Parallel vs series

[Kwest364]

What's the difference?

What practical power usage differences are there?

Pros/cons to either?

With parallel vs series can I run stuff for longer?

Can I use more power with one setup vs the other?

[john61ct]

Rather than asking members to write everything out for something so basic just exercise your Google Fu.

Series increases voltage, so a pair of 6V G s at 200Ah each become 12V,Ah is not increased

Parallel double the Ah, keeps voltage the same

[fo4imtippin]

Series usually brings up your volts, but reduces amps. You can run smaller wire, but the higher the voltage goes, the more dangerous.
I am doing a 48v battery bank for a few reasons I won't get into. It depends on your solar or inverter setup, but I think most here do 12v or 24v.

[dzl_]

Originally Posted by Kwest364

What's the difference?

What practical power usage differences are there?
Pros/cons to either?
With parallel vs series can I run stuff for longer?
Can I use more power with one setup vs the other?

Your asking some really broad/vague open ended questions, that are better answered by reading (or watching) some introductory resources on electricity. Getting an understanding of the basics and then coming back to these questions with enough knowledge to ask more pointed questions.

Before we get to "parallel vs series"

You've gotta understand the basic units of electricity.

Voltage (Volts), Current (Amps), Resistance (Ohms), and Power (Watts of kiloWatts).

Voltage * Current = Power

• Voltage (Volts) is sort of like electrical 'pressure,' its a pushing force. Things don't 'have voltage' its always a measurement between two things.
• Current (Amps) is like an electrical 'flow rate' like water flowing through a pipe.
• Voltage * Current = Power (Watts)

There is another basic formula called Ohms law, i won't get into the weeds with it here, but it underlies basically everything in electricity and its really worth understanding on a basic conceptual level if you want to have a basic understanding of the dynamics that underlie all your questions. The formula is Voltage = Current * Resistance (which can be twisted around to also be Current = Voltage / Resistance or Resistance = Voltage / Current). The main things to takeaway at this point are (1) there is a three way relationship between voltage, current, and resistance, (2) if you know 2 of 3, you can figure out the third.

Series vs Parallel
What's the difference?

The practical difference is that when you wire something in series, the voltage increases but current (Amps) or capacity (Amp-hours) stays the same (so for instance 4 x 12V 100Ah batteries in series = 48V 100Ah)
Whereas with parallel, its the opposite, current increases but voltage stays the same (so for that same 4 x 12V 100Ah in parallel = 12V 400Ah)

Which brings us to your next questions:

What practical power usage differences are there?
With parallel vs series can I run stuff for longer?
Can I use more power with one setup vs the other?

Sticking with the same example above, the 4 batteries in series totaled 48V 100Ah, and the four batteries in parallel totaled 12V 400Ah.

So the 12V battery has more power right? Wrong! This is one of the most common misunderstandings newbies make. They focus on Amp Hours, when realistically what matters is the Watt-Hours, Watts and Watt-hours is the best way to have apples-apples comparisons. Remember back to the formula we learned. Power = Current * Voltage. With that in mind, we can see that whether its 400Ah * 12V or 100Ah * 48V, the power is the same 4800 Wh (or 4.8kWh).

So getting back to your direct question, no neither series or parallel gives you more power, neither arrangement allows you to 'run stuff longer' or use more power. Because at the end of the day, all other things equal you have the power (Watts) and/or Energy (Watt-hours) will be the same.

Higher voltages and lower currents have some benefits when it comes to efficiency at higher power levels, for reasons we won't get into that relate back to ohms law and resistance.

That is the basics of it, there are lots more specifics, but its not worth getting into with such broad questions, because it depends whether we are talking about parallel/series, batteries, solar panels, wiring, etc. And addressing each would probably be information overload.

Series and parallel are just basic concepts in electrical wiring, roughly equivalent to saying "in a row" and "in parallel" (sorry don't know a better word to use, so defining a term with the term itself lol).. Think 1 train on one loop going to 3 stations, vs 3 trains on 3 separate loops each only going to 1 station.

