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12 Volt Inverter with 24 Volt Charger


Paul.Chari
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Already have inverter with only 12volt mode.  Only found out later charge controller at 12 volts caps at 500watt.  At 24 Volt charge controller can give 1000watt max with only four panels.  This means running on sun fully more appliances during the day.

24v inverter is next alternative but budget does not allow.  Planning on expanding battery bank first as back up duration is more important for work.

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9 minutes ago, Paul.Chari said:

Already have inverter with only 12volt mode.  Only found out later charge controller at 12 volts caps at 500watt.  At 24 Volt charge controller can give 1000watt max with only four panels.  This means running on sun fully more appliances during the day.

24v inverter is next alternative but budget does not allow.  Planning on expanding battery bank first as back up duration is more important for work.

Something is just telling me this is not going to work,how much amps is the inverter sucking from the batteries with load? because what I was thinking if you can get an decent 24v to 12v DC converter then you can install it on the 24v battery bank and then it converts to 12v that will go to your inverter,I have never seen an installation like this one,why not try to find an second hand 24v inverter (Maybe have one) if your budget allows it.

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The most the inverter has pulled 27 amps when I checked.  It should however be able to pull 80 amps nominal with tolerance over that for 20 seconds (not that I'd risk finding out).  27.5 amps makes sense considering 300watts is about the current load.  I want to add a fridge now.

How much is a second hand inverter these days (that you might have ;-)

 

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5 minutes ago, Paul.Chari said:

The most the inverter has pulled 27 amps when I checked.  It should however be able to pull 80 amps nominal with tolerance over that for 20 seconds (not that I'd risk finding out).  27.5 amps makes sense considering 300watts is about the current load.  I want to add a fridge now.

How much is a second hand inverter these days (that you might have ;-)

 

Will send you an PM

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4 hours ago, Paul.Chari said:

I would like to find if the configuration in my image attached is safe and if anyone has tried it before.

It is not safe and you will convert your charger to smoke, unless it is auto voltage sensing in which case it will settle at 12v. Your inverter and charger are effectively connected to the same terminals which cant be 12v and 24v at the same time.

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4 hours ago, Paul.Chari said:

Already have inverter with only 12volt mode.  Only found out later charge controller at 12 volts caps at 500watt.  At 24 Volt charge controller can give 1000watt max with only four panels.  This means running on sun fully more appliances during the day.

24v inverter is next alternative but budget does not allow.  Planning on expanding battery bank first as back up duration is more important for work.

Hmm - this looks like TTT territory (aka @The Terrible Triplett). TTT was asking why his SCC was only delivering 200W. I looked at the spec sheet and noticed that it delivered 200W at 12V and 400W at 24V. TTT made the change forgetting he had a 12V inverter and the rest is forum history.

If you look at your drawing you have both series and parallel connections. One can have series and parallel connections but not the way you have suggested.  Your parallel connections introduce a short circuit in what is otherwise a series connection. You are asking certain battery terminals to be different by 12V and the same voltage all at the same time.

Here is a illustration of both parallel and series connections but this does not apply to your predicament. 

http://batteryuniversity.com/index.php/learn/article/serial_and_parallel_battery_configurations

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As far as I can see I agree with Plokster.

According to the drawing your  batteries  have a short circuit and you will likely to have fireworks if you connect the batteries in this way.

Some would say you can have the  battery configeration as I have in my drawing.

Caution: It looks ok however the imbalance in use would cause the unutalised batteries to overcharge and the batteries in use to undercharge in time and will damage the unutilised batteries first and you will not be able to utilise the undercharged batteries properly.:(

 

So I would take Ploksters advice.

2017-12-29-0002.jpg

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Well yes, you could connect the inverter to just half the batteries and it will work, but you're going to overcharge the battery that is not in use. I've done this before to balance a 24v bank, using an old automotive headlamp. If you place the lamp across the one battery, and your charger takes the pair up to absorption voltage, typically 28.8V, then you may well find that one battery sits at 15.5V and the other one at 13.3V. In my case that's what I wanted, the one battery was low and I wanted to push it high to get them back in balance. In this case it's going to shorten the life of all your batteries.

If the load is really small, and you swap the battery over every other day so each one gets the same punishment over time, you might be able to get away with it.

But overall, I'd say rather use it as an excuse to buy a 24V inverter, or get another charger.

Edit: To comment on the two alternative (2x2 or 1x3), the 1x3 option above is by far the worst option. Think of it in terms of impedance. All the current has to go through the battery on the right, after which it has 4 paths to take next (via the inverter, or one of the three batteries). Your battery on the right will therefore be severely overcharged while the 3 batteries on the left takes whatever current remains, unequally divided between them because they have slightly different internal resistances too, which means that all three of them will be poorly charged, with the weakest one probably getting no charge at all.

It would in fact make more sense to reverse that option, put the inverter over a single battery, with three batteries on the other end, just for better current distribution. It would make more sense... but it would still be a bad idea.

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On 29/12/2017 at 8:49 PM, Chris Hobson said:

Hmm - this looks like TTT territory (aka @The Terrible Triplett). TTT was asking why his SCC was only delivering 200W. I looked at the spec sheet and noticed that it delivered 200W at 12V and 400W at 24V. TTT made the change forgetting he had a 12V inverter and the rest is forum history.

If you look at your drawing you have both series and parallel connections. One can have series and parallel connections but not the way you have suggested.  Your parallel connections introduce a short circuit in what is otherwise a series connection. You are asking certain battery terminals to be different by 12V and the same voltage all at the same time.

Here is a illustration of both parallel and series connections but this does not apply to your predicament. 

http://batteryuniversity.com/index.php/learn/article/serial_and_parallel_battery_configurations

Thank you. Looking into 24v inverter as per all the advice.

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  • 2 weeks later...
On 12/30/2017 at 12:06 PM, pilotfish said:

The only solution is to get a 24v inverter or a 12v charger, all these other "almost solution" are going to trash something - it would be nuts to damage 4 batteries trying this workaround.

Amen Brother. (Ja, this is religious ground for me.)

As I have been there, done that ... with spare to go around.

The 12v charger, no no no no. Go for a 24v one if the 24v inverter does not have a charger. Like mine, no charger, so never have I use Eskom to charge me batts for this exact reason - not interested in having more wires nor wanting to touch anything. It works! Don't touch! ... my latest motto.

Do not mix and match. The smoke, she will escape.
Takes one split second of not focusing (or like the Victron Phoenix, +-10 seconds. :D

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