Is "THIS TOO MUCH?" Or "NOT ENOUGH?"

[Wuzabus]

Hey Family! Hope everyone is doing well and all Rig builds are going as planned. I have a question for the group; I bought one of those 5000 watt Cummins inverters and I just ordered (4) 200 watt solar panels and plan to buy (4) 200 Ah 12 v Li Time batteries. Is this too much power or not enough for a refrigerator/tv's/mini split/microwave/ dishwasher/power outlets through the bus? Bus is 30.11 ft. Y'ALL'S THOUGHTS?

 

[nikitis]

The inverter is plenty, maybe overkill. It would depend on the fridge, tv, microwave, etc's power usage.

800 watts solar is a little low however.. 800 Ah battery bank is also plenty. Just a bit light on the panels imo. Might need to up size it more if you can. If space is an issue, they make 400'ish watt panels now. Some say 500'ish but I have my doubts on that being a continuous 500, but assuming 400'ish to save money, you could double your wattage to 1600 within the same spacing.

I don't know if you got your current panels already and for free to cheap, but 800 watts is a tad low for all of that. Also depends on how often you use it. If living in it full time, no. If going on a 2-3 day trip and it charges the rest of the month without using it, it may be enough with such a battery bank, but it would take awhile to charge them up on a small panel array.

Also a 12v configuration will charge more slowly too. have you considered going 24 or 48v?

My 2 cents.

 

[Wuzabus]

Good Morning. This is why I posed the question. Well...I didn't know that panels came in 400-500'ish watts( should have investigated it further). Should that be the case.. I'll return those and upgrade to that specific wattage. Also, I just looked online and saw the 24v 100ah battery. It's about the same price for a 12v one. So you would you suggest (4) 24v batts to go with the (4) 400w panels? Ty bro for your 2 cents- et.al BTW .I'll be PT Living and Travelin with the Rig.

 

[Mr P]

5000 watt inverter powering + stuff with unknown wattage = Unknown answer.

 

[Jono14]

The inverter and the battery bank have to match voltage so if you are committed to an inverter that is designed for 12V DC, you cant use 24V batteries with it.

That said, 5000W is really high for a 12V system. In theory if maxing out the inverter, you will be drawing 417 Amps at 12 volts, but because inverters are often about 90% efficient, it will actually try to draw ~460A which is higher than the rating for 4/0 wire and many battery switches.

So one option is to lower the inverter to 3000W. It should be able to run a mini split and microwave at the same time. Then a 12V system is OK.

But for you, if you think you need the 5000W of peak power (you will need to research what all the big power items you would run together need at max wattage), then you should step up to a 24V system.
This drops the amperage in half for the same wattage and allows smaller wires.

The added step for a 24V (or 48V) system is that you will need a DC converter that drops 24V (or 48V) to 12V to power fans, lights, water pumps and other items that are usually 12V.

For solar panels, most current panels have similar efficiency of watts per area - so in general, a 400W panel will have twice the area as a 200W panel. For a bus, the 400W (house) panels are big (maybe 80" x 40") but there are folks on youTube with good examples of racking systems that can mount these panels effectively to a bus roof - but plan for help getting them on the roof. It is not a free-lunch situation of 400W in the same space as a smaller panel.

For solar, figure out your likely daily watt hours of energy use and see if you can replace that with solar. If you have 4 x 200W panels that is 800W and a decent rule of thumb for summer in Wisconsin is 5 "perfect" hours of sun per day = 800 x 5 = 4000 Wh. A single 24V (actually 25.6V for LFP) 100Ah battery holds ~2,560 Wh when full, so your panels could fill about 1.5 of those batteries in a day of sun (if not using other energy).
So I agree with @nikitis that the panel wattage is low for that size battery bank.

In some ways, it does not matter if your battery bank is really big if you generally don't use much of it. If you have a 800Ah system but typically only use 200Ah of it per day, then if your solar can fill 400Ah, then you can cover your daily needs on solar and even catch back up after a few days of clouds/rain.

This stuff gets complicated because of all the overlapping layers and multiple options available. Just keep watching videos and learning.

 

[Timeline]

Hi Waza!

Like Jono said, this stuff gets complicated...
First step may be to do a do an energy audit, to figure out your daily use in watts. There are many calculators online to help with that. Next is to design a system to meet your needs. I'd stop buying "parts" until you get this far...