I suggest watching this video for a good basic conceptual overview
https://youtu.be/KhgsjzLl0m8

[Kwest364]

Originally Posted by john61ct

Rather than asking members to write everything out for something so basic just exercise your Google Fu.

Series increases voltage, so a pair of 6V G s at 200Ah each become 12V,Ah is not increased

Parallel double the Ah, keeps voltage the same

I have done plenty of google fu and can't seem to find answers to the above questions. It just explains what the differences are. Voltage goes up, ok, but what does that mean? What does that do for your equipment? I have to exclusively run 12v power appliances/equipment, 24v power appliances/equipment, 48v, etc? The forum search turns up no explanation. It's been so frustrating trying to learn all this **** from random forums and YouTube and not getting a clear, straight answer.

So, since parallel = double Ah, then that means I can run the same appliance for longer, correct?
Ex. Power for a 12v 100Ah (or 100W?) fridge. Have 1 x 100Ah battery. That means that battery can run said fridge for 1 hr, correct? Then I put another 100Ah battery in parallel, so now I have 12V 200Ah battery and can power fridge for 2 hrs?

[fo4imtippin]

Yes. If you are feeling overloaded on info now, I would stick to 12v and get a 12v inverter. You have to have at least one 12v system. Only reason to go to 24v would be solar. Until the basics are understood at 12v, then you can always build on that or rewire your battery bank to switch to 24v after it makes more sense.

[Kwest364]

Originally Posted by fo4imtippin

Yes. If you are feeling overloaded on info now, I would stick to 12v and get a 12v inverter. You have to have at least one 12v system. Only reason to go to 24v would be solar. Until the basics are understood at 12v, then you can always build on that or rewire your battery bank to switch to 24v after it makes more sense.

I bought a converted skoolie with solar. I'm trying to understand it more to make it work.

1. The previous owner set up a 24V system.

2. There are 6 x 185 W panels on the top of bus, running the AC system. MPPT charge controller is inside bus, attached to (2x) 12v batteries in SERIES connected in PARALLEL to (2x) 12v batteries in SERIES. So that means I have a 24V battery connected in parallel to another 24V battery, correct?

3. There is a single panel on top that runs a separate DC system. I don't know it's wattage, probably 100W. It's connected to a single battery under the bus, in a compartment and powers the interior overhead led lights, the water pump I'm guessing, and maybe water heater? (at least, I'm pretty sure that's all it powers, don't know what else it could be powering). Have not had a single issue with this system, yet. I limit nightly use till I have this handled.

4. The AC system: I've been having my inverter beeping and mppt controller reading "fault prompt: over discharge protection". Batteries are not holding charge at night. As soon as sun is gone, batteries don't hold any juice, and inverter shuts all 120V outlets and appliances down (my fridge is the only thing it's powering, sometimes charging phone/laptop. So, only getting juice while sun is up and powering panels. How to fix this?

5. Replace batteries? They are deep cycle marine/TV batteries. (Pic attached). When he had bus in storage he said he disconnected batteries. My guess: they discharged and killed em.

6. If replacing them is the ticket, what size batteries do I get? What capacity? How do I build this battery? One guy I met in the Nevada desert recently (@sunnytheskoolie) told me he built his battery bank batteries from blue cell 3.2V batteries by Eve brand, direct from China. This seems the best and cheapest way to go. Thoughts?

[rossvtaylor]

Originally Posted by Kwest364

So, since parallel = double Ah, then that means I can run the same appliance for longer, correct?
Ex. Power for a 12v 100Ah (or 100W?) fridge. Have 1 x 100Ah battery. That means that battery can run said fridge for 1 hr, correct? Then I put another 100Ah battery in parallel, so now I have 12V 200Ah battery and can power fridge for 2 hrs?

Hi Kwest,

If I may, I'd add a bit of clarification to this ^^

A 12V battery with 100 amp-hours of capacity has 1200 Watt-hours of capacity. The math is easy...just 12x100. So, your 100W fridge example could run for 12 hours in a theoretical system. But you don't generally want to drain AGM or FLA (both lead acid) batteries below about 50% DoD (depth of discharge). So, if you have lead acid batteries you should consider their amp-hour capacity to be half the sticker rating. In other words, for design, figure 50 amp-hours...or 600 Watt-hours.

