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Old 04-24-2019, 11:12 PM   #1
Mini-Skoolie
 
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Mostly DC system review

Hey guys, long time lurker here. After reading dozens of threads, I figure it's time to jump in myself.

As I'm designing my electrical system, I'm trying to optimize for three things:

(1) When plugged in, I want things to be comfortable; I want to be able to run a fridge, A/C, projector, laptop, and lights all simultaneously
(2) When NOT plugged in, I'm fine with just functional. My fridge can run on propane, I'm not tryna run an AC or projector, I mostly just need lights, fans, and phone & laptop charging
(3) I really am trying to optimize for price. Everything that helps me limit the number of expensive components I need to buy, the better.

That all said, I've put together a system that I *think* accomplishes those things... but I have so little experience here that I could really, really use your feedback.


While all feedback is welcome—I'd love to know your overall thoughts on whether this makes sense, whether I'm missing anything, whether I've made some terrible mistakes—I do have 4 specific questions:

1. I have a Charge Controller and a Battery Charger here, but only because that's what I've pieced together some other people doing. Are both necessary? Or are there consolidated units that know how to charge the battery from shore power, genny, or solar?

3. I don't have a main inverter in this diagram. My reasoning is that my fridge can run on propane, and I really only need to run aircon and our projector if we're plugged in. The only A/C appliance I feel like we need to be able to charge even if not plugged in is a laptop and occasionally a CPAP (for visitors, not for us), and I'm thinking I can use a small point-of-use inverter for that. Thoughts? Bad idea?

4. I'm having trouble getting started because I'm not sure what all my loads are going to be, so it's hard to size my battery bank and power reqs. But, I think the most pressing thing right now is wiring all the AC & DC appliances, outlets, and lights to fuse boxes, so I can start covering up my walls. Are those pieces of the system dependent on my total draw, or can I just buy those right now? Does anyone have any recommendations for those?

5. One thing that strikes me as suboptimal (but maybe isn't, I just don't know enough about this stuff) is that even when plugged in, all the DC elements are powered from the batteries, which are charged by the shore power. It seems to me it'd be more efficient to run those off shore power directly rather than going through the batteries, but I'm not sure how that would work. What do you think? Is there value in having some way to power the DC from shore power? What kind of modifications do I need to make to this system to support that?



Thanks so much for your help!
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Old 04-28-2019, 09:57 AM   #2
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I'm running completely off solar, so I only have the MPPT Charge Controller for my system, connecting to the batteries.
If you have enough panels/wattage to keep your batteries charged with just the solar, I don't think you need a separate battery charger. You'd only need that if the solar wasn't sufficient.
(I'm also trying to figure out my system, so take that with a grain of salt haha)
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Old 04-28-2019, 12:07 PM   #3
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I am not sure if this helps... but I ran two systems. My solar (2x100w panels on roof). an MPPT solar controller, and I started with 2 100Amh batteries (Duracell from Batteries plus - After a year, I now have 4... I think I should have gone with 6V golf cart batteries - but too late for now. Next upgrade).
My Dometic fridge runs off 12V or 110W - mostly just off the solar. I have 12V lads for light - and phone charge stations all around the bus.
I have a 2000W inverter to charge tool batteries and computer when needed. And a 3500W Champion Generator running off propane for times I need more power and I am boondocking.
I have a separate 110V 30A fuse box to run a few outlets when plugged in at a campsite or someone's house. I use that to run some fans during the summer (though I generally will run those off the inverter) or small heater in the cold of the winter. I don't have an AC unit - but have considered a mini-split if I move somewhere really hot (I am in Montana this coming summer).

I also put in a wood stove (cubicmini) and I have a Mr. Buddy heater.

My 12V solar is separate from Bus batteries / system - and separate from the 110W system.
12V runs above the windows / 110W runs above the seat rail below the windows.

I hope that makes sense - thanks for letting me share!

Note: I would love to add a regulator and connect my alternator to bus batteries to charge them on some of the longer non-sunny stretches. But generally my batteries charge well on cloudy days.
I would like to add one or two more solar panels - just for the heck of it.
I would also like to install a converter to be able to run my 12V off shorepower when I am hooked up - but after almost two years full-time in the bus, I have not ever really needed any of that. My power needs are very minimal...
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Old 04-29-2019, 04:49 AM   #4
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Quote:
Originally Posted by gangstertim View Post
Hey guys, long time lurker here. After reading dozens of threads, I figure it's time to jump in myself.
Howdy and welcome!!

Quote:
Originally Posted by gangstertim View Post
1. I have a Charge Controller and a Battery Charger here, but only because that's what I've pieced together some other people doing. Are both necessary? Or are there consolidated units that know how to charge the battery from shore power, genny, or solar?
Generally speaking, yes (both are necessary). It depends on your typical use, location, and components, of course. DC components/accessories are powered by the battery whether parked or driving. This then means that the ability to charge while parked is necessary and this includes when the sun is not shining. Depending on where you are, there are often weeks (during the winter, at least) where there is insufficient sun (insolation) so the ability to charge from shore/generator is necessary. These chargers are typically labeled 'charger/converter' - see below for details on that.

