Charging 24 volt system with a 12 volt charger-

rickeolis · March 2008

Let's say I have two 12 volt batteries in series running my 24 volt inverter. Could I use a 12 volt battery charger applied to the correct posts on ONE of those batteries to successfully charge both batteries?

mike95490 · March 2008

Re: Charging 24 volt system with a 12 volt charger-

rickeolis wrote: »

Let's say I have two 12 volt batteries in series running my 24 volt inverter. Could I use a 12 volt battery charger applied to the correct posts on ONE of those batteries to successfully charge both batteries?

In theory, if its a deep cycle capable charger (15V vs 14V), it could work, if there are no loads on the system. To insure against reverse charging the other battery, by a load running, you should disconnect the load, till all charging is done.

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

I know that the charged battery(s) will have more amperage than the uncharged one, but will the flow of power simply go towards the lesser charged battery?
I am on a 'time of use' measured system and am thinking about setting a timer to run a small charger during the off-peak times in that manner. Basically, at night when the sun is not feeding the solar array.
(I know my elect. provider would have a cow if they found out)
I've looked around and can't seem to find a 24 volt battery charger anywhere.

crewzer · March 2008

Re: Charging 24 volt system with a 12 volt charger-

Links to basic 24 V chargers with optional "IQ" smart controller:

http://www.iotaengineering.com/24vdc.htm
http://www.iotaengineering.com/iq.htm
http://store.solar-electric.com/bach1.html

HTH,
Jim / crewzer

mike95490 · March 2008

Re: Charging 24 volt system with a 12 volt charger-

rickeolis wrote: »

I know that the charged battery(s) will have more amperage than the uncharged one, but will the flow of power simply go towards the lesser charged battery?

No. What will happen, is that the more charged battery, will, if you have a load on it, will eventually reverse charge the weaker battery. So you have to disconnect load, charge battery A, switch leads, and charge battery B. Or get a 24V charger.

Are you using deep cycle batteries, or car starter batteries ?

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

Mike, I see what you mean. I drew a little diagram of what I am looking at doing, and the weaker battery won't get the higher charge, it will try to pass through the inverter and reverse charge the weaker battery. Not good!
I guess I can look into a 24 volt charger, thanks guys!

-Rick-

crewzer · March 2008

Re: Charging 24 volt system with a 12 volt charger-

I am on a 'time of use' measured system and am thinking about setting a timer to run a small charger during the off-peak times in that manner. Basically, at night when the sun is not feeding the solar array.

Rick,

Doh!!

You can do this with your SW4024 and not buy/connect any additional equipment. From page 69 of the SW manual:

INVERTER/CHARGER MODE

IN BRIEF

The SW Series Inverter/Charger is capable of automatically transferring AC loads from the inverter to a utility grid or generator. Once transferred, the inverter can recharge the battery. The inverter/charger can transfer upon the availability of AC power (FLT mode), either at a specific time each day (using the GRID USAGE TIMER (18 ) menu heading), or upon a low battery condition (LBX mode)

So, just go into your SW, and set it up to connect to the grid for a few hours at night to run your AC loads and charge your batteries. Voila! :cool:

HTH,
Jim / crewzer

niel · March 2008

Re: Charging 24 volt system with a 12 volt charger-

"weaker battery won't get the higher charge"
actually if you only charge 1 of the 12v batteries the other receives nothing unless the charger wires are taken off of the charged battery to be placed on the other battery yet needing a charge. there are difficulties in doing this and though it can be done there is a larger margin of errors that can occur to ruin the batteries and could be considered the ultimate in unequalized batteries. you were advised correctly on getting a proper 24v charger.

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

Hi Jim,
I actually tried that method out a couple of months ago and it went OK for about 5 days and then the 4024 turned itself off due to low battery voltage. Apparently I use too much power during the day to make use of that method. It should have run the battery charger automatically when the batteries got low but it didn't. I have gone back to the default mode and things are OK again for now.
Niel, you're right, I was hoping I could use something I already had, but I guess not! Thanks-

-Rick-

mike95490 · March 2008

Re: Charging 24 volt system with a 12 volt charger-

Why not say exactly what you are powering, what are you trying to do ?

I know it's some sort of load shift, to offload an appliance at peak hours, and recharge the battery at night.

Whats the power draw of the device , and for how many hours ?

It's easier to be helpful with all the info at hand.

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

Thanks Mike,
It's pretty simple actually, I have 24 Trojan T-105's that supply my SW4024, which then feeds about 20 small appliances in the home: Computers, TV, lights, and a game console.
I have a nice 12 volt car battery charger that works very well for my RV and I was considering using it to top off the solar battery system when in off-peak hours.

-Rick-

crewzer · March 2008

Re: Charging 24 volt system with a 12 volt charger-

I actually tried that method out a couple of months ago and it went OK for about 5 days and then the 4024 turned itself off due to low battery voltage. Apparently I use too much power during the day to make use of that method. It should have run the battery charger automatically when the batteries got low but it didn't. I have gone back to the default mode and things are OK again for now.