If you add another 12V 100ah battery in parallel, then yes... you can run the same fridge for twice as long.

If you are using lithium batteries, then you could calculate this based on 80% or even (sometimes) 90% useful amp-hours since they tolerate a greater DoD.

Does this help a bit?

[rossvtaylor]

I just looked at your next post and the photos. It looks like those batteries are not wired correctly...but it's hard to be sure, since some of the wires head out of the frame of the photo.

Have you checked the battery bank voltage with a meter to see if it's showing 24V? If you did and I missed that, my apologies.

Having two 12V batteries in series to make a 24V string, then having that string parallel-connected to another similar string, is completely appropriate and results in a 24V bank. In the photo, the bottom two batteries are in proper series. But the top two batteries have something odd going on. I wish I could draw out what I mean...but I'll try to describe it. I'd remove the two "vertical" cables in the center of that photo which are creating a parallel connection with the bottom batteries. Then, use one of those cables to link the top row batteries in series...just like the bottom batteries.

Granted, I cannot see all the + and - markings so you'll need to confirm all that. I'm going off the stickers on the batteries and hoping they all orient the same. But you want both series strings connected like the bottom batteries and the two strings connected on the ends in parallel.

Not to further complicate things, but after you get the bank set up and confirm you're getting 24V I'd move the black (negative) cable on the left end "down" to the post on the bottom left. But do that later...

My quick thought in looking at that cable setup is that you appear to have both series and parallel all going on at the same time...so the inverter may only be getting 12V? Granted, I just started on the coffee this morning so I'll ask someone else to put eyes on this too. But my quick observation here is that the battery bank may not be wired correctly.

[Booyah45828]

What kind of electrical understanding do you have? Do you know what a volt, amp and watt are? The questions you're asking are kind of basic, intro to electric 101 type, which is why you've received the answers and flack that you have.

With that said, the kind of system you run(series/parallel/combo) is determined by the equipment(Inverters, chargers, and panels) that you have and the amount of power(watthours) you require.

Your current system is setup somewhat odd. The batteries look to be in a series parallel configuration to achieve a total of 24v, but I don't understand what the large cables splitting the system are for, which makes it look like some weird combination of 12v and 24v. You "can" do that in a system, but it makes the batteries unbalanced, which isn't good, and requires separate chargers to bring the unbalanced ones back up.

Take a picture showing the batteries, but with the wall in the background so we can see where all the cables go to. See if you can find some specs on your inverters and chargers too.

And as far as replacing your batteries, I'd split them and remove them from the bus, charge them up, and then have them tested for capacity. They might need watered too, so check that as well. Your batteries all have 2021 date stickers, so it'd be a shame if you ruined them that quickly.

Also, what kind of A/C unit do you have? My gut tells me your current system isn't large enough to power air conditioning, but without knowing the air conditioner, it's just a guess.

Truthfully, your current system might be undersized and overworked as it sits.

[rossvtaylor]

I think Booyah's observation and concern about the bank configuration confirms my pre-coffee thoughts...something's not right there.

In reading back through the other symptoms you posted, it looks like the solar array (through the charge controller) is providing 24 volts and can power the inverter. But if the battery bank is cabled for 12V then that would explain your "system drains/shuts down" after dark problem. If your solar charge controller isn't very sophisticated and is just cranking 24V into the batteries, it will bump up the voltage enough to run the inverter...but after dark, the voltage will drop back to 12V. A good charge controller won't do that, but a "blind" unit can. And, if this is what's going on, you will boil the batteries.

I like Booyah's recommendation to pull the caps off each battery and make sure the electrolyte is topped off...then check them and confirm the bank is cabled correctly.

[djdalfaro]

OK... So from what I can see and ASSUME about your battery configuration, it will work to provide 24v. Yes, it's done weird, but if your batteries are connected the way I show below, the wiring is not the issue. Yes it could be improved, but it's nothing major. I'll explain.



