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A little frustrated after upgrading to 24 volts Growatt 3000

oshky

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Apr 29, 2020
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Hello,

I was at 12 volts LifePo4 battery @ 200Ah. A week ago I upgraded to a 24 volts system, I wired two 12v LifePo4 for a 24 volts series battery bank and a Growatt 3000 inverter. Last night after a blackout my battery bank lasted the same time as when I was @ 12 volts, same load. I wished for a longer battery power, but it's not. I know that in series voltage add and Ah remains the same. If my battery bank is the same capacity, what is my gain after upgrading to 24 volts? Thanks for your input.
 
All else being equal, 24V will give you a very slight advantage in that it tends to be *slightly more efficient because the lower current tends to have lower wire losses. However, the difference is small and the difference is not why one chooses 24V. The primary reason to choose 24V over 12 V is that the DC current is lower and that allows for the use of smaller wires, fuses etc. This benefit gets progressively more important as the wattage of the system increases. A 3000W 12V inverter requires designing for a *very* high current and is far less forgiving of voltage drops and slightly resistive connections. However, a 3000W 24V system cuts the current in half and is easier to build.

As you have experienced, if a system is already built and working with 12V, all of the problems with the high current have already been experienced, and changing it to 24V would not give many benefits.
 
The watt hours of your battery bank hasn't changed.
So, you won't get any more power than you did before.
The new configuration has twice the voltage, but half of the amp hours.
 
I agree with FilterGuy as long as what you are saying is you originally had 2 batteries in parallel at 12v and then you re-arranged your battery bank with same 2 batteries into 24v. This is what it sounds like you are saying if you say the bank has "same capacity" but you don't specify same capacity in Amp-hours or same capacity in watt-hours. If you just rearranged the two batts technically the amp-hour capacity was cut in half when you go from 12v to 24v but the watt-hour capacity is unchanged and thus the ability to do work over time is essentially unchanged. If you didn't add batteries you didn't add watt-hours so it would be surprising that you expected a magical increase in available watt-hours to do work.
So are you really saying that you had 200Ah at 12v and added additional batteries to get "same capacity" 200Ah at 24v? If so, you doubled the watt-hours and all other variable the same you should have approximately doubled your run time. If this is the case there is a problem.
 
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The watt hours of your battery bank hasn't changed.
So, you won't get any more power than you did before.
The new configuration has twice the voltage, but half of the amp hours.
More accurate to say he won't get any more "energy" than he did before as power is an instantaneous measurement. Depending on where any limitation was in his earlier system he could possibly have increased max power by being able to get more power (watts) at same current due to twice the voltage but that is not what this is about. His issue is teh amount of stored energy capacity.
 
More accurate to say he won't get any more "energy" than he did before as power is an instantaneous measurement. Depending on where any limitation was in his earlier system he could possibly have increased max power by being able to get more power (watts) at same current due to twice the voltage but that is not what this is about. His issue is teh amount of stored energy capacity.
I didn't choose the word. I just reused it in the answer. Wasn't trying to confuse them.
 
How are you charging the battery when you were 12v? A 12v SCC at 30a will be able to charge the battery half as fast as a 24v 30a SCC as they can handle higher PV watts.

Seeing you have a growatt, your PV input maybe higher than your previous SCC, so if you have more load during daylight hours you’ll be able to capture more KWHr over a given day and still end up with a fully charge battery at the end of the day.
 
You didn't increase the size of the fuel tank.

You need more batteries.

With the doubling of voltage, your charge controller can now handle twice as many panels as it did before.
 
With the doubling of voltage, your charge controller can now handle twice as many panels as it did before.
Good point!!! I should have mentioned that before. The current rating drives the cost of SCCs more than the voltage rating. In general the cost/watt of the charge controller will be lower for 24V systems.
 
You didn't increase the size of the fuel tank.

You need more batteries.

With the doubling of voltage, your charge controller can now handle twice as many panels as it did before.
Definitely, I’ll have to increase the size of my battery bank. I went with just two in series 12 volts batteries to make it 24 volts, but just with a 200Ah capacity. Thanks for your advice.
 
Thanks everyone for your valuable insights for this matter. I’ll try to upgrade my battery bank -which I did when going from 12 to 24 volts- and also more panels will hopefully help.
 
I was considering going back to my previous 12 volts system and install the two batteries in parallel so I can have 400Ah (2,560 watts x 2 = 5,120 Kw. Not sure what to do…still considering my options.
 
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I was considering going back to my previous 12 volts system and install the two batteries in parallel so I can have 400Ah (2,560 watts x 2 = 5,120 Kw. Not sure what to do…still considering my options.
I think at this point, unless you are going to add more batteries, that you should probably just leave it. If there was no benefit to moving up, then there would also not be one in going back.
 
I was considering going back to my previous 12 volts system and install the two batteries in parallel so I can have 400Ah (2,560 watts x 2 = 5,120 Kw. Not sure what to do…still considering my options.

I think you're not understanding that you're not gaining more stored energy by simply changing the voltage.

2 12 volt 100ah batteries in parallel is 200ah @ 12v=2400 watt hours.

2 12v 100 amp hour batteries in series is 100ah @ 24v = 2400 watt hours.
 
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Also, when going from 2 12V batteries in parallel to 2 12V batteries in series, the need for keeping the two 12V battery cells balanced rears it’s ugly head…
 
Also, when going from 2 12V batteries in parallel to 2 12V batteries in series, the need for keeping the two 12V battery cells balanced rears it’s ugly head…
Yup
That's just adding maintenance to a maintenance free situation.
 
Also, when going from 2 12V batteries in parallel to 2 12V batteries in series, the need for keeping the two 12V battery cells balanced rears it’s ugly head…

Thought they got more out of balance in parallel......

Op also said he was using lithium
 
Thought they got more out of balance in parallel......

Op also said he was using lithium
Lead-acid or lithium doesn’t change anything.

Batteries or cells in parallel self-balance.

Batteries or cells in series slowly stray out of balance (which is why a BMS typically includes at least a passive balance function).

If you put two 8S LiFePO4 batteries in series, each with their own BMS, the BMSes will keep the 8 cells of each 12V battery balanced within the pack, but they won’t do anything to keep the two packs in balance with each other…
 
No, he said lead-acid, but that doesn’t change anything.

Batteries or cells on parallel self-balance.

Batteries or cells in series slowly stray out of balance (which is why a BMS typically includes at least a passive balance function).
He didn't say lead acid, he said this

"I wired two 12v LifePo4 for a 24 volts series battery bank and a Growatt 3000 inverter."


Weird. The moderators over on solar panel talk say the opposite.

Why don't normal 12v batteries or 24v cat batteries have the out of balance issue among cells?

I also thought that's why you were supposed to use 2 6v golf cart batteries on your rvs instead of two 12v?

I don't know anymore....I have 3 8d 12v batteries parallel in my system and they have been thus far.
 
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