Please Help ! Connection 12v Inverter to 24v system ?

[myselfsbs1]

Dear all,

Hello...I am new to forum and in need of urgent help of all you veterans.

Here is my problem...

I've 24v, 250w (2 in number) panel , which is charging 2 100AH batteries, 12v connected in series, via a 24v, 20amp...solar charge controller (PWM).
So far so good..

Now, the inverter that I have is 12v regular inverter (800va)

I need to connect this to 24v system.

I can directly connect this inverter to one of the batteries...and system runs fine...! However my concerns -

1.) Connecting inverter to one of two batteries...will affect the balance of batteries....! I know it's not recommended but can I do that for few weeks ?
2.) What is better way of connecting, if any ?
3) do I need to buy a new 24v inverter or can I continue using this system for long term ?

Any ideas /suggestions will help !

Thanks a lot !

[inetdog]

Connecting to just one of the 12V batteries will quickly unbalance the series string and destroy your battery bank. All of the charging current needed for the battery which has fed the inverter will have to be forced through the still fully charged top battery. Not good.

And getting a high power 24V to 12V converter will cost as much as or more than a proper 24V inverter.

One of the advantages of the 24V bank and 24V inverter is that you can get the power you need at half the current, making the wiring much easier and safer.

[myselfsbs1]

Thank you ....any creative fix ?

Connecting to just one of the 12V batteries will quickly unbalance the series string and destroy your battery bank. All of the charging current needed for the battery which has fed the inverter will have to be forced through the still fully charged top battery. Not good.

And getting a high power 24V to 12V converter will cost as much as or more than a proper 24V inverter.

One of the advantages of the 24V bank and 24V inverter is that you can get the power you need at half the current, making the wiring much easier and safer.

Thanks a lot for replying inetdog !

So, now I can understand better...why this connection is not good.

But can anyone think of some creative fix that won't cost me bucks ? Some alternative fix ? Thanks ...

[Wy_White_Wolf]

Thanks a lot for replying inetdog !

So, now I can understand better...why this connection is not good.

But can anyone think of some creative fix that won't cost me bucks ? Some alternative fix ? Thanks ...

It'll unbalance the batteries. One battery will remain at full charge voltage 12.8 while the other will drop. Let's say you drop it down to 12.4V. Now your string voltage is 25.2V. The charge controller sees that it needs charged. It (the charging process) assumes both batteries are of the same voltage. That would be 12.6 V. so it's trying to overcharge one battery while the discharged will never achieve full charge. The more you use the system the worse the imbalance becomes.

You really have only 2 options.
1. Get a 24V inverter
2. Get an MPPT charge controller and reconfigure into a 12V battery bank.

WWW

[Sunking]

Not going to happen. You need a 24 volt Inverter.

Imagine you have to carry a 100 pound load anytime you are awake. But you can only use your right hand to carry it held on your right side. By the end of the first day, your back is severely injured and you will never walk again.

[myselfsbs1]

It'll unbalance the batteries. One battery will remain at full charge voltage 12.8 while the other will drop. Let's say you drop it down to 12.4V. Now your string voltage is 25.2V. The charge controller sees that it needs charged. It (the charging process) assumes both batteries are of the same voltage. That would be 12.6 V. so it's trying to overcharge one battery while the discharged will never achieve full charge. The more you use the system the worse the imbalance becomes.

You really have only 2 options.
1. Get a 24V inverter
2. Get an MPPT charge controller and reconfigure into a 12V battery bank.

WWW

Thank you WWW and Sunking for your replies...

Just one more doubt, if two batteries are connected in series - won't the higher charged battery also not try to charge the lower charged battery ? Thus, loosing some of it's charge and coming to lower voltage ? This would go on, all night till they arrive at balance ..no ?

Thanks...

[Sunking]

Thank you WWW and Sunking for your replies...

Just one more doubt, if two batteries are connected in series - won't the higher charged battery also not try to charge the lower charged battery ? Thus, loosing some of it's charge and coming to lower voltage ? This would go on, all night till they arrive at balance ..no ?