If we consider (4) 12v 100ah batteries,
Most 2s2p systems are wired like this:

        24v 100ah
   ┌─────┐     ┌─────┐
 ┌─┤-   +├─────┤-   +├─┐
 │ └─────┘     └─────┘ │
─┤                     ├─   Total: 24v 200ah
 │ ┌─────┐     ┌─────┐ │
 └─┤-   +├─────┤-   +├─┘
   └─────┘     └─────┘
        24v 100ah

We do this because when batteries are wired in series, they each receive the same current through them. This results in longer battery life because they charge/discharge at the same rate. So while both legs may not receive the same current, the batteries in each leg receive the same current as it's pair. There are methods to TRY to keep the the current through each leg identical. If they are successful, then you're golden.

You can also wire batteries in 2P2S like this:

  12v 200ah   12v 200ah
   ┌─────┐     ┌─────┐
 ┌─┤-   +├─┐ ┌─┤-   +├─┐
 │ └─────┘ │ │ └─────┘ │
─┤         ├─┤         ├─   Total: 24v 200ah
 │ ┌─────┐ │ │ ┌─────┐ │
 └─┤-   +├─┘ └─┤-   +├─┘
   └─────┘     └─────┘

In this wiring configuration each 200ah pair receives the same current, which is then divided amongst the 2 batteries. This is less desirable because no single battery is in series with any other single battery. Sure there are methods to TRY to keep the current in each pair the same. These are the same methods I mentioned above, however instead of having to employ them once, now you have to employ them twice. So greater chance of non-equal charging/discharging.


Then we have your configuration.

  12v 100ah   12v 100ah
   ┌─────┐     ┌─────┐
─┬─┤-   +├─┬─┬─┤-   +├─┬─
 │ └─────┘ │ │ └─────┘ │
 │         │ │         │    Total: 24v 200ah
 │ ┌─────┐ │ │ ┌─────┐ │
 └─┤-   +├─┴─┴─┤-   +├─┘
   └─────┘     └─────┘
  12v 100ah   12v 100ah

In your configuration, no batteries will receive the same current. How much will the be off? Hard to say. It's more number crunching than I care to put in. What to do about it? As others have said, you need to find out what condition your batteries are in currently. Then ASSUMING THEY ARE ALL EQUALLY GOOD I'd modify the wiring to look like below. Do this by removing the two cables running vertically in the middle of your picture (one red, one black), and switch the red cable on the right side of the picture from the upper battery positive post to the lower battery positive post. That will give your system the best chance at even charging/discharging without much work.

   ┌─────┐     ┌─────┐
─┬─┤-   +├─────┤-   +├─┐
 │ └─────┘     └─────┘ │
 │                     │    
 │ ┌─────┐     ┌─────┐ │
 └─┤-   +├─────┤-   +├─┴─
   └─────┘     └─────┘

[Booyah45828]

*edit, my post is unnecessary, djdalfaro described what needs to be done.

Truthfully, I think they could have a common 2s2p system if they remove the wires circled in blue here.

The wire for the inverter looks to follow the path of the brown line to the large fuse at the top of the picture. And the other lugs that are hidden at the top of the screen could possibly be another jumper cable illustrated by the pink line.

If that's all the case, remove the 2 jumpers circled in blue and you'd have a common system.

With how you have it, it creates a weird paralleled system, that's also ran in series, that I really don't like. Those blue circled jumpers are unnecessary.

[Rwnielsen]

Voltage drop (loss over distance) is significant with DC voltage. I'm running a 24 volt system primarily to get the wire size down on longer runs. It's just easier to run a couple #10 wires than #6s. Wire is not cheap but I have quite a bit lying around. The economical drawback is that you have to step the voltage back down to 12 when it gets where it's going for most uses. Step-down transformers aren't expensive and, so far I have 4 of them for various loads.

[flattracker]

All of the above posting are good stuff (higher voltage smaller wires). I had a discussion with an old friend about voltage loss and he brought up an important point about voltage loss. To consider voltage loss issues in a circuit, think of the wires as a resister. The amount of resistance in a wire is based on its diameter and the frequency of the current flow through the wire (for skoolie wiring frequency isn't an issue).