I'm not sure if combined solar charger and AC/shore chargers exist. A combined inverter/charger is very common but not relevant here (given what you said in #3).

Quote:
Originally Posted by gangstertim View Post
3. I don't have a main inverter in this diagram. My reasoning is that my fridge can run on propane, and I really only need to run aircon and our projector if we're plugged in. The only A/C appliance I feel like we need to be able to charge even if not plugged in is a laptop and occasionally a CPAP (for visitors, not for us), and I'm thinking I can use a small point-of-use inverter for that. Thoughts? Bad idea?
That's ok if you are sure of your needs. The negatives are that powering an inverter (even small ones) requires appropriately sized wire/cable and long runs of high(er-ish) 12V loads is not ideal. Running these to multiple locations could end up being less than ideal. The good news is that - assuming you wire your AC system correctly and have sufficient battery - adding a 'main inverter' later isn't that big of a change.

Not really important but most (not all, I admit) CPAP/BiPAPs run from DC power. The draw from most of them isn't all that significant (about 1 amp@ 12VDC) if you remove the humidifier. I've been running mine from battery/DC for years without the humidifer (365 nights/year).

Quote:
Originally Posted by gangstertim View Post
4. I'm having trouble getting started because I'm not sure what all my loads are going to be, so it's hard to size my battery bank and power reqs. But, I think the most pressing thing right now is wiring all the AC & DC appliances, outlets, and lights to fuse boxes, so I can start covering up my walls. Are those pieces of the system dependent on my total draw, or can I just buy those right now? Does anyone have any recommendations for those?
Yeah, I think that's ok (but not ideal). AC wiring pretty simple (in terms of load - most outlets are 15 amp). DC wiring can be a little more involved due to the previously mentioned load/voltage drop issues. If you planned a 'standard' and stuck to it, you'd be fine. That might be something like every DC outlet/component is limited to 10 amps @ 12VDC and you ran 12GA wire everywhere (for example, you'll have to figure out what really works for you given the wire lengths required). It would be better (less expensive, smaller gauge wire) to know - for example - that the string of DC LED kitchen lights is only going to draw 1 amp and it's only 10 feet from the fuse panel so 18GA wire is sufficient.

Quote:
Originally Posted by gangstertim View Post
5. One thing that strikes me as suboptimal (but maybe isn't, I just don't know enough about this stuff) is that even when plugged in, all the DC elements are powered from the batteries, which are charged by the shore power. It seems to me it'd be more efficient to run those off shore power directly rather than going through the batteries, but I'm not sure how that would work. What do you think? Is there value in having some way to power the DC from shore power? What kind of modifications do I need to make to this system to support that?
An appropriate RV style "charger/converter" takes care of this for you. The charger 'portion' is responsible for maintaining the battery, the converter 'portion' is responsible for providing 12VDC power required by the house (from AC power). Similarly, a reasonable charge controller does the same thing. It's all magic, of course, but it works quite well.
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Old 04-29-2019, 06:14 AM   #5
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Wow, awesome answers! Thanx for taking the time to line answer and delineate so cogently. SO glad I'd subscribed to this thread. My system is still in the imagine stage, largely due to this stuff is just to the left of alchemy to me..!
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Originally Posted by JDOnTheGo View Post
Howdy and welcome!!



Generally speaking, yes (both are necessary). It depends on your typical use, location, and components, of course. DC components/accessories are powered by the battery whether parked or driving. This then means that the ability to charge while parked is necessary and this includes when the sun is not shining. Depending on where you are, there are often weeks (during the winter, at least) where there is insufficient sun (insolation) so the ability to charge from shore/generator is necessary. These chargers are typically labeled 'charger/converter' - see below for details on that.

I'm not sure if combined solar charger and AC/shore chargers exist. A combined inverter/charger is very common but not relevant here (given what you said in #3).



That's ok if you are sure of your needs. The negatives are that powering an inverter (even small ones) requires appropriately sized wire/cable and long runs of high(er-ish) 12V loads is not ideal. Running these to multiple locations could end up being less than ideal. The good news is that - assuming you wire your AC system correctly and have sufficient battery - adding a 'main inverter' later isn't that big of a change.

Not really important but most (not all, I admit) CPAP/BiPAPs run from DC power. The draw from most of them isn't all that significant (about 1 amp@ 12VDC) if you remove the humidifier. I've been running mine from battery/DC for years without the humidifer (365 nights/year).