Nope does not work that way. True if in parallel, but not series.

In a series circuit the current is equal in all components. Current in Battery 1 = current in Battery 2 when charging or discharging. Or put another way I1 = I2 = I3..... Now you come along and tap just one battery and upset the balance. Say you drain 50% of the capacity out of one battery. When you go to recharge, you over charge the crap out of the full battery, and never fully charge the low battery. It destroys both batteries. The over charged battery dies from corrosion, and the other from sulfation.

[lkruper]

Thank you WWW and Sunking for your replies...

Just one more doubt, if two batteries are connected in series - won't the higher charged battery also not try to charge the lower charged battery ? Thus, loosing some of it's charge and coming to lower voltage ? This would go on, all night till they arrive at balance ..no ?

Thanks...

Look at this link for two batteries in series with two 12v chargers (Two Batteries in Series, Two Chargers ) -> http://www.batterytender.com/Connecting-Chargers/

The reason this can be beneficial is that it is possible for the batteries in series to become unbalanced. This set up would not be an advantage if batteries equalized themselves.

[SunEagle]

One other comment.

You mentioned having 2 x 250watt 24v panels and a 20amp PWM CC.

You will need to wire those panels in "series" to the charge controller.

Wiring them in parallel will not provide enough voltage to charge a 24v battery system.

[Raul]

Check if your Controler works for 12v as well . If it does a temporary fix till you get your 24v inverter is posible . Most controllers are 12-24v not fixed voltage.
If the Controler can charge at 12v then run the panels in paralel to the Controler and paralel the batteries , then you can use the inverter of that 12v bank.

[ButchDeal]

Check if your Controler works for 12v as well . If it does a temporary fix till you get your 24v inverter is posible . Most controllers are 12-24v not fixed voltage.

make sure it has the capacity to handle 500W at 12V output, it likely is cut in half at lower voltage.

[Raul]

make sure it has the capacity to handle 500W at 12V output, it likely is cut in half at lower voltage.

He's got PWM 20A so it will only receive the max imp of each panel , the panels will not be able to exceed 16a output.

[jflorey2]

Just one more doubt, if two batteries are connected in series - won't the higher charged battery also not try to charge the lower charged battery ?

Not without a charge transfer battery balancing system. (And no, they're not cheap.)

Your choices are:
Get a 24V inverter
Rewire for 12V
Get a second battery (12V) for the inverter and a 24V to 12V buck converter (not recommended)
Connect to the top and bottom batteries alternatively so that equal power is drawn from each (even less recommended and nearly impossible to do right, plus hard on the inverter)

[Sunking]

I've 24v, 250w (2 in number) panel , which is charging 2 100AH batteries, 12v connected in series, via a 24v, 20amp...solar charge controller (PWM).
So far so good..

Maybe not so good.

What is the Vmp of your panels. Unless it is at least 36 volts or higher, there is no configuration you can use the panels on a 24 volt battery system with a PWM controller. You made a huge mistake buying a PWM controller.

Even if the panels are 36 volts wired in parallel (only possible way to configure them). You just turned your 500 watts of panels into 330 watts. If you wired them in series 115 watts.

[myselfsbs1]

Check if your Controler works for 12v as well . If it does a temporary fix till you get your 24v inverter is posible . Most controllers are 12-24v not fixed voltage.
If the Controler can charge at 12v then run the panels in paralel to the Controler and paralel the batteries , then you can use the inverter of that 12v bank.

Thank you all for responding so promptly and aptly. It's helping me.

I can't do above as my panels are 24v and charger is fixed at 24v too !

One idea that I was reading somewhere was to use a MPPT charge controller ? Can MPPT controller charge 12v batteries in parallel with 24v panel ?
So, if I buy a MPPT 24v, 20 amp charge controller and then connect my batteries in parallel (to make it 12v) and then connect inverter to batteries...
Does that appear to be a quick workaround ?

thank you