There are tables on the net that show the resistance of wire based on gauge.
What you will find when researching the voltage loss issue is that it is a bigger deal at 12 volts DC than at 120 or 240 VAC. If your circuit drops 1.5 volts in the wires carrying the current in the circuit and the voltage is 120 or 240 VAC that is no big deal. Any device that you would connect to these voltages can tolerate that much loss. BUT when you are talking about a 12 - 24 VDC circuit it is a bigger deal. Your 12 VDC ends up at 10.5 VDC.



Lets say you are wiring up your solar panels and the wire gauge you select results in a couple volts lost in the wires connecting up your panels and you have 6 panels and each panel generates 10 amps of current flow in good light. 10 amps x 2 volts = 20 watts per panel 20 watts x 6 panels = 120 watts. That 120 watts is turned into heat not charging ones batteries or running something electrical.



The point of this discussion is to consider using a higher gauge wire than you think is required for your wiring. Based on my examination of solar panel wiring coming out of the panel, I recall the wire is about 10 gauge? I would use wire that size to connect the panels to my charge controller.


I know that in my house (built in 2011) they used 14 gauge wire for 15 amp circuits, 12 gauge wire for 20 amp circuits. Those were 120 VAC circuits though. I am using 10 gauge wire to connect my solar panels to the charge controller. A couple volts lost at those voltages are no big deal.



Is that more expensive? yes. Do I get to use more of the power from my arrays? yes.


For those who want to make the considerations about electricity more complicated, you could bring in Kirchhoffs laws. ( think about that all of the voltages in a circuit (and current flow)).


I spent a semester in college being saturated with Kirchhoff's law. (not entertaining)

[Rwnielsen]

This is a handy little voltage drop calculator, switches from AC to DC and covers a wide range of voltages. It's an eye opener, especially ir you're building a full size bus.

https://jcalc.net/voltage-drop-calculator-nec

[john61ct]

BSS Circuit Wizard app is fantastic for this, exposes all the relevant factors

[Kwest364]

Everyone, thank you for the help. I've been lost on all of this. Getting this bus and going full time in it and having to plan and learn and watch and post etc has been very overwhelming. It's difficult for me to plan ALL of the things at once. Bear with me. It's much appreciated.

***keep in mind, there are solar panels (6x185W) running AC system, and solar panel (1x100W) running DC system. Wiring looks separate from my eye. Batteries/wires pictured should be all AC system. DC batteries and monitor and controller are under bus (not pictured). ***




Pics attached for clarification, hopefully:
1. The battery with red circle around it is boiling. I can strongly smell the sulfuric acid inside. It's the ONLY battery that is warm to the touch.

What does this mean?
Why only that battery?
Is this dangerous to breathe in?
Disconnect it?





2. Why is there a converter (grey box, Powermax brand) attached to the inverter? I thought converters were for DC to DC, and inverter = DC to AC.




3. What amp hrs are my batteries? Only thing listed are:
-CCA: 600
-MCA: 750
-RC: 160




4. Can't make battery into 12 V system because hardware is 24v, so how do I improve my current set up? Add batteries, remove cables?




5. What's the root cause for my batteries getting over-discharged? I have HAD have the fridge plugged in, but it's set to 0 (not cooling anything). I JUST unplugged it to make sure there's no current draw.


Yes, I have lots to learn. Yes, this is overwhelming. Yes, I'm new to this.

[rossvtaylor]

Hiya, Kwest - I have to ask...three of us, above, suggested you rewire your battery bank. Booyah and I described what do do and dj even drew a diagram. Did you do that? Doing so would ensure your battery bank is set up properly for 24V. It sounds like one of your batteries is getting 24V charge into a 12V cell.

As to some of your questions, briefly... Yes, breathing that is bad. Where's the converter? I see a 24V inverter and a charge controller and a battery charger. The Powermax box is a charger, so when you're plugged into shore power your batteries get charged. As to the batteries...any battery with CCA ratings isn't really a deep discharge battery, so it's hard to tell the ah capacity.

Before you do anything else, please help us help you and re-cable your batteries as 3 of us suggested. Then, let's move forward from there.

[BFlinn181]

This is a pretty good explanation of RV electrical systems. https://www.rv-dreams.com/rv-electrical.html