The learning curve is steep when building your first solar system, you'll need some tools your don't have yet too. Lot of information and helpful people can be found here: DIY Solar Power Forum

I took the easy way out and bought a solar power station lately, each year they improve and have reached the point where they are a real option. I spent less than a DIY system would have cost me.

 

[Wuzabus]

The inverter and the battery bank have to match voltage so if you are committed to an inverter that is designed for 12V DC, you cant use 24V batteries with it.

That said, 5000W is really high for a 12V system. In theory if maxing out the inverter, you will be drawing 417 Amps at 12 volts, but because inverters are often about 90% efficient, it will actually try to draw ~460A which is higher than the rating for 4/0 wire and many battery switches.

So one option is to lower the inverter to 3000W. It should be able to run a mini split and microwave at the same time. Then a 12V system is OK.

But for you, if you think you need the 5000W of peak power (you will need to research what all the big power items you would run together need at max wattage), then you should step up to a 24V system.
This drops the amperage in half for the same wattage and allows smaller wires.

The added step for a 24V (or 48V) system is that you will need a DC converter that drops 24V (or 48V) to 12V to power fans, lights, water pumps and other items that are usually 12V.

For solar panels, most current panels have similar efficiency of watts per area - so in general, a 400W panel will have twice the area as a 200W panel. For a bus, the 400W (house) panels are big (maybe 80" x 40") but there are folks on youTube with good examples of racking systems that can mount these panels effectively to a bus roof - but plan for help getting them on the roof. It is not a free-lunch situation of 400W in the same space as a smaller panel.

For solar, figure out your likely daily watt hours of energy use and see if you can replace that with solar. If you have 4 x 200W panels that is 800W and a decent rule of thumb for summer in Wisconsin is 5 "perfect" hours of sun per day = 800 x 5 = 4000 Wh. A single 24V (actually 25.6V for LFP) 100Ah battery holds ~2,560 Wh when full, so your panels could fill about 1.5 of those batteries in a day of sun (if not using other energy).
So I agree with @nikitis that the panel wattage is low for that size battery bank.

In some ways, it does not matter if your battery bank is really big if you generally don't use much of it. If you have a 800Ah system but typically only use 200Ah of it per day, then if your solar can fill 400Ah, then you can cover your daily needs on solar and even catch back up after a few days of clouds/rain.

This stuff gets complicated because of all the overlapping layers and multiple options available. Just keep watching videos and learning.

TY so much for ALL THAT INFORMATION! I'm going to go back and try to piece it together. I think this only part of the build imma hate. Cause like you said.. IT'S CONFUSING AH!

 

[nikitis]

I concur with both @Jono14 and @Timeline.

a 24v or 48v system requires a step down transformer, but if you went 48v, You could have a 48v system, a 24v system, and a 12v system as one system. Which allows you to power multiple types of items. There aren't many 48v items for sale in RV's. There's some 24v items for sale in RV's, so the up in voltage allows for smaller wires as there's less AMPS involved. Volts don't require large cabling, Amps do.

A 48v configuration is likely going to require you have more than 4 panels, you can do 48v with 4 technically.
12v + 12v + 12v + 12v = 48v.

The way a step down transformer works is you just connect a 48v to 24v transformer device and hook that up from your 48v system to a fresh bus bar with the transformer in between them. Everything plugged into that bus bar will use 24v's safely. So that new bus bar becomes a 24v system. You can additionally add a second 48v to 12v transformer in a similar manner and have an additional bus bar, so now you have 3 bus bars, one for 48v devices, one for 24v devices, and one for 12v devices. You'd plug your lights and other 12v appliances into this 12v bus bar. This is all DC current too btw.

If you are using a house appliance not mean for an RV like a 120v AC type current, you would hook the inverter up to a 110 Circuit breaker box like in a house. Instead of a main line coming into the breaker box like in a house, it's your inverter lines instead. Except this can only do 110 instead of 220 like in a house. No 220v welders unfortunately.

I likely wouldn't bother with a 48v inverter but go with a 24v inverter. It's a good happy medium. Gain faster battery charging, but not quite as complex. Your solar panels will need to be wired 2x2. 1 set of 2 in series, and another set of 2 in series, and both sets need to be wired into parallel to make 24v solar system array.

This setup turns 2 of your panels into 24 volts, but the amps stay the same they don't add up. Same for the second set.

When you combine both sets into parallel, now the 24 volts stay the same but the amps double one time instead of 4 times. This is why you can use smaller wires.