Yeah, I think that's ok (but not ideal). AC wiring pretty simple (in terms of load - most outlets are 15 amp). DC wiring can be a little more involved due to the previously mentioned load/voltage drop issues. If you planned a 'standard' and stuck to it, you'd be fine. That might be something like every DC outlet/component is limited to 10 amps @ 12VDC and you ran 12GA wire everywhere (for example, you'll have to figure out what really works for you given the wire lengths required). It would be better (less expensive, smaller gauge wire) to know - for example - that the string of DC LED kitchen lights is only going to draw 1 amp and it's only 10 feet from the fuse panel so 18GA wire is sufficient.



An appropriate RV style "charger/converter" takes care of this for you. The charger 'portion' is responsible for maintaining the battery, the converter 'portion' is responsible for providing 12VDC power required by the house (from AC power). Similarly, a reasonable charge controller does the same thing. It's all magic, of course, but it works quite well.
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Old 05-02-2019, 01:17 PM   #6
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I am no expert--but I think you should definitely check out the AIMS Corp Inverter/Chargers.


Particularly this model: https://www.aimscorp.net/3000-Watt-P...r-Charger.html


It is a battery charger/inverter all in one, and some of their more expensive models include a solar controller as well. I strongly suggest you avoid cheap inverters, because that's just asking to fry your devices and start a fire. But whatever you get make sure it's a "Pure Sine Wave" inverter at the very least. That model I linked to specifically references CPAP machines as requiring Pure Sine Wave.


As for the general "flow" of your electricity, the best idea (and this may be a holdover from my sailboat days) is to have everything run off the battery bank, 120V appliances through the inverter included.


Let's say you get that inverter/charger. When you plug it in to shore power, it directly powers all your AC and DC loads--charging your battery is considered one of those loads. When your batteries are fully charged, it trickle/float charges them as well as power everything else. Some electrical engineer can probably explain it better, that's just what I remember from my boating days.


So basically the changes to your diagram would be that your shore power/generator plugs in to your inverter/charger, and then that plugs in to your AC appliances and Battery Bank.



Again, I am not an expert, but at the very least save yourself a massive headache and don't get a cheap inverter!
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Old 05-02-2019, 03:36 PM   #7
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...have everything run off the battery bank, 120V appliances through the inverter included.
There is a subtlety here that are probably worth going thru to avoid potential confusion. An inverter/charger has an internal transfer switch. When 120VAC is fed into the unit, it is simply passed thru to the AC distribution system. The inverter 'component' stops functioning. This is the same as using an external transfer switch - except it is all done inside one box. In this case, nothing is running off the battery bank (arguably).

There is no right or wrong and it sounds like an large/central inverter is not desired by the OP. However; since we have went down that rabbit hole, a couple things to consider.

An external transfer switch is desirable from a component failure/replacement perspective. If any part (charger, inverter, transfer switch) fails in a combined unit, you get to replace all of them. The combined unit is desirable as everything is well integrated, easy to install, etc.

The following is way down deep in the rabbit hole... I'm not aware of a inverter/charger (in our price range) that will accept 220VAC. So, if you are powering your rig with a 50 amp shore power connection (with is 220VAC) and plan to do what is described above (pass all power thru the inverter), it won't work. You'll have to peel off one leg prior to the inverter and have a separate distribution circuit for the other leg (or don't use the second leg). In that scenario, going with a 50 amp transfer switch and branching off as needed becomes a fairly simple choice.

As always - electronics are so much fun!!!
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Old 05-02-2019, 05:14 PM   #8
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This all makes since to me with the inverter/charger mess and I am going to do it eventually which why I have and am keeping up with it?
But for me now with not house bank and use shore power or genny as power when I need house power I use my battery boost/charger/maintainer hooked directly to a 12v fuse box I built inside a waterproof/airtight container and is wired to reach house batteries one day but I connect the charger alligator clips directly to the one day batteries installed cables with battery connections and plug it into my 120 shore or genny and it runs everything at one time or cycles down as i turn the loads off and will shut down as battery full if no loads.
Ain't my final but I can camp with shore power or genny.
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Old 05-02-2019, 10:00 PM   #9
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Originally Posted by JDOnTheGo View Post
The following is way down deep in the rabbit hole... I'm not aware of a inverter/charger (in our price range) that will accept 220VAC. So, if you are powering your rig with a 50 amp shore power connection (with is 220VAC) and plan to do what is described above (pass all power thru the inverter), it won't work. You'll have to peel off one leg prior to the inverter and have a separate distribution circuit for the other leg (or don't use the second leg). In that scenario, going with a 50 amp transfer switch and branching off as needed becomes a fairly simple choice.

As always - electronics are so much fun!!!

FYI: GoPower! makes them. We have a GP-ISW3000 ... a 3000 watt (6000 watt peak) converter/inverter and it does a full sine wave, 220V (two 50 amp circuits, L1 & L2). [They do carry a heafty price ... over $1,000.00.]



https://gpelectric.com/products/3000...wave-inverter/
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