Puzzeling thru a 12v to 24v solar upgrade

[glennts]

Currently have 400w of 12v panels feeding four 6v US Battery 2200's in series/parallel.The 12V battery output goes to a 1000w inverter dedicated to a single plug output for computers. There is a Blue Sea combiner that flows between the coach battery or back when on shore / generator and the panels are sleeping. And a TM 2025-RV. A simple and effective setup.

Now upgrading to 3 Hanwah Q Peak 325W panels that will feed into a Tracer 4210AN cc that replaces a Rogue cc which died after years of good service. So the questions that arise are (A)to allow the MPPT to down convert the 24v input to 12v and keep everything else as is. Or (B)to switch the batteries to a four 6v series 24v bank. A 24v bank complicates the Blue Sea combiner arraingment and obliges me to either buck the 24v output down to 12v to use the existing 1000W inverter or simply get a 24v / 2000W inverter.

If I lose the charging flexiblity advantage gained by the Blue Sea combiner, would I gain it back by tying a 24v / 2KW inverter into the RV's PD distribution panel and letting the solar panel output find its own way to the coach battery. A further gain from this would be from also having the solar output be available for general AC distribution. If the 24V inverter output is tied into the house distribution panel is there a better way other than manual switching to insure there is no conflict when the AC source becomes generator/shore power? Also, is the Blue Sea combiner which allowed current to flow from the shore power charged house battery to the solar bank now useless? I can see how stepping up the voltage on the solar bank side on the combiner might allow for some use but the combiner relies on voltage monitoring for its switching and that would no doubt be compromised with step conversion. Is there a way around this that would allow for generator / shore power to be available to charge the solar bank?

And, as a secondary issue. If the batteries are to be re-aligned to a 4 s string for a 24V bank. Two of the batteries are 2 yrs older. Is there any consideration to be given as to the order in the series. Older ones in the middle? Older ones at the ends? Alternating? Does it matter? They will be balanced out before re-connecting. When these batteries are past their usefulness in a year or two I'll probably go the re-purposed Tesla car 24V Lipo battery route.

Any input will be appreciated. Thanks.

[BFL13]

It is not June all year, so your 975w might be putting only 30 amps into the 12v battery bank at high noon in February. Now you will be glad you have that third panel.

Just reading about the Battle of the Atlantic where Consolidated made B-24s in Fort Worth as one of the places they were made.

[glennts]

Ok. Thank you all for the input. When the panels arrive I may let you know when I hook them up so you can look in the direction of Ft. Worth and perhaps you get to see one of those ground to cloud lightning bolts.

Go wash your hands.

[BFL13]

glennts wrote:
@BFL13 "You don't get twice as much out of them when they are at 24."

Is the 24v at 40a going to put more into a 24v bank than 12v at 40a will put into a 12v bank? I understand that my usage is a constant but I what understand your comment to mean that there is no practical difference between the two when it comes to charging capacity. Is that correct?

If you try to charge two 100AH batteries as a 12v bank at 40 amps, you can get the same result by wiring them as a 24v bank and charging them at 20 amps. (but you need a "24v" charger)

If you use 40 amps at 24v, you would have the same charging time with four 100AH batts as with two at 12v, and now you would have twice as much you could use.

The controller is a "12/24" so it can do 12-12 or 24-24 or 24-12.

If you do 12-12 or 24-24, the output current will be in the same order as input current. If you do 24-12, output current is almost twice input current.

So if the bank is 12v it will use about twice the current output, but the same bank as a 24 will use the lower current to get to the same amount you can use from the bank.

To get the use of the 40 amps out at 24v you would want to double the size of the battery bank. But you don't need that much for your daily usage---unless you want to start using more with a bigger inverter and MW lots of food and watch longer movies. 🙂

[time2roll]

glennts wrote:
Is the 24v at 40a (960 watts) going to put more into a 24v bank than 12v at 40a (480 watts) will put into a 12v bank? I understand that my usage is a constant but I what understand your comment to mean that there is no practical difference between the two when it comes to charging capacity. Is that correct?

[2oldman]

glennts wrote:
in 15 yrs of being in this forum one of the first things I noticed is that the longest and occasionally heated conversations always included the words "Volts, Amps, Ohms and Watts".

And 'generator.'

[glennts]

@2oldman "...I said you'd be fine at 24v, which I haven't seen is what you're going to do"

It's an evolving conversation with more of the initial comments advising staying with a 12v bank. Subsequent questions have been exploring that option. I'm not tied to any solution and when the smoke clears the obvious solution will hopefully be apparent.

I have to smile because in 15 yrs of being in this forum one of the first things I noticed is that the longest and occasionally heated conversations always included the words "Volts, Amps, Ohms and Watts".

[2oldman]

glennts wrote:
Is the 24v at 40a going to put more into a 24v bank than 12v at 40a will put into a 12v bank?

Yes. Converting to watts will answer that.

[glennts]

@BFL13 "You don't get twice as much out of them when they are at 24."

Is the 24v at 40a going to put more into a 24v bank than 12v at 40a will put into a 12v bank? I understand that my usage is a constant but I what understand your comment to mean that there is no practical difference between the two when it comes to charging capacity. Is that correct?

[time2roll]

Yes as I said earlier the controller will be a bit overdriven. Will be fine although consider a 60 amp controller. Morningstar makes a nice one.

[2oldman]

glennts wrote:
Yes this is true, but doesn't 975w/24v = 40 amps?

Yes, and I said you'd be fine at 24v, which I haven't seen is what you're going to do.

[BFL13]

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[BFL13]

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[BFL13]

glennts wrote:
@2oldman: "I'm not sure why you'd want to buy an controller that won't deliver all the power you're giving it."

I'm putting 975w into a controller that is rated for 1040w.... seems to me at 40a in and 40a out it's going to deliver all the power I'm giving it... or am I missing something?

Rated output power is 40 amps x 13v (battery volts) = 520W

The controller can still do 40 amps with a 24v battery bank, so now 40a x 26v = 1040w.

Input watts at 95% efficiency to do that 520w would be 547w. So you are "over-paneled" by about 400w. (the 975 is really 878w after the usual 10% for heat loss)

Morningstar likes a bit of over-paneling to get more daily AH haul by getting more during the shoulder hours. But not that much!

You could use a higher amp rated controller if you have the daily AH need, or else just use two of those 325W panels.

Now you are going to ask about 24v battery again. You don't get any more you can use if you have two batts as 12 or 24. Your daily usage is whatever, so if the two batts can do that much, you are good. You don't get twice as much out of them when they are at 24.

See my earlier post asking what your plan is and some choices you have.

[glennts]

@ 2oldman: "975w/13v = 75 amps"

Yes this is true, but doesn't 975w/24v = 40 amps?

Is your point that if it takes in 24v at 40a and that is then converted to a 12v output then it should rightly be 12v at 75a and not 12v at 40a and the 35a are lost/wasted? If that is the persuasive case then this argument favors a 24v battery bank.

There is enough roof space for 3 panels. By maximizing the power output what is over production at high noon will hopefully be offset by having increased production in the off hours. Flattening the curve so to speak. At $200/panel cost is not much of a factor vs. optimizing the setup.