Mathematically it's like this for 24v:
200watt/12v=16.7amp + 200watt/12v=16.7amp panels in series = 400watt/24v=16.7amp
200watt/12v=16.7amp + 200watt/12v=16.7amp panels in series = 400watt/24v=16.7amp

Then take the two sets and combine in parallel:

(400watt/24v=16.7amp) + (400watt/24v=16.7amp) = 800watt/24v=33.4amp

So your amps are doubled one time on a 24v system. Still have the 800 watts, but gains are shared half from voltage, half from amperage. Battery setup must be similar. 2 of 4 batters in series, and the other two in series, and then both sets put together in parallel, and you need a 24 volt inverter, and one Step down transformer connected to a 12v bus bar for 12v items only. And a bus bar for anything 24v. So it's like having 2 systems.

-------------------
Mathematically it's like this for a 48v:
(200watt/12v=16.7) + (200watt/12v=16.7amp) + (200watt/12v=16.7amp) + (200watt/12v=16.7amp) = 800watt/48v=16.7amps

So your amps aren't doubled at all on a 48v system. Still have the 800 watts, but gains are from voltage rather than amps. The problem with this setup is you need to wire 4 batteries the same way in parallel to make 4x 12v batteries into a single 48v battery. Also need the 48v inverter. Also need 2 step down transformers, one for a 24v system one for 12v system.

 

[Wuzabus]

OMG THANK Y'ALL SO MUCH! .I APPRECIATE ALL OF Y'ALL!

 

[TaliaDPerkins]

The way a step down transformer works is you just connect a 48v to 24v transformer device and hook that up from your 48v system to a fresh bus bar with the transformer in between them. Everything plugged into that bus bar will use 24v's safely. So that new bus bar becomes a 24v system. You can additionally add a second 48v to 12v transformer in a similar manner and have an additional bus bar, so now you have 3 bus bars, one for 48v devices, one for 24v devices, and one for 12v devices. You'd plug your lights and other 12v appliances into this 12v bus bar. This is all DC current too btw.

Hi, ah, those aren't transformers. Those are DC to DC converters. A transformer is an AC competent*. A DC2DC converter may well have a tiny, usually high freq inverter driving a transformer which is then rectified and smoothed to a final DCv out. You can usually tell because low harmonics make them hum or whine. Generally, if a plain old transformer is hooked up to DC, you'll pop a fuse or breaker . . . or the transformer primary.

*A saturable core reactor is a transformer, usually an autotransformer, built so the effective secondary voltage is proportional to a small DC current. Sort of an amplifier, a DC controlled AC transformer.

 

[nikitis]

I've often heard them referred to as transformers and never as DC to DC. Similar to how it works on actual power lines. Power lines carry around roughly 17,000 volts and transformers step it down to 220v for the houses, but you're right, I've likely been using the wrong terminology because that is actually AC coming in on those power lines. I'll change my terminology. Usually DC to DC is referred to as an alternator to battery charger, but I guess that is stepped down as well. Thanks for the correction.

@Wuzabus The math above still works though. Get a step down DC to DC converter then, not transformer.

 

[desrtdog]

Just gonna add one clarification to the above…solar panels (the residential type) are typically rated at close to 40v open circuit and 30v under load…not sure on the smaller ones …. But point being that it is not necessarily a given you need to put panels in series, unless you are going with a 48v system. There are some definite advantages to having a parallel array, in that if a single panel goes down, you won’t lose your ability to charge a battery bank.

As a primer to help educate yourself on what you need and how to set it up, I’d highly recommend checking out this link:
faroutride.com

 

[Mr P]

Usually DC to DC is referred to as an alternator to battery charger,

What??

 

[nikitis]

What??

"DC to DC Chargers" are often what they are called here on the site which connects your alternator to your in-house battery system to charge it via the engine.

DC to DC Charger by Victron

 

[TaliaDPerkins]

Helluva typo to that Amazon ad:

 

[Mr P]

As a primer to help educate yourself on what you need and how to set it up, I’d highly recommend checking out this link:
faroutride.com

Great link!

 

[AlphaHare]

Please just don't call them transformers.

They are commonly used for isolated charging from alternator, even 12-24 for a 24vdc system. Likewise for 24-12 conversion allowing you to run a 24vdc system and still have a 12vdc service for whatever. Most LED lighting can handle 24v these days.

https://www.victronenergy.com/upload/documents/Datasheet-Orion-Tr-DC-DC-converters-isolated-100-250-400W-EN.pdf