Series vs Parallel

[Juliet 15]

Been working on improving my house bank setup and realized something that I've been puzzling about all day.



My dedicated 12v house bank batteries are wired to a 12v inverter in parallel, so the inverter has a lot of amp hours available at 12v.


My stbd 32v engine start bank has four 8v batteries wired in series to a 32v inverter and serves as a backup house bank.



An inverter selector switch determines which inverter supplies AC power to the house at any one time. They can't both be on.



But the 12v inverter sucks 12v from 4 12v batteries in parallel, while the 32v inverter sucks 32v from four 8v batteries that only reach 32v bcs they're wired in series.



Which is "better"? Are there pros and cons?

 

[ofer]

your 32V bank is 4x 8v batts in series to produce 32 volts in total. that's the only way to get 32V out of 8v batteries. there is no choice its like you have one big 32V batt.

you are using 12V batts for your 12v system by hooking them in parallel you are increasing the amp hours not the voltage.

 

[SteveK]

Which is "better"? Are there pros and cons?

The 12V is better as it most likely has more Ah.
My question is why have start batteries ready to be backup to the AC supply. What will start the engine when both are used?

 

[Juliet 15]

Soo-Valley,


The boat is built for long trips, so it has the primary 12v house bank, the backup house bank (aka stbd engine start batteries), and a 3rd backup house bank- the port engine 32v start bank. This way you can hang o. The hook for a long time before you have to use the gensets (or the engines) to recharge them all. The boat has 3 gensets, each with their own starting battery. And 2400 gal of fuel, all intended to make it long range and long term off-grid capable. I haven't ever used the 32v engine start banks for the house yet. The PO wanted to be able to hang on the hook for over a week before needing to start anything to recharge. Ofer - Yes, thx. I get that one is 12v and the inherent is 32v bcs of the series wiring. I just thot it was interesting, and also I'm thinking (but don't know for sure) that the 12v system will last a lot longer than the 32v despite both banks having similar amp hour ratings.



Is that accurate?

 

[SteveK]

What is the Ah of each bank, that will give you a better idea which will last longer.
Now that the light bulb came on I realize you have a port engine bank to start both engines in case SB bats are worn out inverting.

Generally
The 12v in parallels will add the Ah of each battery, say 200 x 4= 800
while the 8v will remain the same Ah as one of four, will only add up the volts. say 150 total
Of course assumptions are made that both banks are deep cycle

 

[ofer]

Soo-Valley,

and also I'm thinking (but don't know for sure) that the 12v system will last a lot longer than the 32v despite both banks having similar amp hour ratings.

Is that accurate?

no, probably the opposite. the 8V batteries are heavier duty bigger plates than a 12V batt.

i don't think you have a choice. your engine starter alternator etc run on 32V.

the 12V was added later to use as house bank etc since there are many more accessory options available for 12v than 32v.

 

[Barking Sands]

They each have advantages and disadvantages.

If you are trying to see which setup has more usable power...just convert to watt/hours.

You didnt state how many amp hours each battery type was rated for so lets just say all batteries are 100ah batteries.

32 volt bank: 8 volts X 100Ah = 800 watt hours per battery. 800 watt hours X 4 batteries = 3200 watt hours for the entire bank.

12 volt bank: 12 volts X 100Ah = 1200 watt hours per battery. 1200 watt hours X 4 batteries = 4800 watt hours for the entire bank.

How many of those watt hours are actually available to use is dependent on battery type and battery age/condition.

Benefits of the higher voltage is you can use smaller wire to make longer runs due to the high voltage. Wire size is determined by amp requirements. By using twice the voltage you will need half the amps to provide the same wattage to run some appliance or component.

 

[mvweebles]

If the question is, given same overall power and construction but series vs parallel, it's possible to cable multiple batteries in parallel to minimize loss. With 4 batteries in series, there will be a small imbalance between the "end" batteries and the "inside" batteries. For OPs application, a moot point since getting 32v is an awkward number so multiple batteries in series is required. But for other applications where there is a choice, keeping series minimized is preferred, but not a huge difference.

Peter

 

[High Wire]

If the 32v inverter is truly only a spare then shut it down. An inverter with no load on it still consumes watts of power (volts x amps) to keep the semiconductor bits firing to be ready to provide instant AC power when called. Just don’t leave it off forever!!! Shut it down when you are out on the anchor or mooring ball to save the amp-hours for engine starting or refrigeration.

 

[Bacchus]

You don't mention batty chemistry and it can make a difference in how your question is answered.
With FLA battys are most often designed as start or deep cycle and specs provide a clue which it is. Dual purpose FLA and a compromise and not optimal for either.
I'm guessing you 8V are probably GC golf cart and are good deep cycle. If they are over sized they can provide hi A and be used for starting.
12 V batty run the spectrum so using deep cycle for house is important.
Both Trojan and East Penn have confirmed to me that their AGMs will serve both deep cycle and start applications equally well and they spec both CCA and AH to reflect that.
Didn't want to confuse thi gs but above should be a consideration along with other inputs.
From my reading series connection all load and charging goes through all battys in the string equally, important to balance wiring when adding multi strings.
For parallel connection load and charging can vary batty to batty and important to balance the wiring for optimal batty life and performance.