Rick,

This doesn’t quite make sense to me.

The 4024 has a built in charger rated at 120 ADC; that’s plenty (almost 9%) for your 24 V x 1,350 Ah battery bank.

My OutBack 2524 also has a “Grid Use” mode that can switch downstream AC loads from the batteries and inverter to the grid. But, the battery charger won’t work if the charger isn’t set to “AUTO”, and it won’t deliver much charging current if the AC input current setting is too low. Also, the 2524’s “Low Battery Cutoff” will transfer the AC loads to the grid and engage the charger if the battery voltage falls too low, irrespective of the “Grid Use” time-of day settings.

I suspect your 4024 has similar features and settings. It’s possible that you may need to review the 4024 settings menu and doodle with ‘em a bit. These features are included in your 4024 for exactly your proposed application.

HTH,
Jim / crewzer

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

Hi Jim,
I agree with you on that. A few weeks after the failed attempt I reset the inverter back to factory specs and tried it again using the GRID USAGE TIMER mode, and again after about 5 days there was less than 24 volts in the battery bank. Why the low battery cutoff didn't kick in then is anyone's guess, but it works OK now.
The way the SW4024 works by default, it simply charges to a float level all the time regardless of use, so for now that works for me.

crewzer · March 2008

Re: Charging 24 volt system with a 12 volt charger-

Hmmm...

Brock · March 2008

Re: Charging 24 volt system with a 12 volt charger-

The first thing that came to my mind was just get a second matching charger and run them at the same time with one on each side of the 12v. On a bank that size unless it's a beefy charger like 40+ amps it will likely not charge up over night during the cheap rates.

I used to have stacked SW2512's and did exactly what your talking about using the grid timer and it worked fine. Although with my solar input and much lower loads I rarely had the battery bank get below 80% full. It sounds like you have enough loads to run the batteries down when power is expensive.

I can tell you after a while (with the help of everyone here) I realized that it was really costing me more to cycle the batteries daily then it was to just buy the more expensive power during the day. The cost of replacing the batteries WAY offsets the $ saved by load shaving.

You could also add more solar panels to offset the daytime loads.

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

Brock- Thanks, I hear you. I have ordered a new set of panels since our tax refund came in. To me that's an investment.
I'll try again soon to setup the on-peak\off-peak method, but for now, I just need to get more power out of the solar\wind system.

-Rick-

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

WOW, I had to question why the charger wasn't holding a float level in this instance, so I looked into things on my solar project: I actually found the problem. I had two batteries that weren't taking a charge. All the other T-105's were showing 6+ volts and I found these two at about 3 volts.
I removed them from the system, and will try again soon to run off-peak.
Had it not been for this conversation, I probably would not have looked into the state of things as well.
I appreciate you guys for all of your help these months since getting this project up and running!!!

-Rick-

mike95490 · March 2008

Re: Charging 24 volt system with a 12 volt charger-

rickeolis wrote: »

I had two batteries that weren't taking a charge. All the other T-105's were showing 6+ volts and I found these two at about 3 volts.
-Rick-

Were they drinking water ?

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

No, but I checked several of them to see if they were.
These two batteries have since charged up when I took them to a work bench and used a fancy car charger that determines condition and load ability.
I'll put them back into the mix again soon, but keep my eyes on them.
Now my whole system is charging better and giving me the readings that I had when I first started this project, which was a good find for me.
Thanks again everyone!

-Rick-

mike95490 · March 2008

Re: Charging 24 volt system with a 12 volt charger-

have you ever run an equalization charge from your controller ??

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

Not from my controller. The SW4024 is supposed to do that on a monthly basis.

mike95490 · March 2008

Re: Charging 24 volt system with a 12 volt charger-

rickeolis wrote: »

supposed to do that on a monthly basis.

Supposed to, but does it ??

rickeolis · March 2008

Re: Charging 24 volt system with a 12 volt charger-

I'm with you Mike,
If I don't see it actually running an equalize charge, how do I know it has???
I run a manual one about every other month, from the options in the inverter.
That's why a good software tracking program would be nice for this system...

-Rick-

CharlesHenrie · September 2016

Re; Charging a 24 volt serial battery with 12 volts. - I happen to have the solution.

Buy yourself TWO Solar controllers...each can control the charge on ONE 12 volt battery.
Basically, you hook up the red terminals from BOTH Solar controllers to the ONE 12 volt source of your choice (Most can handle up to 7 Amps) Even a car battery.
Same with the negative terminals....you now have FOUR (Two red and two black) charging terminals coming out of these two Solar controllers...for the two 12 volt batteries connected in serial.
The one-way diodes built into the individual controllers should protect everything just fine, so no need to disconnect the two in serial while charging each at 12 volts.
(Good idea to hook up a multi-meter to the source voltage if it's a battery....Don't want to drain it to a dangerous level after all. -Use common sense when applying this technique)
You're welcome everyone.

(Unusual problems...usually require unusual solutions)
Charles.

Charging 24 volt system with a 12 volt charger-

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