 views)
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Old 12-05-2016, 10:07 AM   #8
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Well dang...can't get the layout/plan to open.
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Old 12-05-2016, 11:07 AM   #9
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I keep getting an error when I try to upload it. Take AlleyCat67's diagram, move the Battery Bank down and put a new Transfer switch where the batter bank is current drawn. This allows you to switch between the DC system (Alternator/Solar) and the AC system (Generator/Shore). With this switch in place, it isn't physically possible for the batteries to be charged by more than one source at the same time.
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Old 12-05-2016, 11:28 AM   #10
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I don't see the v2 drawing either. But with regards to the first sketch from AlleyCat67, the transfer switch on the DC side will almost certainly prove unnecessary. Each of those charging sources (mains charger, solar, alternator) should be independently regulated such that they'll work it out amongst themselves if more than one is energized and willing to charge the batteries. The only point of concern might be that the batteries themselves will have some maximum recommended charge rate; with a combination of independent chargers operating in tandem you might conceivably exceed that charge rate. That could cause the batteries to run warm, off-gas, and possibly shorten their life (or at least accelerate the maintenance interval).

The switch mentioned in that last post could prevent this. It could also be avoided through use of a manual-start mains charger rather than automatic, as well as some consideration of what to actually expect from the solar system vs battery bank size. If the solar system is relatively small, or at least its output could be expected to be low while the engine is running (ie, the bus is underway) then maybe it isn't something to stress over.
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Old 12-05-2016, 11:50 AM   #11
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Unfortunately, we experienced a total failure of our battery system in our RV. I'm hoping to find out how it fell apart on us. Could be the charger failed and overcharged the batteries. Could be the relay in the BCC failed closed allowing the Chassis and Coach batteries to be permanently connected. This would have resulted in massive AMP pull on the coach batteries when starting the vehicle (something sure to kill deep cycle batteries in time) and a continuous drain on the starter/chassis battery from using 12v equipment (sure to damage a starter battery pretty quick). Add in that you should never have mixed battery banks (2 deep cycle batteries and one starter battery certainly equals mixed) and you eventually wake up one morning, disconnect from shore power, and find out that all batteries in the vehicle are dead and not taking a charge at all.

That is what I am going to try and avoid in the bus and something I get to experiment with avoiding in the RV once I get it back from the shop (where hopefully the experts can identify what went wrong).
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Old 12-05-2016, 01:51 PM   #12
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Are the DC Transfer Switches necessary?

I've been doing more reading and apparently the alternator and higher end solar charge controllers will automatically reduce the current to zero when voltage reaches a certain threshold to prevent overcharging. As long as the sensor is between the battery bank and the charging sources, the solar charge controller will ensure it doesn't contribute too much current...I think.
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Old 12-05-2016, 10:27 PM   #13
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That DC transfer switch in my diagram was basically just a "better safe than sorry" addition to prevent charging from multiple DC sources at the same time. With a good charge controller setup or other means to regulate the charging current to avoid over-charging the batteries it would not be needed, as others have said.

The additional transfer switch to isolate AC from DC was also a good thing to have, surprised I didn't think of that myself.

My electric plan does not include charging house batteries with the engine alternator so it isn't something I had considered. An option I am looking at is running an alternator off a separate 6-7 hp engine strictly for charging when no shore power is available AND on days when solar isn't putting out much because it's cloudy.

The other alternative is to run a generator and use that for battery charging, but not really keen on subjecting my electronics to the square sine wave that most generators output. My inverter is pure sine so would prefer to run off that. Not that the square wave would hurt anything, but from what I've read, some things are sensitive to it and don't work as well, and others simply refuse to work at all.
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Old 12-06-2016, 08:21 AM   #14
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Alleycat: generators throw a sine wave. It may be a bit distorted if its a cheap set, but it will definitely be a sine wave.

FWIW, i use a pair of Honda EU-2000's and the output is cleaner than grid power. And they are very quiet. Sitting directly on top of them you can hold a normal conversation. Charging batteries you only need one, and it will run 10 hours on a gallon when Eco Mode is enabled.

Food for thought! (And Sams Club has them on sale right now for $899)
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Old 12-06-2016, 08:56 AM   #15
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That's all as may be but 2000 watts isn't gonna power everything I need to run. My inverter is 3000 watts continuous with up to 9000 for a 20s surge so I'm not going below that. With that $900 I can buy an 8000 watt hybrid fueled genset at several different places. Granted it won't be as quiet as the Honda but it will power everything I need twice over, and I could probably fabricate some kind of enclosure to cut down on the noise level.

Or, for about 400-500 I can custom build a 12v (or 24v) alternator setup to charge my battery bank using a 7hp engine, the appropriate voltage alternator, and a couple of pulleys and belts (and of course a 1/4" steel or thick reinforced wooden plate and mounts to set it all up).

