Can charge my battery bank with 24v and use with 12v old inverter?

[505 Tech]

Edit = deleted my diagram because batteries are not connected in series. I will reupload a new correct diagram.
Hey Guys, I am new here.
I know it may be a dumb question and 24 volt system is better than a 12v system to reduce wire size and current draw.
But I have a 60amp MPPT charge controller which support 720watt solar input with 12v system, 1440watt solar input with 24v system. So I will charge my battery 24v battery bank with 24v solar system. And I plan to use it with my old 12v 2000watt pure sinewave inverter as shown in the figure.
Is it possible or what will happen if not?

 

[pollenface]

Current is not an issue if the wire is big enough.

You can't really wire a 24v charging system with a 12v output without creating a short, it either has to be 12v or 24v, not both.

Toss up the price between an additional SCC for 12v if you require the extra solar power, or the price of a new 24v inverter.

My 12v system consists of 385ah of lead-acid, 1kw of pv split between two SCCs (660w output) and a 2000w inverter.

 

[KnobCountry]

Look at your graph again. Your charge controller is putting 24v into the inverter terminals and 24v into each individual battery.

Additionally the batteries are not in 24v series. The positive is not connected to the other negative . Nothing in your graph is actually 24v except the CC.

If the inverter tapped into a single battery it will work as long as they were actually wired in series.

The batteries will become unbalanced because you were only tapping one at a time.

 

[Mattb4]

Many SCC will automatically select charging voltage based on battery voltage. Your have your batteries wired in parallel so they are 12vDC. Depending on the panels specs and hookup will give you total Voc that the SCC must be able to handle. For instance if the SCC has a Voc of 60vDC than your panels can not have a greater than 60Voc after being wired together. It should be less that that if your location gets cold. Since panel voltage is much higher than 12vDC your PV wiring is calculated by the panels Vmp and current at Imp.

The amperage of the SCC is the charging current. If your panels wattage adds up to more than the amperage times the voltage of the SCC it means that your SCC is over paneled. Since panels do not push power, loads draw it, this means that you will not draw more than the SCC's rated charge current.

 

[sun walker]

I'm planning on doing something similar, off grid 48v (4 x 4 12v batt in series) to charge from mppt's, (6mm wire to pv's) with a 48v inverter to run the heat pump & washing machine located next to the inverter/ batt/ mppt's & super capacitor banks (which minimizes the high Amp wiring), but then drawing only 12v for my home which is already internally wired for a 25 year old pv 12v system.

So drawing 12v from each separate batt, by using a relay/timer system, eg drawing 12v from only 1 batt at a time, probably on a 24hr cycle, which would switch from 1 batt to the next in the wee hr's (4am), as there would be a few seconds of off time for the 12v line to avoid blowing fuses, which should more or less address the equalization issue.
Plus a high A diode to prevent the capacitors from feeding back into the batt's (which are tiny as they are mainly there for night time leds), (the batt's are protected by a current limiter). The caps are mainly for the inrush of the heat pump & washing machine. The heat pump is tiny & designed to use surplus power produced during the day, use it or lose it, so its automatically on once the batts are fully charged.
Doing the maths 6mm wire tied to 3=4 430w pv's was the most economical, & left plenty of room for error.
Other solutions could be a buck converter or step-down converter, but that wastes some energy, & may not last as long as a relay.
Pv's are up so just now starting the process of installing the mppt's etc.
But not an expert, so welcome constructive criticism.

 

[Mattb4]

@sun walker it is better to run a 48v to 12v step down than to try and draw 12v from a 48v (4-12v in series) battery by selectively cycling one battery for 12v duty.

 

[robbob2112]

It is always better to run a single battery of the right voltage verse stringing them in series.

I.e. pick a voltage and do everything in that voltage.

@505 Tech - what type SCC do you have PWM or MPPT? The picture you posted is of a PWM. Also what are the specs of your panels? Post a picture of the label from the back. "12v" panels will have a Voc of 18v to 20v.

If either of you insist on stringing batteries together in series and running off 12v one at a time get an active balancer/equalizer of 10amps. This attaches to each battery and keeps them in balance. Otherwise you will get out of balance and a battery will shutdown preventing use or charging of the string. This is not a problem in parallel strings.

 

[mikefitz]

But not an expert, so welcome constructive criticism.

Perhaps starting a new topic, rather than confusing any response to the OP.
Having a series of 12v batteries for a 48 volt system is doomed to fail unless battery balancers are fitted to ensure all batteries are charged fully. Attempting to load any in turn, to as a 12v feed, will unbalance the pack, perhaps beyond the caperbility of the balancer.
Also there is a huge danger of having a SC between the negative of the 48 volt pack and the negative of the selected 12v battery.
Either set up a solar systen for the 12v setup with appropate battery storage , or use DC to DC converters

 

[505 Tech]

It is always better to run a single battery of the right voltage verse stringing them in series.

I.e. pick a voltage and do everything in that voltage.

@505 Tech - what type SCC do you have PWM or MPPT? The picture you posted is of a PWM. Also what are the specs of your panels? Post a picture of the label from the back. "12v" panels will have a Voc of 18v to 20v.

If either of you insist on stringing batteries together in series and running off 12v one at a time get an active balancer/equalizer of 10amps. This attaches to each battery and keeps them in balance. Otherwise you will get out of balance and a battery will shutdown preventing use or charging of the string. This is not a problem in parallel strings.

I am currently using an MPPT 60A controller with one 41V ~13amp (575watt) panel and 12v 2kw inverter. Since my MPPT is 60amp, I cannot add another solar panel with 12v system. I can add another panel only if i add another battery and make it 24v system (MPPT can charge 1440W@24v).
I am just curious if I can use the old 12v inverter with 24v battery bank (2*12v batttery) and 24v solar mppt charging system.

 

[KnobCountry]

Yes but it's not ideal to say the least due to individual series batteries becoming unbalanced.

 

[robbob2112]

You can add another MPPT with another panel and connect it to the same battery as long as you don't exceed the max charge rate of the battery.

 

[mikefitz]

60A controller with one 41V ~13amp (575watt) panel and 12v 2kw inverter. Since my MPPT is 60amp, I cannot add another solar panel with 12v system. I

Yes you can, a 575 watt panel will produce under ideal conditions via a MPPT, just over 40 amps. Add a another panel and get the full 60 amps. In theory you will lose out around midday, but overall a big Improvement in solar yield . Overpaneling is a valid concept.
Don't mess about with running a 12 inverter with two 12v batteries in series . The batteries won't charge correctly and you will most likely accidently create a SC