 

[SteveK]

32 volt bank: 8 volts X 100Ah = 800 watt hours per battery. 800 watt hours X 4 batteries = 3200 watt hours for the entire bank.

Is the above correct. It is IMO if the 4-8v batteries were in parallels, but they are in series

 

[tiltrider1]

Is the above correct. It is IMO if the 4-8v batteries were in parallels, but they are in series

Yes. You have one 32v bank capable of 100 amp hours. V*A=W so 32*100=3200.

 

[SteveK]

Yes. You have one 32v bank capable of 100 amp hours. V*A=W so 32*100=3200.

Thanks. Is it the same if they were parallel for watt hours
My confusion is with 6v house set up series/parallel the Ah is not double when two are in series to make 12v

 

[Barking Sands]

Thanks. Is it the same if they were parallel for watt hours
My confusion is with 6v house set up series/parallel the Ah is not double when two are in series to make 12v

When stacking multiple batteries in any arrangement you can only add/double one parameter (amps or volts). In addition one parameter must be added/doubled.

When doing a series/parallel using 6v batts to eventually make a 12 volt bank:

* you combine two 6 volt batts in series to double the voltage to the desired 12 volts. Since you only get to double one parameter then Ah stays the same. Each grouping of 2 batteries makes a single 12 volt battery bank.

* Combine any number of 12 volt banks (grouping of 2 six volt batts) in parallel . Since we did not double voltage by stacking in this way then Ah will add for every additional 12 volt bank added.

Watt hours remains the same regardless of configuration

 

[danderer]

Thanks. Is it the same if they were parallel for watt hours
My confusion is with 6v house set up series/parallel the Ah is not double when two are in series to make 12v

You're confusing amp-hours with watt-hours. They're not the same thing.

No points off for this mistake. We don't normally talk about watt-hours though they're perfectly valid in this discussion.

 

[SteveK]

Well I learned something today. Thanks

 

[Iggy]

I hope this helps because it does get confusing. For some of us this goes with out saying!


I have a 12V house bank with a total of 570Ah. Using six 6V batteries rated at 190Ah each.

So than three pairs are wired in series. So now I have three sets at 12V and each set is 190Ah. Voltage had doubled and Ah is the same. Now put the three sets in parallel, 3x 190=570Ah

 

[SteveK]

I hope this helps because it does get confusing. For some of us this goes with out saying!


I have a 12V house bank with a total of 570Ah. Using six 6V batteries rated at 190Ah each.

So than three pairs are wired in series. So now I have three sets at 12V and each set is 190Ah. Voltage had doubled and Ah is the same. Now put the three sets in parallel, 3x 190=570Ah

That I get as I have the same except 660 Ah

 

[mvweebles]

I hope this helps because it does get confusing. For some of us this goes with out saying!


I have a 12V house bank with a total of 570Ah. Using six 6V batteries rated at 190Ah each.

So than three pairs are wired in series. So now I have three sets at 12V and each set is 190Ah. Voltage had doubled and Ah is the same. Now put the three sets in parallel, 3x 190=570Ah

In this example, I'd prefer if voltage was specified. "570AH @ 12v".

"Two 6v @ 190AH batteries in series combine to 12v @ 190AH". Same statement, but just easier to follow for those who may be less familiar.

Peter

 

[Lepke]

your 32V bank is 4x 8v batts in series to produce 32 volts in total. that's the only way to get 32V out of 8v batteries. there is no choice its like you have one big 32V batt.

2-12v and 1-8v is another option. I ran it for many years in many boats.

 

[Circumnavigator]

As for the "which is better question", if the watt hours are the same, then the 32V system is better. There's a good reason why inverter setups that run off-grid houses and other large loads run at 48VDC -- the losses in the wires and the inverter are less at the higher voltage. Remember that losses in wires are proportional tot he square of the current -- double the voltage, you halve the current and quarter the loss.






Jim

 

[fgarriso]

Been working on improving my house bank setup and realized something that I've been puzzling about all day.



My dedicated 12v house bank batteries are wired to a 12v inverter in parallel, so the inverter has a lot of amp hours available at 12v.


My stbd 32v engine start bank has four 8v batteries wired in series to a 32v inverter and serves as a backup house bank.



An inverter selector switch determines which inverter supplies AC power to the house at any one time. They can't both be on.



But the 12v inverter sucks 12v from 4 12v batteries in parallel, while the 32v inverter sucks 32v from four 8v batteries that only reach 32v bcs they're wired in series.



Which is "better"? Are there pros and cons?

Volts is Volts and AMPS is AMPS per hour.

Do you know the WATTS per hour you will have as a load?

 

[tiltrider1]

One key difference is that with 32v you can reduce wire size. This becomes important for voltage drop. It is much easier to oversized the wire for 32v than to oversized the wire for 12v. However If you size both runs correctly neither will suffer any voltage drop and then we have no advantage.

 

[SteveK]

One key difference is that with 32v you can reduce wire size. This becomes important for voltage drop. It is much easier to oversized the wire for 32v than to oversized the wire for 12v. However If you size both runs correctly neither will suffer any voltage drop and then we have no advantage.

Yes, let's go with this. No line loss because wires were correctly sized. So if watt hours are also the same, is there a preferred setup.