How long would one of those 2000s take to charge 1380 amp hours of batteries? (And it would be useless with a 24v battery bank since I'm assuming it only puts out 12v on the DC side).
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Old 12-06-2016, 09:55 AM   #16
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Anybody who's serious about charging batteries from a generator shouldn't use the generator's built-in "battery charge" output. It's junk. Even on the Honda EU series it's junk. It's an extra winding on the generator head configured to produce a rectified but unfiltered and unregulated output of up to 8-12 amps (ie up to ~150 watts). There's no over-charge protection for the battery.

Instead, plug in the usual mains-powered battery charger on the AC side of the generator. There are more watts available this way, 24/48/whatever volt banks can be accommodated, and there's also the benefit of supervised multi-stage charging according to the charger selected. Supposing 0.13C rate, 1380 AH could be charged at up to 180 amps, which for a 12v bank is 2152 watts. If it were to be done with an EU2000 one would dial it back to 1600 watts (continuous rating of that generator) or about 130 amps. The battery charger won't spend all that much time at full rate anyway; most of the time in a charge cycle has the rate tapering from max toward zero.

A person could choose a generator sized for the battery charging job rather than sized for the sum of the AC loads. Probably can't charge the battery bank at 3kW-9kW rate anyway, and there's nothing wrong with running the inverter while charging the batteries.
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Old 12-06-2016, 10:53 AM   #17
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Family, what are the formulas you're using for calculating the size of the generator based on the size of the battery bank?

I'm considering a 48v system for our bus...primarily to run a 48v minisplit for the a/c. I'll use a 48v - 12v DC/DC converter for 12v requirements and a 48v inverter for my AC requirements (fridge and computers). Shore and Generator would charge my batteries and I would probably have some additional outlets that are only energized when connected to shore power so I can float the batteries occasionally. I've been trying to figure out the size of the generator I need and if I should go with one large gennerator or two smaller ones.

Thoughts?
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Old 12-06-2016, 11:45 AM   #18
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Apologies.. it's kind of sloppy round-numbers estimating which doesn't make it easy for somebody to follow along and figure out where the numbers came from. Here's what I did in more detail.

AlleyCat67 asked about a 1380 AH battery bank but didn't say the bank voltage. That's OK; battery charge and discharge rates are given in terms of "C" which is amp-hour capacity at 20-hour rate. So I started with 5-13%, or 0.05C to 0.13C, as the max charging rate (this is a range that seems to be commonly called out on lead battery technical data sheets). 0.13*1380=179.4 amps, which I rounded to 180 amps.

To get from here toward generator size the amps needs to be converted to watts. Watts=volts*amps. I had to make an assumption about the bank voltage. Supposing a 12 volt nominal battery bank, 12*180=2160 watts. (but in my sloppiness earlier I didn't actually do 12*180. My calculator still had 179.4 on the screen so I did 12*179.4 instead and got 2152.8, which I truncated to 2152. If I would at least be consistent about sloppy back-of-the-envelope figures it'd help, right??)

That wattage is power from the battery charger into the batteries. The charger isn't perfectly efficient, but I assumed it to be in making the leap to saying the generator would need to provide those 2152 watts.

I happen to have an EU2000 and know that its continuous rating is actually 1600 watts, or actually probably 1600 VA but that's deeper into the electrical engineering than we really want to go.. Anyway, 1600 watts from the generator into a 100% efficient charger making a 12 volt output means there is 1600=12*amps or amps=1600/12=133.33 amps. I rounded down to 130.

A person might be reasonably be uncomfortable with the casual math here. It turns out that basically all the figures are estimates anyway: a 12 volt battery bank isn't exactly 12.0 volts, a 120 volt source isn't exactly 120.0, the 1600 watt continuous from the EU2000 isn't exactly 1600.00 watts, charger conversion efficiency is unknown and ignored, etc.

As to generator sizing: after being around a few generators I decided I valued quiet above all else. That meant choosing among inverter generators. I learned through use that an EU2000 does a pretty good job for me but sometimes (often?) I wanted just a little more. There are good arguments both ways for upgrading to an EU3000 vs a second EU2000. I'm sorry I can't advise you there; I never resolved it for myself. I wanted a generator to serve as home backup as well as bus service which meant choosing something that could give me 240 volts. Once "portable inverter" and "240 volt" are locked in there are just two options: EU7000i and EF6500is. I picked the Honda and watched the local online classifieds for about a year to find one lightly used at 20% discount from new price.
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Old 12-06-2016, 11:55 AM   #19
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Thanks. All those amps are starting to heat the lightbulb filament. Things aren't as dark as they were
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